Effects Of Grazing Management And Changes In Precipitation On The Population Dynamics Of Potentilla Fruticosa On The Qinghai-Tibetan Plateau

Grasslands cover about 40% of the Earth’s land surface and play an important role in terrestrial ecosystems.Due to climate change and human disturbance,49% of the world’s grasslands are facing serious degradation.The alpine grassland of the Qinghai-Tibetan Plateau is the highest grassland ecosystem in the world,and it serves as an ideal place to study the responses of natural ecosystems to climate change.Due to climate change and increased human activities,nearly half of the alpine grasslands on the Qinghai-Tibetan Plateau are currently experiencing degradation.Grassland degradation is accompanied with increased shrub expansion under climate change and overgrazing.Understand how climate change and grazing affect the vital rates(i.e.,growth,survival,and reproduction),and consequently change the long term population dynamics is critical for designing suitable management measures.Population ecology models can accurately incorporate the responses of the entire life history process to environment changes into analysis,and therefore provide as a powerful tool for predicting population dynamics under global change.However,there is still a lack of research on shrub population dynamics under climate change,which limits our ability to predict species survival under climate change.Here,we examined the demographic responses of a shrub species,Potentilla fruticosa to grazing management and changes in precipitation on a grassland of Qinghai-Tibetan Plateau.Four precipitation treatments(-75%,-50%,+50%,+75%)and a control(CK)were included at a site with grazing,and a site with fences to exclude grazing.Two replicates were included in each precipitation treatment in both grazing and grazing excluding sites.Annual censuses were conducted in August of2020,2021 and 2022.The individual survival,growth,reproduction in each study population were recorded during three annual censuses.Based on three years of life history data,General Linear Mixed Model(GLMM)was used to fit the vital rates(survival,growth and reproduction)functions,and integral projection models were constructed to simulate the population dynamics of P.fruticosa under different treatments.The main findings include:(1)The vital rate of the P.fruticosa varied largely among treatments across different years.Grazing increased the survival rate of P.fruticosa but decreased its annual plant growth during the second census period,but such effects were not detected during the first census period;(2)The population growth of P.fruticosa remained relatively stable under all treatments.During the first census period,the populations of P.fruticosa were increasing under grazing and grazing excluding treatments(λ > 1).During the second census period,the populations of P.fruticosa were declining(λ < 1)under-75%precipitation treatment and +75% precipitation treatment at the grazed sites,but populations under the rest of precipitation treatments were increasing(λ > 1)regardless of grazing;(3)The results of elasticity analysis showed that,under all treatments,the population growth rate of P.fruticosa was most sensitive to changes in individual survival,relatively sensitive to changes in individual growth,and the last sensitive to changes in reproduction;(4)The results of Life Table Response Experiment(LTRE)analysis showed that the difference in population growth of P.fruticosa between grazing and grazing excluding treatments and across precipitation treatments were mainly caused by the changes in individual survival.Under grazing excluding treatments,changes in all vital rates showed a positive contribution to population growth.Under grazing treatment,changes in all vital rates showed negative contributions to population growth.The results of this study showed that the population of P.fruticosai can maintain stable growth under different precipitation treatments under both grazing and grazing excluding conditions.Individual survival was the most important vital rates restricting the population growth and driving the changes in the population dynamics of P.fruticosa.Therefore,during the process of grassland management,managers may effectively regulate the growth status of P.fruticosa populations by controlling the individual survival,so as to achieve different grassland management goals.