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Protecting our precious places

Forest fragments: Objectives of restoration and management

An update from the Landcare Research Forest Remnant Resilience programme funded by the Foundation for Research, Science and Technology.

John Innes from Landcare Research in Hamilton discusses the key concepts of restoring and managing forest fragments. He has previously described a two-year research project in tawa-dominated forest fragments in the Waikato. See Forest fragments need fencing and pest control.

How do you work out when a forest fragment is restored? Questions such as: ‘What was this forest really like before it was fragmented and grazed?’ provide the way forward, although natural ecosystems tend to change with time anyway.

Restoring the key elements of natural ecological processes is a better approach than picking a past date (e.g. pre-European) and trying to turn the clock back.

Both scientists and laypeople are likely to agree on the first major steps to take in practice (usually fencing and pest and weed control), and we all do what we can with the time, energy and money available. And there is never enough!

Podocarp forest remnant near Cambridge Photo: Hamish Dean

Above: Michael and Margaret Oliver protected a podocarp forest remnant on their organic farm at Whitehall north-east of Cambridge with a 6.9ha covenant in 1987.

The covenant, seen here above the blocks of bush in the foreground, protects mature tawa, pukatea, rewarewa, kahikatea, rimu and totara.

Podocarp forest remnant near Cambridge Photo: Hamish Dean

Above: With stock excluded by fencing and ongoing possum control undertaken by Environment Waikato, good regeneration is occurring. The landowners have also planted areas alongside the covenant.

Maintaining ecological integrity

There is probably no really clear endpoint when a fragment can be truly declared restored. You can’t just walk away from pest control without pests coming back and even good fencing needs renewal eventually.

However, there are some simple and helpful words and concepts that make scientific sense that can help non-scientists envisage the ecological path ahead and see clearly how they are contributing to national goals.

A major review of biodiversity inventory and monitoring done for the Department of Conservation by Bill Lee, Matt McGlone, Elaine Wright and others in 2005 (Landcare Research Contract Report LC0405/122) suggested that the ‘primary national outcome of conservation management at the highest level is to maintain ecological integrity … defined as the full potential of indigenous biotic and abiotic features, and natural processes, functioning in sustainable communities, habitats and landscapes’.

While ecological integrity is the outcome of many interactions between genes, species, populations, ecosystems and the abiotic (i.e. non-living: soils, geology, climate) environment, they suggested that key elements were indigenous dominance, species occupancy and environmental representation.

The real power of these targets is that they are just as useful for a single forest fragment as for the whole country.

They will even work for the section of stream that meanders through your farm, and the cave underneath it.

  1. Indigenous dominance demands that key ecological processes (like seedling regeneration, litter decomposition, pollination and seed dispersal in a forest fragment) are driven by indigenous plants and animals, not exotic ones.

    Natural regeneration is a key requirement to maintain those species that naturally dominate each vegetation layer, such as tawa or podocarps in Waikato fragments.

    Killing and removing willows, tradescantia, possums and ship rats all increase indigenous dominance by restoring greater roles for native species.


  2. Species occupancy means simply that the species that should be there, are there. It may take some homework to find out what plants and animals used to be at your place, but nearby reserves, or larger forests (even if unmanaged) or patches on a neighbour’s place may show you trees or animals that could be added to your fragment.

    In the Waikato fragments we have worked with, trees like rimu, hinau and rata that were formerly present are now rare or absent and could be planted back.

    Discussion with local DoC staff may reveal native animals that should be in your fragment and could be translocated back there.


  3. Environmental representation describes how ecosystems vary across geological and climatic landscape. This is more of an issue for agencies like DoC who should consider how individual sites contribute to regional and national variation.

Kahikatea remnant and wetland Photo: Rex Webby

Above: Protected since 1999 with a 1.5ha covenant, the edges of Pam Wilkinson’s kahikatea remnant and wetland beside Lake Karapiro south-east of Cambridge have been planted to reduce the effects of wind on the vegetation. Natural regeneration is now flourishing.

Kahikatea remnant and wetland Photo: Rex Webby

Above: After the planting of more kahikatea in 2008, Pam Wilkinson and Ian Bickle admire the encouraging growth of previous plantings on the edge of the fragment.

Pam’s late husband Rob and the Cambridge Tree Trust made major contributions to the revegetation project.

Degraded condition in bush block Photo: Rex Webby

Above: The degraded condition of this block west of Huntly contrasts sharply to the health of recovering vegetation in longstanding covenants.

Browsing stock prevent seedlings regenerating to replace mature trees as they die, damage the roots and bark of existing trees and carry weeds into the bush. The fertility of the soil also increases which favours weed species rather than natives.

Resilience

A final useful concept is that of resilience, which describes how a fragment bounces back when disturbance agents (usually stock, weeds, pests) are removed.

The Waikato fragments that we studied are generally fairly resilient.

Fencing stock out led to a pulse of dense seedlings and saplings that within 10 years thinned out, leaving more native ground ferns and shrubs and fewer exotic weeds than in unfenced fragments.

Possum control additionally increased the number of canopy seedlings in the regeneration pulse, although neither treatment returned all the species present in nearby large ‘reference’ forests, nor probably established sufficient juveniles of shade-reproducing canopy trees to ensure canopy replacement (especially tawa).

Fencing and pest control also increased invertebrate populations and litter mass, decreased soil fertility, and increased bird nesting success.

All of these changes can be cast as increasing indigenous dominance and species occupancy, plus other downstream ecological outcomes.

In essence, they capture naturalness and acknowledge that what is natural varies from place to place. They also avoid the trap of aiming to make a site as it was at a particular time in the past e.g. pre-European.

The concepts can be applied to individual trees, small forest blocks, large DoC forests and the whole North Island.

They also capture what people who manage fenced and unfenced sanctuaries of various kinds do, since intensive pest control aims to increase the roles of indigenous animals, and species translocations enhances species occupancy.

Podocarp-hardwood remnant Photo: Rex Webby

Above: At Waingaro near Ngaruawahia, Mavis and Ralph Skinner have worked on restoring a block of podocarp-hardwood forest for over 30 years by weeding, setting traps and planting gaps with seedlings sourced from the bush.

Two covenants totalling 37ha protect the forest that has a canopy of rimu, kahikatea, miro, totara and tawa. The Skinners’ first covenant was registered in 1987 and the second in 1993. Environment Waikato handles the possum control.

‘We have enjoyed working in the bush and still spend one day a week there,’ says Mavis. ‘It’s nice to have the bush protected and know it’s not going to be bulldozed.’

Rex Webby, QEII Waikato Regional Representative, says the understorey is thick with a diverse range of species.

‘The covenants are in excellent health and are well cared for by these devoted owners.’


Open SpaceTM Magazine No. 78, March 2010 © QEII National Trust

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