Finally, human action is an extremely important factor in soil quality. As soon as the original forest was cleared, some modification of the soil was inevitable. Generally, farmers through the ages have maintained or improved soil quality by draining and manuring; especially noteworthy were the activities of Flemish peasants who virtually created their soil out of a marshy wilderness. Not all human intervention has been as successful, however. For example, the degradation of brown earths under heath in western France is not a natural feature but the product of human clearance and grazing practices. Large-scale arable cultivation with no use of animal manure is leading in places to soil degradation and soil erosion. Climate
The climate of France is generally favourable to cultivation. Most of France lies in the southern part of the temperate zone, although the subtropical zone encompasses its southern fringe. All of France is considered to be under the effect of oceanic influences, moderated by the North Atlantic Drift on the west and the Mediterranean Sea on the south. Average annual temperatures decline to the north, with Nice on the Côte d’Azure at 59 °F (15 °C) and Lille on the northern border at 50 °F (10 °C). Rainfall is brought mainly by westerly winds from the Atlantic and is characterized by cyclonic depressions. Annual precipitation is more than 50 inches (1,270 mm) at higher elevations in western and northwestern France, in the western Pyrenees, in the Massif Central, and in the Alps and the Jura. In winter eastern France especially may come under the influence of the continental high-pressure system, which brings extremely cold conditions and temperature inversions over the cities, during which cold air is trapped below warmer air, with consequent fogs and urban pollution. The climate of France, then, can be discussed according to three major climatic zones—oceanic, continental, and Mediterranean, with some variation in the Aquitaine Basin and in the mountains. The oceanic region
The pure oceanic climate prevails in the northwest, especially in Brittany. It is characterized by its low annual temperature variation, with Brest having an average temperature in January of 43 °F (6 °C) and in July of 61 °F (16 °C); by its extreme humidity and moderate rainfall (35 inches [890 mm] of rain falling through the year), accompanied by cloudiness and haze; by the frequency and sometimes the violence of the west winds that blow almost constantly; and by large variations in the weather, which can change several times a day. This oceanic climate is somewhat modified toward the north, where the winters are cooler, and toward the south, where, in the Aquitaine Basin, the winters are mild and the summers warmer. There is also less rainfall, although at Toulouse great summer storms are quite frequent. The continental region
The plains of the northeast are particularly affected by a continental climate. The city of Strasbourg has the greatest temperature range in France. Winter is cold, with an average of 83 days of frost and with snow cover for several weeks, although the weather is often sunny. In summer, storms cause maximum precipitation in the region in June and July, although total rainfall is comparatively light.
The climate of the Paris Basin is somewhere between the oceanic and the continental. The average yearly temperature is 53 °F (11 °C) in Paris. In addition, the relatively light annual rainfall (23 inches [58 cm]) follows a pattern of moderately heavy rain in spring and early summer and autumn, as in the oceanic countries, but the maximum amount of rain falls in summer, with storms of the continental type. In summer, spray irrigation is needed for crops in the continental climatic region and the Paris Basin. The Mediterranean region
In the southeast the Mediterranean climate extends over the coastal plains and penetrates the valley of the lower Rhône River as far as the Montélimar area. It affects the southern Alps, the southeastern slopes of the Cévennes and the Noire Mountains (in the Massif Central), and the eastern Pyrenees. The latitude and the proximity of the warm Mediterranean Sea contribute to mild winters, with an average temperature of 47 °F (8 °C) in January at Nice and with only a few days of frost. Precipitation is heavy and tends to fall in sudden downpours, especially in the autumn and spring, whereas summer is nearly completely dry for at least three months. In coastal Languedoc-Roussillon, annual rainfall totals can be as low as 17 to 20 inches (430 to 500 mm). It is a unique area because of its clear skies and the regularity of fine weather. This area is also subject to the violent north winds called the mistral, which are peculiar to southern France. The winds are caused by high-pressure areas from central France that move toward the low-pressure areas of the Gulf of Genoa. Permanent irrigation systems are characteristic of the Mediterranean lowlands.
The Aquitaine Basin is intermediate between the oceanic and the Mediterranean climates. Winters tend toward the oceanic type, but springs and summers are warm, although less arid than in the Mediterranean zone.
The mountains have varied climates. West-facing slopes in the Pyrenees have some of the highest precipitation figures in France. Snow cover stays from December to the end of April above 3,000 feet (900 metres) and is perpetual above 9,000 feet (2,700 metres) in the Alps and 10,000 feet (3,000 metres) in the Pyrenees. Locally, the contrast between the sunny south-facing valley slopes (adrets) and the shaded north-facing slopes (ubacs) can be of great importance for land use and settlement, while some intermontane basins can have quite advantageous climates as opposed to that of the surrounding peaks and plateaus. Plant and animal life Plant life
Vegetation is closely related to climate, so that in France it is not surprising that there are two major but unequal divisions: the Holarctic province and the smaller Mediterranean province. Most of France lies within the Holarctic biogeographic vegetational region, characterized by northern species, and it can be divided into three parts. A large area of western France makes up one part. It lies north of the Charente River and includes most of the Paris Basin. There the natural vegetation is characterized by oak (now largely cleared for cultivation), chestnut, pine, and beech in uplands that receive more than 23.6 inches (600 mm) of annual rainfall. Heathland is also common, as a predominantly man-made feature (created by forest clearance, burning, and grazing). Broom, gorse, heather, and bracken are found. South of the Charente, the Aquitaine Basin has a mixture of heath and gorse on the plateaus and several varieties of oak, cypress, poplar, and willow in the valleys. On the causses of the Massif Central and on other limestone plateaus, broom, heath, lavender, and juniper appear among the bare rocks. The vegetation of eastern France, constituting a second part of the Holarctic division, is of a more central European type, with trees such as Norway maple, beech, pedunculate oak, and larch; hornbeam is often present as a shrub layer under oak. The various high mountain zones form a third Holarctic part; with cloudy and wet conditions, they have beech woods at lower elevations, giving way upward to fir, mountain pine, and larch but with much planted spruce. Above the tree line are high mountain pastures, now increasingly abandoned, with only stunted trees but resplendent with flowers in spring and early summer.
The second major vegetation division of the country lies within the Mediterranean climatic zone and provides a sharp contrast with the plant life elsewhere in France. The pronounced summer drought of this zone causes bulbous plants to die off in summer and encourages xerophytic plants that retard water loss by means of spiny, woolly, or glossy leaves; these include the evergreen oak, the cork oak, and all the heathers, cistuses, and lavenders. Umbrella, or stone, pine and introduced cypress dominate the landscape. The predominant plant life of the plateaus of Roussillon is the maquis, comprising dense thickets of drought-resistant shrubs, characterized in spring by the colourful flowers of the cistuses, broom, and tree heather; in most areas this is a form that has developed after human destruction of the evergreen forest. A large part of Provence’s hottest and driest terrain is covered by a rock heath known as garigue. This region is a principal domain of the vineyard, but lemon and orange trees grow there also. At elevations of about 2,600 feet (790 metres), as in the Cévennes, deciduous forest appears, mainly in the form of the sweet chestnut. At elevations of 4,500 feet (1,370 metres) this gives way to a subalpine coniferous forest of fir and pine.