Carry over from previous year environmental conditions alters dominance hierarchy in a prairie plant community

Abstract

Aims To determine if an experimentally applied anomalous weather year could have effects on species composition and community structure that would carry over into the following year. Methods We conducted a field experiment applying two levels of temperature (ambient and +4C) and two levels of precipitation (ambient and doubled) and followed cover of plant species during the treatment year and one post-treatment year. Data analysis included ordination analysis, examination of species frequency distributions and comparison of cover of functional groups and individual species. Important Findings A drought during the summer and fall of the treatment year resulted in significant differences in community structure between the 2 years. C3 and winter annual species were depressed in the spring of the second year following the dry autumn. Species richness and legume cover increased in the second, wetter, year. Treatments caused no overall differences in community structure but did alter the dominance hierarchy of species among treatments as well as years. Warming decreased relative cover of winter annuals and early spring-flowering species but increased other annuals. Warming and double precipitation together increased cover of C4 perennial graminoids. In particular, the warming and precipitation treatments both increased the abundance of Andropogon gerardii, not individually altering the dominance hierarchy but together nearly doubling the relative cover of A.gerardii, making it the most abundant species in the combined treatment, while the cover of Bromus arvensis, the former dominant, decreased by 25%. The following year, Andropogon relative cover increased further in the former warmed plots, becoming dominant in both the formerly warmed and warmed plus double precipitation treatments. The year following treatments also saw an increase in relative cover of summer-blooming species in the formerly warmed plots and differences among the former treatments in species richness of functional groups. If the effects of one anomalous year on plant abundance can carry over into the following year, several warm years could have a significant impact on plant community structure.