Conservation is the process of selecting trees, forest stands, shrubs and under story growth for protection during development. Tree retention is not the same as tree preservation. When trees are retained on a construction site without necessary protection, have a very low long term survival rate. Tree preservation is the process of protecting trees from damage related to the construction process. Conservation and preservation strive to protect specific trees throughout the construction process so there benefits will be available for decades to come. The cost of removing and replacing trees after construction usually exceeds the cost of protection, including many years of the trees benefits would be lost.
The five phases of construction include: planning, designing, pre-construction, construction, and post-construction. Fate of the trees lays in all phases not just the last two. Having the trees protected from phases one to five will also lower the cost and increase there chance of survival.
Planning phase — land, trees and building needs are evaluated and laid out. Large groups or high-value trees and be marked and located on the site plan. Location should be considered including, above and below ground activities (present and future), and root system and canopy spread of the trees. Man things should be considered, tree species, age, health, structure, and soil properties. Individual plant responses can vary greatly also due to tree age, health, site quality, pest, previous injury and time of year. All of these must be considered during the selection. The structures or grade changes in the land should also be noted as this may cause the tree stress or even death.
Design phase – an arborist will recommend trees to be retained, removed, or protected. During this phase location, size, shape of building, is decided and a check list of the following must be done.
Keep in mind trees that might hinder future development or expansion, architectural features, obstruct views, and restrict solar access. Global positioning systems (GPS) and geographic information system (GIS) can be used to locate and map trees locations.
Retaining Group of Trees – this is often preferable. Retaining a mixture of ages, species, and ground cover plants will ensure sustainability through future generations of trees.
Pre-Construction Phase – is between the planning and construction phase. Tree removals, tree protection zones established, building layout, and road construction, occur during this phase. Meeting with all managers of the operation to ensure the understanding of the scope of the tree conservation activities and penalties must be covered.
Defining the TPZ- a trees critical root zone (CRZ) is the area around the trunk where roots essential for the trees health and stability are located. A tree protection zone (TPZ) is an area, defined by the arborist, to ensure future tree health and stability. This area surrounds the trunk and is intended to protect the roots and soil within the critical root zone and beyond. The most common method of TPZ is the dripline method. It uses the trees canopy dripline to define the boundary of the TPZ (the entire area within the dripline is considered the TPZ). TPZ need to be established before any site work begins. Remember trees on neighboring properties may also require a TPZ.
All building foundations, utility routes (above and below ground) and irrigation lines should be identified on the building plans. If they are within a TPZ, relocate them is preferred. If it can not be done and constructing work inside the TPZ is mandatory you may not enter the CRZ. Future planting sites should also be treated the same as the areas within the TPZ.
Soil and Root Protection Within the TPZ – in TPZ areas the have traffic, both pedestrian and vehicular requires protection this can be done by applying 6 to 12 inches of woodchip mulch, plywood on top of mulch 4 inches, gravel or commercial logging or road mats.
TPZ Fencing- install around TPZ area. The fencing must be solid and highly visible.
Trunk Protection – the use of wood to surround the tree or straw bales to prevent trunk damage.
TPZ Signage – all sections of fencing should be clearly marked with tree protection zone area, contact info for contractors and/or arborists and consequences of violations in all relevant languages.