Impacts of land-cover change on the water flow regulation ecosystem
service: Invasive alien plants, fire and their policy implications
Land and water resource issues typically fall under separate governance systems. For example, agricultural
policy regulates land-cover change while water departments regulate water quality. However,
land-use changes can directly affect water resources. Water flow regulation is a key service which is
affected by changes in land-cover but its dynamics are poorly understood by most policy makers and land
management organisations. We simulated and quantified the effects of plant invasions on land-cover,
hydrological soil characteristics and catchment responsiveness on flow regulation using a hydrological
model. The case study was located in the indigenous fynbos shrublands in South Africa. Fynbos requires
fire to regenerate, has moderate biomass, occurs mostly in areas with a potential to erode and is prone to
invasion by woody plant species, particularly trees. Invasions can affect flow regulation by changing community
structure and function and increasing fuel loads. The greater fuel load increases fire intensity and
severity which, in turn, changes the hydrological responses of catchments. Few studies have assessed
the effects of invasion on hydrological responses but studies on plantations have recorded significant
increases in soil water repellence following fire, resulting in increased overland flow similar to impacts
of fires in invaded areas. Simulation of clear-felling of pines and different degrees of water repellency
increased both the responsiveness of the catchment to rainfall and extreme rainfall events. The simulated
fire effects were consistent with other studies of hydrological responses to fire. Our study indicates that
invasions of pines and acacias in the study area could substantially increase the risk of flood damage even
from moderate rainfall events, and highlights the importance of maintaining flow regulation capacity.
New policy approaches are required which take account of the linkages and interactions between landuse
choices, water resources and ecosystem services, and address them when considering governance
arrangements.