Visiting our forest plots in BelizeOne day in Belize on my way to the ATBC conference in Mexico, and I do a quick inspection of our intensive monitoring plots in Belize in the company of Elma Kay and Denver Cayetano of the Environmental Research Institute of the University of Belize. As part of a Darwin-funded project (with Percy Cho, who I catch up with in the evening), we have four intensively monitored plots, two in logged forest at Hillbank, and two La Cuevas nested in the mountains near the Guatemalan border.
We visit one of the Hillbank plots. The drive over to Hillbank is through a mixed landscape of forests, smalls farms and then, as we near Hillbank, extensive areas of land recently cleared for corn and bean farming by highly mechanised Mennonite farmers. Elma recounts with passion the struggles of conservation in the Belizean landscape, and the need to work with large farmers to promote sustainability and biodiversity across the whole landscape. “Belize is such a small country. We should be able too make sustainability work here. If we cannot make it work here, what chance to we have in larger countries?”
It is startling to see the mechanisation and homogeneity cutting swathes through this rich forest landscape. Vast expanses of corn and beans where rich forest stood only five years ago. The forest looks quiet skeletal and picked apart in places. However, this is not due to the (relatively low impact) logging, but because of the hurricanes that steamroller through these systems every few years (the last strong one was just last August). This means the forest species are adapted to frequent and intense disturbance, and may be quite resilient to logging, more than tropical forests in less disturbed areas. Elma argues forcefully that it is the logging approach that Belize has developed (reduced impact longing with long rotations between logging) that protects these private land forests by giving them value - the alternative is often conversion to intense farming, for which there is high demand for land.
We arrive at the plot and a cloud of mosquitoes quickly gathers. The forest is hurricane-disturbed, with some fallen trees and many tree crowns ripped off, but also comes across as extremely dynamic and fertile. This may be a combination of the limestone soils and the high disturbance rate. While we are in the plot an intense rainstorm announces itself with a near-overhead flash of lightning. The rain is intense and soaking, but provides welcome relief from the mosquitoes. After a long plane journey it feels good to be so elemental, trudging through dense forest with water cascading over me.
Denver shows me the measurements he has been doing tracking the carbon dynamics of the plots, including measuring tree growth, leaf and root production, and carbon fluxes from soils and stems. It is great to see these new sites in operation, and we make plans to extend the measurements for another year, to provide enough data for Denver to work up into papers. In the context of our global network, these plots provide a unique combination of limestone soils, an ancient Mayan legacy on the landscape and frequent hurricane events. Working out how these various factors shape the functioning and composition of these forests and their resilience to disturbance and global change will be quite a challenge!
We have just completed the installation of tree water use measuring equipment at the Bobiri field site in Ghana. This is one of our key intensively monitored sites which run in a wet-dry gradient in Ghana, from wet rainforest to woody savanna. Bobiri sits in the middle of the transect, a patch of forest reserve just east of Kumasi and conveniently close to the Forest Research Institute of Ghana (FORIG). With our FORIG colleagues we have been monitoring the carbon cycle of this forest in detail for the last five years, and have shown it to be the most productive tropical forest we have ever monitored. We are still trying to puzzle out why this site is so productive.
I am with Lucy Rowland from Exeter University (who has worked on studying water flow in a drought experiment in Brazil for many years) and our Ghanaian colleagues Stephen Adu-Bredu, Akwasi Duah Gyamfi, Mickey Boakye and Patrick.
Now, with the installation of water flux sensors, we are adding an understanding of the use of water by different trees. Our main measurements are done using sap flow sensors, which measure water flow (transpiration) through the stem by looking at the rate of dissipation of heat injected into the tree via electrodes. The more sap flow, the faster the dissipation. Installation involves hammering electrodes into the tree (often perched precariously on a ladder in the case of large buttressed trees).
Initial data suggest phenomenal levels of water flow through these trees, much higher than we have seen at previous work in eastern Amazonia. This may be related to the high productivity and fertility that we see at the Ghana site, with the fast growth rates requiring high water use, at least in the wet season. These are amongst the first (and maybe the very first) sap flow measurements in the wet tropical forests of Africa, and there is much to learn in the coming years.
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University