A national forest resources assessment for Costa Rica based on low intensity sampling

Abstract

A goal of a National Forest Inventory (NFI) is the provision of information which is relevant and required for national level decision making and monitoring in forestry, but also for related sectors. This paper presents and discusses a pilot study from Costa Rica where in 2000/2001 a low intensity sampling approach was used to generate national level forestry information. On a 15 km × 15 km grid air photo plots were interpreted for forest and land cover type. Readily available 1997 aerial photographs were used that were, however, only available for about 70% of the country: of the 228 grid points for the whole country only 159 could be aerial photo interpreted. Out of the 15 km × 15 km base grid of sample points, a 2 × 3 subset was selected for field assessment, resulting in a sample of 40 cluster plots, each comprising of four elongated rectangular sub-plots of 150 m × 20 m located on the perimeter of a square of 500 m side length. Two novel components were integrated into the inventory: (1) the field plots were established on all lands, so that the tree resource was not only tallied inside forests but also on all other tree-bearing lands outside forests. (2) In addition to the biophysical information gathered on the traditional field plots, interviews were carried out with forest owners on the site of the field plots, in order to obtain data on the use of the forest resource. Field work was carried out by 6 field crews and took altogether about 3 months. Results were generated from the field samples for the entire country. Aerial photo based area estimates were compared to the corresponding estimations from field sampling for the same area. According to the field sampling the forest cover for Costa Rica in 2001 is estimated to be 48.4% (simple standard error percent 9.3%). An estimated 8.2% of the total volume (dbh > 30 cm, all species) is outside forest. This inventory took place with support from Food and Agriculture Organization (FAO) in the framework of FAO–Forest Resources Assessment's (FRA) Program Support to National Forest Assessments; it was carried out jointly by Sistema Nacional de Áreas de Conservación (SINAC), the Costa Rican authority responsible for forestry issues, and Centro Agronómico de Investigación y Enseñanza (CATIE), an international agricultural research center. Experiences of the study were subsequently used to implement similar inventories in three more countries (Guatemala, Cameroon, The Philippines).