Islands of fertility (IOF) emerge when vegetation exerts such a considerable influence on soil properties that sub-canopies become significantly more fertile than inter-canopies. How confounding phenomena such as grazing patterns, seedbank dynamics and temporal changes impact IOF, has not been thoroughly examined. Soil and vegetation characteristics of 43 IOF in the Tankwa Karoo were surveyed along a rainfall gradient spanning three plant communities. Sixteen were in the Tankwa Karoo (TK) plant community, 14 in the Tankwa Wash (TW) and 13 in the Tankwa Escarpment (TE). The IOF were identified from aerial photos as clumps of shrubs separated by bare patches. Soils were described in 2014 and the seedbank composition in 2014 and 2015. Concentrations of nutrients, carbon and sodium were measured in IOF less than 5 years, 5–15 years and 30 years liberated from livestock grazing. Electrical conductivity, clay, nitrogen and carbon were the only soil properties that were significantly different from IOF to bare patch. The seedbank in IOF was identical to that in the bare patches. There was no significant difference in IOF versus bare patch nutrient concentrations in the three sampling locations. The soil in IOF was richer, more fertile and had a better structure than the soil in bare patches between IOF. There was a sharp turnover in seedbank composition in the two, drought-ridden years. Longer grazing exclusion did not influence the nutrient concentrations. Findings here suggest that IOF are dynamic in space and time and are essential elements of landscape heterogeneity with critical ecosystem services. They should hence be managed and monitored to sustain them in landscapes to reverse their degradation, despite being the result of degradation.

中文翻译：

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过度放牧对南非退化多肉植物卡鲁肥力岛土壤和植被的影响

当植被对土壤特性产生如此大的影响以致子冠层变得比冠层间​​更肥沃时，就会出现肥力岛（IOF）。放牧模式、种子库动态和时间变化等混杂现象如何影响 IOF，尚未得到彻底研究。沿着跨越三个植物群落的降雨梯度对 Tankwa Karoo 的 43 个 IOF 的土壤和植被特征进行了调查。16 个在 Tankwa Karoo (TK) 植物群落，14 个在 Tankwa Wash (TW)，13 个在 Tankwa Escarpment (TE)。IOF 从航拍照片中被识别为由裸露的斑块分隔的灌木丛。2014 年描述了土壤，2014 年和 2015 年描述了种子库组成。在不到 5 年的 IOF 中测量了养分、碳和钠的浓度，5-15 年和 30 年从牲畜放牧中解放出来。电导率、粘土、氮和碳是唯一与 IOF 显着不同的土壤特性。IOF 中的种子库与裸斑中的相同。在三个采样位置，IOF 与裸斑营养浓度没有显着差异。IOF中的土壤比IOF之间裸露的土壤更肥沃、更肥沃、结构更好。在干旱肆虐的两年里，种子库的构成发生了急剧的变化。更长的放牧排斥不影响养分浓度。这里的研究结果表明，IOF 在空间和时间上是动态的，并且是具有关键生态系统服务的景观异质性的基本要素。