Cloud Forest, the Massenerhebung Effect, and Ultraviolet Insolation

As usually defined, the Massenerhebung or mountain mass elevation effect means the occurrence of physiognomically and sometimes floristically similar vegetation types at higher altitudes on large mountain masses than on small isolated peaks, especially those in or near the sea. Although the effect was first reported in the European Alps (Schroeter 1908) and in North America (where it is known as the Merriam Effect; Martin 1963), it is best known in the tropics. Perhaps its clearest expression is the occurrence of tropical mountain cloud forest (TMCF) (upper montane rain forest) at lower altitudes on isolated peaks than on the main mountain masses, which are taken as the norm (Figure 1).