Forest Regeneration
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Increase abundance of regenerating trees in 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, 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 a gabion, to retain water in the floodplain area when water is released.
Indicator: the success of this restoration treatment is being monitored by estimating the abundance of seedlings and saplings regenerating since the application of flooding events began.
Methods
Fifty circular plots (25 plots 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 period flooding events began in 2020. The final variable analysed was the regenerating tree abundance below the dam (receiving periodic flooding) between 2019 and 2022, and separately the abundance in the control area above the dam (no flooding) within the same timeframe.
The same plots were used to monitor floodplain forest condition and species composition.
Results
In the control area upstream of the Dali dam (where no restoration action took place), there was no significant change from 2019 to 2022 in the abundance of regenerating trees. Interestingly, this was also the case downstream of the dam – the area receiving restoration action (periodic flooding). The flooding has not yet had an effect on the abundance of regenerating trees in this restoration area.
Figure 1: Comparisons made between 2019 and 2022 within each site. The ‘ns’ denotes statistical non-significance via a Student’s t-test at the 0.05 threshold.
Interpretation
Currently, flooding events have occurred about twice per year 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 abundance of new seedlings and saplings in the floodplain forest area, 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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