Spatial pattern and spatial association of Melica przewalskyi and Artemisia frigida in degraded grassland

Spatial pattern and spatial association are the important means for the study of population diffusion,community succession,and interactions between organisms and environment.In this paper,point pattern method was applied to study the plant height,aboveground biomass,spatial pattern,and spatial association of Melica przewalskyi and Artemisia frigida at their different succession stages in the upper reaches of Shiyang River in Sunan County,Gansu Province of Northwest China.At the stages of no patch formation(CK) and patch formation(A),the M.przewalskyi population showed a clumped pattern at all scales;while at diffusion stage(B),stable stage(C),and degradation stage(D),the clumped pattern transferred to random,and,with the decreases of clumped scale and clumped intensity,the plant height and aboveground biomass of M.przewalskyi decreased after an initial increase.The spatial distribution pattern of A.frigida at its different succession stages all presented a transition from clumped to random,and,with the increase of clumped scale,the clumped intensity increased,and the plant height and aboveground biomass decreased after an initial increase.At the stages CK,A,and D,the spatial association between M.przewalskyi and A.frigida was significantly positive;at stage B,the spatial association transferred from significantly negative to not significantly.The corresponding relationships of the changes in plant height and aboveground biomass with the populations' spatial pattern and spatial association scale transformation under the interference of grazing reflected the populations' competition and ecological adaptable strategies in degraded grassland.