Spring 2007 warmth and frost: phenology, damage and refoliation in a temperate deciduous forest

Summary 1. Climate change is predicted to bring earlier bud break and perhaps a greater risk of frost damage to developing leaves and flowers. Given the rarity and unpredictability of major frost events and limited community‐level phenological observations, comparisons among deciduous forest species experiencing frost damage and refoliation are rare. 2. This study used phenological observations ongoing at the time of a hard freeze to compare leaf and flower development, frost damage and leaf refoliation of 20 deciduous woody species in Trelease Woods, Champaign Co., IL, USA. Freezing temperatures from 5 to 9 April 2007 followed 22 days after very warm temperatures began in March. 3. Bud break was the earliest in 17 years. Frost caused damage to leaf buds, developing shoots and/or expanding leaves of canopy trees of six species and saplings of two species. Undamaged species were inactive, or in bud break or shoot expansion. Among damaged species, 11–100% of individuals exhibited some frost damage. Mean damage level per individual ranged from 20% to 100% among species. 4. Refoliation from dormant buds led to mean final canopy fullness that ranged from 46% to 99% among damaged species, but time of full leaf expansion was extended by 16–34 days for refoliating species. 5. Frost damaged flowers, but not flower buds or developing fruit, of five of eight species that flowered during the frost period. 6. The extent of frost damage in 2007 was unusual; damage was greater than any of the other 4 years with frost damage from 1993 to 2009 because record‐breaking March temperatures in 2007 caused more species to be at later vulnerable stages with the advent of subfreezing temperatures in April. 7. Differences among individuals and species in frost damage and ability to refoliate caused strong selection on individuals and differences in carbon gain that could, in the long‐term, affect species’ abundances. The frost also reduced fruit/seed abundance for insects and mammals.