Half a century of succession in a temperate oakwood: from species‐rich community to mesic forest

Aim Lowland woodlands in Europe went through dramatic changes in management in the past century. This article investigates the influence of two key factors, abandonment of coppicing and increased pressure of ungulates, in thermophilous oakwoods. We focused on three interconnected topics: (1) Has the assumed successional trend lead to impoverishment of the vegetation assemblages? (2) Has it resulted in vegetation homogenization? (3) Are the thermophilous oakwoods loosing their original character? Location Czech Republic, Central Europe. Methods The vegetation in 46 semi‐permanent plots was recorded three times: firstly, shortly after the abandonment of coppicing (1953) and then, after four to six decades of secondary succession and strong game impact (1992 and 2006). Overall trends and changes in species spectra were analysed. Results There is a marked successional shift towards species‐poorer communities growing in cooler, moister and nutrient‐richer conditions. The change was significantly different in parts affected and unaffected by high numbers of ungulates yet only for herbs, not the woody species. However, observed change in species composition was not accompanied by significant homogenization process that is the general process reported from elsewhere. A sharp decline in plant species typical for thermophilous woodland communities and in endangered species indicates that the original character of the woodland has been gradually lost. Main conclusions Thermophilous oakwoods have been largely replaced by mesic forests. Lowland oakwoods in continental parts of Europe historically depended on active management, which kept the understorey conditions light and warm. Successional processes in the 20th century caused a critical loss of species diversity at various spatial levels. However, artificially high numbers of ungulates, which otherwise have a negative impact, probably held up succession, so that the changes may still be reversible.     

From protégé to nurse plant: establishment of thorny shrubs in grazed temperate woodlands

Question: Thorny shrubs play keystone roles in grazed ecosystems by defending non‐protected plants against herbivores, but their establishment in grazed ecosystems is poorly understood. Which factors control establishment of recruits of thorny nurse shrubs in grazed temperate woodlands? Location: Ancient grazed temperate woodlands (52°32′N, 6°36′E), The Netherlands. Methods: We surveyed biotic and abiotic factors for saplings of thorny nurse shrubs in plots with and without saplings. To disentangle these factors, we performed a transplantation experiment over two growing seasons with nurse shrub saplings (Prunus spinosa and Crataegus monogyna) planted in two dominant vegetation types – tall unpalatable swards and short grazed lawns – half of them protected from herbivory via exclosures. Results: Plots with shrub saplings had taller surrounding vegetation, higher soil pH and higher soil moisture than plots without saplings. These plots predominantly contained unpalatable sward species, while plots without saplings mainly contained palatable lawn species. After transplantation, sapling survival was higher in exclosures than in the open, and higher in sward exclosures than in lawn exclosures. Sapling growth was higher in swards than in lawns, higher inside than outside exclosures, and higher for Prunus than Crataegus, while browsing on saplings was higher in lawns. Conclusion: Unpalatable swards form essential establishment niches for thorny shrubs in grazed temperate woodlands: they protect against herbivores before thorns fully develop in saplings, and sapling growth is better due to improved micro‐environmental conditions. Once established and thorny, shrub saplings grow out of the protective range of the swards and in turn facilitate tree seedlings, which are essential for long‐term persistence of grazed temperate woodlands. This study shows that nurse plants may start as protégés before becoming facilitators for other plants in a later life stage. This may be common for nurse plants in various ecosystems. We argue that improved understanding of establishment of nurse plants and their constraining factors is crucial for effective conservation and restoration in various ecosystems.     

Effects of long‐term cutting in a grassland system: perspectives for restoration of plant communities on nutrient‐poor soils

Abstract. The upper courses of brook valley systems harbour Nardo‐Galion saxatilis communities characteristic of oligo‐trophic soils under low‐intensity farming. Most of these communities have disappeared under intensified farming i.e. application of fertilizers. We studied the possibilities of restoration i.e. re‐establishment of the former plant community by adopting various cutting regimes after the cessation of fertilization in 1972. The various cutting regimes revealed different effects after 25 yr. Regimes with cutting every second year with or without removal of the swath, and complete abandonment deviated from the other regimes that included annual haymaking with different frequency and timing. The latter group of cutting regimes came closer to the community of an adjacent field where fertilization stopped in 1967. This field in turn harboured several Nardo‐Galion species after 25 yr of annual cutting, and showed more resemblance with a local reference community (at a distance of 500 m) that had not been fertilized since the 1940s. The local reference still does not match poorly developed Nardo‐Galion saxatilis communities found in the region of ca. 50 km around the study area, and is far from well developed Nardo‐Galion communities in the same region. The study site still harbours several species characteristic of eutrophic soil and few species characteristic of oligotrophic soil after 25 yr of annual cutting and removal of the swath. The soil seed bank harbours only few target species. Although species characteristic of oligotrophic soil are present in an adjacent field and Nardo‐Galion saxatilis species occur at 500 m, they have not (yet) established in the target area.     

The climate sensitivity of carbon,timber, and species richness covaries with forest age in boreal–temperate North America

Climate change threatens the provisioning of forest ecosystem services and biodiversity (ESB). The climate sensitivity of ESB may vary with forest development from young to old‐growth conditions as structure and composition shift over time and space. This study addresses knowledge gaps hindering implementation of adaptive forest management strategies to sustain ESB. We focused on a number of ESB indicators to (a) analyze associations among carbon storage, timber growth rate, and species richness along a forest development gradient; (b) test the sensitivity of these associations to climatic changes; and (c) identify hotspots of climate sensitivity across the boreal–temperate forests of eastern North America. From pre‐existing databases and literature, we compiled a unique dataset of 18,507 forest plots. We used a full Bayesian framework to quantify responses of nine ESB indicators. The Bayesian models were used to assess the sensitivity of these indicators and their associations to projected increases in temperature and precipitation. We found the strongest association among the investigated ESB indicators in old forests (>170 years). These forests simultaneously support high levels of carbon storage, timber growth, and species richness. Older forests also exhibit low climate sensitivity of associations among ESB indicators as compared to younger forests. While regions with a currently low combined ESB performance benefitted from climate change, regions with a high ESB performance were particularly vulnerable to climate change. In particular, climate sensitivity was highest east and southeast of the Great Lakes, signaling potential priority areas for adaptive management. Our findings suggest that strategies aimed at enhancing the representation of older forest conditions at landscape scales will help sustain ESB in a changing world.     

BIODIVERSITY RESEARCH: Native‐exotic species richness relationships across spatial scales and biotic homogenization in wetland plant communities of Illinois,USA

Aim To examine native‐exotic species richness relationships across spatial scales and corresponding biotic homogenization in wetland plant communities. Location Illinois, USA. Methods We analysed the native‐exotic species richness relationship for vascular plants at three spatial scales (small, 0.25 m² of sample area; medium, 1 m² of sample area; large, 5 m² of sample area) in 103 wetlands across Illinois. At each scale, Spearman’s correlation coefficient between native and exotic richness was calculated. We also investigated the potential for biotic homogenization by comparing all species surveyed in a wetland community (from the large sample area) with the species composition in all other wetlands using paired comparisons of their Jaccard’s and Simpson’s similarity indices. Results At large and medium scales, native richness was positively correlated with exotic richness, with the strength of the correlation decreasing from the large to the medium scale; at the smallest scale, the native‐exotic richness correlation was negative. The average value for homogenization indices was 0.096 and 0.168, using Jaccard’s and Simpson’s indices, respectively, indicating that these wetland plant communities have been homogenized because of invasion by exotic species. Main Conclusions Our study demonstrated a clear shift from a positive to a negative native‐exotic species richness relationship from larger to smaller spatial scales. The negative native‐exotic richness relationship that we found is suggested to result from direct biotic interactions (competitive exclusion) between native and exotic species, whereas positive correlations likely reflect the more prominent influence of habitat heterogeneity on richness at larger scales. Our finding of homogenization at the community level extends conclusions from previous studies having found this pattern at much larger spatial scales. Furthermore, these results suggest that even while exhibiting a positive native‐exotic richness relationship, community level biotas can/are still being homogenized because of exotic species invasion.     

Single introductions of soil biota and plants generate long‐term legacies in soil and plant community assembly

Recent demonstrations of the role of plant–soil biota interactions have challenged the conventional view that vegetation changes are mainly driven by changing abiotic conditions. However, while this concept has been validated under natural conditions, our understanding of the long‐term consequences of plant–soil interactions for above‐belowground community assembly is restricted to mathematical and conceptual model projections. Here, we demonstrate experimentally that one‐time additions of soil biota and plant seeds alter soil‐borne nematode and plant community composition in semi‐natural grassland for 20 years. Over time, aboveground and belowground community composition became increasingly correlated, suggesting an increasing connectedness of soil biota and plants. We conclude that the initial composition of not only plant communities, but also soil communities has a long‐lasting impact on the trajectory of community assembly.     

Long‐term rain forest succession and landscape change in Hawai'i: The ‘Maui Forest Trouble’ revisited

Because of their isolation and geographical position, and in contrast to the multi‐species tree canopies of tropical rain forests on the continents, the Hawaiian Islands have only two native dominant canopy species in their rain forests, Acacia koa and Metrosideros polymorpha. The wetter forest ecosystems are dominated by only the latter. In 1905, a dieback of lowland tropical Metrosideros rain forest was observed over a 35 km stretch on the lower east slope of Haleakala Mountain on Maui Island. This was dubbed ‘The Maui Forest Trouble.’ Although the synchronous decline of so many trees was initially believed to be caused by an epidemic disease, a decade of research yielded no pathogen. The conclusion was that the Hawaiian flora consisted primarily of colonizer species that were unable to continue growing on aging soils. Although this made ecological sense at that time, it was a rather limited and thereby unfortunate conclusion. Further research has shown that the Maui Forest Trouble was a ‘bog‐formation dieback’, a process of vegetation dynamics not only related to soil aging but more broadly to geomorphic aging and fundamental landscape change. This process is clearly a marginal‐site syndrome, but a natural process of profound consequence for biological conservation. This will be further explained as a paradigm for vegetation ecology.