The ¯ora of a cultural landscape: environmental determinants of change revealed using archival sources Duncan McCollin a, *, Linda Moore b,1 , Tim Sparks c a School of Environmental Science, University College Northampton, Park Campus, Northampton NN2 7AL, UK b The Wildlife Trust for Northamptonshire, Lings House, Billing Lings, Northampton NN3 8BE, UK c Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS, UK Received 3 April 1998; received in revised form 8 April 1999; accepted 11 May 1999 Abstract In a novel approach to the use of archive biological information, qualitative vascular plant abundance categories from the 1930 Flora of Northamptonshire were matched with quantitative distribution data from the 1995 Flora in order to reveal the species that have changed in commonness relative to their pre-1930 populations. Factors thought to be responsible for these changes were analysed by investigating dierences in habitat preference, dispersal ability and climate change indicators, using information from published sources. Changes in status were most dramatic for plant species associated with arable, wetland and woodland habitats. A highly signi®cant factor was the trophic status of preferred habitats: burgeoning species were associated with higher soil nitrogen levels. In addition, evidence for the eects of habitat fragmentation were detected both in terms of changes in abundance being correlated with dispersal-related ecological characteristics and to the number of habitats with which particular species were asso- ciated. The discussion concerns the changing land use and farming practices in the county of Northamptonshire, which are widely held to be linked with a deterioration in plant biodiversity since 1930. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Land use change; Habitat fragmentation; Eutrophication; Plants; Ellenberg indicators 1. Introduction There is global concern over the current loss of bio- diversity and its consequences for cultural, economic and ecological balance (HMSO, 1994; Heywood, 1995). In order to formulate ecient and successful policies for achieving the aims of conserving and enhancing biodi- versity as outlined in national action plans (e.g. HMSO, 1994; 1995) there is a need for baseline data to establish levels from which to assess and evaluate change. A great deal of qualitative information about vegetation in pre- vious periods exists but is generally considered incom- patible with data derived using more recent quantitative methods (Mason, 1990; Shaer et al., 1997; McCarthy, 1998). In Britain, and probably throughout Western Europe, many species of conservation interest are con®ned to habitats that have survived due to centuries of manage- ment as part of the cultural landscape (Rackham, 1986; Birks et al., 1988; Bignall and McCracken, 1996; Phillips, 1998). It is widely recognised that the period since 1945 has been a time of great change in British agriculture which has led to the decline in semi-natural habitats associated with pre-World War II (WWII) farming methods (O'Connor and Shrubb, 1986). However, with- out long-term data covering this critical period of change, conservation biologists have often focussed their eorts on rare species since they are at most risk of extinction (e.g. Colston et al., 1996). Nonetheless, extinction is a natural process and rare species tend to go extinct even without human intervention, although human modi®ca- tion of ecosystems potentially accelerates rates of extinction through a cumulative process of population decline at both local and regional scales (Diamond, 1984; Pimm et al., 1988; Williamson, 1989). In a bid to extract information about change in vegetation and its causes, here we attempt to relate information on plant abundance from 1930 to contemporary records of plant species in Northamptonshire, eastern England. 0006-3207/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(99)00070-1 Biological Conservation 92 (2000) 249±263 www.elsevier.com/locate/biocon * Corresponding author. E-mail address: duncan.mccollin@northampton.ac.uk (D. McCollin). 1 Present address: Ecologist, Planning Department, Cardi County Council, Atlantic Wharf, Cardi CF1 5UW, UK.