Distinct characteristics of canopy gaps in the subtropical mangroves of Moreton Bay, Australia. (30th June 2019)

• Record Type: Journal Article
• Authors: Amir, A. Aldrie; Duke, Norman C.
• Is Part Of: Estuarine, coastal and shelf science. Volume 222(2019)
• Page Start: 66
• Page End: 80
• Publication Date: 2019-06-30
• Subjects: Canopy disturbance -- Canopy gap -- Gap dynamics -- Mangrove -- Moreton bay -- Australia; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2019.04.007
• Languages: English
• ISSNs: 0272-7714

Abstract

Abstract: Mangroves often form extensive closed forests characterised by the occurrence of canopy gaps consisting of a group of standing dead trees. This article describes the physical characteristics, micro-environmental changes and the regrowth pattern of the naturally created unique circular canopy gaps in the subtropical Avicennia marina mangroves of Moreton Bay, Southeast Queensland, Australia. A survey on 52 canopy gaps was carried out to quantify the size and shape of canopy openings. We found that gap size ranged from a minimum area of 27 m 2 to a maximum area of 474 m 2 with an average (±standard deviation) of 134 ± 102 m 2 . All of the gaps surveyed were circular in shape with the eccentricity of length and width between 0.7 and 1.3. Once a canopy gap is created, the forest physical and biological processes are altered compared with the surrounding forest, such as in an increase in the potential photosynthetic active radiation (PPAR) and canopy openness, and a decrease in leaf area index (LAI). We found that canopy openings also had a significant effect on sediment pore water temperature but not on salinity and pH. The sudden increase in the amount of light following canopy opening stimulated rapid growth of seedlings which were available for the opportunity to take the place of the dead trees. Gap Closure Index (GCI) is introduced to illustrate surveyed gaps in the context of vertical growth of seedlings to fill up gap space to reach the site maximal canopy height, thus demonstrating the phases of gap dynamics in the natural regeneration of the subtropical monospecific mangrove forest. Highlights: Gap formation is a natural process that triggers mangrove forest regeneration. Mangrove canopy gaps are characterised by their distinctive circular shape. Canopy openings provide the opportunity and conducive conditions for seedling growth. Mangrove canopy gaps undergo a series of defined phases from initiation to closure. Seedlings grow to fill up gaps, replacing the dead trees and rejuvenate the forest.