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

Abstract

12Complex old-growth forests with large emergent trees may support more basal area-BA than 13 those without these trees. The so-called additive basal area phenomenon occurs when the 14 presence of these emergent trees does not affect the basal area (BA) of the canopy trees, i.e. BA 15 of emergent and canopy trees add up. We studied two old-growth forests in south-central Chile 16 with similar species composition and structure but contrasting soil quality. We sampled 57 1,000 17 m 2 plots in a relatively high-quality site (Quillaipe) and 65 in a relatively low-quality site 18 (Yaldad), and evaluated total stand BA, BA of emergent trees, BA of canopy trees, and the 19 influence of the BA of emergent trees on total and canopy BA. Quillaipe accumulated on average 20 50% higher BA than Yaldad. The additive BA effect only occurred on the high quality site 21 Quillaipe. A more detailed analysis showed that canopy associates were differentially affected in 22 terms of BA depression with increasing BA of emergent trees in each site. The relative 23 competitive ability of canopy species, as affected by their ecological traits and geographical 24 distribution, presumably explain if BA of individual species or functional groups are depressed 25 by the BA of emergents. Above-and below ground resource partitioning may be decisive 26 mechanisms affecting the occurrence of additive BA accumulation in forest stands.

Evaluation of modeling strategies for assessing self‐thinning behavior and carrying capacity

“…Therefore, pure Nothofagus forests will not likely achieve the maximum potential carrying capacity. This finding is in line with the additive basal area concept (Lawes et al, ; Lusk, ), which has also been suggested in Nothofagus forests as well (Donoso & Lusk, ; Donoso & Soto, ). This idea suggested that both shade‐tolerant species contributed in adding more basal area to a forest because of resource‐use differentiation among various functional groups.…”

Individual-Tree Diameter Growth Models for Mixed Nothofagus Second Growth Forests in Southern Chile

“…However, the fine root biomass for N. dombeyi is concentrated in the first 30 cm of depth sharing the same space that companion species, thus the no nutrients competition between this two cohorts are related to the effect of ectomycorrhizal (Nothofagus), arbuscular mycorrhizae (companion species) and fertility of this volcanic soils [55,56]. This null or limited competition between cohorts agrees with findings from previous reports that support the theory of additive effects in growth for Nothofagus and companion species [55,57,58], that translates into independent behavior (and therefore models) between these two cohorts. Lastly, productivity predictors, such as SI, were not selected for modelling DBH growth in these forests, which is probably due to several factors, such as uncertainty on the quality of dominant height-site models, and measurement errors on dominant height and age, among others.…”

An approach to quantify climate–productivity relationships: an example from a widespreadNothofagusforest

“…Furthermore, as N. alpina is more shade-tolerant than N. dombeyi, the latter species would offer suitable shelter for enhancing growth rates of the former. This last finding is also in agreement with the additive basal area phenomenon (Lusk 2002, Lusk and Ortega 2003, Aiba et al 2007, Donoso and Lusk 2007, Donoso and Soto 2016, Parada et al 2018, where mixed forests can develop more biomass or basal area than pure stands. As far as I am aware, this is the first study in including habitat types for modeling productivity in temperate forests; thus, moving forward toward a better ecological understanding of habitats in forest productivity.…”