Root system architecture of Pinus ponderosa three decades after copper root pruning in a container nursery

We revisited a Pinus ponderosa planting 32 years after it was established with one-year-old seedlings grown in copper-treated containers that modified their root systems. This technique was intended to promote more root egress after outplanting from the entire length of the root plug with a goal of providing greater stem stability. After excavating and digitizing the root systems of five treated and five non-treated plants, we observed that regardless of treatment, all trees initiated more roots and accumulated more root volume in apparent response to mechanical stresses invoked by wind and slope, with more roots occurring windward and downslope. Few differences were noted between treatments for root length and volume for either the cage or the entire root system. Trees treated with copper were taller (8%) with stouter taproots (less taper) and less root volume in the lower soil profile than control trees. Although the copper treatment may have induced short-term changes to root system architecture, the long-term, plastic response of this species to mechanical stresses, and the time duration involved, was more critical to the observed expression of traits.