Mixed-species allometric equations and estimation of aboveground biomass and carbon stocks in restoring degraded landscape in northern Ethiopia

Abstract

Accurate biomass estimation is critical to quantify the changes in biomass and carbon stocks following the restoration of degraded landscapes. However, there is lack of site-specific allometric equations for the estimation of aboveground biomass (AGB), which consequently limits our understanding of the contributions of restoration efforts in mitigating climate change. This study was conducted in northwestern Ethiopia to develop a multi-species allometric equation and investigate the spatial and temporal variation of C-stocks following the restoration of degraded landscapes. We harvested and weighed 84 trees from eleven dominant species from six grazing exclosures and adjacent communal grazing land. We observed that AGB correlates significantly with diameter at stump height D 30 (R 2 = 0.78; P < 0.01), and tree height H (R 2 = 0.41, P < 0.05). Our best model, which includes D 30 and H as predictors explained 82% of the variations in AGB. This model produced the lowest bias with narrow ranges of errors across different diameter classes. Estimated C-stock showed a significant positive correlation with stem density (R 2 = 0.80, P < 0.01) and basal area (R 2 = 0.84, P < 0.01). At the watershed level, the mean C-stock was 3.8 (±0.5) Mg C ha −1 . Plot-level C-stocks varied between 0.1 and 13.7 Mg C ha −1 . Estimated C-stocks in three-and seven-year-old exclosures exceeded estimated C-stock in the communal grazing land by 50%. The species that contribute most to C-stocks were Leucaena sp. (28%), Calpurnia aurea (21%), Euclea racemosa (20.9%), and Dodonaea angustifolia (15.8%). The equations developed in this study allow monitoring changes in C-stocks and C-sequestration following the implementation of restoration practices in northern Ethiopia over space and time. The estimated C-stocks can be used as a reference against which future changes in C-stocks can be compared.

Allometric Models for Predicting Aboveground Biomass of Trees in the Dry Afromontane Forests of Northern Ethiopia

“…We also tested previously published general multispecies models and local species-specific models (Table 2) using our data set. We chose four general multispecies models developed by Chave et al [10], Chave et al [11], Ubuy et al [19], and Mokria et al [2] and three local species-specific models developed by Worku and Soromessa [24], Solomon et al [26], and Kebede and Soromessa [25]. The models developed by Chave et al [10] and Chave et al [11] were chosen because they are supposed to be used generally in tropical regions.…”

“…Aboveground tree biomass (AGB) is an important variable used in quantifying and monitoring forest ecosystem services. Aboveground tree biomass in forest ecosystems is needed for many applications; it can be used to estimate the amount of carbon that forests can sequester or that can be emitted when forests are destroyed [1,2], it can be used to determine sustainable wood harvest [3], it provides information on how many resources are available for use [4], and it is important for assessing forest productivity [5,6]. For these and other applications, reliable and accurate biomass estimates are required.…”

“…However, they generally provide less bias than general models [20] because tree growth characteristics are affected by local geographical conditions such as climate, soil properties, altitude, and land-use history [21]. As it is indicated by Mokria et al [2], lack of local AGB estimation models is the main reason for persistent inaccuracy in biomass estimation, particularly in sub-Saharan Africa.…”

“…None of the models included multiple species. Even though there are developments after the review by Henry et al [22], still very few models (e.g., [2,19]) are multispecies. Species-specific models can result in accurate biomass estimates.…”

The Carbon Sequestration Potential of Degraded Agricultural Land in the Amhara Region of Ethiopia

“…Drought together with a dense grass layer promotes forest fires in the Lowlands, which may occur several times per year [38]. Thus, only so called 'exclosures' [15,75], which are fenced and guarded areas with natural regeneration and no or reduced grazing may help to restore the woodland areas in the Lowlands [76]. Unfortunately, it is especially the Combretum-Terminalia woodlands that are suffering from recent deforestations [27].…”