Effects of altered climates on American ginseng population dynamics

Abstract

As climates change, species with locally adapted populations may be particularly vulnerable as specialization narrows the range of conditions under which populations can persist. Populations adapted to local climate as well as other site‐specific characteristics like soils present challenges for inferring how changing climates affect fitness, as climatic and nonclimatic variables that constitute local conditions decouple. We conducted two transplant experiments involving American ginseng to test how climatic conditions affect performance while controlling for effects of other site characteristics. We first out‐planted populations from differing elevations to gardens arrayed along an elevation/climate gradient. We also grew maternal plants under temperatures corresponding to home‐site and future conditions (16.4–22.4°C), transplanting resultant progeny to two home‐sites at different elevations (400 m, 800 m). Source populations responded idiosyncratically to elevation reflecting how nonclimatic site characteristics strongly affected plant fitness. Germination rates declined for seeds from maternal plants exposed to warmer temperatures, which compounded with diminished seed production of maternal plants, suggested that population growth may decline rapidly as warm years become hotter and more frequent. Controlling for maternal temperature effects provided evidence that plants are adapted to home‐site conditions, both climatic and nonclimatic, with population growth rates for out‐planted populations ranging from below population replacement levels (λ = 0.58) to well above (λ = 1.33). Evidence of local adaptation to climatic and nonclimatic environmental components, in combination with negative fitness impacts of warming climates on offspring via maternal effects, suggests that changing climate may imperil ginseng and other similar understory species.