Western David, Mose Victor N, Worden Jeffrey, Maitumo David
African Conservation Centre, 15289 00509, Nairobi, Kenya.
PLoS One. 2015 Aug 28;10(8):e0136516. doi: 10.1371/journal.pone.0136516. eCollection 2015.
We monitored pasture biomass on 20 permanent plots over 35 years to gauge the reliability of rainfall and NDVI as proxy measures of forage shortfalls in a savannah ecosystem. Both proxies are reliable indicators of pasture biomass at the onset of dry periods but fail to predict shortfalls in prolonged dry spells. In contrast, grazing pressure predicts pasture deficits with a high degree of accuracy. Large herbivores play a primary role in determining the severity of pasture deficits and variation across habitats. Grazing pressure also explains oscillations in plant biomass unrelated to rainfall. Plant biomass has declined steadily and biomass per unit of rainfall has fallen by a third, corresponding to a doubling in grazing intensity over the study period. The rising probability of forage deficits fits local pastoral perceptions of an increasing frequency of extreme shortfalls. The decline in forage is linked to sedentarization, range loss and herbivore compression into drought refuges, rather than climate change. The results show that the decline in rangeland productivity and increasing frequency of pasture shortfalls can be ameliorated by better husbandry practices and reinforces the need for ground monitoring to complement remote sensing in forecasting pasture shortfalls.
我们在35年的时间里对20个永久性地块的牧场生物量进行了监测，以评估降雨和归一化植被指数（NDVI）作为稀树草原生态系统中饲料短缺替代指标的可靠性。这两个替代指标在干旱期开始时都是牧场生物量的可靠指标，但无法预测长期干旱期间的短缺情况。相比之下，放牧压力能高度准确地预测牧场赤字。大型食草动物在决定牧场赤字的严重程度和不同栖息地之间的差异方面起着主要作用。放牧压力还解释了与降雨无关的植物生物量的波动。植物生物量稳步下降，每单位降雨量的生物量下降了三分之一，这与研究期间放牧强度翻倍相对应。饲料短缺可能性的增加符合当地牧民对极端短缺频率增加的认知。饲料的减少与定居化、牧场丧失以及食草动物被压缩到干旱避难所有关，而不是气候变化。结果表明，通过更好的管理措施可以改善牧场生产力的下降和牧场短缺频率的增加，并强调了在预测牧场短缺时需要地面监测来补充遥感监测。
