|One of the few times I have had the fortune of observing a Eurasian Scops Owl in Athens was on a Eucalypt in Attikon Alssos, Tourkovounia.|
For many years I have hated eucalyptus trees. I was a nativist, i.e. someone who despised non-indigenous species. Well that was many years ago, when I was a teen and a purist. As I have grown older I try to look at things more holistically.
The question is what to do with eucalyptus?
It is after all an alien genus from Australia that creates totally alien conditions with the eucalypt resin said to having a "repellent effect" to many terrestrial invertebrates. How do we deal with eucalypts in a wildlife resources and biodiversity conservation sense?
These are some notes on my observations in Greece, Cyprus, and Turkey.
1. Its not everywhere. In the NE Med (outside Israel) eucalyptus is not as widespread or as abundant as it is in Iberia; there are few extensive plantations in fact. Frost does a lot of harm to it and many small plantations have failed (in mountain areas and in northern Greece, for example).
2. Does not spread. It is rarely in self perpetuation. I have seen some growth from seeds in Cyprus (Nicosia etc) and in vacant lots in Athens - but always singular trees (Nothing like the Acacia infestations in Cyprus or the 'tree-of-heavean' problem in Greece's urban areas). So its not invading if not planted.
3. Does not seem to drain wetlands. It does probably cause wetland draining effects due to the amazing evapotraspiration ability. It is frequently planted in wetlands. In some areas there are groves of old outlandishly huge trees. However, the deep-shade cast over wetlands and riparian zones by these huge trees does combat evaporation of surface waters.
4. Native plants do grow beneath it. Very few species on native plants seem to grow under a dense eucalypt groves in my experience. This is a general observation and it needs empirical evidence. This I have observed in Portugal, but also recently in the Germasogeia riparian area on Cyprus. Alien acacias did grow vigorously under eucalypts on Cyprus. I am curious to see if other species grow well - for example Pistacia lentiscus was growing well under these trees. In California it has been shown that many native plants do grow underneath but invertebrate numbers are depressed there.
5. Little evidence for all negative impacts to biodiversity. The wildlife uses of eucalypts has been poorly studied as a wildlife issue or alien invasive problem in Greece, Turkey and Cyprus. Generally most people think they are poor wildlife trees. Few bird species seem to nest in eucalypts.
Positive wildlife/biodiversity observations:
1. Important cover, shelter, roosts for birds. I have evidence that many large birds roost in the monumental eucalyptus trees. Big raptors commonly choose Eucalypts over native trees: Greater-spotted eagles in Amvrakikos chose a Eucalypt grove for several winters as a regular roosting site (Zogaris et al. 2003 - Threatened Birds of Amvrakikos). Many owls do too. Owls such as the Scops Owl pictured above and many other species frequent eucalypt trees. During migration, herons and egrets roost here also (I recall a grove at Koutavos in Argostoli Kefalonia that was full of heronids in spring migration).
2. Some birds feed on it. Although the leaves and resins are said to have an "insect-repellent affect", the flowers do attract diptera, butterflies and there are many little insectivore migrant birds that I have seen feeding in Eucalypts here in Athens.
3. Robust tree where all trees have been felled by humans. Many native large trees have been felled, do the non-indigenous Eucalypts fill vacant niche? In Greece & Turkey large Quercus ithaburensis, Quercus rubor, and othe tall Quercus, Populus, Fraxinus used be common riverside trees and these are now scarcer due to anthropogenic felling. So do eucalypts fill a vacant niche and supplement a key habitat in the landscape? Perhaps yes, in a wildlife habitat sense; they provide habitat that is scarce in the landsape. Eucalypts are also incredibly hardy, they can grow well in very windy locations (much of coastal Greece is very windy!); so these robust trees and tree groves, last long even after many many wind storms. They also can survive some low fires and they also live a very long time 400 -600 years.
4. A tree of monumental proportions; enriches landsapes. Eucalypts grow really fast and become "monumental trees". Trees like this exist in Schinias National Park in Attika - they are gigantic! In wetlands of the south of Greece, the islands - these trees survive well, some are over a 150 years old already. In open landscapes in the south they resemble savanna-like elements in the open landscape. They are used by many birds there where no other trees exist. For example in the dry steppe-like areas of central Cyprus (Kotziatis river near Nicosia); it would be a crime to remove these wildlife trees.
I do not mean to promote the planting of eucalyptus! I am against that. And fortunately many foresters in Greece no longer plant these trees in re-forestation practice. It is wrong to use eucalyptus in riparian zones. Unfortunately, because they are hardy and strong they will survive if panted in the "wrong place" although the native pines, carobs etc may not survive - for example on a windswept salt-sprayed promontory in Southern Attika I have seen eucalypts survive yet other plantings perished (the Municipality of Saronikos planted them).
So in this sense eucalyptuses are a threat. People should NOT plant them. However, old monumental eucalypts should not cut down just because they are non-native. Young trees should be cut down in an effort towards ecological restoration in riparian zones (this has alreadey been proposed in the Nicosia Pediaios stream for example). However, please keep in mind that big old eucalypts often do have wildife values and many amenity values. This is a great research topic. Many aspects of eucalypt's impacts are poorly understood.
See this from California: http://sutroforest.com/2013/04/22/the-importance-of-eucalyptus/
Also from California: Dov Sax. 2002. Equal diversity in disparate species assemblages: a comparison of native and exotic woodlands in California,” Global Ecology and Biogeography, 11:49-52.