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Karri forest regeneration

Large primary hollow bearing trees are retained along with secondary habitat trees (younger trees earmarked to become future primary habitat trees). These are GPSed to ensure their ongoing protection (Photo: FPC)
Management of the karri (Eucaplyptus diversicolor) forest seeks to retain a diversity of forest structures at the local, landscape and whole of forest scale. Of the State-owned karri forest vested in the Conservation and Parks Commission, 66% is within national parks and other protected areas not available for harvesting. Reserves unavailable for harvest include all old-growth forest, rivers and stream zones, travel route zones, diverse ecotype zones, less well reserved vegetation complexes, and fauna habitat zones.

Timber harvesting and reestablishment is guided by natural processes. Harvest patch sizes are limited to a maximum of 20 hectares in karri regrowth (areas that have been harvested before), and 40 hectares in mature stands. In practice, patches are much smaller than this. Within these stands habitat trees and other legacy elements such as logs, are retained.

Karri trees establish directly from seedlings following disturbance events such as wildfire or windstorm, at establishment. In particular, fire is a naturally occurring event in karri forest and as such it is inevitable that karri forests will be exposed to fire during its lifetime. Disturbance removes competition for space, light, nutrients and water, to enable germinating seeds to become established. As such, karri is regenerated as patches of even aged regrowth, amongst retained habitat elements. Karri seeds that have been collected from the forest are germinated at the FPC’s Manjimup nursery and planted on-site after timber harvesting.

Species composition

Species mix in forests is a naturally dynamic process where species representation changes over time during natural successional processes. Karri may occur in pure stands, intermingled mixtures with other species, or as a mosaic of different forest types.

All regeneration operations are conducted to ensure that the mix of native forest species that existed prior to harvest is the same mix that is regenerated. Species composition is assessed and recorded during the planning stage prior to harvesting. The planting rate and mix is then based on this pre harvest assessment. Species that occur with karri include marri (Corymbia calophylla), jarrah (Eucalyptus marginata), and blackbutt (Eucalyptus patens).

Marri, jarrah and blackbutt regenerate from lignotubers (a woody swelling at ground level, which provides a nutrient store and dormant buds). Where marri is present, natural regeneration from seed or lignotubers is successful, without the need for supplemental planting. However, when jarrah or blackbutt lignotuber regeneration is absent or insufficient, seedlings are planted to ensure the natural mix of species is maintained.

Thinning is undertaken two to three times to improve the health and growth of the forest, until the trees reach maturity. Secondary species present in the stand are retained during thinning operations. In addition, stands of pure, mature marri greater than two hectares must be retained.

Left: Karri seedlings are grown at FPC’s Manjimup nursery, Right: 12 month old karri forest regeneration (Photo: FPC)

Maintaining natural forest diversity

Biological diversity is managed by taking into account maintenance of landscape heterogeneity, maintenance of connectivity, retaining key structures as legacy elements, regeneration and compositional diversity. The network of informal reserves along roads and waterways in conjunction with fauna habitat zones ensures that mature forest is interspersed within the younger harvested forest. 

After clearfell, the understorey of karri forest regenerates rapidly, providing a dense structure which offers food and shelter for forest fauna and re-establishes connectivity for those species which dwell in the understorey. Many karri forest species have been shown to re-colonise harvested areas within two to ten years of harvest disturbance (Christensen, 1992). 1

A thick understorey of shrubs and herbs germinates within 1-2 years of harvest, climbing plants quickly establish, and a mid-storey of large shrubs and small trees develop over time. Harvest rotations are around 100 years.

Left: Big Brook forest block clearfelled in the 1920’s and regenerated in 1934, Right: The same spot 78 years later in 2012 (Photo: FPC)

1 Christensen, P 1992, The karri forest, Department of Conservation and Land Management, Perth, Australia.

Monitoring

Regeneration survival is monitored after the first summer following establishment and species mixes are recorded. If survival is not sufficient, in-fill planting is done the following winter.

Information on the FPC’s harvesting and regeneration operations is stored in a computer based program called SILrec, which is managed by the Department of Biodiversity, Conservation and Attractions.

The FPC’s operations are reviewed as part of Forest Management Plan 2014-2023 requirements and are also externally audited against internationally recognised sustainability standards.