Botha Monique, Archibald Sally, Greve Michelle
Centre for African Ecology School of Animal, Plant and Environmental Sciences University of the Witwatersrand Johannesburg South Africa.
Department of Plant and Soil Sciences University of Pretoria Pretoria South Africa.
Ecol Evol. 2020 Sep 20;10(19):10719-10734. doi: 10.1002/ece3.6730. eCollection 2020 Oct.
Fire and frost represent two major hurdles for the persistence of trees in open grassy biomes and have both been proposed as drivers of grassland-forest boundaries in Africa.We assess the response of young tree seedlings, which represent a vulnerable stage in tree recruitment, to traumatic fire and frost disturbances.In a greenhouse experiment, we investigated how seedling traits predicted survival and resprouting ability in response to fire versus frost; we characterized survival strategies of seedlings in response to the two disturbances, and we documented how the architecture of surviving seedlings is affected by fire versus frost injury.Survival rates were similar under both treatments. However, different species displayed different levels of sensitivity to fire and frost. Seedling survival was higher for older seedlings and seedlings with more basal leaves. Survivors of a fire event lost more biomass than the survivors of a frost event. However, the architecture of recovered fire- and frost-treated seedlings was mostly similar. Seedlings that recovered from fire and frost treatments were often shorter than those that had not been exposed to any disturbance, with multiple thin branches, which may increase vulnerability to the next frost or fire event. . Fire caused more severe aboveground damage compared with a single frost event, suggesting that fire is an important driver of tree distribution in these open grassland systems. However, the impact of repeated frost events may be equally severe and needs to be investigated. Also, woody species composition may be influenced by phenomena that affect the timing and frequency of seedling exposure to damage, as mortality was found to be dependent on seedling age. Therefore, changes in fire regime and climate are likely to result in changes in the composition and the structure of the woody components of these systems.
火灾和霜冻是树木在开阔草地生物群落中生存面临的两大主要障碍，二者均被认为是非洲草原与森林边界的驱动因素。我们评估了处于树木更新脆弱阶段的幼树幼苗对创伤性火灾和霜冻干扰的反应。在一项温室实验中，我们研究了幼苗性状如何预测其在火灾和霜冻情况下的存活及重新发芽能力；我们描述了幼苗对这两种干扰的存活策略，并记录了存活幼苗的形态结构受火灾和霜冻伤害的影响情况。两种处理下的存活率相似。然而，不同物种对火灾和霜冻的敏感程度不同。年龄较大以及基生叶较多的幼苗存活率更高。火灾事件的幸存者比霜冻事件的幸存者损失的生物量更多。然而，经火灾和霜冻处理后恢复的幼苗形态结构大多相似。从火灾和霜冻处理中恢复的幼苗通常比未遭受任何干扰的幼苗更矮，且有多个细枝，这可能会增加其在下一次霜冻或火灾事件中的脆弱性。与单次霜冻事件相比，火灾造成的地上部分损害更为严重，这表明火灾是这些开阔草地系统中树木分布的重要驱动因素。然而，反复霜冻事件的影响可能同样严重，需要进行调查。此外，木本物种组成可能会受到影响幼苗遭受损害的时间和频率的现象的影响，因为发现死亡率取决于幼苗年龄。因此，火灾发生规律和气候的变化很可能导致这些系统中木本成分的组成和结构发生变化。
