The effects of gap size and age on natural regeneration of Picea mongolica in the semi-arid region of Northern China

The aim of this work was to study the effects of gap size and age on natural regeneration of endangered tree species Picea mongolica W. D. Xu, which is only found in the semi-arid region of Northern China. For this purpose, six random transect belts of varying size were established in Baiyinaobao Natural Reserve. The number, height and age of P. mongolica saplings were inventoried. Results show that the total number of saplings per hectare and corresponding number and relative share of saplings in height class I (0.1-0.99 m) decreased along with increasing gap size, opposite to height class III (6-9 m). In height class II (1-5.99 m) the number of saplings per hectare and their relative share increased first slightly and then decreased with the increase of gap size. The number of saplings and their relative share in each height class changed similarly with the increase in the distance to the edge of the mature stand (p < 0.05). Gap age also significantly affect the number of saplings per hectare or their height distribution except in height class II. The distance to the mature stand edge played a very important role in the success of natural regeneration for species P. mongolica.