Document: DAV-3-34-53

The effects of late spring frosts on the diversity and abundance of flowering in sub-alpine meadows.

INOUYE, D.W.* ^1,2

University of Maryland, College Park, MD 20742 USA ¹
Rocky Mtn. Biological Lab, Crested Butte, CO 81224 USA ²

Abstract:
Spring frosts are common at high altitudes in the Colorado Rocky Mountains. If they occur early in the spring, before plants are above ground or before they have developed enough to be sensitive to freezing temperatures, these frosts have little if any effect on subsequent flowering. However, if they occur following winters with relatively low snowpack, which result in an early snowmelt and beginning of the growing season, buds and flowers (which are more sensitive than vegetative parts) of some species of wildflowers may be killed. I used data on flowering by Helianthella quinquenervis (Asteraceae) in two permanent plots (365 and 400 m2) to identify five years since 1974 with significant frost damage to flowering at the Rocky Mountain Biological Laboratory (elevation 2,800 m); few if any flowers were produced by this long-lived perennial during those years. I matched these with five years without frost damage (pairs of years were separated by one or two years), and then used data on the timing and abundance of flowering in 14 permanent 2 by 2-m plots to examine the effects of these frost events on the community level (as sampled by plots). In years with frosts, on average 14.5 (range 11 - 18.5) species flowered per plot, compared with 18.7 (range 17.7 - 19.8) in years without frosts. I counted all flowers in the plots about every other day for most of the growing season (most years from 1973 - 1999), and determined the day on which flowering peaked for the summer. In frost years there was on average a peak of 180 flowers per plot (range 95 - 230), compared with 367 (range 252-480) in years without frosts. Flowers of most early-flowering species appear to be immune to frost damage, and most late-flowering species are probably not at a sensitive stage at the time when frosts occur. Several species of mid-season wildflowers in particular appear to be sensitive to frost damage, with potentially significant effects for their pollinators, seed predators and parasitoids, as well as their own demography. If the trend for warming nocturnal low temperatures continues, one of the consequences of global climate change may be a decrease in these late spring frosts; the consequences could be considered beneficial or deleterious, depending on the species or interaction being studied.

Keywords: climate change; diversity; flowering; frost; Helianthella; RMBL; snowpack

This abstract is being presented at: 11:00 AM in session:
Oral Session #43: Plant Community Responses to Climate Change.