Abstract: The spatial distribution pattern of plants is a result of interactions between species’ biological characteristics and environmental factors. The spatial distribution patterns of reproductive clumps can reveal ecological adaptation of species’ sexual reproduction processes to heterogeneous habitats. In this study, the spatial patterns of reproductive clumps of Psammochloa villosa populations were analyzed using community survey and point pattern approaches based on a completely random, Poisson’s cluster and nested double-cluster models. The spatial pattern response and adaptation mechanisms across a precipitation gradient were explored. The results showed that: (1) Aggregate distribution was the main type of reproductive clumps in P. villosa population. The aggregation scales at the precipitation gradient of 89, 107.8, 117.4, 186 and 191.1 mm·a^-1 were 0-90, 0-35, 0-100, 0-125 and 0-70 cm, respectively. (2) The spatial pattern based on the completely random model showed significant responses to precipitation. The overall pattern was that the aggregation scale of reproductive clumps of P. villosa populations decreased from 0-125 cm to 0-35 cm and the intensity of aggregation increased from 24.92 to 97.14 with increasing drought. (3) The spatial pattern based on Poisson’s cluster model was positively deviated from the Poisson’s cluster model in 27-28 cm and 6-7 cm at 89 and 107.8 mm·a^-1 precipitation, respectively, but was consistent with the spatial pattern based on nested double-cluster model. The spatial pattern of P. villosa reproductive clumps reflected the sexual reproduction process and its adaptation strategy to environmental stress. With increasing precipitation, the reproductive clumps of P. villosa populations adopted an expansion strategy and the aggregation scale gradually increased. In the case of intense interspecific competition, reproductive clumps of P. villosa populations adopted the strategy of “clustering”, while the aggregation scale decreased and the aggregation intensity increased. The reproductive clumps of P. villosa populations adopted a strategy of clustering at small scales under low precipitation.

Key words: sexual reproduction, Poaceae, trade-off, adaptive strategy, point pattern.