Biomass and productivity of fine and coarse roots in five tropical mountain forests stands along an altitudinal transect in southern Ecuador

Background: Data on below-ground production of tropical montane forests along elevation gradients are scarce. Aims: To determine fine, coarse and large root biomass and productivity along a 2000m elevation transect. Methods: In five south Ecuadorian mountain forests along a transect from 1000 to 3000m above sea level, fine ( 2 mm diameter), coarse (2-50 mm) and large root biomass ( 50 mm) were analysed by soil coring and excavation of soil pits. Fine root production was estimated synchronously by three different approaches (sequential soil coring, the ingrowth core method, and the mini-rhizotron technique). Coarse and large root production was estimated by recording diameter increment using dendrometer tapes. Results: Fine root biomass increased four-fold between 1000 and 3000 m; coarse and large root biomass doubled. The three approaches for estimating fine root production yielded highly divergent results, with the mini-rhizotron approach giving the most reliable data, and indicating a significant increase in fine root production with elevation. Conclusions: Our results indicate a marked carbon allocation shift from above- to below-ground towards higher elevations, which is probably a consequence of increasing nutrient limitation of tree growth with increasing elevation.