Little is known of warming effects on growth and defence of woody seedlings that potentially invade grasslands. We predicted that elevated temperatures would increase growth and spine length of Vachellia sieberiana seedlings growing (1) with or without grass in the dormant season and early growing season, but (2) only when grass cover is absent in the mid-late growing season. To test these predictions, 120 seedlings were grown in 20 field plots in the dormant season, early growing season, middle of the growing and late growing season. Ten plots were warmed with open-top chambers that raised air temperature by 1.0 to 2.5 °C depending on season. Warming generally increased growth metrics regardless of grass cover across seasons and generally increased spine length only when grass cover was absent. The results imply that under a warmer climate, V. sieberiana will thrive irrespective of grass cover.

人们对变暖对可能入侵草原的木本幼苗生长和防御的影响知之甚少。我们预测高温会增加Vachellia sieberiana的生长和脊柱长度幼苗生长（1）在休眠季节和早期生长季节有无草，但（2）仅在生长后期至中期没有草被的情况下。为了检验这些预测，在休眠季节，生长早期，生长中期和生长后期的20个田间地中种植了120株幼苗。十个地块用开放式顶棚加热，根据季节的不同，顶棚会将空气温度提高1.0到2.5°C。气候变暖通常会增加生长指标，而与整个季节的草覆盖率无关，并且仅在没有草覆盖的情况下，脊柱长度通常才会增加。结果表明，在气候变暖的情况下，西伯利亚葡萄（V. sieberiana）会蓬勃发展，而与草皮无关。