A Study of the Distribution of Several South Florida Endemic Plants in the Florida Keys

Ross, Michael; Ruiz, Pablo

In this Report, the results of a study of the distribution and status of five plant taxa-Indigofera keyensis, Chamecrista lineata var. keyensis, Chamaesyce deltoidea subsp. serpyllum, Melanthera parvifolia, and Linum arenicola-are outlined. Whereas the latter two species are known from the South Florida mainland as well as the Florida Keys, our investigation concerned only the Keys populations. The study was undertaken in order to assess the need for conservation efforts under the Federal Endangered Species Act. Prior to this investigation, what little was known about the distribution of these plants was inferred from species lists (e.g., Austin 1978), herbarium collections, and other anecdotal accounts, as well as published flora (Long and Lakela, 1978). These sources clearly indicate that I. keyensis is a plant of low, coastal areas, and the other four taxa are associated with pine rockland forests, but they provide little notion of the plants' extent, abundance, or habitat affinities within those broad habitat categories. Such information is a necessary initial step in the process of designing management options-particularly fire management in pine rockland forests-capable of increasing the abundance of at-risk plants. For the four pineland herbs, this study builds on results of an earlier synecological investigation undertaken by the senior author and others (Ross et al., 1992a). Management directed at individual plant species may include actions which modify habitat in order to make it more favorable for the species of interest, or efforts to establish plants in appropriate sites in which they do not presently occur for historical or stochastic reasons. Knowledge of species microhabitat relationships necessary to support such activities may be derived from experimentation and/or from careful and critical analysis of spatial or temporal patterns. The latter approach is only possible if, within the range of potential habitats, equal sampling attention is accorded sites where a species does not occur as those where it does. For this reason, we chose as our sampling domain the ca 880 hectares of Lower Keys pine forest rather than known populations of C. lineata, M. parvifolia, C. deltoidea, and L. arenicola. For I. keyensis, on the other hand, it was necessary to limit our efforts to known populations because of the infeasibility of adequately sampling all coastal areas of the Florida Keys. Research objectives for I. keyensis and for the pine rockland endemics were therefore different. For I. keyensis, our objective was to gain a better understanding of the plant's preferred habitat, and the status of and threats to known populations. For the pineland group, our objectives were threefold: 1. Describe the distribution of each species. 2. Determine whether within- and among-island differences in species distributions are explainable on the basis of easily measured structural variables. 3. Assess the relationship between fire history variables and species' abundances.