Fig. 2. Z values reported in studies on the species-area relationship in vascular plants. The points in the left panel correspond to individual studies and are labelled with the biome category of the area studied: T: tropical forest and tropical woodland; F: temperate deciduous forest, C: boreal forest, coniferous forest, wooded tundra and tundra; S: warm mixed forest, shrubland and savannah; D: grassland and desert; N: no specific biome. The red line joins up the means in each type; the error bars represent standard errors. The right panel shows the histogram of z-values of the species-area relationship in island studies of vascular plants, both oceanic islands and habitat fragments in mainland, fitted with a lognormal distribution. Source Sala et al. (2006). Copyright (c) 2005 Millennium Ecosystem Assessment. Reproduced by permission of Island Press, Washington, D.C.