Getting to the root of tree neighbourhoods: hectare-scale root zones of a neotropical fig

Sessile organisms interact locallyon the scaleof their body sizes, and one of the great advances in population and community ecology is the use of individual-based models to examine species interactions (Biondini 2001, Bolker & Pacala 1999, Pacala & Deutschman 1995, Pacala & Silander 1985, 1987; Silander & Pacala 1985). Canopies are often taken as a proxy for body size in the plant literature, even though roots can make up substantial amounts of a plant’s biomass, have productivity that equals or exceeds the above-ground parts, and are critical in both competition and mutualisms involving nutrient capture and water balance (Biondini 2001, Casper & Jackson 1997, Casper et al. 2003, Rajaniemi & Reynolds 2004, Robinson 2004). Root zones, however, are seldom incorporated in plant ecological studies because they are exceptionally difficult to measure, and the importance of intraand interspecific root interactions is little known (Schenk & Jackson 2002). Here we report the results of a field study on the spatial extent of roots in theneotropical fig,Ficus schultesii Durand (Moraceae), a canopy emergent common at the landscape-level in western Amazonia. We find that the area of their rooting zone exceeds their canopy area by a factor of 14–64-fold. While Ficus schultesii may be an extreme case, this example shows that representing plant size with canopy size can grossly underestimate the scale of plant interactions in tropical forests. The expansive root-zones of canopy emergent trees may make them keystone taxa in the structure of tropical soil microbial communities. The study was conducted in mature floodplain forest at the Cocha Cashu Biological Station in Manu National Park, Peru. While lying within the meander-belt of the