Finding answers in the forest
At "Las Casas de la Selva", a 409-hectare experimental forest enrichment project is located on some of the most challenging steep slopes and diverse ecology in the mountains of south-eastern Puerto Rico. The project, which Earthwatch has supported since 2001, is demonstrating an approach for utilising a rainforest environment for profit, without diminishing its species richness, biological diversity or total biomass*.
This example of sustainable forestry is tackling the problem of trying to counter the current worldwide trend of clearing rainforests for the purposes of one-time timber sales; establishing monocultural plantations; and supporting cattle ranches - activities which all result in loss of biodiversity, ecosystem degradation and soil erosion.
Las Casas de la Selva is a secondary rainforest area of low commercial value, formerly used for coffee plantation and other small farming operations. A portion is currently cultivated for timber production. Through planting valuable hardwood trees, these semi-natural plantations can be cultivated so they produce enough timber to deter local landowners from being economically driven to other, more damaging, short-term land use activities such as deforestation. Since 1984 a programme of line planting of a variety of valuable native and introduced hardwood timber trees within the existing forest has been underway, with approximately 40,000 trees planted on 87 hectares by 2008. This planting has been done to test the hypothesis that tropical hardwoods can be cultivated in a secondary growth rainforest using a line planting technique, while still maintaining species diversity. Particular research objectives have included testing the suitability of various native tree species for line planting, the possible effects of line planting on coqui frog populations, a study of Anolis lizard populations, and the effects of tree thinning on mahogany growth.
Line planting experiments
In the line planting experiments, mahogany survival rate was approximately 28 per cent and mahoe survival rate was 66 per cent. The data indicated that west and south facing slopes may produce the best survival rates for mahogany. Mahoe appeared to grow the fastest of the two species, increasing in diameter by 0.91 cm per year compared to 0.6 cm in mahogany, and in height by approximately 1 m per year, compared to 0.5 m in mahogany. Findings have shown that line-planted mahogany is slow to develop and is likely to need a growing time of 43 years to reach a diameter that will give good logs. This is a long time to wait for a commercial return and it was considered beneficial to research other short-term crops that can be grown in conjunction with mahogany and give a faster economic return. In 2008, therefore, the project began a study with two crops, Artemisia annua L. (a traditional Chinese medicinal plant used to treat malaria, now gaining commercial attention) and the coffee plant Coffea robusta. A total of 267 Artemisia plants and 101 plants of C. arabica were planted in mahogany plantation areas. A sample of Artemisia leaves is being tested for artemisinin (the substance in the plant which gives it its malaria-fighting properties) content, and for the coffee plants, data was collected about the condition of the leaves and stalks, and apparent diseases and fungi. The plants will be constantly monitored.
Amphibians are abundant, integral components of many diverse ecosystems and are especially useful as biological monitors of environmental health. As top carnivores, and herbivores in their larval stage, in a variety of ecosystems, a decline in amphibians could have an important impact on insects, plants (including crops) and other organisms. Their population declines could signal deeper ecosystem deterioration and more general environmental problems. Results from studies of the coqui frog populations suggest that line planting has had no significant impact on amphibian populations, and the data has provided a very valuable baseline that will allow monitoring of population fluctuations and potential crashes associated to climate change or disease. This is at a time when amphibian populations are declining globally due to the fungal disease outbreak of chytridiomycosis. The level of incidence of chytridiomycosis was discovered to be 44 per cent and 50 per cent for two frog species in the research area. Preliminary data show that incidence of infection is greater in the wet season, but a larger set of data from other mountain ranges in Puerto Rico suggests there is a much more complex climate-disease interaction at play that needs to be investigated further.
To augment the amphibian studies, the project has more recently started to evaluate populations of Anolis lizards. The team has been monitoring the effects of habitat disturbance due to line planting and tree thinning activities and building up baseline data for future monitoring of Anolis lizards. Different species of Anolis lizard utilise different habitats, so some species are particularly dependent on certain conditions remaining within their habitat. The research has revealed that Caribbean pine monocultures provide poor habitat for the lizards, whereas shade-grown coffee plantations have yielded specimens of three species, A. stratulus, A. gundlachi and A. cristatellus cristatellus. This may be because numerous basking and hunting sites exist due to sunlight being able to penetrate the forest floor, but further study is needed to confirm this hypothesis.
In 2008, a five year vine study began and has already identified and recorded 353 vines and lianas from 14 x 100m2 plots. Vines are a source for fibre used in weaving and handicrafts in the area and thus are secondary forest products of economic importance. Because of their durability, resistance to decay and large diameter, woody vines and lianas appear to be more useful than herbaceous vines, and woody species were found to make up 42 per cent of the total population of the plots studied. Growth assessments for species of particular abundance and commercial interest began in 2009, and the forest is being further surveyed to better determine which species may be most useful and plentiful. Little previous work has been done to measure the growth rate of tropical vines, making this study extremely important for future assessment of the rate at which vines of economic importance could be sustainably harvested.
In 2009, another study (three to five years) began, examining the effectiveness of "liberation thinning" on maturation and biomass of commercially important trees which exist in secondary forests. Liberation thinning is a method in which marketable crop trees are identified and any surrounding trees whose crowns compete for sunlight with the crop trees are removed. This method has been shown to increase growth rates of the liberated crop trees in several tropical locations, but there have been few studies worldwide and none in Puerto Rico. The studies that have been carried out indicate that management methods used to reduce competition can dramatically speed up the growth of crop trees, leading to reduced time to harvest and increasing the amount of marketable wood produced, offering a way to sustainably increase economic viability from secondary forest. Such research could be widely applied. Given a growing world demand for timber, the pressure on primary forests, and the need to make secondary forests more productive and profitable for the people who live there, demonstrating and testing these techniques is extremely important. Data collected by Earthwatch scientists and volunteers from the first year of this pioneering study for Puerto Rico are currently being analysed.
Working with the local community
Collaboration between the project and the local community has increased over the years, and young Puerto Ricans have become involved with the project as full or part-time members of the team. The community is showing an increased awareness of issues such as watershed protection for the local reservoir, where a clean-up of the lake has become an annual event, and the necessity of controlling erosion by keeping the steep slopes of the local terrain covered in trees. The Earthwatch project is an excellent illustration of the benefits of this and, in stark contrast, clear-cut areas just beyond the borders of Las Casas de la Selva show signs of deep erosion gullies and land degradation.
* Biomass is the mass of living biological organisms in a given area or ecosystem at a given time.
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Report by Debbie Winton.