The Ardeid Newsletter, 2002 ~ Audubon Canyon Ranch

8/9/2019 The Ardeid Newsletter, 2002 ~ Audubon Canyon Ranch

1/16

Heron and egret

nesting colonies

disturbance

patterns

Invasive Spartina

marsh protection

Acorns and

ecosystems oak

woodland

restoration

A management

challenge raven

predation

Sudden Oak Death

understanding

impacts

2 0 0 2

the

Ardeid

Research and

Resource M anagement

at Audubon Canyon Ranch


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Audubon Canyon RanchResearch and Resource

ManagementExecutive Staf f

Skip Schwartz, Executive DirectorJohn Petersen,Associate DirectorYvonne Pierce,Administrative Director

Staff Biologists

John Kelly, Ph.D., Director, Research & ResourceManagement

Rebecca Anderson-Jones, Bouverie PreserveKatie Etienne, Research CoordinatorDaniel Gluesenkamp, Ph.D., Habitat Protection and

Restoration SpecialistGwen Heistand, Bolinas Lagoon Preserve

Land Stewards

Bill Arthur, Bolinas Lagoon PreserveDavid Greene, Tomales Bay propertiesJohn Martin, Bouverie Preserve

Field Biologists

Ellen BlusteinNathan FarnauLauren HammackMark McCaustlandMari Ortwerth

Research A ssociates

Jules EvensGrant FletcherRachel KammanFlora MacliseHelen PrattRich Stallcup

Resource M anagement AssociatesLen BluminRoberta Downey

Scientific A dvisory Panel

Sarah Allen, Ph.D.Peter Connors, Ph.D.Jules EvensKent Julin, Ph.D.Greg KammanRachel KammanChris Kjeldsen, Ph.D.Doug Oman, Ph.D.Helen PrattW. David ShufordRich Stallcup

Wesley W. Weathers, Ph.D.

the ARDEID 2002

Dawn Adams (HS); Sarah Allen (S); JennieAnderson (H); Marie Anderson (R);Christina Attwood (R); Audubon CanyonRanch - Bouverie Preserve Juniper Club(N); Autodesk employees (R); Bob Baez(SW); Norah Bain (H); Michele Baker (R);Sharon Bale (R); Melissa Banks (S); TomBaty (W); Anne Baxter (H); Caitlin Bean(W); Gordon Bennett (S); J. Bjork (S);Louise Bielfelt (N); Gay Bishop (HS); SaraBlauman (H); Mike Blick (R); JulieBlumenthal (W); Len Blumin (R); PattiBlumin (HR); Ellen Blustein (M); NoelleBon (HN); Janet Bosshard (HS); PhillipBowman (R); Emily Brockman (HSW);Janet Bruno (R); Ken Burton (W); DeniseCadman (H); David Cain (R); Pam Cain (R);Barbara Carlson (N); Bill Carlson (N); KateCarolan (S); Mike Caselli (R); Ann Cassidy(H); Dave Chalk (R); Roberta Chan (R);Marie Claire Chapman (R); Steve Cochrane(R); Carole Connell (H); Jaye Cook (S); PhilCordle (R); Cynthia Corn (R); HelenCravens (R); Catherine Cumberland (R);Rig Currie (S); Nancy Dakin (R); KarenDavis (H); Melissa Davis (HS); NickDegenhardt (H); Nancy DeSousa (R);Carolyn Dixon (H); Roberta Downey (R);Joe Drennan (W); David Easton (H); April

Eberhardt (R); Ronnie Estelle (S); SergeEtienne (HS); Cathy Evangelista (H); JulesEvens (SW); Nathan Farnau (HSW); KatieFehring (SW); David Ferrera (W); BinnyFischer (H); Grant Fletcher (HPSW); GinnyFletcher (HPS); Johina Forder (R); CarolFraker (H); Jamie Freymuth (R); AudreyFry (R); Randy Fry (R); Tony Gilbert (HSW);Keith Gish (H); Beryl Glitz (H); Dohn Glitz(H); Ellen Goldstone (N); ) Brindy Greene(W); Philip Greene (H); Lauren Hammack(M); Madelon Halpern (H); Diane Hichwa(BHS); Philip Hughes (H); Jeri Jacobson(H); Gail Kabat (W); Lynnette Kahn (HS);Patty Karlin (H); Carol Keiper (SW); MarionKirby (N); Richard Kirschman (SW); EllenKrebs (H); Carol Kuelper (S); Alexis Lee (H);Laura Leek (W); Gail Lester (W); KeithLester (W); Robin Leong (H); Eileen Libby(H); Eric Lichtwardt (HS); Flora Maclise

(H); Art Magill (R); Lyn Magill (R); RogerMarlowe (W); Chris Mc Auliffe (H); PatMclorie (N); Diane Merrill (H); MikeGeorge (R); Frank Herrick (R); HannahHindley (R); Stuart Hindley (R); Nita Hon(R); Jim Hubberts (R); Leena Ilmarines (R);Barbara Janis (R); Rosemary Jepson (R); ArtMagill (R); Lyn Magill (R); Roberta Maran(R); Sandy Martensen (R); Bill Masters (R);Diane McLure (R); JoAnne Meroney (R);Peter Meyerhof (R); Jean Miller (H); JamesMiramontez (R); Anne Murphy (H); DanMurphy (W); Karen Nagle (BH); WallyNeville (H); Terry Nordbye (S); GordonNunnaly (R); John O Connell (H);Brandon Orr (R); Julie Osborn-Shaw (R);Peggy Osterhamp (R); Mari Ortwerth (HS);Richard Panzer (H); Patagonia employees(R); Joelle Peebles (R); James Peebles (R);Kathy Peterlein (S); Myrlee Potosnak (H);Grace Pratt (N); Jorge Presser (S); NancyProctor (R); Clark Rectors Boy Scout Troop(R); Jeff Reichel (H); Linda Reichel (H);Jerry Ricard (R); Lucy Ricard (R); RobinRichard (R); Rudi Richardson (W); CherylRiley (H); John Risberg (R); Sally Risberg(R); Brian Roberts (R); Barbara Rosen (R);Glenda Ross (R); Liz Ruellan (R); EllenSabine (HS); Don Sanders (H); Marilyn

Sanders (H); Fran Scarlett (H); MarieSchabroeck (R); Elisabeth Schlosser (R);John Sciocchetti (R); Craig Scott (SW);Sierra Club Outings (R); Paul Skaj (W);Joe Smith (HW); Craig Solin (S); BetsySpann (R); Anne Spencer (S); RichStallcup (S); Jean Starkweather (H);Elizabeth Stephens (S); Michael Stevenson(SW); Sandy Stoddard (R); Ron Storey (H);Grace Svitec (R); Cathleen Swanson (R);Lowell Sykes (HSW); Judy Temko (HS);Janet Thiessen (H); Gil Thomson (H);Dodie Thomson (H); James Titus (N); SueTredick (H); John Trott (R); Norma Vite (R);Tanis Walters (HS); Sarah Warnock (S); Sue

Weingarten (R); Eric Eisenberg (R); HeatherWhite (H); Rosilyn White (W); Tom White(W); Diane Williams (S); Phyllis Williams(H); Ken Wilson (HW); Jon Winter (H);Rollye Wiskerson (H); Angie Wolfow (H).

In this issue

A Safe Place to Nest: Disturbance patterns in heronries by John P. Kelly ........................page 1

Invasive Spartina: The challenging changeling by Katie Etienne ........................................page 4

Acorns and Ecosystems: Fourteen years of oak woodland restoration at the Bouverie

Preserve by Rebecca Anderson-Jones ................................................................................page 6Resistible Forces? Raven predation in heronries by John P. Kelly ......................................page 8

Sudden Oak Death Understanding the impact of a new epidemic on our forests

and woodlands by Daniel Gluesenkamp................................................................................page 10

In Progress: Project updates ................................................................................................page 13

Cover photo: Great Blue Heron byPhilip L. Greene Ardeid masthead Great Blue Heron ink wash painting byClaudia Chapline

The following list includes ACR field observers and habitat restoration

volunteers since the previousArdeid. Please call (415) 663-8203 if yourname should have been included in this list.

PROJECT CLASSIFICATIONS:

B = Breeding Bird Study at Bouverie Preserve x C = Common Raven Study xH = Heron/Egret Project x M = Livermore Marsh Monitoring x N = NewtSurvey x P = Photo Points x R = Habitat Restoration x S = Tomales BayShorebird Project x W= Tomales Bay Waterbird Census

The Watch


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2002 the ARDEID page 1

An explosion of flapping wingsbreaks the quiet morning air at

ACRs Picher Canyon. The heronsascend quickly into the air, circling, necksextended. Some land in nearby treesbefore gliding gradually back to their nestsites. Herons and egrets are most likely toexhibit fly-ups early in the nesting season,in apparent response to perceived dangerbut often with no obvious threat or stimu-

lus. Because a safe place to nest is a fun-damental requirement for successfulbreeding, the conservation of herons andegrets must consider potentially adverseeffects of nesting disturbance. To whatextent does human or other disturbancethreaten heronries?

Nesting colonies of herons and egretsare spectacular in their beauty. They haveattracted human interest for thousands of

years, inspiring admiration as well asworldwide exploitation of their feathersfor decoration and their eggs and youngfor food. Many heronries occur in close

proximity to people, and direct intrusionand indirect disturbance caused byhuman activities have resulted in adverseimpacts on nesting.

Since 1990, ACRs regional Heron andEgret Project has documented manysources of disturbance to heronries acrossfive northern counties of the SanFrancisco Bay area (Table 1). Any intenseor repeated disturbance can cause birds

to abandon a colony site permanently.However, it is not yet clear whetherheronries are more strongly affected byhuman interference or by other sources ofdisturbance. To complicate the matter,the likelihood of disturbance by native orintroduced nest predators may beenhanced or diminished by human activi-ty or human alteration of habitats.

To avoid investigator disturbance, ACRobservers at heronries follow these guide-lines during field investigations: Our firstconcern is for the birds. Be cautious.Watchfor alert postures and listen for alarm calls

as you approach a colony, and retreat ifthere is any such suggestion of distur-bance. Our best approach is to treat thesebeautiful birds with the cautious respectone should assume when encounteringother cultures, nations, or worlds.

Disturbance patterns in heronries

A Safe Place to Nest

by John P. Kelly

Rainstorm

Windstorm

Power l ine interference

Building construction

Fence construction

Removal of nest tree(s)Removal o f nests

Tree trimming or chipping

Logging and tractor activity

Firecrackers

Army helicopter

Hot-air balloon

Spraying nests with garden hose

Reflective (Mylar) ribbons as deterrents

Shooting with 22 caliber rifle

Skeet shooting

Car doors slamming

Trucks in area

Interested human visitorIncidental human activity

Investigator disturbance

Dog

Domestic or feral cat

Common Raven

American Crow

Red-tailed Hawk

Red-shouldered Hawk

Swainsons Hawk

Golden Eagle

Bald Eagle

Western Gull

Unknown owl

Osprey

Unknown avian predator

Non-native red fox

Raccoon

Unknown predator

Table 1. Types of human or other disturbances

observed or inferred at northern San Francisco

Bay area heronries, 1990-2001.

Continued on page 2

PHILIPL.GREENE


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page 2 the ARDEID 2002

Testing disturbance thresholds

Several years ago, we measured theintraseasonal pattern of disturbanceresponses at 23 nesting colonies

across the Bay Area. During each trial, anobserver approached a colony on foot at asteady pace. We marked the position of

the approaching person when the firstheron exhibited alert behavior and also

when the first heron flew from a nest site.We then measured the distance of eachmarked location from the colony. Werepeated the trials at monthly intervals,but avoided the early courtship period

when arriving birds are extremely sensi-tive to disturbance (respond at greaterdistances). Our results indicated that theresponses of birds varied with stages inthe nesting season (Figure 1).

A similar pattern of responses to othertypes of intrusions was found by Diana

Vos and others (1985, Colonial Waterbirds8: 13-22) of Colorado State University,although they did not interpret the appar-ent mid-season increases in sensitivity(Figure 2). Studies of different types ofdisturbance have shown consistently thatheronries are less disturbed by approach-ing boats than by terrestrial intrusions(Rodgers and Smith 1995, ConservationsBiology 9: 89-99).

Predicting the effects of disturbance atany given colony site, however, is not so

simple. The variability among sites isimpressive (see 95% percentile ranges inFigure 1). At some sites, herons and egretsexhibit considerable tolerance to humanactivity and can be approached at closerangeeven by walking directly undernest treeswithout exhibiting a distur-

bance response. In contrast, birds inother colonies will flee if humansapproach within 200 m or more. Thesedifferences might partly reflect a capacityfor habituation. Some investigators haveeven argued for systematically increasinghuman activity near colony sites to stimu-late habituation and resilience to distur-bance events (Nisbet 2000, Waterbirds 23:312-332). However, habituation has notbeen adequately studied in herons andegrets. Therefore, its importance remainshypothetical and differences in toleranceto disturbances among heronries cannot

be attributed clearly to habituation.One pattern, however, has become

clear. The reactions of breeding heronsand egrets to disturbances dependstrongly on the habitat structure of thecolony. In our study, observers oftenapproached incubating herons at closerange in heronries with densely vegetatedhabitat without causing them to flushfrom their nests. The importance of densevegetation as a barrier to disturbance hasalso been reported for herons along theupper Mississippi River (Thompson 1977,

Proc. Colonial Waterbird

Group 1: 26-37), in Colorado(Vos et al. 1985), in Florida(Rodgers and Smith 1995),and in Europe (Hafner 2000,pp. 202-217 in Kushlan andHafner, Heron Conservation,

Academic Press). Herons and egrets nest-ing in open habitat or in isolated treestend to react earlier and more intensely todisturbance. However, this general pat-tern cannot reliably predict the sensitivityof particular colonies. Heronries in openand isolated patches of trees in Suisun

Marsh and northern Sonoma and Napacounties vary substantially in theirresponses to approaching humans.

Buffer zones established to protectnesting herons and egrets from humanactivity are critical to the effective man-agement of many heronries. Several sci-entific investigators have attempted toidentify general rules of thumb for estab-lishing buffer zones, based on distur-bance distances such as those shown inFigures 1 and 2. In general, minimum rec-ommended buffer zones of at least 200 m(based on behaviors exhibited in

response to two approaching humans;Erwin 1989, Colonial Waterbirds 12: 104-108) agree well with our estimates in theBay Area. Effective buffer zones should bebased on upper 95th percentile ofobserved (standard normal) flushing dis-tances plus 40-50 m because birdsbecome agitated before intruders cause aresponse (Rodgers and Smith 1995), plusan additional 100 m to protect colonysites early in the nesting season whenbirds are first courting and establishingnest sites (Erwin 1989). Although suchbuffers seem to provide a conservative

zone of protection, they remain arbitraryand fail to address differences in toler-ance among colony sites.

Becky Carlson and Bruce McLean(1996, Colonial Waterbirds 19:124-127), ofJohn Carroll University in Ohio, found

Figure 2 . Average distance at which experimental intrusions caused

two or more Great Blue Herons to fly from nests at Fossil Creek

Reservoir, Colorado; adapted from Vos et al. (1985, Colonial Water-

birds 8:13-22). Number of trials is indicated above each bar.

Figure 1. Average distance associated with responses of Great

Blue Herons to an observer approaching on foot at 23 heronries in

the San Francisco Bay area. Error bars indicate 95th percentiles of

standard normal distances. Colonies are most easily disturbed

when at least some individuals are still in the pre-laying/courtship

phase (March). Birds become more site-tenacious as they settle

into the incubation phase (March-April). As nestlings grow large and

begin to thermoregulate, adults may temporarily flee or alter their

behavior without significantly neglecting their young (May). Toward

the end of the nesting season, adults are rarely present at their

nests; nest lings are large and alert to closely approaching observers

but unwilling to flee the safety of the nest (June).


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that the type rather than the width ofbuffer zone was most strongly associated

with nest success in Great Blue Herons.The most productive heronries werethose that were isolated by moat-like

water barriers or fencing, presumably

providing protection from predators orhuman intruders, rather than those iso-lated simply by greater distances tohuman activity. So, occasionally, smallareas near human activity can providesuitable nesting habitat if barriers to dis-

turbance are suitable. A good example ofthis can be seen at the Great Blue Heroncolony on Heron Island in Stowe Lake,in San Franciscos busy Golden Gate Park.

Nevertheless, Bryan Watts and DanaBradshaw (1994, Colonial Waterbirds

17:184-186), of the Center forConservation Biology, College of Williamand Mary, Virginia, found that heronstend to establish colonies away fromhuman activity (Figure 3). Their resultsseem convincing: potential disturbance

by humans influences thedistribution of heronries.

Will the undeveloped por-tions of our landscaperemain adequate for thelong-term needs of thesebirds?

Living with herons

Some heronries exhibitconsiderable toleranceto humans. Black-

crowned Night-Herons, LittleEgrets, and Chinese PondHerons have nested undis-turbed near a village nearHong Kong for over a centuryapparently because they

were thought to bring goodluck (Hafner 2000). In someparts of the world, heronshave been respected andprotected since ancient

times. A colony site in Vedanthangal,India, has been actively protected since1790 (Hafner 2000). Herons and egretshave nested at ACRs Picher Canyon sinceat least 1941 and may have nested therefor as long as 100 years (Pratt 1983,

Western Birds 14:169-184). At other colony

sites in our region where nesting heronsor egrets are not disturbed when observedat close range, we have been pleased toencourage carefully managed educationalopportunities for local residents.

In other cases, intense disturbance hasresulted only in temporary responses

without causing nest failure or colony siteabandonment. Unfortunately, very fewstudies have actually measured the effectsof disturbance on reproductive success orseasonal occupancy of colony sites. Wehave seen colony sites in the Bay Areaabandoned after interference involving

construction activities, tree trimming,and harassment by Golden Eagles,Common Ravens, and humans. In west-ern Santa Rosa, a Snowy Egret and Black-crowned Night-Heron Colony moved fourtimes in five years in response to inten-tional harassment by humans. To whatextent does occasional disturbance affectthe productivity of heronries in the Bay

Area? We may soon have accumulatedenough data to find out.

Disturbances once considered to beminor could become major. Recent popu-lation growth of ravens across the San

Francisco Bay area, possibly related tourbanization and habitat alteration byhumans (see Ardeid 2001), suggestsregional increases in opportunistic nestpredation. If so, adverse effects maybecome more likely after otherwise minordisturbances that temporarily flush adultherons and egrets from their nests.

Even the most careful management ofheronries cannot guarantee their localstability. A fundamental characteristic ofheron and egret colonies is that they shiftlocations over time, often in response tolocal disturbances. These shifts often

result in the formation of satellitecolonies close to or within a few kilome-ters of disturbed sites. Therefore, a region-al management perspective may be cru-cial not only in protecting wetland feed-ing areas, but also in providing suitablealternative habitat for nesting near exist-ing colony sites. Because these beautifulspecies depend widely on the landscapesin which we live, they remind us that con-servation is a central challenge in manag-ing our world.s

Figure 3. Average density of buildings at varying distances from

53 Great Blue Heron colony sites and at 58 random locations in

the low er Chesapeake Bay, Virginia; adapted from Watts and Brad-

shaw (1994, Colonial Waterbirds 17:184-186). Areas are defined

by non-overlapping concentric radii. *Asterisk indicates significant

difference between colony and random locations (P < 0.01).

PHILIPL.GREENE


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The invasion of non-nativeSpartina species (cordgrass) represents one of the

most alarming threats to coastalmarsh systems. AlthoughSpartina is a relatively new chal-lenge for northern California(Figure 1), we must respondpromptly to avoid the serious

biological consequences thathave accompanied Spartina inva-sions along the coasts of Britain,France, Washington State, andthe San Francisco Estuary.

The introduction of non-native Spartina alterniflora to

Washington State began in the1870s, when trains and cargoships used non-native cord grassfor packing material. By the 1950s, S.alterniflora dominated 400 acres of tidalmudflats in Willapa Bay, according tolocal oyster growers. In 1995, following

the discovery of two more non-nativespecies (S. anglica and S. patens) andmounting evidence of biological and eco-nomic impacts, the Washington legisla-ture declared the Spartina invasion anenvironmental emergency. Private andpublic landholders reduced the size ofsome infestations by prioritizing projectsand coordinating efforts. However, in2001, over 5,000 acres of Washington tide-lands had been invaded by non-nativeSpartina species, and recentlyS. densiflo-rawas discovered in Grays Harbortheonly coastal deep water port in

Washington State.This pattern of slow growth followed

by rapid spread has also been observedin San Francisco Estuary. In 1975, S.alterniflora was imported from the

Atlantic seaboard to prevent erosion andreclaim a marsh near Fremont, andtransplants were used to restore the SanBruno Slough. By 1990, at least 650 circu-lar patches ofS. alterniflorawere com-peting with the California native S. foliosaand other native plants (Callaway andJosselyn 1992, Estuaries 15: 218-26). Asubsequent study revealed that most of

these plants wereactually hybrids ofS. alterniflora andS. foliosa (Daehler

and Strong (1997,American Journalof Botany 84: 607-611).

Ongoing research by Debra Ayres andcolleagues at the UC Davis Bodega MarineLab have refined a variety of moleculartools for identifying genetic differencesbetween native and non-native Spartinaand their hybrids. Their research showsthat several generations of crossing haveoccurred and that some hybrids have vari-able morphology and greater reproductivevigor than either parent. The proliferationof these hybrids also reduces the probabil-

ity that pollen from native plants will fer-tilize remnant populations of native S.foliosa (Ayres and Strong 2002, AquaticNuisance Digest 4: 37-39).

Being able to distinguish hybrids fromparent species has also revealed thathybrids tolerate a wider range of condi-tions than either parent. The invasion ofsubtidal habitat byS. alterniflora and itshybrids is facilitated by the presence ofaerenchyma tissue. The aerenchyma formtubes in the stem that increase oxygentransport to below-ground tissue whichhelps plants survive anoxic sediments,

higher levels of hydrogen sulfide, and awider range of salinity (Howes et al. 1986,J. Ecology 74:881-98).

Hybridization between native andnon-native species can represent one ofthe greatest threats to ecosystems. Forexample, S. alterniflora and hybrids canmodify the physical characteristics ofmarsh habitat and reduce tidal circula-tion. Spartina clones have a dense net-

work of rhizomes that stabilize the soil.Above ground, the large stems grow close-

ly together, which reduces the velocity oftide water and facilitates the deposition ofsediment. In Willapa Bay, the diameter ofthe average clone increases by approxi-mately 75 cm per year. If left uncon-trolled, Spartina invasion has the poten-tial to convert the salt marshes and openmud in San Francisco Bay into vast standsof hybrid and invader cord grass (Ayresand Strong 2002). Based on the meantidal range ofS. alterniflora, it is predictedthat 65% of the mudflat in Bodega Baycould be covered if this vulnerable site

were invaded byS. alterniflora or its

The challenging changeling

Invasive Spartina

by Katie Etienne

Spartina alterniflora.

Figure 1. Distribution of introduced Spartinaspecies 2000-2001. Data courtesy

of Invasive Spartina Project httt://www.spartina.org.


7/16

Tomales Bay shoreline. At the time, therewere no genetic tests available to confirmthe identification of 64 S. densiflora plantsgrowing along the east shore of TomalesBay, so we decided to carefully removethese plants based on their physical char-acteristics. S. densiflora tends to grow indense tufts or mounds in the mid-to-highmarsh zone, but we found these plants atthe interface between open mud andmarsh vegetation. S. densiflora usuallyflowers between April and Julyearlierthan S. foliosawhich flowers betweenJune and September.

In November 2001, a single clone ofS.

alterniflorawas discovered at the northend of Bolinas Lagoon. Since then, fivepopulations ofS. alterniflora or hybridshave been discovered around DrakesEstero. Although many of these plantsgrew in round clones, some sparseseedlings were found growing in narrowbands that are characteristic ofS. foliosaand did not have all of the field character-istics of the non-native. These variationsin growth and morphology underscorethe value of genetic identification and theimportance of conducting thorough sur-veys each year. s


hybrids (Daehler and Strong 1996,Biological Conservation 78:51-58).

There are many serious consequencesof transforming exposed mudflats intoemergent marsh vegetation. Invasion bynon-native Spartina species can adverselyimpact native plants and animals.

Research in English marshes showed thatthe spread ofS. anglica resulted indecreased shorebird abundance (Goss-Custard et al. 1995, J. Applied Ecology 32:337-51), and competition with eel grasscan reduce food for certain herbivorous

waterbirds (Way 1991, Washington SeaGrant). In Willapa Bay, vast swards ofS.alterniflora can restrict fish to narrowchannels and limit access to open waterexcept during periods when tide waterrises above the non-native Spartina

which tends to grow taller than the nativeS. foliosa (Cordell et al. 1998, Proc. 8th

International Zebra Mussel and OtherNuisance Species Conf., Sacramento).

The invasion of channel margins bynon-native S. densiflora and its hybridscan restrict flow, cause widening of theflood plain, and reduce or eliminate forag-ing and nesting habitat for the federallyand state endangered California ClapperRail (Rallus longirostris obsoletus). At high-er marsh zones, non-native S. patens growsin dense cowlicks and competes withnative pickleweed (Salicornia virginica),

which provides critical habitat for the saltmarsh harvest mouse (Reithrodontomys

raviventris). Other plants that do not com-pete well with S. patens are salt grass(Distichilis spicata) and the federally listedsoft birds beak(Cordylanthus mollis).

What can we do to protectcoastal marshes from invasion?

It is crucial to be on the look-out forinvasive Spartina. However there areimportant reasons why we shouldnt

rush out and pull up suspicious plants.First, it can be difficult to identify bothnative and non-native plants, particularlyearly in the season, because there is con-

siderable overlap in size and other fieldcharacteristics that can vary with localconditions. Please visit the InvasiveSpartina Project web site (http://

www.spartina.org) to download theirexcellent, full-color field identificationguides. Second, it is extremely importantthat all plant material is removed, partic-ularly seeds and root fragments. Finally, itis essential that we know where non-native plants have been discovered sothese sites can be consistently monitoredin the future.

Therefore, if you see a suspiciousplant, please flag it and mark the locationon a map. Report this information to KatyZaremba, Field Biologist for the InvasiveSpartina Project (ISP), at (510) 286-4091. Ifit is not possible to identify the plant inthe field, it will be genetically tested. Theexact location of all invasive Spartinaplants will be recorded with a GPS unit sothe site can be monitored for resprouts.

ISP was started two years ago by DebraSmith and others with support from theCalifornia Coastal Conservancy. TheProject has an ambitious mission to studySpartina distributions, evaluate treatment

methods, and develop managementstrategies to eliminate non-nativeSpartina in the San Francisco Estuary. TheISP team has also helped to monitor andcontrol the first non-native Spartina dis-covered in coastal estuaries along theMarin County coastline (Figure 1).

The first S. densiflora plants in TomalesBay were detected by Doug Spicher in1999. Local monitoring began in 2001,

when the ISP team assisted local propertyowners and biologists from Golden GateNational Recreation Area, Point ReyesNational Seashore, and Audubon Canyon

Ranch in surveying almost all of the

An ounce of prevention is w orthmuch m ore than an extended period of Int egrated WeedManagement (IWM).

Posted on the Invasive Spartina Project (ISP) web site is an excellent sum maryof IWM methods, which demonstrate that the selection of appropriate methodsdepends on the scale of the problem. For example:

Digging can be 100% effective for removing small , isolated clones, but everyseed and portion of the rhizome must be removed. Because root materialmay extend 1.2 meters below the surface of the mudflat, this approach is notfeasible when clones aggregate to form large patches or meadows.

To contain a population or prevent hybridization, it is possible to control seedproduction by clipping seed heads to prevent pollination and seed dispersal.However, this requires constant attention because species flower over anextended period o f tim e from April-December.

To remove small-to-medium patches (up to 36 feet in diameter), all plantmaterial must be completely covered with geo-textile fabric or plastic for twogrowing seasons.

Mowing can control infestations of any size, except small seedlings. Howev-er, because mowing can initially invigorate the plant and promote root devel-

opment, it must be repeated at least 4-6 times per year for a minimum oftwo growing seasons.

Amphibious equipment has been developed for mechanical smothering andripping of large infestations. This aggressive approach should be conductedduring the fall or winter and is likely to degrade surrounding habitat or waterquality.

Herbicides are 0 to 100% effective, depending upon the conditions, timingand method of application and may have deleterious effects on non-targetorganisms. The use of aquatic pesticides currently requires a revocable-per-mit from the State Water Resources Control Board with extensive monitoringand reporting responsibilities.


8/16


For decades, land managershave noted declines in theregeneration of blue oak

(Quercus douglasii) and valleyoak(Q. lobata) throughoutCalifornia. Some evidence sug-gests that woodland fragmenta-tion may impair acorn produc-tion (see below). Woodland oaks

also face crucial competitionfrom introduced grasses. Oak

woodland conservation can seemdaunting! Success requires us tosupport acorn production andaddress recruitment challenges

while bolstering the survival ofmature trees.

Ecological challenges

Competition. Managing the landto enhance oak survival andregeneration is complicated byinteractions between native oaks andintroduced annual grasses. During thegrowing season, annual grasses are fiercecompetitors for light, water and nutrientsnear the surface, catching water before itpercolates to deeper soil profiles where itcan be used by native perennial grassesand mature oaks. By intercepting water,annual grasses compound the stressesaffecting these magnificent trees.Ubiquitous grass competitors also createsignificant problems for oak seedling andsapling survival.

Regeneration. Early in his tenure withACR, John Petersen, then Bouverie

Preserves Biologist, observed low rates ofoak recruitment with concern, and con-ducted an age-class census in the pre-serves mature oak woodland. Compari-son of seedling numbers in his study areain spring and fall indicated a loss of near-ly three-quarters over the four-monthperiod corresponding with annual graz-ing to manage grass biomass. This is afamiliar story in Californias oak wood-lands, with many ramifications.

Grazing animals can be a tremendousbenefit in controlling the growth of annu-al grasses and reducing problems caused

by thatch build-up (e.g. declines in lightand water penetration), but they can alsohave detrimental impacts on oaks. Cattleconsume seedlings andexcept in verysmall numberscompact the soil. Alien

weedy species and nitrogen enrichmentare introduced to the system in their

wastes. Cattle browse oak branches heavi-ly and can break or crush saplings or top-ple exclosures intended to protect trees.Cattle also need free access to waterthroughout the grazing range to avoidovergrazing near existing water sources.Regular monitoring and careful manage-ment are needed to prevent or correct forthese impacts. While other grazing ani-mals or management techniques may bemore suitable for alien grass control, eachbrings challenges that must be managedto limit adverse effects.

Habitat fragmentation. Lack of connec-tivity among woodlands may also con-tribute to the low regeneration of wood-land oaks in California. Eric Knapp, KevinRice and Michael Goedde, from UC Davis,studied the role of tree density in wind-mediated pollen transfer in blue oaks.They found that pollen density correlated

with distance from the source plant and

with acorn production (blue oaks).They inferred that blue oak regen-eration should benefit when con-nectivity between trees isenhanced. This kind of connectivi-ty is one of the tangible benefits of

ACRs efforts to support habitatprotection beyond the borders ofour sanctuaries.

The oak planting project

Land managers use a variety ofapproaches to restore oak

woodlands. In 1988, JohnPetersen took the direct route,

working with Bouverie PreserveFellow Bruce de Terra, dedicatedvolunteers, area children, and theirteachers to implement an oakplanting project. Their goal was torestore the lower field at Bouverieto the kind of plant community

likely to have existed before it was clearedfor ranching more than a century earlier.This was a wonderful learning opportuni-ty. It was also a hopeful beginning for

what has become a long-term restorationproject at the preserve.

Initially, the project was a straightfor-ward attempt to mitigate for historic oakclearing, partially motivated by concernsabout low levels of natural oak regenera-tion statewide. Since then, our restorationgoals have changed subtly with ourunderstanding of how they are affectedby, and affect, the extensive vernal wet-land system in the lowlands (to learnmore about the vernal wetlands atBouverie Preserve, see the 2001 Ardeid).Fourteen years after the oak planting pro-

jects inception, the restored oak wood-land is showing early evidence of matura-tion that bodes well for the future.

What the data tell us

The oak planting project includes atwo-part monitoring protocol. Thefirst involves direct growth meas-

urements. The second uses a breedingbird census to track the maturation of the

woodlands as avian habitat, relative tomature oak woodland elsewhere on the

Fourteen years of oak woodland restoration at the Bouverie Preserve

Acorns and Ecosystems

by Rebecca A nderson-Jones

Docent M axine Hall and students Amanda Hall, Emily Davis, and Nathan

Todhunter plant an oak at Bouverie Preserve.

COURTESYBOUVERIEPRESERVE

DOCENTS


9/16


preserve. Despite problems with imple-mentation of the monitoring program, wecan draw some useful conclusions fromour data.

Due to the unfortunate loss of locationtags, 1997 was the last year growth datacould be tracked to each trees originalsource stock. Re-plantings were carefullydocumented, allowing us to track treesfrom the initial cohort through 1997. Oaksare known to have high mortality rates inthe first years after planting or transplant-

ing regardless of the type of propagulesused. The five-year survivorship of oaksgrown from acorns in our project is 25%for blue oaks and 47% for valley oaks.These rates are higher than first-year sur-vival rates found by other researchers forvalley oaks and only slightly lower thanpublished first-year survival rates for blueoaks. When contrasted with publishedrates of survivorship after five years, ourresults are strong for both species. Treesinitially planted as saplings showed highsurvivorship, with very similar data forvalley and blue oak. (Figure 1). However,

no trees planted as seedlings survived,and all black oaks (Q. kelloggii), plantedonly from acorns, died.

Despite lost tags, we were able to tracka small number of trees from 1997 to2002, and many of these have shownstrong growth in stature or canopy devel-opment during this interval. Three coastlive oaks increased 59, 62, and 98 cm inheight, with trunk-to-dripline increases of24, 41, and 51 cm respectively, while onevalley oak increased in height by 138 cm

with a trunk-to-dripline increase of 102cm. Although we could not track growth

for most surviving trees beyond1997, many have continued tothrive. Twenty-one trees of fourspecies have grown above thelivestock browse line (approx.1.5 m), attaining a total heightof 2m or greater, with nine of

these greater than or equal to3m in stature. Of these, threevalley oaks stand at approxi-mately 4m (Figure 2)!

Interestingly, while all plant-ings were of blue, coast live,black or valley oak species,three Oregon oak trees (Quercusgarryana) currently thrive inthe study area. Given the ten-dency of species in the whiteoak subgenus to hybridize andthe lack of acorns to distinguishOregon from valley oaks in this

immature woodland, variabilityin leaf shape may have resulted

in misidentifications. However, fieldnotes suggest a more compelling expla-nation. In 1997, a blue oak tree wasnoted to have significant branch die-back, showing only partial resprouting,

while a smaller, healthy Oregon oakseedling grew within the same exclosure.

At this time, the Oregon oak had reached23 cm in height. By 2002, the Oregon oakhad obtained a height of 70 cm, and theblue oak had died. The blue oaks deathmay have resulted from an intolerance of

shade or other competition between thetwo trees, and its presence may haveaided in the establishment of the moreshade-tolerant Oregon oak. The sitepreparation and maintenance at thatlocation almost certainly did. If Oregonoaks have been recruited from seed treesin nearby woodlands, as these observa-tions suggest, the restoration project maybe supplying other habitat values thatsupport recruitment. For example,saplings in the restored woodland mayprovide roosts for birds, such as jays and

woodpeckers, which are capable of dis-

tributing seed. Unassisted recruitment ofoaks into the woodland is a sign of suc-cess, and an indicator that the system ismaturing.

Breeding bird territories in the matureupper oak woodland were delineated andtallied annually from observations ofsinging males. This census was intendedto provide a reference for comparison

with breeding bird use of the lower,restored woodland. To date, our observa-tions indicate that only Red-wingedBlackbirds use the lower, restored wood-land for breeding, although other species

are incidental visitors. Over time, weexpect increased use of the restored

woodland by oak woodland specialistsand a decline in use by grassland birds,but continued use by wetland associates,such as the Red-winged Blackbirds.

What we learned and what wew ould do differently

Project results have helped us modifymethods for use in future oak

woodland restoration efforts. Forexample, future projects should track treelocations with GPS and marktrees ratherthan exclosures, prevent rodent damage

with protective sleeves before trunks canbe girdled, and include more rigorous

weeding during the growing season.Nevertheless, we have evidence that theproject has been successful. Althoughdirect growth measurements are nolonger the most useful indicators of suc-cess, they did help us track establishment

of young trees. We will continue to moni-tor the maturation of the woodland ashabitat for breeding birds and to managethe system to promote oak growth. Themonitoring protocol is being revised toimprove its usefulness as part of a long-term program for monitoring breedingbirds across the Bouverie Preserve. Theresults will benefit other researchersinterested in oak woodland managementand restoration. The challenges of restor-ing whole ecosystems make this an excit-ing time to manage oak woodlands inCalifornia. s

Figure 1. Survival of original oak stock nine years after

planting. Note similar rates of sapling survival and relatively

strong acorn survival in blue and valley oaks. Mortality of

seedlings in all species and acorns in black oaks was 100%.

Figure 2 . Twenty-one oak trees of four species

(including trees showing evidence of hybridization with

other species) show vigorous growth above the live-

stock browse line (1.5 m). Valley oaks are best repre-

sented among the taller trees.


10/16


Managing wildlife is extremely dif-ficult because natural processesthat determine animal abun-

dance and behavior are often complexand mysterious. Among the most myste-rious are the influences of CommonRavens on nesting herons and egrets.Ravens occasionally prey on active heronand egret nests, but more typically they

are scavengers of failed nests and donot threaten the persistence ofheronries. At most heronries, at leastfor now, managing the predatoryactivities of ravens is unnecessary.However, with raven populations growingrapidly in apparent response to theexpansion of agriculture, roads, garbagedumps, and urbanization (see Ardeid

2001), questions have emerged aboutpotential increases in raven predation.

Resident ravens have become special-ized nest predators at some regionallyimportant heronries, such as Marin

Islands National Wildlife Refuge near SanRafael and ACRs Picher Canyon heronryat Bolinas Lagoon Preserve (see box atleft). If ensuring the persistence of partic-ular nesting colonies depends on reduc-ing raven predation, how might such areduction be achieved? In a recent reportto the California Department of Fish andGame (2001), Joseph Liebezeit and LukeGeorge of Humboldt State Universitythoroughly reviewed methods for manag-ing predation by ravens, but suitablestrategies for controlling their effects onheronries remain unclear.

Conditioned Taste Aversion. In recentnesting seasons, we have attempted toestablish conditioned taste aversion(CTA) in ravens at ACRs Picher Canyon.This involves providing chemically treat-ed prey that can produce severe illness inravens and, consequently, alter theirpredatory behavior (Nicolaus and Lee1999, Ecological Applications 9(3): 1039-1049). By associating the taste of normalprey with acute illness, predators developa reflex aversion for that taste. The aver-sion is then stimulated during subse-

quent predation attempts and ultimatelyalters their predatory behavior. If CTAcould be established in territorial ravensat heronries, they might avoid egret nests

while continuing to exclude other ravensfrom their territoryeffectively baby-sit-ting the colony.

In 2001, we captured both of the resi-dent ravens at Picher Canyon and provid-ed each bird with a piece of meat fromfallen Great Egret nestlings found deadunder the heronry. The food was treated

with enough fenthion to cause severe ill-ness. Captive feeding helped ensure that

Raven predation in heronries

Resistible Forces?

by John P. Kelly

Do ravens threaten heron and egret colonies?

For observers of heron and egret colonies, nest predation by Comm on Ravens can bea dramatic example of nature red in tooth and claw. Ravens are expert egg preda-tors, but their greatest threat to heronries seems to be in the predation of 3.5- to 5-week-old nestlings. This is the time in the nesting cycle when adult egrets begin toleave their nests unattended, as both parents forage for food needed by their devel-oping young. At this point, nestlings may be grabbed and torn apart, then eaten orcached for later.

Contrary to popular impressions of serious threats from raven predation, preliminaryresults from ACR research indicate that nest predation by ravens is unlikely at mostcolony sites in the San Francisco Bay areaeven though ravens may be near. How-ever, resident ravens at some sites may specialize on egret eggs and nestlings forfood during much or all of the nesting season. Good examples of such specialization

occur in ravens nesting near the Picher Canyon heronry at ACRs Bolinas Lagoon Pre-serve and at Marin Islands National Wildli fe Refuge near San Rafael.

In 1998, Great Egrets at Picher Canyon suffered severe nest predation by CommonRavens. Most nests were lost or abandoned, and only 26 young were successfullyfledged, compared w ith expected production of 100-150 young. In subsequent years,ravens destroyed fewer nests, apparently because of reduced food demand associat-ed with their own nesting failures. The ravens failed in 1999 and destroyed only asmany as 9 (16%) of 58 Great Egret nests (we found d irect evidence of raven predationat 5 nests). They failed again in 2000 and destroyed a m aximum of 12 (21%) of 75nests (direct evidence at 6 nests). In 2001, the ravens nested late but fledged 3 youngand may have destroyed as many as 33 of 85 (39%) Great Egret nests (direct evi-dence at 8 nests). Egg predation at Picher Canyon has been relatively rare.

At West Marin Island, ravens have fledged 45 young each year since 1999. Estimatesof Great Egret nest mortali ty, based on samples of individually monitored nests, werehigher in 2001 (31%, n = 54 focal nests) than in 2000 (19%, n = 59) or 1999 (20%, n =45). Great Egret nest mortality seemed to be lower in 2002 (12%, n = 68), althoughpredation rates on Snowy Egret and Black-crowned Night-Heron nests were notmeasured. We quantified egg predation at Marin Islands based on the number ofdepredated heron and egret eggs found on East Marin Island where ravens nested.The results suggest a dramatic increase in egg predation in 2001 and a possibledecline in 2002 (Table 1). The overall frequency of raven behaviors associated w iththe predation of heron or egret nests increased at M arin Islands and Picher Canyonthrough 2001 (Table 2) but was not measured in 2002.

Perhaps most alarming has been predation of adult Snow y Egrets indicated by car-casses found near raven roosts on East Marin Island: at least 4 adult Snowies weretaken in 2000 (none found in prior years), at least 7 in 2001, and at least 15 in 2002!We are currently conducting a more rigorous analysis of trends in raven predationand survivorship of heron and egret nests at Marin Islands and Picher Canyon heron-ries. Whether these heronries can to lerate further increases in nest predation byravens remains unknown.


11/16


the treated food was consumed com-pletely by each individual, not shared

with its mate or offspring, cached forlater, or taken by other species. Captivityshould not adversely affect the CTAprocess because the primary stimulus(taste) is transmitted directly through amedullar pathway, bypassing cognitiveprocesses that later associate theresponse with other stimuli such as visualor location cues. When left alone (birds

were observed through a remote videomonitor), both ravens readily consumedthe food ad libitum within 15-30 minutes.Before releasing the ravens, we mounteda radio transmitter to each of them so wecould monitor their movements andbehaviors. However, no subsequentbehavioral changes were detected.

Because we were not able to develop afully controlled experiment, we could not

rule out the possibility of an error in CTAapplication or treatment dosage. Weremain optimistic about the potential useof CTA as a management tool. The mainproblem is that ravens are very difficult tocapture, often requiring two or more

weeks of daily baiting and several addi-tional days of trapping for each bird. Cap-turing individuals a second time at PicherCanyon could be even more difficult.

Disruption of nesting behavior. Nest pre-dation at ACRs heronry on BolinasLagoon has been reduced in years whenraven nesting attempts have failed.

Therefore, preventing or delaying suc-cessful nesting by ravens might help incontrolling nest predation. Potentialmethods of disrupting raven nestingbehavior include the removal of nests oreggs, or treatment of eggs so they will nothatch. Addling (by shaking), oiling, orpuncturing eggs to prevent hatching hasthe potential advantage of delaying theravens detection of nest failure, and thusdelaying or preventing subsequent re-nesting. Disruption of successful nesting

would require annual searches for nestlocations and follow-up searches to locate

one or more renestingattempts each season. Ifravens abandon an area afternest disturbance, a new nest-ing pair might establish a ter-ritory, or, in the absence of anew pair, vagrant groups of

ravens might occupy theundefended heronry.

Repellents. Other options forcontrolling nest predation byravens suggest little promise.There is no consistent empiri-

cal support for the use of raven carcassesor models as effigies to deter raven activi-ty. The use of visual, auditory, or chemicalrepellants to discourage raven predation isunlikely to succeed beyond an initialresponse period, and could disturb nest-ing herons and egrets.

Removal.Any removal of ravens wouldprobably require an ongoing control pro-gram as other ravens move in to fillvacancies. If a new pair of resident ravensdid not immediately fill the vacancy,vagrant non-territorial ravensmight prey on heron and egretnests at equal or greater rates.Removing ravens from a colonysite by any means presents con-siderable difficulties.

Translocation. Ravens cannot betranslocated because of potential

problems with disease transmis-sion and exporting pest speciesto other areas.

Donation to education pro-grams. Trapped individualscould be given to wildlife educa-tion programs, but such programs are notgenerally interested in such a commit-ment. Trapping may be very difficult (seebelow).

Trapping and euthanasia. Trapping fol-lowed by euthanasia may be the most fea-sible method of removal, but some ravens

may be difficult to trap because of theircautious behavior or use of particularhabitats. We found net launchers to bethe most successful tool for trappingravens, but as noted above, successfultrapping may involve weeks of effort. Itmay be extremely difficult to trap bothmembers of a nesting pair. Trapping bothravens at Picher Canyon may be evenharder because they have already beencaptured once.

Shooting. Because ravens are extremelywary, they are very difficult to shoot.

Shooting both members of a nesting pair

may not be possible. Shotguns require aclose range, which is rarely available withravens. Rifles allow a greater range butrequire greater accuracy and carry addi-tional restrictions for safe use. Humanactivity in the vicinity of the ACR heronry

would substantially limit safe firing angles

and positions.

Poisoning. Removal by poisoning wouldrequire a major effort to prevent herons,Turkey Vultures, Scrub Jays, owls, andother native species from taking poisonedbait. Because ravens sample new foodvery cautiously, they might not be easilypoisoned. The overriding issue, however,is that removal by any method would pro-vide only temporary control as otherravens move in to fill vacancies.

At ACR, we have learned to appreci-

ate the challenge of managingravens in heronries. It is importantto remember that ravens are native birds,protected by federal law, and have valu-able ecological roles. Most options formanaging ravens require special permits.

Our best hope is that important heron-ries and, ultimately, heron and egret pop-ulations can tolerate increases in nest pre-dation by ravens. This might be possible atMarin Islands, where several hundredheron and egret nests are susceptible topredation by a single pair of ravens. AtPicher Canyon, nesting egrets have weath-

ered moderate predation pressure duringthe last few years without serious conse-quences. However, the last time ravens atPicher Canyon raised a brood of at leastfour young (1998), their food demandpeaked just as egret chicks became avail-able. The devastating result (see box, page8) suggests that a strategy for controllingraven predation may be necessary toavoid an annual game of raven roulettethat risks future abandonment of thecolony site. For now, however, the likeli-hood of successfully controlling raven pre-dation remains unknown. s

Year 1999 2000 2001 2002

Search-days 8 3 6 4

Heron and

egret eggs 45 16 140 79b

Other eggsa 10 16 31 21b

Total eggs 55 32 171 100b

a Other eggs include Western Gull and Mallard eggs.b Preliminary results as of 6 June.

Number of nest predatory behaviors / 100 hrs

Colony site 1999 2000 2001

West Marin Island 6.5 13.5 17.8

Picher Canyon 2.0 4.6 7.8

Both colony sites 3.1 6.9 10.8

Table 1. Number of depredated eggs found on East Marin

Island, 1999-2002.

Table 2 . Frequency of raven behaviors associated with

mortality of heron or egret nests or nestlings at West

Marin Island and Picher Canyon, 1999-2001. Behaviors

include flying from the colony with eggs, young, or uniden-

tified food, and perching in or adjacent to a failed nest.


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California was not always as it istoday. Ten million years ago, warm

winters and wet summers support-ed forests similar to those in easternnorth America and China: maple, beech,ginkgos, rhodendron and sequoias. As theSierra Nevada transformed from hills tomountains the climate changed dramati-cally. Rainfall decreased, summersbecame drier, and moisture-loving plants

were pushed north into Oregon and

beyond. Or they hid beneath oak trees.Every naturalist knows that oak trees

are important refugia, with deep taprootsthat draw water and nutrients 60 feet tothe surface and a canopy that cools the

weary botanist. Thousands of plant andanimal species rely on oaks for habitatand food, and ten million years ago theoak trees that spread across the dryinglandscape provided shelter for Arcto-tertiary flora retreating northward. Theserefugees speciated into new forms andtoday are an important component of theflora we love; plants with northern affini-

ties (includingDodecatheon, Delphinium,and Stipa) make up about 49% of thespecies in our state. Most of these arefound nowhere else in the world.

Today we see another transformationinvolving oaks, and this time the oak treesare in need of protection. Ancient oaktrees are replaced by developments,acorns are failing to produce adult trees,and now a pathogen is sweeping throughforests and woodlands like wildfire. This

article summarizes current knowledgeregarding Sudden Oak Death (SOD), dis-cusses Audubon Canyon Ranchs responseto the threat, and offers some suggestionsfor what we all can do to save the trees.

What is known about SuddenOak Death?

Sudden oak death was first observedin 1995 by a Marin County extensionagent who noted that oak trees were

dying so rapidly they were dead beforethey could drop their leaves. Other com-mon symptoms of SOD include dark sap

bleeding from the trunk, the presence of

bark beetles, and golf-ball (Hypoxylon sp.) fun-gus on the trunk. Insectsand fungi do not appearto cause SOD, but ratherthey opportunistically

exploit dying trees andare a sign that the tree isalready near death. Treesare most likely killed by adisease that creates largecankers in living trunktissue, destroying con-ductive tissues andgirdling the tree.

The disease agent isan oomycete (not a fun-gus) named Phytoph-thora ramorum; otherPhytopthora species are

responsible for Irishpotato blight, avocadoroot-rot, and the near-

extinction of dozens of plant taxa inAustralia. As is the case with other majorAmerican tree epidemics (includingchestnut blight, Dutch elm disease, andMonterey pine pitch canker), P. ramorumis most likely an accidental introductionfrom Europe, with no evolutionary historyin North America.

P. ramorum produces spores in the wetseason that are dispersed in water, rainsplash, and mud. P. ramorum is known to

kill four oak species: coast live oak(Quercus agrifolia), black oak(Q. kellog-gii), Shreve oak(Q. parvula var.shrevei),and tanoak(Lithocarpus densiflorus).Scrub oak, blue oak(Q. douglassii), valleyoak(Q. lobata), and Oregon oak(Q.gar-rayana) do not appear to contract the dis-ease. Of the susceptible species, tanoak ismost susceptible, and a high proportionof exposed trees develop the disease anddie. Coast live oak is highly susceptible toinfection, but inoculation experimentsshow that about 30% of infected treesmay have some resistance to the disease

Understanding the impact of a new epidemic on our forests andwoodlands

Sudden Oak Deathby Daniel Gluesenkamp

RICH

ARD

BLAIR

Left: Coast live oak tree in a

fog-shrouded forest.


13/16


(Rizzo et. al., 2001, Fifth Symposium onOak Woodlands).

Improved detection techniques haverevealed P. ramorum infection in severaladditional host plant species (Table1),and the list continues to grow. Whilemost of these alternate hosts are notseverely affected (huckleberry, madrone,and rhododendron may be killed), theyare important to the spread and persist-ence of the disease. For example, bay lau-

rel trees probably act as Typhoid Maryin our hardwood forests. Bay trees arealmost unaffected by the disease but pro-duce copious quantities ofP. ramorumspores. In contrast, oak species that arekilled by the pathogen often fail to pro-duce spores even in laboratory cultures.Thus, bay trees that are unaffected by thedisease produce spores that infect andkill oaks; this is shown by recentresearch showing that oaksgrowing near bay treesare more likely to beinfected than areoaks growing

without bay neighbors(Swiecke and Berndhart,2001, Fifth Symposium onOak Woodlands). Sincethese two species maycompete for light andother resources, produc-

tion of oak-killing sporesby bay laurel can be con-sidered a form of biologi-cal warfare between baysand oaks! This curiousrelationship has impor-tant ramifications: sincespores are coming fromresistant host species, it isunlikely that coevolutionof the oak-pathogen inter-action will reduce viru-lence of the pathogen.Plans for combating the

disease must includethese alternate hosts.

It is unlikely thatwe will find a cure for SuddenOak Death. Some chemicaltreatments may reducerates of infection andextend the life ofinfected individuals(Garbeletto et. al.,2001, FifthSymposium onOak Woodlands),but the expense

and potential fornegative sideeffects precludeapplication to wild-lands. Since there areno means for treatinginfected forests, its important that wemap the disease and reduce its rate of

spread (see below). In particular,experiments with seedlings sug-

gest that northern red oak(Q.rubra) and pin oak(Q.

palustris) may behighly sensitive to

the pathogen (D.Rizzo, 2001, Western

International ForestDisease Work

Conference), and dis-persal ofP. ramorum tomidwestern and easternoak forests could haveterrible consequences.

Sudden Oak Death andAudubon Canyon Ranch

Sudden Oak Death has not yet beendetected at ACRs coastal Marin pre-serves, and we continue to monitor

these sites. The disease is present at theBouverie Preserve and has been cultured

by J. Davidson (U.C. Davis) and S. Swain(Sonoma County) from coast live oak andbay laurels at several locations. Symptomsof Phytophthora infection appear on bayleaves in many parts of the preserve, andthe pathogen is likely present in most ofBPs coast live oak stands. Dead and dyinglive oaks with symptoms of SOD are par-ticularly abundant along the length of theLoop Trail leading up to the bark house.

Sudden Oak Death is expected to sig-nificantly affect Bouveries coast live oaks,and black oaks and madrone may also bekilled. Assessing the scale of the problemis complicated by the notable tree diver-sity of the Bouverie Preserve, with nineoak species. It is important to collect datathat will reveal patterns obscured by thevisual complexity of our diverse hard-

wood forests. Current and planned workat the Bouverie Preserve focuses on map-ping the distribution of diseased treesand censusing forests to quantify speciescomposition, age structure, and health oftrees. In addition to addressing SOD con-cerns, this work will provide valuablebaseline data to inform future manage-ment of our forests.

We are also cooperating with otherresearchers and agencies to understandthe distribution and ecology of this newdisease. In the last two years, we have

Common name Scientific name

coast live oak Quercus agrifolia

Califo rnia black oak Quercus kelloggii

Shreve oak Quercus parvula var. shreveitanoak Lithocarpus densiflorus

rhododendron Rhododendron spp.

huckleberry Vaccinium ovatum

California buckeye Aesculus californica

Pacific madrone Arbutus menziesii

manzanita Arctostaphylos manzanita

bay laurel Umbellularia californica

California coffeeberry Rhamnus californica

toyon Heteromeles arbutifoli a

California honeysuckle Lonicera hispidula

bigleaf maple Acer m acrophyllum

viburnum Viburnum bodnantense

Table 1: Sudden Oak Death host list as of April 2002 (from the

California Oak Mortality Task Force).

Continued on page 12

Among the vulnerable species: coast live oak (left)

and tanoak (above).

Species not known to be affected by Sudden Oak

Death include blue oak (left) and valley oak (right).


14/16

page12 the ARDEID 2002

seen field visits and tissue collection byresearchers from UC Davis and by theSonoma County Sudden Oak DeathCoordinator. In addition to assisting

regional studies of this disease, these vis-its have helped ACR staff to identify andassess SOD at the BP. We look forward tocontinued participation by cooperatinginvestigators.

ACR staff are working to develop pro-tocols to slow the spread ofP. ramorumamong sites and within preserves.Options include establishing hygiene pro-tocols in rainy season, including steriliz-ing boots before entering and leaving thepreserve, and even closing specific trailsthat are probable sources of infectivespores. Fortunately, hygiene measures

can be applied seasonally, since risk fromP. ramorum spores is greatest during thewet season. We are re-evaluating methodsused in oak woodland restoration proj-

ects; one approach might include green-house inoculation of seedlings with P.ramorum to screen out susceptible geno-types. This would reduce transplant mor-tality in the field, hasten development ofSOD-resistant forests, and provide valu-able data regarding the frequency of dis-ease resistance in our oaks.

Finally, ACR is contributing to the bat-tle against Sudden Oak Death by main-taining sanctuaries where biologicalprocesses can occur uninterrupted. Sinceit is unlikely that we will find a cure forSudden Oak Death, persistence of oak

forests requires an equilibrium betweendisease and host. This could occurthrough selection for resistant trees,selection for less virulent pathogen geno-

types, or regulation of the pathogen byother components of the community. Byleaving sick trees in place we allow par-tially resistant trees the opportunity toresprout, allow the less virulent P. ramo-rum strains to persist, and provide habitatfor birds, fungi, insects, and oomycotathat may contribute to a new stable equi-librium. In a world where more oaks arekilled by development than by disease,preservation of natural oak forests andwoodlands is an important mission. s

What you can do to fight Sudden Oak Death

1) Do not transport infected plant material

State regulations currently restrict movement of known hosts or soil from or within infected areas. Oregon, Canada, and

South Korea have established quarantines on host plant material from California, and the U.S. Department of Agriculture

has imposed an interim quarantine while regulations are finalized. These rules reflect common sense: material that may be

infected (including soil and branches, leaves, or wood, from any of the known host species) should not be moved. Dead ordying trees should be left in place unless they present a safety hazard and, if trimm ed, material should remain on site. Bay

laurel wreaths and oak, bay, and madrone firewood should not be moved into uninfected areas.

2) Lovers of the natural world must use protection.

Spores are easily transported by humans, and so Sudden Oak Death is most prevalent at sites with high public visitation.

After leaving an area known to be infected, wash mud from shoes, bicycle tires, horses, and vehicles; this simple action also

slows the spread of other problematic non-native species. Muddy cars should be run through a carwash on the drive home.

Tree work or vegetation m anagement should be done in the dry summer months, when abundance of Phytophthora spores

is lowest, and tools should be sanitized after each tree. Potential vectors can be sanitized using Lysol or a solution of 1 part

bleach to 9 parts water.

3) Keep your oak trees healthy

If you have oaks growing around your home or business, you can protect them from disease. When marveling at a giant

oak canopy, remember that most of the tree is below ground. These large root systems are very sensitive. Do not pave,

disturb, or compact within the drip line (outline of branches); if possible, pamper the root zone with 4-6 inches of mulch but NOT bay laurel mulch! California oaks evolved with dry summer conditions and cannot tolerate wet roo ts year round.

Do not water oak trees during the summer, and avoid planting lush landscaping adjacent to mature oaks. Potential

Phytophthora hosts (Table 1) should not be planted near oaks.

4) Support increased protection for oaks in California.

The greatest current threat to Californ ia oaks is clearing of oaks for urban developm ent and agriculture. Groups such as the

California Oak Foundation are working to protect oaks statewide, and many local groups contribute to local oak protection

ordinances. This work has added significance in light of the rapidly spreading epidemic: the oak that you save today may be

great-grandfather to the Phytophthora-resistant forests of tomorrow.

5) Stay informed

Our understanding of th is epidemic is improving rapidly. Sudden Oak Death was first observed in 1995, the causal agent

was identi fied as a species of Phytophthora in 2000, and the species was isolated and named in 2001. The list ofP. ramorum

hosts has tripled in the last year, and the first scientific paper onP. ramorum was published in 2002. While the popular

media have done a fantastic job of covering this subject, recent coverage has favored the sensational over the factual.Fortunately, current state of the science can be found on several websites maintained by researchers and m anagers:

The California Oak M ortality Task Force: http://suddenoakdeath.org

The UC Marin County Cooperative Extension: http://cemarin.ucdavis.edu/index2.html

The Californ ia Oak Foundation: http://www.californiaoaks.org


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In progress:project updates

North Bay counties heronand egret project Annualmonitoring of reproductiveactivities at all known heronand egret colonies in fivenorthern Bay Area countiesbegan in 1990. The data areused to examine regionalpatterns of reproductiveperformance, disturbance,habitat use, seasonal timingand spatial relationships amongheronries.

Picher Canyon heron andegret project The fates ofall nesting attempts at ACRsPicher Canyon heronry aremonitored and reproductive

success is analyzed annually.Field procedures are based onmethods developed by HelenPratt who initiated the projectin 1967 and published severalpapers on heron and egretnesting biology.

Livermore M arsh AsACRs Livermore Marsh trans-forms from a freshwatersystem into a tidal salt marsh,we are studying the relation-ship between increasing tidalprism and marsh channeltopography. The results are

being compared with datafrom mature referencemarshes, and will contribute tofuture restoration designs. Theresults will also contribute tostudies of changing bird useand vegetation in the marsh.

Newt population study Annual newt surveys havebeen conducted along theStuart Creek trail at BouveriePreserve since 1987. Theresults track annual andintraseasonal abundance, andsize/age and spatial distribu-

tions along the creek.Shorebirds Since 1989, wehave conducted annual bay-wide shorebird censuses onTomales Bay. The data areused to investigate w interpopulation patterns of shore-birds, local habitat values, andconservation implications.Other associated work hasinvolved the effects of winterstorms and food availability onenergy balance and habitatuse.

Tomales Bay w aterbirdsurvey Since 1989-90,teams of 12-15 observers haveconducted w inter waterbirdcensuses from survey boatson Tomales Bay. The resultsprovide information on habitatvalues and conservation needs

of 51 species, totaling up to25,000 birds. Baseline statusand conservation concerns forwaterbirds have been evalu-ated and published (Kelly andTappen 1998, Western Birds).

Predation by ravens inheron and egret colonies We are observing nestingravens in Marin County andmeasuring their predatorybehaviors at heron and egretnesting colonies, with anemphasis on heronries atACRs Picher Canyon andMarin Islands National WildlifeRefuge. Radio telemetry andbehavioral studies focus onevaluating home range varia-tion, behaviors at heronries,and diurnal movementpatterns. A road surveyconducted throughout the SanFrancisco Bay area revealedconcentrations of ravens insome urban/suburban areasand along the outer coast.

Plant species inventory Resident biologists maintain

inventories of plant speciesknown to occur at Bouverieand Bolinas Lagoon preserves.Grant Fletcher has establisheda database of shoreline plantspecies on Tomales Bay.

Annual Cordylanthussurvey This projectcontinues earlier field investi-gations on habitat and spatialrelationships among patches ofPoint Reyes birds beak,Cordylanthus maritimus palustris,in Tomales Bay marshes (Kellyand Fletcher 1994, Madrono

41: 316-327). The goal is tofurther address questionsabout long-term stability andbiogeographic relationshipsamong discrete patches onTomales Bay.

Oak restoration Plantingof native oaks at BouveriePreserve was conducted withthe help of school children.Annual monitoring involvedmeasurements of oak saplingsurvivorship and vigor as wellas breeding bird censuses (see

article by Rebecca Anderson-Jones, page 6).

Cape ivy control Workconducted by Len Blumin hasproven that manual removal ofnonnative cape ivy cansuccessfully restore riparian

vegetation in ACRs VolunteerCanyon. Continued vigilance inweeded areas has beenimportant, to combat resproutsof black nightshade, vinca, andJapanese hedge parsely.

Eucalyptus removal atBouverie and BolinasLagoon preserves Eucalyptus from Pike CountyGulch at Bolinas LagoonPreserve, and along theHighway 12 border of BouveriePreserve are being cut andremoved with incremental

annual efforts. Stumps andresprouts w ill be treated bymethods developed in anassociated investigation byDan Gluesenkamp.

Eucalyptus resproutcontrol An experiment isbeing conducted to determinethe optimal method forcontrolling Eucalyptusresprouts. Dan is testing therelative effectiveness ofcutting, use of the herbicideRodeo (glyphosate), andgrinding stumps, to perma-

nently kill cut Eucalyptus treesin the lower field at BouveriePreserve.

Visiting investigators

Elizabeth Brusati (UC Davis),Consequences of speciesinvasion under global climatechange.

Yvonne Chan and Peter Arcese(University of Wisconsin),Subspecific differentiation andgenetic population structure ofSong Sparrows in the San

Francisco Bay area.

Jeff Corbin and CarlaDAntonio (UC Berkeley),Effects of invasive species onnitrogen retention in coastalprairie.

Caitlin Cornwall (SonomaEcology Center), Communitybased assessment of bio logica lhealth of riparian wetlands inthe Sonoma Creek watershed.

Elizabeth Dahm (Sonoma StateUniversity), Larval amphibiansurvey of vernal wetlands.

Christopher DiVittorio (UCBerkeley), Dispersal anddisturbance colonization in aCalifornia coastal grassland.

Peggy Fong (UCLA), Algalindicators of nutrient enrichmentin estuaries.

Brenda Grewell (UC Davis),Species diversity, rare plantpersistence, and parasitism inmid-Pacific Coast salt marshes:functional significance ofinterplant parasitism.

Emily Heaton (UC Berkeley),Bird communities in north coastoak-vineyard landscapes.

Jodi Hilty (UC Berkeley),Carnivore use of ripariancorridors in vineyards.

Martha Hoopes and CherylBriggs (UC Berkeley), Effectsof dispersal on insectpopulation dynamics andparasitoid diversity in galls ofRhopalomyia californica onBaccharis pilularis.

W. Joe Jones (UC Santa Cruz),Population structure of theCa lifornia roach.

Gretchen LeBuhn (CSU SanFrancisco), The effect oflandscape changes on nativebee fauna and pollination ofnative plants in N apa andSonoma counties.

Jacqueline Levy (CSU San

Francisco), Impact of butterflygardens on pipevineswallowtail populations.

Wendy Losee (SonomaEcology Center), Thermalmonitoring, Sonoma Creekwatershed assessment.

Steven Morgan, SusanAnderson, and others (UCDavis Bodega Marine Lab,UC Santa Barbara), Ecologicalindicators in west coastestuaries.

Lorraine Parsons (Point Reyes

National Seashore), Long-termwater quality monitoring,W alker Creek and G iacominiW etland.

Jennifer Shulzitski (USGSGolden Gate Field Station),M ulti-scaled vegetation da ta topredict wildlife speciesdistributions using a wildlifehabitat relationship model.

Bibit Traut (UC Davis), Structureand function of coastal high-saltmarsh ecotones. s



16/16

Ardeid (Ar-DEE-id), n., refers to

any member of the family

Ardeidae, which includes herons,

egrets, and bitterns.

The Ardeid is published annually by Audubon Canyon Ranch as an offering to field

observers, volunteers, and supporters of ACR Research and Resource Management.

To receive The Ardeid, please call or write to the Cypress Grove Research Center.

Subscriptions are available free of charge; however, contributions are gratefully

accepted. 2002 Audubon Canyon Ranch. Printed on recycled paper.

Managing Editor, John Kelly. Layout design by Claire Peaslee.

AUDUBON CANYON RANCH IS A SYSTEM OF WILDLIFE SANCTUARIES

AND CENTERS FOR NATURE EDUCATION

BOLINAS LAGOON PRESERVE CYPRESS GROVE RESEARCH CENTER BOUVERIE PRESERVE

the

Ardeid

Research

and Resource

Management at

Audubon Canyon Ranch

Audubon Canyon Ranch, 4900 Shoreline Hwy., Stinson Beach, CA 94970

Cypress Grove Research CenterP.O. Box 808Marshall,CA 94940

(415) 663-8203

Nonprofit Org.

U.S. Postage

PAID

Permit No. 2

Stinson Beach, CA

Oak forest canopysee pages 6 and 10DANIELGLUESENKAMP

Documents

The Ardeid Newsletter, 2002 ~ Audubon Canyon Ranch