西非森林-可可种植园景观中的碳动态、净初级生产力和人为净初级生产力。
Carbon dynamics, net primary productivity and human-appropriated net primary productivity across a forest-cocoa farm landscape in West Africa.
机构信息
Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK.
Institute of Zoology, Zoological Society of London, London, UK.
出版信息
Glob Chang Biol. 2019 Aug;25(8):2661-2677. doi: 10.1111/gcb.14661. Epub 2019 Jun 6.
Terrestrial net primary productivity (NPP) is an important metric of ecosystem functioning; however, there are little empirical data on the NPP of human-modified ecosystems, particularly smallholder, perennial crops like cocoa (Theobroma cacao), which are extensive across the tropics. Human-appropriated NPP (HANPP) is a measure of the proportion of a natural system's NPP that has either been reduced through land-use change or harvested directly and, previously, has been calculated to estimate the scale of the human impact on the biosphere. Additionally, human modification can create shifts in NPP allocation and decomposition, with concomitant impacts on the carbon cycle. This study presents the results of 3 years of intensive monitoring of forest and smallholder cocoa farms across disturbance, management intensity, distance from forest and farm age gradients. We measured among the highest reported NPP values in tropical forest, 17.57 ± 2.1 and 17.7 ± 1.6 Mg C ha year for intact and logged forest, respectively; however, the average NPP of cocoa farms was still higher, 18.8 ± 2.5 Mg C ha year , which we found was driven by cocoa pod production. We found a dramatic shift in litterfall residence times, where cocoa leaves decomposed more slowly than forest leaves and shade tree litterfall decomposed considerably faster, indicating significant changes in rates of nutrient cycling. The average HANPP value for all cocoa farms was 2.1 ± 1.1 Mg C ha year ; however, depending on the density of shade trees, it ranged from -4.6 to 5.2 Mg C ha year . Therefore, rather than being related to cocoa yield, HANPP was reduced by maintaining higher shade levels. Across our monitored farms, 18.9% of farm NPP was harvested (i.e., whole cocoa pods) and only 1.1% (i.e., cocoa beans) was removed from the system, suggesting that the scale of HANPP in smallholder cocoa agroforestry systems is relatively small.
陆地初级生产力(NPP)是生态系统功能的重要指标;然而,对于人类改造的生态系统,特别是在热带地区广泛种植的小农户、多年生作物(如可可)的 NPP,几乎没有经验数据。人类占用的 NPP(HANPP)是衡量自然系统 NPP 的一部分,通过土地利用变化或直接收获而减少的比例,以前曾用于估计人类对生物圈的影响规模。此外,人类的改造可以改变 NPP 的分配和分解,从而对碳循环产生影响。本研究报告了对森林和小农户可可农场进行了 3 年的密集监测的结果,这些农场分布在干扰、管理强度、距离森林和农场年龄梯度上。我们测量了热带森林中报告的最高 NPP 值之一,分别为 17.57±2.1 和 17.7±1.6 Mg C ha 年,用于完整和砍伐的森林;然而,可可农场的平均 NPP 仍然更高,为 18.8±2.5 Mg C ha 年,我们发现这是由可可豆荚的产量驱动的。我们发现凋落物停留时间发生了巨大变化,其中可可叶的分解速度比森林叶慢,而遮荫树凋落物的分解速度快得多,这表明养分循环速率发生了显著变化。所有可可农场的平均 HANPP 值为 2.1±1.1 Mg C ha 年;然而,根据遮荫树的密度,其范围从-4.6 到 5.2 Mg C ha 年。因此,HANPP 与其说是与可可产量有关,不如说是通过维持较高的遮荫水平而降低的。在我们监测的农场中,有 18.9%的农场 NPP(即整个可可豆荚)被收获,只有 1.1%(即可可豆)从系统中被移除,这表明小农户可可农林系统中的 HANPP 规模相对较小。