Institute for Dryland Environmental Research, BIDR, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel.
J Theor Biol. 2011 Mar 21;273(1):138-46. doi: 10.1016/j.jtbi.2010.12.028. Epub 2010 Dec 25.
A common patch form in dryland landscapes is the vegetation ring. Vegetation patch formation has recently been attributed to self-organization processes that act to increase the availability of water to vegetation patches under conditions of water scarcity. The view of ring formation as a water-limited process, however, has remained largely unexplored. Using laboratory experiments and model studies we identify two distinct mechanisms of ring formation. The first mechanism pertains to conditions of high infiltration contrast between vegetated and bare soil, under which overland water flow is intercepted at the patch periphery. The decreasing amount of water that the patch core receives as the patch expands, leads to central dieback and ring formation. The second mechanism pertains to plants with large lateral root zones, and involves central dieback and ring formation due to increasing water uptake by the newly recruited individuals at the patch periphery. In general the two mechanisms act in concert, but the relative importance of each mechanism depends on environmental conditions. We found that strong seasonal rainfall variability favors ring formation by the overland-flow mechanism, while a uniform rainfall regime favors ring formation by the water-uptake mechanism. Our results explain the formation of rings by fast-growing species with confined root zones in a dry-Mediterranean climate, such as Poa bulbosa. They also explain the formation of rings by slowly growing species with highly extended root zones, such as Larrea tridentata (Creosotebush).
在旱地景观中，一种常见的斑块形式是植被环。最近，植被斑块的形成归因于自组织过程，这些过程在缺水条件下增加了植被斑块获得水分的能力。然而，将环的形成视为一个受水分限制的过程的观点在很大程度上仍未得到探索。通过实验室实验和模型研究，我们确定了两种不同的环形成机制。第一种机制与植被和裸土之间高渗透对比度的条件有关，在这种条件下，地表水流在斑块边缘被截留。随着斑块的扩展，斑块核心接收的水量减少，导致中心枯死和环的形成。第二种机制与具有大侧根区的植物有关，由于斑块边缘新招募的个体的水分吸收增加，导致中心枯死和环的形成。一般来说，这两种机制协同作用，但每种机制的相对重要性取决于环境条件。我们发现，强烈的季节性降雨变化有利于地表水流机制形成环，而均匀的降雨模式有利于水分吸收机制形成环。我们的研究结果解释了在干旱地中海气候下，具有有限根系区域的快速生长物种（如 Poa bulbosa）如何形成环，也解释了具有高度扩展根系区域的缓慢生长物种（如 Larrea tridentata（Creosotebush））如何形成环。
