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Tree Regeneration Strategies in Response to Burning and Thinning Restoration Treatments in a Sierran Mixed-Conifer Forest. Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station 3200 SW Jefferson Way, Corvallis, OR 97331. - PowerPoint PPT Presentation
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Harold S.J. Zald and Andrew N. GrayUSDA Forest Service, Pacific Northwest Research Station
3200 SW Jefferson Way, Corvallis, OR 97331
Tree Regeneration Strategies in Response to Burning and Thinning Restoration Treatments in a Sierran
Mixed-Conifer Forest
•Historic fire return interval 12-17 years•Fire suppression has been a dominant management strategy in Sierran mixed- conifer forests on public lands
Generalized impactsof fire suppression
Increased stand densities Increased ladder fuels
and fuel loadings
Reduced fire frequency Increased fire severity
Increased dominance of fire intolerant and shade tolerant species (firs and
incense-cedar)
Fire History and Suppression in Sierran Mixed-Conifer Forests
Historical Old-Growth Current High Density Stand
•Regeneration dynamics a major driver of future composition, structure and function
•Seeding germination and establishment is a highly sensitive life history stage
•Restoration treatments may impact future regeneration patterns
Forest Regeneration: Species Strategies
P. jeffreyiP. lambertiana A. concolor & C. decurrensA. magnifica
Study Objectives
Past: Pretreatment regeneration composition and abundance
Pretreatment regeneration with respect to environmental conditions
Pretreatment environmental conditions
Present: Treatment mortality and subsequent response
Germinant success in relation to treatments
Post-treatment regeneration with respect to environmental conditions
Future: Treatment effects on environmental conditions
Study Area: Teakettle Experimental Forest
Fresno
California Teakettle Experimental Forest
Forest BoundaryRoadsStreamsStructures
•Full factorial design contrasting two levels of burning and three levels of thinning treatments•Burn treatments: no burn (U), and understory burn (B)•Thinning treatments: no thinning (N), “CASPO” understory thinning (C), and overstory shelterwood thinning (S)•Each treatment unit is a 4 ha plot with three replicates, for a total of 18 plots
Sampling Methodology
Regeneration and Micro-site Conditions
•All trees less than 5cm DBH tallied on 402 systematically placed 3.5m radius plots•Solar radiation estimated by hemispherical photography•Volumetric soil moisture estimated using time domain reflectometry (TDR)•Vegetation and substrate cover tallied
Germination and Survivorship
•Predation exclosures (18 per treatment combination) •Seeded with dominant overstory species in the first post-treatment year (Oct 2002)•Germinants closely monitored during summer 2003 to record total germinants and 1st year mortality
Pretreatment: Regeneration Pool
•A. concolor and C. decurrens are the most common overstory trees, P. jeffreyi and P. lambertiana are major overstory components•Regeneration pool dominated by firs and incense-cedar, with a reduced pine component
Pretreatment Regeneration: Micro-site Conditions
• A. magnifica(ABMA) low DSF, moderate soil moisture, high litter cover
• C. decurrens(CADE) low DSF, high soil moisture
• A. concolor (ABCO) intermediate DSF and soil moisture
• P. lambertiana (PILA) intermediate DSF and soil moisture
• P. jeffreyi (PIJE) high DSF, low soil
moisture
Post-treatment Mortality and Subsequent Response: White fir
•Initial mortality for A. concolor highest in BS, UC, and US treatments•US, UC, BS, and UN (control) treatments had the lowest subsequent regeneration response
A. concolor
TREATMENT COMBINATION
BN BC BS UN UC US
% C
han
ge fr
om P
retr
eatm
ent D
ens
ity
-100
-50
0
50
100 1st year mortality (all size classes)2nd year reponse (size class "A")
•All treatments resulted in regeneration decreases •Immediate post-treatment seedling distribution influenced regeneration response•Only BS treatments resulted in suppressed regeneration response
Post-treatment Mortality and Subsequent Response: Incense-cedar
1742%
•Jeffrey pine regeneration was not present in all treatment combinations•Burning, thinning, and burn/thinning combinations influenced mortality•Subsequent response only found in BS and US plots Unbalanced distribution prevented response model development
Post-treatment Mortality and Subsequent Response: Jeffrey pine
P. jeffreyii
TREATMENT COMBINATION
BN BC BS UN UC US
% C
han
ge fr
om P
retr
eatm
ent D
ens
ity
-100
0
100
200
300
400
500
1st year mortality (all size classes)2nd year mortality (size all "A")
Post-treatment Mortality and Subsequent Response: Sugar pine
• Pretreatment regeneration distribution, thinning, and burn/thinning combinations affected regeneration mortality• Thinned treatments had regeneration mortality, while un-thinned treatments had 1st year increases in regeneration•1st year seedling distribution was the dominant factor influencing regeneration response
P. lambertiana
TREATMENT COMBINATION
BN BC BS UN UC US
% C
HA
NG
E F
RO
M P
RE
TR
EA
TM
EN
T D
EN
SIT
Y
-200
0
200
400
600
1st year mortality (all size classes)2nd year response (size class "A")
1500%
NOSPP
ABCOABMA
CADE
PIJEPILA
PREM
QUKE
AVG02SMAVG03SM
DSF
-0.4
-1.2
0.0 0.4 0.8
-0.8
-0.4
0.0
0.4
TK POSTREAT SDL
Axis 1
Axi
s 2
TRT0
Axi
s 2
Post-treatment Regeneration: Micro-site Conditions
•Increased separation of sugar pine and white fir based on light levels and soil moisture
Post-treatment: Micro-site Conditions
POSTTREATMENT (2002)
DIRECT SITE FACTOR
0.2 0.3 0.4 0.5 0.6 0.7
AV
ER
AG
E S
OIL
MO
IST
UR
E (
% B
Y V
OLU
ME
)
8
10
12
14
16
18UNUCUSBNBCBS
•Thinning treatments have dominant effect on light levels and soil moisture•Burning treatments have a lesser but consistent influence•Increased light levels and increased soil moisture
Post-treatment: Germination Study
•Natural regeneration surveys do not address seed source
•Firs and incense-cedar are prolific seed producers compared to pines
•High proportion of firs and incense-cedar in the overstory indicates regeneration surveys may have a seed input bias
•Pines seeds also tend to have high seed predation
•Seed sowing in predation exclosures allows for a more controlled examination of regeneration with respect to treatments
Post-treatment: Germinant Survivorship
•Burned treatments had higher pine germinant survival •BC and BS also had the lowest white fir and incense-cedar survivorship
0
2
4
6
8
10
12
14
16
BN BC BS UN UC USTREATMENT COMBINATION
1ST
YR
SU
RV
IVO
RS
HIP
ABCO ABMA CADE PIJE PILA
Species Regeneration Strategies: Conclusions
•Pre-treatment regeneration dominated by fir and incense-cedar
•Pre-treatment regeneration distribution and abundance influenced by light levels, soil moisture, and litter cover
•If the goal is to increase pine regeneration and suppress fir and cedar, Burn/Shelterwood was the most effective treatment option
•Burn treatments favored pine germinant survivorship
•High germinant study response of pines combined with low natural regeneration of pines suggests natural regeneration may not be sufficient to accomplish pine restoration
•Post-treatment regeneration suggest pines are occupying lighter and drier sites than white fir and incense-cedar
•Treatment influence on light levels and soil moisture may benefit future pine regeneration when light levels increase with little increase in soil moisture
•Management goals for specific species or structural conditions may not be compatible with restoration activities whose objectives are increased pine components
Species Regeneration Strategies: Conclusions
Primary funding provided by the Joint Fire Sciences ProgramAdditional support provided by The USDA Forest Service PSW Research Station