Alan Knapp

Alan Knapp
Colorado State University | CSU · Department of Biology

PhD

About

365
Publications
102,204
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
34,255
Citations
Additional affiliations
January 2004 - present
Colorado State University
Position
  • Professor (Full)

Publications

Publications (365)
Article
Full-text available
Ecosystem primary productivity is a key ecological process influencing many ecosystem services, including carbon storage. Thus, clarifying how primary productivity in terrestrial ecosystems responds to climatic variability can reveal key mechanisms that will drive future changes in the global carbon budget. Satellite products of canopy greenness ar...
Preprint
Full-text available
Future global changes will impact carbon (C) fluxes and pools in most terrestrial ecosystems and the feedback of terrestrial carbon cycling to atmospheric CO2. Determining the vulnerability of ecosystems to future changes in C is thus vital for targeted land management and policy. The C capacity of an ecosystem (XC) is a function of its C inputs (e...
Article
Full-text available
1. Seeds provide the basis of genetic diversity in perennial grassland communities and their traits may influence ecosystem resistance to extreme drought. However, we know little about how drought effects the community functional composition of seed traits and the corresponding implications for ecosystem resistance to drought. 2. We experimentally...
Article
Vegetation phenology is highly sensitive to climate change, although the data and methods used to estimate key phenological states can influence this sensitivity. Because of its direct relation to leaf photosynthetic carbon uptake, remotely sensed solar-induced chlorophyll fluorescence (SIF) can provide new insight assessing changes in vegetation p...
Article
A quantitative understanding of temporal patterns of soil respiration (SR) and its components, as well as of their controlling factors, are key to the estimation of grassland C sequestration under different scenarios of land-use change and global change. However, the sensitivity of seasonal patterns and magnitude of SR and its components to N addit...
Article
Full-text available
Background and aim As global climate change intensifies, the frequency and duration of extreme droughts are predicted to increase, resulting in extended periods of reduced soil water availability across ecosystems. The allocation of carbon (C) to above- and below-ground plant biomass is a fundamental ecosystem property that varies spatially and tem...
Article
Plant nonstructural carbohydrates (NSC) can reflect community and ecosystem responses to environmental changes such as water availability. Climate change is predicted to increase aridity and the frequency of extreme drought events in grasslands, but it is unclear how community-scale NSC will respond to drought or how such responses may vary along a...
Article
Climate change is predicted to increase the frequency and intensity of extreme events including droughts and large precipitation events or "deluges." While many studies have focused on the ecological impacts of individual events (e.g., a heat wave), there is growing recognition that when extreme events co-occur as compound extremes, (e.g., a heatwa...
Article
Full-text available
Drought, defined as a marked deficiency of precipitation relative to normal, occurs as periods of below-average precipitation or complete failure of precipitation inputs, and can be limited to a single season or prolonged over multiple years. Grasslands are typically quite sensitive to drought, but there can be substantial variability in the magnit...
Article
Full-text available
Climate change is altering precipitation regimes globally, with expectations of intensified precipitation patterns (for example, larger but fewer rainfall events) and more frequent and extreme drought. Both aspects of precipitation change can impact ecosystem function individually, but it is more likely that they will occur in combination. In a cen...
Article
Full-text available
Global change is impacting plant community composition, but the mechanisms underlying these changes are unclear. Using a dataset of 58 global change experiments, we tested the five fundamental mechanisms of community change: changes in evenness and richness, reordering, species gains and losses. We found 71% of communities were impacted by global c...
Article
Precipitation is a primary determinant of plant community structure in drylands. However, the empirical evidence and predictions are lacking for how plant functional diversity in desert and steppe communities respond to altered precipitation regimes. We examined how precipitation changes along the natural and experimental gradients affect different...
Preprint
Full-text available
Plant nonstructural carbohydrates (NSC) can reflect community and ecosystem responses to environmental changes such as water availability. Climate change is predicted to increase aridity and the frequency of extreme drought events in grasslands, but it is unclear how community-scale NSC will respond to drought or how such responses may vary along a...
Article
Aim Precipitation manipulation experiments have shown diverse terrestrial carbon (C) cycling responses when the ecosystem is subjected to different magnitudes of altered precipitation, various experimental durations or heterogeneity in local climate. However, how these factors combine to affect C cycle responses to changes in precipitation remains...
Article
Full-text available
Extreme drought decreases aboveground net primary production (ANPP) in most grasslands, but the magnitude of ANPP reductions varies especially in C3-dominated grasslands. Because the mechanisms underlying such differential ecosystem responses to drought are not well-resolved, we experimentally imposed an extreme 4-year drought (2015-2018) in two C3...
Article
Full-text available
Water‐limited ecosystems are highly sensitive to not only precipitation amount, but also precipitation pattern, particularly variability in the size and timing of growing season rainfall events. Both rainfall event size and timing are expected to be altered by climate change, but the relative responses of dryland ecosystems to changes in rainfall e...
Article
Full-text available
The frequency and magnitude of deluges (extremely large rain events) are increasing globally as the atmosphere warms. Small‐scale experiments suggest that semiarid grasslands are particularly sensitive to both the timing and size of deluge events. However, the assumption that plot‐scale results can be extrapolated across landscapes with variable so...
Article
Satellite derived sun‐induced chlorophyll fluorescence (SIF) has been increasingly used for estimating gross primary production (GPP). However, the relationship between SIF and GPP has not been well defined, impeding the translation of satellite observed SIF to GPP. Previous studies have generally assumed a linear relationship between SIF and GPP a...
Article
Full-text available
The performance of coordinated distributed experiments designed to compare ecosystem sensitivity to global-change drivers depends on whether they cover a significant proportion of the global range of environmental variables. In the present article, we described the global distribution of climatic and soil variables and quantified main differences a...
Article
Effective use of solar‐induced chlorophyll fluorescence (SIF) to estimate and monitor gross primary production (GPP) in terrestrial ecosystems requires a comprehensive understanding and quantification of the relationship between SIF and GPP. To date, this understanding is incomplete and somewhat controversial in the literature. Here we derived the...
Article
Full-text available
AimsFire regimes are key drivers of ecosystem dynamics and are changing worldwide. Uncertainty about how fire history affects responses to individual fires hampers predictions of fire impacts on important ecosystem functions such as C cycling. Thus, we assessed how fire and fire history affect soil CO2 flux and aboveground net primary production (A...
Article
Full-text available
Recent observational studies report weak or flat temperature − growth relationships for many tree species in temperate forests. In contrast, distribution limits of trees are strongly shaped by temperature, and studies show marked short‐term temperature effects on leaf‐level ecophysiology. To better determine the effects of warming on trees, we plan...
Article
Full-text available
1. Biodiversity can stabilise productivity through different mechanisms, such as asynchronous species responses to environmental variability and species stability. Global changes, like intensified drought, could negatively affect species richness, species asynchrony, and species stability, but it is unclear how changes in these mechanisms will affe...
Article
Full-text available
In terrestrial ecosystems, climate change forecasts of increased frequencies and magnitudes of wet and dry precipitation anomalies are expected to shift precipitation-net primary productivity (PPT-NPP) relationships from linear to nonlinear. Less understood, however, is how future changes in the Accepted Article This article is protected by copyrig...
Article
Climate change has intensified the hydrologic cycle globally, increasing the magnitude and frequency of large precipitation events, or deluges. Dryland ecosystems are expected to be particularly responsive to increases in deluge size, as their ecological processes are largely dependent on distinct soil moisture pulses. To better understand how incr...
Article
Full-text available
Understanding how global change drivers (GCDs) affect aboveground net primary production (ANPP) through time is essential to predicting the reliability and maintenance of ecosystem function and services in the future. While GCDs, such as drought, warming and elevated nutrients, are known to affect mean ANPP, less is known about how they affect inte...
Article
Plant‐associated fungi can ameliorate abiotic stress in their hosts, and changes in these fungal communities can alter plant productivity, species interactions, community structure and ecosystem processes. We investigated the response of root‐associated fungi to experimental drought (66% reduction in growing season precipitation) across six North A...
Article
Significance During the Dust Bowl drought, central US grasslands responded unexpectedly to a decade of hot, dry conditions. Grass species adapted to high temperatures with higher water use efficiency (C 4 grasses) decreased, while those preferring cooler climates (C 3 grasses) increased. We reproduced this surprising response by experimentally impo...
Article
Climate change is intensifying the hydrologic cycle globally, increasing both the size and frequency of extreme precipitation events, or deluges. Arid and semi‐arid ecosystems are expected to be particularly responsive to this change because their ecological processes are largely driven by distinct soil moisture pulses. However, since soil moisture...
Article
Changes in rainfall amounts and patterns have been observed and are expected to continue in the near future with potentially significant ecological and societal consequences. Modelling vegetation responses to changes in rainfall is thus crucial to project water and carbon cycles in the future. In this study, we present the results of a new model-da...
Article
Climatic extremes, such as severe drought, are expected to increase in frequency and magnitude with climate change. Thus, identifying mechanisms of resilience is critical to predicting the vulnerability of ecosystems. An exceptional drought (<1st percentile) impacted much of Southern Africa during the 2015 and 2016 growing seasons, including the si...
Article
Full-text available
Semi-arid ecosystems are strongly water-limited and typically quite responsive to changes in precipitation amount and event size. In the C4-dominated shortgrass steppe of the Central US, previous experiments suggest that large rain events more effectively stimulate plant growth and aboveground net primary production (ANPP) than an equal amount of p...
Article
Full-text available
In their letter to the editor commenting on our call for improved characterization and quantification of drought in ecological studies (Slette et al., 2019), Zang et al. (2019) take issue with the use of standardized drought indices, one of the options we suggested for providing needed climatic context for drought studies.
Article
Full-text available
Random species loss has been shown experimentally to reduce ecosystem function, sometimes more than other anthropogenic environmental changes. Yet, controversy surrounds the importance of this finding for natural systems where species loss is non‐random. We compiled data from 16 multi‐year experiments located at a single native tallgrass prairie si...
Article
Full-text available
Critical examination of the approaches ecologists employ to understand complex ecological systems is integral to advancing our science. Recently, Korell et al. (2019) argued that climate change experiments would yield more relevant information on future functioning of ecosystems if the treatments imposed more closely reflected model‐projected clima...
Article
Full-text available
Soil hydraulic properties influence the partitioning of rainfall into infiltration versus runoff, determine plant-available water, and constrain evapotranspiration. Although rapid changes in soil hydraulic properties from direct human disturbance are well documented, climate change may also induce such shifts on decadal time scales. Using soils fro...
Article
Full-text available
Significance Accurate prediction of community responses to global change drivers (GCDs) is critical given the effects of biodiversity on ecosystem services. There is consensus that human activities are driving species extinctions at the global scale, but debate remains over whether GCDs are systematically altering local communities worldwide. Acros...
Article
Full-text available
Direct quantification of terrestrial biosphere responses to global change is crucial for projections of future climate change in Earth system models. Here, we synthesized ecosystem carbon-cycling data from 1,119 experiments performed over the past four decades concerning changes in temperature, precipitation, CO2 and nitrogen across major terrestri...
Article
Full-text available
Background and aims Grasslands are expected to experience droughts of unprecedented magnitude and duration in this century. Plant traits can be useful for understanding community and ecosystem responses to climate extremes. Few studies, however, have investigated the response of community-scale traits to extreme drought on broad spatial/temporal sc...
Article
Full-text available
Plant traits can provide unique insights into plant performance at the community scale. Functional composition, defined by both functional diversity and community‐weighted trait means (CWMs), can affect the stability of above‐ground net primary production (ANPP) in response to climate extremes. Further complexity arises, however, when functional co...
Article
Direct quantification of terrestrial biosphere responses to global change is crucial for projections of future climate change in Earth system models. Here, we synthesized ecosystem carbon-cycling data from 1,119 experiments performed over the past four decades concerning changes in temperature, precipitation, CO2 and nitrogen across major terrestri...
Article
Full-text available
Ongoing intensification of the hydrological cycle is altering rainfall regimes by increasing the frequency of extreme wet and dry years and the size of individual rainfall events. Despite longstanding recognition of the importance of precipitation amount and variability for most terrestrial ecosystem processes, we lack understanding of their intera...
Article
Full-text available
Drought, widely studied as an important driver of ecosystem dynamics, is predicted to increase in frequency and severity globally. To study drought, ecologists must define or at least operationalize what constitutes a drought. How this is accomplished in practice is unclear, particularly given that climatologists have long struggled to agree on def...
Article
Full-text available
Nitrogen (N) enrichment often increases aboveground net primary productivity (ANPP) of the ecosystem, but it is unclear if belowground net primary productivity (BNPP) track responses of ANPP. Moreover, the frequency of N inputs may affect primary productivity but is rarely studied. To assess the response patterns of above‐ and below‐ground producti...
Article
Full-text available
Growing evidence indicates that ecosystem processes may be differentially sensitive to dry versus wet years, and that current understanding of how precipitation affects ecosystem processes may not be predictive of responses to extremes. In an experiment within a mesic grassland, we addressed this uncertainty by assessing responses of two key carbon...
Article
Full-text available
Understanding the effects of climate change, in particular, climate extremes on plant functional traits can provide a mechanistic basis for predicting how plant communities may be altered in the future. Here, we focused on a dominant species in Inner-Mongolia typical temperate steppe, Leymus chinensis (Trin.) Tzvei, to examine the responses of plan...
Article
Full-text available
Community-scale surveys of plant drought tolerance are essential for understanding semi-arid ecosystems and community responses to climate change. Thus, there is a need for an accurate and rapid methodology for assessing drought tolerance strategies across plant functional types. The osmometer method for predicting leaf osmotic potential at full tu...
Article
Full-text available
Climate change will alter global precipitation patterns, making it increasingly important that we understand how ecosystems will be impacted by more frequent and severe droughts. Yet most drought studies examine a single, within-season drought, and we know relatively little about the impacts of multiple droughts that occur within a single growing s...
Article
Full-text available
Herbivores alter plant biodiversity (species richness) in many of the world’s ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet,...
Article
Higher temperatures and evaporative demand forecasted for Colorado forests by the end of the century suggest that soil water limitation increasingly will negatively impact whole plant performance. At the same time, upslope or poleward migration of plant ranges in response to warming may result in species experiencing cooler overnight temperatures,...
Article
Full-text available
The responses of species to environmental changes will determine future community composition and ecosystem function. Many syntheses of global change experiments examine the magnitude of treatment effect sizes, but we lack an understanding of how plant responses to treatments compare to ongoing changes in the unmanipulated (ambient or background) s...
Article
Full-text available
Both the dominance and the mass ratio hypotheses predict that plant internal nutrient cycling in ecosystems is determined by the dominant species within plant communities. We tested this hypothesis under conditions of extreme drought by assessing plant nutrient (N, P and K) uptake and resorption in response to experimentally imposed precipitation r...
Article
Full-text available
1. Context. Precipitation regimes are changing in response to climate change, yet understanding of how forest ecosystems respond to extreme droughts and pluvials remains incomplete. As future precipitation extremes will likely fall outside the range of historical variability, precipitation manipulation experiments (PMEs) are critical to advancing k...
Presentation
Background/Question/Methods Precipitation variability is expected to increase as a result of climate change, resulting in longer, higher severity droughts and changes in seasonality. While the effects of prolonged drought have been widely investigated, less is known about ecosystem responses to changes in rainfall seasonality. Meanwhile, precipitat...
Article
Full-text available
Experiments are widely used in ecology, particularly for assessing global change impacts on ecosystem function. However, results from experiments often are inconsistent with observations made under natural conditions, suggesting the need for rigorous comparisons of experimental and observational studies. We conducted such a ‘reality check’ for a gr...
Article
Full-text available
Understanding ecosystem dynamics and predicting directional changes in ecosystem in response to global changes are ongoing challenges in ecology. Here we present a framework that links productivity dynamics and ecosystem state transitions based on a spatially continuous dataset of aboveground net primary productivity (ANPP) from the temperate grass...
Article
Full-text available
The allocation and stoichiometry of plant nutrients in leaves reflect fundamental ecosystem processes, biotic interactions, and environmental drivers such as water availability. Climate change will lead to increases in drought severity and frequency, but how canopy nutrients will respond to drought, and how these responses may vary with community c...
Data
Supplement of "Asymmetric responses of primary productivity to altered precipitation simulated by ecosystem models across three long-term grassland sites". Tables S1–S14 in the Supplement detail the simulated processes for grasslands in the ecosystem models, including the N cycle, phosphorus (P) cycle, carbon (C) allocation scheme, carbohydrate res...
Article
Full-text available
Field measurements of aboveground net primary productivity (ANPP) in temperate grasslands suggest that both positive and negative asymmetric responses to changes in precipitation (P) may occur. Under normal range of precipitation variability, wet years typically result in ANPP gains being larger than ANPP declines in dry years (positive asymmetry),...