Predicting root biomass of burned and unburned white oak advance reproduction from diameter and height

The size especially the root size, of advance oak (Quercus spp.) reproduction provides the best indication of the growth potential after release or top-kill. This study examined the relationship between the size of the root system and various diameter/height measurements for small (<60 cm) white oak (Q. alba L.) seedlings. Diameters measured at the top of the litter and humus layers and at the root collar were tested for their ability to predict root biomass on burned and unburned sites. Despite their close physical proximity, separate equations were required for burned and unburned sites when predicting root biomass from diameters measured at the humus and root collar locations, as well as height and diameter/height combinations. On burned sites, all diameter measures were good predictors, accounting for 75 to 86% of the total variance of root biomass. On the unburned site, the best predictor was the diameter measured at the root collar, accounting,for 85% of the total variance root biomass. Diameter at the litter level accounted for only 55% of the total variance of root biomass whereas diameter at the top of the humus layer accounted for 53%. When dealing with stands of unknown disturbance history. the diameter measured at the root collar should be used to predict root biomass for small seedlings.