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The Research Program of Alan Knapp, his Colleagues and Students

Our research in general spans ecosystems ecology, with studies at broad spatial and temporal scales, to complementary, more mechanistic plant ecophysiological investigations.  Current specific interests include (1) global (primarily climate) change ecology focused on precipitation and temperature manipulations, and (2) large scale comparative research designed to assess the relative sensitivity of ecosystems, as well as their responses, to alterations in key drivers (climate, N, fire, grazing). Most of our research is conducted in grasslands because they are amenable to field experiments (i.e., tractable), they are dynamic systems that respond rapidly, and because they are ecologically important ecosystems from the perspective of the range of services they provide. Our research approach is centered on a strong appreciation for collaborative, interdisciplinary research across broad spatial and temporal scales.

Research projects highlighted below includes examples of those interests above and a two-decade association with large-scale ecosystem research through the Long-term Ecological Research program.

 

Current Research Projects
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Extreme Drought in the Grassland Experiment (EDGE)


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Although scientists have learned much in the past 20 years about how individual ecosystems are likely to respond to climate change, extending this knowledge to regional, continental and global scales has been a far greater challenge. At these larger spatial scales, both the environment and the attributes of ecosystems vary dramatically. For example, in the central US, there are strong temperature and rainfall gradients from Texas to North Dakota and the dry plains of Colorado to eastern Kansas, and the types of grasslands differ as well (from short grasslands in the west to tall grasslands in the east). In order to better forecast how entire regions will respond to expected climatic changes, there is a pressing need to understand why ecosystems differ in their sensitivity to changes in climate. 
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Species Comping SGS, 2012


In 2012, the Extreme Drought in Grasslands Experiment (EDGE) was established to address two questions of fundamental importance for advancing our knowledge of how ecosystems will respond to climate change at large spatial scales:  1) How do grassland ecosystems differ in their sensitivity to a multi-year extreme drought and what determines their differential sensitivity?, and 2) How important are the attributes of ecosystems per se vs. the environmental context in which climate is changing in determining ecological responses to drought at regional scales? EDGE is a geographically distributed field experiment with six sites in North America in NM, CO, WY and KS, which include the Sevilleta, Shortgrass Steppe and the Konza Prairie LTERs (Fig. 1). The US EDGE project is funded by the NSF Macrosystems Biology Program and involves both LTER and non-LTER researchers from Colorado State University (Drs. Alan K. Knapp and Melinda D. Smith), the University of New Mexico (Drs. Scott L. Collins and William Pockman), and the University of Oklahoma (Dr. Yiqi Luo). In 2013, the Chinese Academy of Sciences agreed to fund six additional grassland sites in Inner Mongolia, China. These will be established in 2014 and follow the experimental protocols of the US sites.
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Konza EDGE Site in the winter


The experiment is designed to impose a severe multi-year drought in grasslands arrayed along a rainfall gradient - from desert grassland to mesic tallgrass prairie (Fig. 1) and along a similar gradient in China - using identical rainfall manipulation shelters (Fig. 2).  Additional experimental treatments will modify or alter the timing of growing season precipitation based on regional predictions from climate models. Key responses measured will include many related to carbon cycling and budgets, and plant biodiversity. The results from this experiment will be used to strengthen an existing process-based terrestrial ecosystem (TECO) model. With the TECO model, the relative importance of ecosystem attributes versus the environment for determining responses to climate change will be evaluated, and then scaling rules for extending site-based knowledge to regional scales will be developed. 

EDGE Sevilleta site
EDGE experiment at the Sevilleta LTER.

Sevilleta EDGE Webpage
The project is designed to be a research platform for others in the scientific community to conduct additional research activities. Scientists interested in utilizing the EDGE experiment for additional research should contact one of the investigators listed above.
 

Map of Edge Sites


RAMPs (Rainfall Manipulation Plot Study)


The structure and function of grassland ecosystems in the Central Plains are strongly influenced by an extremely variable continental climate. The IPCC and global climate models predict that future rainfall patterns will be more extreme in the future and in response to this forecast, we have been assessing the effects that alterations in rainfall variability may have in grasslands since 1997. We do this in the field with Rainfall Manipulation Plots (RaMPs) that allow us to impose more extreme rainfall regimes in a natural ecosystem. A warming treatment was added in 2003 to assess the interactive effects of temperature and altered rainfall patterns. Our approach utilizes field-scale Rainfall Manipulation Plots in which the timing and amounts of rainfall events are experimentally manipulated, independently and in tandem, to assess the effects of altered precipitation regimes on individual plant ecophysiological responses, plant community composition, and ecosystem-level processes. Our results indicate that productivity is usually decreased (10-15%) with increased rainfall variability, plant species diversity at the community level may be slightly increased and soil C cycling is significantly altered. Increased temperatures accelerate spring phenology but usually reduce soil moisture and have had variable effects on productivity. The RaMPs infrastructure has also been used for soil microbial, genomics, and soil respiration studies of climate change impacts. Results indicate that this type of climate change could have significant effects on a variety of ecosystem functions and services.

 

Long-term Ecological Research (LTER) Program


Much of our work is performed at these sites, the Konza Prairie LTER and the Shortgrass Steppe LTER. The Konza Prairie LTER Program is a comprehensive, multidisciplinary program designed to address long-term research questions relevant to tallgrass prairie ecosystems, and the science of ecology in general. The Konza Prairie Biological Station (KPBS), a 3487-hectare area of native tallgrass prairie in the Flint Hills of northeastern Kansas, is the primary site for most of this research. Since 1981, the broadly based Konza Prairie LTER research program has encompassed studies from the organismic through population, community, ecosystem and landscape ecology levels. These studies are linked via an overarching theme that includes the major abiotic and biotic factors influencing this ecosystem. The SGS LTER project represents the continuing development of a research tradition that began with the US/IBP Grassland Biome project in the late 1960's, the time at which ecosystem science was formally recognized as a sub-discipline in ecology.The key questions that guide SGS research are: 1. What factors regulate SGS ecological structure and function over space and time? 2. How do the factors that regulate ecological structure and function, and the coupling of biotic and abiotic components, vary spatially and temporally within the SGS? 3. What are the biotic and abiotic thresholds that determine the vulnerability of the SGS to changes in the factors influencing ecological structure and function?

 

 

Convergence and Contingencies in Savanna Grassland


The goals of this project are (1) to compare how ecosystem and community structure and function respond to key ecological drivers (fire and grazing) in South African vs. North American savanna grasslands, (2) to identify those ecological processes that are similar (convergent) despite the potential contingent factors of differing evolutionary history, herbivore diversity and soil fertility, and (3) to assess the impact of a reduction in herbivore diversity (~14 megaherbivores to Cape buffalo to none) as has occurred in many grasslands throughout the world, on community and ecosystem processes. To achieve these goals, we have established similar herbivore exclusion experiments and have sampled plant and soil responses to fire and/or grazing using identical protocols at two field sites in South Africa, Kruger National Park and the Ukulinga Research Farm (at the University of KwaZulu-Natal, Pietermaritzburg), and at the Konza Prairie Biological Station in northeastern Kansas USA.

 Project website

CEE (Climate Extremes Experiment)


The CEE is an intensive assessment of genomic, physiological and growth responses the two co-dominant grasses in tallgrass prairie, A. gerardii and S. nutans, in response to a broad range temperature treatments (ranging from ambient to extreme) in combination with high (well-watered) and low (severe drought) soil water availabilities. The temperature treatments are imposed as discrete events (i.e., heat waves), such that the timing and length of the events fall within the historic timeframe of temperature extremes for this region. We are focusing on responses of the co-dominant grasses during and recovery after the extreme temperature events, as well as a key aspect of ecosystem functioning (aboveground productivity). Our approach, which includes multiple temperature levels, will allow us to identify critical thresholds and relative magnitudes of response to temperatures that are relevant to both past extreme periods of climateand those predicted with global warming.