Petr Petřík

Microclimate moderates plant responses to macroclimate warming

Significance Around the globe, climate warming is increasing the dominance of warm-adapted species—a process described as “thermophilization.” However, thermophilization often lags behind warming of the climate itself, with some recent studies showing no response at all. Using a unique database of more than 1,400 resurveyed vegetation plots in forests across Europe and North America, we document significant thermophilization of understory vegetation. However, the response to macroclimate warming was attenuated in forests whose canopies have become denser. This microclimatic effect likely reflects cooler forest-floor temperatures via increased shading during the growing season in denser forests. Because standing stocks of trees have increased in many temperate forests in recent decades, microclimate may commonly buffer understory 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.

Combining Biodiversity Resurveys across Regions 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 article, 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 the implementation of multiregion resurvey databases. In so doing, we aim to encourage resurvey database development across other community types and biomes to advance global environmental change research.

Long-term patterns in soil acidification due to pollution in forests of the Eastern Sudetes Mountains

Soil acidification was assessed in the Eastern Sudetes Mountains (Czech Republic) between 1941 and 2003, i.e. before and after the period of major industrial pollution (1950s-1990s). The twenty sites included in our study were distributed along a gradient of altitude ranging 1000 m. Values of pH have decreased in 80-90% of the pairs of samples after the six decades, on average by 0.7 for pH-H(2)O and 0.6 for pH-KCl. Organic matter increased in the topsoil, probably reflecting a change in decomposition conditions. The most important finding is that the acidification varies along the joint gradient of altitude/tree layer composition, and displays a changing pattern in three soil horizons (A, B and C). Contrary to expectations, most acidified were soils in beech forests at lower elevations.

Habitat requirements of Cardaminopsis petraea — Rare and relict species of the Czech Republic

Vegetation with Cardaminopsis petraea was sampled by phytosociological relevés at almost all the known Czech sites, and characterized by indicator values, influence of potential direct solar irradiation, and bedrock type with the aid of multivariate methods. It has been declared that C. petraea prefers open natural or seminatural drier to mesophilous habitats without some preference to the bedrock. It occupies habitats with various slopes, but it prefers more extreme slants and northerly exposed slopes. The classification and ordination methods showed clear distinction between Moravian and Bohemian habitats. Apart from other types, in Bohemia this species occurs uniquely in acidophilous rock communities, whereas in Moravia it grows uniquely within calcareous grasslands. Relictness of the species was discussed in relation to the specific site conditions (light supply, disturbance regime, and geographical isolation) and to the occurrence of other rare taxa and habitats. Occurrence on some man-made habitats was also observed.

Vegetation Succession on River Sediments along the Nakdong River, South Korea

We investigated successional vegetation on river sediments along the Nakdong River in South Korea at the time when a river regulation project, named the Four River Project, was launched. We sampled differently aged stages of succession in 63 plots of 10 × 10 m in 2010 using species cover estimations. To explain the observed species composition, we considered the following environmental variables: successional age, distance from the estuary, altitude, elevation above the river water line, texture of the substrate (silt, sand and gravel content) and cover of forest around each site within a radius of 1 km. We used ordination techniques to relate plant community characteristics to environmental variables. We distinguished three main successional vegetation types based on their floristic composition, which included especially a variety of willow species. Besides the cover of forest and certain components of substrate texture, all the variables exhibited significant effects on species composition of the vegetation over the course of succession. The most important factors determining the seral vegetation were the altitudinal gradient and successional age. Environmental factors in the riverine landscape together form a complex riverine environment and determine the vegetation pattern. Unfortunately, this environment has been largely destroyed by the massive river regulation project, but our results indicate that, under certain conditions, the riverine vegetation has a potential to at least partly recover even after such a large-scale disturbance.

It is time to change land use and landscape management in the Czech Republic

abstract The identity of man‐made landscapes is based on the balance among their ecological, cultural, and economic dimensions. Since the 1950s, short‐term economic benefits have globally often outweighed long‐term interests. This results in decreased landscape quality manifested as increased erosion of agricultural land, decreased water retention capacity, increased landscape uniformity, and loss of biodiversity. A new phenomenon influencing the condition of man‐made landscapes is climate change. Extreme fluctuations of temperature and precipitation have been causing repeated floods and also periods of drought in Europe. Landscapes damaged by inappropriate management are unable to offset these impacts. It is necessary to stop this development by changing land use and management methods to restore the balance among landscape functions. For the Czech Republic, we propose to develop a long‐term landscape vision and to formulate a responsible landscape policy with regional strategic goals, including subsidies and penalties (carrots and sticks), based on the principles of the European Landscape Convention. To promote ecological stability, we recommend allocating funds from the Common Agricultural Policy to both the restoration and maintenance of valuable habitats. Landscape research and management (based on habitat/species monitoring in cooperation with stakeholders) must be strengthened in order to play a proper role in the transformation. It is time for clear communication with the public and the training of state officials and land users in spatial and landscape planning. To fill this gap in interdisciplinary cooperation, we call for the establishment of a platform on sustainable landscape management in the Czech Republic.

Reply to Harwood et al. Thermophilization estimation is robust to the scale of species distribution data

We recently assessed plant community responses to macroclimate warming across European and North American temperate forests (1). To do so, we inferred the temperature preferences of understory species from distribution data by means of ecological niche, or species distribution models (SDMs). Harwood et al. (2) propose that subcanopy temperatures, instead of gridded climate data, should have been used in our analyses. Despite exciting ongoing advances in the downscaling of microclimates from macroclimatic data, Harwood et al.’s suggestion is, at present, simply not possible at the scale of our study: One would need to match the occurrence of every individual of each of 1,032 species with the microclimate in each location across two continents. More fundamentally, such downscaling is not necessary for our purpose: when applied correctly (3), SDMs can infer species’ climatic tolerances without the need of those detailed field data, based on mean field approximation (4). Nonetheless, as SDMs only approximate thermal tolerances, we went beyond common practice to propagate their uncertainties into thermophilization rates (1). Even if microclimates might bias the niche models of some species (2), no bias at the level of among-region comparisons is expected given that we quantified thermophilization as the relative temporal difference in floristic temperatures per unit time. Thus, presence of bias in species’ temperature preferences, as hypothesized by Harwood et al. (2), is not enough to cause bias in thermophilization rates. Our sensitivity analyses removing random subsets of species from the total pool (1) confirm that the reported thermophilization rates are robust.

Observer and relocation errors matter in resurveys of historical vegetation plots

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 24m. 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 non-negligible 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.

Vegetation with Gagea bohemica in the landscape context

Abstract Most localities of the critically endangered species Gagea bohemica (early star-of-Bethlehem) known in the Czech Republic were surveyed using the Braun-Blanquet approach. Based on formal definitions of the expert system for Czech non-forest vegetation, 69% of the 255 samples analysed were classified as already described pioneer plant communities on shallow soils. Samples unsorted by the expert system exhibit local or transient species composition. Ordination and multiple linear regression methods were used to study the effects of adjacent habitats and environmental conditions (altitude, Direct Potential Annual Radiation Index, herb layer cover and landcover) on species richness, the cover of G. bohemica, and the cover of nitrophytes. The geographical component (i.e. two distribution centres: one in Bohemia and one in Moravia) explained more variability in species composition than local environmental conditions or the effect of adjacent habitats. The local species pool significantly enriched the species composition of plots close to artificial and non-forested areas, less so in species-poor forested areas. However, close to areas transformed by humans, the vegetation was invaded by numerous ruderal species. The low variability in species composition of one of the most species-poor grassland communities in the Czech Republic could be associated with the relic character of its habitats. The different impacts of landscape structure on habitat diversity in Bohemia and Moravia may be a result of contrasting historical processes acting in different parts of the Czech landscape.