Older trees prevent erosion

Press, 24 April 1987, Page 26

Older trees prevent erosion

Following serious eroison and stock losses in Uie Cheviot district last winter a field day in the district on erosion control was well attended recently. It was organised by the North Canterbury Catchment Board in association with the Cheviot branch of Federated Farmers and took place on the “Glenkens” farm of Max and Lorna Winskill. The Winskills are in their second five-year soil and water conservation plan and the catchment board has been involved with this district since 1972. Last August rainfall in excess of 250 mm in two days killed an estimated 14,000 ewes and 60,000 lambs and caused $250,000 worth of damage to properties and roads in the Cheviot, Motunau and Scargill districts. The average loss for each farm was 100 breeding ewes, 300 lambs and $2OOO damage to fences and farm tracks due to soil erosion. A board survey following the event found that blocks of trees greater than five years of age prevented erosion while those less than this age or those thinned to wider

spacings while young were susceptible. This emphasised the importance of integrating soil conservation measures into erosion-prone areas in order to achieve land use that was sustainable. Some soils in the coastal hills are erosion prone due to their parent material which is sandstone, mudstone and loess. At the first stop of the day Mr Rob Philips, a soil conservator with the board, outlined the establishment of erosion control forestry. In his opinion the essential ingredients to successful tree establishment were site preparation, quality tree stocks and the correct planting technique. Erosion control forestry, he said, was used when it could be shown that pasture alone was insufficient to prevent soil erosion. Trees had a much better root structure and the ability to intercept up to 30 per cent of the annual rainfall and transpire 40 per cent leaving 30 per cent to remain as groundwater or to run off in streams and waterways. Many of the erosion control blocks of trees established in Canterbury were Pinus radiata be-

cause the drought conditions that prevail during the summer months often robbed the tree of valuable moisture reserves that many other species lacked. However in the more favoured and sheltered sites Eucalyptus obliqua, Eucalyptus regnans, Macrocarpa, Tasmanian blackwood and natives are used. The regional soil conservator, Mr Don Wethey, said that there was still some grant assistance available for this type of planting. Mr Theo Russell, a private forestry consultant, said tree management was important but in recent times good prices had been paid for trees which had no management. With erosion control forestry it was important that any management maintained the function of the trees. A guest speaker and local farmer, Mr Doug Archbold, outlined his experience with both erosion control and production forestry over, a number of years. He emphasised the need for care in growing special purpose timbers, in par-, ticular the choice of planting sites. After going to the top of the Winskills’ property that opened a view from Banks Peninsula to the Kaikoura Peninsula the

group travelled to a site proposed for bush protection under a joint Catchment Board and Queen Elizabeth Trust proposal. Mr Wethey outlined the value of these areas in preventing erosion and how important it was to fence the areas to exclude stock, particularly cattle, from destroying the understory and preventing regeneration. Dr lan Blair, the local representative of the trust, said they were interested in the exological values of the coastal resources particularly the bush and tussock as these areas often had rare species different from those of the foothills and high country. The afternoon session dealt with plant material for erosion control. A video made for the board was used to demonstrate the planting techniques for poplar poles and the versatility of the poplar tree. The use of netting,and pole dams was demonstrated to stabilise stream channels. This technique, borrowed from the East Cape Catchment Board, works by trapping fines and silts, building the base of the stream up to prevent further side slumping and allowing poplar and willow material to become established.