I am interested in how climate change affects the structure and functioning of tropical forests and the ability of tropical forests to store and sequester carbon. In particular, my research focuses on lianas (woody vines). Lianas are a characteristic life form of tropical forests where they peak in abundance and diversity. They are classed as structural parasites, which means they use trees to support their biomass to reach the canopy. As competition with lianas is stronger than competition between trees, trees infested with lianas suffer from reduced growth, survival rates and fertility. On a forest-level, this means that lianas can reduce the amount of carbon that is stored and sequestered by tropical forests. In previous research, using a liana removal experiment in Panama, we have shown that this can be by as much as 76% (van der Heijden et al. 2015), which indicates lianas can have severe impacts on the carbon sink function of tropical forests. As lianas are increasing in Neotropical forests, which is potentially driven by direct and indirect of climate change, this increase in liana dominance and associated impacts on the carbon sink function of tropical forests need to be taken into account to better understand the fate of tropical forests and their carbon balance in a changing climate.
Current research projects are:
1) Determining the effect of lianas on the carbon balance of tropical forests (Anne McLaren fellowship)
In this project, I am focussing on the following two main research questions:
i) Has the increase in liana dominance in the Amazon has persisted over the last decades, and if so, has the rate of increase changed?
Phillips et al. (2002) indicated that the abundance and basal area of large lianas has been increasing in Neotropical forests using a dataset of lianas >= 10 cm diameter. This dataset has now increased spatial and temporal coverage and we'll be using this to assess whether and how patterns of liana abundance and biomass have changed over time. (Collaborators: Prof. Oliver Phillips [University of Leeds]).
ii) Investigating the drivers responsible for the geographical variation in liana infestation across the Amazon and providing a first estimate of the impact of lianas on Amazonian carbon balance.
I am currently collating a large dataset of liana infestation and tree data from sites all over the tropics. This dataset will be used to evaluate the geographical distribution of liana pressures in Amazonia in relation to soil, climate and dynamic forest variables (turnover and wood density) and to construct an Amazon-wide map focussing on liana pressures using remotely sensed imagery of the explanatory variable(s) to interpolate the liana impact to areas for which liana data are not available. By combining these data with forest biomass data for the Amazon, I will be able to provide a first basin-wide estimate of the effect of lianas on carbon uptake and storage. (Collaborators: Dr. Elizabeth Kearsley [University of Ghent])
2) Liana-induced impacts on carbon sequestration of tropical forests
A large-scale liana removal experiment has been set-up in 2008, with lianas being removed in 2011, in the Gigante Peninsula of the Barro Colorado Nature Reserve in Panama. Using detailed growth measurements, we are quantifying the effect of lianas on carbon sequestration in these forests. An earlier paper indicated that lianas reduce net carbon uptake by 76% in the third year of the experiment and that in the presence of lianas forests produce more leaves at the expense of wood productivity (van der Heijden et al. 2015). As a continuation of this study, we are now testing whether the effects of lianas on tree carbon sequestration are more severe in dry than in the wet season. (Collaborators: Dr. Stefan Schnitzer [Marquette University, US and Smithsonian Tropical Research Institute, Panama] and Dr. Jennifer Powers [University of Minnesota, US])
3) Spatial and temporal patterns in liana success in Malaysia
In this project, we will be focussing on two main research questions: i) what are the drivers of regional scale patterns in liana pressures, and ii) is liana success affecting the ability of the forests to store and sequester carbon on a regional scale? We are using hyperspectral and LiDAR data collected by the NERC Airborne Research Survey Facility in 2014 from Danum Valley, Malaysia, in combination with a ground survey of liana infestation of tree crowns in this area to create a regional map of liana infestation. This map will be combined with maps of soil fertility and disturbance to assess which variables may be responsible for regional patterns in liana pressures in this region and will also be used to link liana success to measurements of carbon storage and sequestration and to assess the impact of liana infestation on carbon storage and sequestration. (Collaborators: Chris Chandler, Prof. Giles Foody, Dr. Doreen Boyd - PhD project of Chris Chandler)
4) Using Unmanned Aerial Vehicles (UAVs) to assess liana infestation
i) Ground surveys of lianas are time consuming and we are therefore investigating the use of quadcopter UAVs in the assessment of liana infestation of tree canopies. (Collaborators: Dr. Doreen Boyd, Dr. Richard Field and Catherine Waite [University of Nottingham]).
ii) We are investigated the response of lianas to the 2016 El Niño drought in Malaysia using repeat monitoring of the forest canopy via Unmanned Aerial Vehicles (UAVs) as part of the NERC/DfID funded project Spatio-TEmporal Dynamics of Forest Response to ENSO Drought (STEED). (Collaborators: Dr. Doreen Boyd, Prof. Giles Foody, Dr. Mark Cutler [University of Dundee], Prof. David Burslem [University of Aberdeen])