β-diversity in temperate grasslands is driven by stronger environmental filtering of plant species with large genomes

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS) has long been hypothesized to potentially affect species' capacity to tolerate environmental stress and might therefore help drive community assembly. However, its role in driving β-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and community composition across 52 sites spanning a 3200-km transect in the temperate grasslands of China. By correlating the turnover of species composition with environmental dissimilarity, we found that resource filtering (i.e., environmental dissimilarity that includes precipitation, and soil nitrogen and phosphorus concentrations) affected β-diversity patterns of large-GS species more than small-GS species. By contrast, geographical distance explained more variation of β-diversity for small-GS than for large-GS species. In a 10-year experiment manipulating levels of water, nitrogen, and phosphorus, adding resources increased plant biomass in species with large GS, suggesting that large-GS species are more sensitive to the changes in resource availability. These findings highlight the role of GS in driving community assembly and predicting species responses to global change

Survival and Growth of Residual Trees in a Variable Retention Harvest Experiment in a Boreal Mixedwood Forest

Long-term sustainability of forest resources is in question given wide-spread use of conventional clear-cut silviculture. In response, variable retention (VR) harvest has been increasingly promoted as a landscape-based approach to enhance sustainability by maintaining biodiversity and other ecosystem functions in managed forests. Although the success of the VR approach depends on post-harvest stand dynamics, little is known about growth and mortality of residual trees after harvest and how such trees respond to interactions between amount of retention and tree or site level covariates. We use data from three censuses distributed over a 10-year period of the main merchantable species to study the effects of retention level (i.e., percent of trees retained), mixedwood cover type, tree species, and three tree or terrain covariates (tree stem diameter, percent live crown, and soil wetness) on survival and growth of residual trees in a retention harvest experiment in NW Alberta, Canada. Both mortality and growth of residual trees were negatively related to retention levels. During the first five-year period after harvest, effects of retention levels on mortality were more evident for white spruce (Picea glauca) than for Populus spp., but effects on growth were weaker for white spruce. Tree mortality decreased through time following VR harvest for all species and in most cover types, while trends in tree growth varied by species. During the second five-year period after harvest, growth of residual Populus spp. had decreased from high levels observed in the first period. In contrast, growth of residual white spruce was greater in the second five-year period than in the first period. After the original harvest, re-entry of stands for additional harvest focused mainly on hardwoods may be economically rewarding and ecologically justified, depending on the overall objectives for retention. The positive effect of increased retention level on tree survival was strongest for trees with larger diameter and longer crowns. Thus, retention patches are a management option to protect large trees and trees with greater crown length when retaining such trees is a management goal

Challenges in estimating forest biomass: use of allometric equations for three boreal tree species

Regionally-fitted allometric equations for individual trees and root-to-shoot ratio values are normally used to estimate local above- and belowground forest biomass, respectively. However, uncertainties arising from such applications are poorly understood. We developed both above- and belowground biomass equations using destructive sampling for three dominant upland boreal tree species in northwestern Alberta, Canada. Compared to our equations, the diameter-based national equations derived for use across Canada underestimated aboveground biomass for Picea glauca, but gave reasonable estimates for Populus balsamifera and P. tremuloides. The national equations based on both tree diameter and height overestimated aboveground biomass for the Populus species, but underestimated it for Picea glauca in our study area. The root-to-shoot ratio approach proposed by IPCC overestimated belowground biomass by 16â 41% depending on forest cover type in comparison to our values estimated directly on site, with the greatest bias in deciduous-dominated stands. When the general allometric equations for aboveground and the root-to-shoot ratio for belowground biomass were combined to estimate stand biomass, overestimation could be as high as 18% in our study area. Our study supports development of improved regional allometric equations for more accurate local-scale estimations. Incorporating intraspecific variation of important traits like tree taper may be especially helpful.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

The distribution of <i>C. mandshurica</i> and <i>A. barbinerve</i> in the old growth and secondary forest plots.

<p>The solid points represent the individuals of the two species. The contour lines refer to the topography of the two forest plots.</p

Effects of dbh, stem number in a shrub, neighborhood and soil variables on stem growth or survival of <i>C. mandshurica</i> and <i>A. barbinerve</i> in the old growth forest plot.

<p><i>Circles</i> show the coefficient estimate for each parameter, with 2S.E. indicated by <i>horizontal lines</i>. “Ba” represents basal area. Asterisks represent the probability that the estimates are not different from zero: *<i>P</i><0.05, **<i>P</i><0.01, ***<i>P</i><0.001, ns not significant (<i>P</i>>0.05).</p

Parameters included in models.

<p>Parameters included in models.</p

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-tmH) 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 biasat 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