Introduction

Trees and woodlands are fundamental to our well-being and quality of life, providing a huge range of ecosystem services as well as social and economic benefits. Arguably the most interesting and valuable trees are our old trees, which by their nature are more prone to decay and failure.

Fig 1. Ancient and veteran trees in urban areas can present the greatest risk in terms of defects and decay, but also possess the greatest value (BBC.co.uk)

One of the attributes a good tree risk manager can possess is the ability to balance the benefits of trees with the low level of risk that they present (National Tree Risk Safety Group, 2011).  And, as the Law places values humans far greater than nature, as arboriculturalists, we must seek and generate evidence based knowledge regarding tree defects, and develop and improve tools, to help us make better informed decisions. While there are many areas of substantial research and guidance, there are still many gaps in our knowledge (in terms of empirical evidence) to back up commonly accepted practices in the industry today (such as rates of decay or root plate deterioration thresholds for example). 

Research into some of the factors affecting fungal strategies and colonisation, disease entry points and infection courts, included bark junctions and natural bracing, all offer new or relatively new areas of research to help tree risk managers make better decisions.

For this assignment I have presented what I believe are some interesting cases, mostly from personal experience and where, in some cases, there has been new research. I’m therefore hoping to offer the reader new insight for tree risk management.

For the first part, presenting the two contrasting cases of fungal decay, I have covered Laetiporus sulphurous (a brown rot) and Ganoderma applanatum (a white rot). I selected these as they are fungal types with two different decay strategies but also because they were highlighted as being a significant cause of failure following the 1987 storms by Gibbs and Greig (1990).

For the pages concerning situations where we have found defects and made recommendations, I have included three cases that I have dealt with during my role as Tree Officer over the last year:- a mature Beech with stem cracks, a veteran Beech with a failed union and graft point (as well a multitude of other issues) and a mature Horse Chestnut with a large pruning wound.