Down wood and biodiversity — implications to forest practices

Abstract

Many species require or use down wood (fine and coarse woody debris) as habitat. Where forestry has been practiced for several rotations large proportions of these species are considered threatened. Key attributes determining the suitability of down wood as habitat are decay stage, tree species, and size, specifically diameter. Both quantity and distribution of suitable down wood influence species' presence and abundance. We present a simple framework describing use of down wood based on broad natural history features, derive predictions from the framework, then test these by review and summary of literature. Our focus is terrestrial vertebrates, particularly in the Pacific Northwest. Species other than vertebrates are addressed to ensure that metrics derived for vertebrates also are appropriate for other organisms. Basic metrics are the same, but appropriate values span a larger range among nonvertebrates. Current evidence suggests that the ''extinction debt'' apparent for nonvertebrates is approaching for vertebrates. Predictions derived from underlying natural history hold when tested. From that basis we derive broad guidelines for forest planning and practice, and suggest how regional target values can be derived. Résumé :Plusieurs espèces nécessitent ou utilisent le bois mort (débris ligneux fins ou grossiers) comme habitat. Là où l'on a pratiqué la foresterie au cours de plusieurs rotations, on considère qu'une large proportion de ces espèces deviennent menacées. Les caractéristiques déterminant l'utilité du bois mort comme habitat regroupent l'état de décomposition, les espèces d'arbres et leurs dimensions, surtout le diamètre. Les quantités ainsi que la distribution de bois mort adéquat influencent la présence des espèces et leur abondance. Les auteurs présentent un cadre de travail simple décrivant l'utilisation du bois mort, basé sur des caractéristiques élargies d'histoire naturelle, déduisent des prédictions à partir d'un tel cadre, et les vérifient finalement par une revue et un résumé de la littérature. On met l'accent sur les vertébrés terrestres, particulière-ment de la région du Pacifique nord-ouest. On considère également d'autres espèces que des vertébrés, afin de s'assurer que les chiffres inférés pour les vertébrés sont également appropriés pour d'autres organismes. Les mesures de base restent les mêmes, mais les valeurs pertinentes couvrent un plus large spectre parmi les non-vertébrés. La preuve actuelle suggère que la « dette d'extinction » apparente pour les non-vertébrés approche celle des vertébrés. Les prédictions dérivées de l'histoire naturelle sous-jacente supportent la mise à l'épreuve. Sur cette base, les auteurs déduisent des directives larges pour la planification et la pratique forestière et suggèrent comment on peut en déduire des valeurs cible à l'échelle régio-nale.

Controls on Coarse Wood Decay in Temperate Tree Species: Birth of the LOGLIFE Experiment

“…Apart from its importance for biogeochemical cycling, dead wood in the forest is also a great source of biodiversity (Harmon et al 1986;Jonsson and Jonsson 2007;Wirth et al 2009). Northern forests in cool and cold biomes, for instance, support a wealth of wood-rot fungi (Odor et al 2006;Schmidt 2006;Hottola et al 2009), vertebrates (Bunnell and Houde 2010), diverse taxa of invertebrates (Grosser 1985;Grove 2002;Castro and Wise 2010;Dechene and Buddle 2010;Janssen et al 2011;Ulyshen et al 2011), lichens (Humphrey et al 2002) and bryophytes (Andersson and Hytteborn 1991;Humphrey et al 2002). Bacteria are among the first organisms to colonise dead wood and metabolise especially the easily degradable and accessible substrates (Schmidt 2006;De Boer and Van der Wal 2008).…”

Using reference conditions in ecosystem restoration: an example for riparian conifer forests in the Pacific Northwest

“…These studies suggest that in streams and riparian ecosystems, dead wood in the form of snags and down logs is essential to maintain biological diversity and thus should be important structural attributes to quantify when describing forest reference conditions. Throughout much of the northern hemisphere, old, complex and biologically diverse forested ecosystems have been cleared and replaced by young, structurally simple, species poor forests (Spies et al 1988, Bunnell andHoude 2010). Riparian forests have been particularly impacted because they are often the most accessible areas due to their location on low gradient ground and because transportation routes are often built within river corridors (Sedell and Duval 1985, Meehan 1991, Naiman et al 1993, Naiman et al 2000.…”

Modelling deadwood supply for biodiversity conservation: Considerations, challenges and recommendations

“…With the exception of carbon budget models, branches, roots and stumps are typically ignored in deadwood models. These deadwood elements are a potentially important resource from a biodiversity perspective (Bunnell andHoude 2010, Stokland et al 2012), and they should be accounted for in models designed to address biodiversity concerns, particularly if they are thought to be a limiting resource. However, data on decomposition dynamics for deadwood elements other than boles are lacking for many systems.…”

“…As wood transitions from being recently dead to stronglydecayed, it provides habitat to different organisms (Harmon et al 1986, Kruys et al 2002, Bunnell and Houde 2010, Stokland et al 2012. Commonly, five decay classes are used for downed wood and six to nine classes for live, declining and dead trees in studies related to biodiversity because of the variation in habitat used by wildlife (e.g., Thomas et al 1979, Hunter 1990).…”

“…Research on soil and tree productivity to assess sustainability in relation to biomass removal has been going on for over three decades in Canada (Titus et al 2010), but questions of sustainability related to biodiversity conservation have had far less attention. Recommendations from recent reviews on this topic (Bunnell andHoude 2010, Berch et al 2011) have suggested that deadwood availability could be used as a surrogate for biodiversity to help assess sustainability of high-utilization biomass harvesting systems.…”