Competition Indices Identify Forb Species That Promote Overyielding of a Dominant Grass in Grassland Restoration

Overyielding is a common phenomenon. Overyielding of dominant grasses when in competition with common forbs during grassland restoration could lead to lower plant diversity. My objective was to characterize overyielding of Andropogon gerardii in competition with fcommon forbs. I collected soils representing different stages of restoration (0, 4, and 16 years restored) and conducted a pairwise competition experiment with a dominant grass, Andropogon gerardii, in competition with four subordinate forbs (Oligoneuron rigidum L., Liatris punctata Hook, Lespedeza capitata Michx., or Desmanthus illinoensis Michx.). Relative yield indices (RY) were calculated by comparison with a two-individual monoculture of A. gerardii with both per grass biomass and per grass net absolute tiller appearance rate (TAR). Overyielding of A. gerardii was in competition with Oligoneuron rigidum was indicated by RY values (greater than1) using both biomass and TAR measurements. These findings suggest that O. rigidum should be given low priority for inclusion in tallgrass prairie restoration seed mixes.

Characterisation of the fuel and fire environment in southern Ontario’s tallgrass prairie

Prescribed burning can be an integral part of tallgrass prairie restoration and management. Understanding fire behaviour in this fuel is critical to conducting safe and effective prescribed burns. Our goal was to quantify important physical characteristics of southern Ontario’s tallgrass fuel complex prior to and during prescribed burns and synthesise our findings into useful applications for the prescribed fire community. We found that the average fuel load in tallgrass communities was 0.70 kg m–2. Fuel loads varied from 0.38 to 0.96 kg m–2. Average heat of combustion did not vary by species and was 17 334 kJ kg–1. A moisture content model was developed for fully cured, matted field grass, which was found to successfully predict moisture content of the surface layers of cured tallgrass in spring. We observed 25 head fires in spring-season prescribed burns with spread rates ranging from 4 to 55 m min–1. Flame front residence time averaged 27 s, varying significantly with fuel load but not fire spread rate. A grassland spread rate model from Australia showed the closest agreement with observed spread rates. These results provide prescribed-burn practitioners in Ontario better information to plan and deliver successful burns.