Abstract
Research on the contribution of understory components to the total above ground biomass (AGB) has to date received very little attention because most prior biomass estimation studies have ignored small regenerating trees beneath the main canopy with the assumption that their contribution to biomass is generally negligible. Only a few biomass studies have emphasized a considerable contribution to biomass of understory components in forest ecosystems. However, this study of native, tropical, deciduous forest biomass in the Central Highlands of Vietnam was able to explore the contribution of small regenerating trees to total biomass by exploiting a large field inventory of hundreds to thousands of individually-counted small regenerating trees per hectare. Thus, this study investigated the influence of small regenerating tree biomass on models of the relationship between total AGB and remote sensing data. These analyses were trained with and without topographic variables derived from ASTER-GDEM. Our results demonstrate that the inclusion of small regenerating understory trees (R2 = 0.42, NRMSE or %RMSE = 30.5%) provides a quantifiable improvement in total estimated AGB compared to using only large woody canopy trees (R2 = 0.21, NRMSE or %RMSE = 36.6%) when correlating field-based biomass measurements with optical image-derived variables. All analyses show that the inclusion of terrain factors made an important contribution to biomass modeling. This study suggests that for young, open forests where there are many small regenerating trees, the contribution of understory biomass should be taken into consideration to improve total AGB estimation.
Highlights
Forests play a vital role in the global carbon cycle since their key indicator, known as biomass, contributes significantly to the mitigation of greenhouse gas emissions through carbon sequestration and storage [1]
Overstory biomass makes a major contribution to total above ground biomass (AGB) in multi-layered forests, understory vegetation might add a considerable amount of biomass at some sites, especially in places where there are many young stands of trees [12]
The plot-based total AGB values ranged from 5.37 Megagrams per hectare (Mg/ha) to 210.31 Mg/ha using the UN-REDD equation
Summary
Forests play a vital role in the global carbon cycle since their key indicator, known as biomass, contributes significantly to the mitigation of greenhouse gas emissions through carbon sequestration and storage [1]. Improving the accuracy of AGB estimation is important for developing a better understanding of forest ecosystems, and protecting them [11]. Overstory biomass makes a major contribution to total AGB in multi-layered forests, understory vegetation might add a considerable amount of biomass at some sites, especially in places where there are many young stands of trees [12]. Stand age is an important determinant of the contribution of understory biomass to total ecosystem biomass. In New Brunswick forests, understory biomass was reported to contribute as much as 71–88% of total biomass in 13- and 16-year-old jack pine stands, but as little as 1–6% of total biomass in older stands [12]
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