Abstract: An investigation was conducted on the vegetative and reproductive biom
ass allocation of Stipa grandis at the hill-top and hill-foot of Xilingol
grassland, and relatedness- and factor analyses were made to study the effects
of hill position on the S. grandis seed biomass. Significant differences were ob
served in the vegetative and reproductive growth of S. grandis plants at the
 hill-top and hill-foot. At hill-foot, the height and number of non-flowerin
g S. grandis ramets increased by 2469% and 3537%, respectively, the number o
f flowering ramets increased by 10297%, the vegetative, reproductive, and tota
l biomass increased by 4414%, 9559% and 4745%, respectively, and the
100-grain mass increased by 2500%, as compared with those at hill-top. The
 seed biomass of S. grandis at hill-top was mainly affected by soil moistur
e content, while that at hill-foot was mainly affected by soil pH. Hill positio
n induced the differentiation of soil moisture and N contents, and made the
S. grandis at the fertile hill-foot allocating more energy to its sexual re
production.

Key words: hill topography, Stipa grandis, biomass allocation, relatedness analysis, factor analysis, Quercus variabilis, natural forest, thinning intensity, Qinling Mountains, population regeneration.