From spruce to beech forests - fundamental ecosystem transformation driven by climate change

Beech has a wide distribution in Europe, but reaches its northern limit in South-East Norway. With future climate change, it is expected that the beech will expand northwards, probably at the cost of spruce. Beech thus have the potential to get a far greater distribution than today. At the same time, the spruce is expected to struggle under the climatic conditions expected in this area in the future. The dominant tree species and their impact on ecosystems has great importance for future climate through their potential for binding CO2. Previous studies suggest that CO2 sequestered is somewhat larger in coniferous forests compared with broadleaf forests. However, we need more knowledge about the capability for adaption both of beech and spruce, and about how the two tree species affect decomposition and thus CO2 storage below ground. To understand this, we also need more knowledge about the historical emergence and distribution of beech in Norway, and not least about how likely a future expansion is. Historical forest fires have had great significance for current biodiversity and ecosystem function. Our results show that today?s beech and spruce forests have been little affected by fire, but that forest types that were present in Vestfold before the beech and spruce forests, which established itself here about 1200 years ago, has been highly influenced by fire. This suggests that both beech and spruce have the ability to form forest types that may change the incidence and nature of forest fires. We did a litter-bag experiment to measure decomposition rates of beech and spruce litter in both beech and spruce forests. Spruce litter decomposed quicker than beech litter, but both litter-types showed higher decomposition rates in the beech forest. Beech litter released much more N than did spruce litter. The fungal biomass was higher in spruce litter, but despite the much higher decomposition rates in beech forests there was no difference in fungal biomass between the two forest types. Mesofauna had no effect on the decomposition rates, but both mites and springtails increased in abundance with increasing fungal biomass in the litter-bags. The community composition of fungi and bacteria was very different between both litter and forest types. We sowed beech and spruce in soils from both spruce and beech forest under controlled conditions in greenhouses. Both beech and spruce grew best in spruce soils. In transplantation experiments, litter from beech forest was moved to spruce forests and vice versa. Both species germinate best in spruce litter, also in the beech forest. A basic prerequisite for the beech to outcompete spruce will be its ability to germinate and establish new plants in the spruce forest. Seed-feeding animals play an important role, as beech seeds is good feed. With the help of video surveillance, we see that the seed predation rate is high in both spruce and beech forest, it increases from spring to autumn, and most importantly, that the spruce is most negatively affected by seed predation. Small birds and mice is by far the most important seed predators, but beetles also take spruce seeds, but only in the spruce forest, which is a clear disadvantage for the spruce. Using climate chamber- and field experiments, we try to define the climatic potential of the Norwegian beech provenances. A study of 81 neighboring old spruce and beech trees from the Vestfold area, show that both species already struggle with increasing temperature and decreasing precipitation, and that this effect is strongest in spruce. We also studied six Norwegian beech provenances through the dormant period and tested the importance of photoperiod and temperature on the breakage of dormancy. We see that temperature is most decisive for the Norwegian populations, meaning that a warm spring may give an early flush with the possible consequence of spring frost damage. A test of frost hardiness of dormant buds shows that during the winter months the buds can withstand down to -20 ° C before they freeze and die. This may mean that the beech hardly would thrive in the continental areas of Scandinavia. We also test the beech? potential under different climate conditions in the field in three common gardens along a climatic gradient in Norway, with 6 different beech provenances from a gradient throughout Europe. This study will give indications of how well the beech has acclimated to the growing conditions in southern Norway the time it has been here, how large the potential is today for distributing north and about the factors that primarily restricts the distribution. We examined the amount of carbon, nitrogen, fungal biomass and pH at different depths down to the bedrock in two neighboring forests of the two tree species. The most important finding was that the total carbon storage in the two forests are relatively similar, in contrast to the well-established presumption that spruce stores more carbon in the soil.

Using the HadCM3 climate scenario, recent projections of the future distribution of European tree species and vegetation zones suggest that the northern boundaries of temperate forests and hemiboreal forests in southern Scandinavia would move northwards b y about 300-500 km to achieve equilibrium with the new climate. In a South-East Norwegian perspective, such a future change of vegetation and forest types imply that huge areas and their ecosystems will go through fundamental transformations. For example, today's ecosystems that are dominated by Norway spruce are projected to be transformed to beech and mixed beech forest ecosystems, which will be a truly fundamental transformation as key-stone species composition, biodiversity, ecosystem function and ser vices are to be altered. These expected major ecosystem transformations call for knowledge about their rates, drivers and societal consequences. Regarding this, the importance of Norway spruce in the Norwegian forestry sector deserves to be mentioned - th e species is actually the economically most important tree in Norway. In this project we will combine retrospective, descriptive and experimental approaches to explore the relationships between climate change, land-use stress, and the occurrence and ecolo gically functioning of spruce- and beech forests in South-East Norway. Our reason for focusing on this part of Norway is that it provides a "natural laboratory" with landscapes in which spruce- and beech forests meet as beech reaches its north-western dis tribution limit here. In particular we will target how stress induced by land-use interacts with climate change to alter robustness and tipping-points in spruce forest ecosystems, and thereby speeding up their potential transformation into beech forests. Here, the impact of the land-use stress will have a temporal perspective as both historical stress mainly caused by anthropogenic use of fire and recent stress induced by forestry operations will be examined.