Salt spray and edaphic factors maintain dwarf stature and community composition in coastal sandplain heathlands Megan E. Griffiths 1,2, * 1 Department of Biology, Tufts University, Medford, MA, 02144, USA; 2 School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, South Africa; *Author for correspondence (e-mail: Griffithsme@ukzn.ac.za; phone: +27-332605110; fax: +27- 332605105) Received 19 May 2005; accepted in revised form 26 January 2006 Key words: Martha’s Vineyard, Massachusetts, Plant water relations, Soil, Vegetation zonation Abstract North American coastal sandplain heathlands are unique in species composition and vegetation, but the extent to which edaphic factors influence the structure of these communities is currently debated. It was hypothesized that salt spray and edaphic factors maintain the dwarf stature and community composition of heathlands by limiting plant growth and excluding competitively dominant woody species close to the ocean. Field surveys were carried out to investigate the spatial patterns of salt spray accumulation, soil salt and soil moisture. High salt spray correlated significantly with increased leaf necrosis and water stress in Myrica pensylvanica and with decreased plant height. Plant community composition changed across a salt spray and soil gradient, as well. Distinctive sub-communities were identified that separated according to soil salt and soil moisture but salt spray was the main factor affecting sites occupied only by heathland vegetation. Results from this study suggest that salt spray suppresses the growth of heathland plants in close proximity to the ocean, and therefore maintains the low stature in these dwarf shrublands. This research also demonstrates that the physical environment influences the community structure in heath- lands, particularly by limiting tree species from growing in high salt spray, low water availability sites. Introduction Coastal sandplain heathlands are early succes- sional, dwarf-shrub communities with a maritime distribution in the northeastern United States and southeastern Canada (Dunwiddie et al. 1996). These communities are influenced by disturbance and land use, which limit the establishment and growth of competitively dominant species such as Pinus rigida and Quercus ilicifolia (Dunwiddie 1989; Dunwiddie and Caljouw 1990; Foster and Motzkin 1999; Eberhardt 2000). The effects of burning and domestic livestock grazing have been studied extensively in coastal sandplain heath- lands and these factors are recognized as main- taining heterogeneity on a landscape scale (Patterson and Sassman 1988; Dunwiddie 1990; Stevens 1996). However, very little attention has been given to the role that natural abiotic factors may play in maintaining these communities within sites that have the same disturbance and land use history. Plant Ecology (2006) 186:69 –86 Ó Springer 2006 DOI 10.1007/s11258-006-9113-8