Per Holm Nygaard
Research Scientist
Abstract
Converted forests have highly complex soil carbon dynamics due to changes in litter inputs, succession dynamics, soil disturbance, and microbial composition. With warming climate conditions, the dominant tree species used in forestry may switch to more heat-tolerant species, which will affect the matter in which soil carbon changes in novel ways.In the 1940’s, conifer plots were planted in Hirkjølen using Norway spruce (Picea abies), Subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), and mountain hemlock (Tsuga mertensiana) at different altitudes2. Within these sites, the biomass has been monitored every 5-8 years since 1991, but the soil has yet to be examined. These experiments offer an opportunity to compare how long-term soil carbon storage would be affected following conversion by different species.
Authors
Thomas Wohlgemuth Martin M. Gossner Thomas Campagnaro Hélia Marchante Marcela van Loo Giorgio Vacchiano Pilar Castro-Díez Dorota Dobrowolska Anna Gazda Srdjan Keren Zsolt Keserű Marcin Koprowski Nicola La Porta Vitas Marozas Per Holm Nygaard Vilém Podrázský Radosław Puchałka Orna Reisman-Berman Lina Straigytė Tiina Ylioja Elisabeth Pötzelsberger Joaquim S. SilvaAbstract
In the context of global change, the integration of non-native tree (NNT) species into European forestry is increasingly being discussed. The ecological consequences of increasing use or spread of NNTs in European forests are highly uncertain, as the scientific evidence is either constraint to results from case studies with limited spatial extent, or concerns global assessments that lack focus on European NNTs. For either case, generalisations on European NNTs are challenging to draw. Here we compile data on the impacts of seven important NNTs (Acacia dealbata, Ailanthus altissima, Eucalyptus globulus, Prunus serotina, Pseudotsuga menziesii, Quercus rubra, Robinia pseudoacacia) on physical and chemical soil properties and diversity attributes in Europe, and summarise commonalities and differences. From a total of 103 publications considered, studies on diversity attributes were overall more frequent than studies on soil properties. The effects on soil properties varied greatly among tree species and depended on the respective soil property. Overall, increasing (45%) and decreasing (45%) impacts on soil occurred with similar frequency. In contrast, decreasing impacts on biodiversity were much more frequent (66%) than increasing ones (24%). Species phylogenetically distant from European tree species, such as Acacia dealbata, Eucalyptus globulus and Ailanthus altissima, showed the strongest decreasing impacts on biodiversity. Our results suggest that forest managers should be cautious in using NNTs, as a majority of NNT stands host fewer species when compared with native tree species or ecosystems, likely reflected in changes in biotic interactions and ecosystem functions. The high variability of impacts suggests that individual NNTs should be assessed separately, but NNTs that lack European relatives should be used with particular caution.
Abstract
Mountain birch forest covers large areas in Eurasia, and their ecological resilience provides important ecosystem services to human societies. This study describes long-term stand dynamics based on permanent plots in the upper mountain birch belt in SE Norway. We also present forest line changes over a period of 70 years. Inventories were conducted in 1931, 1953, and 2007. Overall, there were small changes from 1931 up to 1953 followed by a marked increase in biomass and dominant height of mountain birch throughout the period from 1953 to 2007. In addition, the biomass of spruce (Picea abies) and the number of plots with spruce present doubled. The high mortality rate of larger birch stems and large recruitment by sprouting since the 1960s reveal recurrent rejuvenation events after the earlier outbreak of the autumnal moth (Epirrita autumnata). Our results demonstrate both a high stem turnover in mountain birch and a great ability to recover after disturbances. This trend is interpreted as regrowth after a moth attack, but also long-term and time-lagged responses due to slightly improved growth conditions. An advance of the mountain birch forest line by 0.71 m year−1 from 1937 to 2007 was documented, resulting in a total reduction of the alpine area by 12%. Most of the changes in the forest line seem to have taken place after 1960. Regarding silviculture methods in mountain birch, a dimension cutting of larger birch trees with a cutting interval of c. 60 years seems to be a sustainable alternative for mimicking natural processes.