Mangrove expansion and rainfall patterns in Moreton Bay, Southeast Queensland, Australia

Abstract

Changes in rainfall pattern have been suggested as a mechanism for the landward incursion of mangrove into salt marsh. The aim of the research was to assess the relationship between rainfall patterns and the spatial distribution of mangrove forests at study sites in Moreton Bay, southeast Queensland, Australia, over a 32-year period from 1972 to 2004. To identify periods of relatively consistent rainfall patterns points at which rainfall patterns changed (change-points) were identified using the non-parametric Pettitt-Mann-Whitney-Statistic and the cumulative sum technique. The change-points were then used to define the temporal periods over which changes to mangrove area were assessed. Both mangrove and salt marsh area were measured by digitizing aerial photographs acquired in 1972, 1990 (the year with the most significant change-point), and 2004.The rates of change in mangrove area pre-1990 (a wetter period) and post-1990 (a drier period) were estimated. A significant positive relationship was demonstrated between rainfall variables and landward mangrove expansion, but not for seaward expansion. We concluded that rainfall variability is one of the principal factors influencing the rate of upslope encroachment of mangrove. However, the rate of expansion may vary from site to site due to site-specific geomorphological and hydrological characteristics and the level of disturbance in the catchment.

Mangrove expansion and population structure at a planted site, East London, South Africa

“…The authors also mentioned that salt marsh may not keep pace with sea-level rise, which would result in an increase in the frequency of tidal inundation, which again would give the mangrove propagules an advantage over salt marsh establishment. This is because the expansion of mangroves is mainly dependent on the rate of sea-level rise, sedimentation (Rogers et al 2006) and rainfall (Eslami-Andargoli et al 2009). In Park's (2004) study an 'edge invasion' was noted, where a 5-10 m boundary of mangroves was growing on the edge of the salt marsh area and it was suggested that this boundary was kept 'stable' because healthy and thick salt marsh cover prevented the establishment of mangrove propagules.…”

Does spatial scale affect the pattern of mangrove change under different rainfall regimes? An example in southeast Queensland, Australia

“…The results of earlier research in the study area have indicated that, although rainfall was important for mangrove change, it also controlled the contribution of other factors such as land use and human population (Eslami-Andargoli et al 2009. The earlier study showed that the period from 1972-1990 was significantly wetter than the 1990-2004 period (Eslami-Andargoli et al 2009). There were significant differences in the rate of mangrove spatial change between the two periods.…”

“…These may include both natural and anthropogenic factors. Eslami-Andargoli et al 2009;Saintilan et al 2009). Although changes to mangroves have occurred in the past in response to long-term environmental change, these are expected to become more rapid and widespread in coming decades in response to human land use and global climate changes (Lyford et al 2003).…”

“…Mangrove incursion into saltmarshes is related to larger-scale global drivers such as climate change (sealevel rise, changes in precipitation) and smaller scale regional and local drivers (mostly associated with land use/cover change), as well as the interaction between them (Eslami-Andargoli et al 2009Saintilan et al 2009;Morrisey et al 2010). For local conservation management, it is important to identify the effect of spatial scale in order to mitigate the impacts of the drivers (Houlahan & Findlay 2003).…”

“…Although sea-level fluctuations have affected mangrove distribution over the long-term (Field 1995;Gilman 2004), in the short-term, regional rainfall and catchment runoff may be more significant than sea level changes (Snedaker 1995;Eslami-Andargoli et al 2009. Although sea-level fluctuations have affected mangrove distribution over the long-term (Field 1995;Gilman 2004), in the short-term, regional rainfall and catchment runoff may be more significant than sea level changes (Snedaker 1995;Eslami-Andargoli et al 2009.…”