Rattan inventory: determining plot shape and size

Abstract

Increased recognition of the importance of non-timber forest products has led to a need to develop inventory methods for these species. One of the most valuable non-timber forest products are rattans, the stems of climbing palms belonging to the sub-family Calamoideae and the basis of a furniture industry worth an estimated U.S.$ 6.5 billion per annum in international trade. This paper discusses the methodology for determining plot shape and size for the inventory of rattan. This methodology involves selecting a desired level of precision (e.g. a sampling error of 20%) and finding the plot shape and size which minimises the cost, in terms of time, of achieving it. Rectangular plots, oriented parallel to the direction of the slope, are more cost efficient than square plots; however, there are limits to rectangularity, as plots which are very long and narrow are prone to errors in boundary identification and area estimation. Thus, a minimum plot width of 5 m is recommended. The most cost efficient plot size ranges from 0.0025 ha to 0.025 ha, and is positively correlated with the desired sampling error, the total area under inventory, and the plot rectangularity. It also varies with the parameter(s) being assessed. The sample size is then determined by the plot size.