Abstract
Abstract During the Wakarara Period (1770–1800 AD) of warmer, windier climate and accelerated soil erosion and sedimentation, some 35–40% of the forests of the central and northern Ruahine Range was destroyed. Between 1800 and 1870 there was a cooler, more tranquil period during which exposed erosion scars and flood plains were revegetated. From 1870 to 1900, the Tamaki Period of erosion reversed this recovery over about 5% of the forested area of the Ruahines. The present Waipawa Period began about 40 years ago, and has so far destroyed at least 6.5% of the forest standing in 1950. The four worst destructive forces that damage standing forests are gales, drought, heavy snowfalls, and heavy rainstorms and floods. All may strike at any time, but their frequency and intensity vary greatly; damage from gales, drought and floods increases during erosion periods, and damage from heavy snowfalls increases during tranquil intervals. Additional factors include earthquakes, fire and introduced mammals. This paper reviews the evidence of damage to forests of the Ruahine Range by these forces over the last 220 years. A detailed study of 20 erosion scars in the upper Waipawa Basin showed that, during 1950–81, surface material was removed from them at an average rate of about 7 ± 2 mm/year. This greatly exceeds the long-term tectonic uplift rate of 1.3-2.6 mm/year. On scar 6, part of one channel infilled with alluvium downgraded by 40 m in the 30 years. In every case increased erosion resulted in destruction of vegetation.
Published Version
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