Ecological Importance of Large-Diameter Trees in a Temperate Mixed-Conifer Forest

Abstract

Large-diameter trees dominate the structure, dynamics and function of many temperate and tropical forests. Although both scaling theory and competition theory make predictions about the relative composition and spatial patterns of large-diameter trees compared to smaller diameter trees, these predictions are rarely tested. We established a 25.6 ha permanent plot within which we tagged and mapped all trees ≥1 cm dbh, all snags ≥10 cm dbh, and all shrub patches ≥2 m2. We sampled downed woody debris, litter, and duff with line intercept transects. Aboveground live biomass of the 23 woody species was 507.9 Mg/ha, of which 503.8 Mg/ha was trees (SD = 114.3 Mg/ha) and 4.1 Mg/ha was shrubs. Aboveground live and dead biomass was 652.0 Mg/ha. Large-diameter trees comprised 1.4% of individuals but 49.4% of biomass, with biomass dominated by Abies concolor and Pinus lambertiana (93.0% of tree biomass). The large-diameter component dominated the biomass of snags (59.5%) and contributed significantly to that of woody debris (36.6%). Traditional scaling theory was not a good model for either the relationship between tree radii and tree abundance or tree biomass. Spatial patterning of large-diameter trees of the three most abundant species differed from that of small-diameter conspecifics. For A. concolor and P. lambertiana, as well as all trees pooled, large-diameter and small-diameter trees were spatially segregated through inter-tree distances <10 m. Competition alone was insufficient to explain the spatial patterns of large-diameter trees and spatial relationships between large-diameter and small-diameter trees. Long-term observations may reveal regulation of forest biomass and spatial structure by fire, wind, pathogens, and insects in Sierra Nevada mixed-conifer forests. Sustaining ecosystem functions such as carbon storage or provision of specialist species habitat will likely require different management strategies when the functions are performed primarily by a few large trees as opposed to many smaller trees.

Remnants of an ancient forest provide ecological context for Early Miocene fossil apes

“…We reduced the estimates of tree density and basal area of the R3 stumps by an approximation for the ratio of live trees (or basal area) to the sum of live trees, snags and stumps from a forest with long residence time for dead trees because the fossilized stump casts could represent living trees, snags or stumps, and we assumed that dead trees played a limited role in usable forest structure 18 . The total area used as a basis of developing forest estimates was 930.11 m 2 , comparable to other palaeoreconstructions 41 .…”

“…The total area used as a basis of developing forest estimates was 930.11 m 2 , comparable to other palaeoreconstructions 41 . We compared the calculated values of density and basal area for trees Z30 cm DBH and for trees Z60 cm DBH with those of contemporary forests taken from the Smithsonian Center for Tropical Forest Science plot network 18,21,42 .…”

CTFS‐ForestGEO: a worldwide network monitoring forests in an era of global change

“…In the tropics, calculations rely on standard allometric equations (e.g., Chave et al, 2005). In the temperate and boreal regions, species-and even site-specific allometric equations are sometimes available (e.g., Yosemite; Lutz et al, 2012), and generic allometries (e.g., Jenkins et al, 2003) are used when these are not available.…”

Larger trees suffer most during drought in forests worldwide

“…Droughts alter the structure and function of forests 4,5 . Site-and region-specific studies suggest that large trees, which play keystone roles in forests 6 and can be disproportionately important to ecosystem carbon storage 7 and hydrology 8 , exhibit greater sensitivity to drought than small trees 4,5,9,10 . Here, we synthesize data on tree growth and mortality collected during 40 drought events in forests worldwide to see whether this size-dependent sensitivity to drought holds more widely.…”

“…Drought-induced forest decline results in climate feedbacks including reduced CO 2 uptake, reduced carbon stocks, increased albedo and decreased evapotranspiration 21 . The impact of drought on forest structure and function depends on which trees are most adversely affected; greater mortality of small trees may modify future forest succession whereas mortality of large trees causes disproportionate losses of carbon and ecosystem function [5][6][7] . It has not been clear whether large or small trees would suffer more under drought stress.…”