The following abstracts and project descriptions represent ongoing
work that utilize the BSS data. If you are interested in
using the BSS data available on this site, please be sure you are
not duplicating the projects described here.
S. T. A. Pickett and M. Cadenasso
We are examining both temporal and spatial patterns in the Buell-Small Succession Study. In particular, we are examining the following temporal components of the process: community diversity and richness, invasion and demise of species populations, species interactions, and interactions among different assemblages and plant functional groups. We employ such techniques as multivariate statistics (including ordination), community classification, boundary analysis, and information theory.
Spatial trends to be examined are colonization and invasion, the horizontal arrangement of functional groups and how those patterns change through time, and relationship to larger landscape structural features such as edges and adjacent land cover types. We will use such techniques as geostatistics and standard indices of landscape quantification.
S.Bartha, S.T.A.Pickett, and M.L. Cadenasso
We are studying assembly rules, i.e. ecological restrictions on the observed patterns of species presence or abundance that are based on the presence or abundance of other species. Contrary to the traditional non-spatial equilibrium theory of assembly rules, we are looking for rules that are extended from the interaction-based rules to the rules controlling the mechanisms of spatio-temporal persistence and mobility of species and that are constrained by the actual composition, complexity and heterogeneity of vegetation. The calculations are based on the spatio-temporal matrices of local (1 sq.m. scale) vegetation attributes (e.g. total cover, richness, diversity, evenness), and the local attributes of vegetation change (e.g. the temporal change of total cover, the species turnover, rates of local immigration and extinction, and the temporal changes of richness, diversity and evenness). These matrices are tested against static null-models based on constrained randomizations (e.g. Mantel test), and against spatially explicit dynamic null-models (e.g. interacting particle systems and cellular automata). The resolution and continuity of HMF data enable us to scale for both local and patch-based rules, and for other cummulative effects. Rules have been found in the form of spatio-temporal dependence, dominance hierarchy, and dynamic boundary relationships in coenostate-spaces. Comparing to other studies of assembly rules we found a considerable number of significant constraints on coexistence that could be understood via decomposing the community level patterns in the attributum-space into functional groups or species, and via decomposing the stand-scale spatiotemporal pattern in the topographical-space into spatial and temporal patch dynamics.
S.Bartha, S.T.A.Pickett, and M.L.Cadenasso
It is well known that more productive habitats have relatively less diverse vegetation (Grime 1979). Recently, the opposite relationship has been described by Tilman (Tilman and Downing 1994, Tilman et al. 1996, 1997, cf. Tilman 1999) who found that diversity and productivity are positively related. Cross-site comparisons and extensive surveys over different biomes and different taxa showed all kinds of relationships, including positive, negative, and neutral relationships (Waide et al. 1999). Our hypothesis is that the relationship between diversity and productivity is context dependent and can be understood on the bases of a spatially explicit non-equilibrium community theory. Our results calculated from the HMF data showed that within the same secondary successional process, positive, negative, or neutral relationships between diversity and total cover of species can be found in different (pioneer, early and intermediate) stages of succession. Positive relationships are typical for simple, relatively homogeneous, unsaturated stages. Negative relationships are typical for simple, saturated stages, while the relationship is masked, i.e. become neutral above a certain threshold of complexity and heterogeneity. Similarly, the relationship between the change of total cover and diversity become significant only in specific periods, after drought-induced temporal collapse of total cover. More diverse plots recovered faster after serious drought in the early stage of succession, in simple, homogenous vegetation dominated by herbs. A similar relationship was revealed in the later stage in complex, heterogeneous vegetation dominated by various life forms. However, here the community level recovery has prolonged via lag effects.
S. J. Meiners
The invasion of plant communities by exotic species is a major concern for ecologists and natural resource managers. A major limitation to our knowledge of exotic species is the lack of long-term data on invasions. The long-term data from the BSS is ideal for looking at historical plant invasions to determine temporal patterns of invasion. By understanding how invasions function over time, we will be better able to assess and manage exotic plant invasions.
My research, funded by the USDA, focuses on the relationship of exotic species to diversity in old field succession.
| The first part of this project involves determining the patterns of invasion over time (Fig. 1). This work describes changes in populations and community structure with time since abandonment. I am also examining the relationship of diversity to the presence of exotic species in the community. |  |
The goal of this research is to determine how exotic species invasions are associated with community diversity. The diversity of the plant community may be reduced by exotic plant invasions, may regulate community invasibility, or both. Careful examination of the historical data should help to determine which of these mechanisms is operating. Experimental work will also test these hypotheses, utilizing controlled plant introductions into fields at HMFC.
M. H. H. Stevens, M. Cadenasso, and S. T. A. Pickett
Species diversity peaks at intermediate levels of disturbance, and secondary plant succession provides one of the best studied examples. Peak diversity occurs in mid-succession because large numbers of both r- and K-selected species temporarily co-occur. The general mechanisms thought to drive this pattern, however, remain untested. We are using a simple model (Pacala and Rees 1998) and data from the 40+ year Buell-Small Succession Study to estimate the relative importance of two different mechanisms of species coexistence: (1) a tradeoff between rapid growth and competitive ability and (2) a trade-off between colonization and competition. Preliminary results are consistent with a tradeoff between rapid growth and competitive ability, but provide no support for the trade-off between colonization and competition. If this finding is robust, it provides evidence for a general mechanism controlling species diversity in successional systems. It also carries implications for predicting extinction rates in the face of world wide habitat fragmentation and loss.
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