A detailed analysis of the two major VTA safety rules (t/R>1/3 and H/D<50) as well as the SIA breakage safety evaluation shows that these measures are either inappropriate, not applicable or wrong for the typical urban tree to be evaluated in terms of safety.

Arborists prune, drill, and inject trees on a daily basis using industry guidelines and techniques to improve the function of trees, but what happens inside the tree? How do trees biologically respond to pruning? What are the impacts to water and chemical movement with changes in weather? Understanding the concepts of tree biology can help arborists better communicate to home-owners why we prune and care for trees the way we do. We will explore wood production, wound response, water movement, and how trees build themselves into some of the largest, longest-lived organisms on the plant. Research science of tree biology will be used to explain how tree respond to arborists and the environment. This presentation will cover tree biology from an applied perspective of a working arborist.

Trees planted in urban or amenity landscapes (streets, town centres, car parks etc.) face a number of stresses (drought, root de-oxygenation, salinity) that singly or in combination can have devasting impacts on survival of not only newly planted trees but well established mature trees. These symptoms become manifest as leaves yellowing and/or crown/branch die-back, that are visible indicators arborists interpret to assess tree vitality. Visual observations can be very subjective as they are based on human knowledge and interpretation which differs between individuals. Consequently health evaluations can differ markedly between assessors. Assessing the health of trees can be quantified using a suite of non-destructive and non-invasive such as leaf chlorophyll fluorescence (CF), leaf chlorophyll content, root/stem/leaf electrolyte leakage, twig starch analysis and leaf water potential. Aims of this talk are to highlight the practical value of these physiological tests to identify low vigour or damaged plants prior to the onset of visible deterioration.

Trees alter their wood properties and form in response to their mechanical environment in order to maintain their structure in response to gravity, wind and other mechanical loads. This lecture will introduce the attendee to the basics of tree biomechanics and how trees modify their growth to maximize their growth to ensure survival under mechanical loads.

Even cities with dedicated forestry departments often have significant budgetary constraints when faced with removal and replanting of trees due to losses from invasive pests like emerald ash borer (EAB). Community residents, as volunteers, can be a valuable resource for increasing the capacity and success of urban forestry. Through training and technical assistance programs community volunteers are capable of urban forestry contributions beyond Arbor Day planting events. The Community Engagement and Preparedness (CEP) volunteer program was created by the University of Minnesota, Urban Forestry Outreach, Research & Extension team to assess potential community tree losses, due to infestations of emerald ash borer, through the creation of tree inventories. The CEP program worked with 14 different Minnesota communities ranging in population from 700 residents to around 110,000 residents to inventory, measure, and condition rate trees. The program objective was to provide accurate information regarding risk of trees losses due to EAB using volunteer collected data. The research objectives were to: (1) gain insight into methods of training and technical assistance of volunteers for more complex tasks such as tree inventory and condition rating, and (2) evaluate the practical value of volunteer collected inventory data when comparing volunteer data to professionally collected data using iTree Streets valuation. To address the research objectives, the CEP program provided volunteer training, technical assistance, and data analysis in order to achieve the community tree inventories of both public and private lands. Training methods and technical support were developed for the first six communities and relied heavily on initial training with less reliance on technical assistance. The second group of eight communities had increased technical assistance during the volunteer inventory process. University of Minnesota researchers trained in tree identification, tree measurements, and condition rating collected data on a subsample of volunteer inventoried trees to assess the accuracy of volunteer collected data.

Tree architecture analyses provide pertinent data to practitioners in order to perform an architectural diagnosis. This lecture will guide participants step by step how to read the data provided by researchers and how to perform a basic architectural diagnosis as outlined in Jeanne Millet’s diagnosis guide and Christophe Drénou’s ARCHI method.

In recent years, Christophe Drénou’s ARCHI method: Architectural diagnosis of the vitality of trees, has taken the arboriculture community by storm, regarded as a major contribution to the application of tree architecture in the management of arboreal patrimony. This lecture will guide participants through Drénou’s ARCHI method in a comprehensible accessible way.

Even though the ARCHI method provides specific keys by species, its principles based on the nature of substitute shoots, either orthotropic, plagiotropic or ageotropic, can be extrapolated to many urban trees. The ARCHI method considers two distinct images: A sequential image, corresponding to an ontogenetic diagnosis, considering inherent ontogenetic stages of development, and, a reactive image, corresponding to a  physiological diagnosis, considering physiological states induced by the environment, taking into account both mortality and tree reaction.

The ARCHI method enables arborists to understand stress as a pause from a natural state within the inherent sequence of development, leading to physiological states induced by the surrounding environment.

This lecture will describe in detail the 6 different ARCHI types:

Normalcy: Healthy tree presenting normal architecture. Stress: Stressed tree presenting deviations from normalcy. Resilience: Resilient tree returning to normalcy.

Crown retrenchment: Tree presenting a process of construction of a new crown below or nested within the original crown.

Entrenchment: Tree entrenched presenting uppermost crown decline and unaltered lower branches.

Irreversible decline: Declining tree having reached a point of no-return to normalcy.

Tree architecture analyses provide pertinent data to practitioners in order to perform an architectural diagnosis. This lecture will guide participants step by step how to read the data provided by researchers and how to perform a basic architectural diagnosis as outlined in Jeanne Millet’s diagnosis guide and Christophe Drénou’s ARCHI method.

In recent years, Christophe Drénou’s ARCHI method: Architectural diagnosis of the vitality of trees, has taken the arboriculture community by storm, regarded as a major contribution to the application of tree architecture in the management of arboreal patrimony. This lecture will guide participants through Drénou’s ARCHI method in a comprehensible accessible way.

Even though the ARCHI method provides specific keys by species, its principles based on the nature of substitute shoots, either orthotropic, plagiotropic or ageotropic, can be extrapolated to many urban trees. The ARCHI method considers two distinct images: A sequential image, corresponding to an ontogenetic diagnosis, considering inherent ontogenetic stages of development, and, a reactive image, corresponding to a  physiological diagnosis, considering physiological states induced by the environment, taking into account both mortality and tree reaction.

The ARCHI method enables arborists to understand stress as a pause from a natural state within the inherent sequence of development, leading to physiological states induced by the surrounding environment.

This lecture will describe in detail the 6 different ARCHI types:

Normalcy: Healthy tree presenting normal architecture. Stress: Stressed tree presenting deviations from normalcy. Resilience: Resilient tree returning to normalcy.

Crown retrenchment: Tree presenting a process of construction of a new crown below or nested within the original crown.

Entrenchment: Tree entrenched presenting uppermost crown decline and unaltered lower branches.

Irreversible decline: Declining tree having reached a point of no-return to normalcy.

The debate around the exclusive use of native plants for the new projects or, however, their priority toward the exotic species, sometimes assumes tones which can be called “botanical chauvinism”. Anyway, regarding the term “native” and its real meaning there is a lack of clarity; it is a “fluid” term that needs to be related to a precise context to be fully understood.

When planning new green spaces in the urban environment is necessary to always remember that the today’s urban environment is very different from the natural environment where the species evolved out and that, sometimes, exotic species might provide better performances than species which, though native from a specific area, could have serious difficulty to thrive in our cities where the climatic conditions and soil characteristics are completely different. Native plants don’t necessarily survive these conditions any better than exotics. Besides we should answer some more questions when we have to choose the species to be planted:

• Which trees should be planted in order to maximize the carbon sequestration and pollutants removal?
• Which species native and/or exotic can better face the temperature increase foreseen for the next decades?
• Can the drought tolerance of certain species be increased through better management techniques?
• How the interaction between the different species will change in the future?

Based on these questions the use of exotic species shouldn’t be excluded a priori but, more simply, once their potentiality for new plantings has been evaluated by comparing it with that of native species, they can be introduced where they can maximize the benefits in terms of CO₂ sequestration and pollutant removal. On the other hand, it should be highlighted that their excessive use must not end in a sort of “vegetal globalization”, at the expense of the native species of a certain area.

So, it really doesn’t matter if a tree is native or non-native. What’s important is whether the tree’s characteristics and performance are a good fit with where we plant it. Native trees where in the place where we now live before the man, which means that many native trees will not fare well in areas where the surrounding environment has completely changed from the natural to asphalt, concrete and metal rather than a verdant forest with unaltered soils. Rather than try to achieve environmental conformity with regulations that exclude the use of exotic species in the new projects it would be more reasonable to stimulate landscape architects to design pleasant green spaces using a variety of native as well as non-native species.  A goal of 100% indigenous species, although desirable, is not possible on most sites and we do know that there is no perfect tree, but we must strive to plant the right tree in the right space and giving to it the right management.

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