LEAN AND GREEN - VEGITATION TIPS TO GREEN UP YOUR SITE

Site & Landscape

Written by Caye Cook, RLA, ASLA & Lindsey White, RLA, ASLA

Early team collaboration can yield landscape concepts that maximize site assets and minimize costs while harvesting LEED points.   It’s the old “form follows function” recipe which can be revised to include “form follows energy” to match site use with specific site conditions, such as using parking medians to collect and treat surface water runoff.   However, incorporating a few LEED site points does not always consistently equate to a true ecologically balanced ‘green’ site unless a broader more comprehensive complimentary approach is utilized.  Depending on the actual credits pursued, some LEED project sites, although sustainably much better than their non-LEED counterparts, may not be very green after construction completion, especially if existing vegetation is stripped and topsoil is compacted. Even a small clump of trees contributes to the ecosystem and should be spared the blade whenever possible and practical.  As green industry professionals, we are encouraged to think beyond obtaining specific LEED points and adhere to a more wide-ranging philosophy of environmental protection and restoration.   Scraping a site may save dollars on the front end, but may not be the most cost sensitive approach in the long run when new plantings fail to grow due to poor soil conditions as a result of the construction activity.

So, how “green” is your current LEED site?  What are some issues to keep when you are planning the building footprint and site paving?  What are some methods that may be helpful in achieving a healthy site?  The following provide some basic preliminary site planning tips that may help with achieving LEED credits and a healthy green site.

Perform a site evaluation prior to site planning. This simple step can identify drainage patterns, wind and sun patterns, soil and slope conditions, and existing plants.  The building and paving footprint impact the site and possible LEED points.  The Landscape Architect can identify plants that are the most beneficial to preserve and assist in siting the building and paving to take advantage of site vegetation for shade and prevailing winds for comfort.  Taking advantage of natural light and shade benefits EQ credits 8.1 and 8.2 for daylighting and views which may facilitate natural ventilation into the building.

Obtain a tree survey. Request that the tree surveyor clearly indicate specific tree species, trunk caliper size, canopy size, and the extent of the branches on the survey document.  The canopy demarcation should also reflect the extent of the root zone to avoid.  The Landscape Architect can verify the tree species and health of the tree.

Limit site disturbance. Limiting overall site disturbance by restricting construction impact on the site is one of the most effective ways to green the site.  Fence in as much area as possible to protect trees and valuable topsoil from the contractor’s activities.  Construction vehicular and foot traffic on a site further compact the soil which in turn limits the sponge-like quality of soil to absorb runoff.  If construction equipment encroach a tree root zone area, the contractor is encouraged to use protective material coverings such as plywood to minimize vehicular traffic impacts.   A thick mulch layer will reduce the impact of foot traffic.  Stockpile topsoil from areas to be disturbed by construction.

Limit tree disturbance. Plan utilities so that they do not go through tree groves or within 15 feet of a mature tree.  If an underground utility cannot avoid large trees, then bore under the root zone.  Provide canopy and/or root pruning where pavement cuts, walls or buildings that are adjacent to a tree.  Root pruning should occur in the winter with a 24 inch deep irrigation trencher cut at the edge of proposed construction to allow the tree to offset the root severed area prior to spring growth.  Backfill the trench with the removed soil.  Maintain a minimum of 2/3 to 3/4 of the remaining root zone under the tree canopy for tree health and viability.  Most tree roots in the North Texas region are within the top 24 inches of soil.  

Consider transplanting trees. Although a primary goal is to minimize disturbance to existing site vegetation, an option of transplanting existing site trees is particularly helpful if some of the trees are in the way of construction.  Simply moving an existing tree to another area of the site is an effective way of maintaining balance.  Rootballs of transplanted trees should measure about 10 to 12 inches in diameter for every inch of tree caliper.  Usually a tree can be transplanted for less money than a nursery grown container tree of equal caliper inches.  

Amend disturbed soil. Supplement remaining soil areas with compost to replace any lost nutrients.  In the DFW metroplex a large majority of soils are clay that has been previously farmed, stripped, compacted, and imported - oftentimes with very little organic matter.   Tilling 2 inches of well decomposed compost 6 inches into proposed turf areas and 5 inches of compost tilled to 10 inches depth in bed areas will boost the plants root system and increase the survivability of plants with water retention and utilization.  Since compost is regional and recycled material, then it will comply with MR credits 5.1 and 5.2 and help with MR credits 4.1 and 4.2.

Balance site drainage systems. Coordinate and plan proposed drainage patterns that work with existing drainage patterns and slopes.  This simple technique can also save construction costs from extensive grading, piping, and concrete curbing.  The site drainage and paving concept can also complement each other creating permeable parking stalls and bioswales to capture suspended solids (SSc 6.2) and reduce run-off (SSc 6.1).  Lots of mini-water detention pockets can support vegetation and eliminate the need for large storm detention basin areas.  

Enhance the environment with native plants. Achieve biodiversity and aesthetics with a variety of native plants that attract bees, butterflies, birds, and other species to supplement existing plants and achieve SSc 5.1 attainment.   Native plants also reduce the amount of water needed to meet the water efficiency requirements of credit WE 1.1.   Of course, plants are selected not only for function such as shade, erosion control, or screening, but they are also selected to meet site conditions of light, soil moisture, soil nutrients, slopes, drainage issues, and soil stabilization.  Preserved plants can contribute to biodiversity for habitat, reduce runoff and erosion and provide shade for parking and users – all Sustainable Sites (SS) credits.

Trees provide food, cover and habitat for birds and animals. Understory vegetation occurs under the canopy of mature trees and includes ornamental trees, native shrubs and perennials, vines and grasses.   Birds and animals rely on understory for cover, food and habitat. Preservation of understory helps achieve SS credit 6.1 for reduction of runoff and SS credit 5.1 for protection of habitat. Native grass stands aid in reducing runoff and erosion.  Duplicating grass stands is harder than it looks and requires about 2 years of labor to fully establish.  Native grasses must comply with city ordinances that govern tall grass stands and be mown periodically to discourage rodents.

Minimize invasive plants. These plantings, commonly called ‘weeds’, are like a plague in the metroplex – trees like Chinaberry, Chinese Tallow, Mulberry, and Mimosa; shrubs like Japanese Ligustrum and Chinese Privet; vines such as Japanese Honeysuckle; grasses like Johnson Grass and Bermudagrass.  These imported plants can take over and choke out an ecosystem. Some invasive plants, such as Chinese Privet, take years to conquer.  Even then landscape maintenance personnel must be on watch to remove any new sprouts.  The Sustainable Sites Initiative once adopted, will address this issue as a Prerequisite called Control & Manage Invasive Species.

BEST PRACTICE

Addressing these few but simple planning tips can help in providing ‘best practice’ ecologically healthy green sites.  As a result the question of “How green is your site?” becomes a statement of “How green is my Site.”

About the Authors

Caye Cook, RLA, ASLA is a Principal at Caye Cook Associates, a Landscape Design firm located in Dallas.
Lindsey White, RLA, ASLA is a Landscape Architect working at Caye Cook Associates in Dallas.