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Relative growth rate and hemerobiotic state in the assessment of disturbance gradients

Abstract A method is discussed for describing the intensity of disturbance, based on the floristic composition of vegetation types. It includes the development of a hemerobiotic scale (from hemeros = cultivated). We attempted to relate this scale based on floristic patterns with functional parameters. Following a large phytosociological survey of the Roman area, we selected 19 species of herbs and grasses, widely differing in ‘hemeroby’, and measured their Relative Growth Rate (RGR). RGR varies between 0.13 and 0.21 d−1. A significant correlation between mean hemerobiotic value, resulting from the phytosociological study, and measured RGR of juvenile plants emerges. Although Specific Leaf Area (SLA) is highly correlated with RGR, and thus explains most of its variations, as previously found in other studies, it is only weakly related to hemerobiotic state. An additional data set with 78 species from the literature supports the conclusions. This approach allows a functional quantification of hemeroby which enables useful applications, for instance in cartography. A biotope map showing a steep gradient of disturbance impact in the city of Rome is presented as a preliminary test. Nomenclature: Pignatti (1982) for taxa; Rodwell et al. (2002) for syntaxa. Abbreviations: FW/DW = Fresh Weight/Dry Weight ratio; LAR = Leaf Area Ratio; LWR = Leaf Weight Ratio; RGR = Relative Growth Rate; RWR = Root Weight Ratio; SLA = Specific Leaf Area; ULR = Unit Leaf Rate.