Quercus insignis seedling response to climatic transfer distance in the face of climate change

Abstract

Rising temperatures are causing increased tree mortality at lower elevations and upward migrations in montane tree communities. To reduce the risk of extinction from climate change, managed translocation or assisted migration could serve to support the management of endangered species, but is currently a controversial strategy with very limited information available from experimental field studies in the tropics. We examined the effect of climatic transfer distance (CTD; the climatic difference between the site of seed origin and the site of plantation) on the establishment of Quercus insignis, an endangered oak with a distribution restricted to cloud forests. If the natural population (seed origin) occurs at its optimum climate, a decline in seedling transplant performance is expected to occur with greater CTD. Enrichment plantings were established in three sites near the seed origin area (at 1400 m a.s.l.), and in five sites from an elevation similar to the seed source up to high elevations (1365 to 2531 m a.s.l.) in Mexico. We examined the effect of CTD on seedling survival and Relative Growth Rate (RGR) over a period of four years. In the provenance area, a 1.4 °C increase and a 25–30 % annual precipitation decrease were estimated to have occurred during the study period (2018–2021), relative to the reference climate (1960–1990) in which the population in the provenance area developed. We found no significant evidence to support lower seedling survival with greater CTD. High survival occurred in sites with a warmer temperature at present (up to 80 % survival), but also in colder sites at higher elevation (up to 90 %), revealing the high tolerance of Q. insignis to a wide range of climatic conditions. The RGR showed the expected decrease with greater CTD of the Aridity Index, reflecting the importance of the balance between temperature and water availability. These findings support the potential of Q. insignis enrichment plantings, both near the seed origin area and at higher elevation (currently 2–3 °C colder than in the provenance area) to compensate for the expected temperature increase. However, the projected reduction in precipitation and cloud immersion within the cloud forest belt associated with climate change, could act to limit growth and lead to lower establishment success.