Crown & Canopy Management Official Preview Part 2

Tree Physiology for Arborists

Luke Steer is a Fellow of the Arboricultural Association and a Chartered Arboriculturist. Luke has been studying trees and working with them since 1984. In the opening talk of the afternoon session, he’ll guide us through how trees work and how they react when parts are damaged or removed.

“Healthy trees in tune with their environment are ‘balanced’, or more accurately ‘balancing’ organisms with the ability to readjust to ‘expected’ alterations in their environment.

“The ‘balance’ formed by a tree between its different parts will depend to a certain extent on its genetic makeup and the environmental factors it experiences: location and weather. For instance, a tree growing in a dry sandy soil will allocate resources to grow proportionately more roots per unit of foliage than the same species in a moist loam soil. The limiting growth factor: light, water or mineral nutrient(s); will promote the growth of the tree part that obtains that limiting factor from its environment.

“attheck (1994) describes healthy trees as being ‘self optimising mechanical structures’. That means that each tree part is mechanically as strong as it needs to be to withstand ‘normal’ mechanical stresses – no part is excessively over engineered or insufficiently strong enough. Trees achieve this by allocating resources to grow additional tissue where required for function and mechanical strength.”

Natural bracing and bark inclusions

In 2016 Dr Duncan Slater presented his initial identification of a strong relationship between bark-included junctions in trees and the presence of natural braces set above them. Dr Slaters work has caused lots of recent discussion in the world of arboriculture, with its fresh and insightful method of interpreting the structures of trees and how they grow. Focusing in particular on bark-included branch junctions, his continued research over the past few years has a relevance for all aspects of our profession.

This new talk will introduce the audience to a fourth type of reaction wood. Currently, three types of reaction wood are recognised to form in woody plants: compression wood, flexure wood and tension wood. Through x-ray analysis and experiment, a fourth reaction wood is identified that is formed in the axil of a branch junction (the centre of the join), which has been named ‘axillary wood’. The assessment of a branch junction, particularly those with a high diameter ratio, needs to concentrate on the extent of axillary wood production, its position and condition.

Incorporating some of Dr Slaters ‘Trees Over Time’ images this new technical update is significant for arborists in all roles.

“The effects of natural bracing are important for those assessing trees, specifying or carrying out tree work, and this research explains why some bark inclusions are persistent in the structures of trees.

“Previous advice to arborists on bark-included junctions has emphasised that those with large bulges associated with them are more prone to failure. In our most recent experiment, we have generated data by modelling to determine if this previous advice was of use in the assessment of bark inclusions. The outcome of this experiment will be shared with the conference, along with several other papers and research projects.”

Tree Diseases – A Five Year Overview at Forest Research

Since 2013 when she joined Forest Research, Ana has been actively involved in developing early warning systems for the detection of tree pests and diseases in Britain. Over the past five years the Tree Health Diagnostic & Advisory Service at Forest research have been actively working on the early detection of P&D that might be a threat to the health of trees in Britain.

“We developed TreeAlert to facilitate the reporting of P&D in the country and we have a team of pathologists and entomologists investigating the cause of ill-health in trees. The submitted reports have allowed us to gather information on the health of trees and the main issues encountered. It has also allowed us to monitor the spread of recently introduced P&D. An overview will be presented showing the top ten pests and diseases reported along with some of the most interesting cases encountered. These will include the recently detection of quarantine pests and pathogens such as chestnut blight (Cryphonectria parasitica) and pests and pathogens detected for the first time in the UK.”

With Biosecurity now recognised as a central issue across horticulture and landscape sector, and with pests and diseases high on the government agenda, this is not a session to be missed.

Shining a light on tree health

The finale of the opening day sees Jon Banks guide us through the concept of tree vitality and how it can be related to pest and disease resilience. Jon recently completed his PhD assessing drought and variation in drought tolerance within the Acer genus.

Tree health and vitality influences a wide range of physiological processes including pest/disease susceptibility and water stress resilience. As well as the concept of tree vitality, Dr Banks will explain its relationship to tree establishment and survival within the landscape. A range of options for monitoring tree vitality, including chlorophyll fluorescence and the Arborcheck system will be discussed, using “real life” case studies from diagnostic field work and ongoing research trials. Dr Banks will explain how measuring tree vitality is of benefit to those managing trees. The future potential of this stress detection technology will also be discussed.