Markus Bernhardt-Römermann

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.

The impact of study design and life history traits on genetic variation of plants determined with AFLPs

In this study, we analysed the impact of study design and life history traits on genetic variation of plants determined with amplified fragment length polymorphisms (AFLPs), a technique widely applied in all fields of molecular plant ecology. For the proper interpretation and comparison of genetic variation based upon AFLPs, a meta-analysis based upon a large number of studies of the relationship between study design and plant life history traits on the one hand and of AFLP variation on the other hand is needed but is lacking. To bridge this gap, we extracted data on study design and genetic variation from 115 AFLP studies comprising a total of 152 species. Subsequently, we ascribed the life history traits taxonomic status, life span, frequency, mating system and pollination vector to each of the species. Then, we used linear models to analyse the impact of study design and life history traits on genetic variation. In our data set genetic variation within and among populations depended neither on the number of analysed populations nor the number of analysed individuals per population. However, maximum geographic distance between populations strongly affected genetic variation. Variation within populations decreased while variation among populations increased with maximum geographic distance. Concerning the impact of life history traits, both genetic variation within and among populations depended with increasing strength on the life span, the frequency and the mating system of the species. Following the results of this study, the number of analysed populations or individuals per population is not necessarily a problem when comparing results of different studies, at least when not very low sample sizes are used. However, corresponding study ranges would be highly recommendable, since the maximum geographic distance between populations strongly affects genetic variation.

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-distance seed dispersal by wind: disentangling the effects of species traits, vegetation types, vertical turbulence and wind speed

Long-distance dispersal (LDD) of plant seeds by wind is affected by functional traits of the species, specifically seed terminal velocity and height of seed release above the vegetation cover (HAC), as well as by the meteorological parameters wind speed and vertical turbulence. The relative importance of these parameters is still under debate and the importance of their variability in vegetation types, sites and years has only rarely been quantified. To address these topics, we performed simulation studies for different vegetation types, sites, years and plant species with PAPPUS, a process based trajectory model. We found that LDD (measured in terms of migration rates) was higher in forests compared to open landscapes. Forests also showed greater between-year variability in LDD. Terminal velocity had an effect on LDD in both vegetation types, while the effect of HAC was significant only in the open landscape. We found considerable differences in how vertical turbulence and wind speed affect LDD between species and vegetation types: In the open landscape the strength of the positive relationship between vertical turbulence and LDD generally decreases with terminal velocity, whereas it increases in forests. The strength of the predominantly positive effect of wind speed on LDD increases with terminal velocity in both vegetation types, while in forests we found even negative relationships for species with low terminal velocity. Our results generally suggest that the effects of vertical turbulence and wind speed on LDD by wind diverge for species with different functional traits as well as in different vegetation types.

Human impact on population structure and fruit production of the socio-economically important tree Lannea microcarpa in Burkina Faso

Non-timber forest products (NTFPs) are of high socio-economic value for rural people in West Africa. Main factors determining the status of the populations of socio-economically important tree species providing those NTFPs are human activities. This study assesses the impact of human population density, land use, and NTFP-harvesting (pruning and debarking) on population structure and fruit production of the socio-economically important tree Lannea microcarpa that is normally conserved by farmers on fields. We compared L. microcarpa stands of protected sites with those of their surrounding communal sites in two differently populated areas in Burkina Faso. Our results reveal an opposed land use impact on the population structure of L. microcarpa in the two areas. In the highly populated area, the species population was more stable in the protected site than in the communal site, while the opposite was observed for the less populated area. Trees of the communal sites bore more fruits than trees of the protected sites. Debarking and pruning had a negative impact on fruit production of the species. We conclude that low intensity of human impact is beneficial for the species and that indirect human impact facilitates fruit production of L. microcarpa. In contrast, in the densely populated area, human impact has reached an intensity that negatively affects the populations of L. microcarpa. While the extent of protecting L. microcarpa on fields still seems to be enough to guarantee the persistence of this important species in the less populated area, it is no longer sufficient in the densely populated area.

Plant functional traits – fixed facts or variable depending on the season?

Traits are widely used to detect and explain responses of ecosystem processes to environmental changes. Various studies use trait data from databases, often providing one value per trait and species, neglecting intraspecific trait variability along spatio-temporal gradients. Handbooks for standardized trait measurements claim that traits should be measured at an ‘optimal’ stage, which is typically defined to be reached when the plants are in full blossom. However, it is unclear whether this method is appropriate. The main aim of this study was to quantify the extent to which trait values vary with season and phenology, a type of variation that has been overlooked so far relative to other sources of intraspecific variation. Further, we aimed to investigate whether species rankings remain consistent throughout the year.From April to November 2012, we monitored seven leaf traits [specific leaf area SLA, leaf dry matter content, chlorophyll fluorescence parameters (Fv/Fm, performance-index PI], stomatal density, stomatal size and the stomatal pore area index SPI) of 15 summer green woody species weekly under controlled conditions. In parallel, we recorded phenological stages.The results showed that all traits varied significantly throughout the year in a species-specific manner. We detected trait relationships with vegetative but not with flowering phenology. Species rankings were inconsistent throughout the season in all traits.We concluded that the seasonal timing of trait measurements is crucial. Most notably SLA, Fv/Fm and stomatal size were the most robust traits in terms of small intraspecific and large interspecific variation and showed largely consistent species rankings across seasons.

The contribution of termite mounds to landscape‐scale variation in vegetation in a West African national park

Questions Termite mounds are important sources of local-scale soil heterogeneity and thereby affect savanna vegetation. Studies contrasting mound and savanna vegetation usually neglect variation between savanna types. We aim to answer the following questions: (1) is mound vegetation consistently different from the surrounding savanna vegetation at landscape scale; (2) is mound vegetation homogeneous across different savanna types; and (3) are differences between mound and savanna vegetation influenced more by nutrient accumulation or clay enrichment in mounds? Location Pendjari National Park, northern Benin. Methods We analysed the vegetation in 59 pairs of mound and savanna plots in four savanna types. We examined if mounds differed in community composition between savanna types, and from savanna plots using ordinations, and tested for correlations between community composition and soil parameters. We identified characteristic plant species for mounds in each savanna type using the IndVal method. Finally, we evaluated the relative importance of different soil parameters for differences in vegetation between mound and savanna plots using projection to latent structures regression (PLSR). Results There were clear differences between savanna types for both savanna and mound plant communities, and in each savanna type, clear differences emerged between mound and savanna vegetation. Community differences correlated with differences in soil parameters in all cases. We identified ten characteristic plant species for mounds, with little overlap between characteristic species from different savanna types. Across savanna types, 63% of the variation in mound – savanna vegetation contrast was explained by variation in nine soil parameters, most importantly clay content. Conclusion Even at the landscape scale, the influence of mounds on vegetation depends on habitat context. Thus, local mound vegetation patterns can only be understood considering the influence of different soil parameters in each savanna type. However, enrichment of clay and macronutrients together explain the largest part of the differences between mound and savanna vegetation. Further variation in vegetation composition among mounds is likely driven by biotic interactions and spatial distribution of mounds.

Effects of Climate and Land Use on Herbaceous Species Richness and Vegetation Composition in West African Savanna Ecosystems

West African Savanna ecosystems are undergoing severe changes in their vegetation composition due to the impact of human land use and changes in climatic conditions. This study aims to examine the effect of climate, land use, and their interaction on species richness and composition of West African herbaceous vegetation. Plot based vegetation sampling was done in Burkina Faso. Specific richness and diversity indices were used to determine the effect of land use, climate, and their interaction. An importance value was computed to determine herbaceous species dominating the communities. Frequency of species is used to examine their distribution pattern. The results showed that climate significantly influenced herbaceous specific richness more than land use. However, land use had a significant effect on herbaceous vegetation composition. Herbaceous species diversity changed with environmental conditions. The floristic composition of dominant species is driven by both climate and land use. The frequency of distribution demonstrated that herbaceous species occurrences were more influenced by the mixed effect of climate and land use than their separate effects. Occasional and rare species are the most important part of herbaceous vegetation. Thus heterogeneity of Savanna ecosystem and vulnerability of herbaceous species are high.

Effects of climate, habitat and land use on the cover and diversity of the savanna herbaceous layer in Burkina Faso, West Africa

Herbaceous plants account for more than three-fourths of the total biomass in savanna ecosystems. However, which environmental factors mainly drive the biodiversity of herbaceous species is still under debate. In this study, we investigated the influence of climate, habitat and land use on species richness and cover in the West African savanna ecosystems of Burkina Faso. For a broader understanding, we analysed responses of the most important taxonomical groups of the herbaceous layer (Poaceae, Cyperaceae, Fabaceae s.l. and juvenile woody species) to the above mentioned environmental factors. We found light limitation by trees or shrubs and nutrient availability to be the variables that were mainly able to explain the differences in species richness, whereas precipitation and soil water-holding capacity, in general, drive species cover. However, specifically which environmental parameters influenced species richness and cover differed between taxonomical groups. Species richness of Cyperaceae species depended on water availability, while high Cyperaceae cover was found in soils with high water-holding capacity. Cyperaceae species are able to tolerate stagnant water. By contrast, Poaceae species cover was higher in dry habitats, and species richness declined with higher mean annual precipitation. Fabaceae species richness and cover were both higher in communal areas and sandy soils. This study revealed that both species richness and species cover, important aspects to describe the community composition, should be examined, as they are driven by sometimes different environmental conditions. Differentiating between the most important taxonomical groups of the savanna ecosystem increases the understanding in the important ecological processes that effect the herbaceous vegetation composition.

Coppicing systems as a way of understanding patterns in forest vegetation

Coppicing is a short-rotation system based on harvesting the stump regrowth of deciduous trees. In Central and Northwestern Europe, traditional coppicing was a major, and in the lowlands even the most prevalent, type of forest use from prehistory to the mid-20th century, from which time on it was largely abandoned (Hopkins and Kirby 2007; Szabó et al. 2015). In other regions, such as the Mediterranean or France, it remains an important type of forestry management to this day. Coppice systems produced a variety of products such as small poles used for fuel, larger timbers for buildings, litter for animal bedding or fodder for livestock. The ecological consequences of traditional coppicing on forest structure and organisms inhabiting forests were profound (Buckley and Mills 2015a,b). Coppicing created a dynamic mosaic of lighter and darker phases, and in the long-run it altered soil acidity and nutrient pools (Hölscher et al. 2001; Baeten et al. 2009). Coppices thus provided a variety of habitats for a range of organisms. They had potentially strong effects on biodiversity, particularly in combination with standards (individual long-growing trees). Many species-rich forests of high conservation value were apparently coppiced in the past. After the abandonment of coppicing and deliberate transformation into high forests, forests became darker and nutrients accumulated. Several case studies have indicated a more or less pronounced biodiversity decline caused by succession processes after the cessation of traditional coppicing management (Van Calster et al. 2007; Kopecký et al. 2013; Buckley andMills 2015b). Restoration of coppicing systems is therefore being advocated as a means to save endangered species and communities in certain areas; elsewhere, forest management systems are being modified in attempts to create conditions similar to those Folia Geobot (2017) 52:1–3 DOI 10.1007/s12224-017-9297-9