@article{WojcikCeulemansGaedke2021, author = {Wojcik, Laurie Anne and Ceulemans, Ruben and Gaedke, Ursula}, title = {Functional diversity buffers the effects of a pulse perturbation on the dynamics of tritrophic food webs}, series = {Ecology and Evolution}, volume = {11}, journal = {Ecology and Evolution}, number = {22}, publisher = {John Wiley \& Sons, Inc.}, address = {Hoboken (New Jersey)}, issn = {2045-7758}, doi = {10.1002/ece3.8214}, pages = {15639 -- 15663}, year = {2021}, abstract = {Biodiversity decline causes a loss of functional diversity, which threatens ecosystems through a dangerous feedback loop: This loss may hamper ecosystems' ability to buffer environmental changes, leading to further biodiversity losses. In this context, the increasing frequency of human-induced excessive loading of nutrients causes major problems in aquatic systems. Previous studies investigating how functional diversity influences the response of food webs to disturbances have mainly considered systems with at most two functionally diverse trophic levels. We investigated the effects of functional diversity on the robustness, that is, resistance, resilience, and elasticity, using a tritrophic—and thus more realistic—plankton food web model. We compared a non-adaptive food chain with no diversity within the individual trophic levels to a more diverse food web with three adaptive trophic levels. The species fitness differences were balanced through trade-offs between defense/growth rate for prey and selectivity/half-saturation constant for predators. We showed that the resistance, resilience, and elasticity of tritrophic food webs decreased with larger perturbation sizes and depended on the state of the system when the perturbation occurred. Importantly, we found that a more diverse food web was generally more resistant and resilient but its elasticity was context-dependent. Particularly, functional diversity reduced the probability of a regime shift toward a non-desirable alternative state. The basal-intermediate interaction consistently determined the robustness against a nutrient pulse despite the complex influence of the shape and type of the dynamical attractors. This relationship was strongly influenced by the diversity present and the third trophic level. Overall, using a food web model of realistic complexity, this study confirms the destructive potential of the positive feedback loop between biodiversity loss and robustness, by uncovering mechanisms leading to a decrease in resistance, resilience, and potentially elasticity as functional diversity declines.}, language = {en} } @misc{WojcikCeulemansGaedke2021, author = {Wojcik, Laurie Anne and Ceulemans, Ruben and Gaedke, Ursula}, title = {Functional diversity buffers the effects of a pulse perturbation on the dynamics of tritrophic food webs}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1251}, issn = {1866-8372}, doi = {10.25932/publishup-55373}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-553730}, pages = {25}, year = {2021}, abstract = {Biodiversity decline causes a loss of functional diversity, which threatens ecosystems through a dangerous feedback loop: This loss may hamper ecosystems' ability to buffer environmental changes, leading to further biodiversity losses. In this context, the increasing frequency of human-induced excessive loading of nutrients causes major problems in aquatic systems. Previous studies investigating how functional diversity influences the response of food webs to disturbances have mainly considered systems with at most two functionally diverse trophic levels. We investigated the effects of functional diversity on the robustness, that is, resistance, resilience, and elasticity, using a tritrophic—and thus more realistic—plankton food web model. We compared a non-adaptive food chain with no diversity within the individual trophic levels to a more diverse food web with three adaptive trophic levels. The species fitness differences were balanced through trade-offs between defense/growth rate for prey and selectivity/half-saturation constant for predators. We showed that the resistance, resilience, and elasticity of tritrophic food webs decreased with larger perturbation sizes and depended on the state of the system when the perturbation occurred. Importantly, we found that a more diverse food web was generally more resistant and resilient but its elasticity was context-dependent. Particularly, functional diversity reduced the probability of a regime shift toward a non-desirable alternative state. The basal-intermediate interaction consistently determined the robustness against a nutrient pulse despite the complex influence of the shape and type of the dynamical attractors. This relationship was strongly influenced by the diversity present and the third trophic level. Overall, using a food web model of realistic complexity, this study confirms the destructive potential of the positive feedback loop between biodiversity loss and robustness, by uncovering mechanisms leading to a decrease in resistance, resilience, and potentially elasticity as functional diversity declines.}, language = {en} } @phdthesis{Schmidtke2009, author = {Schmidtke, Andrea}, title = {Biodiversity effects on the performance of terrestrial plant and phytoplankton communities}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-38936}, school = {Universit{\"a}t Potsdam}, year = {2009}, abstract = {Die {\"O}kosysteme unserer Erde sind durch das rasante Artensterben infolge von Umweltver{\"a}nderungen durch den Menschen und des globalen Klimawandels stark betroffen. Mit den Auswirkungen dieses Artenverlustes und der damit einhergehenden Ver{\"a}nderung der Diversit{\"a}t besch{\"a}ftigt sich die heutige Biodiversit{\"a}tsforschung. Spezieller wird der Effekt der Diversit{\"a}t auf {\"O}kosystemprozesse wie beispielsweise den Biomasseaufbau von Prim{\"a}rproduzenten oder der Resistenz einer Gemeinschaft gegen die Einwanderung neuer Arten untersucht. Die Quantifizierung des Einflusses der Diversit{\"a}t auf die Prim{\"a}rproduktion und das Verst{\"a}ndnis der zugrunde liegenden Mechanismen ist von besonderer Wichtigkeit. In terrestrischen Pflanzengemeinschaften wurde bereits ein positiver Diversit{\"a}tseffekt auf die Gemeinschaftsbiomasse beobachtet. Dies wird haupts{\"a}chlich durch den Komplementarit{\"a}ts- und/oder den Dominanzeffekt erkl{\"a}rt. Die Komplementarit{\"a}t zwischen Arten ist beispielsweise bei Unterschieden in der Ressourcenausnutzung gegeben (z.B. unterschiedliche Wurzeltiefen). Diese kann zu einer besseren N{\"a}hrstoffausnutzung in diverseren Gemeinschaften f{\"u}hren, die letztlich deren h{\"o}here Biomassen erkl{\"a}rt. Der Dominanzeffekt hingegen beruht auf der in diverseren Gemeinschaften h{\"o}heren Wahrscheinlichkeit, eine hochproduktive Art anzutreffen, was letztlich die h{\"o}here Biomasse der Gemeinschaft verursacht. Diversit{\"a}tseffekte auf {\"O}kosystemprozesse wurden bisher haupts{\"a}chlich auf der Gemeinschaftsebene untersucht. Analysen {\"u}ber die Reaktionen, die alle Arten einer Gemeinschaft einschließen, fehlen bisher. Daher wurde der Einfluss der Diversit{\"a}t auf die individuelle Performance von Pflanzenarten innerhalb des Biodiversit{\"a}tsprojektes „Das Jena Experiment" untersucht. Dieses Experiment umfasst 60 Arten, die charakteristisch f{\"u}r Mitteleurop{\"a}ische Graslandschaften sind. Die Arten wurden in die 4 funktionellen Gruppen Gr{\"a}ser, kleine Kr{\"a}uter, große Kr{\"a}uter und Leguminosen eingeteilt. Im Freilandversuch zeigte sich, dass mit steigender Artenzahl die individuelle Pflanzenh{\"o}he zunahm, w{\"a}hrend die individuelle oberirdische Biomasse sank. Der positive Diversit{\"a}tseffekt auf die pflanzliche Gemeinschaftsbiomasse kann folglich nicht auf der individuellen oberirdischen Biomassezunahme beruhen. {\"U}berdies reagierten die einzelnen funktionellen Gruppen und sogar die einzelnen Arten innerhalb einer funktionellen Gruppe unterschiedlich auf Diversit{\"a}tsver{\"a}nderungen. Folglich ist zu vermuten, dass einige {\"O}kosystemprozesse auf Gemeinschaftsebene durch die Reaktionen von bestimmten funktionellen Gruppen bzw. Arten hervorgerufen werden. Diversit{\"a}tseffekte auf Gemeinschaftsbiomassen wurden bislang haupts{\"a}chlich mit terrestrischen Pflanzen und weniger mit frei-schwebenden Algenarten (Phytoplankton) erforscht. Demzufolge wurde der Einfluss der Diversit{\"a}t auf die Biomasse von Phytoplankton-Gemeinschaften experimentell untersucht, wobei es sowohl zu negativen als auch positiven Diversit{\"a}tseffekten kam. Eine negative Beziehung zwischen Diversit{\"a}t und Gemeinschaftsbiomasse zeigte sich, wenn schnell-w{\"u}chsige Algenarten nur geringe Biomassen in Mono- und Mischkultur aufbauten. Die vorhandenen N{\"a}hrstoffe in der Mischkultur wurden von den schnell-w{\"u}chsigen Arten monopolisiert und folglich standen sie den langsam-w{\"u}chsigen Algenarten, welche viel Biomasse in Monokultur aufbauten, nicht mehr zur Verf{\"u}gung. Zu einem positiven Diversit{\"a}tseffekt auf die Gemeinschaftsbiomasse kam es, wenn die Artengemeinschaft eine positive Beziehung zwischen Wachstumsrate und Biomasse in Monokultur zeigte, sodass die schnell-w{\"u}chsige Algenarten viel Biomasse aufbauten. Da diese schnell-w{\"u}chsigen Algen in der Mischkultur dominant wurden, bestand die Gemeinschaft letztlich aus hoch-produktiven Algenarten, was zu einer erh{\"o}hten Gesamtbiomasse f{\"u}hrte. Diese beiden Versuchsans{\"a}tze verdeutlichen Mechanismen f{\"u}r die unterschiedlichen Reaktionen der Gemeinschaften auf Diversit{\"a}tsver{\"a}nderungen, welche auch f{\"u}r terrestrische Pflanzengemeinschaften gefunden wurden. Ein anderer wichtiger {\"O}kosystemprozess, der von der Diversit{\"a}t beeinflusst wird, ist die Anf{\"a}lligkeit von Gemeinschaften gegen{\"u}ber invasiven Arten (Invasibilit{\"a}t). Die Invasibilit{\"a}t wird von einer Vielzahl von Faktoren beeinflusst und demzufolge wurde der Effekt der Diversit{\"a}t und der Produktivit{\"a}t (N{\"a}hrstoffgehalt) auf die Invasibilit{\"a}t von Phytoplankton-Gemeinschaften in An- und Abwesenheit eines Herbivoren untersucht. Die zwei funktionell unterschiedlichen invasiven Arten waren die Blaualge Cylindrospermopsis raciborskii (schlecht fressbar) und der Phytoflagellat Cryptomonas sp. (gut fressbar). Es zeigte sich, dass der Fraßdruck, welcher selber durch die Produktivit{\"a}t beeinflusst wurde, einen bedeutenden Effekt auf die Invasibilit{\"a}t von Phytoplankton-Gemeinschaften hat. Die funktionellen Eigenschaften der invasiven und residenten Arten waren zudem bedeutender als die Artenzahl.}, language = {en} } @article{SchittkoOnandiaBernardVerdieretal.2022, author = {Schittko, Conrad and Onandia, Gabriela and Bernard-Verdier, Maud and Heger, Tina and Jeschke, Jonathan M. and Kowarik, Ingo and Maaß, Stefanie and Joshi, Jasmin}, title = {Biodiversity maintains soil multifunctionality and soil organic carbon in novel urban ecosystems}, series = {Journal of ecology}, volume = {110}, journal = {Journal of ecology}, number = {4}, publisher = {Wiley}, address = {Hoboken}, issn = {0022-0477}, doi = {10.1111/1365-2745.13852}, pages = {916 -- 934}, year = {2022}, abstract = {Biodiversity in urban ecosystems has the potential to increase ecosystem functions and support a suite of services valued by society, including services provided by soils. Specifically, the sequestration of carbon in soils has often been advocated as a solution to mitigate the steady increase in CO2 concentration in the atmosphere as a key driver of climate change. However, urban ecosystems are also characterized by an often high level of ecological novelty due to profound human-mediated changes, such as the presence of high numbers of non-native species, impervious surfaces or other disturbances. Yet it is poorly understood whether and how biodiversity affects ecosystem functioning and services of urban soils under these novel conditions. In this study, we assessed the influence of above- and below-ground diversity, as well as urbanization and plant invasions, on multifunctionality and organic carbon stocks of soils in non-manipulated grasslands along an urbanization gradient in Berlin, Germany. We focused on plant diversity (measured as species richness and functional trait diversity) and, in addition, on soil organism diversity as a potential mediator for the relationship of plant species diversity and ecosystem functioning. Our results showed positive effects of plant diversity on soil multifunctionality and soil organic carbon stocks along the entire gradient. Structural equation models revealed that plant diversity enhanced soil multifunctionality and soil organic carbon by increasing the diversity of below-ground organisms. These positive effects of plant diversity on soil multifunctionality and soil fauna were not restricted to native plant species only, but were also exerted by non-native species, although to a lesser degree. Synthesis. We conclude that enhancing diversity in plants and soil fauna of urban grasslands can increase the multifunctionality of urban soils and also add to their often underestimated but very valuable role in mitigating effects of climate change.}, language = {en} } @article{SchittkoBernardVerdierHegeretal.2020, author = {Schittko, Conrad and Bernard-Verdier, Maud and Heger, Tina and Buchholz, Sascha and Kowarik, Ingo and von der Lippe, Moritz and Seitz, Birgit and Joshi, Jasmin Radha and Jeschke, Jonathan M.}, title = {A multidimensional framework for measuring biotic novelty: How novel is a community?}, series = {Global Change Biology}, volume = {26}, journal = {Global Change Biology}, number = {8}, publisher = {John Wiley \& Sons, Inc.}, address = {New Jersey}, pages = {17}, year = {2020}, abstract = {Anthropogenic changes in climate, land use, and disturbance regimes, as well as introductions of non-native species can lead to the transformation of many ecosystems. The resulting novel ecosystems are usually characterized by species assemblages that have not occurred previously in a given area. Quantifying the ecological novelty of communities (i.e., biotic novelty) would enhance the understanding of environmental change. However, quantification remains challenging since current novelty metrics, such as the number and/or proportion of non-native species in a community, fall short of considering both functional and evolutionary aspects of biotic novelty. Here, we propose the Biotic Novelty Index (BNI), an intuitive and flexible multidimensional measure that combines (a) functional differences between native and non-native introduced species with (b) temporal dynamics of species introductions. We show that the BNI is an additive partition of Rao's quadratic entropy, capturing the novel interaction component of the community's functional diversity. Simulations show that the index varies predictably with the relative amount of functional novelty added by recently arrived species, and they illustrate the need to provide an additional standardized version of the index. We present a detailed R code and two applications of the BNI by (a) measuring changes of biotic novelty of dry grassland plant communities along an urbanization gradient in a metropolitan region and (b) determining the biotic novelty of plant species assemblages at a national scale. The results illustrate the applicability of the index across scales and its flexibility in the use of data of different quality. Both case studies revealed strong connections between biotic novelty and increasing urbanization, a measure of abiotic novelty. We conclude that the BNI framework may help building a basis for better understanding the ecological and evolutionary consequences of global change.}, language = {en} } @misc{SchittkoBernardVerdierHegeretal.2020, author = {Schittko, Conrad and Bernard-Verdier, Maud and Heger, Tina and Buchholz, Sascha and Kowarik, Ingo and von der Lippe, Moritz and Seitz, Birgit and Joshi, Jasmin Radha and Jeschke, Jonathan M.}, title = {A multidimensional framework for measuring biotic novelty: How novel is a community?}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {8}, issn = {1866-8372}, doi = {10.25932/publishup-52565}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-525657}, pages = {19}, year = {2020}, abstract = {Anthropogenic changes in climate, land use, and disturbance regimes, as well as introductions of non-native species can lead to the transformation of many ecosystems. The resulting novel ecosystems are usually characterized by species assemblages that have not occurred previously in a given area. Quantifying the ecological novelty of communities (i.e., biotic novelty) would enhance the understanding of environmental change. However, quantification remains challenging since current novelty metrics, such as the number and/or proportion of non-native species in a community, fall short of considering both functional and evolutionary aspects of biotic novelty. Here, we propose the Biotic Novelty Index (BNI), an intuitive and flexible multidimensional measure that combines (a) functional differences between native and non-native introduced species with (b) temporal dynamics of species introductions. We show that the BNI is an additive partition of Rao's quadratic entropy, capturing the novel interaction component of the community's functional diversity. Simulations show that the index varies predictably with the relative amount of functional novelty added by recently arrived species, and they illustrate the need to provide an additional standardized version of the index. We present a detailed R code and two applications of the BNI by (a) measuring changes of biotic novelty of dry grassland plant communities along an urbanization gradient in a metropolitan region and (b) determining the biotic novelty of plant species assemblages at a national scale. The results illustrate the applicability of the index across scales and its flexibility in the use of data of different quality. Both case studies revealed strong connections between biotic novelty and increasing urbanization, a measure of abiotic novelty. We conclude that the BNI framework may help building a basis for better understanding the ecological and evolutionary consequences of global change.}, language = {en} } @misc{RomeroMunozFandosBenitezLopezetal.2020, author = {Romero-Munoz, Alfredo and Fandos, Guillermo and Ben{\´i}tez-L{\´o}pez, Ana and Kuemmerle, Tobias}, title = {Habitat destruction and overexploitation drive widespread declines in all facets of mammalian diversity in the Gran Chaco}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {4}, issn = {1866-8372}, doi = {10.25932/publishup-56769}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-567696}, pages = {15}, year = {2020}, abstract = {Global biodiversity is under high and rising anthropogenic pressure. Yet, how the taxonomic, phylogenetic, and functional facets of biodiversity are affected by different threats over time is unclear. This is particularly true for the two main drivers of the current biodiversity crisis: habitat destruction and overexploitation. We provide the first long-term assessment of multifaceted biodiversity changes caused by these threats for any tropical region. Focussing on larger mammals in South America's 1.1 million km(2) Gran Chaco region, we assessed changes in multiple biodiversity facets between 1985 and 2015, determined which threats drive those changes, and identified remaining key areas for all biodiversity facets. Using habitat and threat maps, we found, first, that between 1985 and 2015 taxonomic (TD), phylogenetic (PD) and functional (FD) diversity all declined drastically across over half of the area assessed. FD declined about 50\% faster than TD and PD, and these declines were mainly driven by species loss, rather than species turnover. Second, habitat destruction, hunting, and both threats together contributed similar to 57\%, similar to 37\%, and similar to 6\% to overall facet declines, respectively. However, hunting pressure increased where TD and PD declined most strongly, whereas habitat destruction disproportionally contributed to FD declines. Third, just 23\% of the Chaco would have to be protected to safeguard the top 17\% of all three facets. Our findings uncover a widespread impoverishment of mammal species richness, evolutionary history, and ecological functions across broad areas of the Chaco due to increasing habitat destruction and hunting. Moreover, our results pinpoint key areas that should be preserved and managed to maintain all facets of mammalian diversity across the Chaco. More generally, our work highlights how long-term changes in biodiversity facets can be assessed and attributed to specific threats, to better understand human impacts on biodiversity and to guide conservation planning to mitigate them.}, language = {en} } @article{RomeroMunozFandosBenitezLopezetal.2020, author = {Romero-Munoz, Alfredo and Fandos, Guillermo and Ben{\´i}tez-L{\´o}pez, Ana and Kuemmerle, Tobias}, title = {Habitat destruction and overexploitation drive widespread declines in all facets of mammalian diversity in the Gran Chaco}, series = {Global change biology}, volume = {27}, journal = {Global change biology}, number = {4}, publisher = {Wiley}, address = {Hoboken}, issn = {1354-1013}, doi = {10.1111/gcb.15418}, pages = {755 -- 767}, year = {2020}, abstract = {Global biodiversity is under high and rising anthropogenic pressure. Yet, how the taxonomic, phylogenetic, and functional facets of biodiversity are affected by different threats over time is unclear. This is particularly true for the two main drivers of the current biodiversity crisis: habitat destruction and overexploitation. We provide the first long-term assessment of multifaceted biodiversity changes caused by these threats for any tropical region. Focussing on larger mammals in South America's 1.1 million km(2) Gran Chaco region, we assessed changes in multiple biodiversity facets between 1985 and 2015, determined which threats drive those changes, and identified remaining key areas for all biodiversity facets. Using habitat and threat maps, we found, first, that between 1985 and 2015 taxonomic (TD), phylogenetic (PD) and functional (FD) diversity all declined drastically across over half of the area assessed. FD declined about 50\% faster than TD and PD, and these declines were mainly driven by species loss, rather than species turnover. Second, habitat destruction, hunting, and both threats together contributed similar to 57\%, similar to 37\%, and similar to 6\% to overall facet declines, respectively. However, hunting pressure increased where TD and PD declined most strongly, whereas habitat destruction disproportionally contributed to FD declines. Third, just 23\% of the Chaco would have to be protected to safeguard the top 17\% of all three facets. Our findings uncover a widespread impoverishment of mammal species richness, evolutionary history, and ecological functions across broad areas of the Chaco due to increasing habitat destruction and hunting. Moreover, our results pinpoint key areas that should be preserved and managed to maintain all facets of mammalian diversity across the Chaco. More generally, our work highlights how long-term changes in biodiversity facets can be assessed and attributed to specific threats, to better understand human impacts on biodiversity and to guide conservation planning to mitigate them.}, language = {en} } @article{RochaGaedkeVasseur2011, author = {Rocha, Marcia R. and Gaedke, Ursula and Vasseur, David A.}, title = {Functionally similar species have similar dynamics}, series = {The journal of ecology}, volume = {99}, journal = {The journal of ecology}, number = {6}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0022-0477}, doi = {10.1111/j.1365-2745.2011.01893.x}, pages = {1453 -- 1459}, year = {2011}, abstract = {1. Improving the mechanistic basis of biodiversity-ecosystem function relationships requires a better understanding of how functional traits drive the dynamics of populations. For example, environmental disturbances or grazing may increase synchronization of functionally similar species, whereas functionally different species may show independent dynamics, because of different responses to the environment. Competition for resources, on the other hand, may yield a wide range of dynamic patterns among competitors and lead functionally similar and different species to display synchronized to compensatory dynamics. The mixed effect of these forces will influence the temporal fluctuations of populations and, thus, the variability of aggregate community properties. 2. To search for a relationship between functional and dynamics similarity, we studied the relationship between functional trait similarity and temporal dynamics similarity for 36 morphotypes of phytoplankton using long-term high-frequency measurements. 3. Our results show that functionally similar morphotypes exhibit dynamics that are more synchronized than those of functionally dissimilar ones. Functionally dissimilar morphotypes predominantly display independent temporal dynamics. This pattern is especially strong when short time-scales are considered. 4. Negative correlations are present among both functionally similar and dissimilar phytoplankton morphotypes, but are rarer and weaker than positive ones over all temporal scales. 5. Synthesis. We demonstrate that diversity in functional traits decreases community variability and ecosystem-level properties by decoupling the dynamics of individual morphotypes.}, language = {en} } @phdthesis{Naaf2011, author = {Naaf, Tobias}, title = {Floristic homogenization and impoverishment : herb layer changes over two decades in deciduous forest patches of the Weser-Elbe region (NW Germany)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-52446}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Human-induced alterations of the environment are causing biotic changes worldwide, including the extinction of species and a mixing of once disparate floras and faunas. One type of biological communities that is expected to be particularly affected by environmental alterations are herb layer plant communities of fragmented forests such as those in the west European lowlands. However, our knowledge about current changes in species diversity and composition in these communities is limited due to a lack of adequate long-term studies. In this thesis, I resurveyed the herb layer communities of ancient forest patches in the Weser-Elbe region (NW Germany) after two decades using 175 semi-permanent plots. The general objectives were (i) to quantify changes in plant species diversity considering also between-community (β) and functional diversity, (ii) to determine shifts in species composition in terms of species' niche breadth and functional traits and (iii) to find indications on the most likely environmental drivers for the observed changes. These objectives were pursued with four independent research papers (Chapters 1-4) whose results were brought together in a General Discussion. Alpha diversity (species richness) increased by almost four species on average, whereas β diversity tended to decrease (Chapter 1). The latter is interpreted as a beginning floristic homogenization. The observed changes were primarily the result of a spread of native habitat generalists that are able to tolerate broad pH and moisture ranges. The changes in α and β diversity were only significant when species abundances were neglected (Chapters 1 and 2), demonstrating that the diversity changes resulted mainly from gains and losses of low-abundance species. This study is one of the first studies in temperate Europe that demonstrates floristic homogenization of forest plant communities at a larger than local scale. The diversity changes found at the taxonomic level did not result in similar changes at the functional level (Chapter 2). The likely reason is that these communities are functionally "buffered". Single communities involve most of the functional diversity of the regional pool, i.e., they are already functionally rich, while they are functionally redundant among each other, i.e., they are already homogeneous. Independent of taxonomic homogenization, the abundance of 30 species decreased significantly (Chapter 4). These species included 12 ancient forest species (i.e., species closely tied to forest patches with a habitat continuity > 200 years) and seven species listed on the Red List of endangered plant species in NW Germany. If these decreases continue over the next decades, local extinctions may result. This biotic impoverishment would seriously conflict with regional conservation goals. Community assembly mechanisms changed at the local level particularly at sites that experienced disturbance by forest management activities between the sampling periods (Chapter 3). Disturbance altered community assembly mechanisms in two ways: (i) it relaxed environmental filters and allowed the coexistence of different reproduction strategies, as reflected by a higher diversity of reproductive traits at the time of the resurvey, and (ii) it enhanced light availability and tightened competitive filters. These limited the functional diversity with respect to canopy height and selected for taller species. Thirty-one winner and 30 loser species, which had significantly increased or decreased in abundance, respectively, were characterized by various functional traits and ecological performances to find indications on the most likely environmental drivers for the observed floristic changes (Chapter 4). Winner species had higher seed longevity, flowered later in the season and had more often an oceanic distribution compared to loser species. Loser species tended to have a higher specific leaf area, to be more susceptible to deer browsing and to have a performance optimum at higher soil pH values compared to winner species. Multiple logistic regression analyses indicated that disturbances due to forest management interventions were the primary cause of the species shifts. As one of the first European resurvey studies, this study provides indications that an enhanced browsing pressure due to increased deer densities and increasingly warmer winters are important drivers. The study failed to demonstrate that eutrophication and acidification due to atmospheric deposition substantially drive herb layer changes. The restriction of the sample to the most base-rich sites in the region is discussed as a likely reason. Furthermore, the decline of several ancient forest species is discussed as an indication that the forest patches are still paying off their "extinction debt", i.e., exhibit a delayed response to forest fragmentation.}, language = {en} }