17 SITE PREPARATION GRADING Objectives 1. Be able to describe and explain why grading is done in the landscape. 2. Be able to define and summarize how cutting and filling affect plant growth. 3. Be able to describe and summarize how to minimize the effects of cutting or filling on plants. 4. Be able to describe and explain ways to protect plants during construction. I. GRADING IN THE LANDSCAPE 1. Grading is defined as moving 2. Grading involves molding, reforming, Percent Slope 1. 1% = 1 foot vertical change in in a horizontal direction. 2. 0 to 5% used for high levels of activity. 3. 10% slope or higher considered steep. 4. Slope direction Grading Terms 1. remove soil at a site. 2. add soil to a site. 3. Cuts are fills & fills are cuts?
18 Cut Work Effects on Plants 1. Remove soil lowering the soil level. 2. Plant damage includes: a. Root b. Reduced water c. Impaired plant Determining Roots Loss 1. Use the drip line as a 2. % of roots are located outside 3. Root loss depends on amount of excavation. 4. Removing roots half way from drip line to the trunk 5. Lowering the entire area:
19 Percentage Root Losses 36% 20 16 12 8 4 64% 84% 96% 100% Grade changes around entire root system 6. Leave roots intact if diameter 2 inches Treatment of Exposed Roots 1. Make clean pruning cut. 2. Avoid pruning paints. 3. Keep cut roots moist and cool. Compensation Treatments for Damaged Plants 1. Keep roots moist. 2. Fertilize lightly (P, K, Ca, Mg & micronutrients)
20 a. Use 1/4 to 1/2 of usual fertilizer b. Wait one growing season for adding N. Reasons to withhold N 3. Reduce leaf area - prune shoots 4. Watch for pest 5. Check structural integrity of trees. Trenching 1. Trenching is a type of cutting, usually used for 2. Damage is usually to one side of Percentage Root Losses 20% 30% 37% 44% 20 12 16 8 4 50% Grade change on one side of the tree or a trench
21 3. Trench placement Trenching Techniques for Least Damage 1. Trench 1 to 2 feet off center 2. Trench dug 4 feet deep. 3. Dig mechanically until 4. Hand dig trench from drip line to 5. Bore a tunnel between two trenches. 6. Prune damaged roots and keep Fill Work Reasons for filling include: 1. Change 2. Stabilize 3. Add landscape Effects of Adding Fill 1. Soil drainage a. Make sure soil drains away
22 b. Want to avoid 2. Oxygen content of a. Importance: b. 1 to 3 inches of fill over a clay soil could c. General rule: construct Other Methods to Help Tree Roots Grow into Fill Soil 1. Induce new roots to form on the buried trunk a. Species: b. Method - cut trunk one foot below the final 2. Rock and gravel (USDA method) 3. Sand collar a. Method - medium textured sand is placed around b. Usefulness may be limited to
23 Fill Soil Characteristics 1. Structure and texture - use a 2. New surface drainage should be away from Indications of Plants in Fill Areas 1. Stress symptoms include leaf wilt, 2. Straight trunk appearance at Principles for Raising the Soil Level 1. Time of year - a. Exception: b. Reason: 2. Encourage rooting into fill soil and aid the transition by: a. Remove debris such as b. Loosen soil to a depth of c. Apply a complete fertilizer ( - - ) or d. Thin canopy, perhaps up to e. Maintain moist roots but
24 Protection of Existing Plants from Construction 1. Species tolerance to change. a. Resistant - elm, poplar, willow. b. Susceptible - beech, birch, and most species of conifers. 2. Key: Ability to regenerate Construction Damage to Plants 1. Root damage from: a. Soil compaction b. Physical injury or destruction. c. Drainage pattern changed. d. Sensitive plant species 2. Trunk and limb damage caused by Protective Steps to Avoid Construction Damage 1. Decide if plant should be saved. 2. PREVENT traffic or storage under the tree canopy. a. Build a fence to keep equipment and people out.
25 b. Soil compacts readily. 3. If traffic must get close to a tree, fence off 2/3 AREA under the canopy. a. Cover non-fenced area with 6 inches of coarse mulch. b. Use metal plates on mulch if equipment will be under the canopy. 4. For only foot traffic under canopy, make a 5. Prevent storage or placement of materials, equipment, or buildings under 6. Prevent spills or dumping under the canopy. a. Chemicals - fuel & paint. b. Dumping - clean out concrete truck. Precautions with Protective Steps 1. Sensitive species may be completely intolerant of any traffic. 2. Leave mulch in place for minimum amount of time. Summary 464\sitegrading-11