Riparian forests, although relatively small in extent, contribute greatly to regional productivity and ecosystem services. Rapid expansion of urban areas and growing human populations are increasingly disturbing these ecosystems. This may impair important ecosystem functions, making it essential to better understand the effects of human disturbances and hydrological changes on riparian vegetation. We used Red Butte Creek in the Salt Lake Valley, Utah as a case study to evaluate vegetation structure along land use and hydrological transitions in a semi-arid environment. We used 3D-LiDAR imaging and field observations to map and quantify the structure of the riparian forest along the stream including vegetation density, height, cover and composition of woody species. We compared vegetation in reaches that flowed through different land use types, from a relatively undisturbed Natural Research Area to a highly urbanized residential neighborhood. We evaluated effects of hydrology on streamside vegetation by comparing spatial variation in vegetation to modelled ground water depths as well as vegetation density in gaining versus losing reaches.
Results/Conclusions
Our results showed that land use is strongly associated with the structure of the riparian forest, both in vertical distribution and in the abundance of native and drought-tolerant species. Whereas natural reaches of Red Butte Creek are characterized by native vegetation and typical riparian species (e.g. Betula occidentalis), urbanized reaches have higher numbers of introduced plants and more upland species (e.g. Quercus gambelii). Urban reaches are also characterized by narrower riparian zones, and by exceptionally high trees (>18 m) in older neighborhoods. Throughout all land uses, the south facing bank of the stream had higher cover and canopy height than the north facing bank. We found significant effects of gaining and losing reaches on vegetation density in the natural area, with opposite effects on low and high statured vegetation; low canopies (1.5-5 m) were denser than high canopies (9-18 m) in gaining reaches. In losing reaches, low canopies were less dense in comparison to high canopies. These results show that the use of LiDAR data in combination with traditional field methods can reveal strong influences of land use and management practices as well as hydrology on the community and 3D structure of riparian forests.