Architecture of a Cool-Temperate Rain Forest Canopy

Abstract

There have been few descriptions of tree crown asymmetry and its development. Here I present the most comprehensive geometric description to date of crown asymmetry within a forest canopy and use allometric, trigonometric, and growth analyses to tentatively identify the dominant cause.A 25.6 ϫ 25.6 m quadrat within a pure stand of Atherosperma moschatum Labillardière (Monimiaceae) in Tasmania was mapped with respect to the locations of tree trunks and crowns. Trunk girths and tree heights were also measured. Trunk girths were again measured ten years later. Standing biomass, growth rates, and structural properties of the trees were estimated from models.Crowns were more evenly spaced than trunks and showed a significant alignment by angle, both characteristics consistent with a tendency toward the optimal packing of the canopy. The displacement of crown locations from trunk locations was correlated both with the nearness of neighbors and with the east-facing aspect. For the quadrat as a whole, there was a projected tilt to the trees of 0.73 m 76.3Њ east of north. The displacement of crown locations from trunk locations was largely achieved early in tree development, consistent with a phototropic response to acute photosynthetically active radiation (PAR) limitation to growth in the understory, evident in the lower relative (projected canopy-area-specific) growth rates of the smaller trees, and with the propensity of A. moschatum to reproduce by vegetative sprouting.There was little evidence of size-dependent variation in the mechanical stresses within the trunks, but more detailed analysis of wood structure is needed. The overall height safety factor (a measure of buckling resistance) for the trees in the quadrat was 4.2, the highest reported factor to date for any tree species. Tasmania is an island in the ''roaring forties,'' and the high value of the safety factor is a likely response to strong and persistent winds.The estimates of the maximum growth rates of individual trees were 14.9 and 8.7 kg/ yr for each of two models. The estimates of the growth rate for the whole stand were 12.1 and 7 m 3 ·ha Ϫ1 ·yr Ϫ1 (8.5 and 4.9 metric tons per hectare per year, respectively).

Crown asymmetry in high latitude forests: disentangling the directional effects of tree competition and solar radiation

“…This increase documented in earlier studies is especially evident in aggregated populations, and similar to the findings here (Fig. ), several studies have shown that crown centers are often more regularly spaced compared to stem locations (Ishizuka , Olesen ; but see Getzin and Wiegand ).…”

“…Although our models clearly supported the role of directional solar radiation as a determinant of crown asymmetry, the influence of solar radiation or topography (determinants for the above‐canopy radiation) has been variably reported in earlier studies (Getzin and Wiegand ). In the boreal zone, characterized by low and directional sun angles this has been more consistently documented (Rouvinen and Kuuluvainen , Skatter and Kucera ), compared to studies from lower latitudes (Gavrikov et al , Frech et al ; but see Olesen ). Similarly, earlier studies on asymmetries owing to slope directions have reported varying results (Umeki , Muth and Bazzaz ).…”

“…In forest stands, this structure and the assembly pattern of tree crowns is shaped by the locations of individual trees, their interactions and growth patterns (Waller ). Particularly in structurally heterogeneous stands and within‐canopy light environments the plasticity of tree growth makes it possible for trees to develop asymmetric crowns and to avoid shading and forage solar radiation more efficiently (Sorrensen‐Cothern et al , Umeki , Olesen ). This light foraging behavior (sensu Karban ) has been shown to increase the photosynthetic production of an individual tree (Vincent and Harja ), potentially enhancing its growth, fecundity, and survival.…”

Crown Plasticity and Competition for Canopy Space: A New Spatially Implicit Model Parameterized for 250 North American Tree Species

“…see [13]), with the fact that trees are extremely plastic and opportunistic in their growth ([14], [15], [16], [17]). Because of this growth plasticity, canopy trees form complex, irregular, tessellating crowns, that usually do not grow into each other, and that tend to fill most or all of the canopy space (e.g.…”

Differences in allometry and population structure between native and invasive populations of a tropical tree

“…Allometric variation between height and diameter usually follows one of three main models: (1) geometric similarity (allometric coefficient = 1), with diameter and height increasing proportionally (King 1990;Niklas 1995;Olesen 2001;Silveira et al 2012), which serves as a null model of tree proportions, thus, not related to any mechanical principle (King 2011); (2) elastic similarity (coefficient = 0.67) where the diameter is just large enough to prevent falling or bending resulting from the individual's weight (McMahon 1973;McMahon & Kronauer 1976); and (3) stress similarity (coefficient = 0.5) where the physical stress resulting from the constant action of wind and weight of the plant (Dean & Long 1986) is evenly distributed along the trunk's height (McMahon & Kronauer 1976). Individual tree species may exhibit different height/trunk allometries in different environments (Archibald & Bond 2003;Weiner 2004;Siqueira 2006;Harja et al 2012), and the ability to be plastic for allometry may be important for the survival and spread of an introduced tree species across different environments, because allometry changes may result in an increase in fitness (Chun et al 2007) and/or in homeostasis (Davidson et al 2011).…”