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Global warming is changing the structure and elevational limits of treelines around the world. This could become a threat particularly on islands, where usually high mountain ecosystems occupy small areas. Tenerife, with a maximum elevation of 3715 m, is an excellent example of this. In this subtropical island, the treeline composed by endemic pine forests is expected to go up in elevation due to global warming, invading the summit scrub ecosystem. However, there is a lack of knowledge about shifts and trends of the island treeline from a multitemporal perspective and how invasive herbivores are influencing these changes. In this study, we evaluated the past and current state of the Pinus canariensis treeline on the southern areas of Tenerife, where natural forests persist, and an increase in temperature due to global warming has been already detected in the last decades. For that purpose, we counted the number of pine trees in aerial photographs for the years 1963, 1987 and 2016 and performed generalized additive models to evaluate the role of the different macro-variables involved in the regeneration processes. Complementarily, we performed ten transects to evaluate current forest structure and the influence of invasive herbivores (rabbits and mouflons) from 1600 m to the upper limits (2400 m). Our results reveal an increase in tree density and slow but consistent advance of the treeline in this part of the island during the last 53 years. Interestingly, positive relationships were found between number of trees and temperature. On the contrary, negative correlation was detected between seedlings and saplings and herbivores, a factor that is influencing the forests structure at all elevation levels. Our results show the importance of the herbivore control to ensure a healthy forest structure that allow an adequate migratory capacity of the species with the global warming.