Search

Climate change projections suggest a precarious future for the Monarch butterfly (Danaus plexippus) as the suitable climatic habitat of its exclusive overwintering host Abies religiosa (oyamel, Sacred fir, a conifer endemic to Mexico) inside the Monarch Butterfly Biosphere Reserve (MBBR) is expected to disappear by 2090. Since the upper elevation limit of A. religiosa is approximately 3,500 m and the summits of mountains within the MBBR are ca. 3,550 m, we tested the feasibility of establishing A. religiosa at four locations outside its current geographic range in the MBBR, on a geographically close volcano, Nevado de Toluca at 4000 (timberline, an extreme site), 3,800, and 3,600 m (to test species range expansion upward in elevation), and at 3400 m (a reference site, slightly lower than the upper elevation limit of A. religiosa). Using existing shrubs as nurse plants to protect the seedlings from extreme temperatures, at each site we planted five to eight populations, originating between 3,100 and 3,500 m within the MBBR. After three growing seasons in the field (6 years after sowing), we found that: (a) survival and height increment declined steeply with test site elevation; (b) even at the highest sites (3,800 and 4,000 m), survival was acceptable, at 68 and 44%, respectively, although the growth was very poor at 4000 m; (c) populations responded similarly to transfer; (d) transfer effects were best accounted for by annual dryness index; (e) to compensate for the expected 2.3°C increase in mean annual temperature or 0.009 √°Cmm−1 increase of annual dryness index from the reference period (1961–1990) to the decade centered in 2060, it would be necessary to shift populations approximately 500 m to higher elevations; and (f) upward transfers to compensate for the 2.3°C increase in mean annual temperature are expected to result in height increment and survival that are approximately 47 and 21% lower, respectively, than values expected at zero transfer distance. We conclude that the establishment of A. religiosa at 3600 and 3,800 m is feasible and that planted stands could eventually serve as overwintering sites for the Monarch butterfly under projected future climates.

Societal Impact Statement Mexico's extraordinary tree diversity is threatened by the increasing demand for resources because of the tenfold population growth in the last century. The conservation status of trees and both urban and rural livelihoods are also negatively affected by agriculture, mining and tourism. Nearly 60% of the Mexican endemic and near endemic tree species whose conservation status we have assessed for the Red List of the International Union for Conservation of Nature are threatened, almost double the percentage of threatened trees worldwide. If no measures are taken to protect this tree diversity properly, these resources will be forever lost for human sustainability. Summary Mexico is floristically the fourth most species‐rich country in the world. Currently, 3620 native tree species are reported from this country. Mexico has been a forerunner at global level in recognising the need for plant conservation, yet this is in stark contrast with governmental programmes and actions, past and present that negatively affect(ed) immense areas of primary vegetation. In the framework of the Global Tree Assessment, to date, we have assessed the conservation status of nearly 1500 Mexican endemic and near endemic tree species for the International Union for the Conservation of Nature (IUCN) Red List, the distribution data of which we use here for a first meta‐analysis of conservation statuses and spatial distribution patterns in a newly delimited area we call Natural Mexico. Our database consists of 112,416 taxonomically and geographically very carefully curated distribution points of 1474 tree species endemic to Mexico and adjacent areas, belonging to 98 flowering plant families. The extensive curation methodology we consider essential for both research and conservation purposes is emphasised. Nearly 60% of the assessed tree species are threatened, almost double the percentage of threatened arborescent species at global level. Tropical rainforests and cloud forests house the highest proportions of threatened trees. These assessments have an extensive impact, as they not only are the starting point of urgent species conservation actions but also allow for comprehensive studies including extinction risk estimation, gap analyses for conservation planning and species reintroductions, all this in a framework of land use change, climate change and landscape composition and configuration.