Plant movements and climate warming: intraspecific variation in growth responses to nonlocal soils.

Most range shift predictions focus on the dispersal phase of the colonization process. Because moving populations experience increasingly dissimilar nonclimatic environmental conditions as they track climate warming, it is also critical to test how individuals originating from contrasting thermal environments can establish in nonlocal sites. We assess the intraspecific variation in growth responses to nonlocal soils by planting a widespread grass of deciduous forests (Milium effusum) into an experimental common garden using combinations of seeds and soil sampled in 22 sites across its distributional range, and reflecting movement scenarios of up to 1600 km. Furthermore, to determine temperature and forest-structural effects, the plants and soils were experimentally warmed and shaded. We found significantly positive effects of the difference between the temperature of the sites of seed and soil collection on growth and seedling emergence rates. Migrant plants might thus encounter increasingly favourable soil conditions while tracking the isotherms towards currently 'colder' soils. These effects persisted under experimental warming. Rising temperatures and light availability generally enhanced plant performance. Our results suggest that abiotic and biotic soil characteristics can shape climate change-driven plant movements by affecting growth of nonlocal migrants, a mechanism which should be integrated into predictions of future range shifts.

Genetic structure and seed-mediated dispersal rates of an endangered shrub in a fragmented landscape: a case study for Juniperus communis in northwestern Europe.

BACKGROUND: Population extinction risk in a fragmented landscape is related to the differential ability of the species to spread its genes across the landscape. The impact of landscape fragmentation on plant population dynamics will therefore vary across different spatial scales. We quantified successful seed-mediated dispersal of the dioecious shrub Juniperus communis in a fragmented landscape across northwestern Europe by using amplified fragment length polymorphism (AFLP) markers. Furthermore we investigated the genetic diversity and structure on two spatial scales: across northwestern Europe and across Flanders (northern Belgium). We also studied whether seed viability and populations size were correlated with genetic diversity. RESULTS: Unexpectedly, estimated seed-mediated dispersal rates were quite high and ranged between 3% and 14%. No population differentiation and no spatial genetic structure were detected on the local, Flemish scale. A significant low to moderate genetic differentiation between populations was detected at the regional, northwest European scale (PhiPT = 0.10). In general, geographically nearby populations were also genetically related. High levels of within-population genetic diversity were detected but no correlation was found between any genetic diversity parameter and population size or seed viability. CONCLUSIONS: In northwestern Europe, landscape fragmentation has lead to a weak isolation-by-distance pattern but not to genetic impoverishment of common juniper. Substantial rates of successful migration by seed-mediated gene flow indicate a high dispersal ability which could enable Juniperus communis to naturally colonize suitable habitats. However, it is not clear whether the observed levels of migration will suffice to counterbalance the effects of genetic drift in small populations on the long run.

The effects of sampling method and vegetation type on the estimated abundance of Ixodes ricinus ticks in forests.

Estimating the spatial and temporal variation in tick abundance is of great economical and ecological importance. Entire-blanket dragging is the most widely used method to sample free-living ixodid ticks. However, this technique is not equally efficient in different vegetation types. The height and structure of the vegetation under study will not only determine the likelihood of a tick-blanket contact, but will also determine the rate of dislodgement. The purpose of this study was therefore to determine whether the alternative strip-blanket is more effectively in picking up ticks than the standard entire-blanket. Sampling was carried out in four forest understory vegetation types that differed in height and structure on five collection dates between April and September 2008. A total of 8,068 Ixodes ricinus ticks was collected (778 adults, 1,920 nymphs, and 5,370 larvae). The highest numbers of ticks were collected along the forest trails, where the dominant vegetation consisted of short grasses. The lowest numbers of ticks were collected in bracken-fern-dominated sites, where the vegetation seriously hampered tick sampling. Surprisingly, in each vegetation type, significantly more nymphs and adults were collected using the entire-blanket. However, the strip-blanket was more effectively in collecting larvae, especially in dense and tall vegetation.