1. Winter stresses to crops and native plants during climate change Bjarni E. Guðleifsson Agricultural University of Iceland, Modruvellir, 601 Akureyri, Iceland INTRODUCTION Perennial plants are subject to many kinds of winter stresses. Plants are damaged or killed if the environmental stress passes the tolerance of the plant. The tolerance to winter stresses is much more studied in crops than in wild native plants. Crops are often introduced species or cultivars, not always adapted to the local climate. On the other hand iIndigenious plants are adapted to the local winter stresses and prevailing climate. The proportion of different stresses in damage to hayfields and trees in Iceland has been estimated. Ice damage dominates in herbage crops and frost in wooddy plants. Type of stressIn Icelandic hayfields, % In Icelandic forests, % Frost heaving18 Drought25 Frost585 Energy starvation+? Flooding+? Ice encasement90- Snow molds22 TOLERANCE TESTS Wild indigenious plants are distributed to localities where the stress intensity is lower than the plant tolerance to that particular stress. Preliminary test of a few alpine plant species, indicates that plants living in snow patches (e.g. Sibbaldia) possess fairly low frost tolerance, whereas plants living in dry location (e.g. Three- leaved rush) are tolerant to both frost and ice. SpeciesFrost tolerance LT 50, °C Ice tolerance LD 50, Days Winter wheatTriticum aestivum- 1915 TimothyPhleum pratense-2037 SibbaldiaSibbaldia procumbens-1135 Three-laved rushJuncus trifidus-2049 IMPACT OF CLIMATE CHANGE Temperatures are expected to rise dramatically In futural climate change. During the next 50 years the mean temperature in Iceland is expected to rise 1,5 °C during summer and 3,0 °C during winter. Winter stresses to crops and plants at lower altitudes will decrease and winter damages might disappear. However, warm winter thaws might promote premature plant dehardening and growth, resulting in damages caused by subsequent stresses. The high rise in winter temperature will result in decreased snow cover at higher altitudes, and this might result in increase or change in winter stresses at higher altitudes. Plants adapted to snow mold stress might therefore in the future experience frost or ice encasement to which they are not well adapted. Therefore winter damages at higher altitudes might increase and influence distribution of alpine plants. ABSTRACT The main winter stresses to plants are frost, ice encasement and low temperature parasitic fungi. In Iceland, ice cover mainly damages herbage crops whereas frost causes damage to woody plants. Wild alpine plants are better adapted to these winter stresses than crops, some are frost tolerant, others are ice tolerant, depending on their growing site. The expected increase in winter temperatures, caused by climate change, will reduce winter damages to crops cultivated at low altitudes. Decrease in snow cover at higher altitudes might on the other hand increase frost and ice cover stress to alpine plants which might be damaged. Year 2000 Year 2050 ICE FROST FUNGI