Understory plant community dynamics in southwestern ponderosa pine forest restoration

The research in this dissertation focused on three major components related to understory plant community dynamics in southwestern ponderosa pine forest restoration in northern Arizona. Our first goal was to compare different understory plant monitoring sampling techniques and sampling sizes. Our results illustrated that the sampling technique chosen for monitoring herbaceous and shrub species richness and foliar cover in restoration studies can greatly influence the ability to detect change. We found that large area sampling techniques were the most effective at capturing species richness and rare and exotic species.; Our second goal was to quantify the effect of restoration tree thinning versus thinning and prescribed burning on propagule densities of arbuscular mycorrhizal (AM) fungi and ectomycorrhizal (EM) fungi and their relationships to plant community properties. Our results indicated that population densities of AM fungi increased rapidly following restoration thinning as well as thinning and prescribed burning treatments in northern Arizona ponderosa pine forests. The relative amount of infective propagules of AM fungi was significantly negatively correlated with overstory tree canopy cover and litter cover and positively correlated with herbaceous understory species richness and graminoid cover. In addition, our results indicated that restoration thinning alone and thinning and prescribed burning had no significant effect on EM fungal propagule densities even though their host plant was significantly reduced in thinning treatments.; Our third goal was to quantify the effect of slash pile burning on AM fungal propagule densities, the soil seed bank, soil physical and chemical properties and extant vegetation. In addition, we tested seed and soil amendments for native plant establishment on severely burned slash piles. Our results indicated that severe slash pile burning had a negative effect on AM fungal propagule densities, the soil seed bank and extant vegetation and changes soil physical and chemical properties. In addition, our results indicated that a seed and soil amendment is necessary to facilitate the establishment of native plants on severely burned slash piles in southwest ponderosa pine forests.