Spatial pattern and competition relationship of Stellera chamaejasme and Aneurolepidium dasystachys population in degraded alpine grassland

Abstract

Human activities are affecting the habitat, which decrease the number of habitats and recede the quality. The biggest threat to species diversity worldwide is the loss of suitable habitat. Human activities affect species dynamics and further influence species diversity by changing habitat. Species evolvement at different types of habitat is very complex, so there is an urgency to understand species responses to human-caused habitat degradation. Spatial pattern and competition relationship are important in plant ecology as they affected the dynamics of plant populations, communities and ecosystem processes, which can reveal the dynamic and stability of population and community structure. Stellera chamaejasme and Aneurolepidium dasystachys are the main species in alpine degraded grassland, have a great significance for understanding reproductive strategies of grassland plant resources with studies on spatial pattern and competition relationship of S. chamaejasme and A. dasystachys. In this study for two main aims: First, to describe the scale transformation of population's spatial pattern and spatial association along with the different plot; Second, to analyze the competition relationship and competition intensity of S. chamaejasme and A. dasystachys. Study sites locates in the Ma Changtan grassland in SuNan country of the north Qilian Mountain (38°47'22. 1"-38°52'11" N, 99°45'11. 7"-99°57'41. 2" E). In early August, 2011, four experimental plots were established by the community characteristics and S. chamaejasme population characteristics. At the same time, we recorded fine-scale (0-100 cm) spatial pattern and spatial association of S. chamaejasme and A. dasystachys population from 2 m×2 m grids (2 cm×2 cm quadrats) in different plot. The point pattern analysis and Monte Carlo stochastic simulation method were used to quantitatively analyze spatial pattern and competition relationship. The results showed that: (1) In the process of natural pasture degeneration, the spatial patterns of S. chamaejasme were aggregated at 53-58 cm and 63-100 cm scales under no degradation and light degradation conditions, and subsequently random or regular under moderate degradation and heavy degradation conditions, which meant that the intraspecific relationship converted mutualism into competition within different plot. (2) The spatial patterns of A. dasystachys were aggregated within four plots, which meant that intraspecific mutualism was the most important competition relationship of A. dasystachys in the process of natural pasture degeneration. (3) The spatial association of S. chamaejasme and A. dasystachys population changed on the different scale and degradation gradient. Under no degradation and light degradation conditions, the positive correlation was shown at 8-20 cm and 66-71 cm scales; under moderate degradation conditions, there was no significant correlation as a whole and the scale ranges was from 0 cm to 100 cm; under heavy degradation conditions, negative correlation was shown at 16-28 cm scales. It reflected that the interspecific relationship converted mutualism into competition. The scale transformations of population' s spatial pattern, as well as the spatial association, are not only the antecedent conditions affecting changes of competition relationship, but also the critical factors of population' s competition intensity. It may reflect the adaptive approach of regeneration and reproduction when S. chamaejasme and A. dasystachys population face the outside interference.