Production and stock of coarse woody debris across a hydro-edaphic gradient of oligotrophic forests in the northern Brazilian Amazon

Abstract

Most studies on coarse woody debris (CWD) in Brazilian Amazonia have been done in disturbed and undisturbed upland forests. However, oligotrophic forest types occupying seasonal flooding environments have been neglected, although they occupy about one-third of the Amazon region. We examined the effect of an environmental gradient with different hydro-edaphic features on production and stock of CWD in an area of the Rio Negro-Rio Branco basin, in Brazil’s state of Roraima. We used 60km of trails (production) and 30 permanent plots (stock) in a sampling grid established at Viruá National Park. Our study demonstrated that production and stock of CWD carbon are the lowest in all of Amazonia. The highest CWD carbon production was found in open-canopy submontane rainforest (0.58±0.63MgCha−1yr−1), which occur in environments that are free of any influence of seasonal flooding. The lowest stocks of CWD carbon (0.35±0.30MgCha−1) was associated with low tree biomass in forest types occurring on sandy soils that are strongly influenced by seasonal flooding. CWD stocks in oligotrophic forests at Viruá are partially explained (∼21%) by tree biomass, which is determined by different environmental conditions across hydro-edaphic gradients. Reference values (CWD carbon as a percentage of tree carbon) were among the lowest in Amazonia (0.91–4.38%), with lower values being associated with formations with low production and stock of CWD. This finding suggests that values vary among oligotrophic forest types and that separate reference values should be adopted for estimates of undisturbed forest carbon stocks in the different ecosystems in Brazilian Amazonia. Different reference values represent the variability of CWD among forest types and contribute to reducing uncertainties in current estimates of carbon stock in Amazonia.