Predicting Sapling Recruitment Following Partial Predicting Sapling Recruitment Following Partial Cutting in the Acadian Forest: Using Long-Term Cutting in the Acadian Forest: Using Long-Term

Data to Assess the Performance of FVS-NEData 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 ME2Forest 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 Creation of Stand Structures Over the Past 25-yrs in MainePast 25-yrs in Maine

Structure Type

1980 1985 1990 1995 2000 2005

Pro

port

ion

of to

tal h

arve

st a

rea

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Pro

port

ion

clea

rcut

0.0

0.2

0.4

0.6

0.8

1.0

Even-aged (OSR & CC)MultiagedClearcut

FPA

The Northeastern Variant (FVS-NE)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 DynamicsAssessing 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 WorkFindings From Past Work

Penobscot Experimental Forest (PEF)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 PEFLive BA Following Partial Cutting at the PEFObserved vs. FVS PredictionsObserved vs. FVS Predictions

Ray, Seymour, and Keyser (2006)Proc. ECANUSA Conference

Diameter class midpoint

Summary of Net Growth Comparison Summary of Net Growth Comparison based on ~25 yr Simulation Runsbased on ~25 yr Simulation Runs

~40% above observed production rates

(0.5 cd/ac/yr)

2.5 10 14 >166

Methodology

Code Description Cutting cycle (yrs)

Harvests Plot count

FDL Fixed diameter-limit

20* 3 33

MDL Modified diameter-limit

20 3 32

S05 Single-tree/small groups

5 10 33

S10 Single-tree/small groups

10 5 35

S20 Single-tree/small groups

20 3 37

URH Commercial clearcut

30* 2 41

NAT Untreated control

n/a n/a 20

Characteristics of the Partial-Cut TreatmentsCharacteristics of the Partial-Cut TreatmentsStem density

TP

A

0

2000

4000

6000

8000

10000

Basal area

BA

(ft

2 /ac)

0

50

100

150

200

Stand density index

SD

I

0

100

200

300

400

500

Conifer stockingPro

por

tion

of B

A

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Large regeneration density

FDL MDL S05 S10 S20 URH NAT

TP

A

0

4000

8000

12000

16000

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 TreeLarge Tree Calibration StatisticsCalibration 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

PRODFVS = -0.43 + 0.59 (OBS); r2=0.10 BETAFVS = 0.26 + 1.66 (OBS); r2=0.13

Production Code

Observed (BA, ft2/ac/5-yr)

0 2 4 6 8 10 12 14 16

Pro

duct

ion

(BA

, ft

2/a

c/5-

yr)

0

2

4

6

8

10

12

14

16

FDLMDLNATS05S10S20URH

Beta Code

Observed (BA, ft2/ac/5-yr)

0 2 4 6 8 10 12 14 16

Bet

a (B

A,

ft2/a

c/5-

yr)

0

2

4

6

8

10

12

14

16

Ingrowth Dbh Distribution

Dbh (in)

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

Pro

port

ion

of t

otal

0.0

0.1

0.2

0.3ObservedBetaProduction

Results- Diameter Distribution

Recruitment

Results- Recruitment & MortalityResults- Recruitment & Mortality

Ingrowth BA

0

1

2

3

4

5

Mortality BA

Ba

sal a

rea

(ft

2 /ac/

5yr

)

0.0

0.2

0.4

0.6

0.8

1.0

HardwoodsSoftwoods

73% SW90% SW

75% SW

20% SW 73% SW

70% SW

Ingrowth/Mortality

Observed Production Beta

Ra

tio (

%)

0

5

10

15

20

4 X

Recruitment BA

Recruitment/Ingrowth

Results- Residual Analysis

-0.67***

-0.18***

-0.49***-0.83***

-0.08*-0.18*** 0.14***

-0.16*** 0.10**

Recruitment

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