Streams can act as high-speed corridors for plants

Just a reminder – not all corridors are terrestrial, even for terrestrial species!  Streams often provide networks that help with dispersal of individuals, whether by providing a physical route for travel or a highway for moving propagules through the water.  This can be especially true for plants, where even wind or animal dispersed species can potentially  benefit from stream networks that passively transport seeds.  Little research has been done to investigate how effective streams can be in acting as corridors for plants, or what the potential impact on species richness in habitat patches connected by stream networks might be.  In their new paper in Journal of Applied Ecology, E. A. Calçada and colleagues tackle this question by examining plant diversity throughout a series of of isolated forest patches connected (or not) via streams to a nearby intact ancient forest in an agricultural region of northern France.  They sought to test three main hypotheses: 1) species richness would be higher in connected patches, 2) connected patches would all show similar species composition, and 3) more habitat specialists would be found in connected patches.

Their results are striking in how clearly they demonstrate support (or lack thereof) for each hypothesis.   They show that connected patches were NOT higher in species richness after accounting for habitat effects, contrary to what they expected.  However, connected patches were more similar to each other in species composition than to isolated patches, and did contain more forest specialists and a greater presence of hydrochores (species that disperse via water).  From these results, it becomes clear that streams can act as high-speed corridors for dispersing plants, even plants that are not typically water dispersed.  Those species that are dispersal limited can benefit from an intact stream network that can carry them at high speeds to new habitat patches that would otherwise be too distant to colonize.  This well-designed study provides more evidence about the importance of maintaining intact stream networks, particularly in agricultural landscapes that are interspersed by isolated forested patches.  Streams as highways for plants can provide a crucial function in keeping metapopulations connected and maintaining biodiversity in fragmented landscapes.