Introduction of non-native Douglas fir reduces leaf damage on beech saplings and mature trees in European beech forests.

Recent ecological research suggests that, in general, mixtures are more resistant to insect herbivores and pathogens than monocultures. However, we know little about mixtures with non-native trees, where enemy release could lead to patterns that differ from commonly observed relationships among native species. This becomes particularly relevant when considering that adaptation strategies to climate change increasingly promote a larger share of non-native tree species, such as North American Douglas fir in Central Europe. We studied leaf damage on European beech (Fagus sylvatica) saplings and mature trees across a wide range of site conditions in monocultures and mixtures with phylogenetically distant conifers native Norway spruce (Picea abies) and non-native Douglas fir (Pseudotsuga menziesii). We analyzed leaf herbivory and pathogen damage in relation to tree diversity and composition effects, as well as effects of environmental factors and plant characteristics. We observed lower sapling herbivory and tree sucking damage on beech in non-native Douglas fir mixtures than in beech monocultures, probably due to a lower herbivore diversity on Douglas fir trees, and higher pathogen damage on beech saplings in Norway spruce than Douglas fir mixtures, possibly because of higher canopy openness. Our findings suggest that for low diversity gradients, tree diversity effects on leaf damage can strongly depend on tree species composition, in addition to modifications caused by feeding guild and tree ontogeny. Moreover, we found that nutrient capacity modulated the effects of tree diversity, composition, and environmental factors, with different responses in sites with low or high nutrient capacity. The existence of contrasting diversity effects based on tree species composition provides important information on our understanding of the relationships between tree diversity and plant-herbivore interactions in light of non-native tree species introductions. Especially with recent Norway spruce die-off, the planting of Douglas fir as replacement is likely to strongly increase in Central Europe. Our findings suggest that mixtures with Douglas fir could benefit the survival or growth rates of beech saplings and mature trees due to lower leaf damage, emphasizing the need to clearly identify and compare the potential benefits and ecological trade-offs of non-native tree species in forest management under ongoing environmental change.

Initial changes in soil properties and carbon sequestration potential under monocultures and short-rotation alley coppices with poplar and willow after three years of plantation.

Initial changes in soil structure and C stocks were studied under short-rotation coppices (SRC) planted on former cropland near Göttingen, Central Germany. Plantations were established either as monocultures with willow (Willow-SRC) or poplar (Poplar-SRC), or as an agroforestry system with willow strips and grassland alleys in between (Willow-AF). A neighbouring cropland served as a control. Three sampling campaigns were applied in this study. The first sampling was conducted at a fine scale to reveal the differences in soil C with depth (i.e. 0-3, 3-6, 6-9, 9-12, 12-15, 15-20, 20-30cm). Here, results indicated the main differences between plantations in 0-3, 3-20 and 20-30cm layers. These soil depths were therefore chosen for the second sampling campaign to reveal differences in aggregate composition, C accumulation in aggregates and density fraction, and microbial biomass carbon (MBC) between plantations. Furthermore, quality of soil organic matter and amount of C mineralised by microorganisms were estimated by an incubation experiment. Results here indicated two times higher CO2 emissions from the top layer than from the lower layers under SRCs, as well as higher MBC in SRCs (490-788.7µgCg-1) than in cropland (266.4µgCg-1). The results of the third sampling on the texture of respective soil horizons indicated a significant correlation (R2=78%) of soil clay to C at 0-3cm depth. It was concluded that aggregation and C in microbial biomass and free light fractions were the first indicators of soil quality improvement after conversion of arable land to SRC plantations.

Forest defoliator pests alter carbon and nitrogen cycles.

Climate change may foster pest epidemics in forests, and thereby the fluxes of elements that are indicators of ecosystem functioning. We examined compounds of carbon (C) and nitrogen (N) in insect faeces, leaf litter, throughfall and analysed the soils of deciduous oak forests (Quercus petraea L.) that were heavily infested by the leaf herbivores winter moth (Operophtera brumata L.) and mottled umber (Erannis defoliaria L.). In infested forests, total net canopy-to-soil fluxes of C and N deriving from insect faeces, leaf litter and throughfall were 30- and 18-fold higher compared with uninfested oak forests, with 4333 kg C ha-1 and 319 kg N ha-1, respectively, during a pest outbreak over 3 years. In infested forests, C and N levels in soil solutions were enhanced and C/N ratios in humus layers were reduced indicating an extended canopy-to-soil element pathway compared with the non-infested forests. In a microcosm incubation experiment, soil treatments with insect faeces showed 16-fold higher fluxes of carbon dioxide and 10-fold higher fluxes of dissolved organic carbon compared with soil treatments without added insect faeces (control). Thus, the deposition of high rates of nitrogen and rapidly decomposable carbon compounds in the course of forest pest epidemics appears to stimulate soil microbial activity (i.e. heterotrophic respiration), and therefore, may represent an important mechanism by which climate change can initiate a carbon cycle feedback.

Fast Growing Plantations for Wood Production - Integration of Ecological Effects and Economic Perspectives.

Biomass crops are perceived as a feasible means to substitute sizeable amounts of fossil fuel in the future. A prospect of CO2 reduction (resp. CO2 neutrality) is credited to biomass fuels, and thus a potential contribution to mitigate climate change. Short rotation coppices (SRCs) with fast growing poplar and willow trees are an option for producing high yields of woody biomass, which is suitable for both energetic and material use. One negative effect that comes along with the establishment of SRC may be a decrease in groundwater recharge, because high rates of transpiration and interception are anticipated. Therefore, it is important to measure, analyze, and model the effects of SRC-planting on landscape water budgets. To analyze the effects on the water budget, a poplar SRC plot was studied by measuring hydrological parameters to be used in the hydrological model WaSim. Results reveal very low or even missing ground water recharge for SRC compared to agricultural land use or grassland, especially succeeding dry years. However, this strong effect on plot level is moderated on the larger spatial scale of catchment level, for which the modeling was also performed. In addition to water, nutrient fluxes and budgets were studied. Nitrogen is still a crucial issue in today's agriculture. Intensive fertilization or increased applications of manure from concentrated livestock breeding are often leading to high loads of nitrate leaching, or enhanced N2O emissions to the atmosphere on arable crop fields. SRC or agroforestry systems on former crop land may offer an option to decrease such N losses, while simultaneously producing woody biomass. This is mainly due to the generally smaller N requirements of woody vegetation, which usually entail no need for any fertilization. The trees supply deep and permanent rooting systems, which can be regarded as a "safety net" to prevent nutrient leaching. Thus, SRC altogether can help to diminish N eutrophication. It is important to offer viable and attractive economic perspectives to farmers and other land managers besides of the potential ecological benefits of SRCs. For this reason, an integrated tool for scenario analysis was developed within the BEST project ("BEAST - Bio-Energy Allocation and Scenario Tool"). It combines ecological assessments with calculations of economic revenue as a basis for a participative regional dialog on sustainable land use and climate protection goals. Results show a substantial capacity for providing renewable energy from economically competitive arable SRC sites while generating ecological synergies.

Response of recalcitrant soil substances to reduced N deposition in a spruce forest soil: integrating laccase-encoding genes and lignin decomposition.

A long-term field experiment conducted in a Norway spruce forest at Solling, Central Germany, was used to verify and compare the response of lignin-decomposing fungal communities in soils receiving current and preindustrial atmospheric nitrogen (N) input for 14.5 years. Therefore, we investigated the decomposition of lignin compounds in relation to phenol oxidase activity and the diversity of basidiomycetes containing laccase genes in organic and mineral horizons. Lignin-derived CuO oxidation products and enzyme activity decreased with soil depth, while the degree of oxidative transformation of lignin increased. These patterns did not change with reduced atmospheric N input, likely reflecting a lasting saturation in available N. The laccase gene diversity decreased with soil depth in spring. In autumn, this pattern was only found in the control plot, receiving current N input. Principal component analysis confirmed the depth profile and distinguished a response of the fungal community to reduced N deposition for most organic layers in spring and a roof effect for the Oe layer in autumn. These responses of the fungal community did not translate into changes in enzyme activity and lignin content and decomposition, suggesting that transformation processes in soils are well buffered despite the rapid response of the microbial community to environmental factors.

Response of total and nitrate-dissimilating bacteria to reduced N deposition in a spruce forest soil profile.

A field-scale manipulation experiment conducted for 16 years in a Norway spruce forest at Solling, Central Germany, was used to follow the long-term response of total soil bacteria, nitrate reducers and denitrifiers under conditions of reduced N deposition. N was experimentally removed from throughfall by a roof construction ('clean rain plot'). We used substrate-induced respiration (SIR) to characterize the active fraction of soil microbial biomass and potential nitrate reduction to quantify the activity of nitrate reducers. The abundance of total bacteria, nitrate reducers and denitrifiers in different soil layers was analysed by quantitative PCR of 16S rRNA gene, nitrate reduction and denitrification genes. Reduced N deposition temporarily affected the active fraction of the total microbial community (SIR) as well as nitrate reductase activity. However, the size of the total, nitrate reducer and denitrifier communities did not respond to reduced N deposition. Soil depth and sampling date had a greater influence on the density and activity of soil microorganisms than reduced deposition. An increase in the nosZ/16S rRNA gene and nosZ/nirK ratios with soil depth suggests that the proportion of denitrifiers capable of reducing N(2)O into N(2) is larger in the mineral soil layer than in the organic layer.

The Solling roof revisited--slow recovery from acidification observed and modeled despite a decade of "clean-rain" treatment.

Soil chemistry under the Solling clean-rain roof was simulated using the dynamic multi-layer soil chemistry model SAFE, including sulfate adsorption. Soil was sampled in order to parameterize the pH and sulfate concentration dependent sulfate adsorption isotherm used in SAFE. Modeled soil solution chemistry was compared to the 14 year long time-series of monthly measurements of soil solution data at 10 and 100cm depth. The deposition of N and S under the roof has been reduced by 68% and 53%, respectively, compared to the surrounding area. Despite this the soil solution concentrations of sulfate are still high (a median of 420mumol(c)/L at 100cm depth between 2000 and 2002) and the soil base saturation low (approximately 3% in the whole profile in 1998). Sulfate adsorption is an important process in Solling. The soil capacity to adsorb sulfate is large, the modeled adsorbed pool in 2003 down to 100cm was 1030kg S/ha, and the measured sulfate concentration is high, due to release of adsorbed sulfate. The addition of sulfate adsorption improved the modeled sulfate dynamics although the model still slightly underestimated the sulfate concentration at 100cm. Model predictions show no recovery, based on the criteria of Bc/Al ratio above 1 in the rooting zone, before the year 2050, independent of future deposition cuts.