is climate change driving yellow-cedar decline on haida … · 2018. 3. 13. · haida gwaii is...
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O N D J F M A M J J A S O N D J F M A M J J A S
O N D J F M A M J J A S O N D J F M A M J J A S
1946-1976 1977-2014
Tave
PPT
Live Chronology (detrended with 100 yr spline)
Understory Overstory
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100
200
300
200 400 600 800
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0.4
0.8
Live Declining Dead
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DENSITY (trees/ha)• Proportion of declining
and dead trees does not increase with density
• No evidence of density-dependent mortality
DBH (cm)• Mean DBH of live,
declining and dead trees were similar
• Declining and dead trees were not the smallest
• No evidence of self-thinning
IS CLIMATE CHANGE DRIVING YELLOW-CEDAR DECLINE ON HAIDA GWAII?Vanessa Comeau and Lori Daniels – The Tree-Ring Lab at UBC, Faculty of Forestry, University of British Columbia, Vancouver
BACKGROUND• Yellow-cedar decline is widespread along coastal BC and
Alaska and recently became apparent on Haida Gwaii• The driving factor of this decline is thought to be climatic
warming, which has reduced snowpack and exposed fine roots to freezing damage
• This proposed mechanism may not adequately explain the decline in Haida Gwaii due to the temperate climate and ephemeral snowpack
• This research uses dendrochronology to investigate climate as a driver of decline
• Determining the cause of this decline is the first step to resilience
QUESTIONS• In targeted forests exhibiting decline, what proportion of
yellow-cedar are live (healthy), declining or dead?
• Which yellow-cedar are declining and why?
• Does growth near the outer rings of live, declining and dead yellow-cedar differ?
• How did inter-annual and multi-decadal climate variation in the 20th century influence radial growth of yellow-cedar?
• Can this decline be mitigated through management?
RESEARCH APPROACH• Targeted areas exhibiting yellow-cedar decline
on Graham Island, Haida Gwaii• Census of all yellow-cedar trees (DBH ≥10cm) in
100 x 20m transects at 15 sites (1016 trees)• Increment cores taken from 15 healthy live and
15 declining/dead yellow-cedars at each site (450 trees)
MOST YELLOW-CEDAR DEAD OR DECLINING
DECLINE ACROSS SIZE AND AGE
DEATH AND CESSATION OF RADIAL GROWTH
SUMMARY• At targeted sites, high proportions of declining and dead trees• Trees of all ages and sizes are affected, with greater impacts on
overstory trees, but not due to competition and self-thinning • Trees of all status classes show suppression near the outer rings• Warm temperatures facilitated increasing growth in the 20th century• Decline in growth associated with low winter precipitation (snow) and
warm temperatures, is consistent with the drivers of decline in Alaska • Improved understanding of snow distribution and persistence in
Haida Gwaii is needed to guide management
ACKNOWLEDGEMENTSThank you for funding from Taan Forest, BC FLNRO and NSERC-Engage, collaboration with the Council of the Haida Nation and R. Chavardès (Tree Ring Lab at UBC), and research assistants: G. Knochenmus, I. Jarvis, J. Liu, A. Weixelman, J. Coutu, J. Heredia, D. Hornsberger, S. Bronson and D. Fluharty for assistance in the field and lab. VC received scholarships from NSERC-CGS and the UBC Faculty of Forestry.
• 1016 trees sampled at 15 targeted sites exhibiting yellow-cedar decline
• 74% of yellow-cedar were declining or dead • 59 to 86% of trees were declining or dead per site• 14 to 41% of trees were live, healthy per site
DECLINE NOT DUE TO COMPETITION
HEIGHT CLASS• More dead overstory trees
and fewer live and declining understory trees than expected by chance
• Opposite to patterns expected due to competition and self-thinning
AGE ESTIMATES• Age range: 29 to 908 years• Live, declining and dead trees present
across all ages • Declining and dead trees were not oldest
(reaching lifespan) or youngest (self-thinning)
DIAMETER AT BREAST HEIGHT• DBH range: 10 to 140 cm• Live, declining and dead trees present
across all size classes • Similar distributions of size for live,
declining and dead trees
• If winter precipitation is partly snow, relationships in the winter are consistent
with the snowpack hypothesis from Alaska
CLIMATE-GROWTH SHIFTS THROUGH TIME
Dead46.5%
Live26.1%
Declining27.5%
1946-1976Cool-dry-more snow
1977-2014Warm-wet-less snow
• Spring and summer correlations stronger from 1977-2014 in the warm phase
• Wet springs limit growth
• Precipitation in fall and winter (snow?) has more influence than in the growing season
Subset of 357 trees (live:208, declining:80, dead:69)
Freq
ue
ncy
(tr
ees)
Total Precipitation
Mean Temperature
p=0.16, 0.11, 0.65 p<0.001
Mea
n D
BH
(cm
)
Pro
po
rtio
n (
tree
s)
Co
rrel
atio
n c
oef
fici
ents
Pro
po
rtio
n (
tree
s)
SUPPRESSION AT OUTER RINGS• Decline is visible in radial growth rings before death in many trees• 13% of live and 46% of declining trees had suppressed outer rings• For trees which had died 24% had suppressed outer rings
Freq
ue
ncy
(tr
ees)
Age (years)n=444
20 40 60 80 100 120
0
20
40
60
80
100
120DBH (cm)n=1016
p=0.03
Freq
ue
ncy
(tr
ees)
1920 1940 1960 1980 2000
0
2
4
6
1985 1995 2005 2015
0
2
4
6 OUTER RING DATES• 191 live and 73 declining trees formed rings
the year of sampling• 59 living trees (live or declining) stopped
forming rings after 1918, 70% from 2000 to 2014
• 69 trees died after 1852, 42% from 2000 to 2015
Warm/wet Nov, wet Dec limit growth
Dry Nov/Dec, warm Jan limit growth
Warm spring and summer facilitates growth
marks 50yrs