A decompositional stand structure analysis for exploring stand dynamics of multiple attributes of a mixed-species forest

Abstract

Forest dynamics is a particularly important issue as it describes changes in forest structure over time. Forest structure can be presented from using the attributes of age, diameter, height, abundance, density, etc. During the last few decades, most research has focused on these attributes separately while rarely investigating the dynamics of multiple attributes. This was due to the lack of an appropriate algorithm for this particular purpose. Recently, more attention has been given to investigation of the inter-species dynamics within a mixed forest. The traditional method of probability density function (PDF) fitting is unable either to reveal the compositional changes or investigate competition between species within a given period of time. This paper proposes a novel approach, “Decompositional Stand Structure Analysis (DSSA)” that integrates species-based PDF fitting (SBPDFF) and growth modelling (GM) of tree-size parameters to construct a chronology of individual trees within a forest stand. This enables investigation of the features of diameter, height, and age structures and the changes in the abundance, survival, and mortality rate of the predominant species in a forest canopy. A mixed pristine forest stand primarily composed of Siberian spruce (Picea obovata) and Siberian larch (Larix sibirica) located in a riparian ecotone of boreal forest in Mongolia was used for validating the appropriateness of the DSSA prototype. Results showed that the diameter and height structure of the mixed forest stand can be described using bimodal Weibull distribution composed of a combination of two unimodal distributions contributed by the spruce and the larch respectively. Spruce was found to demonstrate reverse-J distribution while larch had approximately normal distribution. The spruce’s mortality rate followed an exponential decay model while the larch exhibited changes resembling an exponential growth model. Individuals of the spruce and the larch took 51–60 and 42–48years respectively to grow into the overstorey canopy. The results indicate that the DSSA technique is able to achieve an appropriate performance in the derivation of the dynamics of mixed species forest, thus providing information that may facilitate better conservation management.