According to the competitive exclusion principle, species with low competitive abilities should be excluded by more efficient competitors, and yet they generally remain as rare species. Here, we describe the positive and negative spatial association networks of 326 disparate assemblages, showing a general organization pattern that simultaneously supports the primacy of competition and the persistence of rare species. Abundant species monopolize negative associations in about 90% of the assemblages. Contrarily, rare species are mostly involved in positive associations, forming small network modules. Simulations suggest that positive interactions among rare species and microhabitat preferences are the most likely mechanisms underpinning this pattern and rare species persistence. The

Fire regime changes are considered a major threat to future biodiversity in the Mediterranean Basin. Such predictions remain untested, however, given that fire regime changes and their ecological impacts occur over timescales that are too long for direct observation. Here we analyse centennial-3 and millennial-scale shifts in fire regimes and compositional turnover to track the consequences of fire regime shifts on Mediterranean vegetation diversity. We estimated rate-of-change, richness and compositional turnover (beta diversity) in 13 selected high-resolution palaeoecological records from Mediterranean Iberia and compared these to charcoal-inferred fire regime changes. Event sequence analysis showed fire regime shifts to be significantly temporally associated with compositional turnover, particularly during the last three millennia. We find that the timing and direction of fire and diversity change in Mediterranean Iberia are best explained by long-term human-environment interactions dating back perhaps 7500 years. Evidence suggests that Neolithic burning propagated a first wave of increasing vegetation openness and promoted woodland diversity around early farming settlements. Landscape transformation intensified around 5500-5000 cal. yr BP and accelerated during the last two millennia, as fire led to permanent transitions in ecosystem state. These fire episodes increased open vegetation diversity, decreased woodland diversity and significantly altered richness on a regional scale. Our study suggests that anthropogenic fires played a primary role in diversity changes in Mediterranean Iberia. Their millennia-long legacy in today's vegetation should be considered for biodiversity conservation and landscape management.

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Knowledge about vegetation and fire history of the mountains of Northern Sicily is scanty. We analysed five sites to fill this gap and used terrestrial plant macrofossils to establish robust radiocarbon chronologies. Palynological records from Gorgo Tondo, Gorgo Lungo, Marcato Cixé, Urgo Pietra Giordano and Gorgo Pollicino show that under natural or near natural conditions, deciduous forests (Quercus pubescens, Q. cerris, Fraxinus ornus, Ulmus), that included a substantial portion of evergreen broadleaved species (Q. suber, Q. ilex, Hedera helix), prevailed in the upper meso-mediterranean belt. Mesophilous deciduous and evergreen broadleaved trees (Fagus sylvatica, Ilex aquifolium) dominated in the natural or quasi-natural forests of the oro-mediterranean belt. Forests were repeatedly opened for agricultural purposes. Fire activity was closely associated with farming, providing evidence that burning was a primary land use tool since Neolithic times. Land use and fire activity intensified during the Early Neolithic at 5000 BC, at the onset of the Bronze Age at 2500 BC and at the onset of the Iron Age at 800 BC. Our data and previous studies suggest that the large majority of open land communities in Sicily, from the coastal lowlands to the mountain areas below the thornycushion Astragalus belt (ca. 1,800 m a.s.l.), would rapidly develop into forests if land use ceased. Mesophilous Fagus-Ilex forests developed under warm mid Holocene conditions and were resilient to the combined impacts of humans and climate. The past ecology suggests a resilience of these summer-drought adapted communities to climate warming of about 2°C. Hence, they may be particularly suited to provide heat and drought-adapted Fagus sylvatica ecotypes for maintaining drought-sensitive Central European beech forests under global warming conditions.

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The Holocene vegetation dynamics of low-and mid-altitude areas of inland Iberia remain largely unknown, masking possible legacy effects of past land-use on current and future ecosystem trajectories. Here we present a 4000year long palaeoecological record (pollen, spores, microscopic charcoal) from a mire located in the Cabañeros National Park (Toledo Mountains, central Spain), a region with key conservation challenges due to ongoing land-use changes. We reconstruct late Holocene vegetation history and assess the extent to which climate, land-use and disturbances played a role in the observed changes. Our results show that oak (Quercus) woodlands have been the main forested community of the Toledo Mountains over millennia, with deciduous Quercus pyrenaica and Quercus faginea more abundant than evergreen Quercus ilex and Quercus suber, particularly on the humid soils of the valley bottoms. Deciduous oak woodlands spread during drier periods replacing hygrophilous communities (Betula, Salix, hygrophilous Ericaceae) on the edges of the mire, and could cope with fire disturbance variability under dry conditions (e.g. ca.

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Fire on ice and frozen trees? Inappropriate radiocarbon dating leads to unrealistic reconstructions Comment on Carcaillet & Blarquez (2017) 'Fire ecology of a tree glacial refugium on a nunatak with a view on Alpine glaciers'.The questions as to where and how trees survived the Quaternary ice ages are key for understanding climate-driven range expansion processes (Clark, 1998;Giesecke et al., 2017) and the influence of ice-age legacies on current mid-and high-latitude biodiversity patterns (Willis & Whittaker, 2000). Such questions have long intrigued plant ecologists, biogeographers and palaeoecologists (Bennett et al., 1991;Kaltenrieder et al., 2009) and have recently become the focus of combined molecular-ecological and biogeographical studies (Magri et al., 2006;Wagner et al., 2015).The classic southern-refugia paradigm (van der Hammen et al., 1971;Tzedakis et al., 2013) postulates treeless landscapes in central Europe and at the margins of the continental and Alpine ice-sheets for the time of the Last Glacial Maximum (LGM; c. 23 000-19 000 calendar years before present (cal yr BP, where 0 cal yr BP = AD 1950), that is, the interval representing the most extreme conditions of the Last Glacial). Widespread cold-adapted alpine and arctic plants and boreal dwarf shrubs are documented to have occurred north of the Alps (Birks & Willis, 2008;Tzedakis et al., 2013), while small populations of temperate and boreal trees persisted in southern European peninsulas (Iberia, Italy, and the Balkans) (Bennett et al., 1991). Boreal and mountain conifers (e.g. Larix decidua Mill. and Pinus cembra L.) occurred at more northerly locations (up to c. 46°N) in eastern Europe, and grew closer to the southern margin of the Alpine and Carpathian ice-caps than temperate trees Vescovi et al., 2007;Kune s et al., 2008). This view has been challenged by the alternative interpretation that temperate plant species could have survived the LGM further north in locally favourable conditions as small populations that may be hard to detect with palaeoecological tools (e.g. Stewart & Lister, 2001;Heikkil€ a et al., 2009;V€ aliranta et al., 2011). Recently, Carcaillet & Blarquez (2017 presented evidence for the occurrence of an LGM 'tree refugium' located at c. 2200 m above sea level (asl) on a nunatak (a mountain top or peak emerging from or at the edge of an ice sheet or glacier) on the western flank of the European Alps. The reported presence of L. decidua and P. cembra plant macrofossils during the LGM in sediments from Lake Miroir, a site located close to modern treeline altitude (TLA), challenges the consensus on the LGM distributions of trees in