Hardwood re-sprout roots – more than meets the eye

By Dr. Kevin Robertson, Fire Ecology Program Director

Broadleaf woody plants that re-sprout after being top killed by fire make up a large portion of the groundcover plants in natural southeastern U.S. pine forests. Sometimes it is important to estimate the root biomass of groundcover plants because of their contribution to competition, carbon sequestration, soil dynamics, and other ecosystem processes. Under normal conditions, root biomass is related to the biomass of the above-ground part of the plant. However, where there is frequent fire, this relationship breaks down because the top part of the plant is repeatedly killed while the roots stay intact.  

To be able to estimate the root biomass of woody re-sprouts, we measured both their above-ground (stem and leaf) biomass and root biomass to find out the relationship between the two at one year following fire. We studied the five most common woody plant species and selected plants with stems and leaves ranging in height from a less than a meter to overhead height.

Sweet Gum RootsThe results show the expected relationships between stem and leaf biomass and root biomass, but that the relationship is different for different species (see Figure). At one year following fire, there is always much more root biomass than above-ground biomass. An important management implication is that the rate of re-sprout growth and size of re-sprouts, at a certain time since fire, is more strongly related to root size, then to the fire intensity, season, or frequency of fire in the short term. That is to say, when it comes to burning woody re-sprouts, you tend to get back what you had before. However, over the course of multiple fires, fire frequency and season are expected to influence root growth (or root loss) and thereby affect re-sprout growth rate and size.        


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