Overview

In this study we present, evaluate and validate an approach to monitor forest
and grassland disturbance. We apply the approach to both Landsat and MODIS
imagery for the North Island of New Zealand and validate the results based on
high resolution OrbView and Ikonos imagery. We found an overall accuracy of
the disturbance index of 98% for the two studied land cover types. The kappa
value was 0.770 indicating a 77% better agreement than what would have
occurred by chance. We found that there is a difference between the accuracy
received for grassland areas compared to the accuracy received for forest
areas, with the grassland areas outperforming the forest areas (Kappa of
0.855 vs. 0.656). We split the validation results by soil type and also
evaluate the effect of different soil types with respect to grazing
pressures. The disturbance index behaved consistently for all available soil
orders.

We found forest disturbance for approximately 36.2% of the exotic forests,
resulting in an annual clearing rate of 2.6% of the forest over the study
period. Lastly we present a close-up study to evaluate the changes in grazing
in one intensely used catchment. We demonstrate that the December/January
disturbance rates have increased from about 6% in 2000 to about 16% in 2012.
Related project name: Land Management Impacts on Water Quality in New Zealand
across Political Boundaries