Intraspecific trait variation and species turnover in successional tropical forests: assessing trait imputation for community weighted means

Accounting for intraspecific trait variation (ITV) is crucial to plant ecology for vegetation modeling efforts. ITV can be substantial; however, it remains unclear how ITV influences community-weighted mean (CWM) trait estimates. We use leaf and root trait data from 423 trees of 72 species from 15 Angiosperm families in combination with community data from 164 25×25m plots comprising 580 species to evaluate the contributions of ITV and compositional turnover to CWMs, comparing unlogged primary tropical forest to selectively-logged and clear-cut secondary tropical forest. We also examine the effect of imputing missing trait values using phylogenetic generalized linear modeling (PhyloPars) on CWMs. For six of the seven traits, ITV negatively covaried with community compositional turnover to generate larger CWM differences between forest types than observed if ITV was not integrated. For example, plot average weighted mean specific leaf area was 10.7 and 10.4 m2 kg-1 for primary and secondary forests, not accounting for ITV, but shifted to 9.8 and 11.1 m2 kg-1 after doing so. Our results from 72-species assemblages were largely consistent with results using phylogenetically-imputed traits for the entire community. The contribution of ITV to CWMs ranged from 25 to 75%, with nearly all trait variation due to forest type attributable to ITV. CWM trait estimates became more conservative with forest age, whereas ITV for many traits showed an opposing acquisitive shift (i.e., increasing in leaf area or root length), and because of negative covariation between ITV and species turnover, forest age-related weighted-mean trait differences increased.