| Summary: | Orobanche laxissima (Orobanchaceae) is a polyphagous holoparasite of the roots of 14 species of trees and shrubs in the Caucasus (the region on the border of Europe and Asia). This parasite is expansive but in a limited geographic area and it was reported to occur in natural or seminatural forest and shrub habitats, and recently also in horticulture and arboriculture. In this study, the ecological niche modeling (ENM) approach was used to estimate the possible effects of climate change on the niche of O. laxissima and evaluate the effect of its parasitic relationships with 10 trees and shrubs and the chances of survival of this species of forest habitats. Moreover, the model for the Last Glacial Maximum was created to evaluate the general pattern of the distribution of studied species niches. Many of the hosts of this parasite are trees that are the dominant component of the most important forests in the Caucasus. Climate change may affect holoparasites both directly through effects on its physiology and indirectly as a consequence of its effects on their host plants and forest communities. The glacial range of O. laxissima was 82% smaller than currently recorded. Its occurrence is related mostly to precipitation in the driest month (bio 14) as this species requires a substantial amount of rain even in the dry season. According to our models, O. laxissima is likely to increase its current geographical range from 30% to 52%, as a response to global warming, especially in areas in the Caucasus, in the Black Sea Region in southern parts of the Crimean Peninsula in Russia, and northern Turkey. Only the most extreme SSP5–8.5 scenario will be damaging for this species, with a 21–35% range contraction. Monitoring parasite populations is a very important part management, and in our case, it can also be useful for predicting the effects of climate change on trees and, in many cases, unique refugial deciduous forest communities, such as the Colchic rainforests.
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