Ana Mellado, Regino Zamora
The capacity of parasitic plants in structuring natural communities is increasingly recognized. These plants can affect the structure, composition and productivity of plant communities by modifying the competitive balance between hosts and non-host species and by altering the quantity and quality of resources entering the soil. Despite the progress made in this field, there is still a lack of integrative studies showing the structuring capacity of parasitic plants in forest ecosystems, where their effect may be less detectable due to the long life span of the system.
In this study we evaluate the long-term impact of Viscum album subsp. austriacum on the woody-plant community of a Mediterranean pineland. This mistletoe remains several years on the same host, exerting long-lasting, spatially concentrated effects on community and ecosystem characteristics. Mistletoe concentrates zoochorous seeds and induces changes in the soil fertility and light availability beneath the canopy of parasitized trees, which have the potential to facilitate zoochorous–plant colonization, recruitment, and growth at the same time as it weakens the host. Here, we analyse whether mistletoe-driven changes could result in a nucleus of zoochorous woody plants nourished by the abundant organic detritus accumulated under the host. We also analyse whether mistletoe effects can expand after host death.
We selected unparasitized, parasitized, and dead parasitized Pinus nigra trees, in which we studied the joint effect of mistletoe-mediated changes in soil nutrient and light availability, with the seed rain, seed predation, seedling establishment, plant recruitment, and plant growth. Light- and soil-nutrient resources were greater under parasitized trees, and intensified after host death. The seed rain was maximum under parasitized trees, where seedling recruitment proved more likely. Sapling density, richness, and growth increased with the development of parasitism.
Our findings show that V. album exerts a strong and lasting impact on the structure and dynamics of Mediterranean pinelands, with parasitized trees acting as centres for the establishment and growth of colonizing fleshy-fruited woody species, which, over the long term, promote vegetation shifts by limiting dominant pine trees and facilitating less represented fleshy-fruited shrubs.
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