Variation in Organ Biomass with Changing Climate and Forest Characteristics across Chinese Forests

Forest biomass allocation patterns are important for understanding global carbon cycling and climate change, which might change with environmental conditions and forest characteristics. However, the effects of climate and forest characteristics on biomass allocation fractions (the fraction of total forest biomass distributed in organs) remains unknown. The authors use a large Chinese biomass dataset (1081 forests encompassing 10 forest types) to analyse the responses of biomass allocation fractions to biogeography, climate, and forest characteristics. The authors found that the stem mass fraction significantly increased with age and precipitation and significantly decreased with latitude and temperature. The branch mass fraction significantly decreased with age and density, but significantly increased with temperature and latitude. The leaf mass fraction significantly decreased with age and precipitation and significantly increased with temperature. The root mass fraction significantly increased with latitude and density, and significantly decreased with precipitation. The results suggest that latitude, temperature, precipitation, stand age and density are good predictors of biomass partitioning. These findings support the hypotheses that variation in resource availability constrains organ allocation and provides biogeographically explicit relationships between biomass allocation and both environmental and forest characteristics, which might be used for assessing the impact of changing environmental and forest characteristics on forest carbon dynamics and fixation.

Relative importance of overstory canopy openness and seedling density on crown morphology and growth of Acer nipponicum seedlings

We investigated the effects of overstory canopy openness and seedling density on seedling morphology and growth in the mid-successional species Acer nipponicum Hara in a cool-temperate forest. Studied seedlings were 46 seedlings of 30–160 cm height, and their overstory canopy openness ranged between 7.2% and 17.0%. Seedling density, measured as the number of conspecific neighboring seedlings within a 50 cm radius of the target seedling, ranged between 0 and 19. There were no significant correlations between seedling height, canopy openness, and seedling density. Multiple regression analysis showed that crown depth, leaf mass fraction, and leaf area index decreased with decreasing canopy openness and increasing seedling density, while the ratio of trunk-lateral branches mass increased. Overstory canopy openness did not affect crown area, leaf size, or petiole length, all of which decreased with increasing seedling density. Standardized regression coefficients indicated that seedling density affected morphology and growth more than canopy openness did. The morphological responses to canopy openness cannot be considered as adaptive plasticity, as total leaf area and leaf mass fraction decreased with decreasing light levels. In contrast, responses to seedling density indicate adaptive responses to neighborhood competition. The results highlight the importance of seedling density that influenced seedling growth and morphology independently of overstory canopy openness.

Climbing strategies determine light availability for both vines and associated structural hosts

This study investigated biomass allocation traits and shading impact of vines (ground-rooted climbing plants) on their hosts in a tall open forest understorey community (Blue Gum High Forest) in Sydney, Australia. Eighty-six vine individuals from 11 species (7 natives and 4 exotics) were recorded and sampled on 26 individuals from 5 host species. All host species sampled were <3 m in height. Each recorded climber was assigned to one of the five established climbing strategies: tendril climber, petiole climber, stem twiner, scrambler or root climber. No root climbers were recorded. Each species was also recorded as native or exotic. We measured shading effects of the different climbing strategies by removing vines from their hosts and measuring the change in canopy openness (diffuse non-interceptance, DIFN) above the host. Vines had significantly greater specific leaf area than their hosts. The most abundant climbing strategy was stem twining, followed by scrambling, petiole twining and tendril climbing. Leaf mass fraction (leaf mass per total aboveground biomass) did not differ among climbing strategies or between natives and exotics. Vines reached taller heights on taller hosts and the percentage of host’s shoot height reached differed significantly among climbing strategies: petiole twiners and scramblers reached the largest percentage host shoot height (97% and 92%, respectively) whereas stem twiners and tendril climbers reached 68% and 61%, respectively. Total relative shading of the host increased significantly with increasing vine biomass. There were significant differences between climbing strategies in the shading imposed on hosts. In the context of average canopy openness above the understorey for this site (24%), scramblers reduced light availability to their hosts by nearly 25%, compared with petiole-tendril twiners (14%) and stem twiners (8%). Thus, climbing strategies differentially shape the light environment available to their structural hosts.