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NELSON M., SILVERSTONE S., REISS K. C., ROBERTSON M., VAKIL T., 2011. Enriched secondary subtropical forest through line-planting for sustainable timber production in Puerto Rico. Bois et Forets des Tropiques, #309 (3): 51-61

SUMMARY

1984: In general the plantation design was to plant at approximately 3m (10 ft) spacing within the lines and 10m (32.5 ft) from line to line through the forest. In the process of line planting, larger trees and valuable native timber species were left in place and the lines continued with a gap left around them. This technique closely mimics a medium-sized tree fall gap, in which the forest floor litter and soils are undisturbed, but the above ground nearby competition is removed, such as vines and overhanging branches. 2000-2008 19 study plots, 1 acre (0.4 hectare) in size 16 plots of mahogany 3 plots of mahoe. 997 trees studied. Complete sets of reading taken twice. Range 24 to 42 mths between readings. SURVIVAL RATE Mahogany plantings – 28% approx (dependent on plot aspect- see results, sw best) Initial planting approx. 370 trees per hectare (148 trees per acre) Mahoe plantings – 66%. Initial planting approx. 415 trees per hectare (166 trees per acre) DBH Mahogany trees are increasing in dbh by an average of 0.6 cm per year Mahoe are increasing by an average of 0.91 cm per year. HEIGHT since planting: Mahogany has grown in height at a rate of approximately half a meter per year. Mahoe at a rate of approximately one meter per year. INDICATIONS The growth data indicate the Mahoe plantation has been far more successful than the mahogany in terms of wood production.  At current rates of increase it would take the mahogany at Las Casas another 27 years to get 30 cm dbh trunks for logging, giving a total time from planting to harvest of 43 years. It is currently possible to harvest marketable wood from the mahoe at 15 years. Current conservative estimates for standing marketable wood for mahoe are approximately 58 cubic meters per hectare (25,000 board feet per hectare or 10,000 bd ft per acre). This makes the Mahoe a good candidate for sustainable forestry management where the aim is to get the trees on a cycle of harvesting and replanting to provide a continuous income. A final evaluation of this line planting method as a model for sustainable forestry will  be possible when trees have been harvested, replanting begins, and the wood and products successfully sold for profit. Future challenges with the Mahoe plantations will involve working out the best thinning and replanting strategies.

SUMMARY

2000-2004 Amphibians:   Amphibians are especially useful as biological monitors of environmental health (Wake, 1991). Because in Puerto Rico frogs are the most important vertebrate nocturnal carnivores, a change in their population dynamics could have an important effect on the forest food web (Joglar, 1998). Thus, monitoring amphibians at Las Casas de la Selva was a suitable way to assess the impact of a line-planting forestry approach to tropical forest ecosystems.

Main difference between the studied forested areas was that one had been disturbed to plant trees of potential economic value (line-planting), while the other area had been left undisturbed.

There was no difference in species composition between the two areas studied.  Eleutherodactylus coqui and E. wightmanae are the two most common species in both forests, with occasional sightings of E. portoricensis.  Analysis of variance (ANOVA) of mean relative abundance of the two most common species revealed no significant difference between forests.

These results suggest that the degree of disturbance caused by planting economically valuable trees had no effect on amphibian diversity or density in Patillas, Puerto Rico.  At a time when the impact of anthropogenic activities on amphibian populations are being evaluated (Stuart et al., 2005), it is important to show that the type of forestry enrichment practiced at “Las Casas de La Selva”, did not have a negative impact on frog abundance. Our work in Las Casas de la Selva is the first record of population densities of E. coqui in the central cordillera of Puerto Rico, and the first record of population densities for E. wightmanae. At a time when amphibian populations are declining all over the globe, and populations of these two species are declining at El Yunque, these data from Patillas represent a very valuable baseline that will allow us to monitor population fluctuations and potential declines associated to climate change or disease.  Chytrid fungus Since June 2004, various species of frogs at Las Casas de la Selva have been sampled for the incidence of a pathogenic chytrid fungus, Batrachochytrium dendrobatidis (Bd).  This fungus is specific to amphibians and has been associated to their decline in various parts of the world (Longcore, 1999), including Puerto Rico (Burrowes et al. 2004).  Tissue is taken from toe clippings and/or ventral skin scrapes, and analyzed for the chytrid DNA via specific PCR diagnostic methods.  Results show the presence of chytrids in Patillas as early as 2005. At present, the level of incidence of Bd infection in Eleutherodactylus coqui is of 50 % and in E. wightmanae is 44 %. Biodiversity of Trees: Overall the line-planting program has resulted in a small increase in overall diversity of tree species in those areas. See results.