Restoring Our Hurricane-Ravaged Urban Tree Canopy:

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1 ALABAMA A&M AND AUBURN UNIVERSITIES Restoring Our Hurricane-Ravaged Urban Tree Canopy: Best Management Practices for Site Evaluation, Tree Selection, Establishment, and Maintenance

3 Restoring Our Hurricane-Ravaged Urban Tree Canopy: Best Management Practices for Site Evaluation, Tree Selection, Establishment, and Maintenance Best management practices for successful landscape tree establishment in the urban environment depend on the design, site analysis, tree species selection, and proper planting and maintenance. All these factors are interrelated. Compromises to any of the BMPs are cumulative and affect other establishment factors. Successive compromises result in stress to the tree with potential death or failure of the planting. Each factor will be highlighted separately, but keep in mind that all factors are evaluated with attention to each other. 3

4 Site Evaluation and Design Concerns Evaluation of the site to develop the design is the first step in a tree planting program. Once you know the restraints of the site and the design requirements, plants can be selected and planting and maintenance specifications written to meet the site limitations. The following points should be considered during the site evaluation and design process: The USDA hardiness zones for Alabama are zones 7 and 8. Hardiness is not as big a concern as tolerance to heat and low chilling hours or photoperiod required for proper bud set of some tree species. Is irrigation available? What is the light exposure, sun or shade? What is the analysis of the soil nutrition levels, especially ph, phosphorus, and potassium? These nutrients are better adjusted according to the soil test before planting. What is the internal soil drainage? To test, dig a hole 18 inches deep and fill it with water. If water is gone in 1 to 2 hours, soil drainage is good; 12 to 24 hours, soil drainage is moderate; more than 24 hours, soil drainage is poor. What is the distance to the soil water table? Dig a hole 2 feet deep and wait 2 to 3 hours to see if water fills the hole. If water appears in the hole, there is a high water table. Is there a heavily compacted soil layer, or hardpan, that limits drainage, or is it a high water table? Is the soil texture clay, loam, or sand? Is the soil density compacted/hard or loose? Will your trees be planted in an open park setting, a sidewalk tree cut, or a planting strip? What are the dimensions of the root zone space and volume of soil available for tree growth? 4

5 Is there a swimming pool, septic tank, vegetable garden, or annual planting bed within 50 feet of the planting area? What is the distance between the tree planting and any building? Are there underground or aboveground utilities or lights that need to be considered? Are trees sited far enough back from an intersection or sidewalk and limbed high enough to prevent obstruction of views of passing motorists? Also, allow for safe pedestrian traffic on sidewalks. Is there a budget for pruning and maintenance of the trees? Are there landscaping or tree ordinances that would affect selection and size of trees? What is an assessment of tree diversity in the area? Are the trees to be used for a screen, shade, or a focal point? What trees currently exist in the planting area? What construction activities have recently gone on that might affect these trees? Are they healthy, desirable trees? What is the size, shape, texture, color, evergreen or deciduous requirements of the trees needed for the design? Are there storefronts, signs, traffic vision concerns, or other views that may need to be considered for framing or screening in the selection of the trees? 5

6 Specifications for Tree Selection Successful landscape plantings can only occur when high quality nursery stock is selected that has the proper limb structure and root-to-shoot ratio balance. Trees should be healthy, free of disease and insect pests, and the quality should be maintained during transportation from the nursery and throughout the planting process. The following check list offers minimum guidelines for selection of trees for the landscape. Shade trees should have the following characteristics: A strong, straight central leader with no lateral branches greater than two-thirds the caliper, or thickness, of the main leader. Branches equally spaced around the central leader at least 6 inches apart. Each branch should have its own space. A uniform canopy from all sides and free of large voids. Trunks that are free from all abrasions and scratches. There should be no more than 40 percent of the height clear of branches unless the designer specifies otherwise. Tree branches with good spacing and wide angles from the main trunk with no included bark where branches have grown closely together. Proper pruning cuts that are not flush cuts but pruned to a collar. A well-developed root system established from proper root pruning and irrigation during production. Root balls in balled and burlapped plantings that are of the appropriate size. They should be firm with no loose movement between the trunk and the root ball when the trunk is rotated. 6

7 Roots at the interface of the burlap and soil. Container roots that fill the entire container without having any root greater than ¹ 5 the tree caliper and no large roots in the upper 3 inches of media encircling more than ¹ ³ of the root ball. If kinked roots are less than ¹ ³ of the root ball, they can be pruned. Smaller caliper trees establish quicker than large caliper trees. Plant 1.5- to 3.5-inch caliper trees unless instant effect is desired and good soil conditions permit a large planting. Smaller trees also establish better in poorly drained, low oxygen soils. Standards for Various Container- and Field- Grown Balled and Burlapped Trees The following tables, taken from the American and Florida Standards and Grades for Nursery Stock, offer a guide to the minimum acceptable industry standards for root balls and container sizes for field and container grown trees. When selecting trees from the nursery, the nursery stock should meet or exceed these guidelines. Table 1. Root Ball Size Standards Trunk caliper Minimum ball diameter on Minimum root ball Minimum container Minimum tree height Minimum tree height Maximum tree height (inches) field grown shade trees diameter on fabric container grown trees size (gallons) on standard trees on slower grown trees The optimum tree size, depending on your need for instant effect and your site requirements, should fall between 1.5 and 3.5 inches in caliper. 7

8 Table 2. Root Ball Depth and Diameter Root ball diameter (inches) Less than 20 Minimum root ball depth Not less than 75% of diameter 20 to 30 Not less than 66% of diameter 31 to 48 Not less than 60% of diameter Source: American Standard for Nursery Stock, ANSI Z60.1 published by American Association of Nurserymen, Washington D.C. The complete publication can be found on line at: Documents/Docs/ANLAStandard2004.pdf. The University of Florida has developed their own grades and standards for minimum container size recommendations for trees grown in aboveground and fabric containers, ifas.ufl.edu/woody/planting/americanstandard.htm. Caliper is measured 6 inches from the ground on trees less than 4 inches in caliper. If more than 4 inches in caliper is measured at a 6-inch height, move to 12 inches above the ground to measure trunk caliper or diameter. Table 3. Bare Root Caliper, Tree Height, and Root Spread Caliper Average height range Minimum root spread (inches) (inches) (feet).5 5 to to to to to to to to to Example: If your tree is 2.5 inches in caliper, the average height should measure between 12 and 14 feet and the root spread should be a minimum of 32 inches. Table 4. Box Size for Trees Box diameter Maximum caliper range (inches) to to to to to to to 6 8 Source: American Standard for Nursery Stock, ANSI Z60.1 published by American Association of Nurserymen, Washington D.C. The complete publication can be found on line at: Documents/Docs/ANLAStandard2004.pdf. The University of Florida has developed their own grades and standards for minimum container size recommendations for trees grown in aboveground and fabric containers, ifas.ufl.edu/woody/planting/americanstandard.htm.

9 Caliper is measured 6 inches from the ground on trees less than 4 inches in caliper. Above 4 inches in caliper at 6 inch height, move to 12 inches above the ground to measure trunk caliper or diameter. Multistemmed or trunked trees There is a category of trees called multistem, shrub-form trees or clump trees. These are typically large shrubs or small trees with three or more stems arising from a single root system or multiple trees planted together. They are usually less than 15 to 20 feet tall at maturity and measurement is specified by height or the number of trunks preferred. Common examples include crapemyrtles, Japanese maples, river birches, some viburnums, deciduous magnolias, and others. Calipers may be offered for the multistem forms if the measurement procedure is outlined. If there is no explanation of the measurement process, take ½ of the mean caliper of the largest three trunks to calculate the caliper number. Table 5. Root Ball Sizes for Shrub Form and Multistem Trees Height minimum (feet) Diameter Ball Minimum (inches) Diameter Ball (inches)

10 Selection of Hurricane- Resistant Trees for South Alabama Urban Forests The following list of trees has proven to be either highly or moderately resistant to wind. The list was derived from research and observational data. There are a number of factors that contribute to hurricaneinflicted damage. The genus and species of trees are important for urban tree selection. Trees planted in clumps survive better than those sited as single tree specimens. The duration and intensity of the storm are also factors contributing to the damage. The amount of rain before the heavy winds loosens the soil around the roots and increases the potential damage. Road and driveway cuts; compacted, shallow, or low aerated soils; poor planting and pruning techniques; soil chemistry incompatibility; and lack of volume of soil are other factors limiting root growth and stability of the trees. Many trees are diseased and unhealthy, have genetically poor branch structure, are weak wooded, and are subject to breakage with low wind intensity. Other trees are physically more open or aerodynamically designed and have lower resistance to the wind and experience fewer problems. Smaller and younger trees generally withstand wind better than larger, older trees. 10

11 High to Medium-High Wind Resistance If the volume of soil for root growth is limited, small to medium trees should be selected. Small to medium trees offer little damage potential and are better suited to small urban island planting sites. There are many other great trees for the landscape, but these trees have been selected for their stability in hurricane areas. Acer palmatum Japanese maple Amelanchier arborea Downy serviceberry P Carpinus caroliniana Ironwood Cercis canadensis Redbud Chionanthus retusus Chinese fringetree Chionanthus virginicus White fringetree Cornus florida DogwoodP Halesia tetraptera Carolina silverbell Ilex cassine Dahoon holly Ilex opaca American holly Ilex vomitoria Yaupon holly Ilex x attenuata Foster holly and other attenuata cvs. Ilex x Fineline Fineline holly Koelreuteria paniculata Goldenrain tree Lagerstroemia indica Crapemyrtle Magnolia x soulangiana Saucer magnolia Pistacia chinensis Chinese pistache Podocarpus spp. Podocarpus Quercus geminata Sand live oak Vitex agnus-castus Chastetree P indicates better for park setting with improved soil quality and volume. 11

12 Larger Urban Trees To mature to their potential, large trees need room (soil volume) for their roots to expand. A good general rule is for every 1 inch caliper that you envision the tree s mature growth, provide a minimum of 2 feet for each inch on the side of a square root zone planting area. Example: If you envision a 12-inch caliper tree, the root zone required is 2 feet x 12 inches = 24 feet squared or 576 square feet root zone area. Another general rule is you need 15 feet squared planting area for a tree to realize its growth potential. Large trees resistant to high or medium winds include the following: Acer saccharum subsp. floridanum Betula nigra Diospyros virginiana Fraxinus americana Magnolia virginiana Magnolia grandiflora Nyssa aquatica Nyssa sylvatica Ostrya virginiana Quercus alba Quercus laevis Quercus michauxii Quercus myrtifolia Quercus shumardii Quercus stellata Quercus virginiana Ulmus americana Florida sugar maple River birch Common persimmon P White ash Sweetbay magnolia Southern magnolia Water tupelo Black tupelo P American hophornbean White oak Turkey oak Swamp chestnut Myrtle oak Shumard oak Post oak P Live oak American elm P Conifers Cedrus deodara Pinus palustris Taxodium distichum var. distichum Taxodium distichum var. nutans Deodar cedar P Longleaf pine P a Bald cypress Pond cypress Palms Butia capitata Pindo Sabal palmetto Cabbage P indicates the tree is better for a park setting with improved soil quality and volume. a no shallow soils 12

13 Trees with Medium-Low and Low Wind Resistance These trees are not suitable to plant in South Alabama urban forests. Dicots Acer negundo Acer rubrum Acer saccharinum Albizzia julibrissin Carya illinoensis Celtis laevigata Celtis occidentalis Eriobotrya japonica Fraxinus pennsylvanica Liriodendron tulipifera Morus rubra Myrica cerifera Persea borbonia Platanus occidentalis Prunus caroliniana Prunus serotina Pyrus calleryana Quercus falcata Quercus laurifolia Quercus nigra Quercus phellos Sapium sebiferum Ulmus americana Ulmus parvifolia Zelkova serrata b invasive Boxelder Red maple Silver maple Mimosab Pecan Sugarberry Hackberry Loquat Green ash Tulip poplar Red mulberry Wax myrtle Redbay Sycamore Carolina laurelcherry Black cherry Bradford and other pear cultivars Southern red oak Laurel oak Water oak Willow oak Chinese tallow b American elm Chinese elm Japanese zelkova Conifers Juniperus virginiana var. silicicola Southern red cedar Pinus clausa Sand pine Pinus elliottii var. elliottii Slash pine PO Pinus glabra Spruce pine PO Pinus taeda Loblolly pine X Cupressocyparis leylandii Leyland cypress PO indicates the tree should only be used in a park setting with improved soil quality and volume. 13

14 Planting and Maintenance Specifications Once the proper tree has been selected to fit the site and the landscape design, proper planting and follow-up care are required for the success of the project. The following points should be considered during the planting process: Trees should be transported to the site in a covered vehicle that prevents wind and temperature extremes. Plants should be well watered before shipping and checked for moisture at arrival. On-site plant material should be maintained under shade and irrigated twice daily. Plants should be heeled in if balled and burlapped material is used. Trees should be protected from extreme temperatures, freezing, or extreme heat. Always handle the tree by the root ball using straps or powered equipment. Do not lift it using the branches or the trunk. The trunk should be wrapped during shipping and the planting process for protection. Inspect the roots of container trees and remove any large roots that are circling more than ¹ ³ of the root ball, especially in the upper 2 to 3 inches of the root ball. Removing large roots can result in excessive stress and possible death of the tree. The hole should be dug no deeper than the root ball and 2 to 3 times wider than the root ball to give the roots easy access into the surrounding soil. Rough up or score the sides of the hole to prevent glazing or compaction of the planting hole and potential obstruction of lateral root growth. Most urban soils are compacted and poorly drained, resulting in low oxygen for the roots. Plant the tree with the root ball top at least 1 to 3 14

15 inches above the soil line with the trunk flare or root flare and uppermost roots at least level with the backfill surrounding the tree. Soil removed from the hole makes the best backfill unless the whole planting area can be amended uniformly. There is no apparent benefit from root stimulants, water absorbing gels, mycorrhizae, or fertilizer at planting. The planting site should be fertilized according to soil test recommendations for the long-term health of the tree. Gradually straighten the tree as backfill is added. Remove synthetic wraps, rope, and twine from the tree and ball. Wire baskets should be removed when possible, but research and practical application allows for removing at least the top 2 to 3 rungs of the basket. Although wire does not deteriorate, roots grow to encapsulate wire without apparent damage. Slice a shovel or spade around the backfill to settle the soil and remove air pockets. Break up heavy clay clods. Do not step firmly on the backfill, which may cause excessive compaction. Irrigate with 10 to 20 gallons of water to the root ball and surrounding soil. Apply 2 to 3 inches of mulch to the edge of the root ball, extending 6 to 8 feet from the tree. A thin layer (½ inch) of mulch can be applied to the root ball area for aesthetics. Do not pile mulch against the trunk of the tree. Only a thin layer of mulch and no soil should be on the top of the original root ball. This allows the roots surrounding the root ball to be on the surface and water to penetrate into the root ball. Stake the tree if the planting is in a windy area or an area of high traffic. If the tree is leaning due to a lack of taper or strength, tree selection was improper. Many trees with heavy root balls do not need staking. 15

16 Figure 1. Planting specification Planting hole 2 to 3 times width of ball Plant root ball 1 to 3 inches above soil line No soil on root ball Irrigate 2 to 3 times per week directly to the root ball Mulch 2 to 3 inches deep to the root ball Backfill with native soil Plant on a firm soil base and remove upper 2 to 3 levels of wire basket 120 degree angle Plan view Two strands of galvanized wire twisted for support Rubber hose Surveyor s flag Remove burlap and rope from top half of ball ¹ 8 depth of ball 2 to 3 inches of mulch Guying stakes Backfill 16 Figure 2. Principles of tree staking

17 Maintenance Requirements for Successful Tree Planting Trees should be provided with regular irrigation, three times per week, for the first 6 to 8 weeks during the growing season to stimulate greater root growth. Moisture should be monitored carefully for the remainder of the year. Establishment period is about 6 months for each inch tree caliper. For example, a 3-inch caliper requires an 18-month establishment period. Two to 3 gallons of water is required for each caliper inch of tree. Irrigation is applied to the root ball. If root ball is wet, do not irrigate. Pruning should have been done at the nursery. Do not prune for the first year after planting. Pruning can inhibit root growth and establishment. Maintain an 8-foot mulch area surrounding the tree, and limit traffic to prevent compaction. No grass or weeds are allowed close to the trunk. Inspect planted trees to be sure they were not planted too deep and root flare is distinctly visible. Remember to remove all stakes and guying materials after the first year. Pruning is required after year 2 to remove lower limbs to lift the canopy and maintain the central leader, limb spacing, and arrangement of limbs on the central trunk. Proper pruning cuts are required; no flush cuts. Trees respond to fertility after year 1 primarily to nitrogen (N) at a rate of 3 to 5 pounds of N per 1,000 square feet. If phosphorus and potassium have been adjusted to a medium level or better, those nutrients should be sufficient. A split application of fertilizer in winter or spring (February or March) and again in mid-june should result in maximum growth potential. 17

18 Sandy soils can benefit from three applications for maximum growth using the same rate split into three applications in February, late April or early May, and late June or early July. For older trees, one application is needed in February or March. 18

19 NOTES 19

Ken Tilt, Extension Specialist, Professor, and Joe Eakes, Professor, Horticulture, Auburn University, David West, County Extension Coordinator, James Miles, Regional Extension Agent, and William

20 Ken Tilt, Extension Specialist, Professor, and Joe Eakes, Professor, Horticulture, Auburn University, David West, County Extension Coordinator, James Miles, Regional Extension Agent, and William East, Regional Extension Agent Funded in part from an Urban & Community Forestry award from the USDA Forest Service by Auburn University For more information, call your county Extension office. Look in your telephone directory under your county s name to find the number. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability. New May 2006, ANR by the Alabama Cooperative Extension System. All rights reserved.

Section Landscaping.

Section Landscaping. Section 37.05. - Landscaping. A. Applicability. 1. The standards established in this section are to be considered the minimum requirements for the design, plant selection, installation and maintenance