Search

The coastal heathlands of North-western Europe are treeless anthropogenic landscape of high conservation value, now threatened by encroachment by both native (Pinus sylvestris L.) and non-native (Picea sitchensis (Bong) Carr.) conifers. This study wants to gain insight into the different external drivers which interact with the natural successional processes to determine the future development of the heathland landscape. We tested how seedling emergence and establishment is related to competitive effects from the standing vegetation. Heathlands are nutrient-stressed habitats and we tested the seedling emergence and establishment along a nutrient gradient using mean Ellenberg values. In addition we tested if phytotoxic substances are affecting the seedling emergence and establishment related to different successional stages. Study species differed in seed size and we expected different colonization rates and competitive effects from the heathland vegetation. A factorial experiment was carried out in three different successional stages to isolate the effects of competition versus phytotoxins on seedling emergence and establishment by combining vegetation cutting and charcoal addition treatments. Both conifers were able to invade all successional stages, but invasibility decreased during succession. This was largely attributable to competitive effects from the standing vegetation, although phytotoxic effects were also detected, especially in late-successional stages. Seedling emergence and establishment was higher in the larger-seeded P. sylvestris than in P. sitchensis. These results present a management challenge as fire is an important component of the traditional management of the coastal heathlands, while at the same time increasing invasibility. Managers at sites susceptible to invasion should ensure that resources for tree seedling control are available before fire or other management-related disturbances are applied.

Seedling recruitment allows genetic recombination and production of dispersal units. Both the climate experienced by the source populations (seed source effect) and the weather experienced by the seeds during germination and seedling emergence (recruitment site effects) are important for seedling recruitment. Separating these effects in the field is essential to assess potential climate change impacts on plant population. We combine experimental seed transplant and gradient analyses to separate the effects of seed source and recruitment site temperature and precipitation for the seedling emergence of two alpine/lowland species pairs (Viola biflora/Viola palustris, Veronica alpina/Veronica officinalis). Combining these approaches allows us to compare local responses versus responses along environmental gradients, but also tests for local adaptation and/or pre-conditioning effects (adaptive seedling emergence responses). Veronica officinalis emergence increased with increasing seed source temperature in both the experimental and the gradient approaches, and showed adaptive seedling emergence. Viola biflora, Viola palustris and Veronica alpina emergence decreased with recruitment site temperature in both approaches. Both Violas emergences increased with recruitment site precipitation, in both approaches for the alpine violet, and in the gradient approach for lowland one. Emergence was primarily affected by the environment of the recruitment site, whereas seed source climate and adaptive seedling emergence impacted recruitment in only one of our species. The responses to recruitment site temperatures were negative, whereas the response to seed source temperature was positive. Ignoring the distinctions between these different mechanisms can lead to erroneous conclusions regarding potential climate change impacts on plant recruitment.

The European coastal heathlands are important habitats for international conservation. Today, these low-intensity farming systems are threatened by the cessation of traditional management regimes, such as grazing and prescribed burning. In natural systems, the effects of fire on germination responses are often explained by adaptation to fire over extended periods of time. However, Northern heathlands are semi-natural systems with only a limited fire history. We investigated whether and how the keystone species in this system, Calluna vulgaris, responded to prescribed burning, based on previous findings where Calluna germinable seed-bank densities showed a pronounced peak right after fire. Our main findings were (i) an ecophysiological response to smoke; (ii) a potential explanation for this pattern, revealed by a seed-bank experiment where we managed to re-create the germination pattern experimentally by using an aqueous plant-derived smoke solution; and (iii) a history of anthropogenic use of fire and the development of heathlands in the region documented through palaeoecological investigations.

This study presents a quantitative partitioning of the variance infloristic data from grazed semi-natural vegetation of summer farms inRoldal, western Norway. The data consist of 189 taxa recorded in 1074-m2 sample plots within 10 summer farms with differentland-use histories. Thirty-five environmental variables were recorded,includingaltitude, slope, radiation, geology, soil chemistry, and past and presentland-use. A series of (partial) canonical correspondence analyses (CCAs) wereused to partition the total variation into within-farm and between-farmcomponents, and to investigate the explanatory power of different groups ofenvironmental and land-use variables at the two scales. The results show that:(1) although local gradients are of overriding importance for floristiccomposition, landscape-scale processes also contribute significantly to theobserved patterns; (2) the measured land-use and environmental factors accountfor comparable amounts of compositional variance at the two scales; and (3)evenif the relative contributions of the two classes of explanatory variables arecomparable, details differ, showing that broad-scale environmental and land-usepatterns are not just scaled-up versions of the fine-scale patterns or viceversa. These results support a multi-process view of vegetation patterns.