Stand Structure, Aboveground Biomass and Production

Holm oak forests are structurally diverse (Gracia and Retana 1996). Marked variations in the main structural variables, such as stem density, basal area and canopy height, are induced by gradients of environmental heterogeneity (David et al. 1979; Barbero 1988; Romane et al. 1988; Floret et al. 1989), caused by the rough topography of the region and by historical differences in human use (Di Castri 1973; Terradas 1991; Barbero et al. 1992). Moreover, holm oak can reproduce through seeds (acorns) or vegetatively (sprouting from stumps and, to a lesser extent, from roots). Stems of both origins are usually found in the same stand, but, due to the slow rate of holm oak seedling establishment under managed coppice forests (Espelta et al. 1995; Chap. 7), restocking of holm oak forests during the cutting cycle is left to occur by natural regeneration from stump resprouting. Since each stool can produce large numbers of sprouts after disturbances (Giovannini et al. 1992; Retana et al. 1992), stem density can be very high in stands that have been harvested or otherwise disturbed.