Tuesday, June 10, 2008


I like trees. Really I do, I think there's little more satisfying than planting them and watching them grow. This is something I know a great deal about, but within Landcare and the broader NRM (Natural Resources Management) we have this obsession with PMT.

"Plant More Trees" is the catchcry that seems to have embedded in many peoples heads. Trees are good but the real power system of a vegetation community are those things less than a couple of metres, grasses, shrubs, herbs etc, in most circumstances, make up the vast majority of flora biodiversity and a huge amount of the biomass but trees get all the glory.

And while we're at it just how many actual trees do you need to plant? I suppose it all depends on what sort of vegetation community you're trying to recreate, forests tend to have around seventy percent canopy cover while woodland is around thirty. So just doing a few rough calculations giving a mature or semi mature tree a canopy diameter of ten metres we only need around ninety of them per hectare to get a seventy percent cover or forty of them for a thirty percent canopy (or around 230 and 100 trees at a 6 metre canopy spread respectively).

So why do we persist in planting so many? I often go past plantings with two metre spacings and am very tempted to chainsaw at least two thirds of them just to give them a chance to grow. The bigger they're allowed to grow, the more likelihood they have of forming hollows and the larger the logs will be falling to the ground again forming better habitat.

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