Evrona Mistletoe parasitism

Effects In desert ecosystems, the long-term soil effects of oil contamination can weaken trees, and hemiparasitic mistletoes may exacerbate this stress. We investigated how terrestrial oil spills influence host condition and mistletoe parasitism in acacia woodlands. The Evrona Nature Reserve (southern Arava, Israel) offers a time-staggered natural experiment, with sites affected by pipeline spills in 1975 and 2014 and nearby undisturbed controls. In March 2024, we surveyed Acacia raddiana and Vachellia tortilis, assessing host vitality, counting Plicosepalus acaciae infection sites, estimating the proportion of parasitized foliage from photographs, and quantifying the distance to neighboring trees. Using GLMs, we found that host condition was lower in spill-affected areas, and V. tortilis consistently exhibited poorer condition than A. raddiana. Parasitism showed a clear temporal trend, i.e., infection intensity and parasitized foliage peaked 10 years after a spill – when hosts remained present but physiologically weakened – and were lowest after 50 years, reflecting reduced host availability rather than site recovery. Greater neighborhood distance reduced both infection-site counts and parasitized foliage, indicating density-dependent spread. Together, these findings link spill history to predictable shifts in host condition and mistletoe pressure, with consistent species-level differences and a pronounced effect of local host isolation.