#55 - Dec 2022 - Garden Stuff - © Sandy Lang - slang@xtra.co.nz
URBAN FORESTSDecember/January: Early- to mid-summer. On sandy soils, water and fertilise little-and-often. Sand retains little water and minerals. Effectively hydroponics…! Increase soil organic matter (tree chip mulch) to gradually (years) increase the retention of both.
Forests: These days we hear lots about forests and climate. They store CO2 and emit O2, provide habitat for countless species (so deforestation = despeciation), cool and moisten the air, reduce runoff (so deforestation = flooding). According to the FAO, half the world's forests have been destroyed in the last 70 years (expanding farms and cities). Nowadays, forests cover 30% of the land surface, instead of most of it. Leaving aside rising CO2 from burning fossil fuels (coal, oil), deforestation is the next major contributor to climate change.
Your micro-forest: Looked at from above (Google Earth), 30% of Eastbourne is green, and a lot of that is medium/large trees. So ‘forest’ is not entirely lacking from our little bits of urbania. Think twice before removing your garden tree…•Your tree provides habitat (food, shelter) for many wild species. •Your tree anchors the soil, reducing risk of slips/erosion on a sloping site.•Your tree affects your living environment. The wind shelter it provides is alone calculated to reduce power use in your home by an average 10% (chill factor) - so you’ll need less heating in winter and less cooling in summer.
Thermal comfort: Your own ‘thermal comfort’ depends on (1) air temperature, (2) air movement (chill factor), (3) air humidity (skin evaporation) and (4) your net radiation environment. It may surprise you that (1) is usually least important and the others usually more important, while (4) is usually most important.
Cool under a tree: On a hot summer’s day, try a comfy chair (better a hammock) under your tree. You will be much cooler - a much reduced level of net radiation - the temperature of the shaded grass beneath will be maybe 2°C cooler than air temperature (evaporative cooling), the leaves of the canopy above you will be maybe 5°C cooler than air temperature (evaporative cooling). A dense canopy absorbs about 95+% of sunlight so is much shadier than a shade sail (which lets some light through and also heats up well above air temperature) or a veranda roof (which heats up well above air temperature). And neither of these allow wafts of cooling breeze as a tree does.___________________________________