New Zealand Journal of Forestry (1969) 14(1): 25–37
©New Zealand Institute of Forestry
Notes on the Establishment and Thinning of Old Crop Douglas Fir in Kaingaroa Forest
An attempt is made to define the siting limits for old crop Douglas fir in Kaingaroa Forest. To do this it is necessary to trace the establishment history of the crop in some detail. In the early 1920s great care in establishment and species siting resulted in more than 90% of the planted area eventually forming a canopy. From 1925 to 1933, standards of establishment steadily deteriorated and species siting was largely ignored. Two-thirds of the 18,000 acres planted from 1930 to 1933 in Southern Kaingaroa failed. Evidence is presented to support the view that rabbit browsing and frosting were responsible for this heavy loss. From 1934 to 1936, a return to careful siting resulted in 90% success once more. Above 2,000 ft a.s.l, and up to 3,000 ft a.s.l, survival of young seedlings is negligible on slopes of less than 1 in 50 (1°). Slopes of 1 in 50 to 1 in 25 (2i°) support a scattered stocking, and on slopes of more than 1 in 25 full stocking is possible. Survival depends on frost levels. Adequate drainage of cold air is essential and this is strongly influenced by local topography.
Brief notes on site and stocking as they affect growth are followed by comments on thinning as it has been practised over a 20-year period. The practice, which is to some degree fortuitous, of heavily thinning (50 to 60% basal area removed) previously untended stands at 35 to 40 years of age has much to recommend it.