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Quantifying density-independent mortality of temperate tree speciesAuthor(s): Heather E Lintz; Andrew N. Gray; Andrew Yost; Richard Sniezko; Chris Woodall; Matt Reilly; Karen Hutten; Mark Elliott
Source: Ecological Indicators Volume 66, July 2016, Pages 1–9
Publication Series: Scientific Journal (JRNL)
Station: Pacific Northwest Research Station
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DescriptionForest resilience to climate change is a topic of national concern as our standing assets and future forestsare important to our livelihood. Many tree species are predicted to decline or disappear while othersmay be able to adapt or migrate. Efforts to quantify and disseminate the current condition of forests areurgently needed to guide management and policy. Here, we develop a new indicator to summarize rawdensity-independent mortality of forested stands by species from the last decade of the 20th century tothe first decade of the 21st century using forest inventory data. We define density-independent mortalityto be stand mortality by species due to processes unrelated to natural mortality from succession or standmaturation, which is marked by overall increase in tree girth at the expense of density of individuals. Weassess trends for 22 species on national forests in two U.S. states, Washington and Oregon. Populationsof some species including timber species have no or low overall levels of density-independent mortality(Juniperus occidentalis, Abies procera, Thuja plicata, Tsuga heterophylla, Pinus ponderosa, and Pseudotsugamenziesii). In contrast, other species demonstrate unsustainable levels of density-independent mortality(Pinus monticola, Arbutus menziesii, Pinus albicaulis, Abies lasiocarpa, Taxus brevifolia, Pinus contorta, Abiesgrandis, Picea englemanii, and Larix occidentalis). Additionally, the net potential for unsustainable levelsof density-independent mortality in standing populations does not necessarily warrant concern whenexamined across species for our study area and time period; however, when examined by species, thenumber of species in decline exceeds the number of species where mortality can be generally attributedto endogenous self-thinning. We argue that this work can aid management and policy decisions andour understanding of complex vegetation dynamics in a changing climate. Application of the indicatorat larger spatial scales and in conjunction with data on migration and establishment may be used toaddress questions such as, how can we make cost-effective management decisions to ensure long-termsustainability of tree species and forests? Tree species distributions across the landscape are complexsystems, and raw characterization of current trends occurring in forest inventories is important especiallygiven the uncertainty associated with the modeling and prediction of complex systems such as treespecies.
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CitationLintz, Heather E; Gray, Andrew N.; Yost, Andrew; Sniezko, Richard; Woodall, Chris; Reilly, Matt; Hutten, Karen; Elliott, Mark. 2016. Quantifying density-independent mortality of temperate tree species. Ecological Indicators. 66:1-9.
KeywordsTree, population, indicator, species, mortality
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