Author:Grant Lawrence, Miriam Ludbrook, Craig Bishop
Source:Auckland Council Research and Evaluation Unit, RIMU
This report summarises tree loss within the Waitematā Local Board area over the 10-year period from January 2006 to February 2016. The report was written for the Natural Environment portfolio of the Waitematā Local Board, to provide background information and some direction and context for an urban forest strategy and provide evidence to ensure decision-makers are well-informed.
Mapping of tree loss across Waitematā Local Board was undertaken in ArcGIS through digital photo-interpretation. Only canopy losses were captured and mapped in this report. It was evident throughout the aerial analysis that newly established canopy and canopy growth of existing trees has also occurred within Waitematā Local Board, in some cases quite extensively. Given that growth was usually represented by small marginal increments across many tens of thousands of individual trees and shrubs it was impossible to identify and digitise in the same way that tree loss was.
A total of 61.23ha of tree canopy was lost from Waitematā Local Board over 10 years. The loss was made up of 12,879 different detected tree removal ‘events’; meaning a minimum of 12,879 trees were cleared. The actual number of trees cleared is likely to be somewhat greater than this figure because the larger clearances involved the removal of multiple trees.
Tree losses were spread throughout Waitematā Local Board with particular concentrations on privately owned land in the suburbs of Arch Hill, Freemans Bay, Grey Lynn, Parnell, Ponsonby, Western Springs and Westmere. The vast majority of tree clearances were quite small in terms of the quantity of canopy removed at a single location. Fifty-seven per cent of total loss of tree canopy was caused by the combined impact of many thousands of individual clearance events, all of which were individually less than 0.01ha (100m2) in size. In terms of proportional loss of tree canopy the suburbs with the highest rates of clearance were Grey Lynn, Ponsonby and Westmere. In contrast, Herne Bay appeared to have experienced less clearance than the other suburbs within Waitematā Local Board.
In terms of absolute area cleared, tree canopy loss was dominated by tree canopy removal on private land. However, as private land is also the dominant ownership of tree canopy in Waitematā Local Board, this is not an unexpected result. However, our data also showed that in the last 10 years there has been a considerable bias towards loss of tree canopy on private land and a lower rate of loss on public parkland.
More than 75 per cent of all cleared trees had no statutory protection and unprotected trees experienced higher rates of tree canopy clearance; about 60 per cent higher than what would be expected on a proportional basis.
More than half of tree canopy clearance had occurred for no obvious reason. That is, no new structures such as new houses or other buildings, pools, house extensions, decks or driveways had replaced the space that was beneath the cleared forest canopy. Developments, improvements and extensions to existing buildings were the second most important reason for tree canopy clearance (33 per cent). Other causes contributed a relatively small proportion of the total (eight per cent).
Auckland Council technical report, TR2018/021