Plantation Forest Harvesting and Landscape Response – What We Know and What We Need to Know

Authors: Chris Phillips, Michael Marden, Les Basher
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2011, Issue N.Z.J.For. 56(4) 2012, pp 4-12, Jan 2012
Publisher: New Zealand Institute of Forestry

Abstract: Experienced scientists in Landcare Research’s Erosion and Sediment Processes team – Chris Phillips, Michael Marden and Les Basher – expose the gaps in our knowledge regarding landscape responses to forest harvesting in New Zealand. In New Zealand, barely a year goes by without a storm causing damage to a plantation forest from landsliding (i.e. shallow landslides (soil slips), debris avalanches, debris flows, earthflows, slumps). And commonly in association with landsliding there are downstream effects arising from trees or slash being deposited in rivers, on beaches, or on land adjacent to forests. These storms seem to have increased in recent years or at least reporting of them has, with significant events reported from the Bay of Plenty, Auckland Region, Nelson, and Marlborough. It is also likely that more go unreported at a regional level that may be reported within a forest as an “environmental incident”. Ironically, many of our plantation forests were established on erosion-susceptible locations in steeplands, with the purpose of controlling erosion. The fact that many of these forests have moved from a protective function to one of production has not been without consequences; some of which have been relatively severe. We know that mature plantation forests provide protection against erosion (landsliding and surface erosion) and in particular against landsliding. In general terms, the on-site benefits of planted forests for erosion control are well-understood. These include a reduction in shallow landsliding, reduced rates of earthflow movement, reduced gully erosion and the retention of soil (Marden & Rowan 1993; Phillips & Marden 2005; Marden 2005). Off-site benefits include a reduction in the amount of sediment delivered to fluvial and coastal ecosystems, and improvements in water quality and stream habitat in mature forests (Quinn et al. 2004). Reducing the effects of future floods may be another key benefit (Blaschke et al. 2008).