Observations of Natural Recruitment and Human Attempts at Mangrove Rehabilitation After Seismic (Tsunami and Earthquake) Events in Simeulue Island and Singkil Lagoon, Aceh, Indonesia - Post-Tsunami Hazard: Reconstruction and Restoration - page 312

19.4 Observed Natural Recruitment

19.4.1 Simeulue

Of all the sites measured, the previously un-planted sites at Teluk Dalam exhibited
the highest stem density (2,859 stems/ha), average annual rate of recruitment
(408.4 plants/year), and total species diversity (12). Teupah Selatan, an un-planted
site in Eastern Simeulue hypothesized as “in need of human assisted propagule
distribution” exhibited lower average stem density (2,117 stems/ha), average annual
rate of recruitment (302.5 plants/year), and total species diversity (7), exceeding
expected results. With a rate of recruitment expected to add 900 plants/ha over
3 years, this site was re-evaluated as “not requiring human assistance for rehabilita-
tion,” as natural recruitment would exceed CADRE project targets (1,250-2,500
seedlings/ha after 3 years of intervention).
The fi nal site measured in Simeulue was an ex-planting site at Teluk Dalam,
Sambay. This site was planted twice since the tsunami, both with qualitatively high
mortality. At the time of sampling, it was diffi cult for the team to distinguish planted
material from natural recruits for Rhizophora apiculata , yet the other six species
present were all natural recruits as they were not planted by either planting project.
The overall stem density at the time of sampling was 467 stems/ha with a recruit-
ment rate over 7 years of 66.7 comprised of seven species. Results are summarized
in Table 19.1 .

19.4.2 Singkil

Mangrove stem densities, recruitment rates and species diversity were also surveyed
at a trio of sites in Singkil Lagoon; SL1, SL2 and SL3.
SL 1 is located near a newly cut channel between the sea and the lagoon and
exhibited a mean density of Mean density of 2,980 plants per hectare. This site
exhibited the pattern of a shift of species to higher elevations after seismic subsidence
described in Sect. 2.2 . SL2, includes areas previously planted, and then succeeded
by Casuarina due to rapid sedimentation. The mangrove stem density at this site
was 160 plants/ha. SL3 was not formerly mangrove forest, and has been colonized
by Acrostichum aureum after subsidence, indicating this site is now at the upper
intertidal limit for mangrove distribution. The local community with support from
the CADRE project has planned an intervention for this area, razing the Acrostichum
aureum , digging in tidal channels to facilitate water exchange with the lagoon, and
planting woody mangrove species. Findings for all three sites at Singkil Lagoon are
also summarized in Table 19.1 .