Model to define the sampling unit size for forest inventories

Abstract

The objective was to determine the minimum size of the sampling unit or plot that allows for a sufficient estimation of forest inventory parameters such as floristic diversity or richness, timber volume, basal area, biomass, carbon, etc., in the primary alluvial and low hill forests of the Itaya and Tahuaya river basins, Maynas, Loreto. The species–area curve model was applied, which consisted of the cumulative recording of tree and arborescent palm species through square subplots of 400 m², forming a block or grid of subplots. The model generated logarithmic curves for each of the six evaluated grids and by forest type. In general, the curves show a steeper slope with the accumulation of the first subplots, due to a significant increase in the number of recorded forest species. As more subplots are added, the slope of the curve decreases because fewer new species are recorded. The minimum required number of subplots corresponded to the point of greatest inflection on the curve, which represents increments of 1.5–2% in species richness. On average, 20 accumulated subplots (0.78 ha) were needed for the alluvial forest, and 19 subplots (0.76 ha) for the low hill forest.