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Arboriculture and the Law

Arboriculture and the Law

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  • It is generally considered a property owner’s responsibility to ensure that a tree or trees on the property do not pose a risk to other people or property

  • A person or organization whose activities may affect the condition of the tree is assumed responsible for the effects of thee activities.

  • Most cases involving trees fall under the law of Torts rather than criminal law.

  • Liability or legal responsibility determines who pays and how much.

  • Factors in Plant Appraisal – species, size, location, and tree conditions are all factors.

  • If there is any questions please feel free to ask I have just scratched the surface on this topic that is very complicated and important.

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Carpenter Ants in Urban Trees
Carpenter Ants nest

Carpenter Ants in Urban Trees

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Carpenter ants are very common in urban trees as are the myth about these secretive insects. The abundance of these insects in urban settings is due to their lack of available nesting sites as compared to a forest. People put ant infestations in their homes at the same level as termite. To clear one thing up ants live in wood as termites eat and digest wood.


Due to there common occurrence in urban trees and there potential damage to homes we as arborist are asked what to do with these insects. Ants exhibit diversity in size and appearance within a species and there are over 900 species of ants ranging in size, and colour.


A carpenter ant colony forms two types of nests. The main nest (one with the queen) is located in decayed or moist wood however the potential for expansion to un-decayed wood still exists. The nest is usually in contact with the ground or near a source of moisture.

Carpenter ants form satellite nests in locations that are drier and warmer to raise the mature larva. This may not mean you have a water problem in your house as the nest may be in a stump or tree in close proximity to your home and the ants have access to your home through tree branches touching your house or your utility lines.


A few ants on your trees doesn’t mean it is infested however it is a good indicator that the nest is either in that tree or close by.


One thing to look out for in the spring is the ants with the wings in swarms as they are mating and every fertilized female is looking for a new location to start off its new nest.


Carpenter ants have been viewed by arborists as beneficial as they indicate rot in your trees. However their presence in our trees close to houses is a source of potential infestation from either the dispersal of a colony or by forming a satellite nest. Carpenter ants are also beneficial as they can be important predators during outbreaks of defoliating caterpillars. They recycle wood back into the forest. They are a great source of food for many birds (ex Pileated woodpeckers another major sign of carpenter ant infestations)


Management techniques include: removing several decayed trees around your property including grinding of all stumps after removal, disposing of all buried wood and wood lying around. Fixing leaks around your home, limiting access to structures is a good idea as well. This includes building and line clearance and removing shrubs from around the base of your home. Chemical treatment or baiting is also an option however this will not solve the problem just postpone it.

Irrigation and Drainage

Irrigation and Drainage

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Large trees are capable of absorbing over 100 gallons of water in a single day and 95% of this can be transpired into the air.


  • Best time to water is in early morning or late evening.

  • There is a fine line between too much or too little water.

  • trees have many variables to the amount of water they need: species, size, air temp., humidity, light levels / intensity, wind movement, and soil type all play major factors.

  • If there is two much water drainage may be required if to little irrigation may be necessary.

  • Recently transplanted trees require more watering as it deals with transplant shock

Watering Rates – infrequent long soakings are better than frequent short soakings.

Infrequent Long soakings – forces roots to penetrate deeper into the soil to access water making it more tolerable of drought conditions.

Frequent Long Soakings – do not allow water to penetrate deep causing roots to grow near the surface making the vulnerable to drought conditions. This may also lead to soil compaction if soil doesn’t have time to dry.

watering a sapling

Irrigation Methods

Common methods of watering are the hose, sprinkler, drip line, high pressure injection, and soaker systems.


  • may cause runoff and not fully infiltrate into the soil.

  • keep water away from trunk and dispersed evenly around drip line.


  • most common, evenly distributes over entire area.

  • will not cause runoff

Drip Line

  • hose with numerous tiny holes, slowly releasing water

  • hose wrapped around root ball and should be extended outwards to support a wider drip line as the tree grows.

High Pressure Injection

  • water is sprayed in soil below surface vegetation, this waters and aids in aerating compacted soil.

Soaker Systems

  • has many forms from perforated pail to soaker hose.

  • great for water penetrating deep into the soil.

growth factors of a tree represented by various icons

Soil Microbiology

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By: Jim Downer


Question: what is the most important concept in soil microbiology? Answer: really complex! We have a better understanding of microbes (as well as pathogens) and the beneficial roles they play in soil. However we are only beginning to understand the complexities of soil microbiology and how intertwined soil life is. This is why we need to understand the role trees play in the lives of microbes and vise versa.

Web of Life

Trees effect microbial communities and at the same time are at the mercy of microbes, which help with nutrient gathering, and water uptake. Soil limits trees growth, which is why the average lifespan of an urban tree is under ten years. Litter-fall or “O” soil horizon (humus rich layer), also called the organic layer is the life blood to a tree. This is why we put mulch around urban trees to try and simulate forest environment. This layer provides a reservoir of organic nutrients which nourishes animals, fungi, bacteria and ultimately the tree that produced it.

Soil Microbiology

Microbes and Their Role

Two broad categories: prokaryotes and eukaryotes


Prokaryotic organisms: are bacteria, simple genetic make up of one chromosome, without a nucleus, single celled and very small.


Eukaryotes: have nucleus (includes fungi, yeast, algae, nematodes, and animals) some are single celled, most are multi-cellular.


Microbes help trees and trees in turn leave behind cells that contain amino acids, proteins, and sugars in the rhizosphere (is an area of high microbial activity adjacent to roots 1 millimeter).

The Role of Roots

Roots secrete a lubricating substance (mucigel.) which allows roots to slip through soil, pushing aside soil particles and leaving behind carbohydrate-rich slime trail. Fine absorbing roots grow and die leaving behind carbon and nutrients allowing room for microorganisms resulting in more porous soils with greater oxygen content that favor microbial growth and health. Roots must balance the ions inside and outside there roots. Bacteria and fungi function in the rhizosphere as heterotrophs, or organisms that derive energy from dead organic matter. In doing so, they convert organically held minerals to ions trees will absorb. Trees maintain balance by importing and excreting ions it needs to maintain its productivity. If litter layer is denied to the tree, there is a greater tendency for mineral nutrient deficiencies to occur.

The Role of Mycorrhizae

Much research has demonstrated the importance of fungal symbionts for the growth of healthy trees mycorrhizal fungi are a diverse group of fungi that occur in all soils and climates around the globe. They colonize and form symbiotic relationships with plant roots and are broadly grouped into 2 categories: ectomycoorrhizea and endomychorrhizea.


Ectomycoorrhizea: form a shield of fungus around the roots of trees they colonize. Trees such as oak, alder, eucalyptus, pines, firs and other conifers in the Pinaceae do not from hairs but instead have intercellular threads (hyphae) called the Hartig net. Hyphae extend out in soil greatly increasing the trees root system


Endomychorrhizea: do not change shape of roots, endomychorrhizea invade the inside of the roots and create an intercellular relationship within the host root cortex. They form globular vesicles and arbuscles. Arbuscle is a tree like structure that forms inside a root cortical cell in order to exchange nutrients and water for carbohydrates from the tree. They also extend out into the soil increasing the absorptive surface area many fold. One of the key effects of the mycorrhizoshere is the area they produce for rhizobacteria, which fix nitrogen solubilize phosphates. They also serve as a biocontrol agents for root pathogenic fungi. The deeper understanding is not how great mycorrihizae are but rather what great gardeners or cultivators of bacteria mycorrihzae are and ultimately how beneficial these bacteria are to the trees in our urban forest. Without them the host tree would certainly languish.

Managing Soil Microbiology

Soil is made up of minerals, solids, air space, water, and all the organisms that live in them. So applications of single species or even small cocktails of microbes to soil, is analogous to adding salt to the ocean. However disturbed or urban soils where the litter layer has been removed or no longer exist can add value to the soil.


What can arborist do to help this process?

  • Prevent compartion- microbial communities need oxygen to thrive.

  • Maintain or add to litter layer that falls under trees and increase square footage areas of mulch under trees.

  • You need to remember that it is not possible to introduce a microbe and have it establish without creating the conditions to support it first. (Mulch)

  • Irrigate do not flood or frequent irrigations. If land is dry irrigate to increase soil moisture levels

  • If a healthy litter layer and or mulch exists under trees, reduce or eliminate fertilization. Grow for quality not quantity

Trees are a part of ecology of the soil. They have a direct effect on the soil and its microbial communities. They are also dependent on soil microbes for nutrients and water.

Tree Nutrition and Fertilization

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The stated objective for fertilization with typically fall into 3 categories:

  • Correcting a Nutrient Deficiency.

  • Maintenance fertilization.

  • Growth Promoting Fertilization.

Fertilizer Types: are defined by their chemical composition, form, and mode of action

Chemical Composition – Is the analysis of a fertilizer. This simply indicates the elements contained in the fertilizer, and the relative proportions ( % of dry weight) of each element. The percentage of “N” (nitrogen) is always listed first followed by “P” (phosphorus-phosphoric acid P2O5) and then “K” (potassium-soluble potash K2O)

close-up view of saplings in soil
Tree Nutrition and Fertilization

Mode of Action (fast-release & slow-release) – regardless of the mode of action the intent of fertilization is to provide essential elements to the tree in a timely manner. Fast release fertilizers are soluble immediately after their applied. Slow release fertilizers are soluble over time in 1 of 3 mechanisms: Biological decomposition of the fertilizer, hydration (water dissolves the fertilizer) or heat. Over all slow release is preferred due to its many benefits; lower concentration of salt therefore less burning of foliage, can be applied in higher concentrations, les prone to leaching losses.


Fertilizer Form (organic & inorganic fertilizers) – organic fertilizers are recognized as having been derived from once living organisms (ex. Manure, treated sewage, fish meal, bat guano and compost) inorganic fertilizers are manufactured combinations of minerals and essential elements offered in liquid or dry formulations.


Fertilizer Application Methods: 4 methods of delivering fertilizer to a tree: broadcast application, sub-surface application, trunk injection, and foliar application.

  • Broadcast – fertilization is delivered to the surface of soil in either liquid or dry form. In the rooting zone distributed evenly (good if little or no vegetative understory)

  • Sub-Surface – applied 6-12 inches (15-30cm) beneath the soil in either liquid or dry form. Good if high density of competing understory vegetation. 3ft x 3ft (1m x 1m), beneath the crown of the tree (drip-line), divid equally amongst each hole.

  • Trunk Injection – or capsule implants mostly used to treat micronutrients deficiencies, not a viable method for delivery of macronutrients. Technique is a low volume of product inserted directly into the vascular system (xylem) of the tree. Every 6 inches or 15cm around the circumference of the tree at the base (root flare). Disadvantage it wounds the tree therefore not recommended annually

  • Foliar – if essential elements in the soil are not a soluble form and other methods have weak results then consider this method. Fast-release fertilizers sprayed in liquid form onto leafs surface. Effectiveness determined by the formulation and length of time spent on the leaf. Most successful supplements are calcium, potassium, iron, zinc

Rate of Application: ANSI A300 standards (“N” content)

Maintenance fertilization – 1bls (0.5kg) per 1000ft2 (93m2)

Maximum fertilization fast release – 3bls (1.4kg) per 1000ft2 (93m2)

Slow release – 6bls (2.7kg) per 1000ft2 (93m2)

Growth promoting fertilization – 2bls (0.9kg) per 1000ft2 (93m2)


Timing of Application: When the tree can use it! Best time to apply is just as leaves expand


Prescription Fertilization & Nutrient Management Plan: nutrient management plan should address the “tree(s)” needs based on species, growth phase, health, and soil’s ability to meet annual demands for essential elements. The plan should also identify potential limiting factors for maximum tree health. Remember fertilizer helps trees in many ways, however the misapplication can seriously affect the health and longevity of a tree and have tremendous affects on the environment.

Tree Planting and Installation
hand holding young plant

Tree Planting and Installation

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Today there is a lot to know about tree planting and selection in order to gain optimum results, especially under stressful urban conditions. There are four main nursery stocks available to plant they consist of bare root, container, ball and burlap, and tree spade. Each choice has advantages and disadvantages.

Types of Nursery Stock

Bare Root

  • has no soil, light weight which makes it cheaper and easy to Transport.

  • tree must be dug and planted while dormant and in seedling stage.

  • Roots must be kept cool and moist to prevent drying out.


  • easily transport large stock trees with root mass intact.

  • if in pot to long roots will encircle container and causing girdling roots. If this is not corrected when planting it will lead to the tree self destructing due to the tree choking its self.

Ball and Burlap

  • mechanically dug and wrapped in burlap and twine. Wire basket used as well.

Tree Spade

  • large hydraulic spade for large caliper trees, transports and transplanted.

  • stock should be covered during transportation to prevent drying the root ball  (keep root ball moist) and  stress, PVC tarps are best.


Planting Depth

  • not to deep, root ball should be level at base with root flare even or slightly higher than ground elevation (if in clay or poor drainage 1 inch higher)

planting Width

  • 2-3 times the size of root ball at top of hole and sloping inward to the bottom.

  • this encourages stability and better root penetration.

  • Majority of new roots are found in the upper 30 cm or 12 inches of root ball.


  • backfill with existing soil, and lightly tamp with shovel or water to prevent air pockets as backfilling.


  • multiple effect for trees including: adds nutrients as it decomposes, week control, helps soil retain moisture.

  • mulch no thinker than 10cm 4”, do not put mulch around stem


  • allows tree to stay level and should only be on for one year.

Tree Risk Management

Tree Risk Management

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What constitutes a hazardous tree?

  • a structural flaw that will cause part or all of the tree to fail.

  • a target of some value at risk of being damaged. This risk may be heightened if environmental conditions do not coincide (site is prone to heavy wind, wet soil, unstable soil structure, construction)

Trees are always at risk due to gravity. Courts generally accept that there is a level of acceptable risk associated with trees. This risk is considered as “reasonable” risk as opposed to “unreasonable” risk.

Reasonable Risk

healthy tree, few defects, in general tree is in good health with good branch habits, vigour, etc.

Front door of a home surrounded by leafy trees

Unreasonable Risk

fungus, decay, cracks, structural defects deadwood etc.


Tree owners decide how much risk they are willing to accept. Depending on tree condition, how much they value the tree, how much they value the surrounding targets.


Having an arborist or urban forester asses your tree can greatly reduce unnecessary removals by pruning, crown cleaning / dead wooding, cabling and bracing, crown reduction / thinning, or if appropriate removal.

Inspection Process

it is important not to confuse tree health with tree structure. Trees may appear health which can be misleading and be hazardous due to poor branch structure, cavities etc.


tree risk assessors follow a check list which includes: site conditions, species, shape, roots, trunk flare, trunk, branch unions and scaffolding limbs.

Site Conditions

wind, soil, other trees as protection, etc.


strength of trees are species specific, some handle loads better than others. Some species are prone to weaknesses like co-dominate stems or shallow root systems etc.


inspect for dead limbs, branches that extend beyond the rest of the crown, branch structure, tree lean, symmetry


  • inspect for any obstructions like curbs, pavement, water etc.

  • presence of fungus

  • look for root disturbances like excavation or trenching or girdling roots

Trunk Flare

ensure proper flare, soil is not mounded or graded elevated


cavities, cankers, stem decay, horizontal cracks etc.

Branch Unions and Scaffolding Limbs

is there branch bark ridges, included bark, holes, cracks, cavities, moisture, split, decay, extent of dead limbs, and proper branch structure.


Trees with high risk of failure include: target canker, soil mounding, shearing cracks, odd shaped bends or crooks in branches, leaning trees, and included bark.


After assessing these risks steps can be taken to reduce the risk a tree may pose if owner is willing to accept.


Assessing a tree and taking steps to reduce the risk or not, does not necessarily mean that it is classified as safe. There are many hazards that may go undetected due to limited access or the inability to view the inside of the tree.

Tree Species Selection
Closeup image of people preparing to grow a small tree with soil in the garden

Tree Species Selection

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When planting a tree or shrubs there are many things that should come into play. Site conditions – climate, soil, physical limitations à functions – engineering, aesthetics, landscape architecture, climate control à attributes – of the species. Which leads us back to soil conditions. This is a cycle.

Native vs Exotic

Native – proven for climate, less maintenance, and fewer pathological Problems.


there are many cultivars, varieties, and hybrids these days that allow for a wide range of selection to choose from that look exotic and have great advantages.


Exotic – must have a good reason.


Most common used tool to match plants with climate is the hardiness zone maps or seed zones. This is very important to make sure your tree matches your location.



Forest soils – are favoured for planting

urban soils – artificial by: modifications, compation, and design. This will really influence your species selection.

Physical Limitation:

Below Ground 

  • need a root system that can handle the underground condtions

  • soil volume and density

  • H2O infiltration reduced due to paved surfaces, compacted soils which will hinder the trees growth and health

Above Ground

  • consider crown shape and size at maturity (or by regular maintenance

  • overhead utility wires, buildings, road ways and pedestrian areas, lights security concerns


  • Consider primary function and match species to fit. This includes: wind breaks, noise abatement, trespass control, accents and cover, crown shape and available space do not impede shape. Consider size at maturity and you can pick a cultivar or hybrid to fit most spaces.


Many considerations including:

  • fruits or flowers – odours, colour, size, shape, clean ups required, attract insects (bees , wasps)

  • bark characteristics – interesting/attractive (London plane, white birch)

  • root systems – invasive roots may damage septic systems, pools, sidewalks, walls etc. (poplar, willow, silver maple)

  • growth rate

  • pathogens and treatments

  • light tolerance (shade tolerant, intermediate, shade intolerant species)

Success in urban situations depends on three things

  • the right choice

  • good growing conditions (soil preparation at time of planting is very important)

  • after planting care and protection

Managing Tree During Construction

Managing Tree During Construction

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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.

wooden deck

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.

  • Grading and storage of soil, Grade changes and excavation

  • Construction access, including entry and exit, vehicle parking,

  • Utility and drainage corridors including storm water management systems

  • Material storage and staging, concrete washout areas

  • Tree protection zone fencing

  • Sediment control (silt fencing)

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.

Trees in Urban Landscapes
trees and blue sky reflected on the glass wall

Trees in Urban Landscapes

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There are four main tree functions in urban areas these include engineering, architectural, environmental and aesthetic. These can all be broken down further.

Engineering – acoustical, traffic, and erosion control, glare / reflection reduction.

Acoustical Control or Noise Reduction

  • A screen of trees 30m wide will absorb about 6-8 decibels of sound.

  • conifers are year round.

Traffic Control

  • help direct pedestrian and vehicular traffic.

  • screen glare form headlights and other buildings.

  • provides a stream for pedestrians to follow.

Erosion Control

  • both wind and water erosion can be reduced by plantings trees and shrubs on bare soil.

Glare and Reflection Reduction

  • careful placement of trees helps reduce glare and reflection from sun, artificial lights and other buildings.

Architectural Benefits – privacy control, defines and/or encloses architectural spaces, screens objectionable views, softens harsh appearances of buildings.

– examples of these include: trees and shrubs are used to screen parking lots or building structures, as well as soften the view of building surfaces and edges.

Environmental Benefits – trees have numerous influences on urban microclimates including wind, sun, precipitation and humidity control, and air purification.

Wind Control

  • obstructs, guides, deflects and filters airflow

  • reduces radiant heat loss from buildings by reducing wind speed

  • provides and insulation layer of calm air beside buildings

Sun Control

to a great extent urban surfaces either absorb heat light and heat up, (black surfaces) or absorb heat and energy (compacted and dry surfaces). Trees and shrubs can reduce this by absorbing heat as they transpire which provides cooling shade that reduces solar radiation and reflection.

Precipitation and Humidity Control

  • provides a screening from rain

  • reduces fog density by condensing moisture on leaves and twigs.

  • provides snow control

  • excrete water vapour into the air

Air Purification

  • by absorbing CO2 and releasing O2

  • absorbing some airborne pollutants (valuable)

  • trap particulate air pollutants

  • carbon sequestering which all trees do and urban trees are 5-15 times more beneficial than forested trees for reducing air pollution.

Aesthetic Function

  • trees give character to nieghbourhoods

  • this can all be done by variety of form, colour, textures, and patterns in urban landscapes.

  • form vistas, frame views, provide focal points, and define spaces.

  • trees provide pleasing floral displays or leaf colours, fragrances, sounds and serene settings.

  • trees emphasize seasons.

  • provide habitat for urban wildlife, especially birds.

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