Paul A. Keddy

Relative competitive performance of 63 species of terrestrial herbaceous plants

Abstract There is growing evidence that plant and animal species are arranged in hierarchies of relative competitive performance. More work is needed to determine which plant traits best predict relative competitive performance. We therefore measured relative competitive performance of 63 terrestrial herbaceous plant species using Trichostema brachiatum as a reference species (that is, phytometer or target species). The neighbour species came from a wide array of terrestrial vegetation types (e.g. rock barrens, alvars, old fields), and represented a wide array of growth forms (e.g. small rosette species such as Saxifraga virginiensis and large clonal graminoids such as Agropyron repens). The experiment was repeated with two pot sizes: large (control) and small (stress treatment). Relative competitive performance in large pots (controls) was highly correlated with that in small pots (stress treatment) (r = 0.90, p < 0.001). The hierarchy of relative competitive performance in the large pots was also highly correlated with the hierarchy in the small (stressed) pots (rs = 0.91, p < 0.001). Principal components analysis and multiple linear regression showed that plant size (measured by total biomass, above‐ground biomass, below‐ground biomass, canopy area, height and leaf area index) and leaf shape (measured as length to width ratio, length, width) were the two characteristics that best predicted relative competitive performance (large pots, ru200a2 = 0.55; small pots, ru200a2 = 0.48). Nomenclature:Gleason & Cronquist (1963); Morton & Venn (1990).

Patterns of herbaceous plant diversity in southeastern Louisiana pine savannas

Abstract Question: How diverse are Louisiana pine savanna plant communities and how is diversity affected by time since burn and removal of a competitively dominant species? Location: Lake Ramsay, southeastern Louisiana, USA. Methods: Species-area curves were constructed from nine nested quadrats in open savanna differing in time since burn (6, 18 and 30 months). Species frequency was determined for 100 1-m2 quadrats. The dominant grass, Andropogon virginicus, was removed with herbicide from moist and dry sites to test for possible effects of competition. Results: Slopes of log-log species-area relationships were steep (0.195 to 0.379). Time since burn did not affect the richness of herbaceous plants, only woody species. More than half of all species recorded (43/79, 54 %) were infrequent (in < 10 % of quadrats). After two years, there were no differences in species richness and composition for plots with and without A. virginicus. Conclusions: The high species diversity is typical of other savannas across the coastal plain. The large number of infrequent species indicates that the core-satellite pattern of species occurrence found in temperate grasslands does not apply to southern pine savannas. The absence of effects due to removal of a dominant may be due to insufficient observation time, or low competition. Most species have traits, such as diminutive life forms, that suggest they are weak competitors for light in the presence of robust matrix grasses and in the absence of fire. Many species in Pinus palustris savannas are likely either fugitive or peripheral species. Nomenclature: Integrated Taxonomic Information System (http://www.itis.usda.gov/).

Can competitive ability predict structure in experimental plant communities

Question: Two questions were posed: 1. Can an independent measure of relative competitive ability be used to predict the abundance of species in mixtures? 2. Is the success of those predictions affected by low fertility (stress simulation) or clipping (disturbance simulation)? Location: Greenhouse at Carleton University, Ottawa, Canada. Methods: We collected adult plant ramets of 11 species from the field and transplanted one ramet of each species into 56 containers of 60 L. We applied a 4 × 2 factorial combination of fertilization (none, full nutrients except N, full nutrients except P, full nutrients) and clipping (no clipping, clipping to 10 cm above soil) with seven replicates of each treatment. After two growing seasons the aboveand below-ground biomass of each species was determined. Results: Regression analyses uncovered a significant positive relationship between plant biomass (measured in this study) and relative competitive ability (as measured in an independent study) under all experimental conditions. Both the mean slope and mean R2 were lowest in treatments with low nutrients and highest in the full nutrient treatment (irrespective of clipping). Conclusions: Our results show that (1) at high fertility, relative competitive ability can generally predict the abundance of species in experimental plant communities, and (2) the intensity of competition (inferred from the magnitude of the slope or R2) increased with increasing nutrient supply, particularly nitrogen.

Milestones in ecological thought – A canon for plant ecology

Abstract Scientific progress in plant ecology is at risk of being obscured by increasing ignorance of major works in the field. The driving force seems to be the twin seductions of novelty and crowd psychology. I illustrate this tendency with three examples from plant community ecology that span the past thirty years of ecological research. I offer, as one solution, the concept of a canon: a short list of essential books that we assume all students and co-workers have read, a short list that summarizes the wisdom of the discipline. A canon can be likened to DNA, be it in music, art, or science, as it carries forward through time the key ideas that have worked in the past. Without a canon, there is no memory of past achievement, no context for appreciating current work, and no way of judging the quality of newer productions. I suggest 20 essential books (the short canon), and 22 complementary readings, for a total of 42 books needed in any young professionals library on plant ecology.

Patterns of frequency in species-rich vegetation in pine savannas: Effects of soil moisture and scale

Abstract Our principal objective was to document dominant plant composition and the species frequency pattern in a plant community type, longleaf pine savanna, known for its extraordinary number of vascular plant species. We also tested whether an important habitat factor, soil moisture, affected the resulting patterns, and whether the patterns were scale-dependent. We began with a collection of 120 sample plots (1- × 1-m) in a wet coastal plain savanna. These plots contained 126 plant species. The 3 dominant species by cover were Rhynchospora gracilenta (15.37%), Schizachyrium tenerum (13.36%), and Scleria pauciflora (10.07%). The species frequency distribution was a skewed unimodal pattern with most species occurring infrequently, in less than 10% of the plots. There was no evidence for bimodality. To test whether soil moisture affected species frequency patterns, we sorted the plots into 2 groups: 60 representing wetter conditions and 60 representing drier conditions. Measured by percent cover, the dominants in the wetter plots were R. gracilenta, Dichanthelium scabriusculum, and S. pauciflora, whereas in the drier area they were S. tenerum, Ilex glabra, and D. dichotomum. The species frequency pattern was similar for both wet and dry plots (χ2= 8.97, P> 0.05). To explore possible effects of sample area on this pattern, we sampled a further 75 plots in a larger tract of similar habitat in De Soto National Forest, using 4 sample areas of 0.1, 1, 10, and 100 m2. Again, the species frequency distributions all had a skewed unimodal pattern. These patterns are consistent with other studies of savannas but do not appear consistent with the bimodal patterns reported from some grasslands. Further studies of frequency will determine the degree of generality of such patterns and their relationship to mechanistic processes in plant communities. Nomenclature: Kartesz, 1994.

The Management of Wetlands for Biological Diversity: Four Principles

There are vast areas of major kinds of wetlands: swamps, marshes, fens, and bogs (Table 2.1). Because plant and animal species, vegetation, and wetland types are so variable, it may seem difficult to treat all of these together. Far too often, one encounters specialist publications on the plants or animals of a particular bog, fen, marsh, mire, reed swamp or aquatic community; these balkanized treatments detract from the general principles involved in managing wetlands. Furthermore, because so much focus in wetland management is placed on fish and wildlife production this too often takes precedence over other ecological objectives. Large expanses of wetland vegetation are generally ignored or treated in passing as “aquatic plants.” Our objective here is to try to pull together all these disparate vegetation types, species, and physiographic types, and present four general principles necessary for managing them to maintain and enhance biological diversity.

Extending the generality of field experiments

An objective of competition theory and, in fact, of any ecological theory, has to be the ability to make general predictive statements about the structure and behaviour of ecological communities. We have already explored the difficulties in arriving at general conclusions through collecting special cases (Chapter 2), and R. H. Peters (1980b) has provided a useful reminder that, in the absence of general principles, ecology becomes natural history. Therefore,Table 4.4 listed generality as one of the most important criteria to consider when planning ecological research.

Small Changes in Flooding Have Large Consequences: Experimental Data from Ten Wetland Plants

Flooding regime is a major determinant of vegetation composition in wetlands. Flooding regimes are also commonly altered by human activity. We used an experimentally-created elevation gradient on mineral soil to measure the responses of ten common marsh species to flood regimes ranging from 0 to 100xa0% of the growing season. We asked three questions. (1) What are the minimum and maximum tolerances of these ten species to a flood duration gradient? (2) Is there one duration of flooding that is physiologically optimal for a majority of the species? (3) How sensitive are these species to minor changes in flood duration? We found that the number of species, the cover and the aboveground biomass were highest when flood duration was less than a third of the growing season. All species showed a pattern of inclusive fundamental niches for flooding duration, with a preference for shorter periods of flooding, for less than a third of the growing season. Narrow-leaved graminoids became relatively more common with longer flooding duration. This study challenges our notions of the fundamental niches of these wetland emergent plants. Other factors beyond flooding tolerance must be acting to structure wetland communities along wetland depth gradients.

The World's Largest Wetlands: Contents

During the past century, humans have destroyed approximately 50 percent of the world’s wetlands. As wetlands shrink in area, their important functions decline too: there is reduced carbon storage, lower biological diversity, lower fish production, less available water during drought, higher flood levels in spring, and higher risk of water pollution. The world’s largest wetlands have not been described, ranked, and compared previously. For the first time, an international team of scholars shares its understanding of the status, ecological dynamics, functions, and conservation needs of the world’s largest wetlands.

The World's Largest Wetlands: Frontmatter

During the past century, humans have destroyed approximately 50 percent of the world’s wetlands. As wetlands shrink in area, their important functions decline too: there is reduced carbon storage, lower biological diversity, lower fish production, less available water during drought, higher flood levels in spring, and higher risk of water pollution. The world’s largest wetlands have not been described, ranked, and compared previously. For the first time, an international team of scholars shares its understanding of the status, ecological dynamics, functions, and conservation needs of the world’s largest wetlands.