Kraaij Tineke, Cowling Richard M, van Wilgen Brian W, Rikhotso Diba R, Difford Mark
School of Natural Resource Management, Nelson Mandela University, George, South Africa.
Botany Department, Nelson Mandela University, Port Elizabeth, South Africa.
PeerJ. 2017 Aug 10;5:e3591. doi: 10.7717/peerj.3591. eCollection 2017.
Season of fire has marked effects on floristic composition in fire-prone Mediterranean-climate shrublands. In these winter-rainfall systems, summer-autumn fires lead to optimal recruitment of overstorey proteoid shrubs (non-sprouting, slow-maturing, serotinous Proteaceae) which are important to the conservation of floral diversity. We explored whether fire season has similar effects on early establishment of five proteoid species in the eastern coastal part of the Cape Floral Kingdom (South Africa) where rainfall occurs year-round and where weather conducive to fire and the actual incidence of fire are largely aseasonal. We surveyed recruitment success (ratio of post-fire recruits to pre-fire parents) of proteoids after fires in different seasons. We also planted proteoid seeds into exclosures, designed to prevent predation by small mammals and birds, in cleared (intended to simulate fire) fynbos shrublands at different sites in each of four seasons and monitored their germination and survival to one year post-planting (hereafter termed 'recruitment'). Factors (in decreasing order of importance) affecting recruitment success in the post-fire surveys were species, pre-fire parent density, post-fire age of the vegetation at the time of assessment, and fire season, whereas rainfall (for six months post-fire) and fire return interval (>7 years) had little effect. In the seed-planting experiment, germination occurred during the cooler months and mostly within two months of planting, except for summer-plantings, which took 2-3 months longer to germinate. Although recruitment success differed significantly among planting seasons, sites and species, significant interactions occurred among the experimental factors. In both the post-fire surveys and seed planting experiment, recruitment success in relation to fire- or planting season varied greatly within and among species and sites. Results of these two datasets were furthermore inconsistent, suggesting that proteoid recruitment responses are not related to the season of fire. Germination appeared less rainfall-dependent than in winter-rainfall shrublands, suggesting that summer drought-avoiding dormancy is limited and has less influence on variation in recruitment success among fire seasons. The varied response of proteoid recruitment to fire season (or its simulation) implies that burning does not have to be restricted to particular seasons in eastern coastal fynbos, affording more flexibility for fire management than in shrublands associated with winter rainfall.
火灾季节对易发生火灾的地中海气候灌木丛的植物群落组成有显著影响。在这些冬雨型系统中，夏秋季火灾能使上层类帚菊木灌木（非萌芽、成熟缓慢、具闭花受精特性的山龙眼科植物）实现最佳更新，而这些灌木对于花卉多样性的保护至关重要。我们探究了火灾季节对开普植物王国（南非）东部沿海地区五种类帚菊木物种早期定居是否有类似影响，该地区全年降雨，有利于火灾发生的天气以及实际火灾发生率在很大程度上不受季节影响。我们调查了不同季节火灾后类帚菊木的更新成功率（火灾后新植株与火灾前亲本植株的比例）。我们还在四个季节中每个季节不同地点的清理过的（旨在模拟火灾）高山硬叶灌木群落中，将类帚菊木种子种植在用于防止小型哺乳动物和鸟类捕食的围栏内，并监测其发芽情况以及种植后一年的存活率（以下称为“更新”）。在火灾后调查中，影响更新成功率的因素（按重要性降序排列）依次为物种、火灾前亲本密度、评估时植被的火灾后年龄以及火灾季节，而降雨（火灾后六个月）和火灾间隔期（>7年）影响较小。在种子种植实验中，除夏季种植外，发芽发生在较凉爽的月份，且大多在种植后两个月内，夏季种植发芽所需时间要长2 - 3个月。尽管不同种植季节、地点和物种的更新成功率存在显著差异，但实验因素之间存在显著的相互作用。在火灾后调查和种子种植实验中，与火灾或种植季节相关的更新成功率在物种和地点内部及之间差异很大。此外，这两个数据集的结果并不一致，这表明类帚菊木的更新反应与火灾季节无关。与冬雨型灌木丛相比，发芽似乎对降雨的依赖性较小，这表明夏季避旱休眠有限，对不同火灾季节更新成功率变化的影响较小。类帚菊木更新对火灾季节（或其模拟）的不同反应意味着，在东部沿海高山硬叶灌木群落中，燃烧不必局限于特定季节，这为火灾管理提供了比冬雨型灌木丛更大的灵活性。
