Factors Affecting Early Cone Development in Fraser Fir

Plantation-grown Fraser fir Christmas trees produce cones at a much younger age than those in natural stands. Cone-removal is expensive for growers, but cones left to grow consume tree resources and leave behind unsightly stalks and resin. We adopted a comprehensive approach toward understanding and reducing precocious coning in Fraser fir trees. We randomly selected 25 trees from same-age plots at 10 farms representative of the diversity of environmental conditions and cultural practices in Michigan. We obtained climate data from a state-wide automated weather network (Enviro-weather) and measured tree height and number of cones at the beginning of the season, and leader growth weekly throughout the season. We analyzed soil samples for pH, texture, and nutrient content, and foliar samples for nutrient content and C13 discrimination. We also compared paired plots of heavy and low coning areas at three individual farms. At one farm, we applied plant growth regulators to 50 trees to determine their effectiveness at chemically controlling coning. To quantify the effects of cone production on vegetative growth, we picked cones from eight large trees and left cones to grow on eight similar trees in one plot, and measured bud density and shoot and needle length at the end of the season. We also established irrigation studies at two sites to examine the effect of irrigation on cone development. Across state-wide locations, maximum temperature, precipitation, radiance, PET, C13 discrimination, foliar nutrition, soil nutrition, and pH showed little correlation with coning. Soil organic matter and clay content were inversely correlated with coning, and minimum air temperature was strongly correlated, suggesting that warmer nights and decreased soil moisture holding capacity might contribute to early cone development. In our paired plots comparing areas of heavy and low coning, minimum air temperature, C13 discrimination, soil organic matter, and clay content were inversely correlated with coning, consistent with moisture stress as a factor in cone development. We also noted correlations between cone development and nutrition. In our carbon partitioning study, shoots on picked trees were 22% longer than on unpicked trees at the end of the season. Bud density was 23% lower on picked trees. Understanding the factors influencing early cone development and the impacts of cone development on tree growth will enhance our knowledge of tree maturation and assist growers in making cultural management decisions.