Age matters: Demographic senescence in the moss Polytrichastrum formosum

It is known that many animal species senesce demographically, showing a decrease in survival and/or fertility with age. Though there is mounting evidence for and against senescence in various flowering plant species, the question of whether senescence also occurs in other plant taxa, such as mosses and other bryophytes, remains unanswered. We used GAMMs (generalized additive mixed models) and GLMMs (generalized linear mixed models) to assess effects of age on survival, size and the monocarpic female ramets’ sexual reproduction in Polytrichastrum formosum using demographic, ramet-level data collected over 25 years in Solhomfjell nature reserve, Norway. Survival was found to be negatively correlated with ramet age, with one-year survival decreasing from 83% in 1-year-old to 43% in ten-year-old plants. Stem growth was positively correlated with survival but accounting for it in our models did not change the relationship between age and survival qualitatively. Annual growth decreased ...