Use of native annual forbs and early seral species in seeding mixtures for improved success in Great Basin restoration

Background/Question/Methods

Use of native annual and early seral species in Great Basin rangeland reseeding efforts may increase invasion resistance and facilitate succession to desired vegetation, thus improving restoration/rehabilitation success. Early serals may be similar to exotic annual grasses in growth and resource acquisition strategies. Because they occupy a similar ecological niche, theory predicts they would compete more strongly against invasives like cheatgrass and medusahead. As invasion and success of exotic grasses appears to be associated with soil type, competitive interactions may also depend on soil type. We tested emergence and seedling establishment success of two native seed mixes when growing in the presence of cheatgrass or medusahead in two soil types of contrasting texture. Performance of a novel early seral mix (including annual forbs and early seral grasses and forbs) was compared with that of a late seral mix representative of species commonly used in restoration. Representative clay loam and sandy loam soils were sunk in treepots into the ground in Reno, NV using a common garden approach. Natives were seeded with and without an exotic (cheatgrass or medusahead), into both soils in a fully crossed experiment. Emergence and seedling survival were monitored biweekly from first emergence (11/2010) through spring (5/2011).

Results/Conclusions

Cumulative emergence of natives was higher in the early seral mix (P<0.001) and in sandy loam (P<0.01), when growing with exotics or alone. Not surprisingly, cumulative survival of natives was lower when natives were growing in competition compared to alone (P<0.01). Reductions in native survival when growing in competition did not differ between cheatgrass and medusahead (P>0.05). Similar to emergence, survival was higher in sandy loam (P<0.05). However, in contrast to emergence, seed mix did not have an effect on survival (P>0.05). Low success at the seedling stage is likely critical in determining the eventual success of native reseeding efforts. With higher emergence and similar seedling survival, the early seral mix may have a greater chance of persisting in the presence of cheatgrass or medusahead in comparison to the late seral mix. Both emergence and seedling survival were higher in sandy loam relative to clay loam, suggesting that restoration/rehabilitation efforts may have a greater chance of success in sandy loams. Our preliminary findings suggest that use of native annuals and early serals in reseeding efforts may result in greater density of natives in communities where exotics are present.