Forage Production Potential in a Ponderosa Pine Stand: Effects of Tree Spacing on Understorey Plants after 45 Years

We examined the development of understorey forage plant communities in relation to tree density in an experimental ponderosa pine (Pinus ponderosa) stand. We used a 45-year-old ponderosa pine spacing trial near Westwold, British Columbia, Canada, with five spacing treatments (1.22, 2.44, 3.66, 4.88, and 6.10 m) to sample understorey biomass and diversity, with a focus on pinegrass (Calamagrostis rubescens) and rough fescue (Festuca campestris)—two regionally important forage grasses. We predicted that there would be a positive correlation between tree spacing and understorey biomass and a compositional shift from pinegrass to rough fescue under increased tree spacing. We found that rough fescue, the preferred forage species, grew only under tree spacings equal to or greater than 3.66 m, with the greatest biomass at 4.88 and 6.10 m spacings, whereas pinegrass was equally abundant under all spacings. We believe that silvopasture principles could be applied to similar ponderosa pine stands to optimize and maintain both timber and forage productivity.