When a tree falls: Controls on wood decay predict standing dead tree fall and new risks in changing forests

• Published in: PloS one Vol. 13; no. 5; p. e0196712
• Main Authors: Oberle, Brad, Ogle, Kiona, Zanne, Amy E, Woodall, Christopher W
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 09.05.2018; Public Library of Science (PLoS)
• Subjects: Analysis; Biology and Life Sciences; Carbon; Carbon cycle; Climate change; Data bases; Dead wood; Decay; Decay rate; Decomposition; Durability; Earth Sciences; Ecology and Environmental Sciences; Emission standards; Emissions; Environmental changes; Erosion resistance; Forest carbon; Forest ecology; Forest ecosystems; Forest management; Forests; Influence; Internet; Laboratories; Physical Sciences; Public safety; Respiration; Service life; Snags; Sustainable development; Technical education; Temperature; Temperature effects; Terrestrial ecosystems; Terrestrial environments; Topography; Trees; Tropical forests; Wildlife; Wildlife conservation; Wildlife habitats; Wildlife management; Wood; Wooden structures; United States; Florida; United States > US; North America; Arizona; Missouri
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0196712

When standing dead trees (snags) fall, they have major impacts on forest ecosystems. Snag fall can redistribute wildlife habitat and impact public safety, while governing important carbon (C) cycle consequences of tree mortality because ground contact accelerates C emissions during deadwood decay. Managing the consequences of altered snag dynamics in changing forests requires predicting when snags fall as wood decay erodes mechanical resistance to breaking forces. Previous studies have pointed to common predictors, such as stem size, degree of decay and species identity, but few have assessed the relative strength of underlying mechanisms driving snag fall across biomes. Here, we analyze nearly 100,000 repeated snag observations from boreal to subtropical forests across the eastern United States to show that wood decay controls snag fall in ways that could generate previously unrecognized forest-climate feedback. Warmer locations where wood decays quickly had much faster rates of snag fall. The effect of temperature on snag fall was so strong that in a simple forest C model, anticipated warming by mid-century reduced snag C by 22%. Furthermore, species-level differences in wood decay resistance (durability) accurately predicted the timing of snag fall. Differences in half-life for standing dead trees were similar to expected differences in the service lifetimes of wooden structures built from their timber. Strong effects of temperature and wood durability imply future forests where dying trees fall and decay faster than at present, reducing terrestrial C storage and snag-dependent wildlife habitat. These results can improve the representation of forest C cycling and assist forest managers by helping predict when a dead tree may fall.