Abstract
Significant replacement of shrub species by herbaceous species has been observed in the Changbai alpine tundra zone, China, since the 1990s. This study used plot surveys to analyze variations in the spatial distribution of dominant plants and to ascertain the changing mechanisms of dominant species in the alpine tundra zone. We found that the two previously dominant shrubs, Rhododendron chrysanthum and Vaccinium uliginosum, differed markedly in their distribution characteristics. The former had the highest abundance and the lowest coefficient of variation, skewness, and kurtosis, and the latter showed the opposite results, while the six herb species invaded had intermediate values. R. chrysanthum still had a relatively uniform distribution, while the herbaceous species and V. uliginosum had a patch distribution deviating from the normal distribution in the tundra zone. Micro-topography and slope grade had stronger effects on the spatial distribution of the eight plant species than elevation. Herbs tended to easily replace the shrubs on a semi-sunny slope aspect, steep slope, and depression. Overall, the dominance of dwarf shrubs declined, while the herbaceous species have encroached and expanded on the alpine tundra zone and have become co-dominant plant species. Our results suggest that various micro-topographic factors associated with variations in climatic and edaphic conditions determine the spatial distribution of plants in the alpine tundra zone. Future climate warming may cause decreased snow thickness, increased growing season length, and drought stress, which may further promote replacement of the shrubs by herbs, which shows retrogressive vegetation successions in the Changbai alpine tundra zone. Further studies need to focus on the physio-ecological mechanisms underlying the vegetation change and species replacement in the alpine tundra area under global climate change.
Highlights
Alpine tundra environments are characterized by the cold climate, short growing season, intense sunlight, large differences in day and night temperatures, and high precipitation [1]
The abundance of herbaceous plants varied with the elevation and micro-topography, which implies the effects of micro-site associated with climatic and edaphic conditions on plant distribution
Our results showed that the Shannon-Wiener index was mainly affected by the altitude, whereas the shrub/herb ratio and six herbaceous dominant species were significantly affected by micro-topography, slope grade, and slope aspects
Summary
Alpine tundra environments are characterized by the cold climate, short growing season, intense sunlight, large differences in day and night temperatures, and high precipitation [1]. Alpine tundra soils tend to be poorly developed and thin. The alpine tundra is an extremely fragile habitat. The alpine tundra is vulnerable to outside interference and forms an ecologically sensitive zone that responds. Significant changes in climate and vegetation have occurred in alpine and sub-alpine areas worldwide [5,6,7,8,9,10]. Over the past several decades, many species, especially herbs, from lower elevations have extended their ranges into higher elevations such as alpine and subalpine areas [11,12,13,14,15,16]
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