Land Cover

The Southland region covers an area of 3.2 million hectares, with the two major land covers being indigenous forest and exotic grassland.  The land in indigenous vegetation (dominated by indigenous forest, also indigenous scrub, tussock, and natural bare ground areas), amounts to 63% of the region – of which, 42% is located within the Fiordland and Rakiura (Stewart Island) National Parks.  The developed land totals 34%, with exotic grassland (agricultural farmland) being the dominant cover.  Additional areas of rotational cropland and urban areas are also included.  These are mostly located in the lowland plains and river valleys or basins.  The remaining 3% of Southlands ‘land’ cover is surface water, with six of New Zealand’s 25 largest lakes (surface area), including lakes Te Anau, Manapōuri, and Hauroko (which are also New Zealand’s three deepest).  There are also tens of thousands of kilometres of rivers and streams, including the Waiau, Aparima, Ōreti, and Mataura rivers.  Between 1996 and 2018, most land cover classes have decreased in area; exotic forest, cropping/horticulture, and urban areas being the exceptions, all of which have increased.  A steady decline in indigenous forest, tussock grassland, and other herbaceous vegetation (mainly wetlands) is also evident, as the land is continually developed.

 

Southland’s land cover profile is characterised by:

  • A predominance of grassland; this broad class includes mostly exotic grassland, at 982,000 hectares or 31% of Southlands land cover. Tussock grassland covers about 421,000 ha or 13% and Other herbaceous vegetation (mainly wetlands), 36,000 ha or 1% of the region. Overall, the broad land cover class of grassland amounts to roughly 45% of the region.
  • Forest cover totals 42% of Southland; of which the majority is indigenous forest at 39% or 1,239,000 ha. Exotic forest makes up the remaining 3% or 97,000 ha.
  • Scrub/shrubland covers 5% of the region or 167,000 ha and is largely comprised of indigenous vegetation with <1% or 14,000 ha classed as exotic scrub.
  • Urban area and cropping/horticulture comprise very small proportions of the regional land area overall, both around 7,500 ha or <1%. However, the cropping/horticulture class only identifies properties with year round arable rotations. Unlike Canterbury, most of Southland’s arable cropping occurs alongside livestock grazing and is not captured in this analysis.
  • The majority of the urban/bare/lightly vegetated surfaces class is natural bare/lightly-vegetated land at 5% of the region or 144,000 ha.

 

The key changes in land cover between 1996 and 2018 in the Southland region are:

  • The grassland/other herbaceous vegetation category has had a reduction in land cover area between 1996 and 2018 of 10,600 hectares or 1% of the total grassland area.

- exotic grassland cover has decreased in area by 39 ha or less than 1%.

- tussock grassland cover has decreased by about 8,000 ha or 2%.

- other herbaceous vegetation (mainly wetlands) have decreased by about 2,500 ha or 7%.

  • Scrub/shrubland (both exotic and indigenous scrub/shrubland) have also decreased in area.

- exotic scrub by about 3,900 ha or 22% and indigenous scrub by about 9,400 ha or 6%.  Overall a reduction of around 13,200 ha or 7% of the scrub/shrubland area.

  • The forest land cover class has increased in area by around 21,500 ha or 2%.

- exotic forest has increased in area by about 23,300 ha or 32%.

- however, indigenous forest has decreased by around 1,800 ha or <1%.

  • Less significant changes include both an increase in urban/bare/lightly-vegetated surfaces (1,159 ha or 1%) and cropland (806 ha or 12%) between 1996 and 2018.

 

The likely drivers and potential implications of the changes are:

Exotic grassland

  • The reduction in exotic grassland is most likely due to the planting of exotic forest. This has increased over the same time period, as flat exotic grassland areas are planted in eucalyptus and hill country areas in pine tree plantations. The increase in exotic forest area may have been driven by an increased confidence in the forestry industry and/or the introduction of the Emissions Trading Scheme (ETS).  The afforestation of hillslopes at risk of erosion (e.g. steep or with fragile soils, or both) under exotic grassland cover, can be beneficial in terms of improving slope stability and reducing the incidence of soil erosion.
  • The additional areas of cropping/horticulture land cover could also contribute to the reduction of exotic grassland area. This growth may be due to farmers diversifying their enterprises (collecting income from different sources) as commodity prices fluctuate.
  • Other small changes include the growth of urban areas and artificial bare surfaces; areas related to the subdivision and development of towns and cities. In Southland, these changes are relatively minor compared to other regions of New Zealand.

 

Indigenous forest, Tussock grassland, and Scrub/shrubland

  • The areas of indigenous and exotic scrub/shrubland, as well as tussock grassland and indigenous forest have all decreased between the years 1996 and 2018. The developed land has either been planted directly in exotic forest or developed into exotic grassland to offset the previous changes mentioned above.
  • This change could have implications for the conservation of indigenous biodiversity as the habitats of indigenous flora and fauna are modified.

 

Other herbaceous vegetation

  • Other herbaceous vegetation includes wetlands, flax-land, and saltmarshes; these have decreased by approximately 2,500 ha over 22 years (1996-2018). Since human settlement of Southland, around 97% of wetlands have been drained for the development of agriculture. Natural state estimates show around 270,000 ha or 9% of Southlands total land area was covered in wetlands or swamps in approximately 1000AD (Pearson and Couldrey, 2016).
  • In addition to effects on indigenous biodiversity, this change also has implications for flood protection, water availability and water quality, as wetlands provide a significant benefit to the environment.

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