Relative deforestation rate in South East Asia is the highest among any major tropical regions. In Borneo, most of the lowland dipterocarp forests have been already affected either by selective logging or conversion to the oil palm plantations. However, despite their crucial role in human-modified landscape, information on growth dynamics, structure and fine-scale spatial distribution of secondary tropical forests remains scarce. While in primary tropical forests, manually measured permanent plots are a standard tool to study forest structure and dynamics; studies of secondary (logged and fragmented) forests with their dense undergrowth, majority of small trees and the need to capture fine-scale stem dynamics (instead of traditional tree dynamics) poses a new challenge for tropical ecologists. We used a new laser technology for mapping forest structure and fine-scale spatial distribution of trees, based on a combination of interconnected electronic devices and specialized Fie ld-Map software (IFER, Jilove u Prahy, Czech Republic). The technology effectively captures tree positions to the nearest centimetre in three-dimensional space and allows mapping points, lines, polygons, deadwood, horizontal tree crown projections, vertical crown profiles, stem profiles and micro-topography of permanent plots.
Results/Conclusions
We used the Field-Map technology to study fine-scale spatial structure and growth dynamics (dbh measured yearly in 2011–2015) of trees with dbh ≥ 1 cm in logged and fragmented tropical rainforest within the Stability of Altered Forest Ecosystems (SAFE) Project in Sabah, Malaysian Borneo. We tried to explain dbh increment of trees by a) competition between tree individuals, expressed by distance-dbh dependent Hegyi index and second-order spatial statistics, and b) fine-scale topography variation using set of environmental variables (such as elevation, slope and profile curvature expressing convexity-concavity of the relief) derived from the digital elevation model of the Field-Map data. Competition with neighboring trees was found to be an important factor, explaining about 30% of the dbh increment variation. In contrast, fine-scale topography played a minor role, explaining only 6% of the dbh increment variation. Our results suggest that competition is the main factor det ermining the growth dynamics in the secondary forest.