ACTA AGRARIA DEBRECENIENSIS 2020-2 DOI: 10.34101/ACTAAGRAR/2/7900 99 Angle-count sampling method for estimating forest stand volume – a practical approach Károly Rédei 1 – Tamás Ábri 1 – Fruzsina Szabó 1 – Zsolt Keserű 2 ¹University of Debrecen Faculty of Agricultural and Food Sciences and Environmental Management, Debrecen ²National Agricultural Research and Innovation Centre - Forest Research Institute, Department of Plantation Forestry, Püspökladány keseru.zsolt@naik.erti.hu SUMMARY Point sampling, which is also known as angle-count sampling (ACS), can be considered an efficient way of estimating the basal area and volume of forest stands. It is possible to use it in forest management: providing more accurate estimates (precision <10%) of site and stand characteristics needed for management planning. 20 black locust (Robinina pseudoacacia L.) stands were selected at final cutting age to determine the regeneration criteria based on their total volume. It was verified that at P=5% there was no difference between the main volume values of stands indicated in the relevant forest plans as well as calculated by the ACS method. Keywords: forest mensuration, sampling, basal area, volume INTRODUCTION The forest stand is defined as a group of trees occupying a specific area, which is sufficiently uniform in species composition, age arrangement and condition as to be distinguishable from the forest on adjoining areas. It represents the unit for which one and the same silvicultural treatment is prescribed. Quantitative information about stand or forest compartments, therefore, relates directly to silvicultural and management decisions. Stand measurements provide information about age, mean diameter, mean and top height, stand density, stand mixture and stand composition, volume and biomass, site index, site class or yield class, present and future growth, stand quality and vitality as well as yield (Bell and Dilworth, 1990; Laar and Akca, 2007; Veperdi, 2011). Point (angle count) sampling is a method of selecting trees to be tallied on the basis of their sizes rather than by their frequency of occurrence. Sample points, somewhat analogous to plot centers, are located within a forested tract, and a simple prism or angle gauge that subtends a fixed angle of view is used to „sight in” each diameter at breast height (dbh). Tree boles close enough to the observation point to completely fill the fixed sighting angle are tallied; stems too small or too far away are ignored. The resulting tree tally may be used to compute basal areas, volumes, or numbers of trees per unit area (Hunt and Baker, 1967; Barrett, 1969; Avery and Burkhart, 1994). The probability of tallying a given tree depends on its cross-sectional area and the sighting angle used. The smaller the angle, the more stems will be included in the sample. Point sampling does not require direct measurements of either plot areas or tree diameters. A predetermined Basal Area Factor (BAF) is established in advance of sampling, and resulting tree tallies can be easily converted to basal area per unit area (Wensel et al., 1980; Oderwald, 1981). The theory and technique of point sampling, which is also known as angle-count sampling, plotless sampling, Bitterlich’s method, and relascope sampling, and is widely recognised as a breakthrough in forest mensuration, was developed by the Austrian forester Bitterlich, in 1948 (Bitterlich, 1948; Beers and Miller, 1964). In its original version, it was designed in estimate the basal area per hectare. Grosenbaugh (1958) extended the basic principle of point sampling and re-defined the method as PPS sampling (Probability Proportional to Size) (Bruce, 1955; Laar and Akca, 1997). The main aim of our study is to demonstrate how to apply the angle-count sampling method in the practice for estimating black locust (Robinia pseudoacacia L.) stand volume. This method is used as a decision aid to determine the volume of black locust stands that can be regenerated from sprout (Rédei et al., 2012; Rédei, 2015). MATERIALS AND METHODS In the area of Nagykunsági Forest Enterprise (NEFAG), Hungary, 20 black locust (Robinia pseudoacacia L.) forest subcompartments (Figure 1) in final cutting stand age were selected in order to test the accuracy of the angle- count sampling method and to compare the given black locust volume data to that of indicating in the forest plans (Figure 1). In the latter, the determination of tree volume per hectare was done by yield table (Rédei, 1984).