Autecology in forest species
This text was written by Juan José Villarino (died in 2016) for publication in the magazine O Monte, no. 59 in 2016.
Juan José Villarino Urtiaga
Forest Engineer, former Professor of Silviculture at the University of Santiago de Compostela
The foundations of the debate
The question of whether a forest tree is native or not, when posed in this way, can give the layman the false impression that it is referring to an attribute or quality of the species itself. Since this is not precisely the case, it is necessary from the outset to establish a minimal conceptual framework that makes a rational discussion of the matter possible.
The points to consider are, at a minimum, the following three:
First.- The taxon or taxonomic unit. It will normally be the species, although it could also be a higher category (the genus) or a lower one (subspecies or variety).
Second.The geographical-ecological area in which the species' native range is proposed.
A species may not be present in a relatively small area of its natural distribution (a municipality or a district, for example) and yet reappear when the surveyed area is expanded; this fact points to the conclusion that it is pointless to reduce the size of reference areas excessively.
Atlantic Galicia forms part of the Euro-Siberian forest area of the Old Continent and, together with the corresponding North American areas, is part of the Holarctic Floral Kingdom.
The Pseudotsuga menziesii Planted in Galicia can hardly be considered as exotic when it comes from locations within the same Floral Kingdom.
Sometimes controversies arise that originate from disagreements over the species' taxonomic assignment. As an example of the latter, I will say that in relatively recent years a record of Hanging Birch, supposedly a native birch, in the municipality of Guntín, about 20 km from Lugo. As it happens, it is now generally accepted that the correct designation for the birch populations of Galicia is Celtic beech, the logical conclusion would be that this latter species is present as native in the region (Central Plateau of Lugo). Hanging Birch It is not native to Galicia, but that should not prevent us from recognising that it shows good adaptation to the environment – at least in areas with a high density of native birch – and that its ornamental value is superior to that of the native species. B. celtiberica.
Third.The need to take into account dynamic-temporal issues in conjunction with those mentioned above. This point, owing to its importance, merits the opening of a new heading.
Recognition of dynamism
The case of relict species, confined to small enclaves and lacking the means to expand beyond the refuges that allow their short-term survival, is a good example that “native” does not always equate to “competitive in the natural environment”. They face the ever-present threat of extinction, which could be realised as a result of an unforeseen worsening of environmental conditions, perhaps caused by some catastrophic disturbance: fires, insect pests, etc.
Conversely, a species not present at a given moment may end up appearing in the site as a result of the culmination of a migratory dynamic if the following two conditions are met:
- That the edge of the distribution area is not excessively far away (and that there are no insurmountable natural barriers on the route) and
- That the process is favoured by a suitable adaptation of the species: abundant and frequent production of easily dispersed seeds; rapid germination of the seeds, rapid growth of the seedlings and a short time for the fruiting of the next generation of plants.
The laurel, Prunus laurocerasus Legend.
RUIZ DE LA TORRE records as the species“ natural distribution area ”Caucasia, Persia and the Eastern Balkans". This latter area, the Eastern Balkans, could refer to the historical region of Thrace, which today encompasses the European part of Turkey, the easternmost strip of Greece and the south-eastern part of Bulgaria. At this point, it would be particularly interesting to have a good map of the distribution area and, more specifically, a description of the characteristics of that western edge in the eastern Balkans and, if possible, some assessment of potential migratory patterns.
Without such tools and with no more information than that set out above, I will try to arrive at some deduction that might be of some use to us.
The comparison between the distribution areas of two species can allow us to infer some ecological characteristics, at least in relative terms. Thus, in the case of Portuguese cherry and more Prunus laurocerasus, It seems logical to suppose that the latter is better adapted to areas with a somewhat continental climate and cold winters.
In Galicia, we already know that laurel has a good capacity to adapt to its environment and a considerable regenerative potential, both through seeds and vegetatively, although in my opinion the fact of considering it an invasive and exclusionary species is a manifest exaggeration.
RIVERBANK and others. include Prunus laurocerasus as medicinal in his book “Guide to the Medicinal Plants of Galicia”, and RUIZ DE LA TORRE notes that the leaves are used in pharmacy and that they also yield bitter almond essence in pastry making. Other sources indicate medicinal properties, a sedative effect on the nervous system, and that, more than the seeds, they are toxic due to their high cyanide content.
Although not native to Galicia, it should be borne in mind that the natural distribution area of the laurel lies relatively close by, and at a similar latitude, in the Balkan region of eastern Europe.
The key question is whether the species exhibits any qualities that justify its use in the agroforestry environment; and there is no doubt that it must be recognised that it does possess those qualities:
- Because laurel is a hardy and adaptable species in a wide variety of agroforestry settings.
- Because it is useful in the installation of windbreak hedges.
- Because it has medicinal and culinary uses.
- Because it is easy to reproduce, saving money on acquiring nursery stock.
- And finally, because it has social acceptance in rural Galicia.
Nitens and giant eucalypts
The eucalyptus trees species and of the delegation or giantish They are well adapted to areas with cold winters, where the and. Of the two, the nitens is the most recently introduced to the Terra Chá region of Lugo.
The giant eucalyptus (Eucalyptus delegatensisIt was already being planted in the 1970s. It adapts very well to the region, grows very quickly – particularly in diameter – and regenerates naturally, both from stump shoots and from seed, so that after a cut the ground is repopulated at no cost to the owner.
On the other hand, E. nitens It does not regenerate naturally, which requires a silviculture similar to that of pine. radiata or insigne, with new groundwork and planting after the cut has been made.
It seems that the “de facto powers” are interested in promoting the use of E. nitens and in the face of this fact one wonders what the reason might be:
Could it be because the wood of the nitens has some special quality? Because at the same price it seems indisputable that the giant is more profitable.
Or is it because the sector's capital finds the nitens silviculture model more advantageous, with its consequent investments in cultivation and planting every few years in the same place?
To be honest, I don't know what to think. Perhaps a reader of our magazine might have a good explanation for my question.
I don't know, but what I suspect is that those who know the subject inside out aren't readers of forestry publications; what they read are magazines like The Wall Street Journal, The Economist, etc.
And to finish, a bibliographical citation.
Stephen H. Spurr and Burton V. Barnes are two well-known American forest ecologists. Their joint work Forest Ecology – of which I have a translation into Spanish – is considered one of the basic references in the literature on forest ecology.
To avoid making the quotation excessively long, I will limit myself to transcribing two or three paragraphs in which the authors propose, should the reader decide to pick up the gauntlet, a new approach to the discipline: the concept biocentric.
“From a biocentric point of view, the concepts of native and introduced or alien species cease to make sense. To characterise a plant or animal as exotic or indigenous is to define it solely in terms of our relationship with it.
“For the maple tree growing in one place, it is insignificant whether its winged seeds disperse by their own means or are helped or carried by the wings of an aeroplane.
“The ecosystem is made up of all the plants and animals found at a particular point in space and at a given moment. All individuals have migrated to the site, carried there by the wind, by animals, by water or by human beings. Once they arrive and adapt to the environmental conditions, they become members of the local ecosystem until they or their descendants are removed from it.
