A new technique for inventory of permanent plots in tropical forests: a case study from lowland dipterocarp forest in Kuala Belalong, Brunei Darussalam

This paper describes a new technique for inventory of permanent plots in tropical forests and presents the results of its application in a 1 ha permanent plot in a lowland dipterocarp forest at Kuala Belalong, Ulu Temburong National Park, Brunei Darussalam. The technique is based on mapping of positions of tree individuals in three-dimensional space with a high accuracy. Measuring set consists of a distance measuring device (laser rangefinder) and a electronic compass supplying data to a field computer with specialized software (Field-Map®). This method is faster and more exact than methods based on Cartesian grids established in the field. As an example, inventories from 2000 and 2007 of the plot mentioned are compared concerning presence, taxonomical identity and diameter at breast height (dbh) of all tree individuals with dbh ≥ 5 cm. The structural and diversity properties of the forest show similar patterns to the other two permanent plots in Kuala Belalong. In 2007, 1 318 trees were found, out of which 116 were new individuals (i.e. exceeded the 5 cm dbh limit since 2000), 13 were dead individuals. 120 trees died since 2000 (9.2 % of the trees recorded in 2000). Total basal area was 39.18 m² (0.2 m² were dead individuals). Growth dynamics has distinct spatial patterns: about half of the plot shows fast dbh increment in 2000–2007 and appearance of numerous new trees; the other half displays stagnation. This is probably due to topographic conditions and partly to the gap dynamics (several dominant trees have fallen there since 2000). Concerning the taxonomic composition, 47 families were recorded, the dominant ones in terms of basal area being Dipterocarpaceae, Myrtaceae, Euphorbiaceae, Lauraceae, Sapotaceae and Burseraceae (sorted in decreasing order). The Dipterocarp family accounts for about 40 % of the total dbh. The most frequent ones were trees of Euphorbiaceae, Dipterocarpaceae, Myrtaceae, Burseraceae and Anacardiaceae. However, this census concerns mainly trees with dbh ≥ 10 cm, while the rest (dbh 5–10 cm) remained partly undetermined until 2007.