Impacts of climate change on timber production and regional risks of wind-induced damage to forests in Finland

摘要

In this work, we studied the impacts of climate change on timber production and regional risks of wind-induced damage to forests in Finland. The work employed: (i) national level forest inventory data, (ii) current baseline climate (1961-1990) and changing climate scenario (FINADAPT A2, 2001-2099), (iii) a forest ecosystem model (SIMA), (iv) a mechanistic wind damage model (HWIND), and (v) currently applied forest management recommendations as a baseline. The results showed that the timber production will increase significantly towards the end of this century under the changing climate, and in a relative sense the most in Northern Finland. At the same time, the share of Norway spruce (Picea abies L. Karst.) is expected to decrease, especially in southernmost Finland, mainly favoring the presence of birch (Betula spp.), but also Scots pine (Pinus sylvestris L.), when no species preference is given in management. As a result, the proportion of forest area in the two lowest critical wind speed classes (i.e. winds of 11-14 and 14-17msa degree 1) will decrease in the autumn (birch without leaves) throughout Finland. However, in summertime (birch is in leaf) the proportion of forest area with such critical wind speeds will even increase in southernmost Finland. Even though, in summertime the risk of damage should be on average relatively low throughout Finland due to a lower occurrence of such wind speeds compared to the windiest time of the year (i.e. from autumn to early spring). The return period of critical wind speeds of 11-17msa degree 1 is today about every two years in southernmost Finland. In Northern Finland, the critical wind speeds needed for wind damage are, on average, higher due to the larger share of Scots pine and on average lower height to breast height diameter ratios of trees compared to the south. To conclude, the climate change will affect clearly the forest growth and dynamics and, thus increase the need to manage forests more often and/or heavily (e.g. thinning, final felling), which in addition to species preference, will affect the risks of damages. The consideration of the risk of wind damage is crucial especially in Southern Finland when adapting forest management to the changing climate. This is because the unfrozen soil period is expected to increase significantly in Finland, which decreases tree anchorage during the windiest time of year.