Whitebark pine mortality related to white pine blister rust, mountain pine beetle outbreak, and water availability

Abstract

Abstract. Whitebark pine (Pinus albicaulis) forests in the western United States have been adversely affected by an exotic pathogen (Cronartium ribicola, causal agent of white pine blister rust), insect outbreaks (Dendroctonus ponderosae, mountain pine beetle), and drought. We monitored individual trees from 2004 to 2013 and characterized stand-level biophysical conditions through a mountain pine beetle epidemic in the Greater Yellowstone Ecosystem. Specifically, we investigated associations between tree-level variables (duration and location of white pine blister rust infection, presence of mountain pine beetle, tree size, and potential interactions) with observations of individual whitebark pine tree mortality. Climate summaries indicated that cumulative growing degree days in years 2006-2008 likely contributed to a regionwide outbreak of mountain pine beetle prior to the observed peak in whitebark mortality in 2009. We show that larger whitebark pine trees were preferentially attacked and killed by mountain pine beetle and resulted in a regionwide shift to smaller size class trees. In addition, we found evidence that smaller size class trees with white pine blister rust infection experienced higher mortality than larger trees. This latter finding suggests that in the coming decades white pine blister rust may become the most probable cause of whitebark pine mortality. Our findings offered no evidence of an interactive effect of mountain pine beetle and white pine blister rust infection on whitebark pine mortality in the Greater Yellowstone Ecosystem. Interestingly, the probability of mortality was lower for larger trees attacked by mountain pine beetle in stands with higher evapotranspiration. Because evapotranspiration varies with climate and topoedaphic conditions across the region, we discuss the potential to use this improved understanding of biophysical influences on mortality to identify microrefugia that might contribute to successful whitebark pine conservation efforts. Using tree-level observations, the National Park Service-led Greater Yellowstone Interagency Whitebark Pine Long-term Monitoring Program provided important ecological insight on the size-dependent effects of white pine blister rust, mountain pine beetle, and water availability on whitebark pine mortality. This ongoing monitoring campaign will continue to offer observations that advance conservation in the Greater Yellowstone Ecosystem.

Cumulative Drought Stress Leads to a Loss of Growth Resilience and Explains Higher Mortality in Planted than in Naturally Regenerated Pinus pinaster Stands

“…Finally, and although the plantations were installed mainly at low-quality sites, the characteristics of these soils were strongly modified by the soil preparation work, so, the growth responses to climatic stress may be tightly conditioned by local site conditions [58]. All these factors may produce a loss of vigor in individual trees, and thus an increased vulnerability to drought events and other stress factors such as pests [59,60]. In this area, extensive tree damage has been also associated also with the Maritime Pine Bast Scale (Matsucoccus feytaudi; R.M.…”

Ecological monitoring and evidence‐based decision‐making in America's National Parks: highlights of the Special Feature

“…As noted previously, invasive annual grasses are the subject of study by Ashton et al (2016) and Witwicki et al (2016). The 6 years of monitoring in highelevation whitebark pine stands of the Greater Yellowstone Ecosystem by Shanahan et al (2016) revealed alarming rates of pine mortality and shifting tree age class dynamics caused by the Eurasian fungal disease, white pine blister rust. The 6 years of monitoring in highelevation whitebark pine stands of the Greater Yellowstone Ecosystem by Shanahan et al (2016) revealed alarming rates of pine mortality and shifting tree age class dynamics caused by the Eurasian fungal disease, white pine blister rust.…”

“…But NPS is confronted with tremendous conservation challenges presented by other invasions. The 6 years of monitoring in highelevation whitebark pine stands of the Greater Yellowstone Ecosystem by Shanahan et al (2016) revealed alarming rates of pine mortality and shifting tree age class dynamics caused by the Eurasian fungal disease, white pine blister rust. They also describe novel insights about the interactions between rust, mountain pine beetle outbreaks, and water availability that can guide conservation.…”

Trends in vital signs for Greater Yellowstone: application of a Wildland Health Index

“…Milder temperatures lead to higher populations and lethality of mountain pine beetle (Dendroctonus ponderosae), the major pest of pine (Pinus spp.) As a result of tree mortality due to the beetle, there is a shift to smaller trees which may now be more susceptible to blister rust (Shanahan et al 2016). From 1998 to 2010, an eruptive outbreak resulted in moderate to severe mortality of overstory whitebark pine (Pinus albicaulis) across 82% of its range in GYE.…”

“…The proportion of years with temperatures suitable for outbreaks was projected to increase from 0.56 during the 2000-2010 outbreak to 0.94 in 2070-2099. As a result of tree mortality due to the beetle, there is a shift to smaller trees which may now be more susceptible to blister rust (Shanahan et al 2016).…”