Large-Scale Throughfall Measurement System Installed at Agua Salud

by Frank Base

Following the long-term approach of the Agua Salud Project, researchers recently installed three automatic-logging trough systems to measure throughfall in a 5-year-old secondary succession forest at Agua Salud. The purpose of the permanent trough system is to document the temporal changes in throughfall as the secondary forest grows and develops.

Juan Carlos Briseño, technical assistant, finishing one of the new trough systems. Photo by Frank Base.

The trough systems consist of 32 three-meter open tubes (troughs) connected like feathers on the wings of a bird. One wing spreads over an area of 9 m x 3 m. The system in total has an opening of about 12 m². At the center of the construction, a logging tipping bucket catches all drained water and has a capacity of 3 L per tip. Within one hour, 2160 L can be measured. This capacity equals a rain intensity of 195 mm/h, which is sufficient for the strongest rain events in the Agua Salud area based on data from 2008-2010.

Before installing the system, Agua Salud researchers had been using 100 funnels to measure throughfall manually since 2008. The new automatic system now provides continuous measurement of throughfall over the course of the year, enabling us to characterize variations over time and correlate them with rainfall intensity.

Measuring throughfall with trough systems is not new, however. Cuartas et al. (2007) used a trough system covering 1.8 m² with 6-m troughs and a tipping bucket capacity of 125 ml per tip in central Amazonia, Brazil. And McJannet et al. (2007) used 6-m long troughs in a star formation covering an area of 2.4 m² - 3.6 m² in an Australian tropical rainforest. Their tipping buckets had a capacity of 1.8 L - 2.1 L per tip.

Scale is the main difference between the systems used in Brazil and Australia and the one at Agua Salud. We have built, as far as we know, one of the biggest trough systems in the world. Such a large measuring system is necessary to reduce the effect of throughfall on spatial variability caused by extreme structural differences in the canopy of secondary forests. By sampling such a large area, we hope to smooth out the variation caused by canopy structure.

Literature
Cuartas, LA, J Tomasella, AD Nobre, MG Hodnett, MJ Waterloo, and JC Munera. 2007. Interception water-partitioning dynamics for a pristine rainforest in Central Amazonia: Marked differencesbetween normal and dry years. Agricultural and Forest Meteorology 145: 69-83.

McJannet, D, J Wallace, and P Reddell. 2007. Precipitation interception in Australian tropical rainforests: I. Measurement of stemflow, throughfall and cloud Interception. Hydrological Processes 21: 1692–1702.

Seven Censuses over 30 years on BCI

Three decades after Stephen Hubbell and Robin Foster established the first plot in what would become the CTFS-SIGEO network, researchers and field technicians recently completed the seventh census of the 50-ha plot on Barro Colorado Island (BCI), Panama. The 1980 census on BCI marked the beginning of CTFS-SIGEO, pioneering the use of long-term large-scale tree-censusing techniques that researchers have replicated in forests across the globe. Today, CTFS-SIGEO comprises a network of 40 plots in 21 countries in Asia, Africa, the Americas, and Europe. The network involves hundreds of scientists and dozens of institutions around the world working together to study the growth and survival of 4.5 million trees of 8,500 species.

The following figures based on seven censuses (1980-2010) at BCI illustrate the extraordinary scale and intensity of CTFS-SIGEO’s research program.

1,836,533 diameter measurements of stems ≥1 cm

391,278 individual trees counted

174,435 tree deaths

155,955 trees recruited

17,500 person-days of fieldwork

85 person-years of fieldwork

130 people involved in the 7 censuses

This enormous undertaking could not have been possible without the hard work of the many people who have worked at BCI over the past 30 years. Congratulations to all involved!

Publications: Aug – Oct 2010

Baltzer, JL, and SC Thomas. 2010. A second dimension to the leaf economics spectrum predicts edaphic habitat association in a tropical forest. 2010. PloS ONE 5(10): e13163.
Full Text

Jones, FA, and LS Comita. 2010. Density-dependent pre-dispersal seed predation and fruit set in a tropical tree. Oikos 119(11): 1841-1847.
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Malhado, ACM, GF Pires, and MH Costa. Cerrado conservation is essential to protect the Amazon rainforest. 2010. AMBIO 39(8): 580-584.
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Ogden, FL, RF Stallard, H Elsenbeer, and J Hall. 2010. Panama Canal Watershed Experiment—Agua Salud Project. AWRA Summer Specialty Conference Proceedings, 30 Aug - 1 Sep.
Full Proceedings

Stallard, RF, FL Ogden, H Elsenbeer, and J Hall. 2010. Panama Canal Watershed Experiment—Agua Salud Project. Water Resources IMPACT 12(4): 17-20.

Weerasinghe, SM, C Chandrasekara, G Seneviratne, CVS Gunatilleke, and IAUN Gunatilleke. 2010. Growth variations of edaphic specialist species in a reciprocal pot experiment in Sri Lanka. Journal of the National Science Foundation of Sri Lanka 38(3): 171-179.
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Students Study Secondary Forest Succession in Panama Canal Watershed

by Dylan Craven

Enmeshed in a mosaic of land uses, young secondary forests provide vital ecosystem services to the cities of Panama City, San Miguelito, and Colón, as well as to the Panama Canal. Under the auspices of the Agua Salud Project, a collaborative research project of the Smithsonian Tropical Research Institute sponsored by the HSBC Climate Partnership, a group of students from Yale and Harvard spent the summer investigating plant functional traits, functional diversity, and community assembly processes in the young secondary forests of the Panama Canal Watershed.

An extensive series of 0.10 ha transects (10 ha in total) has been established across this human-dominated landscape, where all trees, lianas, and palms have been inventoried yearly since 2008 (~450 tree species, ~150 liana species). Using demographic information from these transects, Dylan Craven (Yale F&ES), Grant Tolley (Yale F&ES), and Julian Moll-Rocek (Harvard) identified and sampled 56 of the most abundant tree species, which represent approximately 75% of basal area of transects between 0 and 20 years old. By looking at varying aspects of species-specific plant function – leaf morphology, physiology, and nutrient content – in combination with abundance and mortality data, these students hope to gain insights about how habitat filtering, niche differentiation, and functional diversity vary with secondary succession.

For more information, please contact Dylan Craven at dylan.craven@yale.edu.