Abstract
We used our database of tree biomass with a number of 433 sample trees of Larix from different ecoregions of Eurasia, involving 61 trees from Mongolia for developing an additive model of biomass tree components. Our approach solved the combined problem of additivity and regionality of the model. Our additive model of tree aboveground biomass was harmonized in two ways: first, it eliminated the internal contradictions of the component and of the total biomass equations, secondly, it took into account regional (and correspondingly species-specific) differences of trees in its component structure. A significant excess of larch biomass in the forest-tundra is found that may be explained by permafrost conditions, by tree growth in low-yielding stands with a high basic density of stem wood and relatively high developed tree crown in open stands. The aboveground biomass of larch trees in Mongolia does not stand out against the background of the most ecoregions of Eurasia. Based on our results, we conclude that the growing conditions of larch in Mongolia are not as tough as it was suggested earlier by other scientists. Biomass relations between regions may be explained by unknown and unaccounted factors and errors of measurements in all their phases (assessment of age, diameter, height of a tree, the selection of supposedly representative samples of component biomass, their drying, weighing, etc.). The question what explains the regional differences in the structure of biomass of trees with the same linear dimensions of their stems, remains open. Undoubtedly, the differences in tree age here play an important role. Also, important factor is the variation in the morphological structure of stands, which, in turn, is determined by both climatic and edaphic factors. The obtained models allow the determination of larch forest biomass in different ecoregions of Eurasia with the help of height and diameter data.
Highlights
Forest ecosystems play an important role as sinks of atmospheric carbon
The regression method of estimating forest biomass when using the results of sampling of model trees, was represented in the whole range of stem diameters is the current standard (Marklund 1983)
Since it has been established that the elimination of the internal inconsistency of biomass equations by ensuring their additivity does not necessarily mean the increase in the accuracy of its estimates (Cunia and Briggs 1984; Reed and Green 1985), it is necessary to clarify whether the obtained additive model (AM) is adequate enough and how its characteristics relate to the indices of the adequacy of initial equations
Summary
Since a significant part of forest cover has been represented by mixed forests, for the correct estimation of their biological productivity in many cases allometric models of biomass are needed, developed at a tree level. In conditions of continuously increasing biosphere function of forest cover of the planet, there is a trend related to the harmonization of allometric models of tree biomass, that is fulfilled either by involving dummy variables into a model (Jacobs and Cunia 1980; Fu et al 2012; Zeng 2015), or by providing additive component composition (Kozak 1970; Parresol 2001; Zheng et al 2015; Zhang et al 2016). According to Sanquetta et al (2015), independent (without additivity) fitting of coefficients for biomass components and total biomass is not satisfactory, but this is not observed in case when the simultaneous fitting is used, accounting the additivity principle and resulting in more effective estimators
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