Improved tree height estimation of secondary forests in the Brazilian Amazon

ABSTRACT This paper presents a novel approach for estimating the height of individual trees in secondary forests at two study sites: Manaus (central Amazon) and Santarém (eastern Amazon) in the Brazilian Amazon region. The approach consists of adjusting tree height-diameter at breast height (H:DBH) models in each study site by ecological species groups: pioneers, early secondary, and late secondary. Overall, the DBH and corresponding height (H) of 1,178 individual trees were measured during two field campaigns: August 2014 in Manaus and September 2015 in Santarém. We tested the five most commonly used log-linear and nonlinear H:DBH models, as determined by the available literature. The hyperbolic model: H = a.DBH/(b+DBH) was found to present the best fit when evaluated using validation data. Significant differences in the fitted parameters were found between pioneer and secondary species from Manaus and Santarém by F-test, meaning that site-specific and also ecological-group H:DBH models should be used to more accurately predict H as a function of DBH. This novel approach provides specific equations to estimate height of secondary forest trees for particular sites and ecological species groups. The presented set of equations will allow better biomass and carbon stock estimates in secondary forests of the Brazilian Amazon.

摘要 本研究针对巴西亚马逊地区两处研究样地——马瑙斯（亚马逊中部）与圣塔伦（亚马逊东部）的次生林，提出一种单木树高估算的全新方法。该方法通过按生态物种群（先锋种、早期次生种、晚期次生种）在各研究样地拟合树高-胸径（H:DBH）模型实现。本研究通过两次野外调查共测定1178株单木的胸径（DBH）与对应树高（H）：2014年8月于马瑙斯样地，2015年9月于圣塔伦样地。我们测试了文献中最常用的5种对数线性与非线性H:DBH模型，经验证数据评估后发现，双曲线模型H = a·DBH/(b+DBH)的拟合效果最优。通过F检验发现，马瑙斯与圣塔伦样地的先锋种与次生树种的拟合参数存在显著差异，这表明应采用针对特定样地与生态物种群的专属H:DBH模型，以更精准地基于胸径预测树高。本研究提出的全新方法可为特定样地与生态物种群的次生林木树高估算提供专属方程，这套方程将有助于更精准地估算巴西亚马逊次生林的生物量与碳储量。