Windbreaks were once a commonplace element in the landscape when farming was small scale intensive and resource efficient. As agriculture practices transformed and land use became the growing of extensive and energy intensive systems, windbreaks and the diversity and stability that they brought to the landscape was withered along with the natural capital around them. Now they are advocated widely through permaculture and are one of the Agroforestry practices that has wide appeal. Windbreaks, formed in a triangular shape, are key elements in sound designs as to deal with sectors. Sometimes it is a drying summer wind limiting growth of crops while other times it’s a cold winter wind whipping valuable heat from the house. Both are leaks of energy causing resource depletion yet blocking this through good design is possible. Furthermore, the Dust Bowl in the Midwest of the states in the 1930’s is the classic example in history of what happens when these valuable resources are taken out and the ensuing effects. The American literature classic called the Grapes of Wrath, by John Steinbeck, details just this and how the social and economic factors are intertwined so inextricably.
With that, the following are things to consider when designing a sound wind break:
- appropriate sighting
- species selection
Thus a windbreak functions to slow winds that can damage crops, it decreases wind evaporation (including aquaculture) and stress in plants, it stabilizes house temperature, and it also moderates soil temperatures. Moreover, animals expel lots of energy in maintaining body temperature so our livestock will also benefit tremendously from the windbreak and shade cast by it. Incorporation of tree belts is vital for animal health and by creating this edge, soil erosion can be slowed by this feature as well. Remember that most animal systems traditionally were savannah like and our putting tree belts back in will push the system closer to this traditional land use or ecosystem mimicking. In essence windbreaks can help maximize yields and warrant the investment in them for not only the economic part but also transfer to social and environmental abundance. Finally, we design for multifunctions and that is addressed below when we look at species selection.
Windbreaks, unlike the traditional system of lining property lines to form hedgerows, are orientated to deal directly with wind sectors. Sectors are defined as wild energies passing through a site. With wind there is usually two scenarios that are present. One is a
constant wind say like in Portugal at Terra Alta known as the North wind. It blows almost constantly but from time to time there is also winds from other directions. They predict oncoming changes in weather with the south wind carrying the presence of the desert with the smell and energy in the air. Sometimes the wind comes from the west bringing heavy rains. So in this case you have a constant wind and a storm wind and one that indicates change. In New Zealand we had a constant wind that blew almost always from that direction. Windbreaks were orientated for that but once or twice a year flat line storm winds would blow off the coast and have damaging winds to crops. A neighbor had half his corn crop flattened after weeding that part earlier in the day. Oddly enough the part that wasn’t weeded, essentially a windbreak, kept the system resilient.
Furthermore, at the family land known as “the lake” in Kentucky, Confluence Permaculture project, we have normal wind patterns of summer winds bringing the heat and humidity from the
southwest (Gulf of Mexico) and cold, dry air in the winter from Canada and even the arctic from the northwest! Once or twice a year we do get some strong winds that come from northeasters blowing off the eastern seaboard or even hurricanes or tropical storms that come up the Mississippi and begin to head east at the Ohio river.
Meanwhile where I worked in South India in Auroville (2009), the drying winds were like putting a blow dryer on ones head for what seemed like endless hours of the day. This parched the landscape and made food production a challenge for sure.
With that, windbreaks should be sighted perpendicular to wind flows you are dealing with. This allows for the wind to be diffused at the most efficient way.
With windbreaks, trees are spaced closer than normal recommended plant spacing of the same species as to tightly pack branches and leaves together. The idea is to diffuse (60-80%) the wind energy and lift it above the windbreak thus tighter spacing is needed. Whether that is in the same row with the same height of vegetation or in between rows of differing species and heights, the trees are packed in tightly. The windbreaks themselves are spaced based on the ratio that the ultimate height of the tallest tree will afford you 20-30 times the protection area. Hence if the tallest tree is 50 ft or 15 m, then it will give you a protection area of at least 1000 ft or 300 m. Meanwhile the length of the tree belt should be ten times longer than the height of the tallest tree. This means with the numbers used above that the tree belt should extend 500 feet or 150 meters for maximum protection. This means that you can scale this system up or down based on your land size and site/ resources context. This design element should be at the very least five rows thick with it going up to nine plus a outer wild area detailed below.
To facilitate this lifting and diffusing, Darren Doherty, my Keyline teacher in 2009, recommended that an equilateral triangle shape, 60 degree entry and exit angle, be designed and created. This is tough because sometimes your tallest tree doesn’t grow as fast as some of the ones that are on the outer edge. This leads to stacking in space and time similar to how food forests evolve over time. With that the your tallest tree is placed in the middle with lower levels radiating outward stepping down on both side. The tree belt should not be one row as this can actually cause the over beck jet phenomenon on the backside causing increased wind damage. The last layer, the herbs, can be a wild strip of land extending beyond the shrubs to invite in more of the native ecology and localized plants that have become common place in that particular bioregion. You will want to mow (or graze with electric fence) these areas to keep it in the herbaceous/ grass layer as over time succession will occur and more woody species will take over. These wild strip areas can be part of biomass creation or often part of your integrated pest management as asters, umbels, alliums, mints, and legumes are sure to colonize rapidly. Thus the shape should have uniformity on both sides making species selection fairly easy as one side will mirror the other. Remember also to take into account the shade that will be cast by the windbreak and acknowledge that in your design.
With our design work we do functional analysis to make sure that our hedgerow is multifunctional by selecting species, which demonstrate these characteristics. Of course how we manage these elements depends on how they will function. With that, relative location and matching interconnections is always maximized when possible. Just because a species can feed chickens, like Mulberries, if that tree species is in our windbreak but the chickens never forage there, that function of course doesn’t count. Windbreaks can perform other functions besides blocking wind through creating this edge and a few of those functions are the following:
- bee and animal fodder
- fertility and biomass
- habitat and biodiversity
- integrated pest management
- food production from outer zone type of plants
- building material and firewood
Remember that if you desire a winter windbreak, the trees themselves need to hold their leaves during that period of the year. Thus windbreak species composition again must be directly tailored to the wind that you desire to block. In warmer climates, this loosing of leaves is not present and creates a concentrated selection of plants to use.
Just as in other systems like food forests, these windbreaks are long-term investments. Thus when designing and implementing know that a feature like this will provide great resources in the long run but in the immediate they need managing. Grasses and trees don’t cooperate so mulching, mowing, animaltractoring and the
like will help to forward succession and drive this more fungal based system onward. Chop and drop will be needed for this and also to manage the heights of the trees. Coppicing certain species that are fast growing will help our longer term tree succeed when that biomass switch is needed. All of that biomass is rolled back into the system thus creating more fertility or other energy needs like fuel wood or building material (i.e. black locust coppice). If designed correctly chicken tractors or grazers with electric fence could go in between the rows when the system is young allowing the vegetation to be cycled into manures. Timing and management is the key to all biological resources so be sure to create a well planned system to maximize animal impact but not degrade the health of the ecosystem.
Overall, our ecosystems and crop production needs these inputs. While the space they chew up may seem intimidating, crop failure is no easy task to deal with. Use inspiration from the food forest, shape it accordingly, sight it to specific wind directions, space the trees tightly, and manage for abundance!
Mollison, B. & Slay, R.M. (1991) Introdcution to permaculture. 2nd Edition. Sisters Creek, Tasmania, Australia. Tagari.
Hill, Dr. D. Kentucky Woodlands Magazine. Volume 3, Issue 1. University of Kentucky, Lexington, Kentucky.