How is climate change affecting the growth of Douglas

How is climate change affecting the growth of Douglas-fir trees in dry coastal ecosystems of BC?
H. Griesbauer1, H. Klassen2,3, D.S. Green2, and S.C. Saunders3
1 Consultant, 2 UNBC, 3 BC Min. of Forests, Lands, and Natural Resource Operations
Contact: [email protected]
Background
CDF-x
Recent climate change studies indicate that dry coastal ecosystems may
be susceptible to impacts of climatic change. This study examines how
climate change may affect Douglas-fir productivity in dry coastal
ecosystems by assessing the relationship between climate and growth, as
determined using tree-rings from mature Douglas-fir trees.
Chronologies
Chronologies for the five sites show generally similar patterns over the last century (Figure 3).
Synchronous growth declines across sites may be related to regional climatic events such as
droughts. As well, growth has significantly declined since approximately 1980 in four of the
five sites. This may indicate changing growth responses to climate or increasing
maladaptation of Douglas-fir populations.
Figure 3: Annual growth
at the five study sites.
Vertical red lines indicate
years with low growth;
green lines indicate years
with high growth. Note
synchronous growth
declines in 1910 and
1930, and growth decline
since ~1980.
Research Question: Is there a relationship between growth patterns of
Douglas-fir trees and climate across site types of dry coastal ecosystems?
CDF-h
North
Central
Sampling Transect
South
CWH-z
CDF-x
CDF-h
TRN-z
CDF-z
Synchronous Growth Declines
Growth and climate
Figure 1: The 5 study site locations on the south
end of Vancouver Island, BC. Inset figure shows
the location of all three study transects.
Sample processing and analysis
TRN-z
At each site, cores were taken from 20 healthy, dominant/codominant trees. Cores
were sanded to enhance the contrast in the annual growth rings (Figure 2). Growth
variation (narrow or wide rings) may be related to drought or other climate-related
events.
Ring widths were measured at the UNBC Dendrochronology Lab
(www.unbc.ca/dendrolab) and averaged together at each site to form a time series
of stand growth, termed a chronology.
Drought?
CWH-z
Drought?
Figure 2: Tree rings along a core from a Douglas-fir tree growing on a drought-prone site.
Annual growth variation was compared to
Environment Canada climate station data from
Victoria to identify important climate variables
that influence growth at each site.
Preliminary results indicate that drought and
summer precipitation are primary climatic
limitations across the transect. Sensitivity to
drought is highest in the driest sites in the
Coastal Douglas-fir zone. Since ~1980,
summer precipitation has generally declined
and growth has become highly sensitive to
summer precipitation (Figure 4).
Projections of future drought and drier
summers in coastal ecosystems may result in
growth declines in Douglas-fir forests,
particularly on drier site types.
R2 = 0.48
P < 0.05
Growth Index
CDF-z
We sampled trees from 5 study sites
on the south end of Vancouver
Island, BC (Figure 1). The study sites
are part of a larger set of transects
that were established to explore the
relationships of climate, soil, and
vegetation across a soil moisture
gradient within the Coastal Douglasfir moist maritime (CDFmm) BEC
subzone and the adjacent Coastal
Western Hemlock very dry maritime
(CWHxm) subzone (see Klassen et
al. 2011). The transect is composed
of zonal sites within the CDFmm
(CDF-z), the transition between the
CDFmm and the CWHxm (TRN-z),
and within the CWHxm (CWH-z), as
well as xeric (CDF-x) and hygric
(CDF-h) sites within the CDFmm.
growth index
Study sites
Figure 4: Strong positive relationship
between growth and summer precipitation
in the CDF-zonal site from 1980-2009.
Acknowledgements
Funding: BC Ministry of Forests, Lands, and Natural Resource Operations (MFLNRO)
Field sites and equipment: BC Parks, Capital Regional District
Sampling and analysis: Canadian Forest Service (CFS), BC Ministry of Environment (MOE) and
MFLNRO tree coring crew, University of Northern BC