Stand height response following variable spacing of wheatfield white cypress pine regeneration in New South Wales

Summary

Long term stand height retardation in dense white cypress pine regrowth is investigated. Extremely high stockings (in excess of 500 000 seedlings per hectare) occurred over widespread areas of central-western New South Wales, as a consequence of favourable climatic conditions in 1952 and 1956.

Mechanically and manually applied stocking reduction treatments were applied to regrowth stands in Strahorn State Forest to prevent stagnation or lock-up. Stand height responses of the tallest 250 trees ha⁻¹ have been calculated for a range of spacing treatments to determine the degree of early release necessary to optimise stand height growth.

At age 3 years, broadscale mechanical spacing was achieved by rotary hoeing 2-metre swathes through the regrowth. However this action did not stimulate stand height growth during the following 11 years. By comparison, a single manually applied, spacing (1.8 m × 2.9 m) at age 7 increased mean height at age 14 by over 2 metres (82%).

At 14 years, a range of manually applied spacing treatments were established in the regrowth, such that some treatment plots overlaid earlier treatments, limiting the extent of growth comparisons. However, it is shown that the optimal spacing treatment of the later treatments was 4.9 m × 4.9 m and that cypress pine regeneration retained an ability to respond markedly to a delayed release from a “locked” condition.

After 32 years, the tallest stands were those that had been manually thinned most frequently.