[MCN] USFS: Doug-fir drought tolerance varies by distance from coast

[Lance Olsen]

Graphic/map identifies areas where drought tolerance is highest, lowest
http://www.fs.fed.us/pnw/sciencef/scifi179.pdf

Some populations of Douglas-fir are more drought tolerant than 
others. In an ongoing study, researchers are testing how seed grown 
from different populations respond to temperature and precipitation 
conditions that differ from current local conditions.

IN SUMMARY
Douglas-fir is an iconic tree in the Pacific Northwest. Although 
individual trees may appear to be identical, genetic differences 
within each tree have resulted from adaptation to the local 
environment. These genetic differences over time have resulted in 
differences among populations that are important to the species' 
survival and growth in changing climates.

Current climate models project that over the next 50 years, the 
Pacific Northwest will experience an increase in summer temperatures. 
Combined with less winter snowpack, warmer summer temperatures will 
likely lead to more frequent and intense droughts, and it is unknown 
how Douglas-fir will respond. Researchers with the U.S. Forest 
Service Pacific Northwest Research Station tested how seedlings from 
different populations of Douglas-fir would grow in temperature and 
precipitation conditions unlike the climate of their current seed 
source. By sampling 35 populations in three common garden sites, 
researchers deter- mined how a combination of genetic factors and 
environmental conditions influence drought-tolerant traits.

Trees grown in a warm, dry environment had lower rates of water loss 
compared to seedlings grown in cooler environments. Furthermore, 
researchers identified populations that had high drought tolerance 
and relatively fast growth. This means that although Douglas-fir as a 
species is relatively drought tolerant, some populations are better 
adapted to future climate conditions than others.

LAND MANAGEMENT IMPLICATIONS
*By measuring an individual tree's minimum transpiration rate, water 
deficit, and specific leaf area, tree improvement programs can 
identify nursery stock that exhibits relatively high drought 
tolerance.

*Models relating drought tolerance to the climates of seed sources 
may be used to predict which populations are naturally more resistant 
to drought stress.

*With this information, land managers can plant seedlings that will 
be adapted to current and future climate conditions. For example, 
populations that are more tolerant of drought stress can be planted 
in drought-prone areas.

Full report here:
http://www.fs.fed.us/pnw/sciencef/scifi179.pdf
-- 
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"The broad pattern of these changes is clear enough."

George Woodwell.  The Energy Cycle of the Biosphere.
Scientific American, September 1970, p. 36


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