PS 42-40 - The role of soil amendments and site characteristics in modifying priority effects during ecological restoration

Background/Question/Methods

Priority effects occur when early arrivals into a plant community affect the success of later arriving species. Priority effects of early and late successional species can be applied in ecological restoration to understand how to increase native richness and productivity, while limiting invasive plants. In addition, environmental factors and soil amendments may change the strength or direction of priority effects.

We established 48 1m² plots each in three experimental sites in Kenna Cartwright Park in Kamloops, British Columbia. Our sites fell within the Ponderosa Pine (PP) biogeoclimatic (BGC) zone, the Bunchgrass (BG) zone, and a transitional PP/BG zone. Our amendment treatments were 10Mg/ha biochar + 10Mg/ha compost, straw matting, biochar/compost + straw matting, and a control with no biochar or straw-matting. We had four seed arrival treatments: early successional first (ES), late successional first (LS), early and late successional species at the same time (ESLS), and annual ryegrass first before ESLS (RESLS). We used a three-month interval between the first and second sowing, with a total seed density of 800g/m². We sampled vegetation by species immediately before the second sowing, and obtained multispectral remote sensing vegetation indices, including the normalized differentiated vegetation index (NDVI), two months after the second sowing.

Results/Conclusions

After three months (before the second seeding), we found significant differences between sites in cover of total, native, and exotic species (P < 0.001). The PP site displayed between 52% and 82% higher total and native cover and richness than the BG and PP/BG sites, while the PP/BG site displayed up to 200% higher cover of exotic species. Surprisingly, control plots had higher native species cover than plots containing amendments. The BG site had a higher grass cover than PP and PP/BG sites, while forb cover was higher in control plots.

Two months after the second seeding, we observed a significant three-way interaction between site type, arrival treatment and order of arrival for NDVI (F_{18, 96} = 1.833, P = 0.032). The PP site had the highest NDVI, with LS first plots showing higher NDVI in biochar treated plots compared to other plots. Results in PP/BG and BG sites were mixed, but plots containing straw-matting generally displayed the lowest cover.

Pre-second seeding results and early post-second seeding results indicate that the progress of a restoration effort may depend on site characteristics. Further monitoring is needed to elucidate the effect of amendments and priority effects