Article

A REDWOOD TREE WHOSE CROWN MAY BE THE MOST COMPLEX ON EARTH

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Abstract

In the coastal forests of northern California, redwood (Sequoia sempervirens) reigns supreme. Individual trees can exceed 112 m in height, and individual forest stands can have a biomass over 3,000 metric tons per hectare. Ancient redwoods often have complex crowns consisting of many reiterated trunks, some of which are larger than full-size trees in other forests. This study focuses on the second largest known living redwood, a 91.5 m tall tree with a total stemwood volume of 1,032.8 m3. There are 134 reiterated trunks in its crown, accounting for 12.3 percent of its total stemwood volume. Five of these trunks are 1.0-2.6 m basal diameter, and fifteen are 0.5-1.0 m basal diameter. One section of the crown includes a class 6 reiteration (i.e., a trunk from a trunk from a trunk from a trunk from a trunk from a trunk from the main trunk). Many of the trunks are hydraulically linked to other trunks by fused branches. Deep layers of crown humus have accumulated on large branches and crotches formed by multiple trunks. This humus supports epiphytic ferns, shrubs, and trees, and it is home to a population of salamanders (Aneides vagrans). The tree also exploits this humus resource via adventitious roots.

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... Old-growth redwood forests contain some of the oldest and most structurally complex trees on the planet. These trees often live over 1000 years and develop highly individualized crowns shaped by natural forces (Van Pelt 2001). Disturbances (e.g., windfall, crown fires) that increase light availability within tree crowns stimulate new growth from damaged trunks and branches. ...
... When a trunk arises from a branch, the branch thickens in response to the added weight and hydraulic demand of the trunk, creating a " limb. " Trunks, limbs, and branches also become fused with each other during crown development (Sillett and Van Pelt 2001). The highly individualized crowns of complex redwoods offer a myriad of substrates and habitats for epiphytic plants and other arboreal organisms (Williams 2006). ...
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... Don) Endl. (Cupressaceae), a species that can live for more than 2500 years, and grows to heights exceeding 100 meters on productive soils (Sillett and Van Pelt 2000b). The term ''old-growth'' is traditionally defined by an absence of substantial logging history (Peterken 1996;Frelich and Reich 2003), but certain characteristics have become associated with these relatively undisturbed stands. ...
... Large lateral branches are also formed, which provide habitat features in the form of deep crotches and platforms, and vegetative sprouting from the tree bole allows for the creation of epicormic branches and root growth into arboreal soils. As a result, the canopies of S. sempervirens are more complex than any other coniferous species (Sillett and Van Pelt 2000b). ...
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... Pseudotsuga can approach 1000 yr in rainforests (Carder, 1995;Sillett et al., 2018b). Accumulation of damage and reiterated structure during longer lifespans allows Pseudotsuga to develop more complex crowns than Picea in the same way that Sequoia, which can live more than twice as long as Pseudotsuga, develops the most complex crowns of all (Sillett et al., 2015b;Sillett and Van Pelt, 2001). ...
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... 1000 years old are considerably larger in SESE than SEGI, and aboveground growth efficiency is more than twice as high in SESE as SEGI. Aside from higher longevity, these facts beg the question why the largest living trees are SEGI, and indeed there is some evidence of even larger SESE felled during the 20th century (Carder 1995, Sillett andVan Pelt 2001). ...
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... While the great height of redwoods has long been recognized, the extreme complexity of their crowns has only recently been appreciated. Canopy studies since 1996 have revealed that large redwoods have individualized crowns with multiple, reiterated trunks arising from other trunks and branches (Sillett, 1999;Van Pelt, 2000, 2001). Reiterated trunks in redwood are orthotropic stems with their own systems of plagiotropic branches (Sillett, 1999). ...
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