Using remote sensing to detect impacts of past droughts on NZ native forests

Posted by Kshama Awasthi

The 2013 drought in New Zealand cost $1.5 million to the economy through lost agricultural production but the impact on native forest is unknown. Drought-induced forest mortality is a global issue but droughts can also have sub-lethal impacts on trees. Water stress, vulnerability to pathogen attacks and reductions in productivity are some other examples of drought effects. Here in New Zealand, more than 80% of plant species are endemic but we have very little information about the impacts of drought on our vegetation. There is serious need for monitoring the effects of drought on native forest because the conservation value of native flora is globally significant. Hence, this study aims to study the effect of drought on the native forest vegetation in New Zealand using remote sensing techniques. I will be integrating Normalised Differentiation vegetation index (NDVI) and Drought severity index (New Zealand drought index, NZDI) methods. These two methods will be able to assess effects of historic droughts in 1992, 2010, 2013 in comparison to wetter and average rainfall years on diverse types of vegetation. The results that I will obtain are expected to detect temporal and spatial vegetation profiles that will be related to soil moisture profiles. I will also assess if there is any recovery period after drought year. I have selected eight different sites from across the country for analysis. This will help us identify vegetation that is vulnerable to drought impacts for future intensive study.

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Image: Ministry for the Environment

While droughts in New Zealand are not severe on the global scale, the vegetation is used to mild and relatively moist conditions and may not be well prepared for drought. A remote sensing approach is ideal for this study because it allows us to look at historical drought impacts in remote areas across the country. This research will help us identify forests vulnerable to drought.

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kshamaKshama Awasthi is an MSc student supervised by Cate Macinnis-Ng and Jay Gao.

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