Resumo:
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.
