Changing species diversity and biomass accummulation

Project summary

Introduction

In 1996, fifty-two field plots were established and surveyed in an area of Malaysian tropical forest that had been selectively logged. The information from this survey has been used to inform our understanding of the impact of disturbance on tropical forests and helped validate monitoring from satellite remote sensing. 

Since 1996, no re-measurement has taken place and the regeneration of the forest managed in different ways, with little understanding of the impacts upon biodiversity. This new project brings together expertise from the Universities of Dundee and Aberdeen to re-survey the original forest plots and, for the first time, observe the long-term effects of different forest management strategies. This project coincides with an exciting campaign to acquire remotely sensed data of the area, and so will provide a valuable dataset for validating remotely sensed methods, as well as addressing fundamental ecological questions about the long-term resilience of tropical forests to disturbance.

Background

Key threats to the stability of tropical forest ecosystems are a direct result of the unsustainable human use of these forests, as well as climate change (Vaz and Agama, 2013). The recently published map of global forest loss and gains in Science by Hansen et al. (2013; 342, p. 850) reports an increase in loss and fragmentation of Malaysian forests since the turn of the Century; this in contrast to a reduction of loss in Brazil. Since threats to Malaysian forests are unlikely to reduce in the short- to medium-term, it is paramount that tools for monitoring these fragile ecosystems are developed, as well as furthering our understanding of the requirements for their sustainable management.

Critical to this latter point is the question of how resilient are tropical forest ecosystems to disturbance? Research in Malaysia pioneered the development of “reduced impact” logging (RIL) techniques in the early 1990s (Pinard and Putz 1996), but a critical comparison of the long-term effects of RIL vs conventional logging techniques on forest ecosystem recovery awaits further analysis. To answer this requires a time series of post-disturbance census data on changes to species diversity and distribution, and the effects upon primary production and ecosystem functioning from forests with known disturbance history. This information is also required to forward model and predict ecosystem responses to change, but important questions remain, such as whether we can predict the responses of ecosystems to environmental change based upon the traits of species (Sutherland et al., 2013). Our understanding is further compounded by both insufficient observations of the magnitude and distribution of biodiversity (Duputié et al., in press) and uncertainties in measuring primary production and biomass accumulation.  Critically, the availability of data required to answer these questions is often limited to observations from large plots (few in number) or to many small plots often visited just once, and at which change is difficult to observe and/or infer. Such data are, however, imperative for forest management and environmental change modelling.

As part of the EU-funded INDFORSUS project (Developing Ground and Remotely Sensed Indicators of the Sustainability of Tropical Forest Exploitation Systems, 1995-1999) 52 permanently marked forest plots were established in a 15 by 15 km area of forest surrounding the Danum Valley Field Centre (DVFC) in north eastern Borneo, Malaysia. The forest here is a mixture of primary and disturbed (mostly by selective logging) lowland forest, dominated by dipterocarp species (Newbery et al., 1992). The forest has been logged using either conventional or reduced impact techniques in a series of annual coupes (blocks) since the 1970s.  From the mid 1990s some of the conventionally logged forest has been rehabilitated by enrichment planting using seedlings of dipterocarp species as part of a carbon sequestration project (http://www.face-thefuture.com/en/projects/malaysia). The original 52 plots established in 1996 are distributed approximately uniformly among primary, conventionally logged, reduced impact logged and rehabilitated forest areas, and represent a unique natural laboratory with forest at different stages of regeneration (and therefore range of forest biomass, structure, degradation and species composition) across a small geographical area. In 1996, measurements of tree species, size and canopy condition were made (Pelz, 2000) and have subsequently formed an important dataset for both characterising forest condition and validating remotely sensed methods for estimating forest species diversity and biomass (Foody et al., 2001 & 2003; Foody and Cutler, 2003 & 2006; Cutler et al., 2012).  Almost two decades have now passed since the first census of these forests plots, during which time they have been largely left to regenerate without management or intervention. A second census of these plots would therefore provide an exceptional opportunity to examine decadal-scale responses of forest ecosystems to contrasting management regimes for lowland dipterocarp forest.

Aims

This 12 month project (November 2014 – October 2015)  aims, therefore, to characterise change in disturbed and conserved forests by re-surveying the 52 forest plots, providing an insight into how critical ecosystem variables, such as carbon sequestration, tree mortality, and the abundance and diversity of different plant functional types, have changed in the time-lapsed since the first study of these forests.  To achieve this we will:

  • revisit each forest plot and record tree species and size (DBH and height) to infer the dynamics of tree populations
  • record the cover and abundance of non-tree taxa (lianas, shrubs and herbs) that may be colonising plots and inhibiting forest recovery from logging
  • measure key functional traits (wood density, specific leaf area and foliar nutrient concentrations) of the most abundant tree, shrub, herb and liana species present on all plots
  • derive indices of tree species diversity, characterise forest composition and biomass/carbon accumulation and compare with previously published information and data from these forests, to assess change associated with forest recovery post-disturbance.
  • determine whether these indices of forest recovery differ between unlogged primary forest, compartments that were logged using conventional or reduced impact techniques in the early 1990s, and compartments that were rehabilitated by enrichment planting in the mid 1990s.

The project also receives support from the NERC Airborne Research and Survey Facility (ARSF) to acquire data as part of an airborne campaign to Malaysia (December 2014). This will enable  the acquisition of airborne remotely sensed data across the region, including the forest plot sites, and whilst not critical to characterising forest change on the ground, if successful the field-data described above will provide extensive ground validation information to evaluate new technologies (including lidar, hyperspectral imaging and airborne Synthetic Aperture Radar) for estimating critical ecosystem variables with remote sensing.