Search

Sequoia sempervirens (redwood) is a long-lived, shade-tolerant tree capable of regeneration without disturbances and thus often present in all sizes within a single forest. In order to evaluate functional linkages among structures, plant distribution, and biodiversity in the canopy, we quantified all vascular plants from ground level to the treetops in an old-growth redwood forest (Prairie Creek Redwoods State Park, California, USA). This involved mapping terrestrial and epiphytic trees, shrubs, and ferns as well as climbing 27 trees up to 101 m tall within a 1-ha plot. We monitored canopy microclimates using sensor arrays that collected hourly data for up to 30 months. The plot held 4283 Mg/ha of aboveground dry mass in living plants, 95.4% of which was contributed by redwood. A high degree of structural complexity and individuality was evident in the crowns of the 14 largest trees in the form of reiterated trunks arising from main trunks, other trunks, and limbs. Thirteen species of vascular plants occurred as epiphytes in the plot, and all but one of these were restricted to the 14 largest trees. The evergreen shrub Vaccinium ovatum had the highest biomass of any epiphyte (212 kg/ha) followed by the evergreen fern Polypodium scouleri (196 kg/ha). The spatial aggregation of reiterated trunks was highly coincident with epiphyte masses, explaining 92% of the variation in fern and 75% of the variation in woody plant distribution along the vertical gradient. In addition to epiphyte biomass, there were 2366 kg/ha of soil in the canopy. Soils in crotches held 2-4 times as much water as soils on branches or limbs, and deeper layers held more water than shallower layers. During two years of monitoring, the volume of water stored in dead wood and soils in the canopy fluctuated between 24.7 m³ and 53.4 m³/ha. The vast majority of the plot's structure and arboreal habitats was held in the crowns of the 14 largest trees. Reiterated trunks and limbs on a small number of trees have important ecological functions in old-growth redwood forests, and it may be feasible to accelerate the development of structural complexity and biodiversity in maturing redwood stands. [ABSTRACT FROM AUTHOR]

Trees grow tall where resources are abundant, stresses are minor, and competition for light places a premium on height growth. The height to which trees can grow and the biophysical determinants of maximum height are poorly understood. Some models predict heights of up to 120?m in the absence of mechanical damage, but there are historical accounts of taller trees. Current hypotheses of height limitation focus on increasing water transport constraints in taller trees and the resulting reductions in leaf photosynthesis. We studied redwoods (Sequoia sempervirens), including the tallest known tree on Earth (112.7?m), in wet temperate forests of northern California. Our regression analyses of height gradients in leaf functional characteristics estimate a maximum tree height of 122-130?m barring mechanical damage, similar to the tallest recorded trees of the past. As trees grow taller, increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth, even with ample soil moisture. [ABSTRACT FROM AUTHOR]