RESUMEN
A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.
Asunto(s)
Betula/crecimiento & desarrollo , Cambio Climático , Picea/crecimiento & desarrollo , Pinus sylvestris/crecimiento & desarrollo , Madera/crecimiento & desarrollo , Carbono/metabolismo , Sequías , Ecosistema , Finlandia , Modelos Biológicos , Fotosíntesis , Transpiración de Plantas , Suelo , AguaRESUMEN
We have developed a forest ecosystem model to assess the effects of climate change on the functioning and structure of boreal coniferous forests assuming that temperature and precipitation are the major variables of the niche occupied by a tree species. We specified weather patterns to a level representing the time constant of different physiological and ecological processes relevant to the survival, growth and death of trees. We thereby coupled the long-term dynamics of the forest ecosystem with climate through physiological mechanisms such as photosynthesis and respiration in terms of energy flow through the ecosystem. The hydrological and nutrient cycles couple the dynamics of the forest ecosystem with climate change through soil processes, which represent the thermal and hydraulic properties of the soil, and the decomposition of litter and humus with mineralization of nutrients. Simulations for southern Finland (62 degrees N) indicated that an increase in temperature of 5 degrees C over one hundred years could reduce soil water in Scots pine-dominated forest ecosystems. At the same time, the temperature increase could enhance photosynthesis up to 6-8% under current CO(2) concentrations (330 ppm) and up to 8-10% under elevated CO(2) concentrations (660 ppm). Because the elevated temperature and CO(2) concentration caused an increase in respiration (12-14% more than under the current climate), total stem production increased only up to 4% with a 5 degrees C increase in temperature and up to 6% when temperature and atmospheric CO(2) concentration were increased simultaneously. Because transpiration only increased up to 5% in response to elevated temperature and CO(2) concentration, the water use efficiency of Scots-pine dominated forest ecosystems increased up to 3%, particularly during the late rotation.