LIBRARY LETTERS

Post-disturbance recovery is a central element of forest resilience against intensifying disturbance regimes. Although recovery signals are strong across Central European forests, the relative roles of different factors contributing to recovery remain incompletely understood. As climate change increasingly challenges recovery, elucidating these processes is essential to adapt forest management to changing climate and disturbance regimes. We extended and applied a biologically grounded model of forest growth to remote sensing data to quantify how management shapes two key drivers of canopy recovery—disturbance legacies and post-disturbance height growth—across Bavaria, Germany. We combined 23,036 ha of quality-filtered photogrammetric canopy height model data with a Landsat-based disturbance map, a forest ownership map and environmental covariates in a Bayesian modelling framework. Post-disturbance growth rates were governed primarily by forest type and site conditions, whereas management strongly influenced disturbance legacies, i.e. the remaining post-disturbance vegetation height structure on site. Legacies varied widely across management types: Federal and set-aside forests retained the highest level of disturbance legacies, while private forests had the lowest legacy levels. Despite marginally lower growth rates, set-aside areas had recovery trajectories that were comparable to managed forests. The median recovery time to 5 m mean canopy height was 14.3 years over all forest and management types. Set-aside areas exhibited the greatest variation in recovery trajectories. We here show that (i) management affects disturbance legacies more strongly than post-disturbance tree growth, (ii) set-aside areas do not differ in recovery speed from managed areas, and (iii) legacies are diversifying forest recovery trajectories, with potential implications for future forest resilience. Our results underline that the post-disturbance reorganization window is a crucial period for management to influence long-term forest development. The framework presented here provides a scalable approach to monitor structural recovery and guide adaptive forest policy and management under increasing disturbance. • Forest management in Central Europe affects post-disturbance recovery more via legacies than tree growth rates. • Set-aside forests recover their canopy height equally fast as managed forests in Central Europe. • Homogenizing and removing disturbance legacies can reduce forest canopy variation across forest stand development. • We combined a biological growth model with remote sensing data to assess forest canopy recovery.

Effects of forest management on biodiversity in temperate deciduous forests: An overview based on Central European beech forests

In Central Europe, anthropogenic coniferous monocultures have been subject to conversion to more diverse mixed forests since the 1990s, however, they are still abundant across many forest landscapes. Artificial and natural tree regeneration both play a key role during conversion by determining the species composition and structure of the future forests. Many abiotic and biotic factors can potentially influence the regeneration process and its specific combinations or interactions may be different among tree species and its developmental stages. Here, we aimed to identify and quantify the effect of the most important drivers on the density of the most abundant regenerating tree species (i.e., Norway spruce and European beech), as well as on species and structural diversity of the tree regeneration. We studied tree regeneration in four former monospecific coniferous stand types (i.e., Norway spruce, Scots pine, European larch, and Douglas fir) in Southwest Germany that have been under conversion to mixed forests since the 1990s. We sampled tree regeneration in four growth height classes together with a variety of potentially influencing factors on 108 sampling plots and applied multivariate analyses. We identified light availability in the understorey, stand structural attributes, browsing pressure, and diaspore source abundance as the most important factors for the density and diversity of tree regeneration. Particularly, we revealed species-specific differences in drivers of regeneration density. While spruce profited from increasing light availability and decreasing stand basal area, beech benefited either from a minor reduction or more strikingly from an increase in overstorey density. Increasing diaspore source abundance positively and a high browsing pressure negatively affected both species equally. Our results suggest that humus and topsoil properties were modified during conversion, probably due to changes in tree species composition and silvicultural activities. The species and structural diversity of the tree regeneration benefitted from increasing light availability, decreasing stand basal area, and a low to moderate browsing pressure. We conclude that forest managers may carefully equilibrate among the regulation of overstorey cover, stand basal area, and browsing pressure to fulfil the objectives of forest conversion, i.e., establishing and safeguarding a diverse tree regeneration to promote the development of mature mixed forests in the future.

Boreal Shield forest disturbance and recovery trends using Landsat time series

Natural dynamics of temperate mountain beech-dominated primary forests in Central Europe

Global change is altering the state of forest ecosystems, threatening their integrity. A number of studies have reported declines in aboveground arthropod diversity over the last decade and indicated management practices or climate as the main drivers. However, belowground communities have rarely been studied in this context, and the extent to which patterns and associated drivers observed aboveground also apply to belowground communities remains unknown. Therefore, research is urgently needed to disentangle the drivers and potential threats that shape soil animal communities, which contribute significantly to the functioning of terrestrial ecosystems by providing key ecosystem functions such as decomposition and nutrient cycling. Here, we studied soil animal communities across forest types of different management intensity, including unmanaged beech forests, managed age-class beech forests and spruce monoculture plantations across three regions located in southern, central, and northern Germany, i.e., Swabian Alb, Hainich-Dün, and Schorfheide-Chorin. We first investigated the spatiotemporal dynamics of oribatid mites (Acari: Oribatida), sampled in three-year intervals from 2008 – 2020 (Chapter 2). In contrast to the linear decline in diversity observed aboveground, oribatid mite density and diversity decreased after years with low preceding winter precipitation and recovered after years with higher precipitation. This correlation differed between regional soil types and was only found in the Swabian Alb and Schorfheide-Chorin, where soil fauna is more susceptible to periodic droughts due to the shallow Rendzinas and sandy soils, respectively. Temporal dynamics were similar between managed and unmanaged forests, suggesting that forestry has little effect on the viability of oribatid mite populations in Central European forests. To gain a more mechanistic understanding of the effects of extensive forest management, we then examined oribatid mite communities one year after two key characteristics of forest management; namely forest gap formation and deadwood availability were manipulated in a full factorial experiment (Chapter 3). We found that both deadwood and forest gap formation significantly affected oribatid mite density and community composition, although the magnitude of these effects differed between regions. One year after deadwood addition, oribatid mite density approximately doubled in the Hainich-Dün, mainly due to a few fast-reproducing species. Presumably, they benefitted from additional microbial resources near deadwood, particularly fungi, which are the prime resource of oribatid mites as shown in Chapter 4. By contrast, forest gap formation reduced the density and diversity of oribatid mites but only in the Swabian Alb and Schorfheide-Chorin. Given the strong correlation between oribatid mite density and precipitation found in these two regions in Chapter 2, it is likely that periodic droughts were aggravated in forest gaps, adversely affecting oribatid mite communities. Notably, negative effects of forest gap formation were not mitigated by the addition of deadwood, indicating that harsh environmental conditions override the positive effects of additional resources. Finally, we linked the dynamics of soil animal communities to their function in the soil food web by analyzing trophic niches of detritivores (Oribatida, Collembola, Diplopoda, Isopoda, Lumbricidae) and predators (Mesostigmata, Chilopoda) across forest types and regions. Trophic niches were derived by analyzing the relative contribution of plants, fungi, and bacteria used as basal resources and estimating trophic positions, using community-level compound-specific stable isotope analysis of amino acids (Chapter 4). Results showed that soil animal detritivores in forests mainly feed on fungi, followed by plants and to a lesser extent on bacteria. Relative proportions of basal resources were consistent across forest types and regions for all taxa. Notably, Chilopoda obtained more essential amino acids from bacteria than other investigated taxa, suggesting that they prey on soil animals not included in the study. Enchytraeidae are known to serve as prey for Chilopoda and have recently been shown to feed on bacteria. Trophic positions were higher in the Schorfheide-Chorin for Oribatida and Collembola but decreased for Lumbricidae. This may in part be related to regional differences in community composition, as shown for oribatid mites in Chapters 2 & 3. Also, increasing trophic positions suggest longer trophic chains, which may be explained by the integration of more root-derived resources and/or rhizosphere prey, due to higher root density in the organic layers of sandy soils. The results of this thesis show that the dynamics of oribatid mite communities are little affected by forest management and are mostly determined by abiotic conditions at regional scales. However, more extensive forest management events, such as the formation of forest gaps, may interact with regional abiotic stressors, leading to aggravated effects on oribatid mites. The thesis also provides the first evidence that fungi are the main resource for mesofauna and macrofauna detritivores and that trophic niches in soil are conserved between forest types of different management intensity. Future studies need to assess the generality of these findings and further explore the complex interactions between forest management practices and regional abiotic factors.

Early natural tree regeneration after wildfire in a Central European Scots pine forest: Forest management, fire severity and distance matters

Thinning decreases above-ground biomass increment in central European beech forests but does not change individual tree resistance to climate events

Development of management strategies to achieve sustainable forest ecosystems has remained an important issue in forestry. An important component of sustainability is the maintenance of structure and functions of ecosystems. Beese (1996) outlined four primary functions of forest use which would need due attention to achieve a long term sustainable system: (a) production and use of resources (wood and other forest products, recreation, water conservation and other functions), (2) maintenance of ecosystem-internal cycles of matter and energy to minimise any effect on the neighboring systems, (3) habitat conservation (biodiversity – structure and functioning), and (4) maintenance of cultural and social role (landscape and heritage conservation).European beech is a dominating tree species in central Europe covering a wide ecological spectrum of site conditions (climate, soil type, soil pH) (Ellenberg 1988, 1996; Leuschner et al. 2006; Bartsch and Röhrig, Chap. 22, this volume). Figure 1 shows some distribution pattern of beech forests in relation to chemical soil properties. Without human influence, forests would have covered most of Germany, while at present only about 30% of land area are covered by forests of which only 15% is under beech and another 25% under other deciduous species (BMVEL 2004). There is a broad consensus among forest managers that in future the area of beech forests in central Europe should increase, mainly as mixed broadleaf stands and as admixtures with conifers. The argument in favour of growing beech, especially in areas which are presently covered by conifers, is based on the fact that conifers had been planted on beech sites in the past, on considerations of forest health, and preservation and enhancement of biodiversity in a changing climate to provide long-term sustainability of forests and the productivity of such stands. The phenotypic plasticity and evolutionary adaptability of European beech to drought and its competitiveness appear to be underestimated (Bolte et al. 2007).KeywordsSoil Organic MatterBeech ForestEuropean BeechChemical Soil PropertyDominate Tree SpeciesThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Using vegetation databases from Poland, the Czech Republic, Austria, Slovakia and our own material collected during a field work, we have analysed the variability of species composition of Abies alba-dominated communities in Central Europe. Analysis was performed using a modified TWINSPAN algorithm in the JUICE software. Ecological analysis was performed on the basis of mean Ellenberg indicator values with a MoPeT_v1.0.r script prepared in R software. In general, the findings indicated that there are at least 8 types of Central European silver fir-dominated forests with different patterns in species composition and habitat conditions. These are the oligotrophic subcontinental silver fir forests of the Polish highlands, oligotrophic (sub)montane silver fir forest, hygrophilous silver fir forests, oligo-mesotrophic (sub)montane silver fir forests, mesotrophic (sub)montane silver fir forests, submontane and montane calcicolous silver fir forests of the Alps and the Carpathians, eutrophic silver fir-beech forests and silver fir ravine forests. The main conclusion is that the diversity of species composition of Abies alba-dominated forests in Central Europe is lower than described in current regional synthesis, which was confirmed by ecological analyses.

Nesting local forestry initiatives: Revisiting community forest management in a REDD+ world

Effects of forest roads on oak trees via cervid habitat use and browsing

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Question: We were interested if and how variation in frequency and/or size of disturbances affect the dynamics of a montane old-growth forest in Central Europe. Location: The forest, co-dominated by Fagus sylvatica, Picea abies and Abies alba, is located in Lower Austria and represents one of the few sizable virgin forests in Central Europe. Methods: We extracted cores from 100 trees using systematic grid sampling (grid cell size 10 m × 10 m) on each of four 1-ha plots distributed across the old-growth remnant of 300 ha. We inferred disturbance events from rapid early growth and release events. For defining release criteria, we applied the boundary line method. We investigated the spatial structure of current age and gap distributions and past disturbance events in grid cells, using a pair density statistic. Results: The disturbance histories indicate decades with peaks and also extended periods without disturbance. Some peaks occurred synchronously at three of the four plots (1910s, 1930s, 1960s...

The research objective was to develop pheromone‐based monitoring of the nun moth, Lymantria monacha (L.), an important defoliator of spruce and pine forests in central Europe. In 38 spruce or pine forests in central Europe, captures of male L. monacha in nonsaturating Unitraps and saturating Delta sticky traps baited with 0.2, 2, 20, or 200 μg of the L. monacha (pheromone) volatile blend [(±)‐disparlure, (±)‐monachalure, and 2‐methyl‐Z7‐octadecene at a 20 : 20 : 1 ratio] were compared with estimates of population densities obtained by counts of larval faecal pellets, pupal cases, and adult moths resting on tree trunks. Total captures of male L. monacha throughout the flight season in both types of trap were correlated with numbers of larval faecal pellets, irrespective of pheromone dose. Nonsaturating Unitraps baited with 2 μg of the L. monacha volatile blend seem to provide a cost‐effective tool for monitoring densities of L. monacha populations. Long‐term testing of this monitoring system has been initiated to substantiate the quantitative relationship between larval populations and trap captures of male L. monacha and to determine the threshold number of captured male moths that indicates an incipient outbreak.