Thinning and chipping small-diameter ponderosa pine changes understory plant communities on the Colorado Front Range

Thin trees within forests: effects on understory plants

A replicated, controlled study in 1994-2005 in temperate coniferous forest in Colorado, USA (Wolk & Rocca 2009) found that thinning increased understory vegetation cover and the proportion of non-native species. Understory vegetation cover (unthinned: 3.9%; thinned: 6.1%; thinned and chipped: 7.1%) was higher in thinned and chipped plots than unthinned plots. The proportion of non-native understory species was higher in the thinning treatments (18% in both) than the unthinned treatment (14%), while the total number of species/1,000 m² was similar between treatments (unthinned: 53; thinned: 47; thinned and chipped: 48).  Data was collected in 2005-2006 in 31 plots (1,000m²) established in 1994. Six plots were unthinned, 13 thinned (harvested matter removed from the site) and 12 were thinned and chipped (harvested matter chipped and distributed on the site).