The effects of fire and firefighting chemicals on soil properties and the soil–plant system were evaluated 5 years after treatment application. Unburnt soils were compared with burnt soils treated with water alone (BS) or with foaming agent (BS+Fo), Firesorb polymer (BS+Fi), or ammonium polyphosphate (BS+Ap). Soils (0–2 cm depth) and foliar material (Ulex micranthus, Pterospartum tridentatum, Erica umbellata and Pinus pinaster) were analysed for total C, total N, δ15N, nutrients (soil-available; plant total), pH and inorganic-N (soils) and vegetation cover and height. No long-term effects of firefighting chemicals on soil properties were found except for pH (BS+Fo > BS+Ap), inorganic-N and P (BS+Ap > other treatments). BS+Ap plants usually showed higher values of δ15N, N, P and Na, but less K. Soil coverage by Pterospartum and Ulex was higher in BS+Ap than in other treatments, whereas the opposite was observed for Erica; shrubs were always taller in BS+Ap. After 3 years of growth, the size of pine seedlings followed the order BS+Ap > unburnt soil > other treatments. Foliar N and P, scrub regeneration and growth of pines showed the long-term fertilising effect of ammonium polyphosphate, although the second highest pine mortality was found in the BS+Ap treatment. The foaming agent did not affect vegetation cover, and Firesorb had no noticeable effect on shrubs but the highest pine mortality.
Long-Term Effects of Forest Plantation Species on Chemical Soil Properties in Southern Rwanda
