Todd Dawson

University of California, Berkeley | UCB · Department of Integrative Biology

Observations show vulnerability segmentation between stems and leaves is highly variable within and between environments. While a number of species exhibit conventional vulnerability segmentation (stem P 50 < ${P}_{50}\lt $ leaf P 50 ${P}_{50}$ ), others exhibit no vulnerability segmentation and others reverse vulnerability segmentation (stem P 50...

The long-standing assumption that aboveground plant litter inputs have a substantial influence on soil organic carbon storage (SOC) and dynamics has been challenged by a new paradigm for SOC formation and persistence. We tested the importance of plant litter chemistry on SOC storage, distribution, composition, and age by comparing two highly contra...

- Producing and maintaining flowers is essential for reproduction in most angiosperms, underpinning population persistence and speciation. Although the physiological costs of flowers often oppose pollinator selection, these physiological costs have rarely been quantified. - We measured a suite of physiological traits quantifying the water and carbo...

Understanding climate change impacts on the Cape Floristic Region requires improved knowledge of plant physiological responses to the environment. Studies examining physiological responses of mountain fynbos have consisted of campaign-based measurements, capturing snapshots of plant water relations and photosynthesis. We examine conclusions drawn f...

Premise: Epiphytes are abundant in ecosystems such as tropical montane cloud forests where low-lying clouds are often in contact with vegetation. Climate projections for these regions include more variability in rainfall and an increase in cloud base heights which would lead to drier conditions both in the soil and atmosphere. While recent studies...

Epiphyte communities comprise important components of many forest ecosystems in terms of biomass and diversity, but little is known regarding trade-offs that underlie diversity and structure in these communities or the impact that microclimate has on epiphyte trait allocation. We measured 22 functional traits in vascular epiphyte communities across...

Plants are critical mediators of terrestrial mass and energy fluxes, and their structural and functional traits have profound impacts on local and global climate, biogeochemistry, biodiversity, and hydrology. Yet Earth System Models (ESMs), our most powerful tools for predicting the effects of humans on the coupled biosphere-atmosphere system, simp...

Root‐associated fungal communities modify the climatic niches and even the competitive ability of their hosts, yet how the different components of the root microbiome are modified by habitat loss remains a key knowledge gap. Using principles of landscape ecology, we tested how free‐living versus host‐associated microbes differ in their response to...

Climate warming in recent decades has negatively impacted forest health in the western United States. Here, we report on potential Early Warning Signals (EWS) for drought-related mortality derived from measurements of tree-ring growth and carbon isotope discrimination (∆ 13 C), primarily focused on ponderosa pine (Pinus ponderosa). Sampling was con...

Epiphyte communities comprise important components of many forest ecosystems in terms of biomass and diversity, but little is known regarding trade-offs that underlie diversity and structure in these communities or the impact that microclimate has on epiphyte trait allocation. We measured 22 functional traits in vascular epiphyte communities across...

Klein (1) challenges two interpretations in Niespolo et al. (2). Regarding his first point, we maintain that Ysterfontein 1 (YFT1) does provide the oldest known example of full coastal adaptation as indicated by the presence of shell middens (cf. ref. 3). Klein inaccurately characterizes the age of the deepest shell midden layers at Klasies River M...

Water stored in tree stems (i.e., trunks and branches) is an important contributor to transpiration that can improve photosynthetic carbon gain and reduce the probability of cavitation. However, in tall trees the capacity to store water may decline with height because of chronically low water potentials associated with the gravitational potential g...

Significance For most of its path through plant bodies, water moves in conduits in the wood. Plant water conduction is crucial for Earth’s biogeochemical cycles, making it important to understand how natural selection shapes conduit diameters along the entire lengths of plant stems. Can mathematical modeling and global sampling explain how wood con...

Significance Novel ²³⁰ Th/U burial dating of ostrich eggshells complements other dating methods applicable to archaeological materials beyond the range of radiocarbon dating. New ages for the Ysterfontein 1 (YFT1) shell midden show it accumulated rapidly between ∼120 to 113 ka closely following the Last Interglacial sea-level highstand. The ages sh...

Significance A fundamental association between sustained water transport and downstream tissue survival should select for xylem that avoids embolism in long-lived woody plants. Previous studies suggest that long-vessel species, such as oaks and vines, are more susceptible to drought-induced loss of function than other species. We show that western...

The large-scale patterns of movement for the Sharp-shinned Hawk (Accipiter striatus), a small forest hawk found throughout western North America, are largely unknown. However, based on field observations we set out to test the hypothesis that juvenile migratory A. stria-tus caught along two distinct migration routes on opposite sides of the Sierra...

The spatiotemporal dynamics of plant water sources are hidden and poorly understood. We document water source use of Quercus garryana growing in Northern California on a profile of approximately 50 cm of soil underlain by 2–4 m of weathered bedrock (sheared shale mélange) that completely saturates in winter, when the oaks lack leaves, and progressi...

In Mediterranean-type climates, asynchronicity between energy and water availability means that ecosystems rely heavily on the water-storing capacity of the subsurface to sustain plant water use over the summer dry season. The root-zone water storage capacity ( S m a x [L]) defines the maximum volume of water that can be stored in plant accessible...

Stable isotope ratios of water (δ ¹⁸ O, δ ² H) have long been used to study a core question in plant ecology and ecohydrology: ‘From where do plants take up water?’ Indeed, decades of research has involved sampling potential plant water sources in the subsurface, classifying those sources as distinct endmembers (e.g. deep vs. shallow soil waters) a...

Tropical montane cloud forests support abundant epiphytic vascular plant communities that serve important ecosystem functions, but their reliance on atmospheric inputs of water may make them susceptible to the drying effects of rising cloud bases and more frequent droughts. We conducted a common garden experiment to explore the combined effects of...

Climate warming is facilitating the expansion of many cold‐sensitive woody species in woodland‐grassland ecotones worldwide. Recent research has demonstrated that this range expansion can be further enhanced by positive vegetation‐microclimate feedbacks whereby woody canopies induce local nocturnal warming, which reduces freeze‐induced damage and f...

Amazonian droughts are increasing in frequency and severity. However, little is known about how this may influence species‐specific vulnerability to drought across different ecosystem types. We measured 16 functional traits for 16 congeneric species from six families and eight genera restricted to floodplain, swamp, white‐sand or plateau forests of...

Globally, coffee has become one of the most sensitive commercial crops, being affected by climate change. Arabica coffee (Coffea arabica) grows in traditionally shaded agroforestry systems in tropical regions and accounts for ∼70 % of coffee production worldwide. Nevertheless, the interaction between plant and soil water sources in these coffee pla...

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 pa...

Relatively mesic environments within arid regions may be important conservation targets as 'climate change refugia' for species persistence in the face of worsening drought conditions. Semi-arid southern California and the relatively mesic environments of California's Channel Islands provide a model system for examining drought responses of plants...

The emergence of critical zone (CZ) science has provided an integrative platform for investigating plant ecophysiology in the context of landscape evolution, weathering, and hydrology. The CZ lies between the top of the vegetation canopy and fresh, chemically unaltered bedrock and plays a pivotal role in sustaining life. We consider what the CZ per...

Fog and low-lying cloud (fog) play a significant role in the maintenance of ecosystems, from desert to alpine and from coastal to inland systems. Our central thesis is that fog provides ecosystems with critical water and nutrient subsidies, and also delivers pollutants, that often control ecosystem function. Fog is a medium, vector, and connector....

To explore the role of past environmental changes in shaping interspecific differences in genetic structure among tuco-tucos (Rodentia: Ctenomyidae, Ctenomys) from the Limay Valley of northern Patagonia, we compared δ¹³C and δ¹⁸O values for modern and historical tooth enamel from the colonial tuco-tuco (C. sociabilis) and the parapatric Patagonian...

Methods are lacking to characterize critical zone (CZ) structure at spatial scales relevant to earth system and dynamic global vegetation models. This knowledge gap results in poor quantification of CZ plant-available water storage capacity, hindering realistic prediction of the response of plants and streamflow to anticipated changes in the hydrol...

The ratio of leaf-internal (ci) to ambient (ca) partial pressure of CO2, defined here as χ, is an index of adjustments in both leaf stomatal conductance and photosynthetic rate to environmental conditions. Measurements and proxies of this ratio can be used to constrain vegetation models uncertainties for predicting terrestrial carbon uptake and wat...

Key message In the Earth’s tallest tree species, axial variation in conduit size matches theoretical predictions minimizing the accumulation of hydraulic resistance with height growth, within a constraint of maximum conduit diameter. Abstract Hydraulic limitations to tree height can be mitigated by widening the conducting elements toward a tree’s...

On a global scale, coffee has become one of the most sensitive commercial crops that will be affected by climate change. The majority of Arabica coffee (Coffea arabica) grows in traditionally shaded agroforestry systems and accounts for ∼ 70 % of the coffee production worldwide. Nevertheless, the interaction between plant and soil water sources in...

Plain Language Summary When does a shortage of precipitation become a shortage of water supply to plants? In rain‐dominated seasonally dry climates, the answer depends on how water is stored belowground. Here we propose—perhaps counterintuitively—that low water storage capacity in Earth's critical zone (which includes soil and weathered bedrock) re...

Current climate change scenarios indicate warmer temperatures and the potential for more extreme droughts in the tropics, such that a mechanistic understanding of the water cycle from individual trees to landscapes is needed to adequately predict future changes in forest structure and function. In this study, we contrasted physiological responses o...

Vulnerability to embolism varies between con‐generic species distributed along aridity gradients, yet little is known about intraspecific variation and its drivers. Even less is known about intraspecific variation in tissues other than stems, despite results suggesting that roots, stems and leaves can differ in vulnerability. We hypothesized that i...

Explanations for distinct adjacent ecosystems that extend across hilly landscapes typically point to differences in climate or land use. Here we document—within a similar climate—how contrasting regional plant communities correlate with distinct underlying lithology and reveal how differences in water storage capacity in the critical zone (CZ) expl...

Tree-ring carbon isotope discrimination (Δ 13 C) and oxygen isotopes (δ 18 O) collected from white pine (Pinus strobus) trees adjacent to Lake Superior show potential to produce the first winter-specific paleoclimate reconstruction with inter-annual resolution for this region. Isotopic signatures from 1976 to 2015 were strongly linked to antecedent...

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 plantꞋs environment. Here we present measured in‐situ drought responses to demonstrate that apparent isohydricity can be conflated with environmental conditions that vary over...

The Middle to Later Stone Age (MSA-­-LSA) transition in Eastern Africa (variably ~60-­-30 ka) has been linked to cooler, drier environments with greater short-­-term variability, but precisely dated local environmental records from archaeological contexts are needed to test this hypothesis. Ostrich eggshell (OES) fragments are commonly found in Afr...

The ecological importance of the common hippopotamus (Hippopotamus amphibius) in aquatic ecosystems is becoming increasingly well known. These unique megaherbivores are also likely to have a formative influence on the terrestrial ecosystems in which they forage. In this study, we employed a novel exclosure design to exclude H. amphibius from experi...

Understanding how climate alters plant-soil water dynamics, and its impact on physiological functions, is critical to improved predictions of vegetation responses to climate change. Here we analyzed how belowground interactions for water shift under warming and drought, and associated impacts on plant functions. In a semi-arid woodland, adult trees...

Tropical montane cloud forests (TMCF) are ecosystems particularly sensitive to climate change; however, the effects of warmer and drier conditions on TMCF ecohydrology remain poorly understood. To investigate functional responses of TMCF trees to reduced water availability, we conducted a study during the 2014 dry season in the lower altitudinal li...

Many recent studies on drought-induced vegetation mortality have explored how plant functional traits, and classifications of such traits along axes of, for example, isohydry-anisohydry, might contribute to predicting drought survival and recovery. As these studies proliferate, the consistency and predictive value of such classifications need to be...

To understand drivers of hydroclimate variability in north-coastal California, we obtained tree cross-sections from eleven coastal redwoods (mean age of 1232 years old) from the northern half of the species range. Tree rings from eight trees were cross-dated and sampled at sub-annual resolution for carbon isotope discrimination (Δ13C) and oxygen is...

Environmental changes have resulted in significant declines in native riparian forests that are comprised largely of dioecious tree taxa, including boxelder and iconic cottonwood/willow gallery forests. Dioecious species may be especially vulnerable to the effects of climate change given that they often exhibit skewed sex ratios that are reinforced...

Contents I. II. III. IV. V. References An often‐overlooked feature of all plants is that their leaf surfaces are wet for significant periods over their lifetimes. Leaf wetting has a number of direct and indirect effects on plant function from the scale of the leaf to that of the ecosystem. The costs of leaf wetting for plant function, such as the g...

Significance Hippopotami exert a strong influence on the biogeochemistry and ecology of freshwater ecosystems by excreting terrestrially derived organic matter into these systems. These impacts are likely to be strongly controlled by hydrology. In sub-Saharan Africa, anthropogenic water abstraction and climate change are significantly altering wate...

The composition of forests in Western North America is changing. The decline in the shade‐intolerant Oregon white oak (Quercus garryana var. garryana) is attributed to increased competition with the tall‐growing Douglas fir (Pseudotsuga menziesii var. menziesii) as a result of widespread fire exclusion. In a warmer, drier future, both species will...

For most angiosperms, producing and maintaining flowers is critical to sexual reproduction, yet little is known about the physiological processes involved in maintaining flowers throughout anthesis. Among extant species, flowers of the genus Calycanthus have the highest hydraulic conductance and vein densities of species measured to date, yet they...

Hotter droughts are becoming more common as climate change progresses, and they may already have caused instances of forest dieback on all forested continents. Learning from hotter droughts, including where on the landscape forests are more or less vulnerable to these events, is critical to help resource managers proactively prepare for the future....

Drought is expected to become an increasingly important stressor on forests globally, and understanding the physiological mechanisms driving tree drought response is essential for developing effective mitigation and conservation measures for these ecosystems. In 2014, during California's 2012-2016 "hotter" drought in which higher temperatures exace...

Trees, the most successful biological power plants on earth, build and plumb the critical zone (CZ) in ways that we do not yet understand. To encourage exploration of the character and implications of interactions between trees and soil in the CZ, we propose nine hypotheses that can be tested at diverse settings. The hypotheses are roughly divided...

Tropical dry forests (TDFs) undergo a substantial dry season in which plant species must endure several months of drought. Although TDFs support a diverse array of plant growth forms, it is not clear how they vary in mechanisms for coping with seasonal drought. We measured organic tissue stable isotopic composition of carbon (δ¹³C) and nitrogen (δ¹...

Epiphytes are common in tropical montane cloud forests (TMCFs) and play many important ecological roles, but the degree to which these unique plants will be affected by changes in climate is unknown. We investigated the drought responses of three vascular epiphyte communities bracketing the cloud base during a severe, El Niño‐impacted dry season. E...

Flowers are critical for successful reproduction, yet we know little about how they remain turgid and showy throughout anthesis to attract pollinators. Recent evidence suggests that early in angiosperm evolution there was a major shift in the hydraulic structure-function relationships of flowers, with early-divergent ANA grade and magnoliid flowers...

In tall trees, the mechanisms by which foliage maintains sufficient turgor pressure and water content against height-related constraints remain poorly understood. Pressure-volume curves generated from leafy shoots collected crown-wide from 12 large Sequoiadendron giganteum (Lindley) J. Buchholz (giant sequoia) trees provided mechanistic insights in...

Trees, the most successful biological power plants on earth, build and plumb the critical zone (CZ) in ways that we do not yet understand. To encourage exploration of the character and implications of interactions between trees and soil in the CZ, we propose nine hypotheses that can be tested at diverse settings. Depending upon one's disciplinary b...

Tropical montane cloud forests (TMCF) are ecosystems particularly sensitive to climate change; however, the effects of warmer and drier conditions on TMCF water cycling remain poorly understood. To investigate the plant functional response to reduced water availability, we conducted a study during the mid to late dry season (2014) in the lower limi...

COSMIC, the Catalogue of Somatic Mutations in Cancer (http://cancer.sanger.ac.uk) is a high-resolution resource for exploring targets and trends in the genetics of human cancer. Currently the broadest database of mutations in cancer, the information in COSMIC is curated by expert scientists, primarily by scrutinizing large numbers of scientific pub...