Forest Degradation

There are five broad levels of degradation, each of which requires a different restoration strategy. They can be distinguished by recognising six critical ‘thresholds’ of degradation; three pertain to the site being restored and three to the surrounding landscape.

Site-critical thresholds:

• The density of trees is reduced such that herbaceous weeds dominate the site and suppress tree seedling establishment
• On-site sources of forest regeneration (i.e. the seed or seedling bank, live stumps, seed trees etc.) decline below the levels needed to maintain viable populations of climax forest tree species.
• Soil degradation has proceeded to such an extent that poor soil conditions limit the establishment of tree seedlings.

Landscape-critical thresholds:

• There are only small and sparse remnants of climax forest in the landscape, such that the diversity of tree species within dispersal distance of the forest restoration site is not sufficient to represent the climax forest.
• Populations of seed-dispersing animals are reduced to the point that seeds are no longer transported to the forest restoration site in sufficiently high densities to reestablish all of the required tree species.
• Fire risk is increased such that naturally established trees are unlikely to survive because of the increased cover of combustible herbaceous weeds in the landscape immediately surrounding the restoration site.

                                                                                  SITE-CRITICAL                                  LANDSCAPE-CRITICAL

RECOMMENDED RESTORATION STRATEGY:

• Protection from encroachment, cattle, fire and any other further disturbances and prevention of
  the hunting of seed-dispersing animals

• Re-introduction of locally extirpated species

                                                                                 SITE-CRITICAL                                  LANDSCAPE-CRITICAL

RECOMMENDED RESTORATION STRATEGY:

• Protection + ANR

• Re-introduction of locally extirpated species

                                                                                SITE-CRITICAL                                  LANDSCAPE-CRITICAL

RECOMMENDED RESTORATION STRATEGY:

• Site protection + ANR + planting framework species

                                                                               SITE-CRITICAL                                  LANDSCAPE-CRITICAL

RECOMMENDED RESTORATION STRATEGY:

• Site protection + ANR + planting framework species + enrichment planting with climax species

• Maximum diversity methods such as the Miyawaki method

                                                                                SITE-CRITICAL                                  LANDSCAPE-CRITICAL

RECOMMENDED RESTORATION STRATEGY:

• Soil improvement by planting green mulches and the addition of compost, fertilisers or soil microorganisms

• followed by planting ‘nurse trees’ — i.e. hardy nitrogen-fixing trees that will further improve
  the soil (also known as the “plantations as catalysts” method)

• then thinning of nurse trees and their gradual replacement by planting a wide range of
  native forest tree species