Forty-year changes in the canopy and the understorey in Wytham Woods

Abstract

Summary This study investigates changes in the composition of part of Wytham Woods (southern England), between the 1960s and 2007. The study focussed on an area of ~ 4 ha shown on a 1961 aerial photograph, part former open common, part ancient woodland. Changes in the canopy appearance were considered using a recent (1999) aerial photograph. Trees and shrubs were recorded in a 200 × 10 m transect to illustrate current stand structure across the historic management division. In the north-east corner of the area, tree diameters and understorey abundance from 1968 were compared with the current stand structure. Since the 1950s, Fraxinus excelsior has colonized the open areas. Tree growth was estimated from comparison of diameter/girth measurements from 1968 and 2007. F. excelsior diameter increment was greater than that of Acer pseudoplatanus and both showed faster growth than Quercus robur . Some canopy trees died, but no large gaps formed in the closed woodland. The abundance of understorey stems declined. The current stand structure refl ects effects of past management, browsing pressure and climatic stresses over the last four decades. Multiple causes of change are probably commoner than single factors in explaining woodland structure.