Species Richness, Diversity and Density of Understory Vegetation along Disturbance Gradients in the Himalayan Conifer Forest

We investigated whether species richness, diversity and density of understory herbaceous plants differed along logging(gap) and grazing(primarily by cattle) disturbance gradients, and sought to identify drivers of richness, diversity and density of understory vegetation of logged sites. A factorial experiment was conducted in the mixed conifer forest of Gidakom in Western Bhutan. Levels of the logging treatment included small(0.15 – 0.24 ha), medium(0.25 – 0.35 ha) and large(0.36 – 1.31 ha) gaps. The grazing treatment included grazed(primarily by cattle) and ungrazed(where herbivores were excluded by a fence) plots nested within each gap. Data were collected from 12 gaps(4 replicates at each level of logging) using the point intercept method. Shannon Weaver Diversity and Margalef's indices were used to estimate species diversity and describe species richness, respectively. Soil samples were analyzed for pH and nutrients. The interaction effect of logging and grazing was significant(p≤0.001) only on species diversity. Relative to ungrazed areas, species diversity was significantly higher(0.01≤p≤0.05) in medium grazed gaps. Under grazed conditions, soil P was negatively correlated with gap size and species diversity. While species diversity was positivelycorrelated(0.01≤p≤0.05) with soil N in grazed plots species richness was positively correlated(0.001≤p≤0.01) with soil N in ungrazed plots. Relative density of Yushania microphylla and Carex nubigena were higher under ungrazed conditions. Our study suggests that the combined effect of cattle grazing and logging results in higher species diversity of understory vegetation in medium and grazed gaps in mixed conifer forests of Bhutan,whereas increase or decrease in relative density of major species is determined primarily by the independent effects of grazing and logging. From management perspective, forest managers must refrain from creating large gaps to avoid loss of nutrients(mainly P and N), which may eventually affect tree regeneration. Managers intending to maintain understory vegetation diversity must consider the combined effects of grazing and logging, ensuring low to moderate grazing pressure.

Strong evidence for latitudinal diversity gradient in mosses across the world

Species richness generally decreases with increasing latitude,a biodiversity gradient that has long been considered as one of the few laws in ecology.This latitudinal diversity gradient has been observed in many major groups of organisms.In plants,the latitudinal diversity gradient has been observed in vascular plants,angiosperms,ferns,and liverworts.However,a conspicuous latitudinal diversity gradient in mosses at a global or continental scale has not been observed until now.Here,we analyze a comprehensive data set including moss species in each band of 20° in latitude worldwide.Our results show that moss species richness decreases strongly with increasing latitude,regardless of whether the globe is considered as a whole or different longitudinal segments(e.g.,Old World versus New World) are considered separately.This result holds when variation in area size among latitudinal bands is taken into account.Pearson's correlation coefficient between latitude and species richness is-0.99 for both the Northern and Southern Hemispheres.Because bryophytes are an extant lineage of early land plants and because mosses not only include most of extant species of bryophytes but also are important constituents of most terrestrial ecosystems,understanding geographic patterns of mosses is particularly important The finding of our study fills a critical knowledge gap.

Lowland pasture in Himalayan highland: edaphic properties and species composition

This study was carried out to investigate if on-farm cut vs. grazed pastures differed in soil fertility and species density in the temperate Himalayan highlands. Soil fertility and species relative density were measured from 30 cut and 30 grazed dairy pastures. In both types of pasture, soil pH, available phosphorus(P) and exchangeable potassium(K) were negatively correlated with pasture age and slope. In cut pasture, cocksfoot(Dactylis glomerata) and pasture age were positively correlated,whereas in grazed pasture, they were negatively correlated. In grazed pasture, unsown species and pasture age were positively correlated. Soil available P was significantly greater in cut pastures whereas soil exchangeable K was significantly greater in grazed pastures. In terms of species density, cut pasture had greater densities of cocksfoot and Italian ryegrass(Lolium multiflorum), whereas grazed pasture showed greater densities of white clover, sedge and local grass. Our study suggests that, if there are no improvements in the current method of pasture management, the cut pastures in the future are likely to have a simple pasture mixture constituting only cocksfoot and white clover(Trifolium repens).Whereas in grazed pasture, the pasture mixture is likely to be comprised of white clover and unsown species such as sedge, local grass and broadleaf weeds.

HPLC Pigment Profiles of 31 Harmful Algal Bloom Species Isolated from the Coastal Sea Areas of China

Chemotaxonomy based on diagnostic pigments is now a routine tool for macroscopic determination of the composition and abundance of phytoplankton in various aquatic environments. Since the taxonomic capability of this method depends on the relationships between diagnostic pigments and chlorophyll a of classified groups, it is critical to calibrate it by using pigment relationships obtained from representative and/or dominant species local to targeted investigation area. In this study, pigment profiles of 31 harmful algal bloom(HAB) species isolated from the coastal sea areas of China were analyzed with high performance liquid chromatography(HPLC). Pigment compositions, cellular pigment densities and ratios of pigments to chlorophyll a were determined and calculated. Among all these species, 25 kinds of pigments were detected, of which fucoxanthin, peridinin, 19'-butanoyloxyfucoxanthin, 19'-hexanoyloxyfucoxanthin, violaxanthin, and antheraxanthin were diagnostic pigments. Cellular pigment density was basically independent of species and environmental conditions, and therefore was recommended as a bridge to compare the results of HPLC-CHEMTAX technique with the traditional microscopy method. Pigment ratios of algal species isolated from the coast of China, especially the diagnostic pigment ratios, were higher than those from other locations. According to these results, pigment ratio ranges of four classes of phytoplankton common off the coast of China were summarized for using in the current chemotaxonomic method. Moreover, the differences of pigments ratios among different species under the same culturing conditions were consistent with their biological differences. Such differences have the potential to be used to classify the phytoplankton below class, which is meaningful for monitoring HABs by HPLC-CHEMTAX.

Successional trends and processes on a glacial foreland in Southern Iceland studied by repeated species counts

Introduction:Primary succession on glacial forelands is increasingly relevant as rapid glacial retreat is exposing growing land areas to plant colonization.We investigated temporal trends,controls,and outcomes in floral succession on a subarctic glacial foreland.Specifically,we examined changes in community composition(mosses,low shrubs,forbs,trees,and graminoids)over long-term(decadal)and short-term(<10 years)scales and attempted to identify the underlying processes responsible for the observed successional patterns.Methods:The study area was the foreland of the Skaftafellsjӧkull,located in Vatnajӧkull National Park near the south coast of Iceland.We established nine transect lines at varying distances from the ice front representing surfaces of age ranging from less than one decade to over 100 years.Each transect consisted of five measurement stations of 1 m2 where we measured vegetative cover(VC),species richness(SR),and species density(SD)and calculated species evenness(SE).Measurements were made initially in 2007 and repeated at the same geographic coordinates in 2014.Results:VC increased with distance from the ice front from 16%to over 90%.SR and SD increased from the youngest pioneer community through a mid-successional stage corresponding to an age of over 60 but less than 100 years.Increased VC but declining SR,SD,and SE characterized the oldest(over 100 years)bryophyte-dominated surfaces.Species turnover,which involved forbs almost exclusively,increased moderately from early through midsuccessional sites and declined on older sites.Comparison of the measurements made in 2014 to those made in 2007 demonstrates increased SR at mid-successional sites while SD remained relatively constant.Conclusion:At a small scale,colonization is controlled by local factors such as microtopography and aspect,particularly in proximity to the glacier.At the landscape level,changes in VC and community structure are controlled by time and nutrient availability.Low nutrient levels and limited site availability favor bryophyte dominance on the oldest surfaces.The greatest community-level changes observed over the 7-year interval were increases in surface cover by mosses and low shrubs,particularly in mid-successional and older sites.These changes suggest that the community on the oldest surfaces has not yet reached equilibrium.

Reinvestigation on species richness and environmental correlates of bryophytes at a regional scale in China

Aims The aim of this article is 4-fold:(i)to update species richness of bryophytes for each of the Chinese provinces based on the most current knowledge on distributions of bryophytes in China,(ii)to provide a set of analyses based on the updated species richness data and the environmental variables used in a recent article on species richness of bryophytes in China,(iii)to expand the analysis presented in the recent article by relating species richness of bryophytes to over 15 additional climatic variables and(iv)to determine the degree to which the relationships between bryophyte species richness and environmental variables that were reported in the recent article might have been biased.Methods Over 180 literatures with national,provincial and local species lists of bryophytes in China were used in this study.Taxonomy and nomenclature of bryophytes in China were standardized according to The Plant List.Correlation and regression analyses were used to examine the relationships between species richness or species density of bryophytes in Chinese provinces and environmental variables.Important Findings On average,each Chinese province possesses 700.6 species of bryophytes,which is 112.1 species more than previously reported.With the updated species richness data reported in this study,stronger relationships between species richness of bryophytes and environmental variables have been found,compared with those found in a recently published study for China.When single environmental variables were considered,precipitation-related variables were,on average,more strongly correlated with species richness and species density than were temperature-related variables.Environmental variables were on average correlated more strongly with species density than with species richness of bryophytes at the regional scale in China.Our study showed that measures quantifying the average and variation of environmental conditions within each Chinese province explained 82.7%and 71.1%of the variation in species richness of liverworts and mosses,respectively,and explained 86.5%and 70.7%of the variation in species density of liverworts and mosses,respectively.