Daily Variation on Soil Moisture and Temperature on Three Restinga Plant Formations

Abstract

Restinga forests and open scrubby formations establish on sandy well-drained soils alongside the Brazilian coastline. Restinga plants are exposed to extreme conditions and vegetation types are mainly structured by species access to groundwater. But to date, no systematic evaluations have been done in order to characterize soil microclimatic conditions and understand how they are associated with variations in climatic drivers. We evaluated hourly soil moisture and temperature along 84 days at Restinga Seasonal Dry Forest (SDF), sparse (Open Clusia Scrubs—OCS), and dense (Open Ericacea Scrubs—OES) tickets at Restinga de Jurubatiba National Park, at Rio de Janeiro state (Brazil). Due to distinctions on physical structure and access to groundwater between plant formations, we expected higher daily soil moisture and lower daily moisture and temperature variations on forests than on open vegetated areas. Daily soil moisture was higher, respectively, on SDF, OES, and OCS, whereas soil moisture and temperature variability presented the opposite trend (SDF < OES < OCS), supporting our hypotheses. Daily soil temperature dynamics are quite well predicted by solar radiation incidence patterns, whereas daily soil moisture is mainly regulated by precipitation at OCS, an interaction of precipitation and temperature at OES and delayed effects of precipitation at SDF. Our results corroborate our expectations that forests are more effective in buffering both air temperature and precipitation effects on soil conditions than open vegetated areas. They also indicate that soil moisture and temperature conditions are important aspects differentiating Restinga vegetation types.