The importance of drought–pathogen interactions in driving oak mortality events in the Ozark Border Region

Abstract

Forests are expected to become more vulnerable to drought-induced tree mortality owing to rising temperatures and changing precipitation patterns that amplify drought lethality. There is a crucial knowledge gap regarding drought-pathogen interactions and their effects on tree mortality. The objectives of this research were to examine whether stand dynamics and 'background' mortality rates were affected by a severe drought in 2012; and to evaluate the importance of drought-pathogen interactions within the context of a mortality event that killed 10.0% and 26.5% of white (Quercus alba L.) and black (Q. velutina Lam.) oak stems, respectively, in a single year. We synthesized (i) forest inventory data (24 years), (ii) 11 years of ecosystem flux data with supporting biological data including predawn leaf water potential and annual forest inventories, (iii) tree-ring analyses of individual white oaks that were alive and ones that died in 2013, and (iv) documentation of a pathogen infection. This forest displayed stand dynamics consistent with expected patterns of decreasing tree density and increasing basal area. Continued basal area growth outpaced mortality implying a net accumulation of live biomass, which was supported by eddy covariance ecosystem carbon flux observations. Individual white and black oaks that died in 2013 displayed historically lower growth with the majority of dead trees exhibiting Biscogniauxia cankers. Our observations point to the importance of event-based oak mortality and that drought-Biscogniauxia interactions are important in shaping oak stand dynamics in this region. Although forest function has not been significantly impaired, these drought-pathogen interactions could amplify mortality under future climate conditions and thus warrant further investigation.

Forty-Eight Years of Forest Succession: Tree Species Change across Four Forest Types in Mid-Missouri

“…Previous studies have cited episodic drought as limiting to sugar maple [60,61], and moisture availability is generally lower in this portion of the range than elsewhere [62]. Following a recent extreme drought at BWREC in 2012, however, sugar maple was reported to have low mortality relative to other tree species [63], although the mortality was disproportionately observed in large-diameter sugar maple trees [42]. Thus, the effects of interactions between site characteristics and climate on sugar maple development and future dominance in this region are not fully understood.…”

“…In general, species in the red oak group are shorter lived than those in the white oak group, with red oak mortality in the Missouri Ozark region associated with a complex of interacting factors that include harsh growing conditions, insects and pathogens, and drought events [37][38][39][40][41]. An extreme drought in 2012 preceded elevated levels of canopy tree mortality at BWREC, with 26.5% of canopy black oaks experiencing mortality in 2013 in portions of the property [42]. Thus, the rate of canopy composition change is partially dependent on the rate of attrition of existing trees, which favors the longer-lived white oak species on these sites.…”

Land‐Atmosphere Responses to a Total Solar Eclipse in Three Ecosystems With Contrasting Structure and Physiology

“…Sensors are deployed on a 32‐m walk‐up scaffold tower that was established in 2004. For a more complete description of the MOFLUX forest and micrometeorological instrumentation, the reader is referred to the literature (Gu et al, ; Gu, Pallardy, Hosman, & Sun, ; Gu, Pallardy, Yang, et al, ; Wood et al, ; Yang et al, , ).…”

“…Sensors are deployed on a 32-m walk-up scaffold tower that was established in 2004. For a more complete description of the MOFLUX forest and micrometeorological instrumentation, the reader is referred to the literature (Gu et al, 2015;Gu, Pallardy, Hosman, & Sun, 2016;Gu, Pallardy, Yang, et al, 2016;Wood et al, 2018;Yang et al, 2007Yang et al, , 2010. Landmark (designated in 1978) and State Natural Area (designated in 1998) is owned, managed, and maintained by the University of Missouri, with support from the Missouri Department of Conservation.…”

Advancing global change biology through experimental manipulations: Where have we been and where might we go?

“…Historical records for precipitation (see also Figure ) often include a wide range of precipitation conditions and variation through time covering both very wet and very dry conditions (if the record is sufficiently long). Precipitation variation shows that we might expect to gather appropriate water availability and drought data from long‐term observational records (e.g., Gu, Pallardy, Hosman, & Sun, , ; Wood, Knapp, Muzika, Stambaugh, & Gu, ). However, if extremes become more extreme or more frequent, using projections of the mean change may not be the best statistic on which to base these conclusions.…”