Understory microclimate of secondary tropical forests in Panama

Abstract

Few studies have addressed the understory microclimate in regenerating secondary tropical forests. While the area of secondary forests is increasing at fast pace in the tropics and succession is driven by environmental conditions, a study of the most ecologically relevant environmental drivers light, temperature and moisture is of great interest. Measurements of light, air and soil temperature and relative humidity were conducted across eleven forest sites aged between 2 and 17 years. Moreover, soil water content was monitored during a five month period spanning the dry season and mini-lysimeters were used to determine soil evaporation. The understory environment became darker, cooler and moister with succession and was increasingly buffered in regard to daily variability. Tree basal area, as an indicator for biomass, was the best structural determinant of the microclimate succession trend but canopy closure showed relevant too. Young succession sites were chiefly determined by high light levels, air temperature and vapor pressure deficits, which constitute important filters for germination and establishment of plant species. Nevertheless, the understory environment reached stabilized values ten years after disturbance already and was close to understory conditions in old-growth forests. Secondary tropical forests in Panama hence seem to recover quickly and will guarantee the provision of beneficial regulatory ecosystem services.