Five-year development of plant
communities and planted Douglasfir with and without annual
herbicide applications
David Peter and Constance Harrington
Olympia Forestry Sciences Laboratory
Olympia, WA.
Objectives
• Document the difference in diversity,
vigor, and successional trajectories of
vegetation with and without vegetation
control.
• Quantify the effect of competing
vegetation on Douglas-fir growth with
and without vegetation control.
The Fall River
Long Term
Productivity Study
Site is about 33
km west of
Chehalis,
Washington.
Site and Stand Characteristics
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Elevation: 335 m
Annual precipitation: 226 cm
Boistfort silt-loam
Plant association: Tsuga
heterophylla/Polystichum munitum-Oxalis
oregana (Henderson et al. 1989)
Overstory: Douglas-fir (Pseudotsuga menziesii
and western hemlock (Tsuga heterophylla)
Age at harvest in 1999: 47
Stand treatment: broadcast burned in 1953;
pre-commercially thinned in 1971; fertilized
with urea 4 times
Site index: 41 m to 43 m breast-height age 50
years (King, 1966)
Vegetation plots are 176.6 m2
(x 8 = 1413 m2)
8 treated plots (veg. control)
8 untreated plots (no veg.
control)
Methods
• Vegetation measurements: July, 2000-2002
and in 2004
• Ocular estimation of canopy coverage
• Height and crown diameter were measured
on 10 trees
• % overlapping of planted tree foliage: ocular
estimation of the % of tree crown overtopped
or intermixed with surrounding vegetation
(10 trees)
• Vascular plant biomass (above ground) was
determined in years 3 and 5
Vegetation control treatments were:
• Oust and Accord 2 weeks prior to
planting (in spring 2000 = year 1)
• Annual application of pre-emergents
(Oust, Velpar and atrazine) each March
• Annual April-June spot spraying with
post emergents (Accord, Transline)
Pre-Treatment Vegetation Assessment
• Forty-eight 1 m2 plots (in 1998)
• Cover ocularly estimated (16 species)
• Combined for a pre-treatment species list :
– the pretreatment species list
– post treatment native tolerant species
– 177 sq. m plot in an adjacent stand
• The final list contains 35 native species
Year 2 with
vegetation control
Year 2 without
vegetation control
Year 5 with
vegetation control
Year 5 without
vegetation control
Attrition of the forest flora
• Without vegetation control 21 of the
original 35 forest species or 60% were
present after 5 years (14 / plot).
• With vegetation control 14 of the
original 35 species or 40% were present
after 5 years (6 / plot).
• Kruskal-Wallis p = <0.01
Forest species that were probably
eliminated by herbicide treatments.
years survival
Species
treated
untreated
Dryopteris expansa
3
5
Trientalis borealis
3
5
Carex deweyana
np
5
Hieracium albiflorum
np
5
Luzula parviflora
np
5
Menziesii ferruginea
np
5
Frangula purshiana
np
5
np=not present in first year
Other Species
Festuca occidentalis
Festuca subuliflora
Trillium ovatum
Vaccinium ovalifolium
Tsuga heterophylla
Galium triflorum
Maianthemum dilatatum
Claytonia sibirica
Angelica genuflexa
Mahonia nervosa
Oplopanax horridus
Rosa gymnocarpa
Achlys triphylla
treated
untreated
1
np
np
2
3
1
np
np
1
3
3
3
3
1
1
1
2
3
3
3
3
np
np
np
np
np
n u m b er o f sp ecies
70
60
50
40
30
20
10
0
Species on
8 untreated
plots.
exotic intolerant
native intolerant
native tolerant
total species
1
2
3
5
Species on
8 treated
plots
n u m b er o f sp ecies
year
70
60
50
40
30
20
10
0
exotic intolerant
native intolerant
native tolerant
total
1
2
3
year
5
• Species persisted on the vegetation
control plots in 3 ways:
• 1) annual seed production or reinvasion by
seed. (grasses, Cirsium sp. Senecio sp.
Hypochaeris radicata)
• 2) resprouting from underground organs.
(ferns, Oxalis oregana, Viola sempervirens,
Dicentra formosa, Sambucus racemosa)
• 3) exploitation of herbicide spray shadows.
(Oxalis oregana, Viola sempervirens)
Survival Strategies
35.00
Hypochaeris
radicata (veg.
cntrl.)
Hypochaeris
radicata ( no
veg. cntrl.)
Oxalis oregana
(veg. cntrl.)
% canopy cover
30.00
25.00
20.00
15.00
10.00
5.00
0.00
2000
2001
2002
Year
2003
2004
Oxalis oregana
(no veg. cntrl.)
Cover on untreated plots
70
60
% cover
50
exotic int.
native int.
native tol.
40
30
20
10
0
1
2
3
year
4
5
Cover on treated plots
8
7
% cover
6
exotic int.
native int.
native tol.
5
4
3
2
1
0
1
2
3
year
4
5
Cover Correlations
%Cover
Spearman Corr. Coef.
P
year 3 herb year 3 herb
0.79
<0.01
year 5 herb year 5 herb
0.73
<0.01
%Cover
year 3
herb
Biomass
% Cover Spearman Corr. Coef.
year 5
0.94
herb
P
<0.01
Significance (p) values from ANOVA comparisons of
mean percent canopy cover values of the two
treatments (vegetation and no vegetation control).
n=8 for each group.
year
1
2
3
5
herbs
<0.01
<0.01
<0.01
<0.01
shrubs
0.29
0.05
0.01
<0.01
trees
0.38
0.11
0.05
<0.01
% of tree crown overtopped
Effects on trees
38
34
30
26
22
18
14
10
6
2
-2
2000
no veg. cntrl.
veg. cntrl.
2001
2002
year
2003
2004
Overtopping by of Douglas-fir by
Hypochaeris radicata
Overtopping Species on Untreated Plots
Year
1
2
3
5
Number of contributing species
7
20
21
21
Top 3 species
Senecio
jacobaea
Hypochaeris
radicata
Agrostis
capillaris
Senecio sylvaticus
Senecio
sylvaticus
Senecio vulgaris
Digitalis
purpurea
Chamerion
angustifolium
Hypochaeris radicata
Chamerion
angustifolium
Senecio
jacobaea
Holcus lanatus
Overtopping Species on Treated Plots
Year
1
2
3
5
Number of contributing species
2
4
3
4
Top 3 species
Polystichum
munitum
Pteridium
aquilinum
Pteridium
aquilinum
Hypochaeris
radicata
Senecio
jacobaea
Hypochaeris
radicata
Sambucus
racemosa
Rubus spectabilis
Senecio
jacobaea
Anaphalis
margaritacea
Solanum
dulcamara
3
no veg. control
2
veg. control
1
0
1
2
3
4
5
year
250
crown diameter (cm).
height in m
4
200
no veg. control
150
veg. control
100
50
0
1
2
3
year
4
5
model
%tree cover yr. 5 =
64.35 - 0.149*herb cover yr. 5
model model intercept
r2
p
p
0.63 <0.01
<0.01
%tree cover yr. 5 =
69.14 - 23.48*overtop yr. 5
0.73
<0.01
<0.01
log10(%tree cover treated) =
-0.566 + 0.497*year
0.99
<0.01
0.04
log10(%tree cover untreated) =
- 0.597 + 0.478*year
0.99
0.04
<0.01
Summary
• Survival of forest (60/46%) and first year
species (78/54%) was lower for treated
plots.
• Exotics increased fastest after harvest.
• Herbicide effect greatest in year 1;
decreasing there-after.
• Survival strategies: 1) reinvasion, 2)
resprouting, 3) exploitation of herbicide
shadows. Canopy cover and overtopping
higher in every year on untreated plots.
Overtopping highest in year 2.
• Overtopping spread over many species;
species changed from year to year;
exotics important in years 1 and 2.
• Tree canopy covers were largest in
untreated plots and inversely related to
herb canopy cover and overtopping.
• Cover and biomass were strongly
correlated.
• Crown closure is predicted for year 6—
somewhat sooner in treated plots.
Thank you. Questions?