Ecol Appl. 2014 Jun;24(4):716-31. doi: 10.1890/12-2253.1.
Tropical forests are important storehouses of carbon and biodiversity. In isolated island ecosystems such as the Hawaiian Islands, relative dominance of native and nonnative tree species may influence patterns of forest carbon stocks and biodiversity. We determined aboveground carbon density (ACD) across a matrix of lava flows differing in age, texture, and vegetation composition (i.e., native or nonnative dominated) in wet lowland forests of Hawaii Island. To do this at the large scales necessary to accurately capture the inherent heterogeneity of these forests, we collected LiDAR data across areas of interest and developed relationships between LiDAR metrics and field-based estimates of forest ACD. This approach enabled us to inventory, rather than merely sample, the entire populations (i.e., forests) of interest. Native Hawaiian wet lowland forests exhibited ACD values similar to those of intact tropical forests elsewhere. In general, ACD of these forests increased with increasing lava flow age, but patterns differed between native and nonnative forest stands. On the youngest lavas, native-dominated forest ACD averaged < 60 Mg/ha, compared to -100 Mg C/ha for nonnative-dominated forests. This difference was due to the presence of the nonnative, N2-fixing trees F. moluccana and C. equisetifolia in the nonnative-dominated forest stands, as well as the corresponding absence of N2-fixing trees in native-dominated forest stands. Following -500 years of primary succession and thereafter, however, both forest types exhibited ACD values averaging -130 Mg C/ha, although it took nonnative forests only 75 80 years of post-establishment succession to reach those values. Given the large areas of early-successional M. polymorpha-dominated forest on young lava flows, further spread of F. moluccana and C. equisetifolia populations would likely increase ACD stocks but would constitute a significant erosion of the invaluable contribution of Hawaii's native ecosystems to global biodiversity.
热带森林是碳和生物多样性的重要储存库。在夏威夷群岛等孤立的岛屿生态系统中，本地和非本地树种的相对优势可能会影响森林碳储量和生物多样性的模式。我们在夏威夷岛潮湿低地森林的熔岩流年龄、质地和植被组成（即本地或非本地主导）的矩阵中确定了地上碳密度（ACD）。为了在准确捕捉这些森林固有异质性所需的大尺度上做到这一点，我们在感兴趣的区域收集了激光雷达数据，并开发了激光雷达指标与实地森林 ACD 估算之间的关系。这种方法使我们能够对整个感兴趣的种群（即森林）进行清查，而不仅仅是抽样。本地夏威夷潮湿低地森林的 ACD 值与其他地方完整的热带森林相似。一般来说，这些森林的 ACD 值随着熔岩流年龄的增加而增加，但本地和非本地林分之间的模式有所不同。在最年轻的熔岩上，本地主导的森林 ACD 平均<60 Mg/ha，而非本地主导的森林则为-100 Mg C/ha。这种差异是由于非本地的 N2 固定树 F. moluccana 和 C. equisetifolia 存在于非本地主导的森林中，以及 N2 固定树在本地主导的森林中相应缺失。然而，经过 500 年的主要演替，两种森林类型的 ACD 值平均为-130 Mg C/ha，尽管非本地森林仅用了 75-80 年的演替就达到了这些值。考虑到年轻熔岩上早期演替的 M. polymorpha 主导森林的大面积存在，F. moluccana 和 C. equisetifolia 种群的进一步扩散可能会增加 ACD 储量，但这将构成对夏威夷本地生态系统对全球生物多样性的宝贵贡献的重大侵蚀。
