Fire and Catchment Chemical Budgets

Abstract

Natural and man-induced disturbances are increasingly being recognized as essential parts of the functioning of ecosystems. Disturbances can be highly variable as they occur at different spatial and temporal scales and with different degrees of intensity. This variability can have significant effects upon nutrient cycling patterns including causing changes in pathways and processes of nutrient transfer within ecosystems. Studies of budgets of elements gained or lost from a catchment have been used to provide a conceptual and empirical basis for understanding ecosystem responses to disturbance. Disturbance effects upon chemical budgets of catchments and in particular stream water draining such catchments have been extensively studied (Tiedemann et al. 1979; Raison 1980; Swank and Waide 1988). Conflicting results and conclusions from these studies show the complexities involved in separating disturbance effects from geographical, seasonal and annual variability in ecosystem behaviour. An important disturbance in the southwestern Cape Province is the burning of the fire-prone fynbos at intervals of 12–20 years. Fynbos is burned to increase water yields of mountain catchments, to reduce fire hazard, to maintain fynbos species diversity and to control invasive plants (van Wilgen et al. 1991). Fires are highly variable events and to a large extent depend on factors such as fuel load and vegetation characteristics (see Chap. 3) and weather patterns (see Chap. 2).