New Zealand Journal of Ecology (1987) 10: 35- 42

Forest Understorey Changes after Reduction in Deer Numbers, Northern Fiordland, New Zealand

Research Article
G. H. Stewart 1
J. A. Wardle 1,2
L. E. Burrows 1
  1. Forestry Research Centre, FRI, P.O. Box 31-011, Christchurch, New Zealand
  2. Present address: P.O. Box 40, Oxford, Canterbury, New Zealand

High deer numbers in northern Fiordland in the 1960s significantly changed forest understorey composition. The density of woody plants in the understorey was reduced in some areas by as much as 50%, and preferred plants became less abundant than those seldom eaten. However, the impact of deer and wapiti varied between forest types. Seral communities and silver beech forests at low altitudes in the unmodified Milford/Bligh Sound area had high proportions of preferred plants in the understorey, and these were the types that were more modified by browsing pressure than those growing at high altitudes or on poor soils.
A resurvey of the Wapiti, Doon, and Glaisnock catchments in 1984/85 showed that densities of woody plants in the forest understorey had increased on average by at least 75% after a c. 80% reduction in deer numbers since earlier surveys (1969 and 1975). Woody food plants highly preferred by deer were rare in most forest types in 1969, but were present in all types by 1984 and had increased in density by as much as 300-400%. However, recovery was still largely confined to understorey tiers < 75 cm high and most of the recovery had occurred since 1975. Proportions of highly preferred species in the understorey of these forests had not reached those recorded in unmodified forests in the Milford/Bligh Sound area in 1969