Vegetation responses to
conifer encroachment in a dry,
montane meadow:
a chronosequence approach
Ryan D. Haugo
MS Thesis Defense
College of Forest Resources
University of Washington, Seattle
Photo: Jim Lutz
Value of open meadow communities
• Biodiversitiy
• Wildlife habitat
• Cultural resources
The problem…
• Conifer invasion of
meadow habitat
• Widespread across
PNW
• Concern over the loss
of unique meadow
habitat
The problem…
• Focus on the causes
– Fire suppression
– Climate change
– Grazing
The problem…
• Very little understanding of consequences
– Vegetation dynamics
– Loss of biodiversity
– Restoration potential
Bunchgrass Ridge, OR
• Dry, montane meadow
• Willamette NF Special Habitat Area
Bunchgrass
Bunchgrass
Meadow
Ridge
• ~ 1300 m
• History of conifer invasion
–
–
Grand fir (Abies grandis)
Lodgepole pine (Pinus contorta)
• Meadow soils
1959
1997
Objectives
1. Temporal changes in vegetation
2. Relationships with changes in the
environment
Temporal changes
in vegetation
•
How does species
composition change?
•
How does abundance
of meadow and forest
species change?
–
–
Richness
Cover
Environmental
changes
• Relationship between
light, forest structure
and:
– Species composition
– Abundance of meadow,
forest species
• Forest structure
– Basal area, density
• Grand fir: live, dead
• Lodgepole pine: live, dead
Environmental
changes
• Are relationships with
environment weaker
for forest than for
meadow species?
– Dispersal
– Competition
– Clonal growth
4, 1-ha study plots
Field sampling
• 356 10 x 10 m subplots
– Basic sample unit
• Census of all overstory trees
– Species, size, age, location
• Light levels
• Vegetation sampling
Chronosequence
• Temporal changes
– Space for time
substitution
• Seven encroachment
classes
– Open meadow to old
forest
Chronosequence
•
•
•
Cluster analysis
20 year age bins
Relative Euclidean
distance
• Ward’s linkage
Encroachment Class 0, n=28
Orthocarpus imbricatus
Number of stems.subplot
-1
Encroachment Class 1, n=17
Class 1
n = 17
8
4
0
20
40
60
80
100 120 140 160 180 200 220
Age (yr)
Number of stems.subplot-1
Encroachment Class 2, n=42
Class 2
n = 42
16
12
8
4
0
20
40
60
80
100 120 140 160 180 200 220
Age (yr)
Encroachment Classes 2-3
Number of stems.subplot
-1
Encroachment Class 3, n=70
Class 3
n = 70
8
4
0
20
40
60
80
100 120 140 160 180 200 220
Age (yr)
Number of stems.subplot
-1
Encroachment Class 4, n=84
Class 4
n = 84
8
4
0
20
40
60
80
100 120 140 160 180 200 220
Age (yr)
Number of stems.subplot
-1
Encroachment Class 5, n=77
Class 5
n = 77
8
4
0
20
40
60
80
100 120 140 160 180 200 220
Age (yr)
Number of stems.subplot-1
Encroachment Class 6, n=38
Class 6 (old forest)
n = 38
8
4
0
20
40
60
80
100 120 140 160 180 200 220
Age (yr)
Encroachment Class 6, n=38
Compositional changes
• Nonmetric Multidimentional Scaling (NMS)
ordination
• Sørensen’s distance
Compositional changes
• Strong meadow to forest gradient
Forest Species
Meadow Species
Ruderal Species
1.0
0.5
NMS 2
Are_mac
0.0
Ach_tri
Phl_dif
Car_pen
Eri_ali
Osm_chi
Lac_mur
Ort_imb
Lup_lat
Smi_ste
-0.5
Ely_gla
Cir_alp
-1.0
-1.5
-1.0
-0.5
0.0
NMS 1
0.5
1.0
1.5
Compositional changes
1.0
Encroachment class centroids
NMS 2
0.5
5
4
3
2
0.0
0
6
1
-0.5
Time
-1.0
-1.5
-1.0
-0.5
0.0
NMS 1
0.5
1.0
1.5
Composition and environment
1.0
Pinus dead BA
Pinus dead density
Abies live density
Pinus live BA
Pinus live density
NMS 2
0.5
Abies dead density 5
Abies live BA
0.0
4
3
2
Abies dead BA
0
6
Light
1
-0.5
Lodgepole
Pine
Grand Fir
-1.0
-1.5
-1.0
-0.5
0.0
NMS 1
0.5
Open
Meadow
1.0
1.5
140
a. Meadow species
Shrubs
Sedges
Grasses
Herbs
120
• Threshold
response for
meadow species
100
80
60
Cover (%)
Meadow /
forest cover
40
20
0
• Gradual increase
in forest species
b. Forest species
60
40
20
– Low overall cover
0
0
1
2
3
4
Encroachment class
5
6
a. Meadow species
Shrubs
Sedges
Grasses
Herbs
14
12
10
• Progressive
meadow decline
• Not completely
lost
8
6
Species richness (no. subplot-1)
Meadow /
forest richness
4
2
0
b. Forest species
14
12
10
8
6
4
2
0
0
1
2
3
4
Encroachment class
5
6
• More rapid forest
increase
• Decline from Class
5 to 6
Class 6 - Old Forest
• Distinct
composition (NMS)
• Dominated by
strongly clonal
species
– Limits cover /
richness of other
species
Smilacina stellata
Meadow / Forest species
and environment
• Multiple regression models
– Meadow species: richness,
cover
– Forest species: richness,
cover
• Predictors
– Light
– Basal area, density
• Grand fir: live, dead
• Lodgepole pine: live, dead
Meadow / Forest species
and environment
• Meadow cover R2 = 0.54
• Meadow richness R2 = 0.48
• Forest cover R2 = 0.34
• Forest richness R2 = 0.42
• Importance of light
Strong meadow to forest gradient
• Clear progression over time
• Closely related to the lodgepole pine
Æ grand fir transition
Rapid decline of meadow vegetation
• Threshold response in cover of
meadow species
• Massive grand fir recruitment, Class 2
• Modal tree age of 40 – 60 yr
Decline of meadow vegetation
• Closely related to light levels and
forest structure
• Few extirpations of meadow species
Assembly of forest communities
• Weaker relationship with light and
forest structure
• Other factors
– Dispersal
– Competition
– Clonal growth
Assembly of forest communities
• Early initial colonization
• Max. richness in Class 5
• Distinctive “old forest” communities
Management and Restoration?
• Early removal of trees
• Persistence of meadow species
• Potential for meadow regeneration
from the seed bank?
– NO! (Lang 2006)
Next steps?
• Is restoration of invaded meadows
possible?
• Age-dependant responses?
• Is fire a necessary for restoration?
Treatments
Control
Cut + broadcast
burn
Cut only (cut +
pile/burn)
Reserve (for future
treatment)
Thanks!
• Charlie Halpern
• Committee – Don
McKenzie and Joe Antos
• Nicole Lang (my grad
school twin…)
• Field Crews: Kyle Smith,
James Freund, Jess
Niederer, Janine Rice,
Jen Leach, Michael
Frank, Markus Koch
Thanks!
• Lab group: Jim Lutz,
Shelley Evans, Martin
Dovciak, Cara Nelson,
Laura Six
• Fred Swanson, John
Cissel
• McKenzie District,
Willamette NF
• Joint Fire Sciences
Program