IACA - SRIV

SUSTAINABLE RETENTION INDEX VALUE (SRIV) © 2005

A visual method of rating the viability of urban trees for development sites and management, based on general tree and landscape assessment criteria.

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INTRODUCTION

SRIV © provides a dual method of rating the viability of urban trees for development sites based on general tree and landscape assessment criteria, and a numeric index for each tree as a tree management tool. SRIV© is designed as an objective system based on set criteria to replace previous subjective systems. SRIV© is based on the principle of sustaining trees in the urban environment including remnant forest trees, but does not cover social aspects of trees, or hedges. Dead trees and environmental or noxious weed species are not considered as removal of these trees is generally encouraged.

SRIV© benefits the arboriculturist by defining each variable providing certainty and clarity to their meaning and by issuing a definite index value to each category. This enables the professional manager of urban trees with an assumed knowledge of the taxa and its growing environment to consider the tree in situ and is based on the physical attributes of the tree and its response to its environment. SRIV© considers its age class, condition class, vigour class and its sustainable retention with regard to the safety of people or damage to property. The ability to retain the tree with remedial work or beneficial modifications to its growing environment or removal and replacement is also considered.

To promote tree retention, remediation works to improve the growing environment should always be attempted where ever possible. Successive assessments may document improvements in a tree where it responded favorably to remediation, or where conditions in its growing environment improved naturally, or conversely a decline, or a static rating if the tree deteriorated, or no change was observed, respectively.

SRIV© is designed to achieve a quick and readily understood value for a tree but does not replace the need for a comprehensive assessment of a tree and as a tool is intended to be used in conjunction with or complementary to a detailed tree assessment. As a management tool the ongoing SRIV© assessment of a tree may indicate its response to remedial works or other modifications to its growing environment over time.

SRIV© is a realistic approach to managing trees but recognises from the outset that as tree taxa are a vast and varied array of organisms, not all will fit easily into the system e.g. tree species with a lifespan shorter than twenty years, most Acacia species. Field trials have revealed that it is suitable for the majority of trees.

An example of a SRIV© for a Mature tree with Normal Vigour and Poor Condition is an assessment value of MNVP and an index value of 6, see page 4. The matrix provides indices as a tree management decision making tool and the Age/Vigour/Condition classes as a tree assessment system.

The Glossary details the values to be used with the SRIV© system and are taken from the Institute of Australian Consulting Arboriculturists (IACA)© (2006), Dictionary for the Management of Trees In Urban Environments.

MATRIX FOR THE SUSTAINABLE RETENTION INDEX VALUE (SRIV) ©

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GLOSSARY

Values for terminology of SRIV©
Sustainable Retention Index Value ©

Vigour

Vigour Ability of a tree to sustain its life processes. This is independent of the condition of a tree but may impact upon it. Vigour can appear to alter rapidly with change of seasons (seasonality) e.g. dormancy of deciduous or semi-deciduous trees.

Normal Vigour Ability of a tree to maintain and sustain its life processes. This may be evident by the growth of leaves, branches, roots and trunk. This is independent of the condition of a tree but may impact upon it, and especially the ability of a tree to sustain itself against predation.

Low Vigour Reduced ability of a tree to sustain its life processes. This may be evident as a decline in the growth of leaves, branches, roots and trunk, and a deterioration of their functions. This is independent of the condition of a tree but may impact upon it.

Abnormal Vigour Accelerated growth of a tree due to incidental or deliberate artificial changes to its growing environment that are seemingly beneficial, but may result in premature aging or failure if the favourable conditions cease, or promote prolonged senescence if the favourable conditions remain, e.g.

water from a leaking pipe;
water and nutrients from a leaking or disrupted sewer pipe;
nutrients from animal waste
a tree growing next to a chicken coop, or a stock feed lot, or a regularly used stockyard;
a tree subject to a stringent watering and fertilising program.

Age

Age Most trees have a stable biomass for the major proportion of their life. The estimation of the age of a tree is based on the knowledge of the expected lifespan of the taxa in situ divided into three distinct stages of measurable biomass, when the exact age of the tree from its date of cultivation or planting is unknown. These increments are Young, Mature and Over-mature.

Young Tree aged less than 20% of life expectancy.

Mature Tree aged 20-80% of life expectancy.

Over-mature Tree aged greater than 80% of life expectancy tending to senescent with or without reduced vigour, and declining gradually or rapidly but irreversibly to death.

Periods of Time

Periods of Time The life span of a tree in the urban environment may often be reduced by the influences of encroachment and the dynamics of the environment and as a result the values of Short Term, Medium Term and Long Term have been applied.

Short Term Period of time less than 1 - 15 years.

Medium Term Period of time 15 - 40 years.

Long Term Period of time greater than 40 years.

Condition

Good Tree is of good habit, a form not severely restricted for space and light, physically free from the adverse effects of predation by pests and diseases, obvious instability or structural weaknesses, fungal, bacterial or insect infestation and is expected to continue to live in much the same condition as at the time of inspection provided conditions around it for its basic survival do not alter greatly. This may be independent from, or contributed to by vigour.

Fair Tree is of good habit or misshapen, a form not severely restricted for space and light, has some physical indication of decline due to the early effects of predation by pests and diseases, fungal, bacterial, or insect infestation, or has suffered physical injury to itself that may be contributing to instability or structural weaknesses, or is faltering due to the modification of the environment essential for its basic survival. Such a tree may recover with remedial works where appropriate, or without intervention may stabilise or improve over time, or in response to the implementation of beneficial changes to its local environment. This may be independent from, or contributed to by vigour.

Poor Tree is of good habit or misshapen, a form that may be severely restricted for space and light, exhibits symptoms of advanced and irreversible decline such as fungal, or bacterial infestation, major die-back in the branch and foliage crown, structural deterioration from insect damage e.g. termite infestation, or storm damage or lightning strike, ring barking from borer activity in the trunk, root damage or instability of the tree, or damage from physical wounding impacts or abrasion, or from altered local environmental conditions and has been unable to adapt to such changes and may decline further to death regardless of remedial works or other modifications to the local environment that would normally be sufficient to provide for its basic survival if in good to fair condition. Deterioration physically, often characterised by a gradual and continuous reduction in vigour but may be independent of a change in vigour, but characterised by a proportionate increase in susceptibility to, and predation by pests and diseases against which the tree cannot be sustained. Such conditions may also be evident in trees of advanced senescence due to normal phenological processes, without modifications to the growing environment or physical damage having been inflicted upon the tree. This may be independent from, or contributed to by vigour.

Dead Tree is no longer capable of performing any of the following processes or is exhibiting any of the following symptoms;

Processes

Photosynthesis via its foliage crown (as indicated by the presence of moist, green or other coloured leaves);
Osmosis (the ability of the roots system to take up water);
Turgidity (the ability of the plant to sustain moisture pressure in its cells);
Epicormic shoots (the production of new shoots as a response to stress, generated from latent or adventitious buds or from a lignotuber - an at ground or underground stem);

Symptoms

Permanent leaf loss;
Permanent wilting (the loss of turgidity which is marked by desiccation of stems leaves and roots);
Shedding of the epidermis (bark desiccates and peels off to the beginning of the sapwood).