Treefall gaps are a dominant force of disturbance in tropical forests. They are implicated in the creation and maintenance of diversity, as well as in biogeochemical cycling and carbon source/sink dynamics. However, the bulk of what is known about treefall gaps and the role they play in ecological processes is largely limited to aboveground and near-surface soil observations. Given that more than 1/3 of Amazonia where forests depend on deep (> 1 m) roots and soil moisture reserves to sustain green canopies year-round, better understanding of deep water and root dynamics is critical. We sought to assess how a treefall gap alters the vertical distribution of rooting density, and how this belowground disturbance in turn affects the limiting resource of deep soil moisture. To this end, we measured the dynamics of rooting density and soil moisture in 10-meter vertical profiles each in a 3-year old regenerating gap and in adjacent intact forest.
Results/Conclusions
We found substantial differences between gap and intact forest sites, including lower root density over the entire profile and a shallower maximum rooting depth in the gap. During the progression of the 2009 dry season, we found significant drying to 5 m depth in the gap, compared to at least 10 m in the intact forest. At the local scale, these results highlight the importance of seasonal dynamics in plant available water in tandem with fine root dynamics in controlling forest phenological patterns, including observations of dry season green-up of the canopy. At the catchment scale, these results suggest that the size and age distribution of gaps across the landscape in moist tropical forests are likely to play an important role in partitioning water cycling between runoff, storage, and subsurface drainage. Future climate change that alters the frequency and intensity of treefall gaps and/or blowdowns may alter regional water budgets across Amazonia.
