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Institute
- FG Bodenschutz und Rekultivierung (108) (remove)
BTU
Climate change is expected in Brandenburg, eastern Germany, in terms of increasing annual temperature and changes in climate variability, as well as the number of extreme weather events. Since agroforestry systems have a planning horizon of several decades, long-term yield assessments are required in order to evaluate the economic profitability and environmental sustainability of such systems. Accordingly, our aim was to simulate the tree growth of poplar trees (Populus nigra x P. maximowiczii) in an agroforestry system in Brandenburg for the next forty years. For this purpose, we used the process-oriented Yield-SAFE model, a parameter-sparse, biophysical model developed for the simulation of plant growth in agroforestry systems. For the investigated period from 2011 to 2014, the validation simulations showed clear correlations with the observed values for woody tree biomass. For the unfolding period from 2015 to 2055, a variety of possible climate changes (including higher evaporation requirements and reduced water availability) and their uncertainties were incorporated into our assessment. The tree yield sensitivity to future climatic conditions was evaluated using 100 realizations of a scenario of the statistical regional climate model Statistical Analogue Resampling Scheme (STAR), which assumes an increase in annual temperature of 2K, as well as decreasing annual precipitation by 30–40 mm. The Yield-SAFE model responded sensitively to changes in the meteorological input data, showing that (1) shifts in temperature and/or precipitation would have a directly proportional influence on tree growth and (2) the impact of potential climate changes on tree growth must be assessed in terms of the complex interaction of various influencing factors. This was evidenced, for example, by the fact that higher average annual temperatures could either increase the tree growth due to a prolonged vegetation period or, on the contrary, decrease the tree growth due to higher potential evapotranspiration. The model results are important for the sustainable planning and management of agroforestry systems, upcoming risk assessments, and example analysis of adaptation scenarios in the near and distant future.
Transitioning towards agroforestry demands systematic productivity assessments of such systems under different climatic and edaphic conditions. In this regard, the Land Equivalent Ratio (LER) serves as a valuable productivity indicator of agroforestry since it evaluates yields from growing trees and crops together in comparison to yields from monocultures over the same period. Consequently, our objective was to evaluate the overall productivity of two agroforestry systems in Forst (Brandenburg) and Wendhausen (Lower Saxony) by means of LER. Our approach followed two assumptions: (i) the yields of trees and crops had equal economic importance and (ii) the economic importance was given solely by the annual crop, the yield of trees representing a supplementary profit. The resulted values for LER were consistently above their specific threshold, corroborating the greater efficiency of agroforestry systems rather than monoculture. Additionally, this study highlighted the importance of choosing the appropriate assumptions when calculating the LER.
The profitability of reclaiming post-mining areas depends on the tree biomass productivity and the restoration of ecosystem functions, such as improving soil and water quality. Agroforestry systems, regarded as combined land-use systems of trees and crops, have the ability to facilitate soil development while reducing wind speed, soil erosion and evaporation. Achieving the maximum biomass productivity of the tree stands depends on the corresponding soil conditions and water availability, but is also influenced by stand structure and the competition between individual trees. For this purpose, black locust (Robinia pseudoacacia L.) trees were planted in a Nelder design in 2010, on a reclaimed post-mining site of the open-cast lignite mining in Welzow Süd (Brandenburg, Germany). Black locust is regarded as a drought-adapted tree species and commonly used for the reclamation of former lignite mining sites in Lower Lusatia, Germany. The Nelder design encompasses angles of arc of equal measure and with the same origin traversed by successive circumferences set at a predefined radial distance. Accordingly, a total of 1071 trees were planted in Welzow Süd at the intersection between 63 spokes and 17 circumferences and at densities ranging from 0.4 to 8.0 m2, with the aim of examining the influence of stand density on the tree growth in a timeframe of six years. In order to evaluate the biomass production of the trees and to determine an optimal planting density on a marginal land, various scenarios were assessed with the help of the Yield-SAFE model, a parameter-sparse process-based agroforestry model. The study revealed the consequences of choosing different tree densities on the tree biomass productivity and water use of trees in relation to the competition for light and water.