Implementing Alternate Watering Technologies - Improving Street Tree Performance In York Region

Issue: 
July-August 2010

THE REGIONAL MUNICIPALITY OF YORK is an upper tier municipality located in the Greater Toronto Area. The Region covers an area of 1,776 square kilometres stretching from Lake Simcoe in the north to Steeles Avenue in the south. It borders Simcoe County and Peel Region in the west and Durham Region in the east. The Region provides a variety of services to its over 1 million residents including transportation services, transit, water, wastewater, emergency services, policing, human services and growth management. York is considered one of the fastest growing areas in Canada and its population is expected to increase to 1.5 million by 2031.

York Region is responsible for the design, construction and maintenance of an 1,076 km arterial road network. An integral part of this network is street trees or “green infrastructure.” The Region has been planting and maintaining street trees since the 1970s, and has had a formal tree planting program since 1996. To date, the Region has planted over 20,000 street trees and currently plants in excess of 2,000 street trees annually. A significant number of these trees are planted as part of the capital road improvement program. Today, the Region’s street tree population in urban areas stands at 33,000 trees.

Regional roads are a very hostile environment and present many challenges for street tree health, survival and performance. Street trees are affected by limited growing space (e.g. available soil volume), poor quality soils, salt from winter maintenance, etc. With the adoption of the Region’s Greening Strategy in 2000 and its Streetscaping Policy in 2001, the Region significantly increased its street tree planting program.

In the early years of this decade, it became evident to both staff and the public that the initial performance of the Region’s newly planted street trees was poor. In 2003, a health assessment was undertaken to benchmark street tree health and determine the extent and factors causing the poor performance of street trees.

The street tree health assessment reviewed the performance of 1,094 trees planted between 1996 and 2003 (8% sample). Trees assessed were assigned an overall health rating in addition to measuring growth by diameter, and assessing crown shape, foliage density and trunk condition. The study identified that 72% of the trees were in potential trouble or worse (worse being declining, death imminent or dead). This was a significant finding and major concern for the Region given the large investment made in street trees as a capital asset.

A variety of cultural and environmental factors were identified as contributing to the poor performance of street trees including:

Cultural
• Planting practices: small planting hole and insufficient amount of mulch
• Stock quality
• Lack of water

Environmental
• Poor soil quality: boulevard soils were compacted and lacked organic matter
• Damage from road salt
• Wind exposure
• Summer droughts

The study also revealed that newly planted street trees have a 3-5 year establishment period. During this period tree health may decline while the tree attempts to focus its resources on root development.

Improving Street Tree Health
It was clear from the street tree health assessment that the Region needed to critically review its planting program and identify strategies to address the poor performance. Based on both of these, numerous improvements were implemented including:

• Revised tree planting specification. Incorporation of a bed preparation area around the planting hole and an increase in the amount of mulch.
• Improved tree planting contract implementation. Pre-selection of trees in the nursery, including tagging. Improved posting planting inspection. Today every tree planted is inspected after planting.

Development of the Street Tree Protection & Planting Design Guidelines
• Improved species selection. Development of a Top Performing Street Tree Species List. Increase planting of top performing species (16 species) while maintaining biodiversity at the urban forest scale.
• Development and implementation of a tree watering program.
• Implementation of soil improvement projects.
• Development and population of a street tree inventory, key to monitoring and adaptive management.
• Increased education and awareness. Held a Street Tree Symposium, Trees Are Everyone’s Business, for Regional staff (engineers, planners, construction administrators, etc.)

Tree Watering
The street tree health assessment identified the lack of available water as one of the major factors contributing to the poor performance of street trees. Many of the trees assessed showed evidence of stem tissue necrosis which can result from a lack of available water. Several years of drought combined with a lack of post plant watering had significantly impacted the performance of street trees. Prior to 2003, post plant watering during the two year warranty period was the responsibility of the tree planting contractor. It was evident from the performance of street trees that little watering occurred during this period.

The health assessment results indicated that post plant watering during the 3-5 year establishment period is critical for the initial survival and performance of street trees. In 2004, the Region began to make improvements to the watering program. Watering of trees during the warranty period is no longer left to the discretion of the contractor. A separate item for watering is included in the planting contract and watering is assigned by the Region. To further ensure that the trees are watered in accordance with the contractor’s assignments, an automated vehicle location system is used to monitor the watering trucks. In 2004, trees were watered four times per year for the first two years. This was increased to six times per year in 2008, and in 2009 it was extended to the first three years. The long term goal is to extend watering to the first five years following planting, and increase the number of waterings per year as required.

In addition to contract delivery, an in-house watering program was developed in partnership with the Roads Maintenance Branch. This in-house program was developed as a contingency to supplement the contracted delivery during droughts. This program utilizes the Region’s liquid anti-icing equipment to delivery water. These 7,500 litre tankers are used in the winter to apply liquid anti-icing agent, in the spring they are converted to street flushers, and in the summer can be converted to water street trees (after a good flushing to ensure the system is not contaminated).

As the volume of watering steadily increased, it became apparent that efficiencies in delivery and improvements in application were required. To deliver the required watering, either an increase in the number of water trucks or a decrease in the time taken to water a tree was needed. It also became apparent that during watering, a portion of the water was draining over the ground surface and not into the root zone. To address both these issues, a review of alternate watering technologies was undertaken in 2007.

Alternate Watering Technologies
Over the past several years, a variety of tree watering bags have been introduced on the market (TreeGator, Ooze Tube). While the various bags look quite different, they operate in a similar fashion: the bag is filled with water which is released slowly over the root zone. The bags can be filled quickly, increasing productivity, and drain slowly, minimizing run off. This technology appeared to address both of the Region’s issues.

In 2007, the Region implemented a trial to evaluate the effectiveness of several tree watering bags. The trial evaluated the durability of the bag, ease of fill, time to fill, installation and water delivery. The water bags were installed and filled once every two weeks during June, July and August. Based on the trial and consultation with other jurisdictions, the TreeGator Original was identified as the most desirable option for our situation. The TreeGator Original holds 75 litres of water which is released through two holes over a five to nine hour period. Installation and filling is simple. The bag is placed around the tree, zipped up and filled through a three inch opening at the top. Beginning in 2008, the Region installed TreeGator bags on all newly planted trees. To date, over 4,000 bags have been deployed.

Despite the positive results in the 2007 trial, several questions remained, including susceptibility to vandalism/theft and the bags durability if left out over the winter months. Vandalism/theft was a concern considering the investment made in the bags. During the trial this wasn’t an issue, but the number of bags deployed was small compared to our annual tree planting program. To deter theft, a plastic identification seal is used to secure the bag. Between spring 2008 and spring 2009, only 3% of the bags were vandalized or went missing.

The durability of the bags, in particular, how they would perform in our winter climate through spring was a concern. Removing the bags in the fall and reinstalling them in the spring was an option, but would require a significant amount of resources. After consulting with other jurisdictions, it was decided to leave the bags in place over the winter and monitor their condition in the spring. In the spring of 2009, the bags were assessed and the majority (97%) were in good condition. A similar assessment was completed in 2010 and again, almost all bags were in good condition.

Other concerns raised included the potential for increased rodent damage and disease issues with the trunk. To date, only a minor amount of rodent damage has been observed and no disease issues have arisen. One drawback to the TreeGator Original is its lack of compatibility with coniferous stock. This wasn’t a significant issue for the Region since 95% of planting stock is deciduous. Currently the Region is exploring the use of Ooze Tubes for coniferous stock.

Implementation: Improvements & Challenges
To realize the benefit of increased productivity, you need the right delivery truck – specifically you need a large water tanker. During the first several fills it became apparent that any increase in productivity at filling was lost due to an increase in the number of trips it took to fill a smaller tank. This was easily overcome with the introduction of a larger tanker truck. Currently, a single water truck can fill approximately 500 and 600 trees per day depending on the distance between locations. This is significantly higher than our previous watering program where 250 trees were watered per day.

After deploying the TreeGator bags in 2008, the Region began to receive inquires from residents, staff and local municipalities regarding the “green tree bags.” This grew into media releases and several interviews leading to a greater awareness of the urban forest and the Region’s street tree program. It also demonstrated to residents that trees are not simply planted and left, but are living things which are monitored and maintained on a regular basis.

Overall, the TreeGator bags have functioned well and provided meaningful improvements in the delivery of the program. Our monitoring and inspections have identified some minor issues including bags that fail to empty and occasional weed trimmer damage.

Tree Performance: Measuring Success
The Region’s street tree planting program is built on the philosophy of adaptive management and continuous improvement. In 2009, the Region undertook a follow-up street tree health assessment to evaluate the effectiveness of the improvements made to date. The early results of the study show that 75% of trees planted between 2002 and 2009 received a health rating of good or satisfactory compared to 28% in the 2003 study.

This is a significant improvement in performance, and a direct result of the improvements made in the program. Despite these improvements, there are still many challenges ahead to maintain tree health over the long term and optimize program delivery. In time, this commitment to maximizing street tree health will have significant benefits for both our residential communities and the urban forest.

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.