Effect of land use on species dispersal
Why does land use influence the dispersal of aquatic and riparian plants and animals?
Plants and animals that live in streams or in their riparian zones primarily use the stream itself as a dispersal waterway, nevertheless terrestrial and aerial dispersal are also important ways by which aquatic and riparian plants and animal can move along the stream network or between catchments (check out lessons on hydrochory and invertebrate dispersal). Therefore human activities and settlements within the whole stream catchment have strong influences on species dispersal.
Forests provide a sheltered environment from winds, which favor the dispersal of adult flying insects (e.g. caddisflies, stoneflies and beetles). Moreover, the forests themselves are potential colonization sources to riparian vegetation. On the contrary urban, agricultural, mining and forestry areas are hostile environments for terrestrial and aerial dispersal of riparian and aquatic species and are potential sources of dispersal of invasive species.
Urban streams are often channelized and lack a proper riparian buffer that would allow for the dispersal of seeds and adult flying insects. On the other hand, cities can be hotspots of invasive species dispersal. Pet and ornamental species can be released to streams (voluntarily or involuntarily) and colonize the aquatic and riparian ecosystems, posing severe threats to their biodiversity.
How does land use affect stream restoration?
Constraints to species dispersal can heavily affect the outcomes of stream restoration measures. A successful restoration of the physical structure of a stream reach may not be followed by the biotic recovery if the aquatic and riparian species are locally extinct in the surrounding areas or if they cannot disperse to the restored reach. Therefore, in heavily modified catchments, it is particularly important to create and conserve dispersal corridors and functioning buffer zones around streams to allow for species dispersal and colonization of restored reaches.
Forestry & agriculture: beside pesticides, which are an obvious threat to dispersing insects, open spaces that are exposed to winds, such as clear-cuts and crops, are unfavorable environment for active flier insects. On the contrary such open landscapes favor the wind-mediated dispersal of seeds and weak flier insects, such as midges. In agricultural areas, hedges are very important for insects’ dispersal as they act both as shelters and swarm markers.