Vegetation dynamics after experimental fire disturbance in the arid Succulent Karoo, South Africa

Disturbance by fire in the Succulent Karoo is rare but fire events could increase as a result of an increase in grassiness (alien and indigenous species). This study assessed the effects of fire eight years after an experimentally induced burn in Succulent Karoo vegetation. Post-fire monitoring was conducted using the line intercept method and species counts per plot (1 m2) for each of three fire disturbance treatments: control/unburnt, high and low fuel load. Vegetation cover and abundance were compared across treatments and growth forms. Vegetation cover and abundance on fire-disturbed plots had not returned to pre-fire levels after eight years. Resprouters exhibited a rapid recovery and early dominance on burnt plots. Succulent seedlings established slower, but after eight years occurred at higher densities on the burnt than control plots. Recovery after disturbance of density and cover of long-lived, woody non-resprouter non-succulents was slow relative to resprouting non-succulents and reseeding succulents. This study of vegetation change following fire disturbance in an arid system highlights the slow return of canopy cover, immediate regrowth of only two resprouter species and slower re-establishment by seed of non-resprouter species. In addition, fire disturbance led to the numerical dominance of succulents within the first decade after the fire.肉质卡鲁（Succulent Karoo）生态系统中的火灾干扰本就罕见，但由于草本盖度（涵盖外来与本土物种）的提升，火灾发生频次可能随之增加。本研究针对实验性火烧发生八年后的肉质卡鲁植被展开评估，探究火灾的生态效应。火烧后监测采用样线截距法，并对三种火灾干扰处理组（未火烧对照组、高燃料负荷组、低燃料负荷组）的每块1平方米样地开展物种计数。研究对比了不同处理组及植物生长型之间的植被盖度与物种丰度。结果显示，火烧干扰样地的植被盖度与物种丰度在八年后仍未恢复至火烧前水平。萌芽型植物在火烧样地上展现出快速恢复与早期优势地位；多肉植物实生苗的定植进程较为缓慢，但八年后火烧样地中的实生苗密度显著高于对照样地。相较于非多肉萌芽型植物与种子繁殖型多肉植物，长寿木本非萌芽非多肉植物的密度与盖度在干扰后的恢复速度相对迟缓。本项针对干旱生态系统火灾干扰后植被变化的研究凸显了以下特征：冠层盖度恢复缓慢，仅两种萌芽类群可实现快速重新定植，而非萌芽类群通过种子完成种群重建的速度则更为缓慢；此外，火灾干扰会使多肉植物在火烧后的首个十年内成为数量上的优势类群。