The 2003 AGM address. Veteran trees and saproxylic invertebrates at Hylands Park
MARK HANSON
3 Church Cottages, Church Road, Boreham, Essex CM3 3EG
Introduction
Over the last 25 years in Britain there has been a growing awareness of the importance of wood-
pasture sites and their mature, old and ancient trees (veteran trees) and the contribution they make
to the conservation needs of a significant percentage of the fauna and flora of the British Isles. So-
called 'saproxylic invertebrates' are those species that depend on wood, usually but not always,
dead and decaying, for some part of their life-cycle.
It is estimated that there are probably at least 1,700 species that fall into this category in Britain, the
vast majority being flies (Diptera) and beetles (Coleoptera). They include species that feed on
wood in its various stages from solid to completely decayed, often with a single species exploiting
a particular niche at any one stage. The term also encompasses those that live on associated fungi,
on sap-runs, in rot-holes (of many types, wet and dry), under bark and those species that prey upon
or parasitise these saproxylic species.
Often a beetle or a fly will occupy a very specific niche in an old tree - a hundred trees, each fifty
years old, are no substitute for a single tree 500 years old and, similarly, a diverse age range of trees
from one to 500 years old is much more desirable than a two or three hundred year old gap in the
age distribution of a group of veteran trees, giving a continuity of habitat over a long period of
time. Many saproxylic invertebrates seem to have poor powers of dispersal - particularly some
beetles - and so it is that many species have collectively come to be used as indicator species for
habitat quality and stability.
The U.K. makes a significant contribution to the population of veteran trees in north-west Europe.
It has been noted on many occasions that there arc relatively few very ancient trees to be seen on
mainland Europe (north of the Pyrenees). It is not until one reaches the U.K. that veteran trees
become at all frequent. However, despite this, the U.K. saproxylic fauna is thought to be
impoverished, compared to some European countries (ie France and Austria), probably due to
post-glacial isolation and later forest (wild-wood) clearance for agriculture with its associated
fragmentation. Climate almost certainly plays a part - for example the mainly tropical jewel beetles
(Buprestidae) have some 100 species recorded in Europe; the damp, cold Atlantic climate is not to
their liking and just 12 species arc recorded in Britain. Of these, just one species has been recorded
at Hylands, the Nationally Notable Agrilus laticornis. The general scarcity of over-mature trees
indicates that many saproxylics are considered to be amongst the rarest invertebrates in Europe.
Evaluation of Wood-Pasture Sites
Because of their often very restricted occurrence, limited powers of dispersal and generally the
isolation of the particular site a saproxylic species occurs in, they have come to be used as indicator
species - enabling conservation workers to grade and rank a particular site for its conservation
significance. Various methods using different criteria have been used, mostly involving known
indicator species that have been given a simple scoring - for example on a three-point scale to
show how strong is that species' association with the wood-pasture/old forest habitat. As a result of
such surveys, the Nature Conservancy Council (now English Nature) introduced the Invertebrate
Essex Naturalist (New Series) 20 (2003)
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