Small tips on Eucalyptus Identification
GIT Forestry Consulting - Consultoría y Servicios de Ingeniería Agroforestal - www.git-forestry.com
Eucalyptus species determination is not just a matter of botanical interest. It can be quite important for its implications in regard to the different genetic pools (be them species, subspecies, provenances, or races) in cultivation. Important issues as cold hardiness (tolerance to winter frosts), growth rates (timber productivity) and physical and chemical properties of wood (timber quality) can depend on this variability, and hence be subject of forestry engineering.
Telling Eucalyptus species apart can be difficult or confusing if differentiation criteria are based on a limited amount of variables. Bark type and characteristics can be one of the criteria for species identification, and can be considerably useful sometimes because some species are so strikingly different nothing else is needed. The chances of using bark successfully as "main criterium" are better for areas where eucalypts are introduced species, simply because the number of possibilities tends to be more limited than in a multispecific natural forest in Australia.
However, bark based identification can also be misleading. Pictured above (Fig. 1) you have two different types of eucalypts. If based on "bark only" criteria, maybe the first thought is they are two different species. But in fact, we are seeing two types of eucalypt belonging to the same species, but different gene pools. Both are Alpine Ash, a type of Tasmanian Oak (Roble de Tasmania).
To the left (Fig. 1), the classical form, rough stringy bark in the lower portion of the main stem, clean withish bark in the upper portion and in the main branches. In mainland Southeastern Australia it has also received the vernacular name of "White Top". To the right, a variant, rough stringy persistant bark almost to the very top and on the main branches too. The latter type is restricted to natural habitats in Tasmania.
So, what the botanists say about this? Let's read Dean Nicolle:
- Eucalyptus delegatensis subsp. delegatensis (mainland Australia Alpine Ash) "Single stemmed tree 30 to 60 metres tall (...) Bark rough on the trunk up to 10 to 30 metres above ground level, moderately fissured and hard-fibrous, grey-brown; smooth above, ribbony, grey to pale grey over white"
- Eucalyptus delegatensis subsp. tasmaniensis (also known as E. tasmaniensis) "Single stemmed tree 20 to 90 metres tall (...) Bark rough over most of the entire trunk, moderately fissured and stringy-fibrous, grey brown to red-brown, smooth on branches, pale grey over cream"
But the most important information to work out what Eucalyptus we are seeing and defining geographically the original gene pools is to be sourced from comparison of flower buds and seed pods (fruit capsules) (Fig. 4) for the case of adult trees.
Of course, once these trees are able to lure us into patient observation of their flower blooms and their seed bearing capsules in order to get them identified, little is left before you start collecting the later to obtain seed, and attempt to raise some plants.
Eucalyptus species identification (II): bark revisited
If you have an unknown eucalypt around and you are able to collect and photograph samples of the key organs needed for identification, do not hesitate contacting GIT Forestry Consulting.
If you are in the USA and find it easier to post fresh samples to a local expert, you can also contact Dr. Matt Ritter, resident eucalypt hunter at the California Polytechnic State University.
© 2007 Gustavo Iglesias Trabado. Please contact us if you want to use all or part of this text and photography elsewhere. We like to share, but we do not like rudeness.