Defining conservation priorities for plant taxa in southeastern New Brunswick, Canada using herbarium records

Abstract

Biological databases are needed for the development of ecologically sensitive land management strategies. Quantitative information that would serve this purpose is typically unavailable or limited to a few species. An alternative is qualitative herbarium data. While often collected unsystematically, herbarium records are usually available for many taxa. We explored the use of herbarium records for defining conservation priorities for plant taxa found in southeastern New Brunswick, Canada. Our objectives were: (1) to identify rare plant taxa collected in the study area; and (2) to group these taxa by habitat affinity, and refine their conservation status based on the vulnerability of the habitats to current and anticipated land use. The temporal and geographical variations in the collection of the herbarium records are described. A total of 351 herbarium records were found, representing 161 different taxa from 46 families. Nine habitat types were identified. Two of these habitats, rich tolerant hardwood forest and wet Thuja occidentalis forest, were classified as endangered. Collections were concentrated near settlements, in areas with road access, or in known species-rich hotspots that were repeatedly revisited. The number of collections varied through time, depending on the presence of botanists working within the study area. Despite limitations, herbarium data served as a valuable first step in identifying species of conservation concern and highlighting information gaps requiring further investigation.

Introduction

Intensive land management has resulted in the loss of plant species diversity in many areas of North America (Duffy and Meier, 1992, Halpern and Spies, 1995, Meier et al., 1995). Concerns over the negative impact of intensive land use have led to calls for increased protection for species intolerant of human disturbance (e.g. Holsinger, 1992, Meier et al., 1995), and for the development of ecologically sensitive management practices to augment existing protected area networks (Falk, 1990, Matlack, 1994, Halpern and Spies, 1995). The need to implement both these initiatives is growing. Given the prevailing political and economic climates in many jurisdictions, opportunities for establishing new reserves have diminished and protection must be focused in locations where it is most needed (Pressey, 1992). Also, in landscapes where large percentages of the area are not protected from human use, there is no guarantee that established reserves will withstand the effects of isolation and invasion by exotics. As a result, provisions must be made to sustain populations of vulnerable species in the areas outside of reserves by conservation stewardship (e.g. Silver et al., 1995, MacDougall and Foley, 1996) or by management operations that reflect natural disturbance intensities and promote spatial and temporal habitat diversity (Freedman et al., 1994).

While the need for increased natural area protection and ecologically sensitive land management practices is recognized, mechanisms for creating and implementing such programmes efficiently are not always well developed. A fundamental limitation in many areas is the lack of species-level information on the composition and distribution of extant flora and their susceptibility to land use intervention. Of particular interest are the uncommon and rare species which make important contributions to local (Miller, 1986, Nilsson et al., 1988, Hill and Keddy, 1992, Johnson and Leopold, 1994) and regional (Gentry, 1986) species diversity, yet may be most at risk due to small population sizes and restricted distributions. Ideally, floristic databases would exist for all areas proposed for land management. Such databases would include information on the biology of member species, including the processes contributing to the limited abundance of rare species. Unfortunately, such information is often not available and may be obtained only through detailed demographic studies.

Conservation management planners thus face a dilemma. On the one hand, there is a need for programmes that promote the long-term viability of populations. On the other, the species- and assemblage-specific information required to effectively design such strategies is incomplete, with the number of species in need of study far outnumbering the number of scientists available to identify, study, and monitor them (Keddy, 1991).

Given this situation, and the fact that economy-driven land management will continue to take priority, alternative information sources are required to assist the design of conservation-oriented management procedures. This includes land use practices that minimize disturbance of sensitive habitats and the creation of protected area networks that maximize the capture of rare taxa in the limited area typically available for reserves in heavily managed landscapes (e.g. Pressey et al., 1994, Csuti et al., 1997). While detailed quantitative data are lacking, extensive qualitative data are often at hand on a region-by-region basis in herbaria. Herbarium data provide two types of information that are especially relevant for conservation planners: locations of species occurrence, indicating where species have been found and may persist, and descriptions of habitat affinities for each species. Habitat information describes the environmental conditions with which the taxon is associated, and can be used to direct Geographic Information Systems (GIS)-based searches for undiscovered locations where these conditions, and their associated species, may occur (Rhoads and Thompson, 1992; MacDougall and Loo, unpublished).

Herbarium data, and biological inventory information in general, do have limitations, leading some to question the value of such information for directing ecologically-based conservation work (e.g. Renner and Ricklefs, 1994). Collection efforts are often unsystematic (Shevock and Taylor, 1987, Stern and Eriksson, 1996); common species may be better represented than rare species (Rich and Woodruff, 1992), or the reverse; taxonomic nomenclature may be outdated (Robinson et al., 1990); and the information accompanying specimens, such as location and habitat descriptions, is sometimes imprecise, especially for older records. Despite these problems, herbarium data are generally available for most or all known plant species within a region, and given the increasing demand for baseline information by land managers and the cost of collecting such data in alternative ways, should be utilized as completely as possible.

In this study, we explored the use of herbarium data for defining conservation priorities for infrequently occurring vascular plant taxa within a 420 000-ha study area in southeastern New Brunswick, Canada (Fig. 1). Our objectives were: (1) to use herbarium records to identify provincially uncommon, rare, and very rare plant taxa recorded in the area; and (2) to further refine conservation priorities among the identified taxa based on habitat vulnerability. The temporal and geographical variations in the collection of the specimens, and the effect of these variations on the usefulness of the herbarium data, are described.