Marismas tropicais como facilitadoras do estabelecimento de plântulas de mangue

Abstract

Ecological interactions shape biodiversity and ecosystem responses to climate change. Understanding those interactions is crucial for developing nature-based solutions (NBS) that promote climate change mitigation and adaptation, such as ecosystem restoration. Restoration success benefits from positive interactions, such as facilitation. Coastal vegetations, such as saltmarshes, seem to facilitate the development of mangroves at the latitudinal limits of their distribution. Tropical saltmarshes are expected to facilitate the establishment of mangrove propagules and seedlings, which can be used in restoration projects. This thesis aims to test whether saltmarshes in tropical environments facilitate the establishment of mangrove seedlings through three lines of evidence: (I) a systematic review of experimental studies on interactions between saltmarsh and mangrove vegetation; (II) mapping of saltmarshes in tropical estuaries and a mensurative experiment on the abundance of mangrove propagules and seedlings in saltmarshes and unvegetated habitats; and (III) monitoring, over a year, the survival and growth of mangrove seedlings naturally established in tropical saltmarshes. The review showed that saltmarshes facilitate the retention and establishment of mangrove propagules but compete with their seedlings for resources, reducing their growth at high latitudes. Seedlings generally overcome this competition, except in extreme climatic conditions. The review also revealed that different species of salt marshes have varying effects on the retention of mangrove propagules. Grass-like species retain more propagules than succulent forms but offer more competition for resources such as light. Both retain more propagules than unvegetated areas. Interactions in the tropics remained unassessed. The second chapter explored the distribution of salt marshes in the three main tropical estuaries in the Baía de Todos os Santos, Bahia, and the presence of mangrove propagules and seedlings associated with saltmarsh vegetation. Saltmarshes of the genus Spartina were found exclusively in the euhaline region of the estuaries, with densities and heights lower than those found at higher latitudes. Mangrove seedlings and propagules were more abundant in saltmarshes than in unvegetated areas. In the third chapter, the survival and growth of mangrove seedlings, naturally colonizing tropical saltmarshes were monitored over a year. During this period, over 75% of the seedlings survived, growing in height and number of branches, potentially reaching reproductive maturity. The study showed that the presence of tropical saltmarshes is fundamental for the colonization of mangroves in the euhaline region of the estuary, facilitating the establishment and survival of mangrove propagules and seedlings, offering little competition, due to their less dense and shorter structure compared to those found at higher latitudes. Saltmarsh facilitation on mangroves should be harnessed in restoration projects.