Prof Michigan State University East Lansing, Michigan, United States
Abstract: Land use and land cover change have profoundly changed land surface property and ecosystem functions, including carbon and water production. We investigate the contribution of landscape composition to its function by examining how land cover and composition may affect gross primary production (GPP) and evapotranspiration (ET) at six landscapes in Mongolia and Kazakhstan. We hypothesize that both ecosystem and landscape GPP and ET are disproportionate to their composition and, therefore, the changes in land cover will have an asymmetrical consequence on landscape functions. We leverage a computational-friendly linear downscaling approach to align the coarse spatial resolution ET and GPP (500m) of MODIS with the fine-grain and localized land use and land cover map developed from Landsat (30m) for six provinces in the countries where the intensive LULCC occurred in recent decades. By establishing two metrics - function to composition ratio (F/C) and function to changes in composition(ΔF/ΔC), we tested our hypothesis and evaluated the impact of land cover change on ecosystem function within and among the landscapes. Our results show that: a) the five landcover types have their signature downscaled ET and GPP, appearing vary between the two countries as well as within the country. b) function to composition ratio(F/C) of ET and GPP of the forest is statistically greater than 1 (i.e., over contributing), whereas F/C of grasslands and croplands is close to, or slightly less than 1 (i.e., under-contribution). F/C of barren class is clearly smaller than 1 but greater than zero. Specifically, a unit of forest generates 1.085 unit of ET and 1.123 unit of GPP, a unit of grassland generates 0.993 unit of ET and GPP; and a unit of cropland produces 0.987 unit of ET and 0.983 unit of GPP; The divergent F/C values among the landcover classes support the hypothesis that landscape function is disproportionate to its composition. c). Within each landscape, ΔET/ΔC and ΔGPP/ΔC of forests and croplands showed negative values, while grasslands and barrens had positive values, indicating that convert a unit of forest to other land cover leads to 0.67 unit decrease in ET and 0.6 unit decrease in GPP. But convert a unit of grassland or barren to other land cover classes will result in increased ET and GPP. This linear downscaling approach and two metrics F/C and ΔF/ΔC is labor-saving and cost-effective for rapid assessment on the impact of land use land cover change on ecosystem functions.
