Showing papers in "Plant Ecology in 1987"

Compositional dissimilarity as a robust measure of ecological distance

Abstract: The robustness of quantitative measures of compositional dissimilarity between sites was evaluated using extensive computer simulations of species’ abundance patterns over one and two dimensional configurations of sample sites in ecological space. Robustness was equated with the strength, over a range of models, of the linear and monotonic (rank-order) relationship between the compositional dissimilarities and the corresponding Euclidean distances between sites measured in the ecological space. The range of models reflected different assumptions about species’ response curve shape, sampling pattern of sites, noise level of the data, species’ interactions, trends in total site abundance, and beta diversity of gradients.

An evaluation of the relative robustness of techniques for ecological ordination

Abstract: Simulated vegetation data were used to assess the relative robustness of ordination techniques to variations in the model of community variation in relation to environment. The methods compared were local non-metric multidimensional scaling (LNMDS), detrended correspondence analysis (DCA), Gaussian ordination (GO), principal components analysis (PCA) and principal co-ordinates analysis (PCoA). Both LNMDS and PCoA were applied to a matrix of Bray-Curtis coefficients. The results clearly demonstrated the ineffectiveness of the linear techniques (PCA, PCoA), due to curvilinear distortion. Gaussian ordination proved very sensitive to noise and was not robust to marked departures from a symmetric, unimodal response model. The currently popular method of DCA displayed a lack of robustness to variations in the response model and the sampling pattern. Furthermore, DCA ordinations of two-dimensional models often exhibited marked distortions, even when response surfaces were unimodal and symmetric. LNMDS is recommended as a robust technique for indirect gradient analysis, which deserves more widespread use by community ecologists.

The analysis of vegetation-environment relationships by canonical correspondence analysis

Abstract: Canonical correspondence analysis (CCA) is introduced as a multivariate extension of weighted averaging ordination, which is a simple method for arranging species along environmental variables. CCA constructs those linear combinations of environmental variables, along which the distributions of the species are maximally separated. The eigenvalues produced by CCA measure this separation.

Climate and plant distribution at global and local scales

Abstract: This paper investigates, with predictive models, the utility of ecophysiological responses to climate as predictors of plant distribution. At the global scale responses to extreme minimum temperatures and to the hydrological budget effectively predict the distribution limits of the major vegetation types of the World. A minimum temperature of −15 °C, for example, appears critical in controlling the poleward spread of vegetation that is dominated by evergreen broadleaved species; however, the presence or absence of more frost resistant species, such as those that are deciduous broadleaved, is not obviously explained in terms of extremes of climate. In such cases, predicting the competitive relationships between species is necessary and dependent on the climatic sensitivity of population dynamics.

Effects of fire, topography and year-to-year climatic variation on species composition in tallgrass prairie

Abstract: Native unploughed tallgrass prairie from Konza Prairie, Kansas, USA is described with respect to plant species compositional changes over a five year period in response to fire and topography. The principal gradient of variation in the vegetation is related to time since burning. Species show an individualistic response in terms of relative abundance to this gradient. Both the percentage of and cover of C4 species and all grasses decrease as the prairie remains unburnt. Forb and woody plant species numbers and abundance increase along this gradient. A secondary gradient of variation reflects topography (i.e. upland versus lowland soils). Upland soils support a higher species richness and diversity. Upland and lowland plant assemblages are distinct except on annually burnt prairie. The interaction between burning regime, topography and year-to-year climatic variation affects the relative abundance of the plant species differentially. The most dominant species overall, Andropogon gerardii, was affected only by year-to-year variation (i.e. climate). Its position at the top of the species abundance hierarchy was unaffected by burning regime or soil type. The other dominant species showed a suite of varying responses to these factors.

A hierarchical consideration of causes and mechanisms of succession

Abstract: Questions of successional pattern and causality have been central concerns in vegetation ecology. In this paper we address the limits of the overextended models of Connell and Slatyer by discussing problems encountered in field tests. To help prevent such problems, we define the essential concepts needed to understand succession: pathway, cause, mechanism, and model. We then suggest a more complete enumeration of successional causes, and place them in a three-level hierarchy. The highest level in the hierarchy defines the general and universal conditions under which succession occurs: (1) availability of open sites, (2) differential availability of species, and (3) differential performance of species at the site. To provide a more detailed understanding of succession, each of these causes is decomposed into ecological processes. A further decomposition results in the third level of the hierarchy, which is required to elucidate the mechanisms of succession at particular sites and to make detailed predictions. The hierarchy allows the appropriate causes to be chosen to answer questions about succession at the desired level of generality or level of organization. Recognizing the appropriate level(s) in the hierarchy is critical for the successful explanation of succession, design of experiments, statement of predictions, construction of models and development of general theory.

Models for the analysis of species’ response to environmental gradients

Abstract: A procedural model for vegetation analysis is presented. Suggestions are made that analysis methods can test theory as well as examine vegetation-environment correlations. Gauch and Whittaker’s propositions regarding species behavioural properties expected for an individualistic continuum are tested on a eucalypt forest data set. The data set is carefully stratified to control environmental heterogeneity. The shape and distribution of species response curves are then examined along a temperature gradient using 750 sites. The conclusions are: (1) Bell shaped response curves to environmental gradients are not universal (2) Positive-skewed curves are characteristic of major canopy species in eucalypt forest in southern New South Wales (3) Species richness increases with temperature along the gradient (4) Tests of other propositions regarding species modes and ranges are confounded by the change in species richness along the gradients (5) More rigorous statistical analysis and analyses on other vegetation types are needed.

Simulation of multidimensional community patterns: towards a comprehensive model

Abstract: Simulated data, derived from descriptive models of community variation along ecological gradients, are useful for the evaluation of ordination techniques and other numerical methods for the analysis of community data. Existing approaches to the simulation of community patterns are based on restrictive assumptions, although there is evidence supporting several alternative models. Simulation studies should aim to assess the robustness of analytical techniques to variations in model properties. This paper describes a modelling procedure which encompasses most current concepts and hypotheses about the properties of community patterns. The procedure has been used to assess the comparative robustness of several ordination techniques and to examine the effectiveness of alternative coefficients of compositional dissimilarity. COMPAS, a FORTRAN 77 computer program which implements the modelling procedure, is available on application to the author.

Seed dynamics during forest succession in Costa Rica

Abstract: Soil seed banks and current seed inputs each play a role in tropical succession We compared the abundance and floristic composition of seeds from these two sources at a Costa Rican site by germinating seeds from the soil, measuring seed inputs for 3 yr, and monitoring the earliest colonists in a forest clearing There were an estimated 6800 viable seeds/m2 in the soil of 33-yr-old vegetation, 9500 seeds/m2 in 11-yr-old vegetation, and 7000 seeds/m2 in a 75-yr-old forest An estimated 10100 seeds/m2 fell on the soil surface of the young successional vegetation during 3 yr and 3700 seeds/m2 fell during that same time in the forest Locally produced seeds accounted for about 75% of the seed input to the soil surface early in succession Seeds dispersed out of young successional vegetation increased the quantity and species richness of the seed input and storage in an adjacent forest Much of the species richness of the young successional vegetation resulted from seeds dispersed there from other communities by animals Deforestation stimulated germination of most seeds in the surface soil of the old forest, including seeds of the dominant canopy tree The recruitment of seedlings from the soil seed bank numerically overwhelmed that from post-disturbance seed rain and sprouts We evaluated patterns of soil seed storage during succession and predicted the ability of vegetation of differing ages to respond to disturbance Immediately after disturbance the number of seeds in the soil plummeted due to mortality, low inputs, and germination As the vegetation regrew, the soil seed bank increased to a peak after 4 to 7 yr, then gradually decreased to its pre-disturbance size High-frequency pulses of disturbance should result in reduced species richness, dominance by species with long-lived seeds, and fast recovery by seedling recruitment from the soil seed bank

The appearance and disappearance of major vegetational assemblages: Long-term vegetational dynamics in eastern North America

Abstract: Contoured maps of pollen percentages from eastern North America illustrate that the vegetation changed continuously during the past 18000 years. The maps show that the geographic distribution for selected pollen types from 500 years ago parallels the major patterns in the vegetation, and that the correspondence is good enough to justify using maps of fossil pollen to interpret the patterns and composition of the broad-scale vegetation from earlier times. Data for Artemisia, Cyperaceae, Picea, Betula, Alnus, Abies, and Pinus pollen illustrate how the changing location and abundance of their plant taxa and populations altered the spatial pattern, local composition, and the overall structure of the vegetation and thus led to the disappearance as well as appearance of major biomes and ecotones. For example, the Picea parkland biome that existed from 18000 to 12000 yr B.P. within a broad region south of the ice sheet disappeared within 2000 years after 12000 yr B.P., and the modern boreal forest biome began to develop across a large area of central Canada only after 6000 yr B.P. On a time scale of 104 to 106 yr, these types of vegetation changes involve a continual overlapping and separation of the abundance distributions for different taxa. Such changes are likely to have been a feature of vegetational dynamics for millions of years.

The individualistic and community-unit concepts as falsifiable hypotheses

Abstract: This study reformulates the community-unit and individualistic concepts of plant communities as hypotheses concerning the distribution of species' boundaries along a gradient. These hypotheses are tested by an analysis of deviance on data derived from a direct-gradient analysis of a freshwater marsh plant community in Breckenridge, Quebec, Canada. Boundaries are clustered at certain intervals along the gradient (p<0.001), contradicting the individualistic hypothesis. Upper boundaries are not consistently clustered at the same intervals as lower boundaries (p<0.001), contradicting the community-unit hypothesis. Thus, neither of the two usual models of community structure explain the patterns found in Breckenridge Marsh, suggesting that the historical dichotomy is too limited. Hypotheses of pattern should be tested using inferential statistics. Hypotheses of mechanism should be tested by experimentation. The way out of the community-unit vs. individualistic community debate is to deny the dichotomy and to consider multiple working hypotheses of community structure.

Ecological amplitudes of plant species and the internal consistency of Ellenberg’s indicator values for moisture

Abstract: Two methods for estimating ecological amplitudes of species with respect to Ellenberg’s moisture scale are discussed, one based on weighted averaging and the other on maximum likelihood. Both methods are applied to phytosociological data from the province of Noord-Brabant (The Netherlands), and estimate the range of occurrence of species to be about 4–6 units on the moisture scale. Due to the implicit nature of Ellenberg’s definition of moisture, it is impossible to improve the indicator values in a statistically sound way on the basis of floristic data only. The internal consistency of the Ellenberg indicator values is checked by using Gaussian logit regression. For 45 out of the 240 species studied the indicator value is inconsistent with those of the other species. The same method is used to estimate the optima and amplitudes of species considered moisture-indifferent and of some species not mentioned by Ellenberg. Some of these ‘indifferent’ species show a remarkably narrow amplitude.

Regeneration dynamics of beech forests in Japan

Abstract: A conceptual model of the regeneration of beech (Fagus crenata) forests in Japan is presented; stand structure, tree population dynamics and characteristics of gap formation are summarized. Beech forest can be recognized as a regeneration complex, and three phases: gap, building and mature, are distinguished through the structure of regenerating populations. The mean return interval is 100–200 yr. Disturbances by typhoons and dwarf bamboos (Sasa) on the forest floor may greatly affect the synchrony of regeneration and, hence, the stability of beech forests in Japan.

Influence of canopy opening on the environment and herb layer in a northern hardwoods forest

Abstract: Single- (33–37 m2) and multi-tree (51–151 m2) gaps were created in an Allegheny Plateau northern hard-woods forest to investigate environmental and herb layer response to canopy opening. After gap creation, noon light on clear summer days was brightest north of opening center. At other times of the day, and when skies were overcast, there was no difference in the light quantity beneath opened and closed canopy. Nor was the distribution of soil moisture or of soil or air temperature greatly affected by gap creation. Species establishment tended to be higher near opening centers; otherwise, there was no pronounced effect of canopy opening on plant cover or species richness during the first four years after gap creation. Biotic responses were not significantly correlated with any environmental factor.

Post-fire stand development of Austrocedrus-Nothofagus forests in northern Patagonia

Abstract: In the rainshadow of the Andean Cordillera in northern Patagonia (ca 39° to 43°S) the steep west-to-east decline in precipitation is reflected by a dramatic gradient from rainforest through open woodlands to shruband bunchgrass-dominated steppe. A recent trend towards aridification of Patagonia and consequent westward expansion of xeric communities into the western rainforest district has been a persistent theme in the ecological literature for nearly 50 years. Specifically, it has been suggested that the xeric trees Austrocedrus chilensis and Nothofagus antarctica are extending their ranges westward and replacing the mesic Nothofagus dombeyi which dominates the rainforests. This hypothesis was investigated by analyzing stand age structures and patterns of tree radial growth along a west-to-east gradient of post-fire stands dominated by Nothofagus dombeyi and Austrocedrus chilensis.

Rates of vegetation change associated with prairie dog ( Cynomys ludovicianus ) grazing in North American mixed-grass prairie

Abstract: A prairie dog (Cynomys ludovicianus) colony with a known history of habitation was studied to quantify the effects of herbivory on plant species composition, dominance, stature and diversity in a North American mixedgrass prairie. Gradient analysis was used to quantify the relationship between plant community structure, prairie dog density, burrow density and habitation history and to document community-level responses of plants subjected to heavy grazing pressure. The results quantify the type, rate and extent of change which plant populations and communities may undergo in response to the differential grazing of plants variously tolerant of defoliation.

Tree population dynamics, stand structure and species composition in the montane virgin forest of Vallibäcken, northern Sweden

Abstract: The population dynamics of Betula pubescens and Picea abies in a boreal forest near Kvikkjokk, northern Sweden, are governed by a process of storm gap regeneration similar to the gap regeneration described for boreo-nemoral forests. Cumulative age distribution curves, interpreted as static survivorship curves, lead to a simple theory of differential survival based on properties of the species, i.e. shade tolerance and relative growth rate. The theory is sustained by diameter and height distributions and by the spatial distributions of logs and of trees in different life-phases. Species of the field and ground layers respond differentially to gap formation and the ensuing successional stages. Browsing by moose (Alces alces) may prevent tree species, mainly Sorbus aucuparia, Betula pubescens and Pinus sylvestris, from developing into a tree layer. The regeneration ability for tree species growing in a stand at 460 m a.s.l. is limited compared with the regeneration at 330 m a.s.l., and typical storm gap formation involving more than one tree seems to occur rarely if at all, while overthrown trees with exposed rootplates are uncommon. Spruce at 460 m a.s.l. shows also a lower growth rate and a lower height/diameter ratio compared to the lower situated stands.

Vegetative reproduction of trees in some European natural forests

Abstract: Various means of vegetative reproduction in unexploited forests in western Europe are illustrated with examples. Root suckers are sometimes almost the only method of forest regeneration near the limits of tree growth on the Wadden islands and they can play an important role in forest gaps and riverine forests. Trunk suckers finally replacing their parent trees occur in Alnus, Tilia and Ulmus. Partial uprooting of trees, favoured by special soil conditions, was shown to be an important condition for vegetative reproduction. Temporary survival after uprooting gives opportunity for development of reiterative sprouts, that can replace the vertical axis of a fallen tree. Contact of living branches or even whole stems with soil or mouldering logs favours the growth of adventitious roots. Thus vegetatively reproduced individual trees establish before the uprooted parent tree finally dies. Examples of the clonal spreading of trees are given and a special strategy of layering its branches in pasture woods has been described for beech. Modern forestry rigorously eliminates conditions suitable for the vegetative reproduction of forest trees so their abilities in this respect are often underestimated. Vegetative reproduction seems to be particularly important under circumstances where natural growth is difficult e.g. near the limits of tree growth, on dynamic sites and under heavy shade.

A transformation of the Domin scale

Abstract: Some of the problems associated with the use of both percentage cover and cover-abundance scales for describing vegetation are discussed. A transformation, referred to as ‘Domin 2.6’, is outlined for use with the Domin scale. This transformation allows more accurate estimates of means of Domin scores to be obtained, than are produced by direct averaging of the Domin scores themselves. The transformation is a close approximation to the relationship between percentage cover and the Domin scale and permits rapid transformation of one to the other. ‘Domin 2.6’ is tested on both simulated and field data. The results show that ‘Domin 2.6’ corrects for the underestimation of means, calculated by the direct averaging of Domin scores. This is particularly noticeable when widely differing Domin scores are involved. A number of possible uses for this transformation are introduced and discussed.

Dispersal of ornithochorous seeds from forest edges in central Florida

Abstract: Dispersal of ornithochorous seeds from isolated forests in the phosphate mining region of central Florida, USA, were studied for two seasons (July to November) to determine patterns of dispersal Three separate studies included (1) dispersal directly from forest edges to early successional herbs; (2) standardized perches (2 m high post with a crossbeam); and (3) snags (dead trees, 113±28 m high, 214±233 stem branches) Perch availability was more important than distance in predicting seed types and quantities of bird-dispersed seeds The greatest concentration of bird-dispersed seeds were found under standard perches (255±249 seeds/m2/fall) followed by snags (147±85 seeds/m2/fall) and early successional vegetation (30±41 seeds/m2/fall) Seed quantities dispersed to snags were positively correlated with the number of stem branches on snags Seeds beneath standard perches were significantly lighter and less diverse than those found beneath snags This difference is attributed to the larger percentage of forest or later successional species found beneath snags (73%) as compared to the standard perches (15%) Perches and vegetative structural development should facilitate ecological succession by increasing the quantity, quality and diversity of seed deposition

Ecology and dynamics of the woody vegetation on the Kalahari Sands in Hwange National Park, Zimbabwe

Abstract: The woody vegetation on Kalahari sand deposits in Hwange (ex-Wankie) National Park, Zimbabwe was classified into nine types on the basis of species composition. Ordination of the data showed that the types which occupy the ends of the major (soil-type) gradient are easily distinguishable, viz. well developed, mature Baikiaea plurijuga woodlands on deep sands, and scrub Terminalia sericea and mixed woodland on soils with a higher clay content or compact layer. The central groups of stands, involving mixed woodlands and scrub, were less easy to interpret, and previous logging disturbance is involved. In the disturbed Baikiaea woodlands recruitment appears to be less than is required for long-term maintenance, even given that some of the measurements may have led to underestimates. Elephants were shown to have only a minor effect, and are relatively insignificant as agents of change in the woodlands. Depth of sand and soil moisture regime are the predominant factors determining overall vegetation structure. Fire is a dominant feature in scrub areas and interacts with frost, which has a periodic severe effect on developing saplings in scrub and in some disturbed woodlands. Although the relief is very flat there is a marked frost gradient from ‘ridge’ areas with mature woodland into the slightly lower-lying scrub areas. A conceptual model of the dynamics of the vegetation, based on the above features, is described.

Description and simulation of tree-layer composition and size distributions in a primaeval Picea-Pinus forest

Abstract: A structural description of a 0.5 ha stand in the primaeval coniferous forest of Fiby in central Sweden is reported, and a simulation model is used to test the hypothesis that the diameter and height distributions of the two most important tree species Pinus sylvestris L. (shade-intolerant) and Picea abies (L.) Karst. (shade-tolerant), are the outcome of simple successional processes following storm-felling 190 yr previously. The simulation model, FORSKA, is a ‘gap model’ treating light and other resource availability as homogeneous within patches. Simple formulations of dimensional relationships, vertical leaf area distributions within trees, light attenuation through the canopy and net assimilation as a function of light intensity allow FORSKA to simulate the species mixture, size distributions and vertical canopy structure of mixed-age, mixed-species forests. Parameters of the model were estimated from literature and from field data on height-diameter relationships, establishment rates and maximum ring-widths. The simulation generated a stand description similar to the real one in all essential characteristics. FORSKA allows vertical overlap between the crowns of nearby trees. The present simulation also differed from many gap model simulations in that the patch size was much greater than the maximum crown size, consistent with field observations that single treefall gaps have little effect; the persistence of shade-intolerant species in boreal forests generally depends on larger-scale disturbance events, such as large storm-gaps and forest fires.

Ecological gradients of boreal forests in South Finland: an ordination test of Cajander's forest site type theory

Abstract: Ecological gradients in the field layer of southern boreal forests in South Finland were studied in relation to the dominant tree species and the age of forest stands. The data are from a systematic sample of 529 plots from an area of 150 × 200 km, collected in the Third National Forest Inventory in 1951–53. Detrended correspondence analysis (DCA) was applied to log-transformed species cover values. It revealed three main gradients: fertility, moisture, and the effect of cattle grazing in forests (still extensive in the early 1950's). The fertility gradient dominated the first axis and the two latter sources of variation confounded with it in a complex manner in the first two axes of DCA. The second DCA axis was associated with canopy effects on understory pattern, with Pinus and Picea having opposite and Betula intermediate effects.

Climatic impacts on the vegetation of eastern North America during the past 2000 years

Abstract: Pollen diagrams from seven lakes with annually laminated sediments sampled at 40-year intervals are analyzed to isolate the climatic effects from other effects on the long-term dynamics of vegetation during the past 1000–2000 years along a transect from Maine to Minnesota. Principal components analysis is used to reduce the dimensionality of the pollen data. The pollen records from all lakes show long-term trends, medium frequency oscillations, and higher frequency fluctuations. The long-term trend is associated with the neoglacial expansion of the boreal forest. The mechanism causing this replacement is a change in frequency of air masses in the area. The medium-frequency oscillations are also associated with climate changes, the most recent of which is the ‘Little Ice Age’. The climate-related mechanism causing the medium-frequency changes may be changes in disturbance frequency. The higher frequency fluctuations may also be related to disturbance. This analysis of pollen diagrams into time scales of variation has enabled the separation of climate from other factors affecting vegetation dynamics. By comparing the principal components across a transect of sites it proved possible to interpret the climatic effects on vegetation at most sites and not only at range boundaries and ‘sensitive’ sites.

The separation of fluctuation and long-term change in vegetation dynamics of a rising seashore

Abstract: Field layer vegetation in four transects across a rising seashore of the island Skabbholmen (59°47′N, 19°12′E) in the Stockholm archipelago, eastern central Sweden, was sampled at the beginning and end of a six-year period. The data were analyzed by canonical correspondence analysis (CCA) with two external predictor variables, year of sampling and elevation (a proxy for the longer-term trend of change). During the sampling period, the vegetation changed in the direction of the longer-term trend at a rate consistent with the known rate of land uplift. However, a major part of the observed change was in a different direction, reflecting a shorter-term response to disturbance. The analysis effectively separated different types of floristic dynamics related to processes with different time-scales. A comparison with (unconstrained) correspondence analysis (DCA) illustrated the interpretive advantages of multivariate direct gradient analysis over conventional floristic ordination.

Alternate plant life history strategies and coexistence in randomly varying environments

Abstract: Environmental fluctuations can in theory allow the coexistence of ecologically similar species by ‘timesharing’ a niche, as envisioned by Hutchinson. The evolution of this situation is studied in a competition model, using as an example the evolution of seed germination strategies. Coexistence occurs via the evolution of ‘low-risk’ and ‘high-risk’ strategies for dealing with the variability by different species. Coexistence is promoted by intermediate levels of variability or disturbance, and by a trade-off between seed yield and seed survivorship. These results may be applicable also to other low vs. high risk life history options in unpredictably varying environments, such as: stress resistance vs. potentially rapid growth, high adult survivorship vs. high reproductive output. The model’s predictions differ from those obtained without consideration of life history evolution in response to environmental variability, and are consistent with some recent studies of plant strategies in intermittently stressed communities.

Gophers and grassland: a model of vegetation response to patchy soil disturbance

Abstract: We present a computer model which simulates population processes and spatial patterning in response to gopher disturbance in an annual grassland community. The model includes the processes of seed production, dispersal, germination and seedling survival of four main grassland species. Runs show that soil disturbance by gophers affects both short-term spatial patterning and long-term species composition. The main determinant of species behaviour is their relative seed dispersal distances, and the model is relatively insensitive to initial species distribution or abundances. The model adequately simulated short-term community patterning, and provided predictions of long-term dynamics which can now be tested using longer-term field experiments.

Biotic regionalization and climatic controls in western North America

Abstract: New methods of weather analysis accompanied by microhabitat ‘bioassays’ have been applied in several case studies to demonstrate effects of atmospheric processes on patterns of community composition and structure and potential species evolution. Average spatial and seasonal airmass dynamics which determine regional and elevational patterns of relative microhabitat favorability, were found to vary between a recent global warming trend (ca 1900 to 1940) and the subsequent global cooling trend (ca 1940 to 1970). These apparently systematic spatial and temporal shifts in weather were related to plant establishment patterns and community composition and structure. The proposed causal mechanisms function, in part, through regional shifts in microhabitat size. These effects are similar to larger scale, longer term shifts deduced from the late Quaternary fossil record. By modifying the spatial approach, month-to-month and year-to-year variability of weather has been examined for the last 130 years at individual points in southwestern North America. Three climatic regimes (the end of the Little Ice Age, the recent warming trend and the recent cooling trend) exhibited distinct year-to-year patterns of weather that can be related to the establishment of different kinds of plants (e.g., C4 grasses versus C3 shrubs). Oscillations between different temporal climatic regimes appear to promote the episodic establishment of different life forms, but not necessarily their local extinction. The two methods of weather analysis have been combined in a regional assessment of climatic controls of different biomes in space and time with a primary focus on the Chihuahuan desert. Natural ecotones between the Chihuahuan desert and neighboring biomes are clearly related to large scale airmass dynamics associated with seasonal oscillations in jetstream position. The weather patterns controlling ecotonal positions result from seasonal topographic influences on the general circulation of the atmosphere. The apparent stability of these patterns allows causal hypotheses of biogeographic dynamics and the evolution of physiological traits and life history characteristics.

Spring grazing by sheep: effects on seasonal changes during early old field succession

Abstract: This paper describes early secondary succession on an old field on limestone released from cultivation four years previously. Seasonal changes in plant composition after spring grazing by sheep are compared with those in ungrazed controls. Grazed and ungrazed paddocks were laid out in Latin squares. Plants were sampled before and several times after grazing in April, at several spatial scales.

Analysis of seedling banks of a climax beech forest: ecological importance of seedling sprouts

Abstract: Most of the common and dominant tree species in gaps of a climax Japanese beech (Fagus crenata) forest have large seedling banks on the forest floor. These seedlings were classified into “true seedlings” and “seedling sprouts”, each of which was further classified into two and three subtypes, respectively. Each species had a characteristic seedling form spectrum. The seedling bank of beech was composed almost solely of true seedlings, whereas, seedling sprouts predominated in the seedling banks of lower tree species such as Prunus grayana Maxim. and some species of Acer. The age structures suggested that seedling sprouts had longer life spans and had been recruited more constantly than true seedlings. The habit of sprouting and creeping seemed to enable seedlings of these species to persist for long periods, thus increasing their chance for eventual success in canopy gaps.