Analysis of tree competition and structural indices with a focus on modelling Silver birch (Betula pendula Roth) stands

A Thesis for applying for the degree of Doctor of Philosophy in Forestry The thesis is designed to establish and assess different approaches of competition measurement, incorporated with various competitor selection methods, focusing on silver birch in Estonia. The effect of competition and some other tree and stand variables on the growth and the mortality of trees are explored. Moreover, stands are characterized employing several structural indices calculated for sample plots of different shapes and sizes. The findings indicate that the measures including the trees spatial information, have superiority over the measures ignoring the trees locations within a forest stand, when studying the dynamics of stands and their effects on the structure and functioning of forest ecosystems. Also, plots with different shapes showed almost equal estimation accuracy, thus circular plots are preferred due to their smaller ratio of perimeter to surface. Besides, the optimum plot size depends on the stand structure, with an attempt to keep sample plots as small as possible to reduce the assessment efforts and costs. Doktoritöö eesmärgiks on uurida erinevaid meetodeid puudevahelise konkurentsi hindamiseks ja konkurentpuude kindlakstegemiseks eelkõige Eestis kogutud arukase puistute andmetele tuginedes. Põhjalikumalt uuriti puudevahelise konkurentsi ning puude ja puistu takseertunnuste seoseid puude kasvu ja suremusega. Lisaks kirjeldati puistute seisundit mitmete struktuuriindeksite abil erineva suuruse ja kujuga proovialasid kasutades. Töö tulemused näitavad, et puistute dünaamika uurimisel on puude ruumilist paiknemist arvestavatel tunnustel eeliseid võrreldes tunnustega, mis ei arvesta puude ruumilist paiknemist. Erineva kujuga proovialad andsid takseertunnuste hinnangu küll sarnase täpsusega, kuid ringikujulisi proovialasid tuleks eelistada nende ümbermõõdu-pindala väiksema suhtarvu tõttu. Optimaalne prooviala suurus sõltub puistu struktuurist, kuid proovialad tuleks siiski valida võimalikult väiksena, et vähendada mõõtmistele kuluvat aega ja vahendeid. Publication of this dissertation is supported by the Estonian University of Life Sciences and by the Doctoral School of Earth Sciences and Ecology created under the auspices of the European Social Fund.