Experimental gaps and
biodiversity responses
in the Vermont Forest
Ecosystem
Management
Demonstration Project
Bill Keeton
Graduate student contributors:
Nicholas Dove, Sarah Ford, Heather
McKenny, and Kimberly Smith
University of Vermont,
Rubenstein School of Environment
and Natural Resources
Photo credit: Sarah Ford
Rothwald Old-growth Forest, Austrian Alps
Vermont Forest Ecosystem Management
Demonstration Project
Structural Complexity Enhancement (SCE)
Structural Objective
Multi-layered canopy
Elevated large snag densities
Elevated downed woody debris densities
and volume
Variable horizontal density
Re-allocation of basal area to larger
diameter classes
Accelerated growth in largest trees
Silvicultural Technique
 Single tree selection using a target
diameter distribution
 Release advanced regeneration
 Establish new cohort
 Girdling of selected medium to
large sized, low vigor trees
 Felling and leaving, or
 Pulling over and leaving
 Harvest trees clustered around
“release trees”
 Variable density marking
 Rotated sigmoid diameter
distribution
 High target basal area
 Maximum target tree size set at
90 cm dbh
 Full and partial crown release of
largest, healthiest trees
Gaps are an Element of the Study
• Crown release in SCE resulted
in clustered harvesting and
small gaps (mean opening size
= 0.02 ha)
• Modified group selection (mean
opening size = 0.05 ha)
Artificial gaps (“groups”)
specifics:
• Gap sizes based on mean 0.05 ha
(1/8 acre) disturbance scale (from
Seymour et al. 2002)
• Gap sizes are
irregular
• Gap shapes are
irregular
• Light retention
within gaps
Study Sites
 Study Areas:
 Mount Mansfield State Forest
 Jericho Research Forest
 Paul Smith’s College (FERDA cooperation)
• Mature, multi-aged northern
hardwoods
• History of thinning and selection
harvesting
• Mid-elevation, moderate productivity
N
100
0
100
200 Meters
FEMDP Research
Response Indicators:
Growth and yield
Stand structure and dynamics
Herbaceous vegetation
Birds
Small mammals
Amphibians
Fungi
Soil invertebrates
Soil OM and macro-nutrients
Economic tradeoffs and
feasibility
 Biomass and carbon
 Tree Regeneration
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© Al Sheldon
Leaf Area Index Changes:
Pre-Treatment to Post-Treatment
Spatial Variability:
• SCE v. GS; not sign.
• SCE & GS > STS; P < 0.05
10
5
LAI Percent Change
0
-5
Controls
-10
Structural
Complexity
Enhancement
Single-Tree
Selection
Group Selection
-15
-20
-25
-30
ANOVA:
Fcrit, 0.05 = 2.867
F = 11.435
P < 0.001
F tests for variance:
SCE > STS: P = 0.031
GS > STS: P = 0.010
SCE > GS: P = 0.296
-35
-40
Keeton. 2006. For. Ecol. and Mgt.
Coarse Woody Debris
Enhancement
Red-backed Salamander Response
Based on Occupancy Modeling
log(λ )(β0 + β1*density CWD 1-2 + β2*density CWD 3-5 +
β
3
*
s
i
t
e
+
β
4
*
%
r
e
l
a
t
i
v
e
d
e
n
s
i
t
y
o
v
e
r
s
t
o
r
y
t
r
e
e
s
)
40
Density CWD 1-2
Mean abundance λi
Density CWD 3-5
Relative density
overstory trees
35
30
25
20
15
10
5
0
-3
-2
-1
0
1
2
3
Standardized covariates
McKenny, Keeton, and Donovan. 2006
Response of Late-successional Understory
Plant Species
2
1.2
0.9
Diversity
Richness
4
Control
Group selection
SCE
Single-tree selection
0
-2
0.6
0.3
0
-0.3
-0.6
-4
-1
1
2
Year
 Richness:*
p = 0.012
 SCE > GS
* Following Hill’s (1973) series of
diversity Indices
3
4
-1
1
2
3
4
Year
 Shannon Index:*
p = 0.009
 SCE > CON
Smith, Keeton, Twery, and Tobi. 2008. CJFR
Locally Extirpated Species
Percent Species Lost by Treatment
% Species Lost
16
12
ANOVA:
p = 0.07
8
4
0
GS
STS
SCE
Treatment
CON
Fungal Responses;
Aboveground Sporocarps
Dove and Keeton. 2014.
Fungal Ecology
Fungi Responses: Classification and
Regression Tree
CWD Volume (Decay classes 3‐5) < 71.42 m3/ha
Initial formula included
7 structural variables
Dead Stem Density < 28.85 trees/ha
12.250
Live Aboveground Biomass < 69.25 Mg/ha
4.188
Total CWD Volume < 68.59 m3/ha
5.625
*Response Variable = Species Richness
5.250
13.500
Dove and Keeton. 2014.
Fungal Ecology
Biomass and carbon in downed logs 10
years post-harvest
30
Mg/ha
25
20
Biomass (Mg/ha)
Carbon (Mg/ha)
15
10
5
0
SCE
Conventional
Control
Treatment Type
Closing Thoughts
• Silvicultural gaps promote some
elements of late-successional
biodiversity, depending on within
gap structure
• Spatial configuration w/closed
canopy patches also important
• Manage for temporal and spatial
variability
• There is no “one-size-fits all”
approach; mix it up!
• Adapt, learn from unanticipated
results
Acknowledgements
• Vermont Monitoring Cooperative
• U.S. National Science Foundation
• Northeastern States Research
Cooperative
• USDA McIntire-Stennis Forest
Research Program
• USDA National Research Initiative