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Premise of the Study: Herb chronology, the study of belowground annual growth rings in perennial forbs, has much potential as a tool for monitoring plant growth as a function of environment. To harness this potential, understanding of the coordination between ring ontogeny, aboveground phenology, and the temporal allocation of carbon products belowground in herbaceous forbs must be improved. Methods: We investigated these relationships in two southern United States tallgrass prairie perennial forb species, Asclepias viridis and Lespedeza stuevei, making monthly excavations for a year. Key Results: Belowground xylogenesis began when starch reserves were at their seasonal low in the spring as shoots reached maximum height. The highest relative radial growth of the ring occurred concurrently with replenishment of root starch reserves in early summer. Xylogenesis concluded with leaf senescence in late summer and belowground starch reserves near saturation. Conclusions: By demonstrating that ring ontogeny is tied to early summer starch replenishment, our results illustrate the mechanisms behind previous findings where ring width was highly correlated with summer climatic conditions for these two species. This study provides a new physiological link between how ring chronologies in herbs often accord with growing‐season environment; further dissecting this phenomenon is vital in unlocking the potential of herb chronology. [ABSTRACT FROM AUTHOR]

Questions While mowing is a viable management tool for the maintenance of diversity in grasslands, the suitability of mowing in grasslands with invasion by exotic plants is poorly understood. In this 18-yr study, we investigate the effects of long-term mowing on a tallgrass prairie community invaded by exotic yellow bluestem ( Bothriochloa ischaemum; BOIS). We explore the influence of BOIS on species richness and composition in the face of different mowing treatments as well as monitoring any post-treatment legacy effects. Location Northeast central Oklahoma, US. Methods A total of 144 permanent plots were laid out comprising eight treatments (i.e. all combinations of Mar, Jun and Sept, mows resulting in three single mows, three double mows, one triple mow and an un-mowed control). Plots were mowed 1996-2011 and recovery was monitored through 2014. Repeated mixed model ANOVA, PERMANOVA and principal response curves were employed to analyse species richness and compositional changes from mowing. Correlation was used to explore the effects of BOIS on species richness. Results Mowing resulted in higher species richness relative to the absence of mowing, with the highest levels being sustained in the late season mown plots throughout the study. Once mowing had ceased, early season mown plots declined in species richness down to the same levels as the un-mown plots, concomitant with the sharpest increased cover of BOIS in these plots relative to all other treatments. Overall, we found a strong negative correlation between BOIS cover and species richness. Species dissimilarity was highest between any plot that was mowed and the un-mown controls, as well as between March and September only treatments. Conclusions Our study highlights the potential of mowing in maintaining high species richness. However, the positive response to early season mowing of the exotic yellow bluestem and ensuing negative effect on species richness suggests that BOIS can confound the favourable effects of mowing. We found only minor post-treatment legacy effects, since BOIS strongly re-established in the absence of mowing in all previously mown plots, especially the early season mown plots. Thus, we recommend sustained late season mowing to help control the spread of BOIS and maintain species-rich grasslands. [ABSTRACT FROM AUTHOR]

Question How does the interaction between silicon ( Si) and vegetation affect local and global ecological processes, higher levels of ecological organization, and terrestrial- and watershed-scale Si fluxes? Location We selected several ecosystems throughout the world, from river headwaters to estuaries, being examples of (i) terrestrial vegetation, (ii) aquatic and floodplain vegetation, and (iii) tidal wetland vegetation. Methods We provide examples of the importance of linking Si use by terrestrial and aquatic vegetation, to larger-scale Si flux consequences towards and through rivers. Cross-disciplinary studies achieve the best understanding of vegetation effects on the global Si cycle, and the role of Si as a plant functional trait. Conclusion Si use by plants has not always received the research attention of other elements. Yet, today the importance of Si for plant functioning is slowly becoming better understood. Silicon is a crucial element for many plant species, being important for decomposition processes, plant competitiveness and stress tolerance. The inclusion by vegetation scientists of Si uptake as a plant functional trait is important to assess links between plant physiology, plant distribution and plant tolerance to environmental changes, but also to understand the role of vegetation on Si fluxes through the watershed. However, lack of knowledge regarding the biological control of the Si cycle hinders accurate quantification. Only a concerted effort bringing scientists together from a broad array of disciplines will provide this new direction for research on vegetation- Si cycling. [ABSTRACT FROM AUTHOR]

Questions: Most modern fire-prone landscapes have experienced disruptions of their historic fire regimes. Are the primary tallgrass prairies of the Flint Hills reflective of a history of continuous fire occurrence? Did fire frequency, severity, size and seasonality change in connection with changes in land use? Has fire occurrence been related to drought conditions? Location: Edges of Cross Timbers forest stands at the Tallgrass Prairie Preserve (TGPP) in the Flint Hills of Osage County, Oklahoma, USA. Methods: Cross-sections of 76 Quercus stellata were collected from Cross Timbers stands at or near the grassland edge in the TGPP. Dendrochronological methods were used to identify years of formation for tree rings and fire scars. Superposed epoch analysis was used to evaluate the effect of drought conditions on fire occurrence. Results: Fires were recorded in 46.6% of the years between 1729 and 2005. In 41 cross-sections at one site, the mean fire interval between 1759 and 2003 was 2.59 years, with fire interval decreasing from a mean fire interval of 3.76 years in the early part of the record to 2.13 years in modern times. No extended periods without fire were recorded in the study area. Drought conditions had no significant effect on fire occurrence. Conclusions: In contrast with many fire-prone landscapes worldwide, the prairies of the Flint Hills have experienced no recent fire suppression or exclusion. Changes in fire frequency mark transitions in land use, primarily from being traditionally used by Native Americans to being managed for cattle production. [ABSTRACT FROM AUTHOR]

Question: Does understory vegetation cover and richness decline along a gradient of increasing Juniperus virginiana midstory canopy cover and is that decline best correlated with litter accumulation? Location: Cross Timbers Forest in Payne County, OK, USA. Methods: We measured vegetation in forest gaps as well as forest areas without J. virginiana, at the inner and outer edge of J. virginiana canopies and near J. virginiana trunks (200 plots) and compared vegetation differences among location to light, litter, soil and microclimate variables. Results: Species richness (11 spp m−2 to 6 spp m−2) and summer vegetation cover (53.3% to 12.7%) declined with proximity to trunks. Regression indicated that richness declines ( R2=0.08) and cover ( R2=0.18) were best correlated with J. virginiana litter accumulation. Partial canonical correspondence analysis (pCCA) revealed two strong canonical axes, one related to litter/light and another to cover of Quercus spp. versus J. virginiana. Tree seedlings and woody vines dominated near J. virginiana. Forbs, graminoids and Quercus spp. seedlings were more common in areas without J. virginiana. Conclusions: Increasing J. virginiana and consequent litter additions alter understory biomass and composition and, through inhibiting Quercus spp. recruitment, may lead to changes in overstory composition. Decreases in herbaceous litter, which historically contributed to fuel accumulation, may have positive feedback effects on midstory encroachment by reducing the potential for prescribed burning. [ABSTRACT FROM AUTHOR]

Questions: (1) How have the composition and structure of undisturbed upland Quercus forests changed over 50 years across a large region and moisture gradient; (2) What factors are associated with long-term and broad-scale changes in these forests? Location: Oklahoma, USA. Methods: We re-sampled 30 forest stands originally sampled in the 1950s across a large geographical area and compared basal area, tree density, and sapling density between the sampling periods using paired t-tests, CCA, and DCA. We examined vegetation dynamics in the context of drought indices compiled for the sample period. Results: Total and Quercus stellata basal area and tree density increased, but Q. stellata and Q. marilandica sapling density decreased. Juniperus virginiana and woody species richness increased for all measures. DCA indicated that re-sampled stands generally changed from Q. stellata-Q. marilandica-dominated forests to forests with greater woody species richness and more J. virginiana. Q. stellata remained a dominant tree species; otherwise, composition shifted towards mesophytic and invasive woody species. Measurements taken in the 1950s immediately followed a major drought; whereas subsequent decades were significantly moister. Conclusions: Fire exclusion and drought may have played an important role in driving changes towards lower dominance by Quercus, increased importance of mesophytic and invasive species, and greater woody species richness. These phenomena are similar to those found in Quercus-dominated forests throughout the northern hemisphere. [ABSTRACT FROM AUTHOR]

Past studies on changes in species distribution have mainly been based on analysis of range boundaries. In contrast, the method used here evaluates shifts in species' geographic centroids within a predefined area. We used presence/absence data on epiphytic lichens collected 1986 and 2003 from 64 sites in southern Sweden. A centroid was calculated each year, for each lichen species and substrate. The distance of centroid movement was evaluated in a permutation procedure. In total, 56 lichen species on 22 tree species were involved in the analyses, yielding 30 cases that had sufficient sample sizes both years to be evaluated. Out of these, three exhibited a significant movement of their centroid. The shift of lichen centroids of Hypogymnia physodes (L.) Nyl. and Vulpicida pinastri (Scop.) J.-E. Mattsson & M. J. Lai on the tree species Juniperus communis L. was 50 and 151 km with the direction 27° and 48°, respectively. For Hypogymnia physodes on Pinus sylvestris L., corresponding values were 41 km and 30°. The northnortheast shifts of these species in Sweden could be a response to a warming climate. [ABSTRACT FROM AUTHOR]

Recent empirical work in numerous systems has demonstrated the interdependence of spatial and temporal accumulation of species in the species-time-area relationship (STAR). The purpose of this study was to develop a process-based stochastic model for the STAR that assumes species neutrality and to compare the model's expectations to data collected on plant species in a tallgrass prairie. We varied two important aspects of the neutral species assemblage: evenness in the species pool and individual replacement rate (R). When R is larger than ∼0.5 and evenness is intermediate to high, the neutral STAR generates patterns qualitatively similar to the empirical STAR. Our model also indicates that space and time were not symmetrical in their effects on species accumulation, except in the special case of R = 1.0. We observed both positive and negative time-by-area interactions in the sampling model, which indicates that nonzero interactions are not necessarily evidence of ecological processes. Furthermore, as accumulated richness approaches the size of the species pool, the time-by- area interaction becomes increasingly negative in our model. This suggests that negative time- by-area interactions should be expected a priori in empirical systems if rates of species accumulation decrease due to increasing rarity of unique species. Given the wide range of STARs that the sampling model generated, the difficulty in estimating key parameters, arid the complexity of assessing the relative abundance distribution and scale of the species pool, we cannot refute the sampling effect, and we suggest caution in accepting ecologically oriented explanations of empirical STARs. [ABSTRACT FROM AUTHOR]

Question: To what extent do bison serve as seed dispersers via epizoochory and endozoochory in tallgrass prairie, and does this differ by age-sex class of bison and by month? Location: Tallgrass Prairie Preserve, Osage County, Oklahoma, USA. Methods: We collected bison hair from 19 bulls, 45 cows, and 47 juveniles in fall and we collected bison dung monthly for a year. We recovered and identified seeds from hair and dung samples, and classified seeds by size and diaspore characteristics. Results: Bison hair samples contained 2768 seeds from at least 76 plant species. Several species found in hair did not feature specialized appendages for adhesive dispersal. Seed species composition differed in hair collected from bulls, cows and juveniles, possibly due to differential habitat use. Dung samples contained 7418 seeds from at least 70 species, from which graminoids accounted for 3936 seeds from 27 species. Species composition of seeds contained in dung samples differed among months, corresponding to availability. Grasses constituted about half the seeds in both dung and hair samples, but Asleraceae were more strongly represented in hair, while Scrophulariaceae and Solanaceae were more strongly represented in dung. Conclusions: We conclude that bison are potentially important dispersers of forbs as well as graminoids. A high abundance and wide diversity of seeds were found in both bison hair and dung. The great majority of seeds found undamaged in bison dung were small seeds, which agrees with the `foliage is the fruit' hypothesis. Dispersal by both epizoochory and endozoochory may play an important role in life history of many species in tallgrass prairie landscapes. [ABSTRACT FROM AUTHOR]

The article comments on the paper "Plant Species Invasions Along the Latitudinal Gradient in the United States," by Curtis H. Flather, Thomas J. Stohlgren, Catherine Jarnevich, David Barnett, and John Kartesz. The authors assert that the study made by Stohlgren and colleagues has two major deficiencies in which the researchers's data set of county richness values underestimates true county richness and the richness values were incorrectly transformed to report for variation in survey area. They argue the conclusions of the researchers which include the absence of relationship between native plant richness and latitude at the country level and the strongest single predictor of exotic species richness is native species richness.

Questions: The Cross Timbers are a mosaic of savannas, grasslands and upland forests, occupying a significant portion of south-central North America. Our questions here were (1) how does a severe tornado affect the two most dominant tree species of the area Quercus marilandica and Q. stellata with respect to damage and mortality; (2) how do such patterns vary as a function of tree size? What are the implications of disturbance for codominance in species-poor systems? Location: The Cross Timbers in Oklahoma, USA. Methods: We established a 14.48-ha permanent plot following a severe tornado in 2003. We identified, numbered and tagged each tree and recorded its diameter at breast height (DBH), spatial coordinates, status (dead or alive), and damage type. We examined (1) relative abundance before and after the tornado; (2) differences in damage and mortality, and (3) the influence of tree diameter on the probability of damage and mortality for each species. Results: Differences in species identity and tree characteristics were significantly related to tree mortality following the tornado, after accounting for spatial locations. The odds of mortality were 12.0 times greater for Q. marilandica than for Q. stellata. Such greater vulnerability of Q. marilandica versus Q. stellata was also reflected in changes in density and basal area. Tree diameter clearly influenced the damage and mortality pattern in Q. stellata; larger trees sustained more damage and mortality. However, Q. marilandica did not exhibit size-dependent mortality. Conclusion: The tornado affected the two dominant species differently. The intra- and inter-specific differences in windstorm susceptibility may allow coexistence of the two species and are potentially important in the dynamics of the Cross Timbers. Species more damaged might finally benefit from the wind disturbance due to their resprouting ability. [ABSTRACT FROM AUTHOR]

Questions: Does distance decay exist in an old-growth neotropical forest? Is this distance decay stronger than expected due to environmental heterogeneity alone? At what spatial scales are distance decay manifested? Location: La Selva Biological Station, Costa Rica, Central America. Methods: An index of distance decay is applied appropriate for small quadrats (the probability of encountering a conspecific tree) to a grid of 11700.01-ha plots. A null model is provided that accounts for environmental heterogeneity. Results: Significant, but weak, distance decay is found. After correcting for known patterns of environmental heterogeneity, the distance decay almost disappears, except for fine spatial scales. Conclusions: These results are inconsistent with models that predict distance decay at all spatial scales. However, biological processes leading to distance decay may be more relevant and detectable at scales broader than this study. Research utilizing objectively-located samples over much broader scales is necessary to evaluate the generality and magnitude of distance decay. [ABSTRACT FROM AUTHOR]

Maize samples were obtained at two depths [0–30 cm (top sample) and 30–60 cm (bottom sample) from the maize surface] at 19–28 locations from a naturally infested maize storage facility in Wisconsin, USA. Based on identification of insects in stored-maize samples from 13 weekly sampling events, four topics were addressed: (i) the seasonal fluctuation in the insect community; (ii) ordination analysis was conducted to examine the association among insect taxa and to determine their distribution along abiotic and geographic gradients; (iii) the demographic characteristics of insect communities in maize samples with high abundance of either Plodia interpunctella ( Plodia samples) or Sitophilus zeamais ( Sitophilus samples); and (iv) to what extent natural enemies were spatially associated with their prey species. We identified a total of 18 different taxa, composed of adults and larvae of 14 determined species, and others identified to genus, family or order. Insect density was significantly higher in top samples compared to bottom samples, and the insect taxa occurred more frequently in top samples compared to bottom samples. In the ordination analysis, the three explanatory variables accounting for eastern, northern and vertical position of maize samples explained the largest part of the total variance. There was a gradual time trend with some of the insect species mainly occurring early or late in the monitoring period. Moisture content of the maize was the weakest of the significant explanatory variables, while temperature in the grain mass did not explain a significant part of the total variance. Plodia samples and Sitophilus samples had significantly different spatial distribution patterns and had markedly different insect species composition. Plodia samples were characterized by low abundance of all granivores and fungivores, except P. interpunctella. Conversely, Sitophilus samples had high abundance of T. castaneum, A. advena, and C. ferrugineus. Consequently, Sitophilus samples seemed to comprise more diverse insect communities than Plodia samples. Natural enemies were not significantly associated with their most common hosts. In a highly homogeneous habitat (stored maize), we demonstrated that stored-product insect species had significantly different distribution patterns mainly along geographic gradients. Stochasticity of the initial infestation process or interspecific competition are two of the possible explanations for the spatial segregation of stored-product insects, and the spatial segregation of insects on the same trophic level may have profound implications for the understanding of how these ecosystems develop over time and thereby how integrated pest management strategies are implemented to control insect pest populations. [ABSTRACT FROM AUTHOR]

Presents information on a study which demonstrated the utility of cross-validation of gradient analysis for uncovering the processes structuring communities. Materials and methods; Results and discussion; Conclusion.

Examines the prevalence of nonrandom distribution of trees and palms in relation to soil type and topographic position in the tropical rain forest of Costa Rica. Classification of topographic position of plots; Measurement of slope; Relationship of tree species to soil types and topographic position; Rate of tree species in the dominant soil type.

Outlines the essential features of the Canonical Correspondence Analysis (CCA) family of ordination methods. CCA as one of the most widely used gradient analysis technique in ecology; CCA algorithm's basis on the Correspondence Analysis (CA); Testing of whether CCA suffers from defects; CCA's performance with skewed species distributions.

We provide algebraic simplifications for the redundancy analysis (RDA) eigenvalue and the canonical correspondence analysis (CCA) eigenvalue in the special case of permanent plots sampled twice. The indices for RDA and CCA are interrelated and are intuitively interpretable. These simplifications also apply to simple split-plot designs and to a balanced design with two independent samples. [ABSTRACT FROM AUTHOR]

A response by the authors to a letter to the editor about their article on the ecological advantage of low-input high-diversity biofuels over many alternative biofuel systems is presented.

We present a data set collected in 1989 of vascular plant occurrences in overlapping grids of nested plots in the Oosting Natural Area of the Duke Forest, Orange County, North Carolina, USA. The purpose of these data is to allow the study of vascular plant biodiversity at multiple spatial scales, in terms of both grain and extent. There are eight distinct plot sizes (grains), with size four times that of the next smallest, from 0.015625 m2 to 256 m2. Larger grains are possible by aggregating adjacent plots. Extents (linear distances between plots) range from 1 m to 362 m. In addition, trees were mapped over the entire 256 m x 256 m study site in 1990, and again in 1998 to assess the effects of Hurricane Fran in September 1996. Tree species, diameters, and damage descriptors (1998 only) were also recorded. Soils were gathered from the entire grid in 1990 and analyzed for nutrients, pH, and organic matter. These data have already been used to assess scale dependence of plant diversity, to evaluate new methods for the study of spatial scale, and to study the importance of spatial scale on the interpretation of hurricane damage to forests. They are presented as a case study for future scale research. [ABSTRACT FROM AUTHOR]

The article speculates whether low-input high diversity (LIHD) biofuels could lead the way for the creation of a sustainable system. It is explained how LIHD cultivation of biofuel feedstocks can become an alternative to high-input low-diversity (HILD) agricultural systems. The benefits of LIHD which include large reductions in agrichemical inputs, soil tillage, and water demand; and conservation and maintenance of ecosystem services, is highlighted.

Presents information on an additional feature in the April 2002 issue of 'Journal of Vegetation Science.'

We studied the effects of windthrow on the understory plant species composition of a pine forest (dominated by Pinus strobus) and an oak forest (dominated by Quercus ellipsoidalis). We recorded the presenceof vascular plant species in randomly located quadrats in the two forests, and in three microsite types associated with tipup mounds (pit, old soil and new soil) in the pine forest at irregular intervals over the course of 14 years. The understories of the two forests remained distinct throughout the study. The frequency of occurrence of a number of forest floor species considerably increased; few species decreased. The disturbance specialists Rubus idaeus and Polygonum cilinode increased in frequency throughout the study in the pine forest, butare beginning to decline in the less disturbed oak forest. Annuals and biennials preferentially colonized the disturbed soil of microsites on tipups, and declined in frequency after about 7 yr. Both forestshave increased in understory species richness, but have not changed substantially in the distribution of growth forms. Despite early differences in species composition, microsite types associated with tipupmounds became more similar through time. Although small in magnitude, there was a directional change in understory composition at both forests, with no apparent sign of a return to pre-disturbance conditions. [ABSTRACT FROM AUTHOR]

We measured tree damage and mortality following a catastrophic windthrow in permanent plots in an oak forest and a pine forest in centralMinnesota. We monitored changes in forest structure and composition over the next fourteen years. Prior to the storm, the oak forest was dominated by Quercus ellipsoidalis, and the pine forest by Pinus strobus. The immediate impacts of the storm were to differentially damageand kill large, early-successional hardwoods and pines. Subsequent recovery was characterized by the growth of late-successional hardwoods. In both forests the disturbance acted to accelerate succession. Ordination of tree species composition confirmed the trend of accelerated succession, and suggested a convergence of composition between thetwo forests. [ABSTRACT FROM AUTHOR]

The study of vegetation dynamics in tallgrass prairie in response tofire has focused on dormant season fire in late successional prairies. Our objective was to determine if late season fire of varying frequency results in divergent successional patterns in an early successional tallgrass prairie disturbed by grazing and cultivation. Specifically, we evaluated the influence of late-summer fires of varying frequency on community composition and species richness. We collected vegetation and environmental data on two sites burned in the late growing-season at varying frequencies. These communities differed in composition depending primarily on edaphic factors, time since the last burn, and year-to-year variation. We interpret the time effect as related to changes in species composition accompanying plant succession that followed disturbance either from cropping and heavy grazing on the loamy site or heavy grazing on the shallow site. Other unidentified factors also have a role in vegetation dynamics on this prairie. Community composition and species richness were not consistently responsive to frequency of growing-season fires. [ABSTRACT FROM AUTHOR]