Tropical forests typically achieve a leaf area index of 4–5 m2 leaf per m2 ground. Such numbers make these forests highly productive, but also indicate the intensity of shading and competition for light among individual plants. Light levels at the forest floor can be as low as 1–2% of open sky. In a large gap, however, light levels may reach 30% or more(Denslow, 1987). A persistent goal in tropical ecology has been to understand how this gradient of recruitment opportunity is exploited by different species (Turner, 2001). Wood density (WD) is one trait commonly assumed to indicate a species’ position along this gradient (Ter Steege & Hammond, 2001), yet empirical evidence supporting this assumption is sparse. Augspurger (1984) showed that saplings with a high WD were better able to resist infection by pathogens, suggesting the main structural benefits of dense wood were in making hard impenetrable stems. More recent studies have confirmed density to be correlated with growth rate and mortality (Enquist et al., 1999; Wright et al., 2003; King et al., 2006), but the mechanisms leading to increased longevity for high WD species were left open. New research by van Gelder et al., in this issue of New Phytologist(pp. 367–378), shows how WD can influence a wide range of structural characteristics likely to benefit saplings in shaded understoreys.