Trudging through treefalls

The post provided by Kwek Yan Chong

This post refers to the article Short‐term responses in a secondary tropical forest after a severe windstorm event by Yee et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12753).

One late afternoon on 11 February 2011, an unexpectedly powerful burst of wind ripped through a part of the nature reserves of the tropical city-state of Singapore. The nearest weather station recorded wind speeds exceeding 60 kilometres per hour—not a big deal elsewhere, perhaps, but a rarity in the equatorial tropics. The wind also brought down swathes of tropical forests on a scale that was unheard of (at least as far as anyone in Singapore who cared could remember).

Back then, I was a postgraduate student struggling with a PhD project that was going nowhere. Alex Yee (the first author of the paper this blog refers to) had just graduated from his first degree and was struggling to come up with a project idea for a PhD. Meanwhile, news of this incident was rapidly making the rounds in the local community of nature enthusiasts. Alex and I probably had other more urgent matters at hand, but our curiosity got the better of us, so we made a trip down to Mandai Road, the road that cuts through the northern part of Singapore’s Central Catchment Nature Reserves around where the tree falls had occurred. What we saw was indeed unlike anything that we had ever seen before. Thousands of trees large and small were snapped or uprooted.

It occurred to us then that this was an opportunity to study forest succession, especially given that the tree falls occurred in patches over an area where older and younger secondary forest were also distributed in a mosaic-like pattern. Such an overlay of a mosaic over another mosaic was ideal for a factorial study design to compare the recovery of young and old secondary forest, with unaffected areas as controls. We pitched the idea to our supervisor, Associate Professor Hugh Tan, who dug out some spare funds for us to recruit helpers to carry out the surveys and helped to get the support of our National Parks Board (NParks) colleagues who provided us preliminary information and allowed us access to the site.

What had started as random curiosity was to become a formative experience as budding botanists and plant ecologists. During our first attempt at setting up a plot, it was evident that this was a crazy idea. Neither of us was familiar with the species-rich native flora in Singapore’s nature reserves. Both of us had also never actually carried out a whole study using vegetation plots before, much less one with plot locations randomly generated across a landscape full of tree falls and regenerating spiny palms (i.e., rattans). I remember panicking during our first plot, where there were simply too many seedlings in a 10 by 10 m plot to count, and I had no idea which ones were seedlings of trees and which were seedlings of climbers.

Eventually, we scaled back our study design and pulled off 40 plots by June that year. We were also very lucky to have the help of Mr Gwee Aik Teck from the Singapore Botanic Gardens herbarium, who rapidly worked through the stacks of voucher specimens we sent him every week to give us a putative identification, neatly written on the newspaper that was used to press each specimen for drying in the oven. I wanted to reduce the number of specimens we were burdening Mr Gwee with, so I started going through the specimens after he returned them. Soon I started sending in specimens with my own guess at the identity written on the newspaper, and he would put either a tick or a cross with the correct identification, like a teacher marking a student’s work.

Alex and I decided that we should monitor our plots yearly, and it became a chapter in Alex’s PhD thesis. Together with Hugh, we applied for small local research grants to fund this work. Twice we were rejected, but Hugh believed in us and dug around again for spare money for another year, until finally we were funded by the Ah Meng Memorial Conservation Fund for two years’ worth of surveys in 2013 and 2014. In 2014, just as Alex was beginning to wind down his PhD work, Hao Ran Lai (the second author of the paper) had just started to work on his one and joined us to add a functional traits aspect to the study. In 2015, as a post-doc with Hugh, I finished off the last year of surveys with an all-star team of young botanists who are co-authors on this paper.

I’m immensely proud of this work, as it must be the first of its kind in tropical Asia. Reported in the Journal of Vegetation Science, our most interesting initial findings include a pulse of nutrients that peaked in the second year, and distinct trajectories in the composition of stems in young and old secondary forest as the recovered over these five years. Hao Ran conducted additional analysis to show how recruitment across the environmental gradients in the tree falls was moderated by species functional traits, published soon after this study at the Journal of Ecology (with an accompanying blog post).

The recovering forest should be entering a phase of self-thinning now, and it would be interesting to see whether mortality, like recruitment, is moderated by trait-environment interactions. The plot corner markers should be still there, re-tagged with an NParks tag when we handed them over after the surveys concluded in 2015, in the hope of an opportunity to return to them as a longer-term study.

Brief personal summary: Kwek Yan Chong is an ecologist from the Department of Biological Sciences at the National University of Singapore. His research interests are in vegetation ecology, urban ecology, and invasive plant ecology.