Long-term tropical rainforest dynamics

Forests play a major role in absorbing carbon from the atmosphere and thereby controlling climate change. However, the ability of forests to sequester carbon is sensitive to climatic variation besides the nature and intensity of local disturbance. Understanding the impacts and implications of climatic variation and disturbance on forest and carbon dynamics requires intensive long-term monitoring across different forests through coordinated, collaborative research.

In collaboration with the Long-term Ecosystem Monitoring Network - India (LEMoN) and National Centre for Biological Sciences (NCBS), Bangalore (Drs Mahesh Sankaran and Jayashree Ratnam) NCF has set up three permanent 1 ha LEMoN plots in the Western Ghats for forest dynamics research. LEMoN India is a collaborative network of 1 ha forest monitoring plots along environmental gradients and across habitat types in India that uses standard protocols (RAINFOR-GEM protocols and CTFS protocols) for research and monitoring. All stems of 3 cm diameter and larger were identified, mapped, and measured in each plot with larger stems tagged with dendrobands for girth (growth) and carbon monitoring.

In the Anamalai Hills, we have established and presently monitor two 1 ha LEMoN plots: one in a degraded rainforest remnant and restoration site, Candura, and one plot in relative undisturbed rainforest in Manamboli within the Anamalai Tiger Reserve. In the first census (Dec 2017), we enumerated, mapped, and identified 1958 stems of 63 species in the Candura 1 ha LeMon plot and 1336 stems of 87 species in the Manamboli 1 ha plot. The plot has been annually re-censused and all stems are also monitored quarterly by dendroband measurements six annual censuses, and 19 dendroband surveys completed by 2022. In 2020-21, we established our third 1-ha LEMoN permanent plot in Kadamane, Karnataka, as well.

Our teams now continuously monitor tree populations, growth rates, carbon capture rates, litterfall dynamics and respiration rates from vegetation and soil within the plot. Overall, this research is yielding interesting and new data on tropical rainforest dynamics in terms of tree growth, recruitment of saplings, tree mortality, and carbon dynamics. Preliminary data analysis is in progress to contrast the patterns in the secondary site versus that in the undisturbed rainforest, which we anticipate will yield insights of relevance to rainforest recovery and restoration.

Trees play a key role in the structure and functions of tropical rainforests. Climate change can affect the natural seasonal rhythms of trees by influencing changes in their patterns of leafing, flowering, ad fruiting. Tree phenology, which is the study of these patterns, can shed light on how trees are attuned to or changing with climate. Phenological studies are also valuable for the practice of ecological restoration as they provide valuable information on when different species fruit and seeds become available.

We initiated long-term phenology monitoring in the rainforests of Anamalai Tiger Reserve in February – March 2017. Seven phenology trails were established in relatively undisturbed rainforests across an altitudinal gradient and about 200 to 300 trees on each trail were inventoried for monitoring (Figure 10). A total of 1808 individual trees (>30 cm GBH) of 173 species were recorded and these were marked by their GPS location, identified to species, and height and girth measured. All marked trees were selected for monitoring except for 9 species that had over 40 individuals, for which we capped the monitoring at 40 individuals. The monthly monitoring covered 1584 trees of 166 species, a good mix of common ones (like Acronychia pedunculata, Mesua ferrea and Villebrunea integrifolia) and some rare species (like Nageia wallichiana, Garcinia pushpangadaniana and Diospyros candolleana).

From 2021 January, onwards our phenology species data set has rationalised based on the number of individuals being monitored per species, focusing on species with at least 10 individuals, and on surveys along six trails. We also included Ficus trees that are being monitored in the wider landscape and a set of 10 globally threatened tree species, which is the focus of a parallel study on their distribution and abundance in the landscape. We are therefore now monitoring 1089 trees of 59 species and have increased the frequency of surveys to twice a month.

In Kadamane, Karnataka, we initiated rainforest tree phenology monitoring in January 2022. Over 600 trees of 40 species are currently being monitored along six trails.

Analyses of data are in progress and we expect new insights to emerge on seasonal patterns in relation to climate and inter-annual variability in rainforest tree phenology from this work.