Above-Ground Water and Nutrient Fluxes in Three Successional Stages of Costa Rican Montane Oak Forest with Contrasting Epiphyte Abundance

21.7 Conclusions

Compared to old-growth forests, early-successional tropical montane forests can have equally high or even higher leaf areas, but their epiphyte biomass is generally much smaller. Rainfall interception was found to be highest in the old-growth forest stand, though epiphytes contributed to less than 10 % of total canopy interception. Stemflow was elevated in those stands which had lowest epiphyte biomass and highest stem densities. Consequently, nutrient fluxes with stemflow were most important in the mid-successional forest stand where stemflow accounted for as much as 17% of incident rainfall. Nutrient fluxes with litterfall were also highest in this stand for most nutrient species. Evidently, epiphytes had only little influence on within-stand nutrient fluxes with throughfall, stemflow and litterfall. We conclude that the cutting of old-growth forest, and its subsequent replacement by secondary forest result in substantial changes in water and nutrient fluxes at the stand level — changes which are not reversed even after 40 years of progressive forest succession. Such changes are mainly due to contrasts in stem density and canopy structure characteristics and, to a lesser extent, are determined by levels of epiphytic biomass which may need many more years to fully recover.