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This study assessed the provision of additional ecosystem services by two alley cropping systems for production of woody biomass located in Germany (Farm A and Farm B) as compared to conventional agricultural management. Stripes of fast growing trees in both farms were planted at different distances from each other and occupied various proportion of the agroforestry area. The results of nine indicators of soil, water and biodiversity related to ecosystem services were thus compared under consideration of different farm conditions and management. The additional provision of benefits in Farm A was expected in terms of reducing erosion by wind and reducing the risk of nitrate leaching to groundwater. In Farm B the main effect was related with improving biodiversity. The design of the tree stripes within the system affected the reduction of wind erosion as well as the improvement in biodiversity and was an essential factor determining the provision of ecosystem services by alley cropping systems.
Linear woody-features, such as hedgerows, windbreaks, and riparian buffer strips, composed of trees and/or shrubs are anthropogenic features, established in the past for different purposes, such as provision of field boundaries, protection from wind and supply of fuelwood. Today, they are primarily valued for their ecological benefit, while their production function has received rather little attention. This study assessed the biomass potential of existing linear woodyfeatures in a study area in southern Brandenburg, Germany. The merchantable tree volume of the measured woody-features ranged between 240 m3 ha-1 and 710 m3 ha-1, depending on the relative proportion of trees and shrubs. The results suggest that the biomass potential of linear woody-features with predominant tree proportion per hectare can be higher than this of forests.
A strategy for utilising the production function of these woody-features should take into account the provision of benefits such as wind protection, habitat provision and landscape aesthetics.
Understanding of soil carbon dynamics after establishment of alley-cropping systems is crucial for mitigation of greenhouse gas CO2. This study investigates soil CO2 flux in an alley-cropping system composed of black locust (Robinia pseudoacacia L.) and poplar (Max 1) tree strips and adjacent to them crop strips (Lupinus/ Solarigol). Soil CO2 flux was measured monthly over the March – November 2012 period, using a LI-COR LI-8100A automated device. Simultaneously with CO2 flux measurements, soil and air temperature, soil moisture, microbial C and hot water-extractable carbon (HWC) were determined for soils collected nearby each measurement collar. Root biomass was measured to a depth of 15 cm. In all sampling areas, soil CO2 flux increased from May to July, showing a significant positive correlation with air and soil temperature, which can be a reflection of increase in photosynthetic activity over the warm summer months. The relationships between soil moisture and CO2 flux showed positive correlation only for the warm period (May - October), indicating enhancing role of soil moisture on microbial mineralization and root respiration. CO2 flux values varied between sampling areas at different vegetation periods, with significantly higher values in trees over the summer. This could be attributed to the higher photosynthetic activity and higher root density in trees coppices compared to crops. In autumn, after seeding catch crop mix Solarigol, CO2 flux was significantly higher in crops compared to trees, which could be related to soil tillage prior to seeding of crops, as well as to the higher photosynthetic activity of newly seeded crops at the period of rapid plant growth. Despite a seasonal variation in CO2 flux between sampling areas, aaverage CO2 flux values observed over March – November period did not differ significantly between sampling areas, showing 2.5, 3.2, and 2.9 μmol m-2 s-1 values for black locust, poplar and crops, respectively. A greater C loss with soil respiration under trees in summer period may be compensated by greater C assimilation and storage in woody biomass, and the greater respiration from crop strips after tillage in autumn.
The production of energy wood on arable land increased in Germany during the last years. Black locust (Robinia pseudoacacia L.) is a suitable tree species in order to ensure substantial woody biomass yields on agricultural sites in eastern Germany. Arranged in hedge structures (alley cropping) positive effects on wind velocity and hence on soil erosion can be expected for the whole agricultural production area.
Results of field measurements carried out in several alley cropping sites located in eastern Germany show that wind velocity can be reduced by more than 50 %, even though tree hedgerows were not higher than four meters. Here, the reduction of wind speed was dependent on the distance to woody crops, the width of the crop alleys and the orientation of hedgerows. As a result of wind speeds reduction the potential of soil erosion by wind decreases considerably. The risk of wind erosion is even nearly negligible for 24 m wide or smaller crop alleys.
The establishment of short rotation hedgerows could contribute to an enhanced protection against wind erosion and thus to an ecological and possible long-term economic appreciation of agricultural sites. Aside from erosion control, further advantages such as a lower evaporation rate, and thus a crop yield increase, may be connected to the establishment of such agroforestry systems. Against the background of the increasing demand for woody biomass for bioenergy, the cultivation of fast growing trees on agricultural sites can furthermore result in an additional incomefor farmers. This is a prerequisite for the spread of this kind of agroforestry in Germany, because a comparable large share of an unprotected field has to be planted with trees in order to ensure an efficient windbreak.