15. Effects of Climate Change on Forest Ecosystems
309
presently cool areas. The increased carbon dioxide concentration may
increase water use efficiency and growth of plants (Eamus & Jarvis, 1989;
Graham et al., 1990; Ausubel, 1991; Michaels & Stooksbury, 1992).
Franklin et at. (1992) and Veblen and Alaback (1995) suggest that disturbance regimes, such as those produced by fire or forest harvesting
and renewal, interact with climate changes creating opportunities for
adaptation by reducing the inertia of established forests. Disturbances can
be viewed as events that speed adjustment of the vegetation to current
environmental conditions, though they may be highly disruptive in the
short to mid term .
Application of the Response Framework
Any analysis requires some form of a model. The problem is what to
include and how to include it. The level of detail and scale depend on the
type of planning being considered (Malanson, 1993). For example,
Running and Namani (1991) assessed regional links between changes in
water use and potential tree growth. Detailed simulations of ecosystem
succession at the site level have been made for unmanaged ecosystems
(Smith et al., 1992). The approaches I use here were chosen in recognition
of the limited data available and the need to present information in a
form suitable for use by forest managers. I will be assessing the effect of
climate changes on a dominant tree species, Douglas-fir (Pseudotsuga
menziesii (Mirb .) Franco), in coastal British Columbia, by considering the
sensitivity of reforestation and growth of Douglas-fir to changes in rainfall
and temperature. The approach is similar to that used by LeBlanc and
Foster (1992) for oak in the midwestern United States.
Douglas-fir is an important commercial tree species occupying mid to
low elevation, relatively dry sites over a wide latitudinal range in the
Pacific Northwest. It is a seasonal rainforest (low summer rainfall) where
disturbance is an important part of the life cycle, and biodiversity and
biomass are high (Meidinger & Pojar, 1991; Boyle, 1995; Veblen &
Alaback 1995). Paleoclimatological data indicate that the shift to modern
forest composition began about 6000 years ago in the Pacific Northwest in
response to a climatic cooling and increased precipitation (Brubaker,
1992). Global climate models predict a warmer climate with drier summers
for the Pacific Northwest (Boer, McFarlane , & Lazare, 1992), which
means that the range of Douglas-fir would move northward and upward
in elevation (Leverenz & Lev, 1987). Woodman (1987) suggested that in
this situation no overall change would be required in the management
of Douglas-fir. I would disagree with this latter assessment, because
responses will be required to manage sites where Douglas-fir ecosystems
are threatened. Also there would be many challenges in introducing or
309
presently cool areas. The increased carbon dioxide concentration may
increase water use efficiency and growth of plants (Eamus & Jarvis, 1989;
Graham et al., 1990; Ausubel, 1991; Michaels & Stooksbury, 1992).
Franklin et at. (1992) and Veblen and Alaback (1995) suggest that disturbance regimes, such as those produced by fire or forest harvesting
and renewal, interact with climate changes creating opportunities for
adaptation by reducing the inertia of established forests. Disturbances can
be viewed as events that speed adjustment of the vegetation to current
environmental conditions, though they may be highly disruptive in the
short to mid term .
Application of the Response Framework
Any analysis requires some form of a model. The problem is what to
include and how to include it. The level of detail and scale depend on the
type of planning being considered (Malanson, 1993). For example,
Running and Namani (1991) assessed regional links between changes in
water use and potential tree growth. Detailed simulations of ecosystem
succession at the site level have been made for unmanaged ecosystems
(Smith et al., 1992). The approaches I use here were chosen in recognition
of the limited data available and the need to present information in a
form suitable for use by forest managers. I will be assessing the effect of
climate changes on a dominant tree species, Douglas-fir (Pseudotsuga
menziesii (Mirb .) Franco), in coastal British Columbia, by considering the
sensitivity of reforestation and growth of Douglas-fir to changes in rainfall
and temperature. The approach is similar to that used by LeBlanc and
Foster (1992) for oak in the midwestern United States.
Douglas-fir is an important commercial tree species occupying mid to
low elevation, relatively dry sites over a wide latitudinal range in the
Pacific Northwest. It is a seasonal rainforest (low summer rainfall) where
disturbance is an important part of the life cycle, and biodiversity and
biomass are high (Meidinger & Pojar, 1991; Boyle, 1995; Veblen &
Alaback 1995). Paleoclimatological data indicate that the shift to modern
forest composition began about 6000 years ago in the Pacific Northwest in
response to a climatic cooling and increased precipitation (Brubaker,
1992). Global climate models predict a warmer climate with drier summers
for the Pacific Northwest (Boer, McFarlane , & Lazare, 1992), which
means that the range of Douglas-fir would move northward and upward
in elevation (Leverenz & Lev, 1987). Woodman (1987) suggested that in
this situation no overall change would be required in the management
of Douglas-fir. I would disagree with this latter assessment, because
responses will be required to manage sites where Douglas-fir ecosystems
are threatened. Also there would be many challenges in introducing or