Open Access

Fred-Günter Schroeder

• Um eine einfache Übersicht über die Gesamtgliederung der Vegetation der Erde zu erhalten, ist es zweckmäßig, die zugrundeliegenden Klimaunterschiede in ihre thermischen und hygrischen Komponenten zu zerlegen. Nach den übergeordneten thermischen Faktoren ergibt sich eine Gliederung in 7 breitenparallele thermische Zonen, deren Klimagrenzwerte und humide Normalvegetation zuerst besprochen werden (Abb. 1, 2). Die anschließend behandelten hygrisch bedingten Vegetationsunterschiede lassen in jeder der 5 nicht-polaren Zonen eine Aufstellung von 4 Humiditätsgraden zu (Abb. 2). Auf dem Hintergrund der historisch bedingten Florenunterschiede kann man die ökologischen Grundlagen der wichtigsten Vegetationstypen der Erde durch die Kombination von thermischer Zone und Humiditätsgrad beschreiben (Abb. 2; Vegetationskarte). Die Höhenstufung der Vegetation in den Gebirgen wird am Schluß kurz diskutiert. Die Stufen der extratropischen Gebirge können als modifizierte Auslieger der weiter polwärts gelegenen Zonen gelten. Die temperierte Waldstufe der tropischen Gebirge ist als eigenständige Einheit anzusehen, für die die Bezeichnung Oreotropische Stufe vorgeschlagen wird (Abb. 3).
• In spite of the very detailed knowledge on the world's vegetation, there is still no generally accepted system of global classification. An attempt for a new, easily understandable interpretation is presented here, using the facts of taxa and community distribution and considering their climatical backgrounds. Based on the vegetation pattern of humid regions, 7 latitudinal vegetation zones are distinguished: the two polar zones beyond the northern and southern timberlines, the Tropical Zone, and four extratropical (temperate) forest zones. Their differences depend on temperature climate, and their delimitations can be connected with certain approximate values within the two thermic gradients of summer warmth and winter minima. From north to south, the seven zones with their determining conditions are: Arctic (summer very cool, no month with mean temperature above +10°C), Boreal (short summer, 1 to 4 months above +10°C; winter cold), Nemoral (summer rather long, at least 5 months above +10°C; winter moderately cold with frosts below -10°C), Meridional (mild winter with frosts between 0 and -10°C), Tropical (no frost at all, no thermic seasons distinct enough to affect plant growth), Austral (same condition as Meridional), Antarctic (similar to Arctic). Within the five thermic forest zones, the vegetation changes according to the conditions of humidity. The hygric gradient from wholly humid to wholly arid can be usefully classified into 4 grades defined by the character of vegetation: Humid (with the forest typical for the respective zone), Semihumid (with forest considerably different from the humid type in life forms and/or taxa), Semiarid (beyond the hygric forest line, but with a + closed cover of woodland, scrub, or grassland), Arid (no closed vegetation cover: semidesert and desert). On the base of historically different floras, the ecological background for most of the world's major vegetation regions can be described by a combination of the thermic zones with the humidity grades (see Abb. 2 and the Vegetation Map). The altitudinal vegetation belts of extratropical mountains are considered as more or less modified outliers of the corresponding latitudinal zones. The temperate forest belt of tropical mountains, which combines genuine tropical characters with those of Austral and Meridional vegetation, is proposed to be called Oreotropical.