Environmental and vegetational gradients on an Arizona ponderosa pine landscape: Implications for ecological restoration

This research was performed in northern Arizona ponderosa pine (Pinus ponderosa) forests to enhance the ecological basis for restoration projects currently ongoing in these forests. My objectives were to: (i) develop a forest ecosystem classification on a 110,000-ha ponderosa pine landscape, (ii) determine geomorphic and soil gradients associated with the distribution of plant communities on this landscape, (iii) assess potential contributions of the soil seed bank for reestablishing understory communities, and (iv) determine understory responses to forest-floor manipulations in an existing ecological restoration experiment. I identified 10 landscape ecosystem types on this landscape, ranging from black cinders/ Phacelia ecosystems low in available moisture and total N, to mesic basalt/Festuca and aspen/Lathyrus ecosystems. Distribution of plant communities was chiefly correlated with soil texture and resource levels reflecting influences of parent materials. Soil seed bank composition was partly ecosystem-specific, and was dominated by graminoids and short-lived forbs such as aspen fleabane (Erigeron divergens). I did not detect any short-term (2 year) treatment effects on understory vegetation in the forest-floor manipulation experiment.