Dead Sea and Arava Science Center, Yotvata, 88820, Israel; Ben-Gurion University of the Negev, Eilat Campus, Eilat, 88100, Israel.
Soil, Water, and Bioenergy Resources, The Ohio State University South Centers, Piketon, OH, 45661, USA.
J Environ Manage. 2023 Nov 1;345:118703. doi: 10.1016/j.jenvman.2023.118703. Epub 2023 Aug 2.
Forestry has long been considered an effective means of restoring degraded drylands worldwide. Often, afforestation in such lands relies on the establishment of runoff harvesting systems that are formed as contour bench terraces on hillslopes, increasing water availability for the planted trees and shrubs. The construction of terraces requires intensive earthworks by heavy machinery. This study assessed the long-term (>10 yrs) effects of forestry-related land-use change on soil properties and herbaceous vegetation in 16-year-old and 12-year-old afforestation sites (established in 2005 and 2009), and in nearby control ("natural") areas in the semi-arid northern Negev, Israel. Mean herbaceous vegetation height in the 2005 afforestation sites (12.1 cm) was significantly (P = 0.0009) and 23% greater than in the control areas (9.8 cm), whereas in the 2009 afforestation sites (6.2 cm) it was 37% lesser than in the control areas. Mean herbaceous vegetation aboveground biomass was similar in the 2005 afforestation (0.39 Mg ha) and control areas (0.38 Mg ha), and almost significantly (P = 0.0510) and twofold greater than in the 2009 afforestation sites (0.19 Mg ha). The effect of hillslope aspect on these variables was substantial; their mean values were higher in the northern (mesic) hillslopes than in the southern (xeric) hillslopes. Soil samples were obtained from depths of 0-5 and 5-10 cm and physio-chemo-biological properties were assessed in the laboratory. The overall soil quality - as calculated by two soil quality indices (SQIs), including the generalized SQI (SQI) and the minimum dataset SQI (SQI) - was significantly (P < 0.0001 for both indices) and 13-22% greater in the control areas (0.52 and 0.61, respectively) than that in the afforestation treatments (0.44-0.46 and 0.50-0.51, respectively). These results are generally attributed to the removal of soil's A-horizon during earthworks, and the exposure of the underlying B-horizon. The similar SQI values of both hillslope aspects, as well as of both soil depths, indicate the generally degraded state of the entire region. In conclusion, while contour bench terracing may facilitate the recovery of herbacaeous vegetation to some extent, the effectiveness of this practice for soil restoration is questionable. Overall, insights of this study demonstrate a caveat that converting natural drylands to forestry systems may not yield sufficient ecological benefits, and therefore should be implemented with caution.
林业长期以来一直被认为是恢复全球退化旱地的有效手段。在这些土地上造林，通常依赖于建立径流收集系统，即在山坡上形成等高阶地，增加种植树木和灌木的可用水量。梯田的建造需要重型机械进行密集的土方工程。本研究评估了与林业相关的土地利用变化对以色列半干旱北部内盖夫 16 年（2005 年建立）和 12 年（2009 年建立）造林点以及附近对照（“自然”）区土壤性质和草本植被的长期（>10 年）影响。2005 年造林点的草本植被平均高度（12.1 厘米）显著（P=0.0009）比对照区（9.8 厘米）高 23%，而 2009 年造林点（6.2 厘米）比对照区低 37%。2005 年造林区（0.39 Mg ha）和对照区（0.38 Mg ha）的草本植被地上生物量相似，且几乎显著（P=0.0510）比 2009 年造林区（0.19 Mg ha）高两倍。山坡方位对这些变量的影响很大；它们在北部（湿润）山坡上的平均值高于南部（干旱）山坡上的平均值。从 0-5 厘米和 5-10 厘米的深度采集土壤样本，并在实验室评估其理化生物特性。通过两个土壤质量指数（SQI），包括广义 SQI（SQI）和最小数据集 SQI（SQI），计算出的整体土壤质量-显著（两个指数均为 P<0.0001）-对照区（分别为 0.52 和 0.61）比造林处理区（分别为 0.44-0.46 和 0.50-0.51）高 13-22%。这些结果通常归因于在土方工程中去除土壤的 A 层，以及暴露下面的 B 层。两个山坡方位和两个土壤深度的相似 SQI 值表明整个地区的土壤通常处于退化状态。总之，虽然等高阶地可能在一定程度上有助于草本植被的恢复，但这种做法对土壤恢复的有效性值得怀疑。总的来说，本研究的结果表明，将自然旱地转化为林业系统可能不会带来足够的生态效益，因此应谨慎实施。
