Trembler's delight! - an aspen tree in autumn, with its leaves motionless on a wind-still day.
(See Species Profile: Aspen)
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Cauliflower galls on an aspen twig, found during this summer's aspen survey.
(See Galls on Aspen)
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Trembling in the Glens
A rustling hiss, not unlike running water, but growing and fading with the breeze. One of the many unique and fascinating features of the aspen is that unlike most trees, it can easily be identified from a distance by the sound of its leaves alone! Its scientific name, Populus tremula, really reflects this characteristic of its foliage.
The term 'trembler' was coined some years ago by Paul Kendall; an aspen spotter being a trembler in the same way that a bird spotter is a 'twitcher'! This summer I had the good fortune of 'trembling', and encountering quite a number of these striking trees during an aspen survey in the TFL Target Area. The aim was to explore certain areas for aspen, record their details, and then write a report with recommendations on how best to protect, expand and otherwise enhance the existing stands.
We have been building up records of aspen in our Target Area since the Aspen Project began in 1991. For each stand we record information such as the height and number of trees and suckers, their health, location and altitude, the type of ground they are on, the availability of roots (for propagation), their aspect, and other interesting observations such as the presence of insects, birds and dead wood. This information helps us to develop effective strategies to inform our practical work. Aspen is a tree that is struggling for a number of reasons including habitat fragmentation and climatic factors, which is why we give it particular attention. There are also some endangered species which depend on this tree for their survival.
Carrying out the survey brought with it many thrills and challenges. Aspen are often found on south-facing rocky crags, which meant exciting moments scrambling around on scree slopes and cliffs. At times it was quite hard work, climbing hundreds of feet in waist-high bracken in the blistering sun, and being mauled by cleggs (ferocious horseflies), or fed upon by midges and ticks! Not that I'm complaining, as this was more than outweighed by the spectacular views of the west coast, the chance to explore new areas of forest, finding strange and interesting creatures (always a winner with me), and meeting friendly locals and hitch-hikers.
Among the resident wildlife, I came across various caterpillars, aphids and a few kinds of gall. The latter are (usually harmless) growths found on many kinds of plants ('oak apples' are a familiar example), and are often caused by an invertebrate laying its eggs in the plant's tissues. This induces a swelling or abnormal growth of tissue, in which the larvae can develop. Among those found during the survey was the cauliflower gall, which is caused by an enigmatic mite known as Aceria populi.
We now have 88 new stands on our database, bringing the total up to 310. Far from being merely a data gathering exercise, this survey has enabled us to build up a clearer picture of the distribution and health of the aspen within the Target Area. The report highlights which areas need priority action, and offers management recommendations to the landowners.
The recommendations vary depending on the condition of the aspen in each area. For example, many of the sites are suffering from overgrazing, which is preventing the young suckers from growing to establish the next generation of mature trees. In these cases protecting the young trees with stock fences or tubes is a priority. Other stands are very remote and isolated, requiring expansion with other clones to ensure genetic and sexual diversity. 'Stepping stone' patches have also been recommended, to bridge some of the gaps between the stands. Certain areas, for example around Strome on the west coast, have areas of native and non-native forest with no aspen, so planting of new stands is suggested.
Some of the most impressive aspen stands I saw during the survey were along the Black Water, at the north-eastern edge of our Target Area. Not only are these very large, but they are also within a large area of ancient semi-natural broadleaved woodland. This area shows great potential for benefiting the community of saproxylic (dead wood-dependent) insects which require large areas of aspen within a matrix of broadleaved forest.
It is rewarding to have had the opportunity to spend this amount of time on the project. A big 'thank you' goes to all the landowners who agreed for survey work to take place, to all those people who helped with locating new stands and to Mark Young and Rex Hancy for identifying some of their weird and wonderful inhabitants. We really feel that this marks a significant step forward for the Aspen Project.
Dan Puplett
The Trees for Life Aspen Project
Aspen - related pages
This article was written for the Winter 2003-04 edition of Caledonia Wild!
