Human land-use change alters ecosystems through modifications of surface and air temperature, biota, hydrologic routing, and carbon and nitrogen cycling. Soil-atmosphere CO2 flux (Rs) is a dominant process influencing ecosystem functioning. To better understand the effects of land-use change on ecosystem processes, we evaluated two complementary questions. First, what regulates the spatial and temporal variation of Rs across mixed-use lands? Second, how do soil temperature and moisture influence the spatial and temporal variation of Rs? We measured Rs during the summer and winter months across three major land-cover types in this region—mesic residential, citrus agriculture, and wildland—at three sites spanning a coastal to desert climate gradient in southern California. Analysis across multiple scales—microsite, land-cover, site, and region—was used to examine scaling relations associated with the variation in Rs. Temporal influences on Rs for each land-cover were measured by sampling in the months of July through September, and December through February (n= 78 land-cover-1 x 3 land-covers x 3 sites x 2 seasons).
Results/Conclusions
The spatial and temporal variability of Rs in the mesic residential-agriculture-wildland mosaic was dependent on the site and the scale considered. For summer and winter measurements, the coastal site had the highest Rs for wildland land-covers, and desert site had the largest Rs for agricultural land-covers. Wildland land-covers experienced, on average, an order of magnitude or more increase in Rs from summer to winter. Soil temperature and moisture had characteristic influences on the variability of Rs. Between land-covers, the variation in Rs was positively related to temperature, and negatively related to soil moisture for summer and winter measurements. The variation in Rs within most land-covers decreased from summer to winter, with the highest variation occurring in the wildlands and the lowest in the mesic residential land-covers. Between land-cover variation was the highest in the desert site and lowest at the coastal site. In conclusion, human land-use change in this system alters soil moisture and temperature, decreasing variance of Rs within land-covers, and between sites along the climate gradient, while increasing the variance of Rs within the sites.