| Summary: | Ultraviolet radiation (UV) is a minor fraction of the solar spectrum reaching the ground surface. In thisassessment we summarize the results of previous work on the effects of the UV-B component(280–315 nm) on terrestrial ecosystems, and draw attention to important knowledge gaps in ourunderstanding of the interactive effects of UV radiation and climate change. We highlight the followingpoints: (i) The effects of UV-B on the growth of terrestrial plants are relatively small and, because theMontreal Protocol has been successful in limiting ozone depletion, the reduction in plant growthcaused by increased UV-B radiation in areas affected by ozone decline since 1980 is unlikely to haveexceeded 6%. (ii) Solar UV-B radiation has large direct and indirect (plant-mediated) effects on canopyarthropods and microorganisms. Therefore, trophic interactions (herbivory, decomposition) interrestrial ecosystems appear to be sensitive to variations in UV-B irradiance. (iii) Future variations inUV radiation resulting from changes in climate and land-use may have more important consequenceson terrestrial ecosystems than the changes in UV caused by ozone depletion. This is because theresulting changes in UV radiation may affect a greater range of ecosystems, and will not be restrictedsolely to the UV-B component. (iv) Several ecosystem processes that are not particularly sensitive toUV-B radiation can be strongly affected by UV-A (315–400 nm) radiation. One example is the physicaldegradation of plant litter. Increased photodegradation (in response to reduced cloudiness or canopycover) will lead to increased carbon release to the atmosphere via direct and indirect mechanisms.
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