Effects of canopy gaps on the microclimate, seedling establishment, growth and survival in a Nothofagus betuloides dominated forest in Tierra del Fuego, Chile

Abstract

In Nothofagus betuloides dominated forests in Tierra del Fuego canopy gaps, regeneration wave systems, partial mortality and blow-downs have been documented. The objective was to analyse the effects of naturally created canopy gaps on the microclimate conditions, the seedling establishment, growth and survival in a N. betuloides dominated forest. The research was conducted in an uneven-aged N. betuloides forest (17 ha, 730 trees/ha, 96.2 m2/ha) in Tierra del Fuego (53º45’S, 69º58’W). In the forest a total of 36 canopy gaps (≥ 20 m2 in surface) were found. For this study 4 canopy gaps (52, 73, 146 and 183 m2) were randomly selected. In and around each canopy gap, five locations were selected (gap centre, gap edges to the North and South and beneath the undisturbed forest to the North and South), and 4 m2 plots were established (a total of 20 plots). To estimate the solar radiation transmittances on each plot hemispherical photographs were taken. The air and soil temperatures and the soil volumetric water content (SVWC) were continually measured from April 2011 on each plot. All seedlings were measured in January 2011 and re-measured in March 2012, after the growing season (October-March). In general, the transmission of solar radiation was higher in canopy gap locations. Withingap locations were found to influence significantly the mean daily maximum air and soil temperature, mean daily minimum soil temperature and SVWC. The seedling density during the first and second year of measurements and the survival of the seedlings were not statistical different between de locations. Therefore, the locations in and around canopy gaps did not make marked density shifts. In average, the seedlings showed similar height growths between the locations in and around canopy gaps. A stepwise multiple regression revealed a significant relationship between the absolute height growth of the N. betuloides seedlings with the height of the plants, the transmittance of the diffuse solar radiation, the plant area index, the competition index and the mean daily maximum air temperature during the growing season (R2=0.518; p<0.001). At the same time, the height growth of the Nothofagus pumilio seedlings is explained by the height of the plants, the SVWC and the mean daily minimum air temperature during the growing season (R2=0.586; p<0.001). Canopy gaps influence some microclimatic variables, which together with the height of the plant and the competition index seemed to be main factors affecting the absolute height growth of the seedlings.