Ecohydrological advances and applications in plant–water relations research:a review

Aims The field of ecohydrology is providing new theoretical frameworks and methodological approaches for understanding the complex interactions and feedbacks between vegetation and hydrologic flows at multiple scales.Here we review some of the major scientific and technological advances in ecohydrology as related to understanding the mechanisms by which plant–water relations influence water fluxes at ecosystem,watershed and landscape scales.Important Findings We identify several cross-cutting themes related to the role of plant–water relations in the ecohydrological literature,including the contrasting dynamics of water-limited and water-abundant ecosystems,transferring information about water fluxes across scales,understanding spatiotemporal heterogeneity and complexity,ecohydrological triggers associated with threshold behavior and shifts between alternative stable states and the need for long-term data sets at multiple scales.We then show how these themes are embedded within three key research areas where improved understanding of the linkages between plant–water relations and the hydrologic cycle have led to important advances in the field of ecohydrology:upscaling water fluxes from the leaf to the watershed and landscape,effects of plant–soil interactions on soil moisture dynamics and controls exerted by plant water use patterns and mechanisms on streamflow regime.In particular,we highlight several pressing environmental challenges facing society today where ecohydrology can contribute to the scientific knowledge for developing sound management and policy solutions.We conclude by identifying key challenges and opportunities for advancing contributions of plant–water relations research to ecohydrology in the future.

Ecohydrological processes and ecosystem services in the Anthropocene: a review

The framework for ecosystem services has been increasingly used in integrated watershed ecosystem management practices that involve scientists,engineers,managers,and policy makers.The objective of this review is to explore the intimate connections between ecohydrological processes and water-related ecosystem services in human-dominated ecosystems in the Anthropocene.We synthesize current literature to illustrate the importance of understanding the ecohydrological processes for accurately quantifying ecosystem services under different environmental and socioeconomic settings and scales.Our synthesis focuses on managed ecosystems that are dominated by humans and explores how ecological processes affect the tradeoffs and synergies of multiple ecosystem services.We identify research gaps in studying ecological processes mainly including energy,carbon,water,and nutrient balances to better assess and quantify ecosystem services that are critical for sustaining natural resources for future generations.To better assess ecosystem services,future ecohydrological studies need to better account for the scaling effects of natural and anthropogenic stressors exerted on evapotranspiration and other water supply and demand processes.Future studies should focus on the bidirectional interactions between hydrological functions and services and human actions to solve real world problems such as water shortages,ecological degradation,and climate change adaptation.

Are Northeastern U.S. forests vulnerable to extreme drought?

In the Northeastern U.S.,drought is expected to increase in frequency over the next century,and therefore,the responses of trees to drought are important to understand.There is recent debate about whether land-use change or moisture availability is the primary driver of changes in forest species composition in this region.Some argue that fire suppression from the early twentieth century to present has resulted in an increase in shade-tolerant and pyrophobic tree species that are drought intolerant,while others suggest precipitation variability as a major driver of species composition.From this debate,an emerging hypothesis is that mesophication and increases in the abundance of mesophytic genera(e.g.,Acer,Betula,and Fagus)resulted in forests that are more vulnerable to drought.This review examines the published literature and factors that contribute to drought vulnerability of Northeastern U.S.forests.We assessed two key concepts related to drought vulnerability,including drought tolerance(ability to survive drought)and sensitivity(short-term responses to drought),with a focus on Northeastern U.S.species.We assessed drought-tolerance classifications for species,which revealed both consistencies and inconsistencies,as well as contradictions when compared to actual observations,such as higher mortality for drought-tolerant species.Related to drought sensitivity,recent work has focused on isohydric/anisohydric regulation of leaf water potential.However,based on the review of the literature,we conclude that drought sensitivity should be viewed in terms of multiple variables,including leaf abscission,stomatal sensitivity,turgor pressure,and dynamics of non-structural carbohydrates.Genera considered drought sensitive(e.g.,Acer,Betula,and Liriodendron)may actually be less prone to drought-induced mortality and dieback than previously considered because stomatal regulation and leaf abscission in these species are effective at preventing water potential from reaching critical thresholds during extreme drought.Independent of drought-tolerance classification,trees are prone to dieback and mortality when additional stressors are involved such as insect defoliation,calcium and magnesium deficiency,nitrogen saturation,and freeze-thaw events.Overall,our literature review shows that multiple traits associated with drought sensitivity and tolerance are important as species may rely on different mechanisms to prevent hydraulic failure and depleted carbon reserves that may lead to mortality.

Preface for the article collection “Ecohydrological Processes and Ecosystem Services”

Water is essential to life on Earth.Ecohydrology,the study of interactions between ecological and hydrological processes,is fundamental to our understanding and quantification of services provided by ecosystems.Our knowledge of ecohydrology is incomplete due to the complex nature of ecosystems,which are constantly changing under multiple stresses from air pollution to climate change,from deforestation to urbanization,and from soil erosion to soil pollution.Ecosystem services,the goods and services that ecosystems provide for human wellbeing,are increasingly adopted as a framework worldwide for ecological restoration and conservation,watershed management,and sustainable development policy making.