Resin Ducts as Anatomical Indicators of Fire in Pinus resinosa in North-Central Minnesota
Anatomical (structural) features of trees are useful in dendroecology because altered structures or anatomy can be used to date disturbance events to calendar years. Resin ducts are one anatomical feature of the annual rings of conifers that are potential indicators of anomalous growth resulting from traumatic events such as fire. Trees produce resin, a mixture of compounds, as a chemical and physical defense against injury by mechanical damage, disease, insect attacks, or fire, for example. Resin ducts in conifers deliver resin to wounded sites on the tree. Resin ducts formed from traumatic events differ from usual resin duct formation in that traumatic resin ducts are found in higher numbers in an area that experienced some form of trauma. When establishing the fire history of a tree, fire scars are traditionally used to identify the year of the injury but can be aided by the presence of traumatic resin ducts. Because resin ducts can be one measure of direct evidence of fire in conifers, I counted resin ducts in Pinus resinosa (red pine) cores from what is currently known as Itasca State Park to determine whether traumatic resin ducts were contemporaneous with the occurrence of fire events. This work aids in the identification of past fire events and helps to understand changes in fire frequency over time in support of developing management activities that support forest resilience.