All Fragmentation is Loss

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Deep in a Southern forest, New Zealand

When we change nature (whether forest, pond, stream or meadow) by, for instance:

  • Adding a persistent toxic chemical, e.g. a herbicide, arsenic from treated timber, asbestos from brake linings…
  • Removing a species permanently
  • Felling trees and/or opening the edge of a closed woodland,

we harm it in ways that will not self-repair within a human lifetime at the earliest.

Some changes we’ve wrought since the industrial revolution include:

  • Increased atmospheric carbon – increased CO2 harms plant growth by lowering plant nutrition and for many species increases their flammability
  • Synthesis of nitrogen fertiliser enabling rapid human population growth that is beyond earth’s life supporting ability
  • Large-scale additions of phosphate leading to algal blooms (toxic to most life)
  • Reduction of forest cover from near 100% to 0% in many regions, resulting in  harsher weather and the loss of micro-climates which make niches for rare species

These are thresholds that we cannot turn the clock back on; we can only partly repair our life-support system, however we lack a manual and the right tools and we only know the names of about 10% of the parts let alone knowing how they fit together.

HPD_Graphics_patches

Graphic above shows how as a forest is cut by roads its life-supporting area is reduced. The left image has no road and has a viable area of 57%. With a road (right graphic) the viable core is 8% of the total and will support fewer, and smaller less mobile species

People talk of restoring a forest that has suffered from being opened to wind, subjected to tree felling, fire or toxins; or loss of birdlife. Some crucial questions usually go unasked:

  • Why is the ‘restoration’ being proposed?
  • When are we ‘restoring’ to? pre-human; pre-European; pre-industrial age; some living person’s memory…
  • How complete does the ‘restoration’ need to be to answer our initial ‘Why‘?
Planting and re-vegetation
Repairing cleared forest areas

I’m often asked to assess forest remnants for land subdivision or building permits. In doing this I’m constrained by a legal framework that assumes forest fragments are able to support a full range of plant and bird species (NZ has no native mammals except bats). This is seldom, if ever, the case as pre-European forests depended on many ground-dwelling birds, invertebrates and reptiles and lacked mammalian pests except for the imported Polynesian rat.

Introduction of deer, thar, pigs, stoats, rats, mice, brushtail possums and others has resulted in a 21% loss of species since 1840 with many of the remaining birds in decline. These pests have, along with human development, ‘opened’ the forest resulting in loss of the stable interior climate that occurs within a forest:

– low wind speed
– lack of artificial noise
– constant cool temperature
– low light (about a hundredth of ‘outside’)
– moist conditions, with the ability to absorb the heaviest rainfalls

This is called the edge effect and can extend for more than a kilometre into a forest for many invertebrates

All this leads to reduced pollination of trees and limited spread of seed,

which leads to forest gaps,

which in turn become prone to invasion of weeds and parasites with many tree and shrub species no longer able to sustain their populations.


Repair and doing as little damage as possible, as well as trying to learn from each case and carry that knowledge to the next repair, is my goal. Seeing birds and insects repopulate a repaired forest fragment is a joy.


Author: Nigel Cowburn, Growplan Ltd. Dunedin New Zealand (2017)

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