Measuring Them all: Individual-Based Functional Spatial Patterns in Mountain Grasslands

Questions: Spatial patterns of plant traits have rarely been studied at distances below 10 cm. Is it possible to detect nonrandom functional patterns at a very fine scale in mountain secondary grasslands? An analysis in terms of trait similarity, magnitude and density correlation can highlight the importance of different biotic and abiotic processes at these scales. We expect species identity to be of secondary importance if all individuals are identified by their measured traits, resulting in consistent patterns whether it is considered or not, especially if ITV (intraspecific trait variability) and functional overlap are high. Location: Natural reserve "Montagna di Torricchio," a strict reserve in the Marche region, central Apennines, Italy. Methods: Plant height, leaf area, and specific leaf area have been measured for each individual (1094 ramets) in 10 quadrats, divided into two grasslands differing in canopy cover. Functional redundancy and ITV were evaluated with overlap measures and variance partitioning. Marked point pattern statistics have been used to test for non-randomness of trait patterns either by considering all individuals at once or by excluding conspecific pairs. Results: At distances below 8 cm, we found evidence of trait convergence, pairs smaller than expected and negative density correlation. Above 8 cm, we found trait divergence and larger than expected pairs. We suggest biotic and abiotic causes for this, linked to physical packing or similarity in soil depth, respectively. The results differed between traits and between grasslands. The results were consistent whether conspecific pairs were excluded or not. There is a high functional overlap among species, and ITV has a large contribution to variability. Conclusions: We found nonrandom functional patterns in grasslands below 10 cm, an almost unexplored scale range in any vegetation. The approach used showed that taxonomic identity is less important than the functional setting of individuals at this scale.