Northwestern University, Chicago Botanic Garden Glencoe, IL, United States
Background/Question/Methods
Spring snowmelt is a vital source of spring soil moisture in high-elevation plant ecosystems. Climate change is causing a shift to earlier snowmelt timing, which can cause changes in flowering phenology and a higher risk of drought for high-elevation plant species. Drought stress represents a significant barrier to plant reproduction and can reduce plant floral characteristics and survival. This project studied the impacts of experimentally induced early snowmelt on four subalpine plant species at the Rocky Mountain Biological Lab in Gothic, Colorado in 2021. Our main questions were Q1) How does early snowmelt influence physiological drought stress of subalpine plants? Q2) How does early snowmelt affect flowering characteristics (phenology, floral size, and reward) in subalpine plant species? Q3) How does early snowmelt affect pollination frequency, plant survival and seed set? We conducted an early snowmelt manipulation and monitored the physiology, phenology, floral characteristics, pollination, and demography of four perennial plant species from May until August. The species studied represent a gradient of flower timing: Delphinium nuttallianum, Linum lewisii, Hymenoxys hoopesii, and Delphinium barbeyi.
Results/Conclusions
The main impact of early snowmelt was earlier flowering, decreased stomatal conductance, and decreased pollinator visitation for all species, with some species displaying specific demographic and floral consequences. First flowering was 6.25 days earlier on average in the early melt plots than the controls, and the peak flowering date was also earlier in the early melt plots (p < 0.05). All species received fewer pollinator visits in the early snowmelt treatment compared to the control (p < 0.05). Linum lewisii also had smaller flowers, fewer flower stalks and lower fruit set in the early snowmelt plots (flower size: p < 0.09; flower stalk number/fruit set = p < 0.05). More years of data collection are necessary to understand the mechanisms and specific effects of snowmelt timing and drought on plant reproduction. The first year of data collection suggests that early snowmelt can lead to increased drought stress and altered interactions with pollinators, but the severity of these affects may be species specific.
