Gambel oak growth forms: Management opportunities for increasing ecosystem diversity

Gambel oak (Quercus gambelii) clones have several different growth forms in southwestern ponderosa pine (Pinus ponderosa) forests, and these growth forms each provide unique wildlife habitat and resource values. The purposes of this note are to review published growth-form classifications for Gambel oak, provide examples of ecological effects of different growth forms, and summarize management strategies for promoting desired growth forms. Four different growth-form classifications have been published, which generally recognize variants of three basic forms: shrubby thickets of small-diameter stems, pole-sized clumps, and large trees. These growth forms exemplify ecological and management tradeoffs. For example, shrubby forms provide browse and cover yet produce few acorns, while larger oaks supply more acorns but offer little accessible browse or cover near the ground. Large oaks can be encouraged by thinning competing trees and protecting existing large stems from damage by prescribed fire or unauthorized fuelwood harvest. Pole-sized clumps may develop from thickets through time by self-thinning. Mechanically thinning within clumps may accelerate growth of remaining stems, depending on resource allocation within clones. Burning or cutting to stimulate sprouting sustains shrub-thicket forms

Effects of smoke and fire-related cues on Panstemon barbatus seeds

Previous research has found that exposure to fire-related cues enhances germination of some plant species, and such species may exist in frequent-fire southwestern United States Pinus ponderosa forests. I performed four greenhouse experiments with Penstemon barbatus, a perennial forb common in P. ponderosa forests, testing seed responses to liquid and air smoke, charred P. ponderosa wood and leachate, heat and emergence substrates. Liquid smoke increased P. barbatus emergence to as high as 63%, 44% greater than controls, and enhanced emergence in all 4 experiments. Air smoke produced by burning P. ponderosa litter for 15 min appeared to increase emergence similar to liquid smoke. In contrast, P. ponderosa charred wood and charred wood leachate did not improve emergence, and sometimes inhibited positive effects of smoke. Heating samples at 100 C for 30 min did not affect emergence. Substrate and liquid smoke interacted in one experiment, with smoke increasing emergence more sharply on basalt and potting soil than on limestone soil. These greenhouse findings have practical implications for germinating P. barbatus, but need testing under field conditions to evaluate their importance in this species’ population biology after fire in P. ponderosa forests