The effects of global climate change on seed germination and plant regeneration have been reported in many species. However, there are no consistent trends in how seed quality and germination are affected by these conditions. Seeds of four native, one invasive, and two pairs of native/invasive species were collected from the USDA-ARS Prairie Heating and CO2 Enrichment Experimental plots in 2007 to 2009, located in the Mixed-grass Prairie near Cheyenne, WY. Field treatments include ambient (385 ppm, c) and elevated (600 ppm, C) CO2 concentrations, control temperature (t) and heating (1.5/3.0°C warmer day/night, T), and deep (ct-d) and shallow (ct-s) irrigation. Seed quality was evaluated and germination tests were conducted under alternating temperatures (10/0, 12.5/2.5, 15/5, 20/10, 25/15, 30/20, 35/25°C). Thermal time requirements (θ50) and base temperatures (Tb) for germination were determined using thermal time models. Elevated CO2 concentrations reduced seed fill and viability, germination and germination rate in Grindelia squarrosa. Heating increased seed viability in Koeleria macrantha from 56% to 79%. Heating, when combined with elevated CO2 concentrations, increased germination while CO2 alone decreased germination by about 14% in Bouteloua gracilis. Heating tended to enhance Tb and to reduce θ50 in Bouteloua gracilis, which may slow the initiation of germination but seeds germinate faster in spring. Elevated CO2 concentrations tended to increase but CT tended to decrease Tb in Centaurea diffusa, but not θ50. Heating tended to increase but all the other treatments tended to reduce Tb in Lanaria dalmatica, leading to a possible earlier start of germination. Irrigation treatments tended to show similar trend of effects on seed quality and germination as that in elevated CO2 concentrations. Species specific changes in seed quality and germination were observed, which may exert substantial cumulative effects on community composition in the long run. Invasive species may be more competitive under future climatic conditions compared with native species. However, the distribution and abundance of some native species, specifically Bouteloua gracilis, may be favored by climate change.

White spruce (<i>Picea glauca</i> (Moench) Voss), black spruce (<i>P. mariana</i> (Mill.) BSP), and jack pine (<i>Pinus banksiana</i> Lamb.) are dominant conifer trees within the boreal forest. Rising CO2 concentrations may create hotter and drier conditions in the Southern Boreal Forest of Canada, and have negative impacts on germination and regeneration of conifers. Conifers vary in their germination requirements and may have different responses to climate change. Experiments were conducted to access the germination potential, variability among collections, and to predict the ability of these conifers to germinate under future climatic conditions. Twelve collections of white spruce and black spruce and ten collections of jack pine seeds were collected from the Boreal Plain Ecozone of Saskatchewan. Seeds of all collections varied in their dormancy characteristics and dormancy breaking requirements because no single stratification or light treatment stimulated germination in all three species. Seed dormancy was greatest in white spruce and least in black spruce. Germination tests at 5, 10, 12.5, 15, 17.5, 20, 25, 30, and 35°C were used to develop thermal time models. Each species had unique temperatures for optimal germination ranging from 20°C in white spruce, 20-25°C in black spruce, and 25-30°C in jack pine. The speed of germination under similar temperature regimes was fastest for jack pine, intermediate for black spruce, and slowest for white spruce. The base temperature for white spruce decreased (r=0.63, P=0.03) with increasing June precipitation while that of jack pine tended to increase with latitude (r=0.60, P=0.07) and April precipitation (r=0.58, P=0.08). No environmental variables correlated with germination of black spruce. The Canadian Global Climate Model, version 2, with emission scenarios predicted future temperature and precipitation at the sites where seeds were collected. Using the base temperature for germination as a guideline, temperatures suitable for germination in the spring are predicted to advance by a few weeks to a month and a half earlier with increased concentrations of CO2. Moisture availability may, however, control seed germination at these sites. Overall, jack pine and black spruce might better adapt to increasing temperature because of their high germination temperatures (>30°C). Variation in most germination parameters existed among collections, suggesting this variability can be used to select seed sources for reforestation or assisted migration in a changing climate.

Orchardgrass (<i>Dactylis glomerata</i> L.) and western wheatgrass (<i>Pascopyrum smithii </i>(Rydb.) L.) seeds have different degrees of dormancy that result in non-uniform seedling emergence in the field. Seed dormancy of the two species, in part, causes disagreement between germination tests in the laboratory and seedling emergence in the field. Experiments were conducted over two years in the laboratory and in the field to determine the effects of alternating temperatures on changes in seed dormancy and germination of orchardgrass and western wheatgrass. The two western wheatgrass cultivars (Walsh and LC9078a) had deeper dormancy than the two orchardgrass cultivars (Arctic and Lineta). Dormancy of both species was broken by temperatures with 10oC amplitude; this temperature variation was similar to that which occurred at a 1 cm depth in the soil. Optimal temperatures for germination of orchardgrass (10-25oC) were broader than those for western wheatgrass (15-20oC). Seedling emergence of orchardgrass was less sensitive to seeding date in the spring than western wheatgrass; seedling emergence of western wheatgrass increased as seeding date was delayed from early to late May if soil water was not limiting. The rate of seedling emergence increased with increasing temperature in both species, therefore, faster and more uniform seedling emergence can be expected from late spring seeding dates. Seeds were often exposed to light during germination tests in the laboratory while planting seeds in the soil usually prevented exposure of seeds to light. Seedling emergence of orchardgrass in the field was usually less than the germination percentage obtained in the laboratory because of light exposure during germination tests could break dormancy in orchardgrass seeds and the small seeds of orchardgrass had limited energy reserves for pre-emergence seedling growth. On the other hand, germination of western wheatgrass seeds was reduced by exposure to light during germination and seeds were larger than those of orchardgrass. Therefore, seedling emergence of western wheatgrass in the field was usually greater than germination tests would predict. The use of thermal time models to study seed dormancy changes and germination revealed the dual effects of temperature on these processes. The modified thermal time model takes the difference between germination and seedling emergence into account and can accurately predict seedling emergence in the field (R2=0.88 to 0.99). Thermal time models for predicting seedling emergence in the field can also be developed for other forages, however, cultivar- and species-specific parameters must be developed for the models.

Orchardgrass (<i>Dactylis glomerata</i> L.) and western wheatgrass (<i>Pascopyrum smithii </i>(Rydb.) L.) seeds have different degrees of dormancy that result in non-uniform seedling emergence in the field. Seed dormancy of the two species, in part, causes disagreement between germination tests in the laboratory and seedling emergence in the field. Experiments were conducted over two years in the laboratory and in the field to determine the effects of alternating temperatures on changes in seed dormancy and germination of orchardgrass and western wheatgrass. The two western wheatgrass cultivars (Walsh and LC9078a) had deeper dormancy than the two orchardgrass cultivars (Arctic and Lineta). Dormancy of both species was broken by temperatures with 10oC amplitude; this temperature variation was similar to that which occurred at a 1 cm depth in the soil. Optimal temperatures for germination of orchardgrass (10-25oC) were broader than those for western wheatgrass (15-20oC). Seedling emergence of orchardgrass was less sensitive to seeding date in the spring than western wheatgrass; seedling emergence of western wheatgrass increased as seeding date was delayed from early to late May if soil water was not limiting. The rate of seedling emergence increased with increasing temperature in both species, therefore, faster and more uniform seedling emergence can be expected from late spring seeding dates. Seeds were often exposed to light during germination tests in the laboratory while planting seeds in the soil usually prevented exposure of seeds to light. Seedling emergence of orchardgrass in the field was usually less than the germination percentage obtained in the laboratory because of light exposure during germination tests could break dormancy in orchardgrass seeds and the small seeds of orchardgrass had limited energy reserves for pre-emergence seedling growth. On the other hand, germination of western wheatgrass seeds was reduced by exposure to light during germination and seeds were larger than those of orchardgrass. Therefore, seedling emergence of western wheatgrass in the field was usually greater than germination tests would predict. The use of thermal time models to study seed dormancy changes and germination revealed the dual effects of temperature on these processes. The modified thermal time model takes the difference between germination and seedling emergence into account and can accurately predict seedling emergence in the field (R2=0.88 to 0.99). Thermal time models for predicting seedling emergence in the field can also be developed for other forages, however, cultivar- and species-specific parameters must be developed for the models.

White spruce (<i>Picea glauca</i> (Moench) Voss), black spruce (<i>P. mariana</i> (Mill.) BSP), and jack pine (<i>Pinus banksiana</i> Lamb.) are dominant conifer trees within the boreal forest. Rising CO2 concentrations may create hotter and drier conditions in the Southern Boreal Forest of Canada, and have negative impacts on germination and regeneration of conifers. Conifers vary in their germination requirements and may have different responses to climate change. Experiments were conducted to access the germination potential, variability among collections, and to predict the ability of these conifers to germinate under future climatic conditions. Twelve collections of white spruce and black spruce and ten collections of jack pine seeds were collected from the Boreal Plain Ecozone of Saskatchewan. Seeds of all collections varied in their dormancy characteristics and dormancy breaking requirements because no single stratification or light treatment stimulated germination in all three species. Seed dormancy was greatest in white spruce and least in black spruce. Germination tests at 5, 10, 12.5, 15, 17.5, 20, 25, 30, and 35°C were used to develop thermal time models. Each species had unique temperatures for optimal germination ranging from 20°C in white spruce, 20-25°C in black spruce, and 25-30°C in jack pine. The speed of germination under similar temperature regimes was fastest for jack pine, intermediate for black spruce, and slowest for white spruce. The base temperature for white spruce decreased (r=0.63, P=0.03) with increasing June precipitation while that of jack pine tended to increase with latitude (r=0.60, P=0.07) and April precipitation (r=0.58, P=0.08). No environmental variables correlated with germination of black spruce. The Canadian Global Climate Model, version 2, with emission scenarios predicted future temperature and precipitation at the sites where seeds were collected. Using the base temperature for germination as a guideline, temperatures suitable for germination in the spring are predicted to advance by a few weeks to a month and a half earlier with increased concentrations of CO2. Moisture availability may, however, control seed germination at these sites. Overall, jack pine and black spruce might better adapt to increasing temperature because of their high germination temperatures (>30°C). Variation in most germination parameters existed among collections, suggesting this variability can be used to select seed sources for reforestation or assisted migration in a changing climate.