15. Effects of Climate Change on Forest Ecosystems
311
Soil Water Status
Adequate
Marginal
Too Dry
1908 1916 1924 1932 1940 1948 1956 1964 1972 1980 1988
Year
Figure 15.1. Interannual variation in the soil water status for establishment of
Douglas fir seedlings. The height of the bar indicates the soil water status. The
percentage in each category is given in Table 15.1
and June rainfall was 38mm for the increased rainfall case , and 26 and
25 mm, respectively , for the reduced rainfall case. These changes could be
considered as only a change in rainfall , or a surrogate for a change in
evaporative demand plus a change in rainfall equivalent to a ±20%
change in water availability. A 20% decrease in rainfall made conditions
much worse (Table 15.1) , particularly since about 65% of the marginal
cases were close to the drier end of the range. Consecutive dry years may
exacerbate conditions. Figure 15.1 shows only one such period of two or
more years long occurred under the present climate . This changed to 4
times with a 20% .reduction in rain. A 20% increase in rainfall gave a
substantial improvement in establishment conditions.
A change in rainfall may be accompanied by changes in air temperature ,
humidity and cloudiness (Boer et al., 1992). This will effect evaporative
Table 15.1. Influence of soil water status on the likelihood of successful establishment after spring planting. Percentage of years from 1908-1989 in the establishment categories described in the text are shown for actual rainfall, and for a 20%
increase and decrease in rainfall
Percentage of years (1908-1989)
Too Dry
Marginal
Adequate
Actual
20% decrease
20% increase
18
31
13
49
56
37
33
13
50
311
Soil Water Status
Adequate
Marginal
Too Dry
1908 1916 1924 1932 1940 1948 1956 1964 1972 1980 1988
Year
Figure 15.1. Interannual variation in the soil water status for establishment of
Douglas fir seedlings. The height of the bar indicates the soil water status. The
percentage in each category is given in Table 15.1
and June rainfall was 38mm for the increased rainfall case , and 26 and
25 mm, respectively , for the reduced rainfall case. These changes could be
considered as only a change in rainfall , or a surrogate for a change in
evaporative demand plus a change in rainfall equivalent to a ±20%
change in water availability. A 20% decrease in rainfall made conditions
much worse (Table 15.1) , particularly since about 65% of the marginal
cases were close to the drier end of the range. Consecutive dry years may
exacerbate conditions. Figure 15.1 shows only one such period of two or
more years long occurred under the present climate . This changed to 4
times with a 20% .reduction in rain. A 20% increase in rainfall gave a
substantial improvement in establishment conditions.
A change in rainfall may be accompanied by changes in air temperature ,
humidity and cloudiness (Boer et al., 1992). This will effect evaporative
Table 15.1. Influence of soil water status on the likelihood of successful establishment after spring planting. Percentage of years from 1908-1989 in the establishment categories described in the text are shown for actual rainfall, and for a 20%
increase and decrease in rainfall
Percentage of years (1908-1989)
Too Dry
Marginal
Adequate
Actual
20% decrease
20% increase
18
31
13
49
56
37
33
13
50