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Clark, D. A. 1998. NPP Tropical Forest: La Selva, Costa Rica, 1969-1985. Data set. Available on-line [http://www.daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A.
Situated about 100 km north of San Jose, near the town of Puerto Viejo, the La Selva study site (10.43 N 83.98 W) covers over 1500 ha, of which 55% is "primary" forest and the rest various types of secondary forest and abandoned land. However, the presence of soil charcoal and human artefacts suggest some level of human activity in parts of the La Selva site between 2500 and 500 years ago. The core La Selva reserve was bought by Dr. L. R. Holdridge in 1953, who protected the old-growth forest and carried out multi-cropping experiments in the disturbed areas. La Selva has been managed and enlarged as a research reserve since 1968, when it was bought by OTS. In danger of becoming an island of forest surrounded by pasture and cultivated land, La Selva was successfully connected to the larger Braulio Carrillo National Park to the south at the beginning of the 1990s. Further details are available on the Web pages maintained by the OTS in Costa Rica.
Long-term climate data comprises mostly daily precipitation records, rainfall at the Rafael's Point station on the forest edge being consistently lower than the later more centrally-located East Bank station, which has consistent climatology for 1984-97. March is normally the driest month, with peak rainfall occurring in June/July and November/December. Daily climate data have been collected since 1992 by OTS, and pseudo-daily maximum-minimum temperature data (April 1984 - March 1997) based on cross-correlation with a nearby station are available from Dr. D. A. Clark (see below).
Detailed data on forest dynamics are available for three 4-hectare long-term forest inventory plots established in 1969 and re-measured in 1982, 1985, and 1990. However, the only reliable components of NPP at present are several estimates of litterfall (800-900 g/m2/year). Estimates of tree growth increment made since 1982 are regarded as more reliable than earlier estimates. High rates of net nitrogen mineralisation have been reported, together with low soil phosphorus availability.
A new long-term NPP study commenced in September 1997. Eighteen 0.5-ha plots were stratified across La Selva's major edaphic gradients, and on-going measurements include: tree mortality and recruitment, aboveground biomass increment, fine litterfall, fine woody litterfall, annual input of coarse woody debris, and fine root biomass (0-50 cm depth). Soil organic carbon stocks have been assessed on the two principal soil types, soil respiration has been measured biweekly since March 1998, and forest carbon exchange has been studied with continuous eddy covariance measurements from an above-canopy tower, for the 3 years from March 1998 to March 2001. Details of carbon flux measurements at La Selva, and access to data from other sites, are available through the FLUXNET pages maintained by the ORNL DAAC.
A crude minimum estimate of NPP for La Selva may be obtained by summing the estimates of litterfall (850 g/m2/year) and unpublished data on root production (550-1250 g/m2/year), giving a range of about 1400-2100 g/m2/year.
Tel. +506 766-6565 ext. 147
Fax +506 766-6535
E-mail: daclark@sloth.ots.ac.cr
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references and summaries for the La Selva site.