More losses than gains during one century of plant biodiversity change in Germany.

Long-term analyses of biodiversity data highlight a 'biodiversity conservation paradox': biological communities show substantial species turnover over the past century1,2, but changes in species richness are marginal1,3-5. Most studies, however, have focused only on the incidence of species, and have not considered changes in local abundance. Here we asked whether analysing changes in the cover of plant species could reveal previously unrecognized patterns of biodiversity change and provide insights into the underlying mechanisms. We compiled and analysed a dataset of 7,738 permanent and semi-permanent vegetation plots from Germany that were surveyed between 2 and 54 times from 1927 to 2020, in total comprising 1,794 species of vascular plants. We found that decrements in cover, averaged across all species and plots, occurred more often than increments; that the number of species that decreased in cover was higher than the number of species that increased; and that decrements were more equally distributed among losers than were gains among winners. Null model simulations confirmed that these trends do not emerge by chance, but are the consequence of species-specific negative effects of environmental changes. In the long run, these trends might result in substantial losses of species at both local and regional scales. Summarizing the changes by decade shows that the inequality in the mean change in species cover of losers and winners diverged as early as the 1960s. We conclude that changes in species cover in communities represent an important but understudied dimension of biodiversity change that should more routinely be considered in time-series analyses.

Evaluating plant lineage losses and gains in temperate forest understories: a phylogenetic perspective on climate change and nitrogen deposition.

Global change has accelerated local species extinctions and colonizations, often resulting in losses and gains of evolutionary lineages with unique features. Do these losses and gains occur randomly across the phylogeny? We quantified: temporal changes in plant phylogenetic diversity (PD); and the phylogenetic relatedness (PR) of lost and gained species in 2672 semi-permanent vegetation plots in European temperate forest understories resurveyed over an average period of 40 yr. Controlling for differences in species richness, PD increased slightly over time and across plots. Moreover, lost species within plots exhibited a higher degree of PR than gained species. This implies that gained species originated from a more diverse set of evolutionary lineages than lost species. Certain lineages also lost and gained more species than expected by chance, with Ericaceae, Fabaceae, and Orchidaceae experiencing losses and Amaranthaceae, Cyperaceae, and Rosaceae showing gains. Species losses and gains displayed no significant phylogenetic signal in response to changes in macroclimatic conditions and nitrogen deposition. As anthropogenic global change intensifies, temperate forest understories experience losses and gains in specific phylogenetic branches and ecological strategies, while the overall mean PD remains relatively stable.

Les changements globaux accélèrent les processus de colonisation et d'extinction locales d'espèces, aboutissant à des gains ou à des pertes de lignées évolutives uniques. Ces gains et pertes se produisent-ils de manière aléatoire dans l'arbre phylogénétique ? Nous avons mesuré: les changements de diversité phylogénétique; et la parenté phylogénétique des espèces végétales gagnées ou perdues dans 2672 placettes semi-permanentes disposées dans le sous-bois de forêts tempérées d'Europe sur une période moyenne de 40 ans. Une fois corrigée par la richesse spécifique, la diversité phylogénétique a légèrement augmenté au cours du temps dans les différentes placettes. Les espèces perdues ont une plus grande parenté phylogénétique que les espèces gagnées. Les espèces gagnées sont donc issues d'un plus grand nombre de lignées évolutives que les espèces perdues. Certaines lignées ont gagné ou perdu davantage d'espèces que ce qui est prédit par le hasard : les Ericaceae, les Fabaceae et les Orchidaceae ayant davantage perdu, tandis que les Amaranthaceae, les Cyperaceae, et les Rosaceae ont plus gagné. Il n'y a pas de signal phylogénétique des gains ou pertes d'espèces en réponse aux changements de conditions macroclimatiques ou des dépôts atmosphériques d'azote. Alors que les changements globaux d'origine anthropique s'intensifient, les sous-bois des forêts tempérées connaissent des gains et des pertes de certaines lignées évolutives et de certaines stratégies écologiques, sans que la diversité phylogénétique moyenne ne s'en trouve véritablement affectée.

El cambio global ha acelerado las extinciones y colonizaciones a escala local, lo que a menudo ha supuesto pérdidas y ganancias de linajes evolutivos con características únicas. Ahora bien, ¿estas pérdidas y ganancias ocurren aleatoriamente a lo largo de la filogenia? Cuantificamos: los cambios temporales en la diversidad filogenética de las plantas; y la relación filogenética de las especies perdidas y ganadas en 2.672 parcelas de vegetación semipermanente en sotobosques templados europeos y re-muestreadas durante un período promedio de 40 años. Al controlar por las diferencias en la riqueza de especies, la diversidad filogenética aumentó ligeramente con el tiempo y entre parcelas. Además, las especies perdidas dentro de las parcelas exhibieron un mayor grado de relación filogenética que las especies ganadas. Esto implica que las especies ganadas se originaron en un conjunto de linajes evolutivos más diversos que las especies perdidas. Ciertos linajes también perdieron y ganaron más especies de las esperadas aleatoriamente: Ericaceae, Fabaceae y Orchidaceae experimentaron pérdidas y Amaranthaceae, Cyperaceae y Rosaceae mostraron ganancias. Las pérdidas y ganancias de especies no mostraron ninguna señal filogenética significativa en respuesta a los cambios en las condiciones macro-climáticas y la deposición de nitrógeno. A medida que se intensifica el cambio global antropogénico, los sotobosques temperados experimentan pérdidas y ganancias en ramas filogenéticas y estrategias ecológicas específicas, mientras que la diversidad filogenética media general permanece relativamente estable.

Combining multiple investigative approaches to unravel functional responses to global change in the understorey of temperate forests.

Plant communities are being exposed to changing environmental conditions all around the globe, leading to alterations in plant diversity, community composition, and ecosystem functioning. For herbaceous understorey communities in temperate forests, responses to global change are postulated to be complex, due to the presence of a tree layer that modulates understorey responses to external pressures such as climate change and changes in atmospheric nitrogen deposition rates. Multiple investigative approaches have been put forward as tools to detect, quantify and predict understorey responses to these global-change drivers, including, among others, distributed resurvey studies and manipulative experiments. These investigative approaches are generally designed and reported upon in isolation, while integration across investigative approaches is rarely considered. In this study, we integrate three investigative approaches (two complementary resurvey approaches and one experimental approach) to investigate how climate warming and changes in nitrogen deposition affect the functional composition of the understorey and how functional responses in the understorey are modulated by canopy disturbance, that is, changes in overstorey canopy openness over time. Our resurvey data reveal that most changes in understorey functional characteristics represent responses to changes in canopy openness with shifts in macroclimate temperature and aerial nitrogen deposition playing secondary roles. Contrary to expectations, we found little evidence that these drivers interact. In addition, experimental findings deviated from the observational findings, suggesting that the forces driving understorey change at the regional scale differ from those driving change at the forest floor (i.e., the experimental treatments). Our study demonstrates that different approaches need to be integrated to acquire a full picture of how understorey communities respond to global change.

Directional turnover towards larger-ranged plants over time and across habitats.

Species turnover is ubiquitous. However, it remains unknown whether certain types of species are consistently gained or lost across different habitats. Here, we analysed the trajectories of 1827 plant species over time intervals of up to 78 years at 141 sites across mountain summits, forests, and lowland grasslands in Europe. We found, albeit with relatively small effect sizes, displacements of smaller- by larger-ranged species across habitats. Communities shifted in parallel towards more nutrient-demanding species, with species from nutrient-rich habitats having larger ranges. Because these species are typically strong competitors, declines of smaller-ranged species could reflect not only abiotic drivers of global change, but also biotic pressure from increased competition. The ubiquitous component of turnover based on species range size we found here may partially reconcile findings of no net loss in local diversity with global species loss, and link community-scale turnover to macroecological processes such as biotic homogenisation.

Environmental drivers interactively affect individual tree growth across temperate European forests.

Forecasting the growth of tree species to future environmental changes requires a better understanding of its determinants. Tree growth is known to respond to global-change drivers such as climate change or atmospheric deposition, as well as to local land-use drivers such as forest management. Yet, large geographical scale studies examining interactive growth responses to multiple global-change drivers are relatively scarce and rarely consider management effects. Here, we assessed the interactive effects of three global-change drivers (temperature, precipitation and nitrogen deposition) on individual tree growth of three study species (Quercus robur/petraea, Fagus sylvatica and Fraxinus excelsior). We sampled trees along spatial environmental gradients across Europe and accounted for the effects of management for Quercus. We collected increment cores from 267 trees distributed over 151 plots in 19 forest regions and characterized their neighbouring environment to take into account potentially confounding factors such as tree size, competition, soil conditions and elevation. We demonstrate that growth responds interactively to global-change drivers, with species-specific sensitivities to the combined factors. Simultaneously high levels of precipitation and deposition benefited Fraxinus, but negatively affected Quercus' growth, highlighting species-specific interactive tree growth responses to combined drivers. For Fagus, a stronger growth response to higher temperatures was found when precipitation was also higher, illustrating the potential negative effects of drought stress under warming for this species. Furthermore, we show that past forest management can modulate the effects of changing temperatures on Quercus' growth; individuals in plots with a coppicing history showed stronger growth responses to higher temperatures. Overall, our findings highlight how tree growth can be interactively determined by global-change drivers, and how these growth responses might be modulated by past forest management. By showing future growth changes for scenarios of environmental change, we stress the importance of considering multiple drivers, including past management and their interactions, when predicting tree growth.

Global environmental change effects on plant community composition trajectories depend upon management legacies.

The contemporary state of functional traits and species richness in plant communities depends on legacy effects of past disturbances. Whether temporal responses of community properties to current environmental changes are altered by such legacies is, however, unknown. We expect global environmental changes to interact with land-use legacies given different community trajectories initiated by prior management, and subsequent responses to altered resources and conditions. We tested this expectation for species richness and functional traits using 1814 survey-resurvey plot pairs of understorey communities from 40 European temperate forest datasets, syntheses of management transitions since the year 1800, and a trait database. We also examined how plant community indicators of resources and conditions changed in response to management legacies and environmental change. Community trajectories were clearly influenced by interactions between management legacies from over 200 years ago and environmental change. Importantly, higher rates of nitrogen deposition led to increased species richness and plant height in forests managed less intensively in 1800 (i.e., high forests), and to decreases in forests with a more intensive historical management in 1800 (i.e., coppiced forests). There was evidence that these declines in community variables in formerly coppiced forests were ameliorated by increased rates of temperature change between surveys. Responses were generally apparent regardless of sites' contemporary management classifications, although sometimes the management transition itself, rather than historic or contemporary management types, better explained understorey responses. Main effects of environmental change were rare, although higher rates of precipitation change increased plant height, accompanied by increases in fertility indicator values. Analysis of indicator values suggested the importance of directly characterising resources and conditions to better understand legacy and environmental change effects. Accounting for legacies of past disturbance can reconcile contradictory literature results and appears crucial to anticipating future responses to global environmental change.

Nitrogen enrichment in host plants increases the mortality of common Lepidoptera species.

The recent decline of Lepidoptera species strongly correlates with the increasing intensification of agriculture in Western and Central Europe. However, the effects of changed host-plant quality through agricultural fertilization on this insect group remain largely unexplored. For this reason, we tested the response of six common butterfly and moth species to host-plant fertilization using fertilizer quantities usually applied in agriculture. The larvae of the study species Coenonympha pamphilus, Lycaena phlaeas, Lycaena tityrus, Pararge aegeria, Rivula sericealis and Timandra comae were distributed according to a split-brood design to three host-plant treatments comprising one control treatment without fertilization and two fertilization treatments with an input of 150 and 300 kg N ha-1 year-1, respectively. In L. tityrus, we used two additional fertilization treatments with an input of 30 and 90 kg N ha-1 year-1, respectively. Fertilization increased the nitrogen concentration of both host-plant species, Rumex acetosella and Poa pratensis, and decreased the survival of larvae in all six Lepidoptera species by at least one-third, without clear differences between sorrel- and grass-feeding species. The declining survival rate in all species contradicts the well-accepted nitrogen-limitation hypothesis, which predicts a positive response in species performance to dietary nitrogen content. In contrast, this study presents the first evidence that current fertilization quantities in agriculture exceed the physiological tolerance of common Lepidoptera species. Our results suggest that (1) the negative effect of plant fertilization on Lepidoptera has previously been underestimated and (2) that it contributes to the range-wide decline of Lepidoptera.

Combining community resurvey data to advance global change research.

More and more ecologists have started to resurvey communities sampled in earlier decades to determine long-term shifts in community composition and infer the likely drivers of the ecological changes observed. However, to assess the relative importance of, and interactions among, multiple drivers joint analyses of resurvey data from many regions spanning large environmental gradients are needed. In this paper we illustrate how combining resurvey data from multiple regions can increase the likelihood of driver-orthogonality within the design and show that repeatedly surveying across multiple regions provides higher representativeness and comprehensiveness, allowing us to answer more completely a broader range of questions. We provide general guidelines to aid implementation of multi-region resurvey databases. In so doing, we aim to encourage resurvey database development across other community types and biomes to advance global environmental change research.

Microclimate moderates plant responses to macroclimate warming.

Recent global warming is acting across marine, freshwater, and terrestrial ecosystems to favor species adapted to warmer conditions and/or reduce the abundance of cold-adapted organisms (i.e., "thermophilization" of communities). Lack of community responses to increased temperature, however, has also been reported for several taxa and regions, suggesting that "climatic lags" may be frequent. Here we show that microclimatic effects brought about by forest canopy closure can buffer biotic responses to macroclimate warming, thus explaining an apparent climatic lag. Using data from 1,409 vegetation plots in European and North American temperate forests, each surveyed at least twice over an interval of 12-67 y, we document significant thermophilization of ground-layer plant communities. These changes reflect concurrent declines in species adapted to cooler conditions and increases in species adapted to warmer conditions. However, thermophilization, particularly the increase of warm-adapted species, is attenuated in forests whose canopies have become denser, probably reflecting cooler growing-season ground temperatures via increased shading. As standing stocks of trees have increased in many temperate forests in recent decades, local microclimatic effects may commonly be moderating the impacts of macroclimate warming on forest understories. Conversely, increases in harvesting woody biomass--e.g., for bioenergy--may open forest canopies and accelerate thermophilization of temperate forest biodiversity.

Drivers of temporal changes in temperate forest plant diversity vary across spatial scales.

Global biodiversity is affected by numerous environmental drivers. Yet, the extent to which global environmental changes contribute to changes in local diversity is poorly understood. We investigated biodiversity changes in a meta-analysis of 39 resurvey studies in European temperate forests (3988 vegetation records in total, 17-75 years between the two surveys) by assessing the importance of (i) coarse-resolution (i.e., among sites) vs. fine-resolution (i.e., within sites) environmental differences and (ii) changing environmental conditions between surveys. Our results clarify the mechanisms underlying the direction and magnitude of local-scale biodiversity changes. While not detecting any net local diversity loss, we observed considerable among-site variation, partly explained by temporal changes in light availability (a local driver) and density of large herbivores (a regional driver). Furthermore, strong evidence was found that presurvey levels of nitrogen deposition determined subsequent diversity changes. We conclude that models forecasting future biodiversity changes should consider coarse-resolution environmental changes, account for differences in baseline environmental conditions and for local changes in fine-resolution environmental conditions.

Short wind pulses consistently change the morphology of roots, but not of shoots, across young plants of different growth forms.

Wind is an environmental stimulus that stresses plants of all growth forms at all life-stages by influencing the development, architecture, and morphology of roots and shoots. However, comparative studies are scarce and no study directly investigated whether shoot and root morphological traits of trees, grasses and forbs differ in their response to short wind pulses of different wind intensity. In this study, we found that across species, wind stress by short wind pulses of increasing intensity consistently changed root morphology, but did not affect shoot morphological traits, except plant height in four species. Wind effects in roots were generally weak in tree species but consistent across growth forms. Furthermore, plant height of species was correlated with changes in specific root length and average diameter.Our results indicate that short-pulse wind treatments affect root morphology more than shoot morphology across growth forms. They further suggest that wind stress possibly promotes root anchorage in young plants and that these effects might depend on plant height.

The response of forest plant regeneration to temperature variation along a latitudinal gradient.

BACKGROUND AND AIMS: The response of forest herb regeneration from seed to temperature variations across latitudes was experimentally assessed in order to forecast the likely response of understorey community dynamics to climate warming. METHODS: Seeds of two characteristic forest plants (Anemone nemorosa and Milium effusum) were collected in natural populations along a latitudinal gradient from northern France to northern Sweden and exposed to three temperature regimes in growth chambers (first experiment). To test the importance of local adaptation, reciprocal transplants were also made of adult individuals that originated from the same populations in three common gardens located in southern, central and northern sites along the same gradient, and the resulting seeds were germinated (second experiment). Seedling establishment was quantified by measuring the timing and percentage of seedling emergence, and seedling biomass in both experiments. KEY RESULTS: Spring warming increased emergence rates and seedling growth in the early-flowering forb A. nemorosa. Seedlings of the summer-flowering grass M. effusum originating from northern populations responded more strongly in terms of biomass growth to temperature than southern populations. The above-ground biomass of the seedlings of both species decreased with increasing latitude of origin, irrespective of whether seeds were collected from natural populations or from the common gardens. The emergence percentage decreased with increasing home-away distance in seeds from the transplant experiment, suggesting that the maternal plants were locally adapted. CONCLUSIONS: Decreasing seedling emergence and growth were found from the centre to the northern edge of the distribution range for both species. Stronger responses to temperature variation in seedling growth of the grass M. effusum in the north may offer a way to cope with environmental change. The results further suggest that climate warming might differentially affect seedling establishment of understorey plants across their distribution range and thus alter future understorey plant dynamics.

Divergent roles of herbivory in eutrophying forests.

Ungulate populations are increasing across Europe with important implications for forest plant communities. Concurrently, atmospheric nitrogen (N) deposition continues to eutrophicate forests, threatening many rare, often more nutrient-efficient, plant species. These pressures may critically interact to shape biodiversity as in grassland and tundra systems, yet any potential interactions in forests remain poorly understood. Here, we combined vegetation resurveys from 52 sites across 13 European countries to test how changes in ungulate herbivory and eutrophication drive long-term changes in forest understorey communities. Increases in herbivory were associated with elevated temporal species turnover, however, identities of winner and loser species depended on N levels. Under low levels of N-deposition, herbivory favored threatened and small-ranged species while reducing the proportion of non-native and nutrient-demanding species. Yet all these trends were reversed under high levels of N-deposition. Herbivores also reduced shrub cover, likely exacerbating N effects by increasing light levels in the understorey. Eutrophication levels may therefore determine whether herbivory acts as a catalyst for the "N time bomb" or as a conservation tool in temperate forests.

ReSurveyGermany: Vegetation-plot time-series over the past hundred years in Germany.

Vegetation-plot resurvey data are a main source of information on terrestrial biodiversity change, with records reaching back more than one century. Although more and more data from re-sampled plots have been published, there is not yet a comprehensive open-access dataset available for analysis. Here, we compiled and harmonised vegetation-plot resurvey data from Germany covering almost 100 years. We show the distribution of the plot data in space, time and across habitat types of the European Nature Information System (EUNIS). In addition, we include metadata on geographic location, plot size and vegetation structure. The data allow temporal biodiversity change to be assessed at the community scale, reaching back further into the past than most comparable data yet available. They also enable tracking changes in the incidence and distribution of individual species across Germany. In summary, the data come at a level of detail that holds promise for broadening our understanding of the mechanisms and drivers behind plant diversity change over the last century.

Litter removal through fire - A key process for wetland vegetation and ecosystem dynamics.

Fire is a major driver of global vegetation patterns. It strongly reduces litter and thus alters physical and chemical properties of the environment. Studies investigating the interplay of fire and litter are scarce, and wetland ecosystems are strongly under-represented in research focusing on litter dynamics. We present data on short-term effects of fires in floodplain wetlands along the Amur River in the Russian Far East, an area with a high fire recurrence rate. We analysed vegetation and plant growth patterns as well as soil temperature and nutrient concentrations on recently burnt and unburnt control plots. Directly after fire, litter was reduced by more than 50% on burnt plots. This effect was no longer visible 15 months after fire, probably due to the high productivity of the floodplain ecosystem. Litter was found to act as a key determinant in the net of direct and indirect fire effects, by influencing early plant growth patterns of herbs and grasses. Furthermore, litter removal through fire significantly increased plant species diversity and soil temperature. Contrary, N and P concentrations in living plant biomass of grasses and herbs decreased with decreasing litter cover. Combustion during burning seems to be responsible for the negative direct fire impacts on nutrient concentrations, which were found for N and Mg. Litter removal through fire can strongly affect diversity patterns, dominance structures, and nutrient cycling in wetlands. With increasing fire frequency in the course of global change, significant structural and compositional changes in herbaceous wetland vegetation must be anticipated and the studied ecosystem may shift to reinforced N-limitation.

Response to Comment on "Forest microclimate dynamics drive plant responses to warming".

Schall and Heinrichs question our interpretation that the climatic debt in understory plant communities is locally modulated by canopy buffering. However, our results clearly show that the discrepancy between microclimate warming rates and thermophilization rates is highest in forests where canopy cover was reduced, which suggests that the need for communities to respond to warming is highest in those forests.

Response to Comment on "Forest microclimate dynamics drive plant responses to warming".

Bertrand et al question our interpretation about warming effects on the thermophilization in forest plant communities and propose an alternative way to analyze climatic debt. We show that microclimate warming is a better predictor than macroclimate warming for studying forest plant community responses to warming. Their additional analyses do not affect or change our interpretations and conclusions.

Forest microclimate dynamics drive plant responses to warming.

Climate warming is causing a shift in biological communities in favor of warm-affinity species (i.e., thermophilization). Species responses often lag behind climate warming, but the reasons for such lags remain largely unknown. Here, we analyzed multidecadal understory microclimate dynamics in European forests and show that thermophilization and the climatic lag in forest plant communities are primarily controlled by microclimate. Increasing tree canopy cover reduces warming rates inside forests, but loss of canopy cover leads to increased local heat that exacerbates the disequilibrium between community responses and climate change. Reciprocal effects between plants and microclimates are key to understanding the response of forest biodiversity and functioning to climate and land-use changes.

Replacements of small- by large-ranged species scale up to diversity loss in Europe's temperate forest biome.

Biodiversity time series reveal global losses and accelerated redistributions of species, but no net loss in local species richness. To better understand how these patterns are linked, we quantify how individual species trajectories scale up to diversity changes using data from 68 vegetation resurvey studies of seminatural forests in Europe. Herb-layer species with small geographic ranges are being replaced by more widely distributed species, and our results suggest that this is due less to species abundances than to species nitrogen niches. Nitrogen deposition accelerates the extinctions of small-ranged, nitrogen-efficient plants and colonization by broadly distributed, nitrogen-demanding plants (including non-natives). Despite no net change in species richness at the spatial scale of a study site, the losses of small-ranged species reduce biome-scale (gamma) diversity. These results provide one mechanism to explain the directional replacement of small-ranged species within sites and thus explain patterns of biodiversity change across spatial scales.

Environmental filtering predicts plant-community trait distribution and diversity: Kettle holes as models of meta-community systems.

Meta-communities of habitat islands may be essential to maintain biodiversity in anthropogenic landscapes allowing rescue effects in local habitat patches. To understand the species-assembly mechanisms and dynamics of such ecosystems, it is important to test how local plant-community diversity and composition is affected by spatial isolation and hence by dispersal limitation and local environmental conditions acting as filters for local species sorting.We used a system of 46 small wetlands (kettle holes)-natural small-scale freshwater habitats rarely considered in nature conservation policies-embedded in an intensively managed agricultural matrix in northern Germany. We compared two types of kettle holes with distinct topographies (flat-sloped, ephemeral, frequently plowed kettle holes vs. steep-sloped, more permanent ones) and determined 254 vascular plant species within these ecosystems, as well as plant functional traits and nearest neighbor distances to other kettle holes.Differences in alpha and beta diversity between steep permanent compared with ephemeral flat kettle holes were mainly explained by species sorting and niche processes and mass effect processes in ephemeral flat kettle holes. The plant-community composition as well as the community trait distribution in terms of life span, breeding system, dispersal ability, and longevity of seed banks significantly differed between the two habitat types. Flat ephemeral kettle holes held a higher percentage of non-perennial plants with a more persistent seed bank, less obligate outbreeders and more species with seed dispersal abilities via animal vectors compared with steep-sloped, more permanent kettle holes that had a higher percentage of wind-dispersed species. In the flat kettle holes, plant-species richness was negatively correlated with the degree of isolation, whereas no such pattern was found for the permanent kettle holes.Synthesis: Environment acts as filter shaping plant diversity (alpha and beta) and plant-community trait distribution between steep permanent compared with ephemeral flat kettle holes supporting species sorting and niche mechanisms as expected, but we identified a mass effect in ephemeral kettle holes only. Flat ephemeral kettle holes can be regarded as meta-ecosystems that strongly depend on seed dispersal and recruitment from a seed bank, whereas neighboring permanent kettle holes have a more stable local species diversity.