EM 8994 December 2009 Tree Protection on Construction and Development Sites A Best Management Practices Guidebook for the Pacific Northwest introduction ................... 1 What’s at Stake protect forest Purpose of remnant Guidebook stands ........ 2 Who Should Use protect This Guidebook Excellent Stand Protection Zone individual trees .......... 3 Poor Stand Protection Zone changing Why Protect Trees grade around BMPs for Tree Protection trees .......... 8 maintain Protecting Native Techniques trees Raising the Existing Forest Remnants properly ... 10 Critical Root Zone Grade contents Protection Lowering the Don’t Top Trees! BMPs for Tree Existing Grade Tree Maintenance Protection Trenching BMPs for Tree planting & Pruning establishing Proper Tree new trees ..14 Removal and Replacement Proper Tree Planting BMPs for Tree Removal and BMPs for Tree Replacement Establishment INTRODUCTION Purpose of Guidebook Contact your local planning department for This publication is a guide for protecting, conserv- specific regulations for your area. What’s at Stake ing, selecting, maintaining, removing, and replacing Urban forests consist of the native forest trees on development sites in the Pacific Northwest. Who Should Use This Guidebook remnants and the planted forested land- The guidebook is designed to assist people who This guidebook is intended to support the scapes in our cities. work with trees during the development and building, development, and construction The urban forest is a valuable resource construction phases of both new and existing industries. If you are a construction contrac- that provides economic, environmental, projects to keep healthy trees a part of the urban tor or employee, builder or land developer, and social benefits. Quality of life in cities environment through the use of accepted tree care heavy equipment operator, landscape is enhanced when we have a canopy of standards and practices. maintenance contractor or employee, tree trees shading our homes and streets, miti- This publication provides best management prac- care service contractor or employee, or gating stormwater effects, providing energy tices (BMPs) developed and recommended by pro- utility employee, this guidebook is for you. savings, and improving property values. fessional arborists, urban and community foresters, You are an important part of successful tree Research by the USDA Forest Service and landscape architects. BMPs are widely accepted protection efforts! 1 indicates that, for every $1 spent on urban practices and standards used by industry profession- This publication will also be helpful to introduction trees, $2.70 in benefits is returned. als and based on the best available research. The engineers, landscape architects, and planners As forests in the Pacific Northwest guidebook provides basic and practical information that are involved in planning and designing become more fragmented through about methods to give trees planted or retained on construction projects. It can be used as a urbanization and development, we lose development sites the best chance to survive and project planning and implementation tool, as a significant amount of the ecosystem thrive during and after the construction process. well as a resource for community education. services that forests provide, such as storm- Please note that while the BMPs in this guidebook The guidelines in this publication could water and flood control, and mitigation of are widely accepted practices and standards, they make a significant difference to your con- greenhouse gases. don’t guarantee 100% successful tree survival. struction site for years to come. Trees that This guidebook is designed to help the While these practices are presented here as are treated as assets rather than liabilities user retain healthy trees that contribute voluntary guidelines, some local jurisdictions have may save thousands of dollars on a project these services and benefits. tree protection regulations that must be followed. through reduced stormwater infrastructure needs and increased property values. PROTECT FOREST REMNANT STANDS Poor Stand Protection Zone Scattered trees with a highly disturbed or Stands, groves, or patches of native Pacific Northwest trees, such as missing understory may not be worth saving. A Oregon white oak, Western red cedar, red alder, bigleaf maple, and poor stand protection zone has the following Douglas-fir, are often found in urban or urbanizing areas. These characteristics: ecosystems are remnants of the larger forests that previously covered • Trees blow over easily due to lack of support. the area. They may range from less than a quarter acre to several • Soil dries out and soil erosion occurs due to acres in size. Conservation of existing groves of native trees often disturbed soils and lack of understory. provides greater economic and environmental benefit than preserv- • Forest microclimate is disturbed. ing individual trees in the developing landscape. A stand that may not be stands • Sunlight and temperature increase. worth saving. Reproduced • Weeds and invasive species take over. with permission by the City of Excellent Stand Protection Zone Chattanooga. High tree densities with an undisturbed understory are characteris- • Forest succession is interrupted and little tics of a high-quality forest remnant worth preserving. An excellent regeneration occurs. remnant stand protection zone has the following characteristics: • The stand is visually unattractive. 2 • Trees structurally support one another. • Ecological functions are severely interrupted. forest • Soil remains undisturbed. BMPs for Protecting Native Forest Remnants • Wildlife uses are relatively unimpaired. • Shady microclimate encourages natural • Fence the entire stand, grove, or patch to protect understory vegetation and soil as well as trees. Healthy soils require little if any protect woodland plants. • Natural forest succession continues and fertilization, pesticides, or irrigation to support tree health. forest regeneration is ongoing. • Avoid removing vigorous, healthy trees and vegetation from the stand. • The stand is visually attractive. • Do not retain isolated single, tall, spindly trees; such trees are more • Ecological functions are relatively likely to become structurally unstable, bend or blow over in storms, or become diseased and/or infested with insects. unimpaired. • Avoid creating new forest edges that may not be wind-firm; retain A stand to protect. Reproduced with large trees that are on the windward side of a stand to provide sup- permission by the City of Chattanooga. port and protection to the interior of the stand. PROTECT INDIVIDUAL TREES Tree protection may be passive or active. Passive tree protection, most commonly used during the planning or post-development stages, Why Protect Trees simply means avoiding any disturbance or harmful activity near the Trees should be protected throughout their lives from damage to tree. Active tree protection, by contrast, involves physical protective maximize their health, safety, functionality, and benefits. Young, barriers and is generally required during any site disturbance that newly planted trees need protection as much as large, mature may impact retained trees, such as grading, building construction and trees. maintenance, infrastructure and utility installation and maintenance, Protecting trees in new and existing developments and other landscape changes that may affect the structural integrity • reduces long-term tree maintenance and replacement costs; and stability of retained trees. • reduces site preparation and grading costs; trees Critical Root Zone Protection • provides immediate aesthetic and economic benefits because properties with more mature trees and greater tree canopy cover A critical step in retaining healthy trees during construction and sell faster and accrue property value faster in comparison to development is the protection of tree roots from disturbance. Each tree properties without these assets; has a critical root zone (CRZ) that varies by species and site condi- 3 individual tions. The International Society of Arboriculture (ISA) defines CRZ • generates positive response from neighbors and the surround- ing community; as an area equal to 1-foot radius from the base of the tree’s trunk for • generates good public relations; and each 1 inch of the tree’s diameter at 4.5 feet above grade (referred to as protect • provides healthier trees, forest ecosystem, and environment for diameter at breast height). a healthier, safer, more vital community. Critical root zone radius distances calculated by tree diameter at breast height. Tree Protection Techniques Tree diameter Critical root Total protection zone diameter, Tree protection involves activities designed to preserve and protect zone radius including trunk tree health by avoiding damage to tree roots, trunk, or crown. Site 2 inches 2 feet 4+ feet development planning prior to site disturbance should include 6 inches 6 feet 13.5 feet identifying tree protection zones (TPZs) for all trees designated for 20 inches 20 feet 42 feet retention. 46 inches 46 feet 96 feet Another common rule of thumb • Post appropriate signage to help convey the importance of the is to use a tree’s dripline to estimate CRZ to workers. the CRZ (see figure). We recommend • Avoid cutting tree roots over 4 inches in diameter. you evaluate both of these and choose • Make all necessary cuts to tree roots cleanly with sharp tools; whichever provides the larger CRZ. never tear with