Increase in mangrove forest area in the Auckland Region, New Zealand, is mainly driven by land use change in the catchments

In some regions an increase of mangrove forest area has been observed. However, the factors influencing changes in mangrove area are not well investigated. The objectives of this study were (1) to quantify to change in... [ view full abstract ]

In some regions an increase of mangrove forest area has been observed. However, the factors influencing changes in mangrove area are not well investigated. The objectives of this study were (1) to quantify to change in mangrove area from 1940-2014, and (2) to identify the factors driving mangrove cover change across 38 estuaries in the Auckland Region, New Zealand, using remote sensing and field based surveys. The study showed that mangrove forest area in the Auckland Region, New Zealand, increased from 2,313 ha in 1940 to 10,483 ha in 2014 (on average 3.2% yr^-1). Separating tall and dwarf mangroves revealed that the proportion of tall mangroves decreased from 89% to 55% whereas the area covered by dwarf mangroves increased. In contrast to other studies we found that the increase in mangrove area was mainly through gap filling. Boosted regression tree analysis revealed that sea level and mean annual air temperature explained 36% of the variation mangrove cover change in the Auckland Region. However, the loss of forest cover in the catchment and associated sediment loads was the strongest predictor explaining up to 62% of the variation in mangrove area. Our findings highlight that catchment management to reduce sediment loads is an important aspect of mangrove management