15. Effects of Climate Change on Forest Ecosystems
313
& Childs, 1990). Fourth , increasing planting density or planting a mix in
genetic sources of seedlings could be used on the expectation that withinpopulation genetic variability will mean that some of the seedlings are
more drought tolerant than others and will survive. Ledig and Kitzmiller
(1992) suggest that since future change is unknown , it is prudent now to
plant seedlings from families that do well under a range of climates. It is
not feasible to plant alternate species now, in the expectation that they
will be suited to future climates, when we do not know what these
climatic conditions are or when they will occur. A fifth option is research
to develop drought tolerant planting stock. This could including redesigning the seedling, e.g. , larger root mass , or selection of droughttolerant genotypes (Farnum, 1992).
Monitoring
The response strategy is not complete without a commitment to monitor
what is happening. Whatever the chosen responses , there has to be a
follow-up program in place. This acts both as an early warning system for
future change as well as determining how and when actions should be
taken.
Tree Growth
Issue of concern
Changes in growing season rainfall and air temperature will affect the
annual growth of established Douglas-fir trees. Interannual variation in
rainfall significantly affect the growth of Douglas-fir in coastal British
Columbia (Spittlehouse 1985; Giles , Black, & Spittlehouse, 1985;
Robertson , Jozsa, & Spittlehouse, 1990). From the timber management
viewpoint, changes in the rate of tree growth will affect the time to harvest and the amount of wood available for harvest. Nontimber resources,
such as the development of understory vegetation and animal habitat, will
also be affected.
Scenarios
A forest water balance model was used to simulate April to October
water use at two locations. Precipitation is adequate at other times of the
year. The simulations for the first location (49°51' N , 125°14' W) were
from 1965 to 1980 for a O.75-m-deep gravelly sandy loam on an 8% NEfacing slope , 150 m elevation . Diameter growth varied annually by up to
±20% , and 80% of this was explained by differences in water use linked
to variation in summer rainfall. A lack of rain in Ma y and June had a
greater effect than in August (Spittlehouse, 1985).
In the second analysis, I applied the water balance model to the seven
sites described in Giles et al. (1985). These sites are on a SW-facing 10 to
313
& Childs, 1990). Fourth , increasing planting density or planting a mix in
genetic sources of seedlings could be used on the expectation that withinpopulation genetic variability will mean that some of the seedlings are
more drought tolerant than others and will survive. Ledig and Kitzmiller
(1992) suggest that since future change is unknown , it is prudent now to
plant seedlings from families that do well under a range of climates. It is
not feasible to plant alternate species now, in the expectation that they
will be suited to future climates, when we do not know what these
climatic conditions are or when they will occur. A fifth option is research
to develop drought tolerant planting stock. This could including redesigning the seedling, e.g. , larger root mass , or selection of droughttolerant genotypes (Farnum, 1992).
Monitoring
The response strategy is not complete without a commitment to monitor
what is happening. Whatever the chosen responses , there has to be a
follow-up program in place. This acts both as an early warning system for
future change as well as determining how and when actions should be
taken.
Tree Growth
Issue of concern
Changes in growing season rainfall and air temperature will affect the
annual growth of established Douglas-fir trees. Interannual variation in
rainfall significantly affect the growth of Douglas-fir in coastal British
Columbia (Spittlehouse 1985; Giles , Black, & Spittlehouse, 1985;
Robertson , Jozsa, & Spittlehouse, 1990). From the timber management
viewpoint, changes in the rate of tree growth will affect the time to harvest and the amount of wood available for harvest. Nontimber resources,
such as the development of understory vegetation and animal habitat, will
also be affected.
Scenarios
A forest water balance model was used to simulate April to October
water use at two locations. Precipitation is adequate at other times of the
year. The simulations for the first location (49°51' N , 125°14' W) were
from 1965 to 1980 for a O.75-m-deep gravelly sandy loam on an 8% NEfacing slope , 150 m elevation . Diameter growth varied annually by up to
±20% , and 80% of this was explained by differences in water use linked
to variation in summer rainfall. A lack of rain in Ma y and June had a
greater effect than in August (Spittlehouse, 1985).
In the second analysis, I applied the water balance model to the seven
sites described in Giles et al. (1985). These sites are on a SW-facing 10 to