Assisted migration across fixed seed zones detects adaptation lags in two major North American tree species

Boreal forests are experiencing dramatic climate change, having warmed 1-1.9°C over the last century. Yet forest regeneration practices are often still dictated by a fixed seed zone framework, in which seeds are both harvested from and planted into predefined areas. Our goal was to determine whether seedlings sourced from southern seed zones in Minnesota USA are already better adapted to northerly seed zones because of climate change. Bur oak (Quercus macrocarpa) and northern red oak (Quercus rubra) seedlings from two seed zones (i.e. tree ecotypes) were planted into 16 sites in two northern seed zones and measured for three years. Our hypotheses were threefold: 1) tree species with more southern geographic distributions would thrive in northern forests where climate has already warmed substantially, 2) southern ecotypes of these species would have higher survival and growth than the northern ecotype in northern environments, and 3) natural selection would favor seedlings that expressed...

北方针叶林（Boreal forests）正经历剧烈的气候变化，过去一个世纪以来升温幅度达1至1.9摄氏度。然而当前的森林更新实践仍多遵循固定的种源区（seed zone）框架，即种子均采自预设区域，并种植于对应区域内。本研究旨在探究：受气候变化影响，源自美国明尼苏达州南部种源区的苗木，是否已能更好地适应北部种源区的环境。本研究选取了来自两个种源区（即树木生态型，tree ecotypes）的大果栎（Bur oak，学名*Quercus macrocarpa*）和北美红栎（northern red oak，学名*Quercus rubra*）苗木，将其种植于两个北部种源区的16个样地中，并开展了为期三年的观测。本研究提出三项假说：1）地理分布更偏南的树种，在已显著升温的北部森林中可更好生长；2）相较于对应物种的北部生态型，南部生态型在北部环境下拥有更高的存活率与生长速率；3）自然选择将青睐于表达……的苗木。