Where do trees grow in the tropics?
by Trisha Gopalakrishna -- June 23rd, 2015
The relatively high diversity of tropical forests has enamored tropical ecologists for a couple of decades now. Slowly and steadily, tropical ecologists have also been trying to compare the diversities of the three main tropical belts of the world- Neotropics, Afrotropics and the Asian tropics. Various mechanisms and patterns of maintenance of diversity have been proposed and are still being tested in the field, opening doors to more answers and better yet, more questions.
As part of my Master’s Project, I am looking at the spatial pattern of recruitment of Gambeya and how this is different in pristine and hunted areas. In the case of hunted areas, I hypothesize that more saplings and seedlings are present closer to the parent tree (due to loss of dispersal), exposing them to more host specific enemies including a myriad of insects, fungus and seed predators such as rodents. Alternately, more seedlings and saplings would recruit away from the parent tree with incidences of herbivory pressure. Hence, mapping the spatial recruitment dynamics of Gambeya will give me more insight into the various factors that determine survival and growth.
Therese, Monsieur Nicholas and I started work in the hunted areas around the villages of Ntsibelong and Etkanyabe this week. I was a tad nervous, as our sampling protocol is a little complicated and has many components to it. The basic idea involves searching the area around the parent tree for seedlings and saplings and mapping the same with respect to that parent tree.
We first mark out the eight cardinal directions around the parent tree giving eight sections to sample. Using the distance tape, we flag distances in the order of 5m in all the directions up to 30m. We then choose every alternate section and walk in a zig-zag pattern looking for Gambeya conspecifics. On finding these conspecifics, we tag them and measure the distance from the parent Gambeya using the hypsometer (when the conspecific is too far from the parent) or the distance tape, its angle with the parent using the back bearing of the compass, height, diameter and number of leaves.
We also record the canopy cover above the seedling/sapling using a toilet paper roll. Yep, you read that right. Ideally, one would use a densiometer, which gives a relatively better percentage of canopy cover. But considering the time at hand and the logistical difficulties, we proceeded to collect categorical data of the canopy cover. Looking through the toilet paper roll into the canopy , one can imagine the circle to be divided into four quadrats. Based on the amount of open space one sees in each quadrat, one can classify the closed canopy cover into four categories- 0 when it is completely open and 4 when the canopy cover is 75%-100% closed. Though approximate, this method is still widely used to estimate canopy cover. I can’t imagine any other field of science in which one could get away using a toilet paper roll to collect data. This is field ecology, innovative and adaptive.
Over the past week I have slowly begin to understand the requirements of a strong field ecologist. I am growing more and more confident about using field equipment, right from measuring the angle using the back bearing method of the compass to using the calipers to measure the diameter of tiny seedlings. Understanding how to formulate a sampling protocol from my advisor Dr. John Poulsen and one of the Duke University field technicians Megan Sullivan has been an amazing learning experience. Also, I have slowly progressed from stopping and dropping everything at hand to study every insect bite, itch and rash immediately to ignoring much of it while collecting data. The joy of identifying porcupine burrows and duiker scat while crawling through brush and knots of lianas looking for Gambeya is immeasurable.
But then again there have been times when I had to deal with Monsieur Nicholas and the village guides not wanting to work and/or taking longer breaks than usual. The pain of crawling through thorny lianas and thickets of shrub and also the constant itching and scratching are a challenge to work around. Now I know for a fact that being a field ecologist, especially in the tropics, is not for the faint hearted and is truly an important skill one can boast about.
As we wrap up all the trees in the focal areas, we plan on another trip to Kongou camp inside Ivindo sometime this week. Maybe this will be the trip I come across some chimps!