Perspectives on ozone reduction and tropical vegetation

Abstract

Even though the relative reductions of the stratospheric ozone layer are much smaller at tropical than at higher latitudes, the resulting predicted absolute increase of solar UV-B radiation is larger in the tropics than at higher latitudes. These changes are superimposed on a natural latitudinal gradient of solar UV-B. The biologically effective UV-B radiation for both the ozone reduction scenarios and the natural latitudinal gradient depend on the biological weighting functions used to convolute the spectral irradiance. Only biological weighting functions with specific characteristics yield: 1. An appreciable latitudinal gradient of biologically effective solar UV-B. 2. Significant changes of biologically effective solar UV-B as a result of ozone reduction at any latitude. Lines of evidence are presented indicating that plants at low latitudes may be more capable of withstanding high solar UV-B flux than plants at high latitudes. However, the paucity of research with tropical plants, especially woody species, leaves the ultimate consequences of ozone reduction in considerable question. As with temperate vegetation, the indirect ecological effects on plants resulting from increased solar UV-B may be of greater consequence than the immediate damaging effects. Indirect effects include alterations of the balance of competition and changes resulting from altered secondary chemistry of plants.