Rivers and Vegetation of the Iberian Peninsula
Rivers of the Iberian Peninsula
Factors Influencing Rivers
Peninsular rivers are conditioned by several factors:
- Climate: Rainfall significantly influences river flow throughout the year.
- Relief and Topography: These factors influence the organization of watersheds.
- Lithology: Determines the dominance of surface runoff or underground water.
- Vegetation: Slows evaporation, erosion, and flood risk.
- Human-made Works: Impact water supply and river regulation.
Fluvial Volume and Rate
a) River Flow
River flow is the amount of water passing through a given point in the river per second. It’s measured in m3/sec at gauging stations.
- Over the river’s course, the mouth typically has the highest flow. The largest rivers are the Ebro, Tagus, and Duero.
- Over time, river flow can vary annually, with periods of floods or low water levels.
b) River Regime
River regime refers to the changes in river flow.
- Nival Regime: Rivers originating in high mountains with frequent snowfall.
- Rainfall Regime: Rivers relying solely on rainfall.
- Mixed Regime: Rivers influenced by both snowmelt and rainfall (e.g., nivo-pluvial or pluvio-nival).
Watersheds
a) Watershed Definition
A watershed is the territory whose waters drain into a main river and its tributaries.
- Watersheds are separated by divides formed by mountain ridges.
- Within a basin, rivers flow through channels and form a hierarchical network from tributaries to the main river.
b) Watershed Basins of Spain
A watershed basin is the set of watersheds draining into a particular sea.
- Cantabrian Rivers: Short rivers originating in mountains near the coast. They have high erosive power due to steep slopes and regular flow.
- Atlantic Rivers: Long rivers originating near the Mediterranean and flowing into the Atlantic. They have low erosive power as they flow through plains. Their flow is abundant but with low water levels in summer.
- Mediterranean Rivers: Except for the Ebro, these rivers are short, originating in mountains near the sea. They experience severe erosion on deforested slopes. Their volume is low, and the rainfall regime is irregular, with low flow in summer and potential for catastrophic floods in autumn.
Balearic Islands and Canary Islands
The Balearic and Canary Islands lack proper rivers, instead having creeks or streams with low flow.
Vegetation of Spain
Factors Influencing Vegetation
Vegetation consists of plant formations or groups identified by their size and appearance. The three basic types are forests, scrublands, and grasslands.
- Physical Factors: Climate diversity (temperature and precipitation), relief diversity, and soil variety influence vegetation distribution. The Iberian Peninsula’s geographical location and the unique Canarian vegetation also play a role.
- Human Factors: Introduction of plant species for economic value. Vegetation resulting from human intervention is called secondary vegetation.
Vegetation Landscapes of Spain
2.1. Oceanic Climate Vegetation
a) Deciduous Forest
- Beech: Tall trees with straight trunks, smooth bark, and large leaves that fall in autumn. Tolerates heat and cold well and requires high humidity. Its wood is hard and of good quality.
- Oak: Doesn’t tolerate hot summers as well as beech and requires less moisture. Its wood is hard.
- Chestnut: A secondary vegetation formation that has expanded at the expense of oak, valued for its fruit and durable wood.
Due to deforestation, fast-growing trees like pine and eucalyptus have been planted.
b) Meadows, Moors, and Heaths
Moors and heaths are dense thickets. Meadows are herbaceous vegetation occupying large areas in oceanic landscapes.
2.2. Mediterranean Climate Vegetation
a) Evergreen Forest
- Holm Oak: The most characteristic tree of the Mediterranean climate. Drought-tolerant and adaptable to various soil types.
- Cork Oak: Needs mild winters, some moisture, and siliceous soils.
- Pine: A secondary formation adaptable to extreme temperatures, humidity, and dryness, as well as diverse soils.
b) Mediterranean Scrubland
Scrubland is a result of forest degradation by humans.
- Maquis: Dense, tall shrubland.
- Garrigue: Low-lying shrubs and bushes, leaving some areas uncovered.
- Steppe: Low grasses interspersed with thorny bushes, exposing poor soils.
2.3. Riparian Vegetation
Riparian forests consist of species like alder, willow, poplar, and elm, thriving in moist environments along rivers.
2.4. Mountain Vegetation
a) Alpine or Pyrenean Mountains
- Base Floor (up to 1200m): Holm oaks and other species.
- Subalpine Floor (1200-2400m): Conifers.
- Alpine Floor (above 2400m): Small shrubs and meadows.
- Snowy Floor (above 3000m): No vegetation.
b) Other Peninsular Mountains
- Base Floor: Forests typical of the surrounding climate (e.g., deciduous in the Atlantic, evergreen in the Mediterranean).
- Supraforestal Floor: Small shrubs like heather.
- Summit: Meadows in the Atlantic area and scrubland in the Mediterranean.