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Windbreaks

Windbreaks have been a part of Iowa's forest since settlement. 
During the 1930's, establishment of windbreaks for farmstead protection was very intensive; at one time, the goal of the windbreak program was to establish a demonstration windbreak in every township in the state to encourage additional windbreak planting. These windbreaks functioned into the 1960's, when, because of low energy costs and high farmland values, many of them were removed. Renewed interests in windbreaks surfaced during the energy crisis of the 1970's and continues today.  

Windbreaks provide many benefits. 
Windbreaks reduce wind speeds, control snow drifting and accumulation in farmsteads, provide wildlife habitat, enhance farmstead value, and provide a more pleasant environment. Reduced wind speeds in winter months provide monetary benefits. Homes or confinement buildings require 7 to 25 percent less fuel for heating. Livestock protected by a windbreak are 3-7 percent more efficient in conversion of feed to weight gain. Other benefits of windbreaks are measured in quality of life improvement.  

Check out our publication on Windbreaks for Wildlife.

Windbreaks should be properly designed and located for maximum benefits. 
Some basis design considerations follow:

  • Plant a minimum of three rows; additional rows up to 8-11 rows will improve protection and increase benefits.
  • Incorporate conifers as the major tree in the windbreak where soil conditions allow. Deciduous trees are only 5-20 percent as effective as conifers.
  • Locate on the north and west site of the property; avoid surrounding the farmstead with a solid barrier of trees.
  • Use several different species in the windbreak; plant within rows in blocks to minimize competition caused by different growth rates. For example, one half of the first row could be Norway spruce with the other half blue spruce.
  • The distance between all rows should be at least 20 feet; the spacing between trees/shrubs within a row will vary from 4 to 20 feet depending on mature size of the species.
  • For optimum wind lift, plant the tallest trees inside and the shortest shrubs on the upwind (north and west) side of the windbreak.
  • The inside row of the windbreak should be 50 feet away from the protected site (to minimize snow accumulation) or with wider windbreaks 100 feet from the outside rows. The greatest wind protection will occur closest to the windbreak. Protection becomes minimal at 15 to 20 times the height of the windbreak.
  • If snow accumulation is a serious problem, use a double row of shrubs on the outside of the windbreak spaced at least 30-40 feet apart.
  • Where possible, take advantage of contours and locate the windbreak uphill from the protected site; height is relative for most wind protection.

The standard L-shaped, square corner windbreak can be modified. Trees can planted in groups instead of rows. Corners can be rounded or merged together. The key for optimum protection is providing wind protection on the NW quadrant.

Other Resources: 

Farmstead Windbreaks: Planning

Farmstead Windbreaks: Establishment, Care, and Maintenance

Pruning Landscape Trees

Landscape trees need proper care and management throughout their lives, and one of the most important tree management practices is pruning. When done properly, pruning can improve the health and structure of trees, and provide a safer environment for people, pets, and property. Pruning is more than just indiscriminately removing branches. Proper pruning includes knowing which branches to remove, when to do it, and how to minimize damage to the tree.

The main reason to prune young trees is to develop good branch structure and tree strength. Removing weak branches and correcting poor form when branches are small, will minimize the size of the pruning wounds. Early pruning will also promote strength and balance that will make a tree less susceptible to damage from wind, ice, and snow storms. Attention to developing good structure is most critical in the first 15-20 years of a tree's life.

When To Prune 

The best time to prune is in mid to late winter (January-March). When pruned during this time of the year, the tree will begin responding to the wounding early in the spring. A coniferous tree planted in a suitable site, will need minimal pruning throughout its life.

Pruning at other times of the year will not hurt a tree; however the process of sealing the wound may be slowed. Do not prune during the spring from bud break through leaf expansion, and during the period of leaf color change in the fall. A tree is going through major changes at these times, and branch removal can reduce the vigor of a tree. One species where timing of pruning is critical, is oak. The pathogen that causes the disease Oak Wilt can be transmitted to open wounds by a small beetle. Avoid wounding (pruning) oak between early March until late July.

Training Young Trees

Limit pruning of newly planted trees to the removal of dead and broken branches or the correction of multiple leaders. Begin developmental pruning of deciduous trees 2-3 years after planting. Other key things to remember when pruning young trees are to:

  • Know the general growth habit of a tree before beginning.
  • Leave the temporary lower branches on the tree until they reach 1 inch in diameter to increase trunk growth and root development.
  • Always leave 70 percent of the tree height with live branches (see Figure 1).
  • Avoid removing lower branches too quickly, keeping lower branches longer allows for larger and stronger tree trunks (see Figure 2).
  • Concentrate efforts on removing crossing, rubbing, broken, diseased and weak-angled branches in the upper portion of the tree.
  • Eliminate double leaders and basal sprouts.
  • Develop one main leader on shade tree species such as: oak, maple, ash, and linden.
  • Concentrate efforts on removing rubbing and competing branches on species such as crabapple.
  • Space permanent branches 15-35 inches apart.
  • Remember developmental pruning is an on-going process over the first 15-20 years of a tree's life.

How to Make a Pruning Cut

Before deciding which branches to remove, always examine the tree carefully. Before making a pruning cut, identify the branch bark ridge and branch collar. The branch bark ridge is where the branch and trunk tissue meet. The branch collar is the swollen area just outside the branch bark ridge (see Figure 3).

  • Do not cut behind the collar and branch bark ridge creating a "flush cut". Removal of these two structures impedes the tree's ability to respond to the wound, which increases the chances of decay development.
  • Do not leave a stub.
  • Do not top a tree, which is the indiscriminate removal of branches without regard to the location of lateral branches or buds (see Figure 6).
  • Always remove branches back to their point of origin or to a side branch of sufficient size to assume dominance.

The best indicator of the proficiency of your pruning is the development of wound closure tissue on the tree. Usually within a year after branch removal, a ring (donut-shaped) of callus tissue will begin to develop around the existing wound (see Figure 7).

Note: If callus tissue develops only on the sides of the wound, this may indicate the pruning cut was too close to branch bark ridge and branch collar.

Wound Treatment

Proper pruning is the key to good wound closure. A number of studies have shown that the use of wound dressings or paints does not speed up the tree's ability to seal a wound. In most cases, pruning paints create a more favorable environment for decay causing organisms compared to doing nothing at all. At this time pruning paints are no longer recommended.

For additional information check out this tree pruning publication from Iowa State University Extension

 

Tree Injury and Stress

Every year in Iowa, ornamental woody plants, trees and shrubs, die without showing any glaring and obvious causes.  In addition, insects and diseases cause their share of decline and mortality in trees.

In some cases, if the trees are stressed or if they have been wounded (a major cause of tree stress), they may be more susceptible to damage caused by insects and diseases.  Stresses in trees may be caused by natural factors and conditions or through the activities of man or animals.  These factors may be chronic (recurring and lasting for a long time) or acute (immediate impact).  Examples of chronic damage are wet soils caused by site selection, soil compaction, or poor nutrition; acute damage includes flooding, freezing conditions, severe construction damage, and deer browsing.

Causes of stress in trees and shrubs:

  • Environmental: nutrient deficiency, drought, wind, flooding, freezing, sun scorch
  • Man-caused: pollution, mechanical, soil compaction, excess water, excess fertilizer, improper pruning
  • Animal: nematodes, insects, birds, deer, rabbits, mice
  • Other organisms: viruses, fungi, vines, weeds, bacteria, mycoplasmas

Tree stresses may be very dramatic and obvious or in many cases not easily observed or recognized.  Obvious stresses may include basal damage or storm damage; stresses from grade changes, soil compaction or pollution are not very visible.  

Trees often do not display immediate responses to stresses because of their accumulated growth habit.  However, with stresses come several changes within the tree depending on the damage caused by the stress.  In some cases, the process of photosynthesis, which is the primary supply of carbohydrates for all tree functions, is reduced and the tree’s stored food reserves are depleted.  When root systems are damaged by construction damage, compaction, or poor drainage, they cannot supply adequate water and nutrients for the trees growth and survival.  When this happens, often the tree is unable to produce sufficient carbohydrates and growth regulating chemicals.  When trunks or stems are damaged, the carbohydrates movement to where it is needed for growth and function is stopped, and may result in death of roots or other growing points of the tree. The end result of these reduced processes is that the tree at best, operates at less than peak efficiency and in many cases it begins a downward spiral of all of its growth functions.

As stresses continue, the tree does eventually exhibit external symptoms.  Annual incremental growth is reduced and becomes significantly less than normal.  Leaves may be fewer in number and smaller in size.  Sometimes, the tree produces excess fruit or seed as a survival mechanism.  The tree may exhibit summer scorch symptoms because of insufficient water provided to the leaves during weather.  With continued stresses, branches begin to die, and at the same time the root system of the tree is reduced because the crown is producing inadequate food for good root expansion and growth.  These processed continue into a downward spiral, usually resulting in the continued decline and eventual death of the tree over a period of 2-15 years.  In most cases, once the tree has tipped the balance of not providing sufficient carbohydrates for continued growth of the tree, it cannot recover.

If the physical stresses do not kill the tree, it will often be exposed to more stresses through opportunistic diseases and insect attacks.  These biotic attacks may speed up and/or complete the demise of the tree.

Much of the survival, growth and health of our woody vegetation in our landscapes is dependent on the homeowner/manager working to prevent stress and provide the optimal growing environment of the tree.  This may begin with plant selection to ensure that the selected plant will perform well on the specific site and soil.  Avoid injuries to trees and their expansive root systems during construction or when working around trees.  Don’t over fertilize trees; excessive leaf production often results in moisture stress during hot dry periods in Iowa.  Avoid basal damage to tree trunks because this is the direct connect from the roots to the leaf tissue and area.  Lawnmowers are still one of he major causes of damage to trees.  Use proper pruning techniques, and avoid pruning during the spring period of leaf expansion.  Use mulches to reduce temperature and moisture extremes.  Use caution when using lawn irrigation systems; trees often suffer because of too frequent watering resulting in soils which are too wet for good root growth.

Trees and Construction

Trees and construction activities (new buildings, roads, and utility lines) often interact non-constructively, resulting in damage or death to trees. Injury to above ground parts of trees (trunk and crown) and its effect on the health and vigor of trees is easy to see and evaluate. It is easy to avoid damaging the above ground portion of a tree because of its high visibility. However, during construction, damage to the root system and/or the soil around the root system results in more loss and death than above-ground damage during construction. Root and soil damage is less obvious and may result in tree death or damage which may not be evident for as long as 8 to 10 years. 

Soils and Tree Growth

Most of the non-infectious disorders of trees in Iowa are related to the roots and/or the soil. Soils have physical, chemical and biological characteristics or systems which can be changed by construction activities. Ideal soils for tree growth consist of about half of its volume composed of solid matter including mineral particles and some organic matter; the other half consists of pore spaces filled in varying proportions with air and water. 

Soil texture refers to the size of individual mineral particles-clay, silt or sand. Soils with high clay content, will hold more water for plant growth, yet may be more susceptible to soil compaction. Sandy soils, hold less water and are less susceptible of soil compaction. Water and air movement and the ease of root growth through soils are determined by pore size, not necessarily the size of individual mineral particles. This soil structure is an indication of the degree or level to which soil particles are aggregated together, creating more pore space. In general, the more structure a soil has, the more desirable it is for tree growth. Bulk density of a soil is the weight of a given volume of soil; soil compaction increases the soil bulk density, resulting in less pore space and greater difficulty for tree roots to grow and expand. 

Many of our urban soils have been disturbed. These soils are often shallow with little soil depth and often consist of subsoil material covered with less than 6 inches of top soil. Root growth will often be slowed by soil layers which are significantly different than the soil above or below. For example, a sandy surface soil on top of a compacted clay layer, may be excessively wet at times because of poor drainage and droughty during dry periods because of poor root penetration. 

Tree Roots

Tree roots are made up of large permanent roots (provide mainly anchorage and transport) and many small, temporary feeder roots and root hairs. These small roots are the primary water and nutrient absorbers. They are functional for only 1 to 3 years, and then either die or become part of the large root system. Most trees replace at least one third of their feeder roots each year. 

Tree roots do not penetrate soils to great depths. Most roots will concentrate in the top 6 to 18 inches of topsoil. Tree roots occupy a larger area than previously believed. They will often extend out from the trunk in an irregular area which is 4 to 7 times larger than the area of their crown. 

How to Minimize Damage 

The surest method of minimizing damage to a root system or soil during construction is to do nothing around, in, or on top of a tree's root system. Construct a sturdy fence at least at the outer dripline of the tree or trees to be saved and allow zero activity within this area. The larger the area of zero activity around the tree, the less damage. The more this zone is violated by construction activities, the more the tree may be damaged. Activities which will damage tree roots are cutting or stripping surface soils, lowering grades, trenching, parking or operating any machinery in this area, storing supplies, filling or storing soil or excavation materials, building sidewalks and streets, creating sand or gravel piles over the roots, removing ground covers, and many others. 

In most cases, zero activity in the root zone is not possible. If construction activity cannot be avoided, strive to minimize their affect on both the root system and the soil. For sidewalks minimize any grade changes and excavation. When trenching for utilities, bore under the root system instead of cutting through roots and combine utilities in the same trench where possible. Use retaining walls as much as possible instead of complete site grading. Minimize compaction by working when soils are dry and using hand equipment instead of large mechanical equipment. When filling around a tree, make provisions for both air and water drainage and supplies and/or use fill material which is well drained. If possible build structures on posts rather than footings or extensive foundations. Strive to minimize activities which cut roots or adversely affect soil characteristics. 

Trees vary significantly in their tolerances to construction damages. In addition to species differences, the root distribution pattern for each individual tree will affect its tolerance to construction. If most of a tree's roots are located away from the construction zone, it will suffer minimal damage.

Tree saving practices during construction can be both time consuming and expensive. First make sure that the tree is worth saving; it should be a desirable species, in reasonably good health, and have a projected life expectancy of at least 20 years. In some cases, removal and replacement after construction may be the most viable alternative.

Watering Newly Planted Trees

Water is often the most limiting growth requirement for trees and shrubs in the landscape.  Trees and shrubs are mostly water, which is a major part of its cells, is used in chemical reactions and photosynthesis, and aids in the movement of materials throughout the plant.  However, most water is lost from the plant through transpiration from pores on the leaf surfaces.  As the water is lost through transpiration, it creates the pull necessary to move the water from the roots to the leaves.  Water is also essential to cool the plant, as it is lost from the leaf surfaces.

In Iowa, during the establishment period of one to two years, supplemental watering during periods of drought and high temperatures will increase survival and improve tree health and growth.  Drought conditions can lead to tree decline, pest problems and in some cases damages so severe that the plant will die.  In addition, excessive water can cause very similar problems with tree growth and survival.  Tree roots require oxygen to survive and excess water can cause their decline and death, resulting in tree mortality.

When first planted, trees often have insufficient root systems or at least their roots are not expansive enough to gather enough water for good growth and survival.  Tree roots mostly occupy the upper 16-20 inches of soil; this is the region to add supplemental water.  Ideally, watering should begin when this soil region becomes dry and can no longer supply the needed water to the plant.  One can also used the “hand” method to determine moisture condition of the soil.  Simply feel a handful of soil from a depth of 6-12 inches to determine its moisture level.  In Iowa, an average time frame is to water new trees every 7 to 14 days if less than one inch of rainfall is received during the same time period.  Sand soils dry out faster than clay soils.  As the root systems expand, the trees will require less frequent watering.  By the end of the first growing seasons, most trees and shrubs should have sufficient root systems to survive without supplemental watering.  Supplemental watering may be required for very large planting stock and for newer plantings during periods of drought during the second year of establishment.

When watering is necessary for new plantings, use enough water to soak the entire root system to that root depth of 20 inches or more.  The best watering technique is to use soaker or drip systems, ensuring that applied water enters the soils rather than running off.  Surface soaking allows the tree more chances to absorb water and helps maintain nutrient cycling by moving nutrients down to the root system.  The use of wands to deep soil water is not as efficient as watering from the top and often results in incomplete watering.  It is important not to over water with respect to frequency.  Allow the root system to dry out moderately to stimulate root expansion and growth.  Use 3 to 4 inches of organic mulches to help conserve water.  

Turf watering and tree watering are sometimes in conflict.  Proper turf watering is too frequent and usually insufficient to penetrate down to the tree’s root system.  This pattern may encourage the tree to develop a shallow, ineffective root system.  Where possible, strive to isolate the tree roots away from turf watering system or when planning the irrigation system, have a separate zone for the trees.

In some cases, especially on clay soils, frequent turf irrigation will keep the upper root zone of the tree so wet, that roots suffer mortality and the trees decline and die.  Trees perform best when their root system is soaked, either naturally or with irrigation and then allowed to dry significantly before receiving more water.

Check out the Iowa State University Horticulture article on Care of Newly Planted Trees

Buffer Strips for Riparian Zones

Iowa is a landscape of fertile soil, agriculture crops, and networks of streams and rivers for drainage of the abundant rainfall. The woodland resource of the state at the time of settlement was concentrated, in part, along these streams and rivers. With settlement and the increased mechanization of agriculture, many of these natural woodland corridors were removed to provide more lands for crop production. These losses resulted in reduced ability of the riparian forest ecosystem to assimilate chemical and soil losses from agriculture lands and because of reduced diversity of the ecosystem, less wildlife habitat.

Management practices for riparian corridors along creeks and streams can be modified for improved benefits. The riparian zone is the last area for interception and biological processing of up-hill materials produced by agriculture practices before they enter the stream. If these zones are kept in perennial vegetation with  extensive and dynamic root system, large quantities of water, associated chemicals, and moving sediments from adjacent fields can be kept on site before they are lost and contribute to water pollution. 

Riparian buffer strips of perennial vegetation contribute to sustainable agriculture by reducing soil loss, improving water quality and stabilizing the banks of the drainage system. Combinations of perennial grasses, forbs and woody vegetation along stream corridors improve aesthetics and wildlife habitat providing increased number and diversity of wildlife populations. Trees are especially valuable because they reduce atmospheric CO2 through carbon storage and provide alternative sources of renewable energy. 

Design of Buffer Strips

The basic design component is multiple rows of trees and shrubs adjacent to the stream with an additional filter of perennial grasses on the outside of the trees. As size of the stream and/or effected watershed increases, the width of the buffer strip must be increased to maintain its effectiveness. 

Minimum total width of a filter strip is 33 feet; spacing between rows and trees within a row varies with species and objectives. Common plantings will be 8 to 10 feet between rows and 4 to 6 feet between trees within the row; shrubs will be planted at closer spacings. 

Tree and shrub species and planting design will vary depending on the site and the ultimate use of the woody vegetation produced. Fast growing hardwoods such as cottonwood and hybrid poplars, silver maple, willows, and green ash can be used on a variety of bottomland sites. Their advantage is that they grow fast and coppice after being harvested. These trees can harvested for biofuels within 4-6 years or can be left longer to produce small dimension lumber and biofuels.  

These trees are harvested in the winter and resprout vigorously in spring producing even more growth than the original stems. As such they continually function in taking up agricultural chemicals during the growing season. It is also possible to produce high quality sawlogs (oak and walnut) by planting the oak and walnut in the middle row of trees with the faster growing species listed above in the outside rows.  

The faster growing species will not become over competitive because they can be harvested on a short-rotation. The high quality species are more site specific and should not be planted in poorly drained soils. The choice of shrubs can include species such as ninebark, red-osier dogwood, Nanking cherry, serviceberry and others. The selection of shrubs should depend on site conditions and wildlife attraction. 

It is recommended that several different species be used on one site. The up-hill grass strip can also be planted to several different permanent cover species.

The establishment of buffer strips will reduce soil loss and ground and surface water pollution, provide improved wildlife habitat, increase diversity of agricultural operations by producing biofuels and timber products, improve the aesthetics of the agricultural landscape and reduce the effects of global warming.

For additional information on buffer strips check out our publication Buffer Strip Design, Establishment, and Maintenance

What Story is your Land Telling?

May 4, 2017 2:40 PM

We can learn about our land in a variety of ways. Local history books report on the native cultures that hunted, gathered, farmed and traded there. General Land Office surveys from the 19th century record the locations of natural features and early settlements. Historical aerial photographs provide high-resolution snapshots through time dating back to the Hoover Administration. Stories of past hunts and or family memories in old fields and forests are passed down through generations. All reflecting a transfer of information through shared stories or archival records....

To continue reading this article on the Acreage Living Newsletter, click here.

Start a Legacy this Autumn

September 20, 2019 12:00 PM

Hello Iowans! My name is Billy Beck - your new Forestry Specialist with Iowa State University Extension and Outreach. I hail from the Midwest, having earned my Bachelor’s degree in Forestry from Michigan State University, my Master’s degree in Forest Hydrology from Southern Illinois University at Carbondale, and my Ph.D. in Environmental Science (water quality emphasis) from Iowa State. I am honored to serve the people, forests, and water resources of “the land between the rivers” in my new role. I am also elated, as this position offers the opportunity to pursue my two passions – forestry and water quality! Feel free to follow our efforts on the ISU Extension Forestry webpage, Twitter, and Instagram accounts.

To continue reading this article the Acreage Living Newsletter, click here.

Windbreaks for Wildlife

Windbreaks for Wildlife
Windbreaks provide many benefits to farms such as reducing energy consumption, controlling odor, protecting buildings and livestock from the elements and improving aesthetics. This publication discusses the importance of windbreaks, their design and the best species of trees or shrubs to plant.

Roles of trees may change from Lee to Lyon, but their value to Iowa farmers doesn’t waver

November 22, 2019 4:17 PM

One of my first exposures to Iowa came in the form of a motorcycle ride my Dad and I took across northwest Iowa in 2014. As we roared across the landscape, my mind was actively engaged in “70 mph forestry”. I delighted in the streamside timber lining the valleys of the Big Sioux, Little Sioux, and Floyd Rivers. Even more impressive than these water-cleaning beauties, however, was the prevalence of windbreaks and shelterbelts working to protect the region’s homes, farmsteads, and livestock. Looking back to that ride, I now realize that although roles of trees may change across our state, be it 300 acres of timber in Lee County or a shelterbelt protecting 300 head in Lyon, their strong value to Iowa agriculture does not waver.  

As far as trees acting as assets to farm enterprises, windbreaks and shelterbelts represent top practices for northwest Iowa producers. Both practices entail single or multiple rows of trees or shrubs arranged in linear configurations - “linear forests”, as some folks say. Shelterbelts protect our homes, outbuildings, and feedlots again temperature extremes – decreasing heating and cooling costs, as well as improving livestock gains. Windbreaks benefit our crop fields through reduced soil erosion from wind, increased moisture retention, and protection from wind-related damage. In addition, both practices boost aesthetics, wildlife habitat, carbon sequestration, and even water quality across our landscape.

You may have windbreaks or shelterbelts already established, but are they doing their job? Performance can, and does, decrease over time as plantings age and decline. Windbreak / shelterbelt renovation is an absolutely critical, yet often overlooked, practice necessary to maintain peak performance. Pruning, thinning, planting, and row additions act to maximize functionality and allow for resilience in the face of climatic, insect and disease, and herbivory stressors. As with all forestry practices, monitoring and maintenance are key – you can’t just plant, walk away, and expect success!

Trees can be challenging to grow and maintain, but the rewards are worth it. District Foresters and Forestry Specialists with the Iowa Department of Natural Resources can provide the technical expertise required for successful projects. ISUEO Forestry and the Natural Resources Stewardship Team provide online resources, as well as in-field programming and educational events. Cost share for establishment and renovation may be available through the Conservation Reserve Program (CRP), Environmental Quality Incentives Program (EQIP), and Resource Enhancement and Protection (REAP) – see your county USDA Service Center for details. In closing, I am thrilled for the opportunity to promote windbreaks and shelterbelts across northwest Iowa. Join me on the leeward side of one in mid-January, and I’ll let you be the ultimate judge of their value!

Additional Resources:

Farmstead Windbreaks: Planning

Farmstead Windbreaks: Establishment, Care, and Maintenance

Windbreaks for Wildlife

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