Long-term dynamics of herbaceous vegetation structure and composition in two African savanna reserves
Long-term dynamics of herbaceous vegetation structure and composition in two African savanna reserves
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DOI：
10.1111/j.1365-2664.2010.01895.x
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发表时间：
2011-02-01
影响因子：
5.7
通讯作者：
Peel, Mike J. S.
中科院分区：
文献类型：
--
作者：
Buitenwerf, Robert;Swemmer, Anthony M.;Peel, Mike J. S.
P>1。小型围栏保护区被认为需要管理干预，以维持生态系统的自然状态。这些干预措施通常是根据短期观察启动和评估的，而缓慢的变化往往被误解或完全错过。因此，长期监测对于了解保护区管理对生态系统结构和功能的影响至关重要.我们分析了一个15年的数据集的草本植被数据的59个监测点在两个自然保护区的不同规模和不同的管理制度，在半干旱，南非稀树草原。群落组成和植被结构（基底覆盖）进行了评估，以响应降雨量和管理变量。随着时间的推移，没有方向的变化被发现。基覆盖测量的两个代理（到最近的簇和簇直径的距离）增加与当前和前一年的降雨。功能组的相对丰度也对降雨量作出了反应，多年生草本植物的相对丰度增加后，一个潮湿的一年。通过物种相对丰度的相异性指数衡量，组成响应显示出2年的滞后，并且干旱年份的响应大于潮湿年份。4.在较小的保护区，距离最近的簇状植被对降雨的响应明显较弱，而在干旱年份，组成变化大于较大的保护区。合成与应用。草本基底覆盖和群落组成的变化与年（时间）在每个站点之间的差异，而不是与站点之间的差异（空间），这表明降雨量的年际变化是这些系统中草本层动态的最重要的驱动因素。然而，管理修改的影响，降雨对草本植物结构和群落组成。较小的储备，有较高的放牧和水坑密度，表现出较大的波动，在关键的草本植物变量。这种储备在南部非洲很常见，面对全球气候变化，可能需要比大型储备更谨慎的管理。
P>1. Small fenced reserves are perceived to require management interventions to maintain ecosystems in a natural state. Such interventions are typically initiated and assessed on the basis of short-term observations, while slow changes are often misunderstood or missed entirely. Long-term monitoring is therefore crucial to understand the effect of reserve management on ecosystem structure and functioning.2. We analysed a 15-year data set of herbaceous vegetation data for 59 monitoring sites in two nature reserves of different size and with different management regimes in a semi-arid, South African savanna. Community composition and vegetation structure (basal cover) were assessed in response to rainfall and management variables.3. No directional changes over time were found. Basal cover as measured by two proxies (distance to the nearest tuft and tuft diameter) increased with current and previous year rainfall. The relative abundance of functional groups also responded to rainfall, with perennial grasses increasing in relative abundance following a wet year. Compositional responses, as measured by a dissimilarity index of species relative abundance, showed a 2-year lag and responses were larger following dry years than wet years.4. The response to rainfall of distance to the nearest tuft was significantly weaker in the smaller reserve, while compositional change during dry years was larger than in the larger reserve.5. Synthesis and applications. Most of the variation in herbaceous basal cover and community composition was associated with differences between years (time) at each site, rather than with differences between sites (space), indicating that inter-annual variation in rainfall is the most important driver of herbaceous layer dynamics in these systems. However, management did modify the effects of rainfall on herbaceous structure and community composition. The smaller reserve, which had higher grazer and waterhole density, showed greater fluctuations in key herbaceous variables. Such reserves are common in southern Africa and probably require more careful management than larger reserves in the face of global climate change.