Ecosystem Science and Management Program, University of Northern BC, Prince George, BC, Canada.
College of Science and Engineering, Centre for Tropical Environmental and Sustainability Science, James Cook University, Cairns, Qld, Australia.
Glob Chang Biol. 2017 Nov;23(11):4873-4883. doi: 10.1111/gcb.13741. Epub 2017 May 31.
Our ability to model global carbon fluxes depends on understanding how terrestrial carbon stocks respond to varying environmental conditions. Tropical forests contain the bulk of the biosphere's carbon. However, there is a lack of consensus as to how gradients in environmental conditions affect tropical forest carbon. Papua New Guinea (PNG) lies within one of the largest areas of contiguous tropical forest and is characterized by environmental gradients driven by altitude; yet, the region has been grossly understudied. Here, we present the first field assessment of aboveground biomass (AGB) across three main forest types of PNG using 193 plots stratified across 3,100-m elevation gradient. Unexpectedly, AGB had no direct relationship to rainfall, temperature, soil, or topography. Instead, natural disturbances explained most variation in AGB. While large trees (diameter at breast height > 50 cm) drove altitudinal patterns of AGB, resulting in a major peak in AGB (2,200-3,100 m) and some of the most carbon-rich forests at these altitudes anywhere. Large trees were correlated to a set of climatic variables following a hump-shaped curve. The set of "optimal" climatic conditions found in montane cloud forests is similar to that of maritime temperate areas that harbor the largest trees in the world: high ratio of precipitation to evapotranspiration (2.8), moderate mean annual temperature (13.7°C), and low intra-annual temperature range (7.5°C). At extreme altitudes (2,800-3,100 m), where tree diversity elsewhere is usually low and large trees are generally rare or absent, specimens from 18 families had girths >70 cm diameter and maximum heights 20-41 m. These findings indicate that simple AGB-climate-edaphic models may not be suitable for estimating carbon storage in forests where optimal climate niches exist. Our study, conducted in a very remote area, suggests that tropical montane forests may contain greater AGB than previously thought and the importance of securing their future under a changing climate is therefore enhanced.
我们对全球碳通量建模的能力取决于对陆地碳储量如何响应不同环境条件的理解。热带森林包含了生物圈中大部分的碳。然而，对于环境条件梯度如何影响热带森林碳，人们尚未达成共识。巴布亚新几内亚（PNG）位于最大的连续热带森林区域之一，其特点是受海拔驱动的环境梯度；然而，该地区的研究严重不足。在这里，我们使用跨越 3100 米海拔梯度的 193 个样地，首次对 PNG 三种主要森林类型的地上生物量（AGB）进行了实地评估。出乎意料的是，AGB 与降雨量、温度、土壤或地形没有直接关系。相反，自然干扰解释了 AGB 的大部分变化。虽然大树（胸径>50 厘米）驱动了 AGB 的海拔模式，导致 AGB 出现一个主要峰值（2200-3100 米），并在这些海拔高度形成了一些最富碳的森林。大树与一组遵循驼峰形状曲线的气候变量相关。在山地云雾林中发现的一组“最佳”气候条件与那些拥有世界上最大树木的海洋温带地区相似：高降水与蒸散比（2.8）、适中的年平均温度（13.7°C）和低年内温度范围（7.5°C）。在极端海拔（2800-3100 米），树木多样性通常较低，大树通常稀少或不存在，18 个科的标本的胸径>70 厘米，最大高度为 20-41 米。这些发现表明，简单的 AGB-气候-土壤模型可能不适合估计存在最佳气候小生境的森林中的碳储量。我们在一个非常偏远地区进行的研究表明，热带山地森林的 AGB 可能比以前认为的要大，因此在气候变化的背景下保护它们的未来变得更加重要。
