Relationship Between pine decline symptomology and mineral nutrition at Fort Benning military reserve

Background/Question/Methods

Pine decline is a relatively new forest health issue in the southeastern United States which is characterized by sparse, chlorotic crowns, low annual stemwood production, and isolation of fungal pathogens from roots. The sustainability of Pinus on sites where soil resources are inherently low or depleted is due, in part, to physiological mechanisms that allow the tolerance of water and mineral nutrient deficiencies. Disruption of these tolerance mechanisms impairs tree health. We speculate that pine decline at Fort Benning Military Reserve is linked to ecophysiological events that cause intolerance of soil resource limitations. Our present objective is to analyze the foliar and root mineral nutrition of longleaf pine trees that are asymptomatic or symptomatic of pine decline. 

On the Fort Benning Military Reserve in Georgia, 16 plots represent three ages of longleaf pine (i.e., <10 yr, 10 to 40 yr, and > 40 yr), and two levels of pine decline (i.e., asymptomatic (A), and symptomatic (S)).  Symptomology was assigned to plots using the Loblolly Pine Decline Risk Map. In July 2007, a series of measurements and sampling was conducted on three dominant longleaf pine trees per plot (i.e., 48 trees). At this time, small woody roots and two age classes of upper-crown foliage were sampled, and their mineral nutrition was evaluated.

Results/Conclusions

Foliar macronutrient concentrations were sufficient or nearly sufficient, and did not differ by symptomology or age. Concentrations of N, P, K, Ca, and Mg in the last flush of 2006 averaged 0.81, 0.08, 0.45, 0.24, 0.09%, respectively. Similar results were found for most foliar micronutrients (i.e., B, Cu, Fe, Zn). Foliar and root Mn concentrations were 28% and 58% less on the S plots compared to the A plots. Symptomologies differed regarding relationships between tissue Mn concentration and both Ca and Mg concentrations. On the A plots, for example, Mn concentration explained 50% of the variation associated with the Ca concentration of the last flush of 2006, but on the S plots, the relationship between foliar Mn and Ca was not significant. Our assessment of mineral nutrient concentrations indicates that one component of pine decline may be interference of Mn with the function of Ca and Mg. Together with tree growth, root disease, and site quality data, this information will be used to hypothesize the central cause of pine decline at Fort Benning Military Reserve, and provide insight to its origin elsewhere in the southeastern United States.