Does site quality affect the additive basal area phenomenon?: results from Chilean old-growth temperate rainforests.

Complex old-growth forests with large emergent trees may support more basal area-BA than those without these trees. The so-called additive basal area phenomenon occurs when the presence of these emergent trees do not affect the basal area (BA) of the canopy trees. We studied two old-growth forests in south-central Chile with similar species composition and structure but contrasting soil quality. We sampled 57 1,000 m2 plots in a relatively high-quality site (Quillaipe) and 65 in a relatively low-quality site (Yaldad). We evaluated total stand BA, BA of emergent trees, BA of canopy trees, and the influence of the BA of emergent trees on total and canopy BA. Quillaipe accumulated on average 50% higher BA than Yaldad. The additive BA effect only occurred on the high quality site Quillaipe. A more detailed analysis showed that canopy associates were differentially affected in terms of BA depression with BA of emergent trees. The relative competitive ability of canopy species, as affected by their ecological traits and geographical distribution, presumably explain if BA of species or functional groups are depressed by the BA of emergents. Above-and below ground resource partitioning may be decisive mechanisms affecting the occurrence of additive BA accumulation in forest stands.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author