We evaluated the impacts of site type, fertilization, and climate on the relationship between foliage biomass and cross-sectional area at the tree crown base, referred as to the pipe model ratio. The pipe model approach was compared with foliage biomass models by using the cross-sectional area at the tree crown base for predicting foliage biomass of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.).
Our study (1) provides information applicable to predictions of growth and biomass allocation in old boreal stands and (2) suggests taking age effect into account when structure equations are implemented in forest growth models. (2) PMT-based structure equations were well-suited to Scots pine and Norway spruce in all age groups however, age dependence was detected in the parameters of these equations, except for the branch-related equations in Scots pine and stem form coefficient below the crown base in both species. (1) Stem biomass proportion increased with age, while branch and foliage biomass proportion decreased biomass allocation and most tree variables became steady after maturing.
Biomass of stem, branch and foliage was estimated from destructive measurements, and with other tree dimensions, they were used to present the tree growth patterns. This study (1) tested the age independence of the PMT-based structure equations and (2) provided general information about the stability of tree structure with age.Ī total of 162 Scots pine and 163 Norway spruce trees in four age groups were analysed to test the age effect on the parameters of structure equations using a linear mixed model. However, more data concerning old-growth trees is needed to test the reliability and generality of the structure equations. Pipe model theory-based (PMT-based) structure equations have been incorporated in many process-based models. However, age dependence of parameters should be accounted for when applying the equations. Tree structure equations derived from pipe model theory (PMT) are well-suited to estimate biomass allocation in Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies Karst.). We were able to predict changes in the branchiness of the tree but not in the foliage mass supported per unit of branch area. Models based on Φ were simpler, since no other variables were able to explain between-stand variation in the presence of Φ. Models based on absolute height or tree diameter were usually weaker. The relative height of a tree in the stand (Φ) was the major factor that determined the variation in the relationship between the branch cross-sectional area and the stem cross-sectional area. The lowest site fertility class had a higher foliage mass to stem area ratio than better sites. We studied how these relationships varied within and between stands. Our analysis allowed a separation of the relationship between stem and branch cross-sectional areas and the relationship between the branch cross-sectional area and foliage mass. We investigate how the foliage mass to wood area ratios depend on tree and stand characteristics of previously collected data from Scots pine (Pinus sylvestris L.).
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