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 本研究提出了一种新颖方法，用于估算巴西亚马逊地区两个研究样地——马瑙斯（Manaus，亚马逊中部）与圣塔伦（Santarém，亚马逊东部）的次生林中单株树木的树高。该方法依据生态物种群（先锋种、早期次生演替种、晚期次生演替种），在各研究样地中调整胸高树高与胸径（Height-Diameter at Breast Height, H:DBH）模型。总体而言，研究团队在两次野外调查中测量了1178株单株树木的胸径及其对应树高：2014年8月于马瑙斯，2015年9月于圣塔伦。我们基于现有文献选取五种最常用的对数线性与非线性H:DBH模型开展测试。经验证数据评估后，发现双曲模型：H = a·DBH/(b+DBH) 具备最优拟合效果。通过F检验发现，马瑙斯与圣塔伦样地的先锋种及次生演替物种的拟合参数存在显著差异，这表明应针对样地及生态物种群分别构建H:DBH模型，以基于胸径更精准地预测树高。该新颖方法可为特定样地与生态物种群的次生林树木树高估算提供专属方程。本次提出的方程组可助力优化巴西亚马逊次生林的生物量与碳储量估算工作。