[52] A great vegetation zone, essentially homogeneous in character, stretches from Central Europe to Portugal (Fig. 9). Troll calls this the Holly Region. Nearest the ocean, it is the first of his three divisions of the forests of Western Europe. ⁽¹⁾ The second is the Beech Region, some of whose species are found mixed with those of the Holly Region in Iberia; the third, and farthest from the ocean, is the Oak Region, with which we shall not be concerned, as it does not extend into the peninsula.

The Holly Region, an area of mild winters and summers and with rainfall in all seasons of the year, includes northwestern Iberia on the west, and northern and central Germany on the east. Besides the eponymous holly (Ilex aquifolium) it is characterized by common gorse (Ulex europaeus), several of the heathers (especially Erica tetralix and E. cinerea), and the primrose (Primula acaulis). Troll's Beech Region lies to the [53] east and south of the Holly Region, but a large number of its species occur also in the latter and accompany it westward into humid Iberia. Some of these are : English oak (Quercus robur, which replaces beech in Galicia and Portugal), elm, ash, poplar, black alder, plane, birch (only in the extreme north of Portugal in the mountains), yew, sweet-gale (Myrica gale), foxgloves, the common fern, brambles, broom (Sarothamnus scoparius), wild plum (Prunus spinosa), hawthorne, ivy, and wild pear (Pyrus communis).

The striking difference in floristic composition and physiognomy of the vegetation between the humid Iberian border and the meseta, in the lee of the mountains in interior Iberia, is immediately apparent. None of the plants given above as typical of the Holly Region can tolerate the climatic conditions of the meseta. The same is true of other plants of Central and Western Europe such as the heather (Calluna vulgaris) and the brake (Pteris aquilina). The maritime pine (Pinus mantima) and the edible European chestnut (Gastanea sativa) of the northwest periphery of Iberia cannot tolerate the meseta [54] because of its drought. The cultivated olive, almond, and fig, Mediterranean plants that are grown in North Portugal, are excluded by winter cold. Although it is true that many of the species of the Beech Region are found not only in the Holly Region, but also on the meseta, in the latter area they form a negligible part of the plant community, whereas in the former the individuals are more numerous, show exceptional growth and there reach their southwestern distributional extreme in Europe. On the contrary, some species find suitable conditions for existence on the meseta but cannot tolerate the dampness of the extreme north and northwest. Perhaps the most common example is that of the hoim oak (Q. ilex).
 

The humid outer edges of Iberia can be subdivided into a northern zone and a western zone. The first includes all of Galicia except for a narrow area of the west coast below the [55] latitude of Santiago de Compostela. The second is essentially North Portugal but with an extension along the coast that includes the rias of Vigo, Pontevedra, and Arosa of Galicia. The western zone is distinct from the northern zone for two obvious reasons. In the first place, beech is not found in the western zone nor is birch (Betula sp.), except in remote, high mountains. Secondly, many of the Mediterranean species follow the west coast up into southern Galicia, but most of them are not to be found in the northern zone. Willkomm recognized the western zone as being one of special character because of the surprising combination of plants from diverse regions which thrive there. To quote him:

. . . this mixture of cultivated plants of south and central Europe is mostly in the north of Portugal and west Galicia, which gives to the picturesque valleys of this mountainous region an enchanting aspect, for there one sees trees of both pip and stone fruits, walnuts and chestnuts at the side of and mixed with figs, almonds, olives, oranges, Vines, and maize fields next to fields of rye and meadows of trefoil. . . . one finds araucarias, eucalyptus . . . willows, poplars, elms, ashes, lindens . . . associated with ornamental trees of North America, Cape of Good Hope, Japan and China. . . ⁽³⁾

The change between the two vegetational areas results especially from the difference in rainfall, in total amount as well as seasonal distribution. The extreme northwest of Galicia is a region of rainfall in all months of the year and its total is the highest of any Iberian littoral, whereas the North Portuguese area, plus the extension into southwest Galicia, has less rainfall in total and a summer drought period (Fig. 7). The northern limit of intensive olive, grape, and citrus cultivation occurs at approximately this division line, the line of Santiago-Orense.

The North Portuguese area, i.e. Willkomm's Western Zone of Humid Iberia, in its floristic composition and appearance, is [56] similar to northwest Europe. The maritime pine, the principal species on the predominantly siliceous soils, is found on the western slopes of the mountains to an elevation of forty six hundred feet. Along the open river valleys ( i.e. especially the Mondego and Tejo valleys ) it reaches into the interior. Even as far south as the valley of the Tejo it is the dominant tree Associated with it, but more restricted in range -- extending less far into the western littoral and not reaching to the same elevations on the mountain sides -- is the oak common to northwestem Europe, Quencus robur, which is largely replaced above thirteen hundred feet elevation by the Pyrenees oak ( Q. toza) . Both oaks are almost entirely strange to the region south of the Tejo. This is also true of gorse ( Ulex europaeus), Armenia manitima, A. elongata and Rhododendron baeticum, which are important members of the community. Endemics are few.

Within Portugal itself, other vegetational subdivisions can be recognized. The area north of the Mondego River differs greatly from that south of the Tejo River. Between the two rivers is an area of transition, particularly marked on the coastal fringe. The sharp differences in floristic composition between the areas are due fundamentally to climate. It is in these latitudes that there are considerable contrasts in rainfall and in the length of the summer drought. From north to south there is a diminution in total rainfall and an increase in the period of drought, the combination of which reaches a critical point at approximately the mouth of the Mondego River. The yearly total of rainfall at this point is only half of that at the mouth of the Douro River (approximately 24 inches compared to 50 inches). The summer drought period lasts almost five months at the mouth of the Mondego River as compared to less than three months at the mouth of the Douro River. ⁽⁴⁾ It may be added that drought conditions are accentuated toward the south by an increasing rate of evaporation.

[57] This area is strongly affected by the seasonal alternation between the periods of dominance of North Atlantic cyclones, with rainfall, and of South Atlantic high pressures, with subsident, stable air and drought. Thus while one might expect a transition in vegetational complex from that of the north, an edaphic factor, actually, is responsible for the abruptness of the change. The Mondego River marks the meeting of the siliceous rocks of the north with the calcareous materials on the seaward fringe of Portuguese Estremadura, lying between the Mondego and Tejo rivers. A great number of the northwest European plants of northern Portugal are siliceous and cannot tolerate, or tolerate poorly, the limy soils of western Estremadura. Most of the species limited to North Portugal have their southern coastal limit to the north of the Mondego.

In this area there is nearly a balance, in terms of numbers, between the species of northwestern Europe and those of the Mediterranean region. Thirty-eight per cent of the species are those of northwestern Europe (compared to 58 per cent in the area north of the Mondego River), and 42 per cent belong to the Mediterranean. In contrast to the north, in this middle area Iberian species have importance, and there is a greater degree of endemism. African (Mauritanian) species are almost four times as numerous (85 to 22). Maritime pine is far less important, due both to lower rainfall and to the calcareous soils. The English oak (Q. robur), its northern companion, is found in the transition area also, but both are largely restricted to the wetter slopes and siliceous soils, whereas the Portuguese oak (Q. lusitanica), a pronounced calciphyte, grows vigorously. This tree belongs quite properly in a transition area, for it is intermediate in appearance and morphology as compared to the other Portuguese oaks, deciduous, but with a tendency toward permanence of its leaves. Both the wild and the cultivated olive grow in the transition area, although on the calcareous soils they appear more as spiny bushes than as trees. Among the bushy plants, Quercus coccifera and Q. humilis are common, although somewhat exclusive of each other. Quercus humilis requires siliceous soils, whereas Q. coccifera, although [58] preferring siliceous, can tolerate calcareous soils. The genus Cistus is far more important here than in the area of the north ( thirty species compared to nine ) and Genista even more so ( fifty species as compared to ten ) . The same relation exists with regard to certain members of the mint family ( Labiatae). The genera Phlomis and Sidenitis, common in the transition area, do not appear at all north of the Mondego. Of thirteen species of Teucrium in Portugal, only one appears in the north, and of twenty species of Thymus only two are found there.
 

Portugal south of the Tejo River is quite a different floristic area. The species common to northwest Europe amount to less than one-third of the total, whereas Mediterranean species are the most numerous of all. While a few Iberian species are common and there is a liberal admixture of Algerian and Moroccan species, there is also an abundance of endemics. Maritime pine extends southward only to the Setúbal Peninsula, as it cannot tolerate the high summer temperatures and relatively low rainfall of the Alentejo. It is replaced, in the western Alentejo, by the Italian stone pine (Pinus pinea), which grows well on the quartzite sands of the region. However, the Alentejo in general is not a pine region. The dominant trees of the large eastern section are the cork and holm oaks (Quercus suber and Q. ilex respectively). Olives grow well, both the cultivated and, on the calcareous "islands," the wild olive. In large areas bushes are dominant, often to the complete exclusion of trees. Especially common is the gum cistus (Cistus ladaniferus), Genista spp., and Stauracanthus sp. Important also are Kermes oak (Quercus coccifera), Q. humilis, Halimium sp., various Ulexes and Pterospartum sp. The dwarf Mediterranean palm (Chamaerops humilis) and carob (Ceratonia siliqua), with their Portuguese center in the Algarve, reach their northern limit just to the south of the Tejo River in the Setúbal Peninsula.
 

It is difficult, at best, to establish vegetation areas where complex mixing of species occurs. This is made more difficult through alteration by man. For at least three thousand years the nature and the extent of forests has been under attack. The results of this pressure are difficult to determine, but there can be no doubt that extensive changes have taken place. For example, in the western Minho the forest ordinarily reaches to no more than about eighteen hundred feet elevation. There is no evident pedologic or climatic reason why the forests do not extend to the summits of the mountains. As can be readily seen from present practices, the need for fuels, fertilizers (especially for the species of the nitrogen-fixing Ulex), and pastures has led to the destruction of trees and their consequent replacement by shrubby vegetation and weeds. It has also added to the erosion of the upper mountain slopes. Nevertheless, whatever changes have been made by man, it may be safely assumed that the broad vegetational distinctions between the humid northwest and the interior, and those between the area with the Central European complex and the region with the Mediterranean complex, exist in response to environmental conditions.

Perhaps no reader will be surprised at the close coincidence between the areas of landforms, climate, soils, and vegetation that has been indicated in this and in previous chapters, but it will do no harm to emphasize the fact again, as it has decisive bearing upon the differences between culture regions in this part of the peninsula, the subject now to be considered.

1. Karl Troll, "Ozeanische Züge im Pflanzenkleid Mitteleuropas," Freie Wege Vergleichender Erdkunde, pp. 307-325.

2. With regard to the vegetation of Portugal, I am chiefly indebted to J. Daveau, "Géographie botanique du Portugal." 1. "La Flore littorale du Portugal," Boletim Sociedade Broteriana, XIV (1897), 3-54. 2. "La Flore des plaines et colimes voisines du littoral," ibid., XIX (1902), 3-140. 3. "Les Stations de la zone des plaines et collines," ibid., XXI (1904-1905), 16-85.

Also helpful has been H. Gaussen, "Le Milieu physique et la forêt au Portugal," Revue Géographique des Pyrénées et du Sud-Ouest, XI, Nos. 3-4 (1940), 219-267, and M. Willkomm, "As Regiões botánicas de Portugal," trans. from Grundzüge der Pflanzenverbreitung auf der iberischen Halbinsel (Die Vegetation der Erde, Vol. I) in Boletim da Sociedade Broteriana, XVII (Coimbra, 1900), 89-154; and in this chapter, as in so many others, Hermann Lautensach, especially in his 1932 work on Portugal, "Das Land als Ganzes," Petermann's Mitteilungen, No. 213 (Gotha, 1932), as well as his "A Individualidade geográfica de Portugal no conjunto da Península Ibérica," Boletim da sociedade de geografia de Lisboa, XLIX (1931), 362-409.

3. Willkomm, "As Regiões botánicas . . . ," p. 130.

4. O Clima de Portugal, Pts. V, VI.