The effect of manuka encroachment on water yield from the tussock catchment, Glendhu experimental study, upland east Otago, New Zealand

摘要

The WATYIELD water balance model is used to demonstrate that increased transpiration and interception associated with manuka (Leptospermum scoparium) encroachment in the tussock catchment comprising part of the Glendhu experimental catchment study, Otago, New Zealand, is responsible for the flattening and subsequent decline in the difference in water yield between that predicted and observed for the planted (Pinus radiata) catchment from 2005 until 2013. Linear extrapolation based on aerial photographic coverage taken in 1980 and 2015 suggests that manuka could cover up to three-quarters of the tussock catchment by 2090, which is approximately equivalent to the proportion of forest cover in the planted catchment prior to harvesting. Statistical modelling shows that this could result in an annual reduction in water yield of about 216 mm (25%) in the tussock catchment.