Distance decay in spectral space in analysing ecosystem β‐diversity

Abstract

The use of spectral distance for explaining the phenomenon of distance decay in species similarity between two sites (based on the niche difference model) is presented here. Distance decay is based on the first law of geography: ‘the similarity between two sites decays with increasing the distance between them’. From an ecological point of view, this could be expressed as: ‘the β‐diversity between two sites should increase with an increase in spatial distance’. Beta‐diversity is defined as the amount of turnover in species composition from one site to another; and it plays a key role in biodiversity management and conservation, as it allows the detection of spatial gradients that act functionally in determining the spatial variation in species composition. This work demonstrates how the celebrated distance decay pattern achieved by means of spatial distance can be attained even with spectral distance, measured on Landsat near‐infrared images. It is argued that spectral heterogeneity represents a good proxy of β‐diversity of an area, becoming a valuable tool in biodiversity characterization at regional and global scales.

Acknowledgements

I would like to thank the Editor A.P. Cracknell and two anonymous referees for their assistance in improving a previous version of this paper. This study was part of the MONITO 3 – TopModel project (paper no. 29), which was funded by the European Community under the Regulations EEC 2157/92 and 3528/86 and the Regional Administration of Tuscany, represented by G. Vignozzi, R. Boretti and G.L. Landi. Many people contributed to the field work, including A. Gabellini, F. Casini, I. Bonini, A. Riva. L. Frati, M. Cetoloni, F. Ghini, D. Viciani, M. Boddi and G. Nicoletti. M. Ferretti, F. Bussotti, A. Cozzi, E. Cenni were involved in discussions on different aspects of the whole project and allowed the integration of the biodiversity sampling. I would particularly like to thank A. Chiarucci and C. Ricotta for their kind support and their advice on distance decay measurements. Finally, many thanks to G. Bacaro, who provided information about the forest estates analysed and interesting discussion regarding β‐diversity measurement.