Northwest German Forest Research Station

Göttingen, Germany

Northwest German Forest Research Station

Göttingen, Germany
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Enderle R.,Forest Research Institute of Baden Wuerttemberg | Busskamp J.,Forest Research Institute of Baden Wuerttemberg | Busskamp J.,Northwest German Forest Research Station | Metzler B.,Forest Research Institute of Baden Wuerttemberg
Baltic Forestry | Year: 2017

Ash dieback, caused by the ascomycete Hymenoscyphus fraxineus, is a tree disease, which currently devastates European ash populations. Only a very small fraction of ash individuals exhibits a high degree of quantitative genetic resistance and is likely to survive the disease. We investigated the growth performance of differentially diseased saplings in order to assess the impact of ash dieback on individual competitiveness in dense natural ash regeneration. The research took place on three sites in southwestern Germany. From summer 2013 to winter 2014/2015, 20.4% of the monitored ash saplings died. In general, shorter trees were more severely diseased. There were no differences in shoot length between healthy or moderately infected trees, whereas shoot length was significantly reduced in trees with more than 50% of symptomatic shoots (p ≤ 0.006). These highly impacted trees significantly lost tree height to the disease, whereas only marginal height reduction could be detected for lesser affected trees. Our results indicate that trees resistant enough to maintain at least 50% of their crowns are generally able to survive competition in dense regeneration. Thus, promotion of natural ash regeneration could be an effective measure complementary to breeding for resistance to preserve ash as a tree species in the forests. © Lithuanian Research Centre for Agriculture and Forestry.

Bonten L.T.C.,Wageningen University | Groenenberg J.E.,Wageningen University | Meesenburg H.,Northwest German Forest Research Station | De Vries W.,Wageningen University
Environmental Pollution | Year: 2011

Various dynamic soil chemistry models have been developed to gain insight into impacts of atmospheric deposition of sulphur, nitrogen and other elements on soil and soil solution chemistry. Sorption parameters for anions and cations are generally calibrated for each site, which hampers extrapolation in space and time. On the other hand, recently developed surface complexation models (SCMs) have been successful in predicting ion sorption for static systems using generic parameter sets. This study reports the inclusion of an assemblage of these SCMs in the dynamic soil chemistry model SMARTml and applies this model to a spruce forest site in Solling Germany. Parameters for SCMs were taken from generic datasets and not calibrated. Nevertheless, modelling results for major elements matched observations well. Further, trace metals were included in the model, also using the existing framework of SCMs. The model predicted sorption for most trace elements well. © 2010 Published by Elsevier Ltd.

Petritan A.M.,Forest Research and Management Institute ICAS | Nuske R.S.,Northwest German Forest Research Station | Petritan I.C.,Forest Research and Management Institute ICAS | Petritan I.C.,Transilvania University of Brasov | Tudose N.C.,Forest Research and Management Institute ICAS
Forest Ecology and Management | Year: 2013

In recent decades, natural forest remnants have become increasingly important as reference objects for maintaining or restoring old-growth characteristics in managed forests. Canopy gaps play an important role in forest regeneration, particularly for the establishment and development of tree species with different ecological recruitment patterns. Yet quantitative descriptions of such patterns are still scarce, particularly for oak-dominated forests. The old-growth sessile oak-European beech forest remnant in the Runcu-Grosi Natural Reserve provided a unique opportunity to study natural disturbance regimes with minimal human influence in an ecosystem type rarely investigated. The study site comprised the best preserved part of the Reserve. Its 32.3 ha are dominated by sessile oak. A complete gap survey was carried out. The size, shape, spatial pattern and traits of the gapmakers of all 321 gaps were recorded. Additionally, the gap age as well as the structure and composition of gapfillers were investigated in 70 randomly sampled expanded gaps.The canopy gaps and the expanded gaps covered 12.8% and 28.5% of the study site, respectively. The frequency distribution of the canopy gap sizes corresponded to the negative exponential distribution, with most of the gaps (60%) smaller than 100 m2, 34% between 100 and 300 m2 and only 2% larger than 500 m2. Canopy gaps smaller than 300 m2 were responsible for 71% of the total gap area, suggesting a dominance of small and intermediate gaps in this forest. The pattern of the canopy gaps is characterized by a pronounced soft-core effect, and in one part of the study area a tendency towards regularity. Most of the gaps (84%) were caused by more than one gapmaker and seemed to be created in more than one disturbance event since, in 72% of the gaps, gapmakers of at least two different decay classes were found. The disturbance regime was driven by the mortality of sessile oaks, the main gapmaker species, caused mostly by uprooting. The other main canopy tree species was European beech, which died often by snapping. It was less common as gapmaker (20%), but was the main gapfiller (91%). In contrast sessile oak was almost absent among the gapfillers.These results suggest that the current small-scale disturbance pattern dominating this old-growth forest is more suitable for shade-tolerant species such as European beech, accentuating the already steady decline of oaks in mixed sessile oak-European beech stands. © 2013 Elsevier B.V.

Legner N.,University of Gottingen | Fleck S.,University of Gottingen | Fleck S.,Northwest German Forest Research Station | Leuschner C.,University of Gottingen
Trees - Structure and Function | Year: 2014

Key message: The relative shade tolerance of T. cordata, F. sylvatica, and C. betulus in mature stands is based on different species-specific carbon and nitrogen allocation patterns. The leaf morphology and photosynthetic capacity of trees are remarkably plastic in response to intra-canopy light gradients. While most studies examined seedlings, it is not well understood how plasticity differs in mature trees among species with contrasting shade tolerance. We studied light-saturated net photosynthesis (A max), maximum carboxylation rate (V cmax), electron transport capacity (J max) and leaf dark respiration (R d) along natural light gradients in the canopies of 26 adult trees of five broad-leaved tree species in a mixed temperate old-growth forest (Fraxinus excelsior, Acer pseudoplatanus, Carpinus betulus, Tilia cordata and Fagus sylvatica), representing a sequence from moderately light-demanding to highly shade-tolerant species. We searched for species differences in the dependence of photosynthetic capacity on relative irradiance (RI), specific leaf area (SLA) and nitrogen per leaf area (Na). The three shade-tolerant species (C. betulus, T. cordata, F. sylvatica) differed from the two more light-demanding species by the formation of shade leaves with particularly high SLA but relatively low Na and consequently lower area-based A max, and a generally higher leaf morphological and functional plasticity across the canopy. Sun leaf morphology and physiology were more similar among the two groups. The three shade-tolerant species differed in their shade acclimation strategies which are primarily determined by the species' plasticity in SLA. Under low light, T. cordata and F. sylvatica increased SLA, mass-based foliar N and leaf size, while C. betulus increased solely SLA exhibiting only low intra-crown plasticity in leaf morphology and N allocation patterns. This study with mature trees adds to our understanding of tree species differences in shade acclimation strategies under the natural conditions of a mixed old-growth forest. © 2013 Springer-Verlag Berlin Heidelberg.

Molder A.,Northwest German Forest Research Station | Molder A.,University of Gottingen | Streit M.,University of Gottingen | Schmidt W.,University of Gottingen
Forest Ecology and Management | Year: 2014

Current nature conservation policy is going to alter the tree-layer composition of many Central European deciduous forests. As a consequence of ceasing silvicultural management, the competitive ecosystem engineer European beech (Fagus sylvatica L.) will spread and the proportion of secondary tree species will considerably decrease. Thus, changes can also be expected in herb-layer diversity, productivity and composition. To predict these changes, we analysed relationships between tree- and herb-layer diversity and composition along tree-diversity gradients in the Central German woodland areas of the Hainich National Park (unmanaged) and the Göttinger Wald (managed by close-to-nature forestry).The flora of both study areas was dominated by typical forest species. In the Hainich, the herb-layer vegetation in beech-dominated stands was less diverse compared to stands richer in canopy species. Herb-layer productivity was also lower in beech-dominated stands. In the Göttinger Wald, herb-layer diversity and productivity were not related to tree-layer diversity and beech proportion, instead to the light transmissibility of the canopy layer. The different results can be explained by logging effects in the Göttinger Wald, which promoted the light factor as significant for herb-layer diversity and productivity. In the consistently darker stands of the Hainich, soil variables, particularly influenced by the ecosystem engineer beech, were decisive. Areas of high canopy diversity in the Hainich result from former management practices and can, in the future, be expected to decrease with the spread of beech.We conclude that forest management cessation will result in decreasing herb-layer diversity and productivity in many Central European deciduous woodlands, especially in landscapes where historical management practices led to unnaturally low proportions of beech. The short-term consequence of management cessation is a loss of herb-layer diversity due to reduced light availability; in the long-term, herb-layer diversity is expected to decrease due to the expansion of beech.If the key aim of nature conservation policy is to preserve and develop the typical diversity of near-natural beech forests, then a complete cessation of forest management can be advised. However, if the typical forest herb diversity of the semi-natural, century-old cultural landscape is to be maintained, close-to-nature forestry management is necessary. © 2014 Elsevier B.V.

Molder I.,Northwest German Forest Research Station | Molder I.,University of Gottingen | Leuschner C.,University of Gottingen | Leuschner H.H.,University of Gottingen
Trees - Structure and Function | Year: 2011

We conducted dendroecological analyses in 80-year-long tree ring chronologies to detect neighborhood effects (competition intensity, species identity) on the δ13C signature of tree rings and radial stem increment of Fagus sylvatica trees growing either in monospecific or mixed patches of a temperate forest. We hypothesized that tree ring δ13C is a more sensitive indicator of neighborhood effects and the impact of climate variability on growth than is ring width. We found a closer correlation of summer precipitation to δ13C than to ring width. While the ring width showed a decline over the test period (1926-2005), the mean curve of δ13C increased until the mid of the 1970s, remained high until about 1990, and markedly decreased thereafter. Possible explanations related to ontogeny and environmental change ('age effect' due to canopy closure; elevated atmospheric SO2 concentrations in the 1960s-1980s) are discussed. Beech target trees surrounded by many allospecific trees had a significantly lower mean δ13C in the period 1926-1975 than beech with predominantly or exclusively conspecific neighborhood, possibly indicating a more favorable water supply of beech in diverse stands. Contrary to expectation, trees subject to more intense competition by neighboring trees (measured by Hegyi's competition index) had lower δ13C values in their tree rings, which is thought to reflect denser canopies being linked to increased shading. We conclude that tree ring δ13C time series represent combined archives of climate variability, stand history and neighborhood effects on tree physiology and growth that may add valuable information to that obtained from conventional tree ring analysis. © 2010 The Author(s).

Sprauer S.,Northwest German Forest Research Station | Nagel J.,Northwest German Forest Research Station
European Journal of Forest Research | Year: 2015

The aim of this study was to compare increment in mixed stands to the respective pure stands adopting, as an example, mixed stands comprising Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.). Using data from two mixed stand age series, in the Solling and in Harz Mountains, first we investigated whether the growth reduction effect arising from competing trees is dependent on the species of the competitors. We than explored whether increment predictions from the forest growth simulation package TreeGrOSS revealed differences between pure and mixed stands and, if so, what factors play a role and what may cause these increment differences. The analysis was based on a simulated trial series in which the parameters such as percentage mixture, age, site quality class, and stocking level were varied. The results indicate that neighboring Norway spruce restrict the basal area increment of both European beech and Norway spruce more than European beech competitors with the same crown cross-sectional area. In the majority of cases, the simulation produced an increment gain in mixed stands compared with pure stands. The amount of increment gain in a mixed stand depended on the percentage mixture, age, site quality class, and stocking level and could be related to changes in stand structure and their effects on aboveground competition. © 2015, Springer-Verlag Berlin Heidelberg.

Albert M.,Northwest German Forest Research Station | Schmidt M.,Northwest German Forest Research Station
Forest Ecology and Management | Year: 2010

The aim of the presented research project is to fit a site index model capable for predicting changes in site-productivity in a changing climate. A generalized additive model is used to predict site index as a function of soil and climate variables. The climate parameter values are estimated using the regional climate model WETTREG, based on global climate simulations with the global circulation model ECHAM5/MPI-OM for the reference period from 1961 to 1990. The climate values are further regionalized on a 200 m × 200 m grid. The generalized additive model quantifies the partial linear and non-linear effects of the predictor variables on site index. The model is parameterized for Norway spruce (Picea abies (L.) Karst.) and common beech (Fagus sylvatica L.) in Lower Saxony, Germany. Two case studies investigate the model's ability to generate information in order to support forest management planning decisions under a changing climate. One example analyzes the possible shift in site index of spruce along a precipitation gradient under the International Panel on Climate Change (IPCC) emission scenario A1B in the period from 2041 to 2050. The other case study shows possible future changes in site index of beech along a temperature gradient. © 2009 Elsevier B.V. All rights reserved.

von Lupke N.,University of Gottingen | Hansen J.,Northwest German Forest Research Station | Saborowski J.,University of Gottingen
European Journal of Forest Research | Year: 2012

For a current inventory using double sampling for stratification with a reduced second-phase sample size, compared with a previous inventory, we develop a three-phase sampling procedure that exploits plot data from the previous inventory or their updates based on a growth model to increase precision. The three-phase procedure combines double sampling for stratification with a two-phase regression estimator within strata. We consider sampling from an infinite population in the first phase. The combined estimator is tested in a case study using data from two consecutive inventories in four State Forest Districts in Lower Saxony, Germany. Data from a reduced number of sample plots from the second occasion are combined with (1) volumes from the first occasion or (2) growth simulations on the sample plots from the first occasion. The data from the previous inventory or their updates serve as the auxiliary variable for the regression estimator of the strata means of the target variable. This case study indicates a remarkable increase in precision and thereby an enormous cost-saving potential for reduced intermediate inventories in a periodic inventory design with both types of auxiliary variables. © 2012 The Author(s).

Saborowski J.,University of Gottingen | Marx A.,Freilandstr. 12 a | Nagel J.,Northwest German Forest Research Station | Bockmann T.,Lower Saxony Forest Planning Office
Forest Ecology and Management | Year: 2010

Double sampling for stratification is a sampling design that is widely used for forest and other resource inventories in forest ecosystems. It is shown that this sampling design can be adapted to repeated inventories including estimators of net change, even for non-proportional allocation of second-phase units and periodically updated stratification. The method accounts for the transition of sampling units among strata. Moreover, it may outperform classical single phase designs if sample plots are appropriately allocated to strata with respect to predefined target variables, here: volume per ha of bigger trees of the main tree species. The latter requires a clear definition of predominant aims of the inventory and an appropriate optimization method. Access to inventory data of a state forest district from two occasions allowed for an optimization of the design based on the first occasion, which proved to be still advantageous on the following occasion. Estimators are developed under the infinite population approach, which is generally deemed more appropriate for forest inventories. © 2010 Elsevier B.V.

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