Changes in land use, the introduction of exotic and invasive species of flora and fauna, and climate change are some of the main threats facing laurel forests. The study of the vulnerabilities and strengths of the species that make up these forests is essential for the creation of effective strategies and tools that guarantee the conservation and recovery of nature’s jewel.
Laurel forests are subtropical forests that occur in extratropical areas with high relative humidity and mild average temperatures. During the Tertiary, these forests occupied vast extensions in Europe and North Africa. Nowadays, they represent a relict of a type of thermophilic forest that took refuge in the Macaronesia biogeographic region, which is made up of five volcanic archipelagos of the North Atlantic (Azores, Madeira, Savage Islands, Canary Islands, and Cape Verde).
Macaronesia is characterized by its exceptional biodiversity, with a large proportion of endemic marine and terrestrial species, and by housing one of the most unique laurel forests in the world. Laurel forests are found only on some of the islands of three of the five Macaronesian archipelagos (Azores, Madeira, and the Canary Islands) (Fig. 1.). These forests, dominated by tree species with lauroid leaves, appear between 300 and 1,500 m a.s.l. (depending on the island), normally immersed in low clouds, which provides the necessary humidity for their persistence in these areas.
Terceira is one of the 9 islands that make up the Azores Archipelago (36°55′ 39°43′ N and 25°00’–31°15′ W) and one of the few where laurel forests appear. On this island, the laurel forest is represented by a forest formation with a low tree canopy, between 3 and 5 meters, with the tallest trees reaching 6 m. Some of the most abundant species, and endemic in Azores, are Erica azorica Hochst. Ex Seub, Juniperus brevifolia (Seub.) Antoine, Ilex azorica (Loes.) Tutin and Laurus azorica (Seub.) Franco.
Over time, human activities have profoundly altered forest ecosystems, deforestation associated with changes in land use and the introduction of exotic species (Hedychium gardnerianum Sheppard ex Ker-Gawl., Hydrangea macrophylla (Thunb.) Ser., Pittosporum undulatum Vent., etc.) (Fig.2.) have been the main threats to the conservation of the laurel forest in the Azores and specifically on the island of Terceira. Currently, we must add one more to these threats, climate change. The decrease in rainfall and the increase in the frequency of droughts seriously endanger a type of ecosystem for which, until now, water availability has not been a problem. The threats that these forests face make their study of vital importance, since only by knowing these forests can we generate comprehensive management strategies that allow us to maintain over time this jewel that is the laurel forests.
The study that we are carrying out on the island of Terceira is included within the LAUREL project, which has as its main objective to determine the vulnerability of the different forest species of the Macaronesian laurel forests to climate change, detect more sensitive areas, and understand their forest dynamics in the face of disturbances. To study the laurel forests of the Azores, we selected three well-preserved forests on Terceira Island and established three circular plots. In these plots we sampled all tree species with Pressler Augers, extracting wood cores from the trees. During my stay at the University of Azores, at the Angra do Heróismo Campus (Terceira, Portugal) I processed and analyzed the samples using standard dendrochronological techniques.
The results obtained so far through the LAUREL project show the dependence of the secondary growth of tree species on water availability in the humid period, confirming the vulnerability of forests to global warming. On the other hand, strong storms play a fundamental role in the growth dynamics of laurel forest trees, showing large increases in the secondary growth of temporary trees in strong winds.
The great capacity of Macaronesian tree species to recover after the cessation of human disturbances and strong storms highlights the great potential of the species for the natural and/or artificial establishment of new individuals. These results open a window of opportunity for the regeneration and conservation of the native forests of these islands.