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Response of ground vegetation and epiphyte diversity to natural age dynamics in a Central European mountain spruce forest
No full textQuestion Natural forest age dynamics is often more or less cyclic, with profound temporal changes in stem density and tree size, tree age structure, deadwood frequency and the abundance of canopy gaps. We investigated the response of ground and epiphyte vegetation to the natural forest age dynamics of an old‐growth spruce forest focussing on (1) the influence of stand age‐related shifts in forest structure and related changes in soil conditions on the diversity and composition of plant communities, (2) differences in the species turnover of cryptogamic epiphytes and ground vegetation in relation to forest age development, and (3) the importance of later (advanced) forest development stages for characteristic epiphyte communities. Location High‐montane old‐growth spruce forest (Picea abies (L.) Karst.) on Mt. Brocken, Harz Mountains, Germany. Methods Five defined forest development stages (regeneration to decay) were investigated with five 100‐m² plots for each stage, in which we studied forest structure, ground vegetation and the epiphytes of living trees and dead trunks. Results The ground vegetation did not significantly change across the forest development stages. Epiphyte diversity on dead standing trees markedly increased towards later stages, with the highest diversity in the over‐mature and decay stages. Diversity of epiphytes on lying trunks was highest in early development stages. Trees in decay as well as regeneration stage included a set of characteristic epiphytes, being rare or absent in the other stages. Conclusions Deadwood, i.e. trees and lying trunks and their epiphytes, outlast the oldest individuals of the tree layer and are still present in the early stages of the following forest generation. Epiphyte diversity on lying deadwood was higher in young than late forest development stages. Habitat continuity presents a fundamental difference to managed forests; it promotes species with dispersal limitations, which are common among cryptogamic epiphytes
Ergebnisse einer Fallstudie aus dem Harz
No full textKurzfassung: Wirtschaftswälder unterscheiden sich grundlegend von Naturwäldern durch die Seltenheit von Bäumen jenseits des Umtriebsalters in der Alters- und Zerfallsphase sowie durch einen radikaleren Bruch der Bestandeskontinuität zwischen den aufeinanderfolgenden Waldgenerationen. Die natürliche Bestandesdynamik infolge altersbedingter Mortalität und externerr Störungen in vom Menschen nicht genutzten Wäldern führt zu einem heterogenen Muster von unterschiedlich großen Teilflächen unterschiedlicher Waldentwicklungsstadien und zur Bildung von Bestandeslücken. In Mitteleuropa sind Waldbestände, die zumindest seit mehreren Jahrhunderten einer natürlichen Bestandesdynamik ausgesetzt sind, äußerst selten. In einer Fallstudie im Harz (Deutschland) hatten wir die Gelegenheit, einen solchen Bestand zu untersuchen (Brockenurwald). Ziel der Untersuchung war die vergleichende Analyse der pflanzlichen Diversität (Bodenvegetation, Epiphyten) sowie ausgewählter Ökosystemeigenschaften (oberirdische Biomasse, ökosystemarer Kohlenstoffvorrat) in fünf altersabhängigen Waldentwicklungsphasen (Verjüngungs-, Aufwuchs-, Optimum-, Alters- und Zerfallsphase). Während sich die Bodenvegetation kaum zwischen den Entwicklungsstadien unterschied, war der Artenreichtum epiphytischer Moose und Flechten auf den stehenden Bäumen in der Alters- und insbesondere der Zerfallsphase signifikant größer als in den jüngeren Entwicklungsstadien, die auch im Wirtschaftswald vorkommen. Der Artenreichtum auf liegendem (aus der vorangegangenen Waldgeneration stammendem) Totholz war am höchsten in der Verjüngungs- und der Aufwuchsphase. Die oberirdische Biomasse und die Kohlenstoffvorräte waren in der Alters- und in der Zerfallsphase größer als in den anderen Waldentwicklungsstadien. Der Kohlenstoffvorrat im Boden war unabhängig vom Waldentwicklungsstadium konstant hoch. Unsere Ergebnisse unterstreichen die große Bedeutung der Alters- und Zerfallsphase und einer natürlichen Bestandesdynamik für die pflanzliche Diversität von Wäldern und für die Fähigkeit, große Vorräte an Kohlenstoff zu speichern
Ergebnisse einer Fallstudie aus dem Harz
No full textKurzfassung: Wirtschaftswälder unterscheiden sich grundlegend von Naturwäldern durch die Seltenheit von Bäumen jenseits des Umtriebsalters in der Alters- und Zerfallsphase sowie durch einen radikaleren Bruch der Bestandeskontinuität zwischen den aufeinanderfolgenden Waldgenerationen. Die natürliche Bestandesdynamik infolge altersbedingter Mortalität und externerr Störungen in vom Menschen nicht genutzten Wäldern führt zu einem heterogenen Muster von unterschiedlich großen Teilflächen unterschiedlicher Waldentwicklungsstadien und zur Bildung von Bestandeslücken. In Mitteleuropa sind Waldbestände, die zumindest seit mehreren Jahrhunderten einer natürlichen Bestandesdynamik ausgesetzt sind, äußerst selten. In einer Fallstudie im Harz (Deutschland) hatten wir die Gelegenheit, einen solchen Bestand zu untersuchen (Brockenurwald). Ziel der Untersuchung war die vergleichende Analyse der pflanzlichen Diversität (Bodenvegetation, Epiphyten) sowie ausgewählter Ökosystemeigenschaften (oberirdische Biomasse, ökosystemarer Kohlenstoffvorrat) in fünf altersabhängigen Waldentwicklungsphasen (Verjüngungs-, Aufwuchs-, Optimum-, Alters- und Zerfallsphase). Während sich die Bodenvegetation kaum zwischen den Entwicklungsstadien unterschied, war der Artenreichtum epiphytischer Moose und Flechten auf den stehenden Bäumen in der Alters- und insbesondere der Zerfallsphase signifikant größer als in den jüngeren Entwicklungsstadien, die auch im Wirtschaftswald vorkommen. Der Artenreichtum auf liegendem (aus der vorangegangenen Waldgeneration stammendem) Totholz war am höchsten in der Verjüngungs- und der Aufwuchsphase. Die oberirdische Biomasse und die Kohlenstoffvorräte waren in der Alters- und in der Zerfallsphase größer als in den anderen Waldentwicklungsstadien. Der Kohlenstoffvorrat im Boden war unabhängig vom Waldentwicklungsstadium konstant hoch. Unsere Ergebnisse unterstreichen die große Bedeutung der Alters- und Zerfallsphase und einer natürlichen Bestandesdynamik für die pflanzliche Diversität von Wäldern und für die Fähigkeit, große Vorräte an Kohlenstoff zu speichern
The significance of deadwood for total bryophyte, lichen, and vascular plant diversity in an old-growth spruce forest
No full textModern silviculture has led to a reduction in deadwood, especially that of large diameter, and thus the loss of an important habitat niche in most European forests. We analyzed the significance of deadwood for the total species diversity in three plant groups (bryophytes, lichens, and vascular plants) in one of Central Europe’s few remnants of unmanaged old-growth forest. The site is a montane forest of Picea abies on Mt. Brocken, Harz Mountains, Germany, which has not been managed for at least several centuries, undergoes natural forest dynamics, and thus harbors large amounts of standing and downed deadwood. Epiphyte vegetation of live trees and the ground vegetation were studied for comparison. We did not find any obligate deadwood species. Nevertheless, 84 % (70 species) of the total species were found on standing or downed deadwood. One-third of these species, or 28 % of the total species in the forest, were only sampled on deadwood, whereas the remaining species were also found on live trees and/or the ground. Bryophytes were the largest group of species on deadwood (47 % of the deadwood-inhabiting species), followed by lichens (37 %) and vascular plants (16 %). Large-diameter deadwood in an advanced stage of decay harbored more species than smaller fragments in the early stages of decay. Despite the lack of obligate deadwood colonizers, deadwood apparently plays a key role for forest plant diversity, mainly by providing an environment with low competition and thus facilitating the establishment of species
Results of a case study in the Harz Mountains
No full textManaged forests differ principally from old-growth forests by the scarcity of ageing and decaying trees beyond the rotation age as well as by the more radical disruption of stand continuity between consecutive forest generations. The natural dynamics due to age-dependent mortality and external disturbance in unmanaged stands results in a heterogeneous spatial pattern of differently sized patches of different forest development stages and in the formation of gaps. Forest stands, which follow natural forest dynamics since at least several centuries, are extremely rare in Central Europe. In a case study in the Harz Mountains, Germany, we had the opportunity to study such a forest stand (Bracken old growth forest). The objective of our study was the comparative analysis of plant diversity (ground vegetation, epiphytes) as well as of selected ecosystem properties (aboveground biomass, ecosystem carbon pool) in five age-dependent forest development stages (regeneration, initial, climax, over-mature, and decay stages). While the ground vegetation did hardly differ between the forest development stages, the species richness of epiphytic bryophytes and lichens on standing trees was significantly greater in the over-mature and decaying stages than in the earlier ones, which are also found in managed forests. The species richness on downed deadwood (originating from the preceding forest generation) was highest in the regeneration and initial stages. The aboveground biomass and carbon pools were higher in the over-mature and decaying stages than in the other forest development stages. The pool of soil organic carbon was consistently high across the forest development stages. Our results confirm the great importance of the over-mature and decaying stages for plant diversity and for the capability of forests to store high amounts of carbon
Chemical properties of decaying wood in an old-growth spruce forest and effects on soil chemistry
No full textLive trees influence the nutrient status of the soil by the interception of substances from the atmosphere, the uptake of nutrients from the soil, and the deposition of litter. In an unmanaged old-growth spruce mountain forest on acidic soil, we analyzed how the death and decay of spruce trees affects the acidity and element concentrations of the soil, tree bark (or outermost stemwood) and stemflow. Key study objective was to examine whether the element release from decaying deadwood significantly increases the available soil nutrient stocks in the senescence phase of coniferous forests. Bark and stemflow chemistry responded to the death and decay of the trees with lowered acidity and reduced nutrient concentrations, which was attributed to the gradual loss of the intercepting canopy surface. Bark and stemflow concentrations of base cations (K, Ca, Mg) showed a transient peak in the course of wood decay. Published evidence suggests that the variability in bark and stemflow chemistry detected across the sequence of wood decay stages was sufficient to shape the epiphytic lichen and bryophyte communities. The death and decay of spruce trees also resulted in elevated base saturation near standing deadwood. Downed deadwood had a negligible effect on soil chemistry, among others due to slow decomposition in the studied cold mountain forest. Soil acidity was not significantly affected by deadwood. The release of base cations from standing deadwood to the soil suggests that sparing part of the trees in managed forests from logging could counteract nutrient depletion through timber harvesting
Productivity of temperate broad-leaved forest stands differing in tree species diversity
No full text• Understanding the effects of tree species diversity on biomass and production of
forests is fundamental for carbon sequestration strategies, particularly in the
perspective of the current climate change. However, the diversity-productivity
relationship in old-growth forests is not well understood.
• We quantified biomass and
above-ground production in nine forest stands with increasing tree species diversity from
monocultures of beech to stands consisting of up to five deciduous tree species
(Fagus sylvatica, Fraxinus excelsior, Tilia
spp., Carpinus betulus, Acer spp.) to examine
(a) if mixed stands are more productive than monospecific stands, (b) how tree species
differ in the productivity of stem wood, leaves and fruits, and (c) if beech productivity
increases with tree diversity due to lower intraspecific competition and complementary
resource use.
• Total above-ground biomass and wood production decreased with increasing
tree species diversity. In Fagus and Fraxinus, the basal
area-related wood productivity exceeded those of the co-occurring tree species, while
Tilia had the highest leaf productivity. Fagus trees
showed no elevated production per basal area in the mixed stands.
• We found no evidence of
complementary resource use associated with biomass production. We conclude that
above-ground productivity of old-growth temperate deciduous forests depend more on tree
species-specific traits than on tree diversity itself
Leaf litter decomposition in temperate deciduous forest stands with a decreasing fraction of beech (Fagus sylvatica)
Full text linkWe hypothesised that the decomposition rates of leaf litter will increase along a gradient of decreasing fraction of the European beech (Fagus sylvatica) and increasing tree species diversity in the generally beech-dominated Central European temperate deciduous forests due to an increase in litter quality. We studied the decomposition of leaf litter including its lignin fraction in monospecific (pure beech) stands and in stands with up to five tree genera (Acer spp., Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia spp.) using a litterbag approach. Litter and lignin decomposition was more rapid in stand-representative litter from multispecific stands than in litter from pure beech stands. Except for beech litter, the decomposition rates of species-specific tree litter did not differ significantly among the stand types, but were most rapid in Fraxinus excelsior and slowest in beech in an interspecific comparison. Pairwise comparisons of the decomposition of beech litter with litter of the other tree species (except for Acer platanoides) revealed a “home field advantage” of up to 20% (more rapid litter decomposition in stands with a high fraction of its own species than in stands with a different tree species composition). Decomposition of stand-representative litter mixtures displayed additive characteristics, not significantly more rapid than predicted by the decomposition of litter from the individual tree species. Leaf litter decomposition rates were positively correlated with the initial N and Ca concentrations of the litter, and negatively with the initial C:N, C:P and lignin:N ratios. The results support our hypothesis that the overall decomposition rates are mainly influenced by the chemical composition of the individual litter species. Thus, the fraction of individual tree species in the species composition seems to be more important for the litter decomposition rates than tree species diversity itself
Nitrogen mineralization peaks under closed canopy during the natural forest development cycle of an old-growth temperate spruce forest
No full text• Context Old-growth forests with natural forest development and complex stand structure have become extremely rare in Central Europe. Changes of biogeochemistry and the N cycle across a full forest development cycle are not well understood. • Aims We tested the hypothesis that net N mineralization and the relative importance of nitrification are increasing with proceeding forest development from regeneration to decay stages. • Methods In an unmanaged old-growth spruce forest, we measured net ammonification and nitrification rate in the five forest development stages in 2 years using the intact soil core incubation method. • Results Net N mineralization (and ammonification) rates were higher in the closed stands of the optimum and over-mature stages than in the more open decay and regeneration stages. Only a small proportion of NH4+ was oxidized to NO3− in the studied acidic soils. • Conclusion Lower N mineralization in the more open than the closed patches of this natural forest is unexpected, contrasting with the findings from artificial gaps. Possible reasons are reduced litter supply and lower canopy N interception in gaps in this forest under exposure to high N deposition. Further studies in other old-growth forests are needed to better understand the mechanisms causing long-term change in N cycling with forest development. • Key message Nitrogen mineralization was higher in the optimum and over-mature stages with closed canopy than in the more open decay and regeneration stages of an unmanaged old-growth forest with high atmospheric nitrogen load, in contrast to published experiments with artificial gaps
Separating forest continuity from tree age effects on plant diversity in the ground and epiphyte vegetation of a Central European mountain spruce forest
No full textForest continuity has been identified as an important factor influencing the structure and diversity of forest vegetation. Primary forests with centuries of continuity are usually more diverse than young secondary forests as forest are colonized only slowly and because the former are richer in old tree individuals. In the present study, performed in unmanaged high-elevation spruce forests of the Harz Mountains, Germany, we had the unique opportunity to separate the effects of forest continuity and tree age on plant diversity. We compared an old-growth spruce forest with century-long habitat continuity with an adjacent secondary spruce forest, which had naturally established on a former bog after 1796 when peat exploitation halted. Comparative analysis of the ground and epiphyte vegetation showed that the plant diversity of the old-growth forest was not higher than that of the secondary forest with a similar tree age of >200 years. Our results suggest that a period of >200 years was sufficient for the secondary forest to be colonized by the whole regional species pool of herbaceous and cryptogam forest plants and epiphytes. Therefore, it is likely that habitat structure, including the presence of old and decaying trees, was more important for determining plant diversity than the independent effect of forest continuity. Our results are probably not transferrable to spruce forests younger than 200 years and highly fragmented woodlands with long distances between new stands and old-growth forests that serve as diaspore sources. In addition, our results might be not transferable to remote areas without notable air pollution, as the epiphyte vegetation of the study area was influenced by SO2 pollution in the second half of the 20th century
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