The dynamics of expanding mangroves in New Zealand

In contrast to the global trend of mangrove decline, New Zealand mangroves are rapidly expanding, facilitated by elevated sediment inputs in coastal waters as a consequence of large-scale land use changes following European settlement. New Zealand mangroves are at the southern limit of the global mangrove extent, which limits the tree height of Avicennia marina var. australasica, the only mangrove species present. Mangroves in New Zealand thrive in the sheltered environments of infilling drowned river valleys with abundant supply of fine terrigenous sediments, showing various stages of mangrove succession and expansion dynamics. Bio-physical interactions and carbon dynamics in these expanding temperate mangrove systems show similarities to, but also differ from those in tropical mangrove forests, for instance due to the limited height and complexity of the mangrove communities. Likewise, ecosystem services provided by New Zealand mangroves deviate from those offered by tropical mangroves. In particular, the association of mangrove expansion with the accumulation of (the increased supply of) fine sediments and the consequent change of estuarine ecosystems, has provoked a negative perception of mangrove expansion and subsequently led to mangrove clearance. Over recent decades, a body of knowledge has been developed regarding the planning and decision making relating to mangrove removal, yet there are still effects that are unknown, for example with respect to the post-clearance recovery of the original sandflat ecosystems. In this chapter we discuss the dynamics of New Zealand’s expanding mangroves from a range of viewpoints, with the aim of elucidating the possible contributions of expanding mangroves to coastal ecosystem services, now and in the future. This chapter also reviews current policies and practice regarding mangrove removal in New Zealand and addresses the (un)known effects of mangrove clearance. These combined insights may contribute to the development of integrated coastal management strategies that recognise the full potential of expanding mangrove ecosystems

Coastal marsh vegetation assemblages of Galveston Bay: Insights for the East Texas Chenier plain

Coastal marshes are composed of distinct vegetation assemblages that contribute to ecosystem functions and services over time and space. In recent decades, natural and anthropogenic changes have led to large-scale marsh loss along the Chenier Plain of the Gulf of Mexico. An understanding of the composition and dominance of the vegetation assemblages that form these coastal marshes is necessary to effectively assess and monitor their stability under changing conditions. To investigate marsh vegetation assemblages along the Texas Chenier Plain, we analyzed the composition and dominance of 135 marsh plots distributed across two study areas bordering the East Bay of Galveston Bay in Chambers County, Texas using cluster analysis. Seven general vegetation assemblages were identified. The assemblages were evaluated using indicator species analysis and Multi-Response Permutation Procedures and compared to marsh vegetation assemblages found in the Louisiana Chenier Plain. Our data provide a foundation for better understanding of vegetation patterns found along the East Texas Chenier Plain allowing managers and conservationists the ability to better evaluate the effects of marsh change due to climatic and human driven pressures. © 2013 Society of Wetland Scientists