Disturbance -Based Management

Disturbance-Based Management• Landscape-Level

– Pattern and complexity – Stand age class distributions – Patch distributions: type, size, – shape, and continuity– Habitat representation– Historic range of variability

• Stand-Level– Vertical structure

– Horizontal structure

– Cohorts

– Tree age class distributions

– Biological legacies

Figure adapted from Franklin and Spies (1991).

Structural Change Through Stand Development

Photos courtesy of Jerry F. Franklin, University of Washington

Recovery facilitated by biological legacies at

Mount St. Helens

Large-scale Windthrow: Hurricanes

Fine-scale Windthrow

Ice Storms

Insect and Pathogens Outbreaks

Coarse Woody Debris in Northern Hardwood Forests

Even-aged Single-tree Selection Old-Growth

• Habitat

• Nitrogen Fixation

• Soil organic matter

• Mycorrhizal fungi

• Nurse logs

• Erosion reduction

• Riparian functions Figure from McGee et al. (1999)

Teakettle Ecosystem Experiment

Forest Ecosystem Research Network

0 %

100 % 80 %

20 % 80 %

20 %Removal at Harvest

Retention at Harvest

Entries per Rotation

Age Classes

12 - 3

4 or more

Even-aged (1 class) Multi-aged (2-3 classes)

Uneven-aged (4 or more classes)

Figure from Franklin et al. (1997)

Variable Retention Harvest System

“Demonstration of Ecosystem Management Options”

Weyerhaeuser Co. Variable Retention Adaptive Management (VRAM) Experiment

Weyerhaeuser Co. Variable Retention Forestry in B.C.

VRAM

Year 0

Year 15

Long-Term Implications ?

What have we learned about natural disturbance effects?

• Scale and frequency of disturbance

Figures from Seymour et al. 2002

Mimicking scale and frequency of disturbances

0

0.5

1

1400 1500 1600 1700 1800 1900

Year

Prop

ortio

n of

Lan

dsca

pe in

Old

-gro

wth

HRV

Historical Range of Variability

Figure from Aplet and Keeton (1999)

0

0.5

1

0 100 200 300 400 500

Years

Pro

po

rtio

n o

f L

and

scap

e in

Old

-gro

wth

0

0.5

1

0 100 200 300 400 500

Years

Pro

po

rtio

n o

f L

and

scap

e in

Old

-Gro

wth

0

0.5

1

0 100 200 300 400 500

Years

Pro

po

rtio

n o

f L

and

scap

e in

Old

-Gro

wth

HRV

HRV

HRV

Scale: Small Watershed

Scale: Drainage Basin

Scale: Region

Hurricane

Hurricanes

Source: Aplet and Keeton (1999)

HRV

Historical Range of Variability

Figure modified from Aplet and Keeton (1999) using data from Cogbill (2000)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1300 1350 1400 1450 1500 1550 1600 1650 1700

Year

Pro

po

rtio

n o

f L

and

scap

e in

Ear

ly-S

ucc

essi

on

What have we learned about natural disturbance effects?

• Coarse-woody debris: snags and downed wood

Coarse Woody Debris in Northern Hardwood Forests

Even-aged Single-tree Selection Old-Growth

• Habitat

• Nitrogen Fixation

• Soil organic matter

• Mycorrhizal fungi

• Nurse logs

• Erosion reduction

• Riparian functions Figure from McGee et al. (1999)

What have we learned about natural stand development?

• Importance of large trees as structural elements

Crown Release to Increase the Representation of Large Trees

30

60

150 300

Age (Years)

DB

H (

cm)

No release

Partial crown releaseFull crown release

Data from Singer and Lorimer (1997)

What have we learned about natural stand development?

• Vertical complexity

• Horizontal complexity

Structural Complexity Index (Zenner 2000)

A)

B)

= Ratio of 3D area in A to 2D area in B

Uneven-aged Forestry

• Single-tree selection

• Group selection

BDq prescriptions are based on the desired:

1. residual basal area

2. maximum dbh

3. q-factor

00 24

7

14

83610

7

94

0

20

40

60

80

100

120

2.0-4.0 4.0-6.0 6.0-8.0 8.0-10.0

10.0-12.0

12.0-14.0

14.0-16.0

16.0-18.0

18.0-20.0

20.0-22.0

22.0-24.0

>24.0

Current

Target

Cull

Single-Tree Selection Prescription for Mt. Mansfield Unit 4: q-factor of 1.3, maximum diameter of 24", and residual basal area of 80 ft2/acre

Diameter Class in Inches

# S

tem

s p

er A

cre

Diameter Distributions

Figure from Goodburn and Lorimer (1999)

Unbalanced Diameter Distributions:

Figure from Goodburn and Lorimer (1999)

• Density-dependent mortality reduced with fewer stems in smaller size classes

• Equal allocation of growing space not found consistently

Figure from Seymour 2005

Multi-modal distributions due to old-tree legacy

Rotated Sigmoid Diameter Distribution

Shift in basal area allocation to larger size classes

• Often found in old-growth northern hardwoods and mixed-woods

• Varies with disturbance history, stand composition, and competitive dynamics

• Theoretical silvicultural utility proposed (O’Hara 1999, Leak 2003); tested experimentally by Keeton (2005).

# of

Tre

es

Diameter Class

Yield vs. Big Tree Structure in Northern Hardwoods

40 cm max. 50 cm max. 80-100 cm max.

Data from Hansen and Nyland (1987) Data from Goodburn and Lorimer (1999)

Maximized volume production

Selection harvest + old-growth structure

after multiple cutting cycles

Maximized large sawtimber volume and value growth

An Alternative: Multi-aged Silviculture

• Recognizes that “reverse J” is limiting

• Other stand structures are sustainable

• Ecological functions more closely associated with canopy structure

• All-aged stands exceedingly rare in actuality

• Management based on the desired number of canopies provides a better alternative

• Set objectives based on canopy strata two-aged and multi-aged are possibilities

Multi-aged distributions resulting from multiple disturbances

Diameter Class

Trees/ha

– Leaf area index

– Stand density index

– MASAM model (O’Hara 1998)

Growing space allocation approachesPercent of trees per acrePe

rcen

t of

basa

l are

a

Bottom Layer Mid Layer Top Layer

Percent of growing space

553510

25

33

42

57

33

10

Shift in growing space from one strata to another also shifts growth increment

Hig

hL

ow

Understory growth

Overstory growing space occupied (%)

0 50 100

Overstory growth

High

Low

Understory

Overstory

Figure from O’Hara (1998)

Conversion to Multi-Aged or Multi-Canopied

Managing for Canopy Strata

• Fewer and longer cutting cycles

• Management across multiple spatial scales– Need combination of single and multi-layered

stands to maximize biodiversity potential

Ind

epen

dan

t

Geomorphology

Geology

GPM type

Mode ofdeposition

Intial static conditionsHydrology

Waterways

Watershed

Topography

slope,orientation,

altitude

Meteorology

Temperature,precipitation

Climate

Climaticzone

Non-forested

Agriculturalland,roads

Natural disturbances

Dynamic processesFire

Size,Intensity,

Frequency

Epidemics

Size,Intensity,

Frequency

Windthrow

Size

Landscape

Watershed

Stand

Scale

Scale

Stand

Watershed

Landscape

Imp

ose

d

Statusquo

Harvesting scenarios

Management scenarios

Multiplepass

Partialcutting

Triad

Scale

Stand

Watershed

Landscape

Constraints expressed in terms of indicators

Sustainable forest managementSoils Regeneration Biodiversity Aquatic

Rotation period,geology,

stand type,harvesting

method

Age structure,composition,

configuration, roads,bird monitoring

mineral soil,stocking and growth

of seedlings,compétition

Distance to seedtrees, age and

species ofseed trees

% watershedharvested,

dissolved P and C,transparency

Governmentstandards

Forested land

Initial dynamic conditionsProductive

Initial ForestConditions

Poor soils,slow growing

species

Unproductive

Barren,semi-barren,

Marginal

Modelling elements

Indicators of biodiversity

• Crit1: Maintenance of ecosystem diversity– Ind1.1: Age structure of the forest (P)– Ind1.2: Forest species composition (P)– Ind1.3: Configuration of the forest (P)

• Crit2: Maintenance of species diversity– Ind2.1: Road density (P)– Ind2.1: Monitoring bird populations (M)

100 year forest rotation

100 year fire cycle

Proposed age class distribution for managed forest

Ind1.1: Age class structure

Extended Rotations

Mean annual increment

Periodic annual increment

Stand age10 100

Cub

ic f

t./ac

re/y

ear

0

300

Advantages of extended rotations:

• Reduced land area in regeneration and early-development stages, hence:

1. Reduced visual impacts

2. Lower regeneration and respacing costs

3. Less need for herbicides, slash burning, etc.

4. Reducing frequency of intense disturbance

• Large tree and higher-quality wood

• Adjust precently unbalanced age distributions

• Higher quality habitat for species associated with late-successional forest structure

• Hydrologic benefits

• Increased carbon stock associated with increased net biomass/larger growing stock

• Preservation of options for future adaptive management

Landscape Management System (LMS)

Simulated landscape based on individual stand structures + important features (e.g. roads, streams, etc.)