Project Funding: 2009 - 2010

NRA: 2008 NASA: Terrestrial Ecology   

Funded by NASA

Abstract:
Global savanna biomes are spatially and temporally complex systems in which woody vegetation (trees, shrubs) and herbaceous vegetation (grasses, forbs) both contribute significantly to system level functions such as primary production, carbon, water and nutrient cycling. The tropical and temperate savannas represent ~30% of the global land area and support unique communities of pastoral and agricultural peoples alongside wild and domestic herbivores. Savannas are subject to highly dynamic interactions between climate, soils, fire and herbivory, which depend strongly on human management and land use, and will be significantly affected by future changes in climate. Savanna regions are also subject to directional changes in the balance between woody and herbaceous cover (shrub encroachment) that remain poorly understood and can have large impacts on land surface-atmosphere interactions and system biogeochemistry. The production of the herbaceous layer, which naturally consists largely of grasses, has been co-opted by humans in many regions to form vital centers for grain production. In earlier years, NASA has invested in several research programs in savannas (HAPEX-Sahel, SAFARI, dry end LBA). However, despite these activities, remote sensing of mixed tree-grass systems remains challenging because of the separation of the vegetation into two distinct layers (woody species of varying cover, density, height, leaf area and biomass, over a herbaceous layer of varying density, cover and leaf area), and because the woody and herbaceous layers can have distinct and contrasting seasonality, physiology and phenology which vary in both space and time. Further, fire dynamics in savannas require not only assessment of the timing, extent, and intensity of fires, but also their impacts on vegetation structure. Without reliable methods to adequately assess vegetation structure in savannas, parameterization of higher order models of vegetation function (primary production, vegetation dynamics, water and energy balance) is difficult and model results unreliable. While there has been substantial research in savannas, the complexity of savanna vegetation limits the effectiveness of model-data integration, scenario and predictive analysis. Recent advances in active and passive remote sensing and, in particular, the potential for combined Lidar and synthetic aperture radar (SAR) in the proposed DESDynI mission, offer potential for significant advances in capturing the dynamics of these systems and delivering accurate system level predictions into the decision-making and policy domains. There is a need for a coordinated and targeted field and remote sensing campaign in appropriate locations to integrate existing radar, lidar and passive (broad-band and hyperspectral) remote sensing with modeling and field measurement to realize this potential and prepare the way for new instruments planned as part of the Decadal Survey missions. We propose a scoping exercise for a future field activity focused on the challenges and opportunities for remote sensing in mixed tree-grass systems. We will use input from NASA program managers and instrument teams, savanna ecologists and the modeling community, to develop recommendations for NASA, detailing optimal approaches and geographical locations for a remote sensing oriented field program focused on the savanna biome. Our proposal is relevant to NASA Terrestrial Ecology program goals for scoping studies (subelement 2) and studies of vegetation structure using radar and lidar (subelement 1). The study aims to fully realize the potential of satellite remote sensing in the measurement and modeling of savanna vegetation structure and dynamics. It will develop a program of research focused on new opportunities in active remote sensing and how these can be utilized in synergy with new and historical passive remote sensing.

2011 NASA Carbon Cycle & Ecosystems Joint Science Workshop Poster(s)

• 'Tree-Grass': Proposal for a NASA Terrestrial Ecology Field Activity in Savannas and Mixed Tree-Grass Ecosystems   --   (Niall P Hanan, Michael J Hill)   [abstract]   [poster]

More details may be found in the following project profile(s):

• NASA Terrestrial Ecology (TE) Project Profile