Novus participants Arjan Meddens and Jeff Hicke (University of Idaho) recently published a Tansley Insight study analyzing the recent wide-spread die-off of piñon pine throughout the southwestern United States. The study (full citation below) combines 21 different observational studies throughout New Mexico and Arizona to assess current understanding of the roles of abiotic and biotic factors on pine mortality. For example, the role of drought in tree mortality is apparent (though the exact mechanisms are not clear), while the link with beetle infestations is poorly understood. Of particularly importance is the interaction of multiple stressors on tree mortality. The authors developed a conceptual framework linking the impact of various stressors on carbon limitation and hydraulic failure, which result in tree mortality.
The authors recommend several strategies for addressing our current knowledge gaps, including assessing explanatory variables such as beetle attack rates, drought severity, and stand characteristics; standardizing metrics for quantifying mortality severity; assessing beetle outbreak metrics (such as number of exit holes, distance to nearest attacked tree); temporal and spatial patterns of mortality following stressors; long-term growth and recovery of stands following stressors; and incorporation of manipulation experiments (ex. rainfall exclusion studies). Finally, the authors recommend that future studies include a broad range of potential mortality causes in order to reduce uncertainties about individual causes and better understand interactions between drivers of mortality. Such studies will help to increase our knowledge of tree mortality mechanisms, improve mortality forecasting, and aid in management of forest ecosystems.
Meddens AJH, JA Hicke, AK Macalady, PC Buotte, TR Cowles, CD Allen. Tansley Insight: Patterns and causes of observed piñon pine mortality in the southwestern United States. New Phytologist, DOI: 10.1111/nph.13193, available online.