Effects of experimental sedimentation on the phenological dynamics and leaf traits of replanted mangroves at Gazi bay, Kenya

Abstract

Sedimentation results in the creation of new mudflats for mangroves to colonize among other benefits. However, large sediment input in mangrove areas may be detrimental to these forests. The dynamics of phenological events of three mangrove tree species (Avicennia marina, Ceriops tagal, and Rhizophora mucronata) were evaluated under experimental sediment burial simulating sedimentation levels of 15, 30, and 45 cm.While there was generally no shift in timing of phenological events with sedimentation, the three mangrove tree species each responded differently to the treatments.Partially buried A. marina trees produced more leaves than the controls during the wet season and less during the dry season. Ceriops tagal on the other hand had higher leaf loss and low replacement rates in the partially buried trees during the first 6 months of the experiment but adapted with time, resulting in either equal or higher leaf emergence rates than the controls.Rhizophora mucronata maintained leaf emergence and loss patterns as the unaffected controls but had a higher fecundity and productivity in the 15-cm sedimentation level.The results suggest that under incidences of large sedimentation events (which could be witnessed as a result of climate change impacts coupled with anthropogenic disturbances), mangrove trees may capitalize on “advantages” associated with terrestrial sediment brought into the biotope, thus maintaining the pattern of phenological events.

Infestation mechanisms of two woodborer species in the mangrove Sonneratia alba J. Smith in Kenya and co-occurring endophytic fungi

“…However, for two decades S . alba has been experiencing elevated levels of insect infestation that is contributing to the dieback of infested branches and even killing of some infested trees [21,23,34] within and far beyond the sites with siltation.…”

“…alba in Gazi (Kenya), mainly where other challenges like sedimentation (increased surface elevation with sand and silt on the S . alba stand) contributed to the further weakening of the stand [23]. An aerial survey conducted in 2002 along the Kenyan coastline revealed that infestation was spreading north towards the mangroves of Somalia [22].…”

Wide Ranging Insect Infestation of the Pioneer Mangrove Sonneratia alba by Two Insect Species along the Kenyan Coast

“…In addition to anthropogenic degradation such as overharvesting of mangroves for fuel wood, timber and fish traps, clearing and conversion to other land uses such as agriculture, aquaculture, urban development, tourism and salt production and pollution of mangroves in Kenya [ 42 , 43 , 44 ], S . alba is experiencing a dieback due to sedimentation and silting [ 30 , 45 , 46 ]. For almost two decades, insect damage has also led to the loss of infested S .…”

“…For almost two decades, insect damage has also led to the loss of infested S . alba branches and trees [ 14 , 46 ]. In October 1991, a project was initiated to restore the mangroves in Gazi by replanting various tree species, including S .…”

Mangrove trees survive partial sediment burial by developing new roots and adapting their root, branch and stem anatomy

“…Squared plots of 2 m by 2 m were selected within the plantations, surrounded with a netting material of 0.5 mm mesh size and filled with terrestrial sediment to 15, 30 and 45 cm levels as described in Okello et al (2014). In the controls, no sediment was added but the plots were surrounded with the same netting material and restrained to the ground using pegs as in the treatments.…”