Abstract Background Perennity of giant rosette species in combination with a single “big bang“ reproduction followed by death of the genetic individual is relatively rare among plants. Such long-lived monocarpic plants are usually slow growing and can be found in deserts, bogs or in alpine regions of the tropics or subtropics. Due to their longevity monocarpic perennials risk to lose everything before reproduction, which make them particularly susceptible to disturbances. Because of the inherent difficulties to assess if long-lived populations are growing or declining, usually neither their demography nor the consequences of increasing grazing pressure are known. Methods We used integral projection modelling (IPM) to measure growth rate and passage time to flowering of Rheum nobile, a monocarpic perennial, and one of the most striking alpine plants from the high Himalayas. We estimated the impact of grazing cattle (yaks) by including in the models those rosettes, which were not found any more due to disturbances or grazing by yaks, either as missing or dead. Data was collected from plants at 4500 m a.s.l. in Shangri-la County, Yunnan Province, southwest China. In four consecutive years (2011-14) and in two populations, 372 and 369 individuals were measured, respectively, and size-dependent growth, survival and fecundity parameters were estimated. In addition, germination percentage, seedling survival, and establishment probability were assessed. Key results The probability of survival, of flowering and fecundity were strongly size-dependent. Time to reach flowering size was 33.5 years (95% CI from 21.9 to 43.3, stochastic estimate from pooled transitions and populations). The stochastic population growth rate (λs) of Rheum nobile was 1.013 (95% CI from 1.010 to 1.017). When disturbance by grazing cattle (yaks) was accounted for in the model, λs dropped to values below one (0.940, 95% CI from 0.938 to 0.943). Conclusion We conclude that natural populations of this unique species are viable, but that conservation efforts should be taken to minimise disturbances by grazing and to protect this slow-growing flagship plant from the high Himalayas.

The demographic data of Rheum nobile was collected at two sites in the eastern Himalaya: Huluhai (28°31′N, 99°57′E, 4450 m a.s.l.) and Yongjiongyi (28°24′N, 99°55′E, 4490 m a.s.l.), in Shangri-la County, Yunnan Province, SW China. In four consecutive years (2011-14), 372 and 369 individuals (rosettes), respectively, were marked and measured. Table 1 includes the data of four consecutive years (2011-14) that was used to estimate the size-dependent growth, survival and fecundity parameters for the Integral projection Model (IPM). For each rosette the table includes the following: number of leaves, largest and shortest diameter of rosette (cm), length and width of largest leaf (cm); when an individual was flowering, the table includes: the number of flowers, fruit set, the number of fruits, the abortion rate, mature seeds, the predation rate, the number of viable seeds. Flowering plants died after seed ripening. In the column "status" it is inicated if a plant flowered in a particular year, was found dead due to natural mortality (die), or was missing or dead due to disturbance by grazing yaks (missing). 

Table 2 includes the data that was used to calculate the germination rate: the number of seedlings around all the 8 and 9 plants reproducing in 2013 in Huluhai and Yongjiongyi respectively, were counted in 2014 and divided by the number of seeds produced by their mother plants.

Table 3 includes the data that was used to calculate seedling survival: 5 (Huluhai) and 6 plots (Yongjiongyi) of size 80 x 80 cm were established early in 2011 close to all plants which had reproduced in the preceding year. Emerging seedlings until the end of season 2011 in these plots were counted and the surviving seedlings and their size (diameter) was measured in the following year. Seedling survival was calculated by dividing the number of seedlings surviving in 2012 by the number of seedlings counted in 2011. 

Table 1-3 are excel-sheets.