1. What are the controls on community structure and composition within a landscape unit?

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Global Linkages Climate Change Ocean Productivity Rain Chemistry Albedo Sediment Transport Greater Wind Erosion Greater Precipitation Lower Precipitation Greater Evapotranspiration & Latent Heat Flux Lower Evapotranspiration & Latent Heat Flux Cooler Soils Warmer Soils Infrequent, Intense Precipitation Less Variable Precipitation • AREAS OF RESOURCE LOSSES • Denitrification (N, NO) • Ammonia Volatilization (NH) • Sediment Transport plants and interspaces Greater Pool Organic N Smaller Pool Organic N Plants and interspaces within patches Greater Soil Moisture Lower Soil Moisture Lower Fluvial Erosion Soil Heterogenity Greater Fluvial Erosion shrubs/ grass Patches within landscape units Lesser Runoff shrubs Greater Runoff • AREAS OF RESOURCE • ACCUMULATION • Salinity • Dune Encroachment abiotic biotic Islands of Fertility SEMIARID ARID grass Local Water Accumulation HUMAN INTERACTIONS Landscape units within the Jornada basin bajada playa/ tobosa flats sandy basin Sites within region Big Bend JRN SEV Chihuahuan desert Mapimi JORNADA MODEL OF DESERTIFICATION AS RESOURCE REDISTRIBUTION KEY QUESTIONS TO BE ADDRESSED UNDER LTER IV 1. What are the controls on community structure and composition within a landscape unit? 2. What are the controls on ecosystem processes and fluxes, both within and among landscape units? 3. What is the relative importance of processes occurring within landscape units compared to transfers of materials or organisms among units, in determining ecosystem structure and function? Our approach is to synthesize information from our long-term experiments and core data sets with data to be collected to fill in gaps in our knowledge. Most of our new studies will improve our understanding of controls on community structure and ecosystem dynamics among landscape units. We will use simulation modeling to synthesize and integrate our information in order to determine the relative importance of controls within and among units. We will also generate new hypotheses to be tested about these major controls and their feedbacks to vegetation structure and ecosystem dynamics. The general framework of our LTER research is presented here. Individual research posters contain more specific information about the status and goals of our research. • 1. Controls on plant population and community dynamics: • Plant populations. • Contact - Peters, Huenneke • Ecophysiological analysis of NPP patterns. • Contact - Gutschick, Huenneke • Community structure by automated image analysis. • Contact - Gutschick, Rango • 3. Synthesis and integration to determine the relative importance of controls within and among landscape units: • Identify key controls using analysis of long-term data. • Simulation model analyses comparing results with and without redistribution among landscape units. • Generate testable hypotheses concerning key processes and potential feedbacks. Our previous LTER research focused on individual shrub or grass plants and their associated interspaces. We have studied a number of physical and biological processes that determine the dominance of either shrub (arid) or grass (semiarid) patches. Shifts between these alternative states of the Chihuahuan desert are influenced by changes in climate and management with important feedbacks from the vegetation. SCALING UP THE RESOURCE REDISTRIBUTION MODEL ECOTONE model Between landscape units • 2. Major controls on ecosystem dynamics within and among landscape units: • Geomorphology and soils. • Contact – Monger, Herrick, Schlesinger • Wind and aeolian redistribution of nutrients. • Contact – Gillette, Schlesinger • Hydrology and alluvial redistribution of nutrients. • Contact – Abrahams, Parsons, Wainwright, Schlesinger • Remote sensing component. • Contact - Rango • Herbivory and livestock impacts. • Contact - Lightfoot, Havstad • Animals as agents of soil disturbance. • Contact - Lightfoot, Herrick water Landscape unit A Within unit Hydrology and wind models seeds nutrients Landscape unit B Spatially-interactive ECOTONE model that links the vegetation, hydrology, and wind erosion models to simulate biotic processes and flows of materials both within and among landscape units. The model will simulate vegetation, soil water, and nutrient dynamics on a grid of interactive plots within each landscape unit. Under LTER IV, we will expand from the scale of plants and interspaces to patches, landscapes, and the Chihuahuan desert region. We will examine biological and physical processes across spatial scales, and will investigate the importance of flows of water, nutrients, seeds, and animals both within and among units to patterns in vegetation and ecosystem processes. • Long-term Experiments and Core Data Sets: • Net Primary Productivity Patterns • Plant phenology at NPP sites • Soil water at NPP sites. • Consumers at NPP sites. • Small Mammal Exclosure Study. • Transects of LTERI. • JORNEX. • Instrumented watersheds. • Stressor Experiments. • Gravelly Ridges Experiment. • JER permanent quadrats. • Plant diversity experiment. • Fire study • Weather and climatological data. • Deposition studies. Decrease in spatial scale among units water nutrients propagules herbivory Patch redistribution Landscape redistribution Precipitation Upslope Local precipitation Local herbivory Local propagules Available water Within a unit Infiltration capacity AWHC Biodiversity and NPP Soil texture + depth SOM Local Nutrients Conceptual model of flows of materials within and among landscape units. Water, nutrients, propagules, and herbivory are spatially distributed across the landscape, and contribute to localized inputs within each landscape unit. Redistribution of water is shown as an example. Within a landscape unit, these materials exert controls on biological processes that influence patterns and dynamics in biodiversity and NPP.