Impact of global warming on the tree species composition of boreal forestsin Finland and effects on emissions of isoprenoids

This study aims to identify how climate change may influence total emission s of monoterpene and isoprene from boreal forest canopies. The whole of Fin land is assumed to experience an annual mean temperature (T) increase of 4 degreesC and a precipitation increase of 10% by the year 2100. This will in crease forest resources throughout the country. At the same time, the propo rtions of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) in southern Finland (60 degrees less than or equal to latitude <65<degrees>N) will be reduced from the current 40-50% to less than 10-20%, with increased dominance of birches (Betula pendula and Betula pubescens). In northern Fi nland (65 degrees less than or equal to latitude <70<degrees>N), the propor tions of Norway spruce and Scots pine will be balanced at a level of about 40% as the result of an increase in Norway spruce from the current 21% to 3 7% and a concurrent reduction in Scots pine from 63% to 40%. The proportion of birches is predicted to increase from the current 17% to 23%, but these will become the dominant species only on the most fertile sites. Total mean emissions of monoterpene by Scots pine will be reduced by 80% in southern Finland, but will increase by 62% in the north. Emissions from No rway spruce canopies will increase by 4% in the south but by 428% in the no rth, while those from birch canopies will increase by about 300% and 113%, respectively. Overall emissions of monoterpene over the whole country amoun t to about 950 kg km(-2) y(-1) under current temperature conditions and wil l increase by 17% to 1100 kg km(-2) y(-1) with elevated temperature and pre cipitation, mainly because of an increase at northern latitudes. Under current conditions, emissions of isoprene follow the spatial distribu tion of spruce canopies (the only isoprene-emitting tree species that forms forests in Finland) with four times higher emissions in the south than in the north. The elevated temperature and the changes in the areal distributi on of Norway spruce will result in increases in isoprene emissions of about 37% in southern Finland and 435% in northern Finland. Annual mean isoprene emissions from Norway spruce canopies over the whole country will increase by about 60% up to the year 2100.