Text and Photos: Javier Pinzón
Mature forests are important biodiverse sources of oxygen for all living beings and act as our allies in the face of climate change. But what benefits and environmental services do they provide? Do secondary forests, plantations, and paddock areas provide these same benefits? Is reforestation a good idea and, above all, how is it accomplished? To answer these questions, Smithsonian Tropical Research Institute (STRI) scientist Dr. Jefferson Hall and his team have launched the Agua Salud project in the Panama Canal watershed.
Their objective is understanding how forest ecosystems work and measuring the environmental services they provide in order to reproduce these services. They also hope to develop new models to predict the behavior of water and carbon sequestration in these new forests in the face of climate change.
Jefferson explains that secondary forests are those that result from natural processes when the land recovers after being used for other purposes, such as pasture. He adds that, in order to restore a forest’s environmental services or ensure the success of a timber plantation or even a cattle ranch, intelligent reforestation is a must. The goal is to place the right species of trees in the right place at the right time, for the right reason. And all of this depends on why an area is being reforested.
The Sponge Effect
The goal of the project is to analyze whether a forest is truly a reservoir, working like a sponge to absorb water in the soil during the rainy season and releasing it during the dry season. To measure this effect, “spillways” or microbasins are created to precisely measure a stream’s current. The results of the measurements are then compared: a micro-basin in the Soberanía National Park forest is compared to a mosaic-like area that includes agriculture, mature secondary forest, and pasture land, and to another located in a paddock. The results from both dry and rainy seasons are also compared.
The project was able to demonstrate that, although trees use a lot of water, they also facilitate infiltration of large quantities of water into the soil thanks to their roots and the work of insects associated with trees, such as ants, which create holes in the ground that increase infiltration. It also showed that planting trees of any kind –teak plantations, silvopastoral systems, secondary forests, or native species– helps improve water infiltration.
In 2013, during an especially dry season, the scientists found that the forest retained 25% more water than the paddock. This additional water supplied the Canal, as well as the nearly two million people who depend on the basin, during the four months of drought, even during that difficult year.
Jefferson’s group is interested not only in the possibility of preserving mature forests and biodiversity, but also in the environmental services provided by secondary forests, their importance for water conservation, and their carbon-capturing capacity, as well as their contribution to mitigating climate change.
Scientists use a chronosequence system in plots with forests of different ages to understand the trajectory of a secondary forest over a period of years. Chronological results show that, by the fifteenth year, the light inside a secondary forest is similar to that of a mature forest, and the forest is home to up to six hundred different tree and vine species. By the twentieth year, the same forest is already producing fifty tons of biomass for every 2.5 acres, and although this is far from the 125 tons produced by a mature forest on Barro Colorado Island, for example, it nevertheless represents a considerable amount of carbon sequestration. Secondary forests have been found to be a viable and economical strategy for lowering the costs of carbon capturing.
Jefferson adds that we need to do more than lower the rate of deforestation to reduce the effects of climate change; we must also strive for a low-carbon economy and continue to reforest.
We know that secondary forests increase biodiversity, water, and carbon sequestration, but what happens if we reforest with native species? According to Jefferson, four species are most often used to reforest: teak, eucalyptus, pine, and acacia, because their seeds are easy to access and we know how to plant and care for them. However, they don’t grow well everywhere or in monocultures.
The Native Species Reforestation Project (PRORENA, in Spanish) began with a collaboration between the Yale School of Forestry and Environmental Studies, the Panama Canal Authority, and the Ministry of the Environment. It aims to understand the right native species to use for reforestation and how to generate income for landowners through reforestation.
PRORENA is particularly interested in understanding why people don’t use native species. According to Jefferson, it’s due to a lack of knowledge of how to germinate them, care for them in the nursery, and manage their growth. The first trial project produced a book that illustrates how to manage 120 native species in the nursery and germinate their seeds. One example is the corotú seed (Enterolobium cyclocarpum), which is so hard that a piece of it must be cut and soaked in water for a while before planting. If this procedure is not followed, the seed can take up to a year to germinate. The second stage of the project produced a second book with guidelines for growing 64 other native species.
Another goal of the project is to understand how species behave with their neighbors, whether they help each other grow or compete for resources, space, and time. Two species –one with shallow roots and one with deep roots– for example, can be alternated so that one takes water from the top of the soil and the other draws from a deeper level, eliminating competition for water.
There are many cases of people who set up teak plantations only to abandon them. An analysis of these plantations carried out in 2015 in the Panama Canal Basin found that the tree only does well in soil with sufficient limestone; a crop without the proper soil will not give consistent returns on investment. But a study of this type of plantation helps us understand how trees can be planted in degraded soils.
There are now about 7.4 billion people on the planet and good soil is generally reserved for agriculture. The planting of trees for carbon sequestration and timber usually takes place in poor soil. Agua Salud and Smart Reforestation are working to learn how to use these areas, converting timber plantations that have failed to produce the necessary yields (by planting the wrong tree in the wrong soil) into profitable businesses by taking advantage, for example, of shady areas to plant native trees. The existing teak trees can be used as a “nursery” and cut down later when the new ones reach a good height.
An analysis of these plantations has also demonstrated that amarillo trees (Terminalia amazonia) and cocobolo trees (Dalbergia retusa) grow very well in poor soil. In just three years, the cocobolo –whose wood is worth more than US 2,000 dollars per cubic meter– reaches the same height as a ten year-old teak tree.
The mountain almond tree (Dipteryx panamensis), which grows well in shade, attracts animals and birds. And one of Jefferson’s favorites, the quira (Platymiscium pinnatum), sells for nearly the same price as the cocobolo and is often straighter and acts as a nitrogen fixer. A study conducted with this plant and published in Nature showed that, from age twenty on, this species fixes substantial amounts of nitrogen, making it a very important part of the secondary forest. The project hopes to take advantage of this knowledge of secondary forest behavior and apply it to plantations, as this tree grows very well below the teaks.
It is also important to note that livestock is one of the main causes of deforestation in Latin America. Additional studies are being made of the silvopastoral system, its relationship with water, and the ways this system could increase meat or dairy production.
According to Jefferson, a pasture studied in Colombia, as a part of his research, can handle one head of cattle per hectare, whereas under the silvopastoral system, this increases to five heads per hectare. Trees provide livestock with shade as well as part of the food they require.
Ultimately, Jefferson’s team wants to use science to find solutions to improve selection of species based on specific objectives and, in the short term, achieve smart reforestation.