Soil fertility response to Ulex europaeus invasion and restoration efforts.
Invasive plant species can substantially alter the soil fertility of the ecosystems they invade, and in doing so have the potential to reduce the suitability of the soil for native species. Even after removal of the invader these alterations can inhibit the reestablishment of native species. We evaluated the impact of invasion by the leguminous shrub Ulex europaeus on soil properties on Mauna Kea, HI. We also investigated the effect of efforts to remove U. europaeus and restore native ecosystems in the study area; where the efforts included bulldozing the U. europaeus and planting introduced Cryptomeria japonica to compete with regenerating U. europaeus. Mauna Kea supports a strong rainfall gradient and substantial associated variation in soil properties. We use statistical models to extract the effect of invasion and restoration from the influence of rainfall. We found U. europaeus decreases soil pH, calcium content, base saturation, and labile phosphorus. Restoration efforts over an 11-year period restored the soil's calcium and phosphorus content to levels comparable to those found in uninvaded soils on Mauna Kea, demonstrating that the effects of U. europaeus on soils are reversible.