Plant Biomass
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Increase biomass of grassland plant species
Improving
Iori River Valley
Georgia
Problem: Combined pressures in this landscape such as overgrazing, increasing temperatures and less rainfall leading to erosion and desertification are contributing to fewer and smaller grassland species.
Action: SABUKO is working with farmers and shepherds to increase their participation in rotational grazing, which means that portions of the pastures will be left ungrazed at any given time to rest and regain biomass.
Indicator: the quality of a grassland can be described partly by how vigorously its plant species grow, or how large the plants are (biomass). An increasing biomass will indicate a reversal of the negative trends that are symptomatic of overgrazing.
Marinus Gebhardt and drone expert Giorgi Lebanidze from GIZ deploying a drone for assessing grassland quality. Photo: SABUKO
Students from Ilia State University assisting in data collection for assessing grassland quality through biomass. Photo: SABUKO
Methods
SABUKO used two different approaches to assess grassland biomass: (1) plot-level monitoring that entailed manual data collection, and (2) remote-sensing, landscape-level monitoring. The plot-level monitoring provided ground-truth data, which SABUKO could use to assess if the remote-sensing variables provided consistent results at a larger scale.
Plot-level measurements were taken in areas where rotational grazing was trialed on 600 ha of pilot sites in the 2019/2020 grazing season. Grassland quality was quantified by above-ground biomass production of primary species in 50 x 50 cm plots. These metrics were obtained by repeatedly visiting 16 fixed sampling plots, selected according to a stratified random sampling design in both treatment (rotational grazing implemented) and control (conventional grazing practices) sites. Biomass was harvested on 4 randomly selected 50×50 cm subplots within the plots. The samples were oven-dried and subsequently weighed. Final variables investigated were mean and sum of dried biomass, per plot. Measurements have been repeated twice annually, before and after the grazing period.
In parallel, a sustainable management approach (combining rotational grazing and traditional management) was laid out on ~4357 ha of two different land users (2132 ha and 2245 ha). Similar territories (1960 ha and 2400 ha) were identified as control sites in the nearer catchment of comparable grassland. Satellite imagery was used to remotely assess grassland above-ground biomass by using the Soil Adjusted Vegetation Index (SAVI) of Sentinel 2 data. Mean SAVI values per vegetation period (per year) were compared between 2019 and 2022.
Results
After one grazing season of implementing rotational grazing, significant changes were observed between the control and rotational grazing sites. The above-ground biomass production dropped significantly between 2019 and 2022 in the control site — meaning those areas demonstrated a decline in biomass production. This was true of both the mean dried biomass, and sum of all dried biomass. The sustainably grazed plots (treatment sites), however, did not differ in their biomass production between 2019 and 2022. After just one year of implementation, outcomes can be observed between the control and treatment groups in biomass production. The years between 2019 and 2022 had little rainfall and very high temperatures, and during this time the sustainably grazed sites did not suffer from a loss in biomass production as the control sites did. This is early evidence that sustainable grazing can promote grassland resilience, compared to the continued degradation of sites subject to overgrazing, which is so commonplace in this landscape.
These findings were corroborated with the remote-sensing method, using the SAVI index. This method was able to analyse data from 2019 to 2022, and SAVI values significantly increased on sustainably managed grasslands during that time, while the SAVI values from the control plots did not.
Comparisons were made between the 2019 and 2020 within the control group, and also separately within the treatment group; ‘ns’ denotes statistical non-significance at the 0.05 threshold, while statistical significance is denoted by * at the <0.05 threshold and ** at the <0.01 threshold.
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