Quantifying the area of the small-scale owners’ forest estate in the East Coast, Hawke’s Bay and Southern North Island

Authors: Bruce Manley, Justin Morgenroth, Cong Xu, Final year BForSc students of 2017 and 2018
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2019, Issue N.Z.J.For. 64(4) 2020, pp 18-26, Jan 2020
Publisher: New Zealand Institute of Forestry

Abstract: The National Exotic Forest Description (NEFD) estimated that, as at 1 April 2016, the small-scale forest estate area in the East Coast, Hawke’s Bay and Southern North Island (SNI-West and SNI-East) wood supply regions was 268,233 ha. As part of the Management Case Study in 2017 and 2018, Bachelor of Forestry Science (BForSc) students mapped the small-scale estate in these regions. Forest boundaries were mapped in a geographic information system (GIS), based on visual interpretation of aerial photography and satellite imagery. It was found that the mapped area of small-scale estate in these regions totalled 248,331 ha, with the NEFD area being 8% larger. On a wood supply region basis, the NEFD over-estimates the small-scale forest area by 20% for the East Coast and 15% for Hawke’s Bay, but underestimates by 2% for SNI-East and 0.5% for SNI-West. The results also vary at the level of territorial authority (TA). Only eight of the 22 TAs have the NEFD area within 10% of the mapped area, while another eight are within 10-20% of the mapped area. While the NEFD over-estimates net forest area in the overall study region by 8%, the Land Cover Database (LCDB) over-estimates it by 17%, and the Land Use and Carbon Analysis System (LUCAS) overestimates it by 27%. These differences arise because LCDB and LUCAS are based on gross rather than net area and because of some misclassification of land uses in those spatial databases. In the case of the LCDB, the gross/net difference is 8% of the mapped area, while net misclassification causes over-estimation by another 8%. For LUCAS, the gross/net difference is equal to 11% of the mapped area, with net misclassification also equal to 11% of the mapped area. Additional differences arise because of new planting not captured by the mapping. The study confirms the urgent need for an accurate and up-to-date spatial database of New Zealand’s plantation forests. Not only would this provide accurate estimates of plantation area, it would also enable detailed transportation and logistics planning, as well as quantification of the potential wood supply within specified distances from current and potential wood processing sites. It could also improve New Zealand’s international carbon accounting and reporting.