Land Cover

The 12,247 sq km Bay of Plenty region extends from Pōtikirua in the east, to Waihi Beach in the west.  Inland, the region is mostly bounded by the watersheds of the river catchments that flow into Te Moana-a-Toi, the Bay of Plenty, and includes the Rotorua lakes.  Forestry and exotic pasture cover most of the region (69% and 21%, respectively), dominated by the large production forests of the Kāingaroa Plateau, the indigenous forests of Te Urewera National Park, and large tracts of high-producing farmland in the river plains, surrounding the lakes, and near the coast.  Just under 50% of the region is covered by indigenous forest, scrub-, and shrub-land.  The Bay of Plenty is also home to unique species and ecosystems, including its own variety of kanuka at Thornton, the only known mainland populations of the native broom Carmichaelia williamsii, and most of New Zealand’s monoao-dominated frost flats on the central plateau.  The region’s volcanic ash soils are particularly susceptible to erosion if they have insufficient vegetation cover.  The Ministry for the Environment has identified 680,000ha of land in the Bay of Plenty that could be potentially at risk from erosion.  About 20 percent (153,000 ha) of this land is currently used for pastoral farming.

 

 

Bay of Plenty’s land cover profile is characterised by:

  • A predominance of forest cover (more than two thirds of land area), of which most (46%) is indigenous.
  • A substantial area of grassland/other herbaceous vegetation (almost one quarter of land area), of which most is exotic.
  • Scrub/shrubland cover is predominantly indigenous.
  • Urban area and cropping/horticulture comprise relatively small proportions of the regional land area overall.

 

The key changes in land cover between 1996 and 2018 in the Bay of Plenty are:

  • Exotic grassland and exotic forest cover, and indigenous scrub/shrubland have decreased in area.
  • Cropland, urban area, and indigenous forest have increased in area.

 

The likely drivers and potential implications of the changes are:

  • The increase in the area of cropland may be largely driven by growth in horticultural industries such as kiwifruit, avocados, and viticulture. This is reflected in the largest changes seen in ‘orchards, vineyards or other perennial crops’, rather than in ‘short-rotation cropland’ such as maize, or other seasonal vegetable crops. Soil cultivation, more commonly associated with short-rotation cropping, can result in increased losses of soil carbon, sediment and nutrients, and soil structural degradation over time.
  • The increase in urban area is likely to have been driven by population growth and increased demand for housing, particularly in the Western Bay. The expansion of urban areas on to surrounding rural land will reduce the land area available for primary production and, in some areas, could result in the loss of highly productive and versatile land from productive uses (e.g., horticulture/viticulture or dairy farming).
  • The decrease in the area of exotic forest may have been driven by the conversion of forested land into pasture, particularly for dairy farming. Some forested land is also being returned to local Maori under Treaty of Waitangi settlements as it is harvested; this may also account for the increase in area of scrubland as potential future uses of the land are considered. Planting trees on hills at risk of erosion (e.g., steep or with fragile soils, or both) under grassland cover can help improve slope stability and reduce the risk of soil erosion.

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