Streams are efficient corridors for plant species in forest metacommunities

1. The maintenance, restoration or construction of corridors are among the most important conservation strategies world-wide in the face of global changes such as habitat fragmentation and climate change, although their effectiveness still remains an open question. Metacommunity ecology provides a useful framework to answer this question but so far relatively few studies have concerned plant species. 2. Here, we evaluate the connectivity effect of small streams originating in a large forest for plant communities of forest patches within an agricultural landscape. We compared - and -diversity of patches connected to a large forest with isolated patches whilst controlling for habitat effects and patch area. Species composition of each patch type was examined with a nonparametric MANOVA and an indicator species analysis. 3. We found that forest patches connected to the main forest through streams were not more species rich after accounting for habitat effects but were more similar than isolated patches, be the latter crossed or not by a stream. Connected patches exhibited a different species composition with more forest habitat specialists and more hydrochores than nonconnected patches. 4. Many forest herb species well known for being dispersal-limited appeared to be efficiently transported by water as incidental hydrochores over long distances and relatively short-time scales. Using streams as high-speed corridors', these species increased their colonization speed by at least 15 times compared with conventional dispersal. 5. Synthesis and applications. This study demonstrates that streams can act as efficient corridors for plant species across agricultural landscapes and contribute to the dynamics of forest metacommunities. From a management perspective, preserving the longitudinal integrity of streams is likely to increase the connectivity within and between forest metacommunities and can assist dispersal-limited species to be resilient to projected climate warming by increasing their migration speed. Restoring not only wooded elements but watercourse networks is thus a suitable strategy to manage landscapes efficiently for the forest flora conservation.