Plant-plant interactions influence post-fire recovery depending on fire history and nurse growth form

Plant-plant interactions are among the most important factors affecting the natural recovery of vegetation. While the impacts of nurse plants on species composition and biodiversity are well documented, the effects of different nurse’s growth forms on all biodiversity components including taxonomic, functional, and phylogenetic diversity have been less studied and compared, especially for their effects on different times after fire disturbance. This research was focused on comparing the effects of a perennial grass (Elymus hispidens), a perennial herb (Phlomis cancellata), and a high shrub species (Lonicera nummulariifolia) on species composition and the biodiversity components, and how these impacts change across five sites with short-term (1 and 4 years sites), long-term (10 and 20 years sites) times since last fire and a control site where no fire was known in recorded history in semi-arid shrublands of Fereizi Chenaran located in Northeast of Iran. The changes of species composition and taxonomic, functional, and phylogenetic diversity were calculated with respect to the presence/absence of nurse’s growth forms, fire history, and their interactions. Nurse shrubs affected species composition and all biodiversity components, whereas all indices were reduced when considering Elymus grass as nurse plant. On the other hand, the herb Phlomis enhanced species composition and taxonomic diversity, while it had a negative effect on functional and phylogenetic diversity. Such specific effects of nurse types were mostly observed under long timescales (i.e., 10- and 20-year sites). Interestingly, the relative importance of nurse types and time since the last fire largely explained the variation of species composition and biodiversity components, with larger effects of nurse types on all biodiversity components. However, we found a significant contribution of fire explaining variation of species composition and phylogenetic diversity. These results indicated nurse plants can affect the post-fire recovery of vegetation by providing specific mechanisms controlling beneficiary relatedness depending on their growth forms and time scales since the last fire. Therefore, these findings suggest perennial plants in the form of nurse species as a useful factor to develop techniques of active restoration in burned ecosystems.