La. Bruijnzeel et Ej. Veneklaas, CLIMATIC CONDITIONS AND TROPICAL, MONTANE FOREST PRODUCTIVITY - THE FOG HAS NOT LIFTED YET, Ecology, 79(1), 1998, pp. 3-9
Tropical montane cloud forests (TMCF) differ from lowland moist forest
s in structure (low stature, small and tough leaves, low diversity) an
d functioning (low productivity, low nutrient-cycling rates). To expla
in these differences, a variety of hypotheses have been proposed, most
of which are related directly or indirectly to climate, but none of t
hese provides a satisfactory explanation for all typical TMCF traits.
The single climatic factor shared by all TMCF, the frequent occurrence
of low cloud, has multiple effects, but not all are well understood,
In this paper we describe and analyze the climatic and soil-moisture c
onditions prevailing in TMCF as reported in the literature. TMCF evapo
transpiration is limited by both climatic conditions and canopy conduc
tance. TMCF productivity is low, but our understanding of these forest
's carbon balance is incomplete. Leaf photosynthetic capacity is not p
articularly low, but canopy photosynthesis probably is, due to persist
ent cloudiness (low radiation) and a low leaf-area index (LAI). We sug
gest that the low LAI of TMCF is controlled by light climate and by le
af structure and longevity. TMCF productivity is probably further limi
ted by a substantial investment of carbon in the growth and functionin
g of a relatively large root system, which is itself a consequence of
unfavorable soil conditions.