This week we looked at trees and forests and the benefits they provide. Forest edge species buffer the wind, collect nutrients and support a greater diversity of wildlife than the forest itself; it’s important to retain those edges. Trees cool the air (by evaporation) and warm it (by condensation). Of the rainfall that hits a forest, 25% is evaporated from leaf surfaces, 50% is returned to the atmosphere by transpiration and 25% leaves as groundwater runoff. That means 75% is returned to the air. Inland rain occurs primarily because of forest transpiration. Remove the trees and the rain goes too; something humans with chainsaws don’t seem to have woken up to yet.
We looked at windbreaks and shelterbelts and how to design them. We learned how to assess the wind strength and direction at a site simply by observing the shape of the trees.
We discussed agroforestry and began with a pertinent quote from David Holmgren: “In a low energy future, the wealth of nations will be measured by the quality and quantity of their forests”. Yes, well. I can see there will be a lot of poor nations in the future (think: Saudi Arabia; no more oil; no trees; lots of desert; not a good future for them).
Agroforestry isn’t about growing acres and acres of the same tree species. An agroforestry system should aim for a diversity of species and ages, so that a varied yield is obtained over time. Timber trees, fodder trees, honey production, wildlife habitat, fuel, fibre, nuts. These are some of the beneficial products of a diverse system.
Out into the garden and we learned how to coppice and pollard trees and how and when to prune for timber production; a nice straight trunk being the desired, valuable end product.
I learned quite a bit about firewood (important, as we have a slow combustion heater). You want trees that grow fast and burn hot when young. Black Wattle and Casuarina are excellent. Generally, the heavier it is the hotter it burns. If you have a larger property, with some native bush (as we have), then general thinnings and prunings will provide most of your needs without a specific woodlot required. (We’ve been on our bush block for 10 years now and have never needed to buy firewood).
Another tip: leave cut firewood in lengths of 1.5 metres and stand them upright against a tree trunk or fence for a couple of months. The sap drains out much faster and they dry quicker (I always wondered why people did that!). Coppiced trees are ideal because they produce many new branches from the stump and these can be cut at 150 cm diameter and don’t need to be split. If you do have to split wood, it’s much easier when it’s still green.
After lunch we visited the sites for our final design project for the course. There were two options—a 5 acre hobby farm and a local community garden. I opted for the garden, believing it would provide an opportunity to showcase permaculture, plus having the potential for some varied design concepts. Over the last 5 weeks of the course we’ll spend increasing amounts of time on completing our designs and finally presenting them.
So it’s on the downslope now. I’ll be sorry when the course ends. I’m enjoying it immensely.