Spatial relationships between leaf area index and topographic factors in a semiarid grassland: Joint multifractal analysis

A considerable portion of Canada’s landmass is covered by grassland ecosystems. Insight into the grassland spatial heterogeneity will not only contribute to better understanding of the scale dependent ecological processes but will also help in management and monitoring. Leaf area index (LAI) is a key structural attribute of grassland that reflects primary production. It is well-known that topography controls grassland productivity and heterogeneity but little is known which topographic index correlates best with LAI at multiple scales. In this study, we have used multifractal and joint multifractal techniques to investigate how leaf area index in a semiarid grassland is linked with topographic factors at multiple scales. The topographic indices assessed in this study were wetness index, upslope length, and relative elevation. Our results show that field LAI is significantly correlated (P < 0.01) with the studied topographic factors and the effect of topography on grassland primary productivity is better explained by wetness index than upslope length or relative elevation. LAI, wetness index, and upslope length are multifractally distributed whereas distribution of relative elevation is monofractal. Joint multifractal analysis shows that the relationships between LAI and topographical factors are highly scale dependent, however, LAI is weakly correlated to relative elevation. Overall, this study suggests that the effect of topography on bioproductivity should be considered at multiple scales and multifractal and joint multifractal techniques are particularly useful in elucidating multi-scale spatial patterns of grassland ecosystems.