Didham Raphael K, Barker Gary M, Bartlam Scott, Deakin Elizabeth L, Denmead Lisa H, Fisk Louise M, Peters Jennifer M R, Tylianakis Jason M, Wright Hannah R, Schipper Louis A
School of Animal Biology, The University of Western Australia, Perth, Australia; CSIRO Land & Water Flagship, Perth, Australia.
Landcare Research, Hamilton, New Zealand.
PLoS One. 2015 Jan 9;10(1):e0116474. doi: 10.1371/journal.pone.0116474. eCollection 2015.
Land-use intensification is a central element in proposed strategies to address global food security. One rationale for accepting the negative consequences of land-use intensification for farmland biodiversity is that it could 'spare' further expansion of agriculture into remaining natural habitats. However, in many regions of the world the only natural habitats that can be spared are fragments within landscapes dominated by agriculture. Therefore, land-sparing arguments hinge on land-use intensification having low spillover effects into adjacent protected areas, otherwise net conservation gains will diminish with increasing intensification. We test, for the first time, whether the degree of spillover from farmland into adjacent natural habitats scales in magnitude with increasing land-use intensity. We identified a continuous land-use intensity gradient across pastoral farming systems in New Zealand (based on 13 components of farmer input and soil biogeochemistry variables), and measured cumulative off-site spillover effects of fertilisers and livestock on soil biogeochemistry in 21 adjacent forest remnants. Ten of 11 measured soil properties differed significantly between remnants and intact-forest reference sites, for both fenced and unfenced remnants, at both edge and interior. For seven variables, the magnitude of effects scaled significantly with magnitude of surrounding land-use intensity, through complex interactions with fencing and edge effects. In particular, total C, total N, δ15N, total P and heavy-metal contaminants of phosphate fertilizers (Cd and U) increased significantly within remnants in response to increasing land-use intensity, and these effects were exacerbated in unfenced relative to fenced remnants. This suggests movement of livestock into surrounding natural habitats is a significant component of agricultural spillover, but pervasive changes in soil biogeochemistry still occur through nutrient spillover channels alone, even in fenced remnants set aside for conservation. These results have important implications for the viability of land-sparing as a strategy for balancing landscape-level conservation and production goals in agricultural landscapes.
土地利用集约化是旨在解决全球粮食安全问题的拟议战略的核心要素。接受土地利用集约化对农田生物多样性产生负面影响的一个理由是，它可以“避免”农业进一步扩张到剩余的自然栖息地。然而，在世界许多地区，唯一可以避免的自然栖息地是农业主导景观中的碎片。因此，土地节约论点取决于土地利用集约化对相邻保护区的溢出效应较低，否则随着集约化程度的提高，净保护收益将减少。我们首次测试了农田向相邻自然栖息地的溢出程度是否会随着土地利用强度的增加而扩大。我们确定了新西兰牧区农业系统中连续的土地利用强度梯度（基于农民投入和土壤生物地球化学变量的13个组成部分），并测量了21个相邻森林残余地中肥料和牲畜对土壤生物地球化学的累积场外溢出效应。对于围栏和未围栏的残余地，在边缘和内部，11种测量的土壤性质中有10种在残余地和完整森林参考地点之间存在显著差异。对于七个变量，通过与围栏和边缘效应的复杂相互作用，效应的大小与周围土地利用强度的大小显著相关。特别是，随着土地利用强度的增加，残余地内的总碳、总氮、δ15N、总磷和磷肥中的重金属污染物（镉和铀）显著增加，并且相对于围栏残余地，未围栏残余地的这些效应更加明显。这表明牲畜进入周围自然栖息地是农业溢出的一个重要组成部分，但即使在为保护而预留的围栏残余地中，土壤生物地球化学的普遍变化仍然仅通过养分溢出渠道发生。这些结果对于土地节约作为平衡农业景观中景观层面保护和生产目标的战略的可行性具有重要意义。
