Comparison of arboreal and terrestrial soil characteristics in a lower montane forest, Monteverde, Costa Rica

In many tropical and temperate forests, live and dead components of canopy-held organic matter (COM) form communities that are distinct from terrestrially rooted plant and forest floor soil communities, but that interact with whole-forest processes. We quantified some of the soil characteristics of dead organic matter held within the canopy of mature trees in a tropical lower montane forest of Monteverde, Costa Rica, and compared them to soils from the upper horizons on the ground. The concentration of canopy organic matter was significantly higher than terrestrial soil, but similar for P and Ca. Canopy humus had very low pH compared to terrestrial soils. The terrestrial soil had a tenfold greater amount of extractable cations, but the C/N ratios and cation exchange capacity of COM and the upper soil horizon did not differ significantly. Canopy organic matter has rarely been considered in forest ecosystem studies due to its inaccessibility, the lack of rigorous sampling and extrapolation methods, and because its mass is small relative to total forest soil mass. However, in habitats where COM is large, a canopy root-humus mat occurs on branch and trunk surfaces, similar to that which occurs on the forest floor. Organic matter in the forest canopy may thus have more ecological importance than its mass implies, as the nutrient-retaining capacity of the root-humus mat layer could play an important role in nutrient conservation for the individual trees and epiphytes whose roots are imbedded within the mats, and for the forest ecosystem as a whole.