The analysis of long-term changes in plant communities: case studies from the Netherlands
Schaminée, Joop H.J.; van Kley, James E.; Ozinga, Wim A.
The nature of the plant community has been a long-standing point of discussion in vegetation science. Already in the early decades of the last century, debate focussed on whether plant communities existed as discrete, intra-dependent entities or merely as loose assemblages of species each responding individualistically to local environmental conditions. Despite the fundamental nature of this question, the issue is generally ignored in many studies. For example, within the study of succession, a major topic in vegetation science, the question of stability within vegetation types is rarely addressed. Generally, succession research investigates vegetation development in terms of communities passing through a series of vegetation types, without considering the nature of these types; they are implicitly regarded to be constant. To some extent, this idea is a misconception, as can be concluded from studies within the framework of the national vegetation classification of the Netherlands. During this program, a large data set has been built up, comprising more than 350,000 vegetation relevés, made in the period 1929-2001. Comparison of sets of relevés from different decades revealed that in most ecosystems the floristic composition of the vegetation types involved has changed, although the appearance of the vegetation and the presence and abundance of - most of - the diagnostic species have remained the same. In the present study, three examples were elucidated: an aquatic vegetation type dominated by Stratiotes aloides (Stratiotetum), a species-rich grassland type on river dunes (Medicagini falcatae-Avenetum pubescentis), and a forest community (Betulo-Quercetum roboris).