Soil water content and nitrogen differentially correlate with multidimensional leaf traits of two temperate broadleaf species

The variation and correlation of leaf economics and vein traits are crucial for predicting plant ecological strategies under different environmental changes.However,correlations between these two suites of traits and abiotic factors such as soil water and nitrogen content remain ambiguous.We measured leaf economics and vein traits as well as soil water and nitrogen content for two different shade-tolerant species(Betula platyphylla and Acer mono)in four mixed broadleaved-Korean pine(Pinus koraiensis)forests along a latitudinal gradient in Northeast China.We found that leaf economics traits and vein traits were decoupled in shade-intolerant species,Betula platphylla,but significantly coupled in a shadetolerant species,A.mono.We found stronger correlations among leaf traits in the shade tolerant species than in the shade intolerant species.Furthermore,leaf economic traits were positively correlated with the soil water gradient for both species,whereas vein traits were positively correlated with soil water gradient for the shade intolerant species but negatively correlated in the shade tolerant species.Although economic traits were positively correlated with soil nitrogen gradient in shade intolerant species but not correlated in shade tolerant species,vein traits were negatively correlated with soil nitrogen gradient in shade tolerant species but not correlated in shade intolerant species.Our study provides evidence for distinct correlations between leaf economics and vein traits and local abiotic factors of species differing in light demands.We recommend that the ecological significance of shade tolerance be considered for species when evaluating ecosystem functions and predicting plant responses to environmental changes.

Effects of gaps on regeneration of woody plants: a meta-analysis

Forest gaps, openings in the canopy caused by death of one or more trees, have a profound effect on forest regeneration and drive the forest growth cycle. It is therefore necessary to understand the effects of forest gaps on regeneration for modern forest management. In order to provide a quantitative assessment of the effects of forest gaps on regen-eration of woody plants, we conducted this review of gap effects on woody plant regeneration on the basis of 527 observations from 42 indi-vidual papers, and reported the results of these data in a meta-analysis. Overall, densities of regenerated woody plants were significantly greater （359%） in forest gaps than on the closed-canopy forest floor. The regen-eration density in gaps of plantation forests was significantly greater （P＆lt;0.05） than that of natural forest because the regeneration in gaps of plan-tation forests was improved by both gap effects and experimental meas-ures. Similarly, in comparison to natural gaps, regeneration was better enhanced in artificial gaps. Regeneration density exhibited a significantly positive correlation with gap size, but a negative correlation with gap age because the gap size decreased with increasing gap age. Shade tolerance of woody plants affected regeneration density in gaps and understory. Average regeneration density of shade-tolerant species exhibited a sig-nificantly positive response to gaps but densities remained lower in total than those of intermediate and shade-intolerant species. Gap effects on regeneration decreased in response to increasing temperature and pre-cipitation because of the limiting effects of lower temperature and moisture on woody plant regeneration. In summary, forest gaps enhance woody plant regeneration, and the effects of gaps varied by forest type, gap characteristics, environmental factors and plant traits. The results of this meta-analysis are useful for better understanding the effects and roles of gaps on forest regeneration and forest management.

Height growth, diameter-height relationships and branching architecture of Pinus massoniana and Cunninghamia lanceolata in early regeneration stages in Anhui Province, eastern China: effects of light intensity and regeneration mode

To determine the growth strategies during early regeneration stages of two major coniferous species （Pinus massoniana and Cunninghamia lanceolata） in a secondary mixed coniferous forest in the Huangshan region of Anhui Province, eastern China, we examined height growth, diameter-height relationship and the relationship between main stem and lateral branch elongation in saplings, with a particular focus on the effects of light intensity and regeneration mode （seedlings versus sprouts）. When light intensity was sufficiently high, the extension growth of main stems was greater and more positively related to initial size for P. massoniana than for C. lanceolata. The slenderness of the stem form increased in the following order： C. lanceolata seedlings 〈 P. massoniana seedlings 〈 C. lanceolata sprouts. P. massoniana became less slender with increasing light intensity. P. massoniana had shorter branches than C. lanceolata given the same main stem elongation. Growth allocation depended more strongly on light intensity for P. massoniana than for C. lanceolata, with more growth allocated to the main stem under dark conditions. These results suggest that P. massoniana is a typical shade avoider; this species gives priority to extension growth of the main stem, especially when it is shaded. In contrast, C. lanceolata is a shade tolerator; this species allocates more biomass to radial growth of its main stems and to extension growth of branches. Based on these results, the ecological characteristics of P. massoniana and C. lanceolata and the roles of seedlings and sprouts are discussed in relation to stand dynamics of the mixed forests of P. massoniana and C. lanceolata in eastern China.

Afforestation,restoration and regeneration——Not all trees are created equal

Undulations in weather patterns have caused climate shifts of increased frequency and duration around the world. The need for additional research and model data on this pressing problem has resulted in a plethora of research groups examining a particular tree species or biome for negative effects of climate change. This review aims to （1） collect and merge recent research data on regeneration within old- and new-growth forests, （2） highlight and expand upon selected topics for additional discussion, and （3） report how shade tolerance, drought toler- ance, and inherent plasticity affect tree growth and development. Al- though shade and drought tolerance have been well studied by a number of research groups, this review reveals that in-depth analysis of a single or a few species in a given area will not generate the data required to implement a successful regeneration plan. Studies using historical accounts of previous species composition, information regarding site sea- sonality, species competition, and individual responses to drought and shade are needed to （1） develop best management plans and （2） ensure future modeling experiments are focused on a greater variety of species using more innovative methods to evaluate climate change effects.

Tree diversity effects on forest productivity increase through time because of spatial partitioning

Background: Experimental manipulations of tree diversity have often found overyielding in mixed-species plantations. While most experiments are still in the early stages of stand development, the impacts of tree diversity are expected to accumulate over time. Here, I present findings from a 31-year-old tree diversity experiment(as of2018) in Japan.Results: I find that the net diversity effect on stand biomass increased linearly through time. The species mixture achieved 64% greater biomass than the average monoculture biomass 31 years after planting. The complementarity effect was positive and increased exponentially with time. The selection effect was negative and decreased exponentially with time. In the early stages(≤ 3 years), the positive complementarity effect was explained by enhanced growths of early-and mid-successional species in the mixture. Later on(≥ 15 years), it was explained by their increased survival rates owing to vertical spatial partitioning — i.e. alleviation of self-thinning via canopy stratification. The negative selection effect resulted from suppressed growths of late-successional species in the bottom layer.Conclusions: The experiment provides pioneering evidence that the positive impacts of diversity-driven spatial partitioning on forest biomass can accumulate over multiple decades. The results indicate that forest biomass production and carbon sequestration can be enhanced by multispecies afforestation strategies.

Effects of light availability on leaf attributes and seedling growth of four tree species in tropical dry forest

Background:In tropical dry forests,variation in understory light availability due to season and canopy tree density could be a governing factor in establishment and growth of tree seedlings.Species with varying life history traits are expected to respond differentially to such heterogeneity.We investigated the response of seedlings of four tree species in a tropical day forest in relation to spatiotemporal variability of light.We attempt to explore the role of leaf attributes in explaining intra-and inter-specific variations in relative growth rate.Four study sites,each with three contrasting canopy conditions,were selected along a soil moisture gradient.Seedlings of four tree species(viz.,Acacia catechu,Bridelia retusa,Lagerstroemia parviflora,and Shorea robusta),varying in life history traits,were monitored for seasonal variations in growth traits across canopy condition and sites for 2 years.Results:We observed a larger variation in leaf attributes for pioneer species.A.catechu showed highest mean values for leaf dry matter content,leaf nitrogen concentration,leaf phosphorus concentration,net stomatal conductance,net photosynthetic rate,and relative growth rate in high light conditions.S.robusta and B.retusa demonstrated highest mean values for all the leaf attributes(except leaf dry matter content)in low light conditions.However,intermediate values for leaf attributes were observed in L.parviflora which preferred moderate light conditions.Conclusions:Seasonal variations in light availability at the forest floor appear to play an important role in the establishment and growth of tree seedlings in seasonal dry forests.Leaf attributes can be used to explain intra-and inter-specific variation in response to light availability.Leaf attributes in combinations can be used to predict relative growth rate of tree species in tropical dry environment,which apart from soil moisture is also determined by light availability due to seasonal changes and canopy tree density.