Large plants enhance aboveground biomass in arid natural forest and plantation along differential abiotic and biotic conditions

Abstract

Big-sized trees, species diversity, and stand density affect aboveground biomass in natural tropical and temperate forests. However, these relationships are unclear in arid natural forests and plantations. Here, we hypothesized that large plants (a latent variable of tall-stature and big-crown, which indicated the effect of big-sized trees on ecosystem function and structure) enhance aboveground biomass in both arid natural forests and plantations along the gradients of climate water availability and soil fertility. To prove it, we used structural equation modeling (SEM) to test the influences of large plants located in 20% of the sequence formed by individual size (a synthetical value calculated from tree height and crown) on aboveground biomass in natural forests and plantations while considering the direct and indirect influences of species diversity as well as climatic and soil conditions, using data from 73 natural forest and 30 plantation plots in the northwest arid region of China. The results showed that large plants, species diversity, and stand density all increased aboveground biomass. Soil fertility declined aboveground biomass in natural forest, whereas it increased biomass in plantation. Although climatic water availability had no direct impact on aboveground biomass in both forests, it indirectly controlled the change of aboveground biomass via species diversity, stand density, and large plants. Stand density negatively affects large plants in both natural forests and plantations. Species diversity positively affects large plants on plantations but not in natural forests. Large plants increased slightly with increasing climatic water availability in the natural forest but decreased in plantation, whereas soil fertility inhibited large plants in plantation only. This study highlights the extended generality of the big-sized trees hypothesis, scaling theory, and the global importance of big-sized tree in arid natural forests and plantations.

Aboveground Biomass Prediction of Plots in the Natural Forests of Arid Mountains Based on Large Trees

“…Previously, studies based on 73 plots ranging from 25 to 400 m 2 in the arid northwestern region have demonstrated that the upper 20% of large vegetation contributes to an impressive 59.25% of the total plot AGB [25]. This outcome is corroborated by the findings of this research.…”

“…In the arid region of Northwestern China, a recent study utilized structural equation models to investigate the influence of the top 20% of large trees on AGB in both natural and artificial forests. The findings underscore the substantial contribution of large trees to forest biomass, underscoring their significance in arid region ecosystems [25]. Nevertheless, there is currently no established prediction model for AGB specific to large trees in arid regions.…”

“…There exists no universally accepted definition for "large trees" [16,26]. In the current relevant studies, the definition of large trees depends on the species and forest types [25]. In tropical forests, trees with a diameter at breast height (DBH) greater than 100 cm are often referred to as large trees; in temperate deciduous forests, large trees may have a DBH of 60 cm or more.…”

Precipitation and Temperature Influence the Relationship between Stand Structural Characteristics and Aboveground Biomass of Forests—A Meta-Analysis

“…Particularly in even-aged stands that regenerated after fire, since the relationship between competition and habitat conditions are more complicated, the association of TD and AGB might be affected by insect outbreak or windthrow [68]. TD significantly affected AGB in temperate forest, consistent with the findings of Yang et al [69]; meanwhile, an allometric relationship of TD and AGB was found within this biome. Most likely, community type and species diversity should be considered, such as in broadleaf and conifer forests or mixed forests [70], since trees' biological traits (e.g., leaf area, thickness) may regulate different nutrient uptake and partitioning.…”