Past, Present, and Future of Marcescent Mediterranean Forests

Abstract

Mediterranean forests are unique and one of the most threatened biomes worldwide (Klausmeyer and Shaw 2009). They are distributed through marked ecological gradients that are supported by a wide variety of diverse geology and contrasting bioclimatic conditions. Marcescence (i.e., the abscence of leaf fall abscission; Addicott 1982), is a life-history trait related to contrasting or transitional climatic areas such as those across Eurosiberian and Mediterranean Regions (García-Mijangos et al. 2014). Thus, marcescent forests are ecotones located in the transition between temperate areas with cold winters and mild rainy summers and mediterranean regions with dry and hot summers (Rivas-Martínez et al. 2017). We aim to provide a global overview of marcescent forests in the Mediterranean basin, a significant ecotone in terms of biogeography and conservation, by exploring the main ecological drivers that have promoted past, current and future changes in the distribution ranges of several oak species. We used a subset of oak species from the subsection Galliferae (Quercus L.), to unveil biogeographic relationships and recent or past contact between taxa, thus bringing insights to its evolutionary history and speciation. A database was built with records obtained from extensive fieldwork, herbaria review and online resources (e.g., Global Biodiversity Information Facility (GBIF), scrutinized by taxonomic experts. We used downscaled climate data to obtain potential distribution of each species through an ensemble-modelling framework (biomod2 - R package, Araújo and New 2007, Thuiller et al. 2009), across different past (Last Glacial Maximum and Middle Holocene), present and future scenarios (2050 and 2080 Hijmans et al. 2005; Representative Concentration Pathway (RCP) 4.5 IPCC 2013). Results provide new insights to advance our current understanding of the biogeographic trajectories of transiently co-occurring oak species, at the boundary of two major biomes and biogeographic regions in Southern Europe and North Africa. Furthermore, we highlight the importance of these forests for biodiversity conservation, not only as refuge of relict and narrow endemic species, but particularly for understanding white oak biogeography and evolution in Europe, anticipating future shifts driven by anthropogenic climate change.

The Ant-like Tachydromia Complex in the Iberian Peninsula—Insights from Habitat Suitability Modelling for the Conservation of an Endemism (Diptera: Hybotidae)

“…The Central System corresponds to the largest continuous area of suitable habitat. Unsuitable regions comprise most of the Southern parts of the Peninsula and, especially, the warmer and dryer plains (e.g., northern and southern sub-plateau and Ebro depression) with typical Mediterranean influence where evergreen forests have a higher representation [ 8 , 30 ].…”

“…Additionally, its presence is very likely at the Los Alcornocales National Park area, which receives horizontal precipitation in the summer. Indeed, there are several habitat patches that retain high humidity in the submediterranean life zone and, thus, function as ecological “islands” [ 8 , 9 ]. Due to their inherent Temperate Eurosiberian influence, these patches act as refugia for paleoclimatic relict forests.…”

“…These areas include Monchique and surrounding mountains in southwest Portugal, the Penibaetic system, and the Catalonian coastal range. These particular forest-habitats, distributed across submediterranean ecotone-areas, which are mostly composed of marcescent oaks, will be severely affected by predictable climatic changes [ 8 , 9 , 29 , 39 , 48 ]. Particularly, the Iberian southwest and the Catalonian coastal mountains harbor remarkable oak taxa, including endangered species (e.g., Quercus canariensis ) and species with unique evolutionary characteristics (e.g., Q. estremadurensis or Q. xcerrioides [ 49 ]).…”

“…In contrast, the submediterranean variant of the temperate macrobioclimate corresponds to areas commonly fed by moderate summer precipitation, ascribed to the potential distribution of marcescent oaks ( Q. broteroi, Q. canariensis, Q. xcerrioides, Q. faginea, Q. lusitanica, Q. marianica, Q. pyrenaica, and Q. subpyrenaica ) [ 9 , 28 ], with the overlap areas between both, considered as transitional between temperate to submediterranean. By exclusion, the Mediterranean areas are mainly linked with the potential distribution of evergreen oaks ( Q. coccifera , Q. suber , and Q. rotundifolia ) from subgenus Cerris [ 8 , 28 ].…”

“…Tachydromia species are often present in climactic deciduous and marcescent forests, primarily dominated by Quercus L. spp. and Fagus sylvatica L. [ 1 ], mainly across temperate bioclimatic belts, but also in transitional submediterranean areas [ 8 , 9 , 10 ]. Most populations are found in highly fragmented landscapes, often due to disturbances of anthropic origin, driven by land-use change and invasive plant species.…”