Abstract
The objective of this study was to develop the models that predict both timber and branch volumes of Norway spruce (Picea abies/L./Karst.), the most abundant tree species in Europe, and determine the relationships among timber and branch volumes and various site and stand characteristics. The data used in this study come from 76 sample plots in the different stands and site conditions across Norway spruce forests in the Czech Republic. Timber volume was determined by Huber’s formula and branch volume (logging residue) was determined by drying and weighing of 10 samples from the 10-chipped trees on each sample plot, meaning that a total of 760 samples were analyzed. The results showed that timber volume was significantly positively correlated with branch volume, mean diameter at breast height (mean DBH) per sample plot, mean height per sample plot, slope of sample plot, and stand age, but negatively correlated with stand stocking. The branch volume was more significantly affected by stand stocking than timber volume. The timber-to-branch volume ratio (TBR) reached the mean value of 3.7 (±0.14 SE) and significantly increased with increasing elevation. The trees on the nutrient-rich sites were characterized by higher branch volume, while TBR reached higher values on the acid sites. Site quality class had a significant effect only on the branch volume production. Compared to the timber volume (root mean square error, RMSE = 3.6176; adjusted coefficient of determination, R2adj = 0.7310), the branch volume was relatively poorly described by the model (RMSE = 1.928; R2adj = 0.2517). The volume prediction models show that timber volumes increase with increasing slope and branch volume increases with decreasing site quality class. For effective forest management practice, the highest branch volume in favor of timber production is characterized for lowland forests with stand stocking ≤60% (TBR 1.5), while the highest share of timber volume (TBR 9.5) can be reached in the mountains with a full stand stocking.
Highlights
Plant biomass has been becoming one of the popular energy sources [1,2] and it has a significant contribution to the nonproductive functions as well [3,4]
Elevation, and timber-to-branch ratio (TBR), all other variables were significantly correlated with timber volume (Table 2)
Both slope and aspect showed very small effect on timber volume (p < 0.09), but aspect did not show any significant effect on the timber volume, branch volumes, and to-branch volume ratio (TBR)
Summary
Plant biomass has been becoming one of the popular energy sources [1,2] and it has a significant contribution to the nonproductive functions as well [3,4]. Its value as a source of energy has increased in recent years because of the trends based on the principles of sustainable development The important objective of the EU and its member countries including the Czech Republic is to increase the share of renewable energy sources that help reach sustainable development and independence [6]. There are other reasons for using a larger amount of plant biomass due to the tax relief, subsidy supports, and availability of the plant biomass sources in each member country. The dendromass is a part of the plant biomass which covers a huge portion of total available biomass sources. The heat from burning wood waste is cheaper than fossil fuels, as derived primarily from the local sustainable sources [7,8]. In forestry, a specific type of the dendromass, which is known as logging residues or small wood, is usually considered as an alternative energy source
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