Forest Composition
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Increase proportion of flood-tolerant tree species within floodplain forest area
No change observed
Iori River Valley
Georgia
Problem: since the construction of the Dali dam, the floodplain forest downstream of the dam has been drying out, suffering a loss of native floodplain forest tree species. As a result, the floodplain forest extent and condition 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 a gabion, to retain water in the floodplain area when water is released.
Indicator: a shift in the composition of the regenerating floodplain forest towards more saplings that are associated with flooding – rather than species preferring drier habitats – will indicate successful initial restoration of the native floodplain forest.
Methods
Fifty circular plots (25 in the control area and 25 in the treatment area), each spanning an area of 500 m², were established to systematically record the occurrences of seedlings and saplings within them. Two sub-plots were established in each plot (one north of the plot centre, one south), with radii of 1.5m. Within the sub-plots, all seedlings and saplings (< 8cm in diameter) were recorded. Data collection occurred in 2019 and 2022, enabling the evaluation of changes over time since periodic flooding began in 2020, in both the control area (no flooding) and the treatment area (receiving periodic flooding). The final variables analysed include species richness and abundance of flood-tolerant and flood-requiring species, which were classified using existing literature (Nakhutsrishvili, 2013; Dolukhanov, 2010; Ketskhoveli, 1962; Craft, 2016).
The same plots were used to monitor forest condition and regeneration.
Ilia State University representatives collecting data within floodplain forest plots. Photo: Vasil Metreveli
Results
In the control area upstream of the Dali dam (where no periodic flooding or gabion exists), there was no change from 2019 to 2022 in the richness or abundance of flood-associated saplings. Interestingly, this was also the case for downstream of the dam – the area receiving restoration action (periodic flooding). The flooding has not yet had an effect on the composition of the regenerating floodplain forest. The figures below denote the difference between 2019 and 2022, at the control and restoration sites (‘ns’ denotes ‘not statistically significant’ through a Student’s t-test, at the 0.05 threshold).
Interpretation
Currently, flooding events happen about twice per year, and have been ongoing since 2020. This initial data suggests that this frequency of flooding is insufficient to restore the floodplain forest downstream of the Dali dam. In order to achieve the desired floodplain forest composition (i.e. more flood-tolerant and flood-requiring species), this site will require more flooding events, as well as more time for the trees to respond and grow. Ongoing monitoring efforts are in place to track this progress across longer time-scales.
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