Forest Boundary Management Strategies
Operational Research Project Code: FRM 235
Programme Leader: Bruce Burns, Landcare Research Ltd
Goal
Identify potential risks and deleterious effects to forest health and stability associated with forest edges in managed New Zealand indigenous forests, and provide a framework on which best-practice guidelines for management of forest edges can be based.
Context of the project
The original fragmentation of New Zealand’s native forest cover probably led to a vast increase in the area of forest close to edges. As well, ongoing management of forest fragments continues to create new edges in formerly continuous forest. Trees and other organisms that live close to edges are exposed to conditions from the different adjacent ecosystem, and this may have deleterious effects. However, it is unclear where, when and what types of significant effects occur in New Zealand native forests due to existing edges and after creation of new edges. This information will also lead to identification of appropriate mitigation strategies to reduce or eliminate any deleterious edge effects resulting from current activities or management. This review seeks to compile the best existing information on this issue.
Approach
A literature search was carried out on published local and international research pertaining to forest edge effects and management, and the implications for indigenous forest management in New Zealand were assessed.
Outcomes
Although limited research has been carried out directly in New Zealand forests, the evidence from this and international literature shows a range of edge effects is likely following the creation of edges in New Zealand native forests. These include increased windthrow and tree mortality at edges, increased susceptibility to weed invasion (particularly for weedy lianes), reduced habitat quality for shade-tolerant and/or exposure-intolerant canopy tree species at edges (e.g., tawa), increased deposition of pollutants and nutrients, and possibly heightened depredation of birds. However, the importance of edge effects is highly dependent on the environmental context within which the edge is set. Edge effects are particularly significant when there are strong contrasts between conditions of the forest interior and the adjacent ecosystem. Therefore, mitigation of edge effects needs to be focused on situations or regions with high patch contrast, e.g., edges with northerly orientations, or where extremes of climate can occur — the hottest, driest, or coldest regions. Windthrow is more likely to be an issue when the edges face the prevailing wind, are not protected by topography (i.e. occur on an exposed ridgeline), where forests are on shallow soils, or are in very windy regions. Weed invasion is more likely when there is an existing pool of weeds near to the created edge (e.g., close to cities or settlements). Edges will often develop a 'sidewall' of dense vegetation over time that will reduce the depth to which edge influence affects forests. Management to facilitate the rate of development of this sidewall can reduce edge effects. Development of buffer vegetation (secondary forest, e.g., mānuka, kānuka; or exotic plantations) can also reduce edge effects. If edges are to be created, where possible avoid creating edges that bisect strong environmental gradients, e.g., avoid creating edges that will face prevailing winds. More research to understand the impacts of edge effects in New Zealand forests (and any differences to impacts described in the overseas literature) is necessary.
Summary
This report seeks to identify potential risks and deleterious effects to forest health and stability associated with forest edges in managed New Zealand indigenous forests, and provide a framework on which best-practice guidelines for management of forest edges can be based. Edges are increasingly abundant in New Zealand managed landscapes, but it is unclear where, when and what types of significant effects occur in New Zealand native forests as a result of edge creation. A literature search was carried out on published local and international research pertaining to forest edge effects and management, and the implications for indigenous forest management in New Zealand were assessed. Although limited research has been carried out directly in New Zealand forests, the evidence from this and international literature shows a range of edge effects is likely following the creation of edges in New Zealand native forests. These include increased windthrow and tree mortality at edges, increased susceptibility to weed invasion, reduced habitat quality for some canopy tree species at edges, increased deposition of pollutants and nutrients, and possibly heightened depredation of birds. However, the importance of edge effects is highly dependent on the environmental context within which the edge is set. Edge effects are particularly significant when there are strong contrasts between conditions of the forest interior and the adjacent ecosystem. Therefore, mitigation of edge effects needs to be focused on situations or regions with high patch contrast or other potential threats in the ecosystems adjacent to the forest. Mitigation measures include avoiding edge creation where possible or careful location of edges, facilitating development of a dense understorey at edges, and managing adjacent ecosystems to act as buffers. More research to understand the impacts of edge effects in New Zealand forests (and any differences to impacts described in the overseas literature) is necessary.
Publications
Burns, B 2006: Management strategies for forest boundaries: what to do about edge effects in managed indigenous forest. Landcare Research Contract Report LC0506/078.
Contact for Enquiries
Manager, Innovation Policy
Ministry of Agriculture and Forestry
MAF Policy
PO Box 2526
Wellington
New Zealand
Tel:+64 4 894 0618
Fax:+64 4 894 0741
Contact this person
