Effects of biophysical constraints, climate and phylogeny on forest shrub allometries along an altitudinal gradient in Northeast China

Abstract

Whether there is a general allometry law across plant species with different sizes and under different environment has long been controversial and shrubs are particularly useful to examine these questions. Here we sampled 939 individuals from 50 forest shrub species along a large altitudinal gradient. We tested several allometry models with four relationships simultaneously (between stem diameter, height, leaf, stem and aboveground biomass), including geometric, elastic and stress similarity, and metabolic scaling theory’s predictions on small plants (MSTs) and trees (MSTt). We also tested if allometric exponents change markedly with climate and phylogeny. The predicted exponents of MSTt, elastic similarity and stress similarity (models for trees) were not supported by our data, while MSTs and geometric similarity gained more support, suggesting the finite size effect is more important for shrub allometries than being a woody plant. The influence of climate and phylogeny on allometric exponents were not significant or very weak, again suggesting strong biophysical constraints on shrub allometries. Our results reveal clear differences of shrub allometries from previous findings on trees (e.g. much weaker climatic and phylogenic control). Comparisons of herbs, shrubs and trees along a same climatic gradient are needed for better understanding of plant allometries.

Developing Allometric Equations for Estimating Shrub Biomass in a Boreal Fen

“…Our testing indicated that the relationship between basal diameter and aboveground biomass did not differ significantly across genera, and that there was no significant difference between phylogenetic equations and the general equation developed for our study area. These findings are similar to Sun et al [31], who found phylogeny to exert little influence on allometric coefficients for shrubs in China. In our study area, the physical differences were most apparent between Alnus and Betula.Alnus individuals, in comparison with the other two genera, had a more tree-like appearance, were generally larger and had a lower number of stems, whereas Betula individuals were much smaller and many-stemmed ( Table 1).…”

“…For example, Berner et al [28] found that allometric relationships for dwarf birch (Betula nana L.) varied little across forest and tundra ecosystems in Siberia and Alaska. Other authors [29][30][31] have emphasized the controls of plant size on allometrics, highlighting the importance of remaining within the size domain of the equations. Portability of equations is important in allometric studies because an equation that can be used across multiple regions can greatly reduce the amount of time, labor, and destructive sampling involved with biomass estimation.…”

Are fine roots ‘leaves underground' in terms of allometry? A test in a tropical forest successional series in southwest China

“…Current MST has extended the MST w model and has proposed models with flexible exponent (flexible MST, hereafter) which can explain the variation of allometry with environmental gradient and species composition (Niklas and Spatz 2004, Enquist et al 2007a). The flexible MST suggests that the allometry of vascular plants is a continuum that varies with plant size: the scaling exponents for herbs and shrubs conform to the MST's predictions for small plants (Niklas 2004, Sun et al 2017a), but gradually changed to be closer to the predictions of MST w with increasing tree size (Niklas and Spatz 2004, Enquist et al 2007a, Duncanson et al 2015). The flexible MST further suggests that plant size is the main driver of changes in allometry, and the observed significant changes of scaling exponents with species composition and climate may be simply caused by the fact that species composition and environmental gradients affect tree size, which in turn lead to changes in allometry (Niklas and Spatz 2004, Price et al 2007).…”

“…root mass versus diameter), we explained log‐Y using log‐X together with other explanatory terms as follows: 1) the potential factors affecting allometries we selected above for SEM (i.e. total biomass, MDS1, stand density and soil bulk density); 2) the interactions between log‐X and each of the potential factor, which were used to test whether the allometric exponents were significantly affected by tree size, species composition, competition and environmental factors (Sun et al 2017a); 3) we also used plot as a random effect in GLMM, because the nine samples cored from a same plot were statistically not fully independent. We conducted GLMM with the R package of lme4 (Bates et al 2015).…”

Effects of climate, biotic factors, and phylogeny on allometric relationships: testing the metabolic scaling theory in plantations and natural forests across China

“…However, we also found that these effects were weak, which means that biophysical constraints still strongly influence allometric relationships. This may explain why the effect of external factors was almost insignificant over a small gradient in some studies (Poorter et al 2012;Sun et al 2017b).…”