Transcript Modeling Sapling Recruitment Following Partial Cutting in the

Predicting Sapling Recruitment Following Partial
Cutting in the Acadian Forest: Using Long-Term
Data to Assess the Performance of FVS-NE
David Ray1, Chad Keyser2, Robert Seymour1 and John Brissette3
1School
of Forest Resources, The University of Maine, Orono ME
2Forest Management Service Center, USDA-FS, Fort Collins, CO
3Northeastern Research Station, USDA-FS, Durham, NH
Outline
• Background
– Motivation
– Findings from past work
• Objectives
• Methods
– Dataset
– Analysis
• Results
• Conclusions
Creation of Stand Structures Over the
Past 25-yrs in Maine
0.7
Structure Type
0.8
0.6
FPA
0.5
0.6
0.4
0.4
0.3
0.2
0.1
Even-aged
(OSR & CC)
Multiaged
Clearcut
0.2
0.0
1980
1985
1990
1995
2000
2005
Proportion clearcut
Proportion of total harvest area
1.0
The Northeastern Variant (FVS-NE)
• Covers the 14 Northeastern States
– Formerly NE-TWIGS (Teck and Hilt 1991)
– Lacks a “full” establishment model
• Newly coded Beta version incorporates
some major changes
– Small tree height and diameter growth
– Background and density dependent mortality
– Growth modifier function
Assessing Recruitment Dynamics
• Partial cutting leads to cohort recruitment
– Regeneration is prolific in this forest type (Brissette
1996)
– Heavy cutting favors intolerant hardwoods; lighter
cuts promote tolerant conifers
• Long-term forecasts require consideration of
regeneration/recruitment dynamics
• Compare performance of the production and
beta versions of the Northeastern Variant
• Provide feedback that can be used to improve
model performance
Findings From Past Work
Penobscot Experimental Forest (PEF)
• US Forest Service Compartment Study
– 50 yrs of remeasurement data (numbered
trees since the mid-70s)
– Inventoried before and after harvests and at
approximately 5-yr intervals between harvests
– 2 reps/treatment (~10 ha units)
• Tolerant Northern Conifers (BF, RS, EH)
• Range in silvicultural intensity
– From 5-yr selection to commercial clearcutting
Live BA Following Partial Cutting at the PEF
Observed vs. FVS Predictions
40 Unregulated harvest (URH)
Fixed diameter limit (FDL)
Modified diameter limit (MDL)
10-yr selection (S10)
20-yr selection (S20)
2
Live basal area (m /ha)
30
20
10
0
40 5-yr selection (S05)
30
20
10
0
1970
1980
1990
2000
1970
1980
1990
2000
1970
1980
1990
2000
2010
Ray, Seymour, and Keyser (2006)
Proc. ECANUSA Conference
2
Obs>Pred
Uncalibrated
Calibrated
2
Observed - Predicted (BA, ft /ac/yr)
Summary of Net Growth Comparison
based on ~25 yr Simulation Runs
1
0
-1
Pred>Obs
-2
cm
cm
cm
cm
cm
0
0
0
0
0
-1 2.5 0-2 6 0-3 10 0-4 14 >4 >16
5
.
1
2
3
2
Diameter class midpoint
Diameter size class
l
ta
To
~40% above observed
production rates
(0.5 cd/ac/yr)
Methodology
Characteristics of the Partial-Cut Treatments
10000
TPA
8000
MDL
Cutting
cycle
(yrs)
Harvests
Fixed
diameterlimit
20*
3
Modified
diameterlimit
20
Singletree/small
groups
5
Singletree/small
groups
10
Plot count
6000
4000
2000
0
200
33
2
FDL
Description
BA (ft /ac)
Code
Stem density
3
150
100
50
0
32
Basal area
500
400
S20
Singletree/small
groups
33
200
100
0
20
5
3
35
37
Proportion of BA
S10
10
SDI
300
S05
Stand density index
1.2
1.0
0.8
0.6
0.4
0.2
0.0
16000
Conifer stocking
Large regeneration density
URH
Commercial
clearcut
30*
2
41
TPA
12000
8000
4000
NAT
Untreated
control
n/a
n/a
20
0
FDL
MDL
S05
S10
S20
URH
NAT
Nested Plot Design
Simulation Run Details
• Focus on 5-yr runs at the plot level
– 250 plots; 1,182 plot/interval combinations
•
•
•
•
Calibration of LT diameter growth (≥1-in dbh)
Forest wide SI for balsam fir set at 55-ft
Large regeneration only- issues with SDImax
Regeneration specified by mid-point of height
class interval
– Beta model equations used to derive species
specific heights for trees ≥ 4.5-ft tall but <0.5-in dbh
• Key in on saplings crossing the 0.5-in dbh
threshold (1-in dbh class)
Performance Criteria
• Presence absence of new recruits
• Compare diameter distributions
• Rates of sapling recruitment and
mortality (BA, ft2/ac/5-yr)
• Correlation analysis between residuals
and plot attributes
Results
Large Tree Calibration Statistics
The Nested Plots
• Recruitment was observed on 55% (653/1,182)
of the plot/interval combinations
– Tall regeneration was present on 68% of plots where
recruitment was observed (‘appeared’ on 32%)
• Simulated recruitment was limited to plots with
large regeneration present (n=729)
– Recruitment was observed on 61% of these plots
– PRODFVS predicted recruitment on 35%
– BETAFVS predicted recruitment on 68%
• Agreement between observed and predicted
– For PRODFVS was 29%
– For BETAFVS was 56%
more on The Nested Plots
• Backwards extrapolation of observed
diameter growth
– 10% may have been smaller than large
regeneration (URH- intolerant broadleafs)
• Sufficient abundance of large regeneration
– 96% of plot/intervals had more than enough to
account for observed recruitment
Results- Recruitment Basal Area
16
Production Code
FDL
MDL
NAT
S05
S10
S20
URH
12
10
8
6
4
12
10
8
6
4
2
2
0
0
0
2
4
6
8
10
12
14
Beta Code
14
2
2
Production (BA, ft /ac/5-yr)
14
Beta (BA, ft /ac/5-yr)
16
16
2
Observed (BA, ft /ac/5-yr)
PRODFVS = -0.43 + 0.59 (OBS); r2=0.10
0
2
4
6
8
10
12
14
16
Observed (BA, ft2/ac/5-yr)
BETAFVS = 0.26 + 1.66 (OBS); r2=0.13
Results- Diameter Distribution
Ingrowth Dbh Distribution
Observed
Beta
Production
0.3
Proportion of total
Recruitment
0.2
0.1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Dbh (in)
1.6
1.8
2.0
2.2
2.4
Results- Recruitment & Mortality
5
2
Basal area (ft /ac/5yr)
4
Ingrowth
BA BA
Recruitment
3
Hardwoods
Softwoods
75% SW
2
1
73% SW
90% SW
0
1.0
Mortality BA
0.8
70% SW
0.6
0.4
0.2
Ratio (%)
0.0
20
20% SW
73% SW
Ingrowth/Mortality
Recruitment/Ingrowth
15
10
4X
5
0
Observed
Production
Beta
Results- Residual Analysis
Recruitment
-0.18***
-0.67***
-0.49***
-0.83***
-0.08*
-0.18***
0.14***
-0.16***
0.10**
Summary of Findings
Conclusions I
• Difficult hoop for the model to pass through
• Large tree calibration statistics were closer for
BETAFVS than PRODFVS
• Recruitment rates were underestimated by
PRODFVS (~50%) and overestimated by BETAFVS
(~100%) relative to that observed on partially cut
plots at the PEF (~2 ft2/ac/5yr)
• Mortality rates were too high, particularly for
BETAFVS
Conclusions II
• The changes implemented in BETAFVS should
improve model performance
• Model biases were related to
– Large regeneration density for BETAFVS (strong)
– QMD, % SW regen, Harvests for PRODFVS (weak)
• Resetting GMOD to 0.5 (from 0.15), too high?
– Shade tolerant saplings can just sit there in the
understory (GMOD by shade tolerance?)
• The Northeastern Variant covers a large
geographic range; the Acadian Forest Region
represents a relatively small part
Acknowledgements
• US Forest Service
– PEF Dataset
– Support with FVS
• Northeastern States Research Cooperative
(NSRC)
• UMO School of Forest Resources