Intraspecific trait variation and covariation across environmental gradients and the foliage–stem scaling in a widespread tree species

Background/Question/Methods The focus of the trait–based approach to study community ecology has mostly been on trait comparisons at the interspecific level.  This is mainly because at large–scale environmental gradients, species turnover overrates intraspecific trait variation.  In nature, however, there are many generalist species that can prevail in different environments.  For these species natural selection should favor mechanisms that maintain crucial trait relationships in the face of environmental challenges.  Here I first quantified intraspecific variation and covariation of leaf mass per area (LMA) and branch wood density (BWD) in monospecific forests of the widespread treeline species Nothofagus pumilio to determine its magnitude and whether it is related to environmental conditions (elevation and moisture).  Second, I determined whether foliar area–branch diameter scaling differs between environments or remain invariant within species between contrasting elevation and latitudinal situations.  I collected sun–exposed branches from 10 trees of Nothofagus pumilio from each of four populations at differing elevations and placed at each of four locations differing in soil moisture along 20 degrees of latitude in the southern Andes of Chile; from a Mediterranean–like climate in central Chile to Subantarctic climate in Tierra del Fuego.

Results/Conclusions Preliminary results show that the total variation in LMA (coefficient of variation (CV) = 23%) was twice that of BWD (CV = 11%).  The total variation in traits was never less than 25% when compared with interspecific studies.  Differences in elevation (temperature) for the most part explained variation in LMA, while differences in soil moisture explained the variation in BWD.  Traits covaried similarly in the elevational gradient only.  Thus, functional traits of Nothofagus pumilio exhibited no negligible variation; LMA varied for the most part with temperature, while BWD mostly varied with moisture.  Thus, I demonstrate that environmental variation can cause important trait variation without species turnover.  Secondly, given the strikingly different appearance between krummholz (crooked) trees at the elevational treeline and erect–stem, tall trees growing at lower elevations, and trees growing in Mediterranean–like climate in central Chile and others growing in the southernmost region of South America, I found that the foliar area–branch diameter scaling relationship was identical.  I conclude then that functional traits do vary with environmental gradients at the intraspecific level (without species turnover) and that these variations follow tight universal foliage–stem scaling rules (the maintenance of crucial relationships between traits).