The McMurdo Dry Valleys have no rainfall and most snowfall sublimates before wetting the soils significantly. Glacial melt streams are also seasonal, flowing for only 4 to 6 weeks per year. Consequently, hydrology does not provide significant connections among ecosystem components. Conversely, wind is a persistent daily feature of the McMurdo Dry Valleys environment throughout the year. In summer, cool air from the ice-covered oceans flows into the relatively warm valleys creating a strong thermal gradient in the valleys.

Landscapes at the Sevilleta LTER site are dominated or codominated by two perennial grasses from different biomes, Bouteloua eriopoda (black grama) from the Chihuahuan Desert and B. gracilis (blue grama) from the shortgrass steppe, and the Chihuahuan Desert shrub Larrea tridentata (creosotebush). We used a long-term removal study to examine inter-specific interactions between these dominant species, and to determine which species would eventually dominate following the removal of the others.

 The productivity of giant kelp forests is highly variable across time and space. Winter storms and summer periods of nutrient limitation act as bottom-up regulators of kelp abundance and growth in a geography-dependent manner. Our goal is to develop a predictive understanding of giant kelp forest dynamics in the nearshore waters of California using a combination of (i) bio-optical modeling of kelp productivity, (ii) high-resolution remote sensing of kelp cover, biomass and its physiological state.

This session is intended both for social and biophysical scientists who want to help develop a proposal for the kind of “multi-site, highly collaborative and integrated research initiative” envisioned by the LTER planning group. The focus will be on what the LTER planning process calls the “centerpiece” of the group's conceptual framework, as well as one of “Grand Challenges” to be addressed at the network level – “the dynamics of coupled human-natural ecosystems.”

Human settlements in both arid lands and cities must, of necessity, alter hydrological regimes and geomorphology to provide clean, reliable drinking water, water for agriculture, and protection from flooding. Additionally, people also create substantial modifications to provide water for manufacturing, recreation, aesthetics, and sense of place. All of these practices can result in elimination or degradation of existing aquatic ecosystems, as well as creation of new ecosystems such as artificial lakes, stormwater retention basins, mitigation wetlands, groundwater recharge ponds, etc.

Aquatic systems in urban areas may receive enhanced nutrient inputs from the surrounding landscape. The landscape structure within watersheds is hypothesized to influence nitrogen flux into aquatic systems. In urban areas, impervious surfaces and vegetation may be the structural elements which control these inputs. It has been hypothesized that increased impervious surface cover increases discharge to urban streams, which may be correlated with increased nitrogen flux. On the other hand, vegetation slows water flow and retains nutrients on the landscape.

The conversion of agricultural and rural lands for development purposes reflects one of the greatest threats to key ecosystem services in the United States. This poster addresses land use change dynamics in southern Florida, linking them to local governance-zoning institutions. Study of land use and zoning patterns informs broader questions of relevance to the LTER, including: “What is the pattern of land and water use change in urban and working systems: what are the temporal and spatial patterns of human activity and ecosystem dynamics in LTER regions?

Despite the increased recognition of the importance of urban sprawl and landscape fragmentation on social-ecological systems, comparative research on cities across the United States is limited. Therefore, we developed a cross-site comparative study on the land spatial pattern across five LTER sites in the US Southwest. This poster examines the land pattern characteristics for an individual site - Central Arizona Phoenix (CAP).

The Chihuahuan Desert, similar to many arid and semiarid ecosystems, has experienced dramatic changes in vegetation structure and ecosystem processes over the past 150 years. This “desertification” is manifested by the broad-scale expansion of unpalatable woody plants into perennial grasslands with associated loss of grasses and increase in soil degradation that compromise the ecosystem services provided to human populations.

Regime shifts from grasslands to shrublands in arid and semiarid ecosystems are thought to be irreversible, similar to state changes in other systems. We analyze long-term data from the Jornada Basin LTER site to determine if a directional change in climate provides an opportunity to reverse this conversion in the Chihuahuan Desert. We compare historical dynamics based on 140 years of landscape change (1858-1998) with 18 years (1990-2007) of detailed ecosystem responses under a variable climate to predict future responses under either a directional increase or decrease in rainfall.