Forest Condition
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Increase condition of the floodplain forest
Data collection in progress
Kakheti Steppes
Georgia
Problem: Since the construction of the Dali dam, the floodplain forest downstream of the dam has been drying out, resulting in a loss of native floodplain forest tree species. As a result, the floodplain forest extent has been declining, in part due to a lack of regeneration of new trees.
Action: SABUKO is working with the dam managers to recreate flooding events by periodically releasing water from the Dali dam. They have also constructed one gabion, and are building more, to retain water in the floodplain area when water is released.
Indicator: The success of this action has been monitored by assessing the amount of forest, and the condition of regenerating trees in the floodplain forest area, quantified by height of new seedlings and saplings. If heights of regenerating trees are taller in the flooded area than in the control area (receiving no flooding upstream of the dam), we will be able to infer that the flooding events are benefiting the overall condition of the young trees.
Methods
This monitoring work is a continuation from the Iori River Valley project, which has been monitoring seedling and sapling abundance in the floodplain forest area since 2019. Fifty circular plots (25 in control and treatment areas, respectively), each spanning an area of 500 m², were established to systematically record the trees within them. Two sub-plots were established in each plot (one north of the plot centre, one south), with radii of 1.5m. Data collection occurred in 2019 and 2021, enabling the evaluation of changes over time since flooding events began in 2020.
In 2023, the number of sampling plots was increased to 151, and regenerating abundance was documented using the previous methodology. Fifty-four plots were located in the treatment area (below the dam), while 97 plots were established in the control area (above the dam). A subset of these plots are the fifty plots from the Iori River Valley project (25 above the dam, 25 below). The same plots were also used to monitor forest regeneration.
The final variable analysed was the regenerating tree heights below the Dali dam (receiving periodic flooding), compared to the tree species in the control area above the dam (no flooding). Each tree observed was assigned to one of three height classes: < 50, 50-150 and >150 cm. Next, the proportion of trees in each height class was computed, compared to the overall abundance of regenerating trees observed. Finally, the change between years in proportion of trees in each height class was computed. This allowed for the fact that all trees will grow over the period. Analysing the difference in the proportion of trees added to certain height classes will assess whether trees in the restoration area are disproportionately adding taller trees, compared to the control site, due to the flooding events.
Results
There was a significant difference in the proportion of trees in the shortest height class (< 50 cm) between years (F(2,172) = 4.99, p = 0.008), with fewer trees in this height class in 2021 compared to 2019 and 2023 (Fig. 1). However, there was no significant difference between treatment and control sites. There was no significant difference among years for proportion of trees in the taller height classes (50 – 150 cm and > 150 cm), and this also did not differ between treatment and control sites.
Figure 1: Mean proportion of trees in in each height class, in treatment and control plots. Error bars denote standard error of the mean (SEM).
Further monitoring will be conducted as the restoration progresses.
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