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A windbreak is a linear arrangement combining trees, shrubs and
plants established for the purposes of modifying the local wind flow through
and over the trees and thereby exerting influence on local environmental
factors such as wind speed, temperature and humidity across neighboring
crop fields. Windbreaks are commonly established with one or more closely
spaced rows, containing one or more species of plants. In ideal circumstances
one or more repeated linear structures are established in parallel
series across larger farm field landscapes.
Figure 1. (left). Two parallel
radiata pine field windbreaks
protecting sheep grazing paddocks
in Marlbourgh, NZ. G. Horvath.
Figure 2. (left). A one row shrub
(left row) and 3 row conifer (mixed cedar, pine, spruce and firs)
field windbreak protecting soybean
and corn fields. This windbreak also operates effectively
as a living snow fence. Franklin
Co., Iowa, USA. G. Horvath
Dependent on their use and location in the world, field windbreaks may also be commonly known as: shelterbelts, hedgerows, timberbelts, living snow fences or conservation buffers.
Shelterbelts are most often found as multiple rows (4 or more) established around several sides of a farmstead or groups of farm buildings thereby providing a small but very intense zone of protection.Timberbelts are field windbreaks or other linear tree arrangements that in addition to their environmental influence are also managed to produce a crop of wood fiber or timber.
Snow fences are specifically designed to catch drifting snow and are often established in the vicinity of roads and driveways with the objective of keeping the travel routes clear.
The primary purpose of a field windbreak is to reduce, as opposed to
stopping, the speed of the wind across a landscape. There has been a considerable
amount of research conducted on shelterbelts and windbreaks around the
world, which indicates that properly established lines of trees or shrubs
provide protection from the force and turbulence of the wind. Many shelterbelt
benefits resulting from this reduced wind flow have been identified:
1) Yield increases in grain crops such as wheat (Triticum spp.) and corn (Zea spp.)Figure 3. (above-right). Even without leaves deciduous trees are still effective at catching winter snow drift, as seen with this single poplar row. In the long-term the longer lived spruce will takeover as the primary provider of shelter effects. Guelph, Ontario, Canada. G. Horvath.2) Reduced sandblasting effects and therefore improved quality in horticultural crops such as tomatoes (Lycopersicon spp.), peppers (Capsicum spp.), and tobacco (Nicotiana spp.),
3) Control of soil erosion, particularly on exposed sandy or dry soils,
4) Snow deposition control along roadways, driveways and across fields,
5) Provision of shelter in stockyards and around farm buildings through control of temperature and wind chill factors,
6) Improved aesthetics and value in the landscape, assuming of course that one likes trees!
7) Provision of wildlife habitat,
8) Provision of carbon sequestration,
9) Provision of alternative tree-based resources such as timber, fiber or biomass, and,
10) Provision of alternative tree-based crops such as nuts or berries
Many of these widely accepted benefits of shelterbelt establishment
are difficult to quantify, particularly in terms of precise economic value
or gain for the farmer or landowner. Many farm operations are independent
businesses and there must be an economic benefit to balance the costs incurred
and the time involved, before the landowner will undertake to establish
and maintain shelterbelt networks. Therefore, the ability to predict benefits
and to show specific gains is of major importance when trying to encourage
the widespread establishment of shelterbelts.
This website has been developed in order to present the research conducted
jointly by the Departments of Forestry, Agricultural and Biosystems Engineering,
Agronomy, Geologic and Atmospheric Sciences (Meteorology) and Economics
at Iowa State University, along with the School of Natural Resource Sciences
at the University of Nebraska. Assistance has also been provided by a significant
number of NRCS Regional and District Conservationists and by the property
owners themselves in Iowa, Indiana and Minnesota, who have with considerable
foresight established these windbreaks on their farms in the first place!
Any questions or comments concerning this website or the overall research
program should be directed to:
Gaspar Horvath
Forestry Department, ISU
ghorvath@iastate.edu
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