Comparative research on microclimate between forest gaps and non-gaps of Smith fir forests in the Sejila Mountains, southeastern Tibet

Through the microclimate observation of gaps and non-gaps (under-canopy and open spaces) of Abies georgei forest in the Sejila Mountain, southeastern Tibet, we monitored daytime total radiation, air temperature, relative humidity, surface temperature and 5 -15 cm layer soil temperature, and analyzed the similarities and differences of microclimate between forest gaps and non-gaps in summer time. The results showed that, the annual change of total solar radiation to fir gaps presented bimodal curve and the peak values appeared in May and August. The diurnal and annual variation ranges of total solar radiation in forest gaps were less than that of open spaces, and meanwhile, the annual total solar radiation of gaps was 1 173.28 MJ/ m2, which was significantly lower than that of the open spaces (P 0.01). The changing curves of air temperature in gaps and non-gaps during summer daytime were of inverted S, and the diurnal variation range of air temperature in gaps was small, ranging between open spaces and under- canopy, and it was closed to that in under-canopy and significantly lower than that in the open spaces. The relative humidity of gaps was higher than that of open spaces and under-canopy, meanwhile the variation range of it was small. The diurnal variation trend of surface temperature in forest gaps and non- gap was basically consistent with the change of air temperature. The temperatures of land surface and soil layers in open spaces were significantly higher than that in gaps and under-canopy. The soil temperature decreased with the increase of soil depth, and there was no obvious diurnal variation under 10 cm layer. Due to the influence of solar radiation to the surface temperature, the diurnal variation amplitude of it was much higher than that of the soil temperature.