Density of foliage mass and area in the boreal forest cover in Finland, with applications to the estimation of monoterpene and isoprene emissions

The distribution of the density of foliage mass and area in forest canopies throughout Finland (60–70°N) were determined on the basis of the permanent sample plots used in the Finnish National Forest Inventory. These parameters were linked to the long-term monthly mean air temperatures for 1961–1990, which had been converted to hourly temperature and radiation values with the help of a weather simulator in order to calculate the spatial distribution of mean yearly emissions of monoterpene and isoprene over Finland. The mean total density of foliage mass in southern Finland (60° latitude<65°N) was around 500 g m−2, equivalent to 4–5 m2 of total foliage area per m2 of land area. In northern Finland (65° latitude<70°N), the maximum values remained below 200–300 g m−2, or 2–3 m2 m−2. The highest values were achieved in forests dominated by mature Norway spruces. The higher temperatures and longer growing season in southern Finland led to greater emissions than in the rest of the country. Total annual emissions of monoterpene were 1070 kg km−2 yr−1 in southern Finland and 460 kg km−2 yr−1 in the north, and those of isoprene from Norway spruce canopies 150 and 40 kg km−2 yr−1, respectively.