Weather underground: Subsurface hydrologic processes mediate tree vulnerability to extreme climatic drought.

Drought extent and severity have increased and are predicted to continue to increase in many parts of the world. Understanding tree vulnerability to drought at both individual and species levels is key to ongoing forest management and preparation for future transitions in community composition. The influence of subsurface hydrologic processes is particularly important in water-limited ecosystems, and is an under-studied aspect of tree drought vulnerability. With California's 2013-2016 extraordinary drought as a natural experiment, we studied four co-occurring woodland tree species, blue oak (Quercus douglasii), valley oak (Quercus lobata), gray pine (Pinus sabiniana), and California juniper (Juniperus californica), examining drought vulnerability as a function of climate, lithology and hydrology using regional aerial dieback surveys and site-scale field surveys. We found that in addition to climatic drought severity (i.e., rainfall), subsurface processes explained variation in drought vulnerability within and across species at both scales. Regionally for blue oak, severity of dieback was related to the bedrock lithology, with higher mortality on igneous and metamorphic substrates, and to regional reductions in groundwater. At the site scale, access to deep subsurface water, evidenced by stem water stable isotope composition, was related to canopy condition across all species. Along hillslope gradients, channel locations supported similar environments in terms of water stress across a wide climatic gradient, indicating that subsurface hydrology mediates species' experience of drought, and that areas associated with persistent access to subsurface hydrologic resources may provide important refugia at species' xeric range edges. Despite this persistent overall influence of the subsurface environment, individual species showed markedly different response patterns. We argue that hydrologic niche segregation can be a useful lens through which to interpret these differences in vulnerability to climatic drought and climate change.

Beyond isohydricity: The role of environmental variability in determining plant drought responses.

Despite the appeal of the iso/anisohydric framework for classifying plant drought responses, recent studies have shown that such classifications can be strongly affected by a plant's environment. Here, we present measured in situ drought responses to demonstrate that apparent isohydricity can be conflated with environmental conditions that vary over space and time. In particular, we (a) use data from an oak species (Quercus douglasii) during the 2012-2015 extreme drought in California to demonstrate how temporal and spatial variability in the environment can influence plant water potential dynamics, masking the role of traits; (b) explain how these environmental variations might arise from climatic, topographic, and edaphic variability; (c) illustrate, through a "common garden" thought experiment, how existing trait-based or response-based isohydricity metrics can be confounded by these environmental variations, leading to Type-1 (false positive) and Type-2 (false negative) errors; and (d) advocate for the use of model-based approaches for formulating alternate classification schemes. Building on recent insights from greenhouse and vineyard studies, we offer additional evidence across multiple field sites to demonstrate the importance of spatial and temporal drivers of plants' apparent isohydricity. This evidence challenges the use of isohydricity indices, per se, to characterize plant water relations at the global scale.

Hydrologic refugia, plants, and climate change.

Climate, physical landscapes, and biota interact to generate heterogeneous hydrologic conditions in space and over time, which are reflected in spatial patterns of species distributions. As these species distributions respond to rapid climate change, microrefugia may support local species persistence in the face of deteriorating climatic suitability. Recent focus on temperature as a determinant of microrefugia insufficiently accounts for the importance of hydrologic processes and changing water availability with changing climate. Where water scarcity is a major limitation now or under future climates, hydrologic microrefugia are likely to prove essential for species persistence, particularly for sessile species and plants. Zones of high relative water availability - mesic microenvironments - are generated by a wide array of hydrologic processes, and may be loosely coupled to climatic processes and therefore buffered from climate change. Here, we review the mechanisms that generate mesic microenvironments and their likely robustness in the face of climate change. We argue that mesic microenvironments will act as species-specific refugia only if the nature and space/time variability in water availability are compatible with the ecological requirements of a target species. We illustrate this argument with case studies drawn from California oak woodland ecosystems. We posit that identification of hydrologic refugia could form a cornerstone of climate-cognizant conservation strategies, but that this would require improved understanding of climate change effects on key hydrologic processes, including frequently cryptic processes such as groundwater flow.

Predicting ecosystem carbon balance in a warming Arctic: the importance of long-term thermal acclimation potential and inhibitory effects of light on respiration.

The carbon balance of Arctic ecosystems is particularly sensitive to global environmental change. Leaf respiration (R), a temperature-dependent key process in determining the carbon balance, is not well-understood in Arctic plants. The potential for plants to acclimate to warmer conditions could strongly impact future global carbon balance. Two key unanswered questions are (1) whether short-term temperature responses can predict long-term respiratory responses to growth in elevated temperatures and (2) to what extent the constant daylight conditions of the Arctic growing season inhibit leaf respiration. In two dominant Arctic species Eriophorum vaginatum (tussock grass) and Betula nana (woody shrub), we assessed the extent of respiratory inhibition in the light (RL/RD), respiratory response to short-term temperature change, and respiratory acclimation to long-term warming treatments. We found that R of both species is strongly inhibited by light (averaging 35% across all measurement temperatures). In E. vaginatum both RL and RD acclimated to the long-term warming treatment, reducing the magnitude of respiratory response relative to the short-term response to temperature increase. In B. nana, both RL and RD responded to short-term temperature increase but showed no acclimation to the long-term warming. The ability to predict plant respiratory response to global warming with short-term temperature responses will depend on species-specific acclimation potential and the differential response of RL and RD to temperature. With projected woody shrub encroachment in Arctic tundra and continued warming, changing species dominance between these two functional groups, may impact ecosystem respiratory response and carbon balance.

Scholarship of Teaching and Learning Research in Communication Sciences and Disorders Journals: An Exploratory Survey of the Recent Literature.

PURPOSE: Inspired by a preliminary survey of the Scholarship of Teaching and Learning (SoTL) literature conducted by Friberg et al. (2014), the current study aimed to expand the original study's findings-that SoTL was rarely published in the communication sciences and disorders (CSD) literature from 2009 to 2013-to the subsequent 8-year period (2014-2021). The latter period was of particular relevance considering the dissolution of one American Speech-Language-Hearing Association (ASHA)-affiliated publication and the addition of another non-ASHA-affiliated publication during that time. METHOD: Ten peer-reviewed CSD journals and the articles published in them were identified via a survey of the literature that used narrowly defined criteria developed in collaboration with a librarian. Five trained CSD graduate student raters compared a definition of SoTL to article abstracts to determine whether each should have been categorized as SoTL. Part 1 of the study investigated an 8-year time span, Part 2 investigated the remaining nine journals in the subsequent 5 years, and Part 3 investigated publication rates of SoTL in Teaching and Learning in Communication Sciences & Disorders (TLCSD) alone. RESULTS: Part 1 of the study revealed that publication rates of SoTL were extremely low in the 10 surveyed CSD journals in the 8-year time span investigated. A similar and diminishing trend was found in Part 2. Even smaller percentages of journals were dedicated to SoTL. Part 3 confirmed that relatively large amounts of CSD-specific SoTL have been published in TLCSD since its inception in 2017. CONCLUSIONS: As of 2021, SoTL articles continued to be uncommonly published in CSD journals. Until recently, scholarly teachers attempting to apply SoTL in the classroom had limited resources. Beginning in 2017, TLCSD has provided an outlet for SoTL, whereas other CSD journals seem to have published less of it. Reform of publication, peer review, tenure, and promotion policies and procedures is called for so that SoTL might be included as a valid scientific endeavor.