Conditions for translocation of a key threatened species, Dianthus inoxianus Gallego, in the southwestern Iberian Mediterranean forest

Abstract

Natural Mediterranean forest ecosystems, especially pine plantations, are severely affected by human disturbances and global change consequences. To achieve an appropriate and complete management of these areas, key species beyond dominant ones that would support vulnerable ecosystem functions should be considered. Dianthus inoxianus Gallego is a rare and endemic species with unique traits that occurs in southwestern Iberian pine forests. Thus, the development of an efficient translocation protocol disentangling the factors that affect the establishment of this species, its physiological status and long-term survival is crucial to the future integrated forest management. In this study, we aimed to assess several influential treatments and their cost trade-offs by monitoring survival and stomatal conductance (gs) of D. inoxianus transplants for a short period. We performed an experimental translocation of individuals from exploitation areas to a fenced reserve site, subjecting them to the interaction of three treatments: transplant time (January or March), transplant source (in situ direct translocation or ex situ rooted cuttings) and water supply (constant drip irrigation or no irrigation). Benign environmental conditions (winter) during the establishment phase and additional irrigation until the end of the dry season were revealed as key factors determining survival through the stressing periods (i.e., transplant shock and first summer). This survival pattern was characterised by two major peaks (resprouting), which correspond to gs increases after these stressing events. The source treatment also played a significant role by interacting with transplant time: direct transplants showed a higher survival in January and those from cuttings in March. However, survival results were evaluated with respect to the costs of each treatment combination: direct transplants in January without irrigation and those from cuttings in March with irrigation were identified as the best choices. Moreover, radiation and minimum temperature were the two climatic variables with the greatest effects on survival and gs. Overall, our results suggest that the success of D. inoxianus translocation is constrained by climatic conditions and characterised by its great stress tolerance to root damage, drought and high temperatures. We suggest that the inclusion of this type of species in ecosystem management strategies would provide an enhanced stability as well as long-term resilience to Mediterranean forests.