Mgr. Cannell et al., UK CONIFER FORESTS MAY BE GROWING FASTER IN RESPONSE TO INCREASED N DEPOSITION, ATMOSPHERIC CO2 AND TEMPERATURE, Forestry, 71(4), 1998, pp. 277-296
Site studies have shown that conifer plantations in northern Britain h
ave increased in General Yield Class (GYC) by 1 m(3) ha(-1) a(-1) per
decade or more (20-40 per cent) since the 1930s. Large increases in fo
rest productivity have also occurred in many other regions of Europe.
Are these increases due to improved silvicultural practices or to incr
eases in N deposition, CO2 and temperature? Two process-based mathemat
ical models of forest growth were used to simulate the responses of co
nifer forests growing in the Scottish southern uplands to increases in
atmospheric N deposition, CO2 concentration and temperature, during t
his century and next century. The models differed substantially in the
ways in which underlying processes were represented: one simulated a
managed plantation, the other a natural forest. Nevertheless, both sho
wed that: (1) increases in N deposition, CO2 and temperature together
might account for up to half of the observed increase in GYC this cent
ury; (2) increased N deposition and CO2, considered separately, probab
ly increased forest productivity by a modest amount (7-14 per cent), b
ut their combined effect has been approximately additive; (3) increase
d temperature, even when combined with increasing CO2 concentrations,
promoted growth less than expected from site studies relating GYC to t
emperature; and (4) substantial further increases in productivity, GYC
, leaf area index and standing biomass are forecast during the next ce
ntury as a result of increasing CO2 concentrations and continued N dep
osition, with or without climatic warming. The predicted increases in
GYC could be large enough to have profound effects on the forest indus
try.