The importance of large-diameter trees to the creation of snag and deadwood biomass

Abstract

Background Baseline levels of tree mortality can, over time, contribute to high snag densities and high levels of deadwood (down woody debris) if fire is infrequent and decomposition is slow. Deadwood can be important for tree recruitment, and it plays a major role in terrestrial carbon cycling, but deadwood is rarely examined in a spatially explicit context. Methods Between 2011 and 2019, we annually tracked all trees and snags ≥1 cm in diameter and mapped all pieces of deadwood ≥10 cm diameter and ≥1 m in length in 25.6 ha of Tsuga heterophylla / Pseudotsuga menziesii forest. We analyzed the amount, biomass, and spatial distribution of deadwood, and we assessed how various causes of mortality that contributed uniquely to deadwood creation. Results Compared to aboveground woody live biomass of 481 Mg ha−1 (from trees ≥10 cm diameter), snag biomass was 74 Mg ha−1 and deadwood biomass was 109 Mg ha−1 (from boles ≥10 cm diameter). Biomass from large-diameter trees (≥60 cm) accounted for 85%, 88%, and 58%, of trees, snags, and deadwood, respectively. Total aboveground woody live and dead biomass was 668 Mg ha−1. The annual production of downed wood (≥10 cm diameter) from tree boles averaged 4 Mg ha−1 yr−1. Woody debris was spatially heterogeneous, varying more than two orders of magnitude from 4 to 587 Mg ha−1 at the scale of 20 m × 20 m quadrats. Almost all causes of deadwood creation varied in importance between large-diameter trees and small-diameter trees. Biomass of standing stems and deadwood had weak inverse distributions, reflecting the long period of time required for trees to reach large diameters following antecedent tree mortalities and the centennial scale time required for deadwood decomposition. Conclusion Old-growth forests contain large stores of biomass in living trees, as well as in snag and deadwood biomass pools that are stable long after tree death. Ignoring biomass (or carbon) in deadwood pools can lead to substantial underestimations of sequestration and stability.

Crowding, climate, and the case for social distancing among trees

“…By creating advantageous local neighborhoods around specific trees, targeted density reduction could provide a way to minimize mortality risk for trees that are of particular socioecological importance (Larson & Churchill, 2012). Large‐diameter trees, for example, are a key component of fire‐tolerant old‐growth forests (Larson et al, 2013; Lutz et al, 2018, 2020; Lutz, Struckman, Furniss, et al, 2021; Lutz, Struckman, Germain, et al, 2021), yet they are in decline at regional and global scales (Lindenmayer et al, 2014; Lutz et al, 2009) and are particularly vulnerable to compound disturbance events (Furniss, Larson, et al, 2020; Stephenson et al, 2019). These results provide further evidence that targeted silvicultural management (e.g., density reduction around large trees) could be an effective strategy to mitigate the susceptibility of these long‐lived individuals to rapid ecological changes.…”

Litter eco-hydrological function characteristics of three typical plant communities in the area of Karst peak-cluster depressions from Guizhou, China

“…Scholars have carried out a large number of studies on the ecological functions of forest litter in China and other countries, mainly focusing on the litter reserves [8,9], hydrological function [10], decomposition process and rate [11][12][13], nutrient release characteristics [14,15], ecological stoichiometry [16,17], characteristics of the microbial community in the litter layer [18,19], the response of litter decomposition to the environment [20,21], and decomposition law model [22]. Litter is abundant in Pacific Northwest forests that have been without fire and timber harvest long enough for trees to grow, die, and fall [23]. In a study of changes in the physical properties and water repellency of litter in central Poland, litter was found to increase water storage in forest ecosystems [24].…”

The largest trees in Australia

“…Relatively little is known about the global distribution of trees with a large circumference (Lutz et al, 2018). Our list of the 20 trees with the largest circumference suggests that, in Australia, these trees are primarily found in the southeast and southwest of the continent (Table 2, Figure 3).…”