Inventory of the degree of tree defoliation in small areas

Abstract

The employment of small-area surveys for evaluating forest health is becoming increasingly important because in recent years, new ecological methods of management and conservation have been introduced in commercial forests and in the partial protection zones of national parks. In Poland, in relatively small areas, including forest sections, nature reserves or their fragments, close-to-nature management and near-natural management have been introduced and, in protected areas, typical partial protection is giving way to passive protection. Radical changes in the ways of management and conservation have developed a need for monitoring possible changes in the condition of trees, mainly through the application of precise, small-area methods for assessing their health. The aim of this paper is to present a small-area survey for assessing the degree of tree defoliation and its preliminary verification, in particular the evaluation of the degree of defoliation to fir ( Abies alba Mill.), beech ( Fagus sylvatica L.), pine ( Pinus sylvestris L.), larch ( Larix decidua Mill. subsp. polonica [Racib.] Domin) and oaks ( Quercus robur L. and Q. petraea [Matt.] Liebl.) on Chełmowa Góra Hill in the Świętokrzyski National Park (Poland). Part of the area of Chełmowa Góra comprises a strict nature reserve, set up in 1921, which is one of the oldest strict nature reserves in Poland. The area of Chełmowa Góra is slightly more than 183 ha. The degree of tree damage, determined on the basis of the degree of defoliation, was shown in sub-blocks P 3 of the system of information on natural environment (SINUS). To estimate the spatial distribution of the degree of tree defoliation, survey sampling – based on the scheme of simple random sampling with replacement (SRSWR) – was used. In 1999, Chełmowa Góra's beech and larch were in the best condition, and the worst were young-generation fir, pine and oak. During preliminary verification of the applied method, the mean total errors of the evaluation of proportions of trees in the distinguished defoliation classes, calculated as α = 0.05, reached almost 31% in particular sub-blocks P 3 of the SINUS system; however, in most cases they did not exceed 20%. The average values of mean total errors, calculated for particular tree species in all sub-blocks P 3, were generally lower than 20%. The applied method of inventory enables the assessment of the degree of defoliation and spatial differentiation of tree health in small areas, which in turn, allows the detailed planning of protection and silvicultural measures. The proper assessment of the extent of tree defoliation and its spatial distribution is of fundamental importance for employing the ecological methods of management and rational protection of forest ecosystems, and should be included in the monitoring of both economically used and protected forests.