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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.
Als mehrjährige Bioenergiepflanze kann Sida hermaphrodita eine wichtige Rolle für den Anbau auf marginalen Standorten in der nahen Zukunft spielen. In einem kontrollierten Topfexperiment wurde der Einfluss von verschiedenen Kompostgehalten (10, 20, 30, 50%) und mineralischem Stickstoffdünger (100 kg N ha–1) auf Biomasse, Wuchshöhe und Kohlenstoffallokation während der Etablierungsphase untersucht. Weiterhin wurden ökophysiologische Parameter (Gaswechsel, Chlorophyllfluoreszenz, Chlorophyllgehalte) mit nicht-destruktiven Methoden bestimmt. Die Ergebnisse des Experimentes zeigen, dass sowohl die Stickstoffdüngung als auch die Kompostgabe positive Effekte für das Wachstumsverhalten hat. Während der Etablierungsphase erreichten die gedüngten Pflanzen eine mittlere Pflanzenhöhe von bis zu 127 cm (maximale Wuchshöhe 168 cm). Die Photosynthese wurde nicht durch die unterschiedlichen Behandlungen beeinflusst. Die mittlere CO2-Austauschrate variiert zwischen 5,8 und 9,9 μmol m–2 s–1 und die Elektronentransportrate zwischen 34,5 und 53,9 μmol m–2 s–1. Die Verwendung von Kompost und Stickstoff ist für eine bessere Biomasseproduktion von Sida in marginalen Böden möglich, auch wenn das Wachstum im ersten Jahr limitiert ist und es negative Rückwirkungen auf die Bestandesetablierung gibt.
Robinia pseudoacacia L. is a pioneer tree species which grows under a wide range of edaphic and climatic conditions. It is native from North America and its original range is a climatic region classified as humid to sub-humid, with a mean annual precipitation of 1.020 to 1.830 mm. However, in Central Europe the species has proven to be relatively drought tolerant in comparison to other temperate deciduous tree species. In the State of Brandenburg (Germany) for instance, with a continental climate and annual precipitation below 600 mm, the species has been successfully cropped for wood production for more than 250 years. The tree notably grows also in post-mining recultivated sites where soil water availability is limited and in spring and summer drought can occur. The importance of the species has increased over the lasts decades, after the CO2 reduction policy spread across the world, just as did the need for further sources for renewable energy. Therefore, due to its adaptability to water constraints, its fast growing and resprouting rate, together with the ability of nitrogen fixation, black locust could become a key species for short-rotation plantation on marginal land. Several studies have been already carried out to quantify the production and water use efficiency of the black locust. However, the effect of water scarcity on biomass production and the plant’s response to drought stress has still to be examined. In ourinvestigation we aim to evaluate the growth performance and the ecophysiological response of black locust to water limitation. The study of the soil-plant-atmosphere system for the evaluation of the relation between water availability, atmospheric evaporative demand and plant water status is critical to identify the ecophysiological adaptation and growth response in relation to different edaphic and climatic conditions. Different irrigation regimes and cycles of drought were chosen, to test the plant’s performance in a lysimeter experiment for the duration of two vegetation periods, under semi-controlled environmental conditions. The results obtained from studies were satisfactory. We assessed the drought tolerance and resilience of black locust, together with its water use efficiency. Both at whole-plant and leaf level the link between the soil water retention, plant water status and growth rate has been elucidated and the intertwined relation between primary production, transpiration, CO2 uptake and water limitation, together with the evaporative atmospheric demand, has been clarified.
Short-rotation forestry and agroforestry systems have the potential to become an ecologically valuable and economically profitable land use alternative on marginal lands. Therefore, our project focuses on determining the water demand for biomass production of black locust in the Lusatia region (Eastern Germany). The area is characterized by relative low annual rainfall (560-600 mm/yr) and drought periods during spring and summer. Black locust (Robinia pseudoacacia L.) is planted in short rotation plantations as well as in agroforestry systems at reclaimed post-mining sites of the opencast mining area “Welzow Süd” and on a conventionally managed field near the town Forst (both study sites are located about 120 km to the south of Berlin). Due to mining activities the ground water table in “Welzow-Süd” is below 100 m, while on the field site in Forst the ground water table is about 2 m below the soil surface. Because of the water accessibility directly affecting the yield, it is crucial to identify the spatial variation of the soil water availability and its influence on black locust growth. The main question of this study is how the drought periods affect black locust’s growth and recovery and about the drought mitigation effect obtainable by an accessible water table. The growth rate is being estimated monthly by measuring the maximum height and the trunk diameter at 10 and 130 cm. Furthermore, several trees are equipped with dendrometers to record their diameter increment in daily intervals. The pre-dawn water potential for selected trees is evaluated periodically to quantify plant water stress and relate it to the growth pattern. Water availability and microclimatic condition are monitored continuously. At the end of the vegetation period, information gathered from the field will be used to develop a growth model to link the soil water availability and plant water status with the growth rate of the trees.
The importance of short rotation forests and agroforestry systems for woody biomass production for bioenergy will increase in Central Europe within the next decades. In this context, black locust (Robinia pseudoacacia) has a high growth potential especially at marginal, drought-susceptible sites such as occur in Brandenburg State (Eastern Germany). As a pioneer tree species black locust grows under a wide range of site conditions. The native range of black locust in Northern America is classified by a humid to sub-humid climate with a mean annual precipitation of 1020 to 1830 mm. In Central and Eastern Europe, this species is cultivated in a more continental climate with an annual precipitation often below 600 mm. Therefore, black locust is known to be relatively drought tolerant compared to other temperate, deciduous tree species. Because of its N2-fixation ability black locust plays generally an important role for the improvement of soil fertility. This effect is of particular interest at marginal sites in the post-mining landscapes.
In order to estimate the N2-fixation potential of black locust at marginal sites leaf samples were taken from black locust trees in short rotation plantations planted between 1995 and 2007 in post-mining sites south of Cottbus (Brandenburg, NE Germany). The variation of the natural 15N abundance was measured to evaluate the biological nitrogen fixation. The nitrogen derived from the atmosphere can be calculated using a two-pool model from the quotient of the natural 15N abundances of the N2-fixing plant and the plant available soil N. Because representatively determining the plant available soil N is difficult, a non-N2-fixing reference plant growing at the same site with a similar root system and temporal N uptake pattern to the N2-fixing plant is often used. In our case we used red oak (Quercus rubra) as a reference.
The average nitrogen content in the leaves of black locust ranged from 3.1% (C/N 14.8) in 15 years old trees to 3.4% (C/N 14.4) in 3 year-old trees, respectively. A higher content of nitrogen was found in leaves of re-sprouted trees with 4.3% (C/N 11.5). The estimated percentage of nitrogen derived from the atmosphere (% NdfA) in black locust was 63% – 83% compared to 56% in seabuckthorn (Hippophaë rhamnoides) and 79% in common broom (Genista scuparia). The annual leaf biomass production of black locust varied between 1325 (2 years old trees) and 2576 kg/ha a (4 years old trees). The estimated leaf nitrogen fixed by Robinia was approx. 30.5 - 59.2 kg/ha a.
From the results, we can conclude that the biological nitrogen fixation by Robina is an important factor for the nitrogen balance of short-rotation plantations on nutrient poor-soils.