Not just about the trees: Key role of mosaic-meadows in restoration of ponderosa pine ecosystems

Abstract

Abstract Historical pre-settlement conditions in ponderosa pine ecosystems ranged from savannas ( 6 m from overstory trees) on understory vegetation in five recently thinned ponderosa pine stands and one long-undisturbed stand in Colorado. We also compared historical spatial patterns in mosaic-meadows to current conditions in ponderosa pine stands and determined whether thinning treatments are recreating historical conditions. Mosaic-meadows in ponderosa pine ecosystems declined substantially from a mean of 55% of stand area in 1860–1875 to 7% in 2010–2013 prior to tree thinning. The loss of mosaic-meadows has ecological consequences for the function of ponderosa pine ecosystems because spatial patterns of mosaic-meadows strongly influenced understory vegetation. At our sites, understory cover increased by 3%/m with distance from overstory trees, and understory richness increased from 6 species/m2 within 1 m of overstory trees to 9 species/m2 at 10 m away from overstory trees. Cover and richness of understory vegetation (especially native forbs) responded rapidly to creation of mosaic-meadows within 1 to 4 years after treatment. Thinning treatments at two stands brought the coverage of mosaic-meadows within the historical range of variation, but there was a noticeable lack of mosaic-meadows >12 m from overstory trees at all treated stands. Restoration of the fundamental ecological characteristics of ponderosa pine ecosystems should intentionally include variably sized mosaic-meadows.