Background: Resurveying historical vegetation plots has become more and more popular in recent years as it provides a unique opportunity to estimate vegetation and environmental changes over the past ...decades. Most historical plots, however, are not permanently marked and uncertainty in plot location, in addition to observer bias and seasonal bias, may add significant errors to temporal change. These errors may have major implications for the reliability of studies on long-term environmental change and deserve closer attention of vegetation ecologists. Methods: Vegetation data obtained from the resurveying of non-permanently marked plots are assessed for their potential to study environmental change effects on plant communities and the challenges the use of such data have to meet. We describe the properties of vegetation resurveys, distinguishing basic types of plots according to relocation error, and we highlight the potential of such data types for studying vegetation dynamics and their drivers. Finally, we summarize the challenges and limitations of resurveying non-permanently marked vegetation plots for different purposes in environmental change research. Results and conclusions: Re-sampling error is caused by three main independent sources of error: error caused by plot relocation, observer bias and seasonality bias. For relocation error, vegetation plots can be divided into permanent and non-permanent plots, while the latter are further divided into quasi-permanent (with approximate relocation) and non-traceable (with random relocation within a sampled area) plots. To reduce the inherent sources of error in resurvey data, the following precautions should be followed: (i) resurvey historical vegetation plots whose approximate plot location within a study area is known; (ii) consider all information available from historical studies in order to keep plot relocation errors low; (iii) resurvey at times of the year when vegetation development is comparable to the historical survey to control for seasonal variability in vegetation; (iv) retain a high level of experience of the observers to keep observer bias low; and (v) edit and standardize data sets before analyses.
Aim: Revisits of non-permanent, relocatable plots first surveyed several decades ago offer a direct way to observe vegetation change and form a unique and increasingly used source of information for ...global change research. Despite the important insights that can be obtained from resurveying these quasi-permanent vegetation plots, their use is prone to both observer and relocation errors. Studying the combined effects of both error types is important since they will play out together in practice and it is yet unknown to what extent observed vegetation changes are influenced by these errors. Methods: We designed a study that mimicked all steps in a resurvey study and that allowed determination of the magnitude of observer errors only vs the joint observer and relocation errors. Communities of vascular plants growing in the understorey of temperate forests were selected as study system. Ten regions in Europe were covered to explore generality across contexts and 50 observers were involved, which deliberately differed in their experience in making vegetation records. Results: The mean geographic distance between plots in the observer+relocation error data set was 24 m. The mean relative difference in species richness in the observer error and the observer+relocation data set was 15% and 21%, respectively. The mean "pseudo-turnover" between the five records at a quasi-permanent plot location was on average 0.21 and 0.35 for the observer error and observer+relocation error data sets, respectively. More detailed analyses of the compositional variation showed that the nestedness and turnover components were of equal importance in the observer data set, whereas turnover was much more important than nestedness in the observer+relocation data set. Interestingly, the differences between the observer and the observer+relocation data sets largely disappeared when looking at temporal change: both the changes in species richness and species composition over time were very similar in these data sets. Conclusions: Our results demonstrate that observer and relocation errors are nonnegligible when resurveying quasi-permanent plots. A careful interpretation of the results of resurvey studies is warranted, especially when changes are assessed based on a low number of plots. We conclude by listing measures that should be taken to maximally increase the precision and the strength of the inferences drawn from vegetation resurveys.
Colonization studies may function as natural experiments and have the potential of addressing important questions about community assembly. We studied colonization for a guild of epiphytic lichens in ...a former treeless heathland area of 170 km
2
in southwest Norway. We investigated if epiphytic lichen species richness and composition on aspen (
Populus tremula
)
trees corresponded to a random draw of lichen individuals from the regional species pool. We compared lichen communities of isolated young (55-120 yr) and old (140-200 yr) forest patches in the heathland area to those of aspen forest in an adjacent reference area that has been forested for a long time. All thalli (lichen bodies) of 32 selected lichen species on trunks of aspen were recorded in 35 aspen sites. When data for each site category (young, old, and reference) were pooled, we found the species richness by rarefaction to be similar for reference sites and old sites, but significantly lower for young sites. The depauperated species richness of young sites was accompanied by a skew in species composition and absence of several species that were common in the reference sites. In contrast, genetic variation screened with neutral microsatellite markers in the lichen species
Lobaria pulmonaria
showed no significant differences between site categories. Our null hypothesis of a neutral species assembly in young sites corresponding to a random draw from the regional species pool was rejected, whereas an alternative hypothesis based on differences in colonization capacity among species was supported. The results indicate that for the habitat configuration in the heathland area (isolated patches constituting <0.4% of the area) lichen communities may need a colonization time of 100-150 yr for species richness to level off, but given enough time, isolation will not affect species richness. We suggest that this contradiction to expectations from classical island equilibrium theory results from low extinction rates.
Background: The effect of the anticipated climate change on the stability of vegetation and the factors underlying this stability are not well understood.Aims: Our objective was to quantify long-term ...vegetation changes in a range of habitats in northern Europe by exploring species co-occurrences and their links to diversity and productivity gradients.Methods: We re-sampled vegetation in 16 arctic, mountain and mire sites 20 to 90 years after the original inventories. A site-specific change in species assemblages (stability) was quantified using species co-occurrences. Using a randomisation test we tested whether the changes observed were significantly greater than those expected by chance. Relationships between patterns in vegetation stability and time between surveys, numbers of plots, or species diversity and proxies for productivity, were tested using regression analysis.Results: At most sites the changes in species co-occurrences of vascular plants and bryophytes were greater than those expected by chance. The changes observed were found to be unrelated to gradients in productivity or diversity.Conclusions: Changes in species co-occurrences are not strongly linked to diversity or productivity gradients in vegetation, suggesting that other gradients or site-specific factors (e.g. land use or species interactions) may be more important in controlling recent compositional shifts in vegetation in northern Europe.
Alpine vegetation is considered to be particularly sensitive to climate changes. Here we document changes in species richness, distribution and composition over the past 50 years by resurveying ...vegetation in Rondane, a well-studied alpine area in central Norway. We estimated changes in species occurrences, species richness and species' realized optima to study relationships between vegetational and environmental change. We used a weighted average approach with elevation and indicator values for light, temperature, pH, moisture, nutrients and tolerance to snow-cover duration. Permutation tests, allowing for unequal sampling in the original survey and the resurvey, indicated whether vegetation changes were statistically significant. We found no significant change in the average number of species per plot since 1950. Of 21 species analysed for changes in frequency and realized optimum, ten showed statistically significant changes in frequency (six decreased, four increased), and six exhibited statistically significant changes in their optimum along the soil-pH gradient. Statistically significant optimum changes were found along the nutrient and light gradients (three species) and the elevation and snow-cover gradients (two species). No statistically significant changes were found along the temperature or moisture gradients. In comparison with other studies, our results suggest that recent climate changes have had a relatively low impact on alpine vegetation in the Rondane mountains. This is indicated by our species optimum analysis, which revealed few changes along gradients that can be directly linked to the climate (temperature and soil moisture) whereas most detected changes appear to be responses to factors related to soil pH. The relative constancy of species' optima and hence species composition may be explained most parsimoniously by the species pool in the Rondane area, which consists largely of common and widespread species with wide ecological amplitudes and hence broad tolerances to environmental change.
Recent studies from mountainous areas of small spatial extent (<2500 km2) suggest that fine‐grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected ...for the coming decades. Such variability in temperature provides buffering to mitigate climate‐change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine‐grained thermal variability across a 2500‐km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000‐m2 units (community‐inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1‐km2 units; (2) the relationship between CiT range and topographically and geographically derived predictors at 1‐km resolution; and (3) whether spatial turnover in CiT is greater than spatial turnover in GiT within 100‐km2 units. Ellenberg temperature indicator values in combination with plant assemblages explained 46–72% of variation in LmT and 92–96% of variation in GiT during the growing season (June, July, August). Growing‐season CiT range within 1‐km2 units peaked at 60–65°N and increased with terrain roughness, averaging 1.97 °C (SD = 0.84 °C) and 2.68 °C (SD = 1.26 °C) within the flattest and roughest units respectively. Complex interactions between topography‐related variables and latitude explained 35% of variation in growing‐season CiT range when accounting for sampling effort and residual spatial autocorrelation. Spatial turnover in growing‐season CiT within 100‐km2 units was, on average, 1.8 times greater (0.32 °C km−1) than spatial turnover in growing‐season GiT (0.18 °C km−1). We conclude that thermal variability within 1‐km2 units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains.
•We studied whether a single large or several small aspen trees should be left in clear-felling areas to serve as life boats for epiphytic species.•We show that large and small host trees had the ...same number of thalli and species per m2 bark.•Our results do not support a strategy of retaining large and old trees only.
Retention of selected trees in clear-felling areas has become an important conservation measure in managed forests. Trees with large size or high age are usually preferred as retention trees. In this paper we investigated whether a single large or several small trees should be left in clear-felling areas to serve as life boats and future habitat for epiphytic species. The focal species were 25 Lobarion epiphytic lichens hosted by aspen (Populus tremula). We analyzed the relationships between: (1) proportion of trees colonized and tree size, (2) number of lichen thalli (lichen bodies) and aspen area, and (3) number of lichen species and aspen area, for 38 forest sites. Mixed effect models and rarefaction analyzes showed that large and small host trees had the same proportion of trees colonized, the same number of thalli, and the same species richness for the same area of aspen bark. This indicates that larger aspens do not have qualities, beyond size, that make them more suitable for Lobarion lichens than smaller sized aspen trees. None of the species, not even the red-listed, showed any tendencies of being dependent on larger aspens, and our results therefore did not support a strategy of retaining only large and old trees for conservation of epiphytic Lobarion lichens. Additionally, young aspens have a longer expected persistence than old aspens. However, old retention trees might be important for other species groups. We therefore recommend a conservational strategy of retaining a mixed selection of small/young and large/old aspens.
AIM: Previous research on how climatic niches vary across species ranges has focused on a limited number of species, mostly invasive, and has not, to date, been very conclusive. Here we assess the ...degree of niche conservatism between distant populations of native alpine plant species that have been separated for thousands of years. LOCATION: European Alps and Fennoscandia. METHODS: Of the studied pool of 888 terrestrial vascular plant species occurring in both the Alps and Fennoscandia, we used two complementary approaches to test and quantify climatic‐niche shifts for 31 species having strictly disjunct populations and 358 species having either a contiguous or a patchy distribution with distant populations. First, we used species distribution modelling to test for a region effect on each species' climatic niche. Second, we quantified niche overlap and shifts in niche width (i.e. ecological amplitude) and position (i.e. ecological optimum) within a bi‐dimensional climatic space. RESULTS: Only one species (3%) of the 31 species with strictly disjunct populations and 58 species (16%) of the 358 species with distant populations showed a region effect on their climatic niche. Niche overlap was higher for species with strictly disjunct populations than for species with distant populations and highest for arctic–alpine species. Climatic niches were, on average, wider and located towards warmer and wetter conditions in the Alps. MAIN CONCLUSION: Climatic niches seem to be generally conserved between populations that are separated between the Alps and Fennoscandia and have probably been so for 10,000–15,000 years. Therefore, the basic assumption of species distribution models that a species' climatic niche is constant in space and time – at least on time scales 10⁴ years or less – seems to be largely valid for arctic–alpine plants.
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.
Questions: How are the fine-scale spatial distribution and abundance of epiphytic lichens explained by factors related to environmental filtering and local dispersal? Are spatial distribution and ...abundance explained by the same underlying factors across sites for: (1) each species separately; or (2) groups of species with similar dispersal strategies? Location: Ten lowland deciduous forests at the southwest coast of Norway (60°N, 5°E). Methods: We investigated the spatial distribution and abundance, given occurrence, of 15 epiphytic Lobarion lichens in ten forest sites: six 1800-m 2 study sites and four 5000-m 2 study sites. We divided each site into a grid of 1-m 2 sampling units, marked all trees and recorded the abundance of individual lichen species. We assessed the relative impact of factors related to environmental filtering and local dispersal for each lichen species using multiple regressions and variation partitioning. Finally, to compare the results between species and between sites, we applied linear mixed effect models. Results: We found that the occurrence of lichen species on a tree is explained primarily by factors related to environmental filtering. The abundance of lichen species that occur on a tree is explained by a combination of environmental filtering and local dispersal, but the relative importance of these factors was found to vary greatly between sites. We found no differences in this respect between species with different dispersal strategies. Conclusions: Our results indicate that both environmental filtering and local dispersal dynamics are important processes explaining the distribution and abundance patterns of Lobarion lichens at fine spatial scales. However, spatial variations in environmental factors within sites interact with propagule distributions to produce a range of inter-site variation. Accordingly, the relative importance of these two structuring mechanisms varies among sites, particularly in the case of abundance patterns. Since single-site patterns are not readily generalized, we emphasize the importance of multiple study sites for evaluation of the role of different processes in shaping the spatial distribution patterns of species.
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