Zhanqing Hao

Rate of tree carbon accumulation increases continuously with tree size

Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle—particularly net primary productivity and carbon storage—increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age. Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree’s total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.

Rates and patterns of landscape change between 1972 and 1988 in the Changbai Mountain area of China and North Korea

Satellite imagery was used to quantify rates and patterns oflandscape change between 1972 and 1988 in the Changbai MountainReserve and its adjacent areas in the People‘s Republic of Chinaand North Korea. The 190,000 ha Reserve was established as anInternational Biosphere Reserve by The United Nations Educational,Scientific and Cultural Organization (UNESCO) in 1979. It is themost important natural landscape remaining in China‘stemperate/boreal climate. The images used in this research cover atotal area of 967,847 ha, about three-fourths of which is in China.Imagery from 1972 and 1988 was classified into 2 broad cover types(forest and non-forest). Overall, forests covered 84.4% of thestudy area in 1972 and 74.5% in 1988. Changes in forest coverwithin the Reserve were minimal. The loss of forest cover outsidethe Reserve appears to be strongly associated with timberharvesting at lower elevations. Landscape patterns in 1988 weremore complex, more irregular, and more fragmented than in 1972.This is one of the few studies to assess landscape changes acrosstwo countries. The rates and patterns of forest-cover loss weredifferent in China and North Korea. In North Korea, extensivecutting appears to have occurred prior to 1972 and this hascontinued through 1988 while in China, most cutting appears to haveoccurred since 1972.

Scale‐dependent relationships between tree species richness and ecosystem function in forests

1. The relationship between species richness and ecosystem function, as measured by productivity or biomass, is of long-standing theoretical and practical interest in ecology. This is especially true for forests, which represent a majority of global biomass, productivity and biodiversity.

A simulation study of landscape scale forest succession in northeastern China

Abstract Changbai Natural Reserve in northeastern China provides an excellent opportunity to explore how temperate and boreal forest ecosystems in northeastern China will evolve and recover over large spatial and temporal scales. Such studies are increasingly needed to design scientifically sound forest management and restoration plans in this region. Long-term (300 years) successional trajectories of the dominant tree species are simulated on the heterogeneous, undisturbed area (within the reserve) using a spatially explicit landscape model. We also examine the spatial and temporal constrains of landscape recovery on the human disturbed areas (surrounding the reserve). Simulation results suggest that an equilibrium in landscape structure and composition is approached on the large landtypes dominated by shade tolerant species, but not on landtypes altered by humans. Such equilibrium can be observed in spruce-fir, mountain birch, and larch forests and not in aspen-birch forests. Our results suggest that direct and indirect human impact may produce long-term alterations to forest landscape patch structure that persist for decades to centuries. For example, even with complete natural succession over 300 years, Korean pine only recovers on 1/3 of the areas in the landtypes it can dominate. We estimate a full recovery would take another 200–300 years without human disturbance. Our results also indicate that landscape-scale recovery is often limited by the available seed sources and this is particularly true for Korean pines in this region. Comparison of simulation results for the entire study area with land types (two scales) reveals the greatest variations at the land type scale. This discrepancy indicates that the ‘space-for-time’ substitutions can be flawed as species composition and age class at a given site and time may represent only the specific successional history of that site. This is particularly true for human disturbed forest landscapes where higher variations are observed.

Testing the independent species’ arrangement assertion made by theories of stochastic geometry of biodiversity

The assertion that the spatial location of different species is independent of each other is fundamental in major ecological theories such as neutral theory that describes a stochastic geometry of biodiversity. However, this assertion has rarely been tested. Here we use techniques of spatial point pattern analysis to conduct a comprehensive test of the independence assertion by analysing data from three large forest plots with different species richness: a species-rich tropical forest at Barro Colorado Island (Panama), a tropical forest in Sinharaja (Sri Lanka), and a temperate forest in Changbaishan (China). We hypothesize that stochastic dilution effects owing to increasing species richness overpower signals of species associations, thereby yielding approximate species independence. Indeed, the proportion of species pairs showing: (i) no significant interspecific association increased with species richness, (ii) segregation decreased with species richness, and (iii) small-scale interspecific interaction decreased with species richness. This suggests that independence may indeed be a good approximation in the limit of very species-rich communities. Our findings are a step towards a better understanding of factors governing species-rich communities and we propose a hypothesis to explain why species placement in species-rich communities approximates independence.

The Contribution of Rare Species to Community Phylogenetic Diversity across a Global Network of Forest Plots

Niche differentiation has been proposed as an explanation for rarity in species assemblages. To test this hypothesis requires quantifying the ecological similarity of species. This similarity can potentially be estimated by using phylogenetic relatedness. In this study, we predicted that if niche differentiation does explain the co-occurrence of rare and common species, then rare species should contribute greatly to the overall community phylogenetic diversity (PD), abundance will have phylogenetic signal, and common and rare species will be phylogenetically dissimilar. We tested these predictions by developing a novel method that integrates species rank abundance distributions with phylogenetic trees and trend analyses, to examine the relative contribution of individual species to the overall community PD. We then supplement this approach with analyses of phylogenetic signal in abundances and measures of phylogenetic similarity within and between rare and common species groups. We applied this analytical approach to 15 long-term temperate and tropical forest dynamics plots from around the world. We show that the niche differentiation hypothesis is supported in six of the nine gap-dominated forests but is rejected in the six disturbance-dominated and three gap-dominated forests. We also show that the three metrics utilized in this study each provide unique but corroborating information regarding the phylogenetic distribution of rarity in communities.

Comparative evolutionary diversity and phylogenetic structure across multiple forest dynamics plots: a mega-phylogeny approach

Forest dynamics plots, which now span longitudes, latitudes, and habitat types across the globe, offer unparalleled insights into the ecological and evolutionary processes that determine how species are assembled into communities. Understanding phylogenetic relationships among species in a community has become an important component of assessing assembly processes. However, the application of evolutionary information to questions in community ecology has been limited in large part by the lack of accurate estimates of phylogenetic relationships among individual species found within communities, and is particularly limiting in comparisons between communities. Therefore, streamlining and maximizing the information content of these community phylogenies is a priority. To test the viability and advantage of a multi-community phylogeny, we constructed a multi-plot mega-phylogeny of 1347 species of trees across 15 forest dynamics plots in the ForestGEO network using DNA barcode sequence data (rbcL, matK, and psbA-trnH) and compared community phylogenies for each individual plot with respect to support for topology and branch lengths, which affect evolutionary inference of community processes. The levels of taxonomic differentiation across the phylogeny were examined by quantifying the frequency of resolved nodes throughout. In addition, three phylogenetic distance (PD) metrics that are commonly used to infer assembly processes were estimated for each plot [PD, Mean Phylogenetic Distance (MPD), and Mean Nearest Taxon Distance (MNTD)]. Lastly, we examine the partitioning of phylogenetic diversity among community plots through quantification of inter-community MPD and MNTD. Overall, evolutionary relationships were highly resolved across the DNA barcode-based mega-phylogeny, and phylogenetic resolution for each community plot was improved when estimated within the context of the mega-phylogeny. Likewise, when compared with phylogenies for individual plots, estimates of phylogenetic diversity in the mega-phylogeny were more consistent, thereby removing a potential source of bias at the plot-level, and demonstrating the value of assessing phylogenetic relationships simultaneously within a mega-phylogeny. An unexpected result of the comparisons among plots based on the mega-phylogeny was that the communities in the ForestGEO plots in general appear to be assemblages of more closely related species than expected by chance, and that differentiation among communities is very low, suggesting deep floristic connections among communities and new avenues for future analyses in community ecology.

Effects of Soil Water and Nitrogen on Growth and Photosynthetic Response of Manchurian Ash (Fraxinus mandshurica) Seedlings in Northeastern China

Background Soil water and nitrogen (N) are considered to be the main environmental factors limiting plant growth and photosynthetic capacity. However, less is known about the interactive effects of soil water and N on tree growth and photosynthetic response in the temperate ecosystem. Methods/Principal Findings We applied N and water, alone and in combination, and investigated the combined effect of different water and N regimes on growth and photosynthetic responses of Fraxinus mandshurica seedlings. The seedlings were exposed to three water regimes including natural precipitation (CK), higher precipitation (HW) (CK +30%) and lower precipitation (LW) (CK −30%), and both with and without N addition for two growing seasons. We demonstrated that water and N supply led to a significant increase in the growth and biomass production of the seedlings. LW treatment significantly decreased biomass production and leaf N content, but they showed marked increases in N addition. N addition could enhance the photosynthetic capability under HW and CK conditions. Leaf chlorophyll content and the initial activity of Rubisco were dramatically increased by N addition regardless of soil water condition. The positive relationships were found between photosynthetic capacity, leaf N content, and SLA in response to water and N supply in the seedling. Rubisco expression was up-regulated by N addition with decreasing soil water content. Immunofluorescent staining showed that the labeling for Rubisco was relatively low in leaves of the seedlings under LW condition. The accumulation of Rubisco was increased in leaf tissues of LW by N addition. Conclusions/Significance Our study has presented better understanding of the interactions between soil water and N on the growth and photosynthetic response in F. mandschurica seedlings, which may provide novel insights on the potential responses of the forest ecosystem to climate change associated with increasing N deposition.

Local-Scale Drivers of Tree Survival in a Temperate Forest

Tree survival plays a central role in forest ecosystems. Although many factors such as tree size, abiotic and biotic neighborhoods have been proposed as being important in explaining patterns of tree survival, their contributions are still subject to debate. We used generalized linear mixed models to examine the relative importance of tree size, local abiotic conditions and the density and identity of neighbors on tree survival in an old-growth temperate forest in northeastern China at three levels (community, guild and species). Tree size and both abiotic and biotic neighborhood variables influenced tree survival under current forest conditions, but their relative importance varied dramatically within and among the community, guild and species levels. Of the variables tested, tree size was typically the most important predictor of tree survival, followed by biotic and then abiotic variables. The effect of tree size on survival varied from strongly positive for small trees (1–20 cm dbh) and medium trees (20–40 cm dbh), to slightly negative for large trees (>40 cm dbh). Among the biotic factors, we found strong evidence for negative density and frequency dependence in this temperate forest, as indicated by negative effects of both total basal area of neighbors and the frequency of conspecific neighbors. Among the abiotic factors tested, soil nutrients tended to be more important in affecting tree survival than topographic variables. Abiotic factors generally influenced survival for species with relatively high abundance, for individuals in smaller size classes and for shade-tolerant species. Our study demonstrates that the relative importance of variables driving patterns of tree survival differs greatly among size classes, species guilds and abundance classes in temperate forest, which can further understanding of forest dynamics and offer important insights into forest management.

Density dependence on tree survival in an old-growth temperate forest in northeastern China

Abstract• Density dependence is a major mechanism for shaping plant communities. However, its role in regulating diverse, mixed natural tree communities is less certain.• In this study we investigated density-dependent effects in a large-scale (25 ha) old-growth temperate forest in northeastern China. Spatial patterns of neighborhood distribution in the plot were analyzed using various methods for inferring competition, including (1) pair correlation function to determine spatial patterns of pre-mortality and post-mortality and (2) neighborhood analysis of individuals to examine the extent to which tree survival is correlated with other covariates.• Results showed that, for common species, 3 of 5 canopy species and 3 of 8 midstory and understory species were random in mortality. Negative density-dependent mortality was not found when trees reach 1 cm in DBH. There was no significant correlation for canopy species between tree survival and conspecific abundance, but largely positive correlations for midstory and understory species. In contrast, tree survival was found to negatively correlate with conspecific basal area for most species, indicating strong intraspecific competition. No strong interspecific density dependence was found in the forest.Résumé• La dépendance par rapport à la densité est un important mécanisme pour la formation des communautés végétales. Toutefois, son rôle dans la régulation de diverses communautés mélangées d’arbre est moins certain.• Dans cette étude, nous avons enquêté sur les effets densité-dépendance à une grande échelle (25 ha) dans une ancienne forêt tempérée, dans le nord de la Chine. Les modes de distribution spatiale de voisinage ont été analysés en utilisant diverses méthodes pour estimer la concurrence, y compris : (1) des paires de fonction de corrélation afin de déterminer les structures spatiales de pré et postmortalité et (2) l’analyse du voisinage des individus pour examiner dans quelle mesure la survie de l’arbre survivant est corrélée avec d’autres variables.• Les résultats ont montré que, pour les espèces communes, 3 des 5 espèces de la canopée et 3 des 8 de l’étage moyen et du sous-étage, la mortalité était aléatoire. Aucune mortalité densité-dépendante négative n’a été détectée lorsque les arbres atteignent 1 cm de diamètre à hauteur d’homme. Il n’y avait pas de corrélation significative pour les espèces de la canopée entre la survie des arbres et l’abondance conspécifique, mais il y avait des corrélations positives pour l’étage moyen et le sous-étage.• En revanche, la survie des arbres était corrélée négativement avec la surface terrière conspécifique pour la plupart des espèces, indiquant une forte concurrence intraspécifique. Aucune dépendance visible de la densité interspécifique n’a été détectée dans la forêt.