A New Approach to Phenological Research — Relationships Between Environmental Factors and Days to the Appearance of the First Leaf in Four Perennial Species1

Abstract

AbstractPlant‐climate‐soil relationships were studied during the years 1968 and 1969 on the basis of the phenological pattern of appearance of the first leaf in spring of four perennial species, spirea (Spirea spp L.), orchardgrass (Dactylis glomerata L.), fall aster (Aster azureus L.), and big blue stem (Andropogon gerardi L.). Plantings of these species were previously established in plots adjacent to official weather stations at all five locations in Indiana. Comparisons between the environmental factors and the appearance of the first leaf were made using two multiple regression analysis methods. First leaf appearance during the 2 years did not follow Hopkins' bioclimatic law at these locations. In a northern Indiana muck soil at Wanatah, the growing season began 6 to 10 days later in the 1969 year than on a sandy loam soil located only 250 m from that location. Appearance of the first leaf at all locations for the four species over both years was 2 or 3 weeks earlier at the southern location than on the heavier soils in central and northern Indiana. Regression analysis show that six parameters contributed to much of the R2 value, with each independently contributing to a high R2 value. The regression included those factors that would develop R2 values to .9000+. Parameters consistently contributing to this value were daylight hours and soil temperatures at 20, 5.0, and 2.5 cm (base OC bare soil).Daylight hours from the last frost to first leaf were the most consistent parameter correlated with appearance of the first leaf. Soil temperature at 20 cm was also important and contributed to increasing R2Soil differences, based on detailed physical and chemical analyses, accounted for plant response variation indirectly, especially as related to texture that influenced water‐holding capacity and subsequently temperature.This is an interesting parameter as it relates to soilplant‐climate interactions in heavy‐textured soils. The correlation for soil and air temperature relationship was linear. Degree‐day accumulation was different in the 2 years, indicating that other factors, such as the soil temperature‐moisture interaction, minutes of sunshine, net radiation, etc., may be important environmental parameters involved in initiation of plant growth in the spring as indicated by the appearance of the first leaf.