Plant Life History Traits of Rare Versus Frequent Plant Taxa of Sandplains: Implications for Research and Management Trials
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BIOLOGICAL CONSERVATION 136 (2007) 44– 52 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/biocon Plant life history traits of rare versus frequent plant taxa of sandplains: Implications for research and management trials Elizabeth J. Farnsworth* Harvard University, Harvard Forest, 324 North Main Street, P.O. Box 68, Petersham, MA 01366, USA ARTICLE INFO ABSTRACT Article history: I apply a comparative, functional group approach to coastal sandplain grassland taxa in Received 10 May 2006 order to examine whether rare plant species share certain aspects of rarity and life history Received in revised form characters that are distinct from their more common, co-occurring congeners in these hab- 14 September 2006 itats. I compiled a comparative data set containing 16 variables describing biogeographic Accepted 26 October 2006 distributions, level of imperilment, habitat specialization, vegetative versus sexual repro- Available online 8 December 2006 duction, seed dispersal, and dormancy of 27 closely-related pairs of plant species that con- trast in their abundance (infrequent versus common) in coastal sandplain grasslands. Keywords: Frequent and infrequent species were paired within genera (or closely related genera) Sandplains and thus distributed equivalently across families to control for phylogenetic bias. Paired Plants comparisons revealed that infrequent species were intrinsically rarer range-wide, and Rarity exhibited a narrower range and more habitat specialization than their common relatives. Life history A classification tree distinguished infrequent species from common species on the basis Comparative method of higher habitat specialization, larger seed size, smaller plant height, less reliance less on vegetative (colonial) reproduction, and tendency toward annual or biennial life history. Research and management steps to reduce competition from larger-satured, colonial, perennial species are recommended for these infrequent species. Basic research involving more species and more data on ecophysiological characters, demography, and competitive interactions are needed to identify critical life history traits that will influence responses to particular management regimes. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction comparisons, species can be categorized conceptually into functional groups on the basis of shared traits and responses It is challenging to design effective management strategies (Gitay and Noble, 1997). Suites of species can thus be identi- that foster the survival of several rare species simultaneously fied that will respond predictably and similarly to particular (Groves, 2003; Pa¨rtel et al., 2005). Taxa can differ widely in types of environmental manipulation. their apparent habitat ‘‘preferences,’’ their vulnerability to Likewise, large numbers of species can be grouped and competition and other threats, and fundamental aspects of studied separately based on the degree of rarity and severity their life histories; hence, they may respond in contrasting of range restriction they exhibit. Globally-rare taxa may exhi- ways to management activities. However, the comparative bit certain traits that consistently distinguish them from taxa method can be a useful approach for detecting commonalities that are regionally rare but globally secure (Kunin and Shmi- and differences among species (Harvey and Pagel, 1993; Kunin da, 1997; Pa¨rtel et al., 2005). Several multi-species studies of and Gaston, 1997; Bevill and Louda, 1999). Using systematic national or regional floras identify and prioritize groups of * Present address: Ecology Wise Consulting, 163 NE Fitzwilliam Road, Royalston, MA 01368, USA. Tel.: +1 978 724 3302x251. E-mail address: [email protected]. 0006-3207/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2006.10.045 BIOLOGICAL CONSERVATION 136 (2007) 44– 52 45 species based on range-wide versus localized rarity patterns In this review, I use multi-variate analyses of a data set (e.g., Schnittler and Gu¨ nther, 1999). These are useful for pin- that brings together information on biogeography, habitat pointing species that are intrinsically rare throughout their breadth, rarity, and life history characters of 27 congeneric range (‘‘naturally rare’’ in the parlance of Pa¨rtel et al., 2005) or closely-related pairs of ‘‘infrequent’’ and ‘‘common’’ spe- and those that may be declining due to more local, usually cies found primarily in coastal sandplain grassland habitats. human-imposed, causes that may be addressed with prudent I define ‘‘infrequent’’ plants in the context of this study as management. However, consistent data that allow for in- species that are targets of concerted conservation and man- depth comparisons of many autecological features across agement in the coastal sandplain grasslands of northeastern species are very scarce (Bevill and Louda, 1999). While some North America. Most of these species are typically noted as studies have identified certain reproductive or life-history absent or very infrequent in botanical surveys of managed traits that are associated with species of particular rarity plots, despite the fact that management efforts are often de- types (e.g., Kunin and Shmida, 1997; Pilgrim et al., 2004), oth- signed in part to create amenable habitat for them (Patter- ers have not discovered patterns that meaningfully inform son and Clarke, 2006; Beattie et al., this issue). By contrast, management (Lozano et al., 2003). I define ‘‘common’’ species as native taxa that are frequently In inland grassland ecosystems, the functional group con- encountered in managed plots or sandplain grasslands gen- cept has been useful for understanding species sorting and erally (e.g., Dunwiddie, 1998; Patterson and Clarke, 2006; Lez- niche-partitioning along environmental gradients (Tilman berg et al., 2006). I ask first, what is the range-wide rarity and Wedin, 1991) and for predicting patterns of invasibility status and habitat specificity of the infrequent species in (Symstad, 2000). Functional group approaches also have been northeastern sandplain grasslands? Second, are there suites applied successfully in tailoring specific management re- of traits that are consistently exhibited by infrequent species gimes for particular groups of grassland plants, particularly that distinguish them from more common, closely related in Europe (Kleyer, 1999; Cousins et al., 2003; Ku¨ hner, 2004) taxa? I examine the biogeographic distribution, reproductive and Australia (McIntyre et al., 1995). Despite the demon- modes, dispersal capacity, seedbanking, and architecture of strated utility of these methods, these concepts have not been these species – features related to fitness, colonization po- used to date to inform rare species research and conservation tential, and competitive ability. I also ask if these informa- in North American coastal sandplain grasslands, which share tive traits yield insights for designing research and similar ecological characteristics – including droughty soils management strategies, tailored to particular life histories. and a propensity for burning – with other types of grasslands. Instead, rare plant species of coastal sandplains typically 2. Methods have been studied singly, with careful autecological observa- tions made about their life history and responses to distur- I assembled a list of plant species (Table 1, nomenclature fol- bance (Lamont et al., 1988; Dunwiddie, 1990; Vickery, 2002; lows USDA, NRCS, 2006) reported from coastal sandplain Martine et al., 2005). These are extremely valuable data, grasslands, sensu lato, incorporating the set of multiple grass- but do not by themselves necessarily yield insights into land types defined by Dunwiddie et al. (1996). Like Dunwiddie multi-species management. Only rarely have suites of rare (1998), I focused on forb, graminoid, and shrub species, the species been studied together in order to detect commonal- predominant life forms of grasslands. I identified a set of 27 ities in habitat preferences (Clarke and Patterson, this is- infrequent native species based on listing as Division I–III in sue). From a different angle, phytosociological studies have the Flora Conservanda: New England (Brumback et al., 1996); revealed distinct species assemblages within coastal sand- state-listing by northeastern Natural Heritage Programs (Nat- plain grasslands, their affinities with certain soil types, ureServe Explorer, 2006); the botanical studies of Bicknell and their successional relationships (Harper, 1905; Conard, from 1908 to 1919 on Nantucket Island, Massachusetts (sum- 1923; Wells and Shunk, 1931; Latham, 2003; Dunwiddie marized in Bicknell, 1919); floristic inventories and reviews et al., 1996; Goebel et al., 2001; Jordan et al., 2003); these (e.g., Olmsted, 1937; Stalter et al., 1986; Martha’s Vineyard studies occasionally make reference to rare species, from Sandplain Restoration Project, 1998; Dowhan and Rozsa, which we can glean more information. Finally, there is a 1989; Sutton et al., 1990; Sorrie and Dunwiddie, 1996; Fair- growing collection of published and unpublished studies brothers, 1998); Conservation and Research Plans recently about the generalized effects of particular management completed by the New England Wild Flower Society (Farns- techniques (particularly grazing, mechanical clearing, fire, worth, 2003), in which the species were noted as declining and the interaction between the three) on common and or sporadic in occurrence; and personal