Plant Biomass
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Increase biomass production
Data collection in progress
Kakheti Steppes
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. Reducing grazing pressure should allow greater regeneration.
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.
Example of a degraded grassland. Photo: Marinus Gebhardt.
Example of a healthy grassland. Photo: Marinus Gebhardt.
Methods
This data collection is a continuation of a previously funded project, Iori River Valley. Therefore data from the Iori River Valley project is used as a baseline for this work. In autumn 2019 SABUKO conducted manual data collection at 16 plots (see Fig. 1 for sampling design). This monitoring design employed a stratified random sampling approach, where four plots were selected in four types of grasslands: hilly grassland, fragmented grasslands within arid light forests, grasslands within Badlands, and plain pastures. The selection was made digitally using 30m resolution maps of the area in ArcGIS. Of the four plots, two were located in control areas where no restoration treatment was planned, and two were located in treatment areas, where rotational grazing was planned to occur on 600 ha of pilot sites after from 2019 onward.
Figure 1: Map of sampling sites. Solid black circles show treatment plots (with rotational grazing) and dashed circles show control plots (no restoration action planned). Within the circles, pink squares show subplots for vegetation sampling.
In each plot, four randomly placed 50 x 50 cm sub-plots were established in one quadrant of the plot (see Fig. 2). In these subplots, grassland quality was quantified by clipping above-ground biomass of primary species, differentiating between green and dry biomass. The samples were then oven-dried and subsequently weighed, producing final variables of sum of green standing biomass, or dried standing biomass, per plot. Repeat measurements are planned for autumn 2024 and autumn 2027, to assess the impact of rotational grazing on plant biomass over the funding period.
Figure 2: Sampling subplot design within each plot.
Results
Baseline results of dry standing biomass show variation between the different grassland types (Fig. 3), attributable to the presence of difference dominant species in each type. Comparing the control and treatment sites (all four grassland types combined) through a Wilcoxon test showed no significant difference in dry biomass production (W = 494.5, p = 0.819).
Figure 3: Sum of dried biomass (dry standing biomass) for the different sampling units within control and intervention plots.
Interestingly, green standing biomass showed different trends (Fig. 4). Intervention sites exhibited significantly higher values for green biomass compared to control areas (W = 400, p = 0.023). Green biomass during the autumn/winter period is highly influenced by moisture regimes, so it is possible that the two grassland types that had more green standing biomass were on slopes and facing aspects that retained more moisture, enabling more growth. SABUKO will soon have 2024 and 2027 data to show how these sites change over time, and if changes in the treatment groups differ from those in the controls.
Figure 4: Sum of dried biomass (green standing biomass) for the different sampling units within control and intervention plots.
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