The relationship between available area efficiency and area exploitation index in an even-aged coast redwood (Sequoia sempervirens) stand

The relation between the growth efficiency of individual trees and stands is critical for scaling up tree-level effects to stand-level phenomena. In this paper, we introduce a new measure of space occupancy - the area exploitation index (AEI), computed as the ratio between the leaf area and the area potentially available (APA) - which has the ability to scale up to the stand area. In this study, efficiency is defined as basal area increment per unit of individual projected tree leaf area (leaf area efficiency; LAE) and as basal area increment per unit of area potentially available for the tree (available area efficiency; AAE). Data were collected from a 28-year-old coast redwood (Sequoia sempervirens [D. Don] Endl.) plantation in California. Thirteen plots with five different treatments and a control were measured two times (2003 and 2007) for diameter, height, sapwood and bark thickness. Leaf area was estimated from the sapwood area of each tree. Using the coordinates of the trees, the area potentially available was calculated, weighted by the individual tree leaf area. A model to estimate leaf area efficiency from the area exploitation index and the leaf area index was developed. Multiplying LAE by AEI results in the efficiency of the area potentially available, which appears to depict a zone of optimal efficiency over AEI. Despite a rather weak correlation of the model (r = 0.59), an optimum area exploitation index (AEI(opt)) could be found for coast redwoods depending on LAI, with decreasing LAI leading to increasing AEI(opt).