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Sporobolus vaginaeflorus (Torr.) Wood in the vegetation of Croatia
Stjepan Horvatić
; Hrvatska
Ljerka Gospodarić
; Hrvatska
Sažetak
The authors report on an interesting finding of the species Sporobolus vaginaeflorus (Torr.) Wood over a wide area round Zagreb where this North American grass is in places very frequent along either banks of the Sava river. Since this plant has not been previously registered as belonging to the flora of this country (and probably not of Europe either) various authors have paid it particular attention (it was first collected by Ljerka Gospodaric in the Zitnjak-Bogdani district in 1954) as an interesting neophyte.
In the first chapter of this paper the authors compare the plant from the Zagreb area (Fig. 1 and 2) with the available herbal specimens of the corresponding plant from North America as well as with diagnoses, analytic keys and drawings in the works of Wilder-Savage (1904), F e r n a 1 d (1933) and Hitchcock (1935), and state that it represents the grass Sporobolus vaginaeflorus (Torr.) Wood var. inaequalis Fernald.
The second chapter includes a list of all stands of Sporobolus vaginaeflorus var. inaequalis in the wider countryside round Zagreb. The stands are shown in Map 1.
The third chapter deals with the phytocoenological (phytosociological) relations of the plant and the most essential ecological characteristics of its habitat in a wider area round Zagreb. While in North America the plant is present probably in more or less different plant communities on dry, bare and sandy soil (which, the authors believe, can be concluded from the writings of Wilder-Savage, 1904:158, Hitchcock, 1935:397, and Young, 1935:133—142, as well as from a comparison of the total North American areal of the species Sporobolus vaginaeflorus — as outlined by Hitchcock, 1935:397, Fig. 821 — with the areals of the main vegetation zones and regions of this territory — as characterized and specified by R. Knapp, 1957), in the new stands around Zagreb it is attached to a rather specific habitat. These are chiefly flood areas with a sandy or gravel-containing porous soil which dries up completely during the summer months and on which, owing to human influence and occasional powerful action of the river’s current (such as the deposition of new layers of sand, local changes in the river bed, and the like) no vegatation of any higher organisational level has developed. In such uninhabited areas Sporobolus vaginaeflorus var. inaequalis develops a quite specific plant community to which, as a separate association, the authors have given the name of Poa-Sporoboletum vaginaeflori. The association is shown in Table I on the basis of seventeen phytocoenological records.
As can be seen from the table, the association Poa-Sporoboletum vaginaeflori consists of a comparatively large number of species. But of these species only 13 per cent, is present to the two highest degrees of constancy, while more than 70 per cent, is present only to the 1st and 2nd degrees of constancy. Nevertheless the association is extremely well characterized, its total characteristic grouping consisting of Sporobolus vaginaeflorus var. inaequalis, Poa compressa var. psammophila, Poa angustifolia, Blackstonia serótina, Vulpia myuros and Barbula acuta, as territorial and locally characteristic plants of the association; and Achillea millefolium ssp. pannonica, Tunica saxífraga, Sedum boloniense, Euphorbia cyparissias, Thymus pulegioides var. chamaedrys, Centaurea rhenana, Daucus carota, Plantago lanceolata, Medicago hipulina, Lotus corniculatus and Cichorium intybus as plants of the two highest degrees of constancy. Of the plants listed as characteristic for the association the greatest diagnostic value is offered by grasses such as Sporobolus vaginaeflorus var. inaequalis and Poa compressa var. psammophila, of which the former in particular is as a rule abundantly present and, in the typical facies of the association, even dominant. In addition to the typical facies (Table I, records 1—11) the authors have also encountered facies of the species Vulpia myuros (records 12 and 13 in the table), Thymus chamaedrys (record 14), Achillea pannonica (record 15), Festuca pseudovina (record 16), Dactylis glomerata (record 17) and others.
The table further shows that the association of Poa-Sporoboletum vaginaeflori, in view of its total floral structure, undoubtedly belongs to the vegetation class Festuco-Brometea Br.-Bl. et Tx. This is clearly proved by the fact that the typical species of this class (including also the separate characteristic species of the communities of the orders Festuco-Sedetalia Tx. and Festucetalia vallesiacae Br.-Bl. et Tx.; E. Oberdorfer, 1957:244—299), shown in the table, are present in the association in a comparatively large number, and in places even very abundantly.
On the other hand, however, no definite solution can yet be offered for the question of a more precise systematic position of this association within the class Festuco-Brometea, and the authors believe it will even be impossible to solve this question until the rest of the meadow vegetation in the region of our river sandbanks is investigated in a wider sense of the word. At present the authors consider it most likely that it will be possible to connect this association with the order Bromeialia and perhaps even with the Bromion alliance (in a wider sense), and therefore the common characteristic species of these two vegetation units are separately pointed out. For the same reason the table also shows separately the characteristic species of communities of the meadow class Molinio-Arrhenatheretea, which — in spite of a minor degree of constancy within the structure of our association — can be regarded within the scope of the class Festuco-Brometea as differential elements of the alliance Bromion s. 1. (cf. E. Oberdorfer, 1957:264—299).
From the syngenetic point of view the association Poa-Sporoboletum vaginaeflori forms an explicitly pioneer-type of community which is the first to settle on bare, sandy or gravelly ground in areas of river sandbanks more or less affected by floods, which are exposed to strong droughts during the summer and the beginning of the autumn. These are then habitats without vegetation, which in any case favour the development of various neophytes, as is Sporobolus itself, which therefore in our so far investigated area and within the association Poa-Sporoboletum vaginaeflori is joined individually by some other species of American origin, such as Stenactis annua, Asclepias syriaca, Erigeron canadensis, Ambrosia artemisiifolia, Oenothera biennis, and others.
In all places where the development of the pioneer vegetation of woods and undergrowth (Populetalia) is prevented, a specific meadow community of a higher organisational level is bound to develop from the association Poa-Sporoboletum in a further progressive series. Comparatively most important in this community are species like Andropogon ischaemum, Brachypodium pinnatum, Teucrium chamaedrys, Ononis spi- nosa, Potentilla verna f., Centaurea rhenana, Thymus chamaedrys, Achillea pannonica, Leontodón taraxacoides and others. This community no doubt belongs to the Festuco-Brometea class, and probably also to the order Brometalia or the Bromion (s. 1.) alliance, unless — as will be shown only by future investigations — it forms with the association Poa-Sporoboletum vaginaeflori a separate vegetation unit of a higher order.
Ključne riječi
Hrčak ID:
152785
URI
Datum izdavanja:
31.12.1960.
Posjeta: 1.174 *