Where we live, and the need for good wind shelter belts!

Our bit of dirt is in an area called West Melton in the Cantebury plains of the South Island of New Zealand. The soil is fertile but shallow laid atop alluvial flood plain ie. stones so is free draining. In summer the Northwest wind is a problem - strong and gusty and warm. It is a product of the Fohn effect where the wind passes over a mountain range dumping rain on one side and on the other blowing onto the plains as a warm (sometimes hot) dry wind.



Extended periods of this wind can test your emotional stability and it is thought that some people can become quite "down" while it blows :(. When it arrives in winter it is a bit of a novelty because the temperature can rise by 10 degrees (celsius) or more).


In the West Melton area we seem to have a lower rainfall than areas west towards the mountains and east towards the sea. So it can be raining on both sides of us but we get none! Not fair! We do, however, seem to be in a corridor where hail rarely falls - I think I would rather have the rain as well as the hail :).


If we wanted to live in a reasonable environment and have a large garden, it became very obvious that our first priority was to provide shelter, not justaround the house but around the whole 8 hectares - for us (house and garden), for the animals and the pasture. This need for shelter was reinforced after surviving our first season.


We arrived in August 1981, late winter here, and from September to March we had very little rain. What we had a lot of, however,  were Northwest winds - or Norwesters as we call them. So things got dry, very dry as dry as a crisp and we did wonder if we had done the right thing to shift to the country. 

It had always been our dream to own a few acres, and we had just invested all we had and with a minimum of working capital so our options were limited. I remember thinking "What the hell have we done" - the marketers call it post purchase dissonance. But, we had made the decision, there was no turning back so looked for solutions and set priorities, hence the urgency for shelter.


Being a scientist in those days I undertook a great deal of research into the work done on shelter belts - what tree species, what spacings, how many rows, the best way to plant and when etc. Fortunately, because Canterbury can experience extended drought periods made much worse by the Norwester, there was a lot of information to be studied.

Clearly pine trees (Pinus Radiata) were the most popular species to use, and clearly the performance of these trees in Canterbury is impressive. Some people don't like pines because their needle like foliage gives them a "hard look" but they do the job. Cedars (Cedrus Deodara) are hardier than pines, but they are very slow growing so if you plant this species your children will most probably be the ones to benefit.


The neighbours to the east of us planted their west/northwest boundary using cedars, and these trees are now 33 years old. Our 27 year old pines, which are planted in the same direction, are now more than twice the height of their cedars.


Now only having 20 acres we didn't want to take up too much land in shelter belts - looking back this was plain stupid. One expert I talked to in 1981, Mr Peter Smail, suggested I plant three lines of trees 2 meters apart wth trees spaced at 6 meter intervals. I thought I didn't want a forest so I compromised and planted the primary shelter belt as two rows, 2 meters apart with 4 meter spacings. I had also done some research on eucalypts or blue gums thinking they would be adapted to dry conditions and so interspersed the pines with eucalypts. I wouldn't repeat this because the eucalypts didn't really turn out as expected. Whether they didn't like the pines or the wind or both I am not sure. I have planted eucalypts in secondary shelter belts in association with other species such as Leyland and Arizonica and they have done well.

The southern boundary was also planted in pines. Peter mentioned to me that the perfect shelter is not solid trees and topping trees to a hedge is also ill advised. When driving along the road a well spaced shelter belt will enable you to catch regular images or glimpses of what is behind the trees.


The technical reason for this is the shelter belt needs to filter and slow down the wind speed in a laminar fashion, this means keeping turbulence to a minimum. If the shelter belt is too solid (trees to close together) or has been hedged (tree branches more numerous) then it acts like a "dam or weir" to the wind so the wind rolls over the top of the shelter belt increasing turbulence significantly on the other side and rendering the shelter belt much less effective.


The Southwesterly wind in Canterbury comes straight off the South pole and it can be gale force and it can be very cold. Our southern shelter has proved its worth and attests to Peter Smail's expertise; in a strong, cold Southwesterly with the wind in the trees sounding like waves crashing on a shore, if you stand about 50-60 meters out from the shelter belt on the leeward side you can light a match no trouble! Apparently an effective shelter belt will give shelter for 10-15 times its height.


All our internal shelter is planted in leylands of various types. Castlewellan Gold is a bit slower than the others, but I planted: Naylors Blue, Haggerston Grey, Fern Down and the most common leighton Green. In my experience some of the leighton Green can get canker. To figure what order to plant them - of course you may want a regular order - but if not work out the number of trees you need in the shelter belt, divide this by the number of varieties you intend to plant and this will give you the number of each variety required. Give each tree in the shelter belt a number, write the numbers out (using computer or just use long hand), separate all the numbers and put them in a hat or a bowl etc. Now take each number out and record which tree type it is and this will give you a random order for planting.


I have more to share........