A 50-hectare plot of rainforest in Panama where every tree thicker than one centimeter has been tagged, mapped, and measured since 1980. The data helps explain why tropical forests contain so many species packed into such a small area.
A monumental tree census
On Barro Colorado Island, on the Panama Canal, is a 1000-by-500-meter rectangle of tropical moist forest. This is the Barro Colorado Island Forest Dynamics Plot, the site of a continuous scientific study. Since the first census was completed in 1982, researchers have identified, tagged with a unique aluminum number, and mapped every free-standing woody tree and shrub with a stem diameter of one centimeter or more. This census is repeated every five years, creating a long-term dataset of a tropical forest ecosystem.
The project was established in 1980 by ecologists Stephen P. Hubbell and Robin B. Foster, affiliated with the Smithsonian Tropical Research Institute (STRI) and Princeton University. The first census alone documented approximately 240,000 individual stems from over 300 species. Over the decades and through multiple census cycles, the total number of individual trees ever tagged has grown to more than 423,000. This meticulous work involves teams of researchers systematically moving through the entire 50-hectare area, measuring tree diameters, and recording new saplings that have reached the minimum size. The data is detailed that it has been used in over 1,300 scientific publications.
Insights from the forest
The massive dataset generated from the Barro Colorado plot allows scientists to ask fundamental questions about forest ecology. One significant findings supports the theory of negative density dependence. This concept suggests that individual trees are less likely to survive when surrounded by others of the same species, which may be due to shared pests or pathogens. This mechanism prevents any single species from becoming overly dominant and helps maintain the forest's high biodiversity.
The plot contains more than 325 tree species, a density of diversity that is remarkable for such a small area. Long-term data has also revealed the forest's dynamic nature. The average residency time for a canopy tree is only about 45 years. The data has documented the effects of major climate events, like the severe El Niño drought in 1982, which dramatically increased tree mortality rates. This information helps understanding how tropical forests might respond to future climate change.
The success of the Barro Colorado Island plot led to the creation of a global network. Now called the Forest Global Earth Observatory (ForestGEO), this network includes over 70 similar plots in nearly 30 countries, all using the same standardized methods. This global collaboration allows scientists to compare forest dynamics across different continents and climate zones.
💡Fun Facts
Barro Colorado Island was formed in 1913 when the Chagres River was dammed to create Gatun Lake, a major part of the Panama Canal.
The 50-hectare plot was the first of its kind and became the model for the global ForestGEO network, which now monitors roughly 7 million trees.
To date, scientists have documented 328 different tree and shrub taxa within the plot's boundaries.
In addition to the main census, researchers established nearly 20,000 smaller 1-square-meter plots in 2001 to specifically track the growth and survival of seedlings.
Access is restricted. The Smithsonian Tropical Research Institute offers a limited number of guided public tours on specific days, which must be booked far in advance.
Admission
A fee is charged for the all-day tour, which includes the boat transfer from Gamboa, a guided hike, and lunch.
Accessibility
The tour involves a 2-3 hour hike on rainforest trails with moderate inclines, which can be uneven and muddy. Closed-toed shoes are mandatory.