Wednesday 20 March 2019

Paleo-autochtonous species (1): Carpinus



Leaves and inflorescences of European or common hornbeam (Carpinus betulus).



If one species deserves more than any other, the name of "paleo autochthonous", whatever the meaning one may wish to give to this neologism, this is without question the European or common hornbeam (Carpinus betulus). This species is still present reliquely in the valley of Bidasoa (Spain), but in the recent past has had a much more extensive distribution area in the Iberian Peninsula. And you do not have to go back too much in time or in the past to find marks of it's presence. In much of northern peninsula and the Atlantic strip, its presence was confirmed during the climatic optimum of the Holocene, when it reached the Iberian Central System [1]. Their current locations are therefore, the last testimonies of a much wider presence. It would then be necessary to ask why it disappeared from many of the localities that it reached at that time. The most probable explanations of such regression are the progressive increase of the seasonality after this climatic optimum reached between 9000 and 5000 years before the present and the beginning of the agricultural exploitation of the lands that were more favorable to this species.




The common hornbeam is a very demanding species, with water and soil requirements that are not often found on the Peninsula today. It is not a species that tolerates drought and develops preferentially in rich and deep soils that are usually what we normally find in lowland areas. It is, on the other hand, a species that bears the heat very well, being perfectly capable, if irrigated, of enduring the implacable summers of the center of the Peninsula. Some specimens planted in my neighborhood (Madrid) already measure about 4 to 6 meters, bloom and bear fruit each year, bearing without much trouble the 40 degrees that are reached in July and August. At most, some of the leaves dry up, but this does not endanger the survival of these trees.



Maps of the current distribution of European hornbeam (C. betulus) and Oriental hornbeam (C. orientalis) [2].



In times prior to the last ice age, the common hornbeam was present in much of the Peninsula, it must also be highlighted the presence at the end of the beginning of the Pliocene and during the Pleistocene of Eastern hornbeam, today present only in the East of the continent and the Mediterranean basin, what should also be noted. The Eastern hornbeam is not a vicarious species. It is a hornbeam better adapted to the drought than C. betulus, which makes it, in Eastern Europe, a typical element of the sub-Mediterranean vegetation, living there with species such as the downy oak (Quercus pubescens), the Turkey oak (Quercus cerris) or the European hop-hornbeam (Ostrya carpinifolia). That is because of its ecology, is quite different from the common hornbeam, which is a species of sub-Atlantic and central European environment.


CarpinusFamilia: BetulaceaeOrden: Fagales

Trees or shrubs. Fusiform and sharp buttons. Leaves oval or oval-elliptic, acute, doubly serrated, with 9 or more pairs of very marked and regular secondary nerves. Male catkins are solitary and sessile; bare flowers, solitary in the armpit of each bract, without bracing; Stamens 6-20, pubescent, with bifid filaments, very short. Female terminal limbs, relaxed, pendent at maturity, with leafy bracts; twinned flowers, with perianth; seminal rudiments 1 (2); style divided into 2 filiform, green branches. Achenes arranged in hanging ears, small and compressed, surrounded by a large folium, trilobed or serrated, with sharp venation, originated by addition of the single bract.



Also noteworthy here is the unexpected presence of the hornbeam in the Canary Islands until the end of the Holocene. [3] More surprising perhaps, because of the distance than because of the climatic conditions. This presence is not so surprising, however, knowing that it was also present in the mountainous masses of the Sahara in times much more humid than today.





Fruit of Carpinus betulus (top) compared to Carpinus orientalis (bottom).


The common hornbeam is a species commonly cultivated in our country (Spain), where it surprises in many places by its capacity to withstand the high summer temperatures. As mentioned earlier, lack of water seems to be the true limiting factor for this species. On the other hand, surprisingly, the cultivation of Eastern hornbeam did not aroused much interest in our country (Spain). This being a much less demanding tree, it is curious that it has not been tried at least in our parks and gardens. Being a tree of relatively small dimensions, which often is not even more then a bush, it can be understood that it did not arouse the interest of the foresters. It would, however, be an element to take into account to increase the biodiversity of our forests in areas of sub-Mediterranean climate, where in addition to the everlasting Quercus, the hardwoods do not abound.

I planted some seeds of Carpinus orientalis a few years ago, with no treatment and none of them germinated. Last year, however, I saw two small little trees appear in my pots that may well correspond to this species or perhaps to the European hop-hornbeam, I can not name them for now. Next year I will have to try again, since this species seems very interesting for the climatic conditions of the Iberian Peninsula.


Author: Adrián Rodríguez
Translation: João Ferro


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