Graves Rose A, Pearson Scott M, Turner Monica G
Ecol Appl. 2016 Mar;26(2):515-29. doi: 10.1890/15-0545.
Rural landscapes face changing climate, shifting development pressure, and loss of agricultural land. Perennial bioenergy crops grown on existing agricultural land may provide an opportunity to conserve rural landscapes while addressing increased demand for biofuels. However, increased bioenergy production and changing land use raise concerns for tradeoffs within the food-energy-environment trilemma. Heterogeneity of climate, soils, and land use complicate assessment of bioenergy potential in complex landscapes, creating challenges to evaluating future tradeoffs. The hypothesis addressed herein is that perennial bioenergy production can provide an opportunity to avoid agricultural land conversion to development. Using a process-based crop model, we assessed potential bioenergy crop growth through 2100 in a southern Appalachian Mountain region and asked: (1) how mean annual yield differed among three crops (switchgrass Panicum virgatum, giant miscanthus Miscanthus x giganteus, and hybrid poplar Populus x sp.) under current climate and climate change scenarios resulting from moderate and very high greenhouse gas emissions; (2) how maximum landscape yield, spatial allocation of crops, and bioenergy hotspots (areas with highest potential yield) varied among climate scenarios; and (3) how bioenergy hotspots overlapped with current crop production or lands with high development pressure. Under both climate change scenarios, mean annual yield of perennial grasses decreased (-4% to -39%), but yield of hybrid poplar increased (+8% to +20%) which suggests that a switch to woody crops would maximize bioenergy crop production. In total, maximum landscape yield increased by up to 90 000 Mg/yr (6%) in the 21st century due to increased poplar production. Bioenergy hotspots (> 18 Mg x ha(-1) x yr(-1)) consistently overlapped with high suburban/exurban development likelihood and existing row crop production. If bioenergy production is constrained to marginal (non-crop) lands, landscape yield decreased by 27%. The removal of lands with high development probability from crop production resulted in losses of up to 670 000 Mg/yr (40%). This study demonstrated that tradeoffs among bioenergy production, crop production, and exurban expansion in a mountainous changing rural landscape vary spatially with climate change over time. If markets develop, bioenergy crops could potentially counter losses of agricultural land to development.
乡村景观面临着气候变化、不断变化的发展压力以及农业用地流失等问题。在现有农业用地上种植多年生生物能源作物，或许能在满足生物燃料需求增长的同时，为保护乡村景观提供契机。然而，生物能源产量的增加和土地利用方式的改变引发了人们对粮食 - 能源 - 环境三元困境中权衡取舍的担忧。气候、土壤和土地利用的异质性使得在复杂景观中评估生物能源潜力变得复杂，给评估未来的权衡取舍带来了挑战。本文所探讨的假设是，多年生生物能源生产能够提供一个避免将农业用地转为其他用途的机会。我们使用基于过程的作物模型，评估了阿巴拉契亚山脉南部地区到2100年多年生生物能源作物的潜在生长情况，并提出以下问题：（1）在当前气候以及中度和极高温室气体排放导致的气候变化情景下，三种作物（柳枝稷、巨芒草和杂交杨树）的年均产量有何差异；（2）在不同气候情景下，最大景观产量、作物的空间配置以及生物能源热点地区（潜在产量最高的区域）如何变化；（3）生物能源热点地区与当前作物种植区或具有高发展压力的土地有何重叠。在两种气候变化情景下，多年生草本植物的年均产量均下降（-4%至-39%），但杂交杨树的产量增加（+8%至+20%），这表明转向木本作物将使生物能源作物产量最大化。总体而言，由于杨树产量增加，21世纪的最大景观产量每年最多增加90000公吨（6%）。生物能源热点地区（>18公吨×公顷⁻¹×年⁻¹）始终与高郊区/远郊区发展可能性区域以及现有的行栽作物种植区重叠。如果生物能源生产仅限于边缘（非作物）土地，景观产量将下降27%。将具有高发展可能性的土地从作物生产中移除，导致每年最多损失670000公吨（40%）。这项研究表明，在山区不断变化的乡村景观中，生物能源生产、作物生产和远郊区扩张之间的权衡取舍会随着时间的气候变化而在空间上有所不同。如果市场得以发展，生物能源作物有可能抵消农业用地转为其他用途造成的损失。
