Future Forests Research Update – Trees Value in Preventing Erosion

At a recent Future Forests Research (FFR) members meeting in Wellington Chris Phillips and Mike Marden from Landcare gave a superb presentation on erosion prevention. An interesting fact is that some 17% of NZ's GDP is associated with the top 15cm of soil. Loss of productivity due to hill country erosion is estimated to cost New Zealand $100- $150 million per year; in addition there are other significant costs such as flooding, siltation and reduced water quality.

A good example of the protection provided by tree cover in highly eroding gullies.

After erosion occurs, pasture productivity is severely compromised and it is only after several decades of recovery that productivity returns to about 80% of former levels. Forestry can largely fix this problem and we need to know the best trees for erosion control and the best management. Unfortunately there is a shortage of good data worldwide for obvious reasons – it is time consuming and expensive to dig up trees, even small ones, so a new trial has been established in the Gisborne area to compare the performance of a range of species in reducing erosion.

With extreme rainfall events forecast to increase, the risk of soil erosion rises. Dave Palmer, a scientist at Scion, has used NIWA weather predictions overlaid onto national maps of erosion susceptibility and land use to produce an experimental methodology for predicting the impact of extreme events. Whilst the methodology needs refinement, his conclusions are worrying – currently 1.0 million ha of farmland (7.6%) is erosion prone. With current management and with the predicted 2 deg C warming, the proportion of vulnerable farmland might increase to 1.4 million ha (10.3%).

The conclusion is that we can prevent some of the predictable consequences of climate change by afforestation of some of the erosion prone hill country farmland, particularly on eastern and lower parts of the North Island. The increased financial returns available via afforestation under the Emissions Trading Scheme make this argument even more compelling. FFR, via its Environmental and Diversified Species themes, is committed to providing targetted research to enable land owners and land use managers to get the most from this opportunity.