Carbon stock and biomass estimate by additive models applied to Ilex paraguariensis

ABSTRACT Ilex paraguariensis is an important non-timber forest product in southern Brazil, where it is cultivated in association with native species, given its demand for shading, which contributes to the conservation and carbon fixation in its biomass. However, determining this biomass is difficult, since the estimates do not guarantee additivity between the compartments and the total aboveground biomass. This study aimed to evaluate additive (seemingly unrelated regression - SUR) and non-additive (ordinary least squares - OLS) biomass models in an Ilex paraguariensis stand and comparing its carbon stock with other land use types, consolidating its potential in the face of climate change. A total of 30 trees were cut, compartmentalized and weighed on a digital scale, and four biomass models were adjusted. The carbon stocks were compared with values found in the literature. The bias in the SUR model was less than 2 %, except for the leaves, while the bias in the OLS model varied between 1 and 14 %. The error ranged between 23 and 49 % for SUR, and between 31 and 50 % for OLS. The models adjusted by SUR ensured the accuracy and additivity of the compartments. The Ilex paraguariensis stand stored more carbon than agriculture and pasture areas, removing more CO2, evidencing the sustainability of this system and favoring the climate stability.

摘要：巴拉圭冬青（Ilex paraguariensis）是巴西南部重要的非木材林产品，因其需荫蔽环境，常与乡土物种伴生种植，该模式有助于生态保护与生物量碳固存。然而，由于各生物量组分与地上总生物量间的可加性无法通过估算得到保障，该物种的生物量测定颇具难度。本研究旨在针对巴拉圭冬青人工林，评估可加性模型与非可加性模型的性能：其中可加性模型采用似不相关回归（seemingly unrelated regression，SUR）方法，非可加性模型采用普通最小二乘法（ordinary least squares，OLS）方法；同时将该林分的碳储量与其他土地利用类型进行对比，以明确其应对气候变化的潜力。本研究共采伐30株树木，对其进行组分拆分后使用电子天平称重，并拟合了4种生物量模型。将测得的碳储量与文献报道值对比后发现，除叶片组分外，似不相关回归（SUR）模型的偏差小于2%；而普通最小二乘法（OLS）模型的偏差介于1%至14%之间。似不相关回归（SUR）模型的误差范围为23%至49%，普通最小二乘法（OLS）模型则为31%至50%。经似不相关回归（SUR）拟合的模型可保障各生物量组分的准确性与可加性。巴拉圭冬青人工林的碳储量高于农业与牧草地，可固定更多二氧化碳，证实了该种植系统的可持续性，有助于气候稳定。