Abstract
Principal features of alpha and beta diversity for nine ecozones and two altitudinal gradients are presented (Fig. 17 and 16), although the types of diversity in them may vary considerably depending on community structure, topographic variety and different evolutionary processes. Under extratropical climatic conditions (including Mediterranean conditions), natural forests general exhibit fewer species and a less pronounced community diversity (Fig. 4 and 5) than traditionally cultivated landscapes (Fig. 9). The Mediterranean region of old in particular must be regarded as a very important genetic pool for weeds. As the result of man’s influence, plants originating there, and annuals in particular, have enriched neighbouring floristic regions. Under natural conditions, alpha and beta diversity are, in comparison, normally greater in ecozones with treeless tundras and steppes than in the forests of cold and temperate regions (Fig. 3 and 7).
In contrast to the situation in extratropical zones, it must be considered a general fact that any human impact on tropical regions and most subtropical regions with summer rain will reduce diversity. This is due to the loss of three characteristic life forms which constitute heterogeneity in tropical and subtropical forests: trees, climbers and epiphytes (Fig. 14 and 15). As a result, secondary successions lead to increasing species richness after abandonment — in contrast to Central Europe and the Mediterranean where it leads to a decrease (Fig. 6).
Consequently, when developing concepts for sustainability and environmental protection one has to consider these two contrasting zonal features of diversity: For the extratropical type of diversity, the maintenance of a dense pattern of different traditional land-use systems guarantees the highest level of alpha and beta diversity. In the tropics, greater diversity is ensured by combining nature conservation with optimized agriculture that imitates the structures and nutrition cycles of the region’s predominant natural ecosystems.
Resumen
Las principales caracteristicas de la diversidad alfa y beta en nueve ecozonas y dos gradientes altitudinales están presentes (figuras 17 y 16), aunque los tipos de diversidad pueden variar considerablemente dependiendo de la estructura de comunidades, la variedad topográfica y los diferentes procesos evolutivos. Bajo condiciones climáticas extratropicales (incluyendo las condiciones mediterráneas), los bosques naturales muestran por lo general menos especies y una diversidad de comunidades menos pronunciada (fig. 4 y 5) que los paisajes muy cultivados (fig. 9). La región mediterránea en particular ha de ser considerada una fuente genética muy importante de maleza. Como resultado de la influencia humana, las plantas ahí originadas, y en particulara las plantas anuales, han enriquecido las regiones vegetales colindantes. Bajo condiciones naturales, la diversidad alfa y beta suele ser también mayor en ecozonas con tundras despobladas de árboles y estepas que en los bosques de regiones frías y templadas (fig. 3 y 7).
Frente a la situatión en las zonas extratropicales, hay que considerar el hecho general de que cualquier impacto humano en las regiones tropicales y en la mayoria de las regiones subtropicales con lluvias de verano reducirá la biodiversidad. Esto se debe a la pérdida de très formas de vida características que constituyen la heterogeneidad tropical en los bosques tropicales y subtropicales, es decir: árboles, trepadoras y epifítas (flg. 14 y 15). Como resultado, sucesiones secundarias llevan a un aumento de la riqueza de especies después del abandono, frente a lo que ocurre en Centroeuropa y el Mediterrá;neo, donde llevan a un descenso (fig. 6).
Por lo tanto, a la hora de desarrollar conceptos para la sostenibilidad y protección medioambiental, hay que tener en cuenta estas dos características contrastivas de diversidad según zonas: Para el tipo de diversidad extratropical, el mantenimiento de un patrón denso de sistemas diferentes de uso tradicional del suelo garantiza el más alto nivel de diversidad alfa y beta. En los trópicos, se garantiza una mayor diversidad combinando la conservación de la Naturaleza con una agricultura optimizada que imite las estructuras y ciclos de nutrición de los ecosistemas naturales predominantes en la región.
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Richter, M. (2001). Zonal features of phytodiversity under natural conditions and under human impact — a comparative survey. In: Barthlott, W., Winiger, M., Biedinger, N. (eds) Biodiversity. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-06071-1_7
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DOI: https://doi.org/10.1007/978-3-662-06071-1_7
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