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Questions: Does the presence of salt marsh vegetation affect the long‐term regeneration of the pioneer mangrove species Avicennia germinans in a degraded dwarf forest? Does immobilized coarse woody debris (CWD) affect regeneration similarly? Do larger trees suppress or facilitate intraspecific saplings? Location: Dwarf mangrove forest in the high intertidal zone on the Bragança peninsula in northern Brazil. Methods: The spatial patterns of A. germinans, the herbaceous halophyte Sesuvium portulacastrum, and CWD were mapped in three sample plots (each 400 m2) during two consecutive vegetation surveys, conducted in 2011 and 2014. Inhomogeneous Poisson and Thomas point process models were used to assess the distribution of A. germinans life‐history stages (seedlings, saplings, and adult dwarf trees), conditioned on the presence of S. portulacastrum and CWD. In addition, intraspecific interactions between trees and regeneration were assessed based on crown projection mapping. Bivariate point pattern analyses were used to assess the dependence of advance regeneration on dwarf A. germinans trees and S. portulacastrum. Results: Avicennia germinans saplings and trees were positively associated with S. portulacastrum and CWD, whereas seedlings were located around tree crowns. The density of fruit‐bearing trees was positively associated with sapling density, indicating that regeneration relied on locally dispersed propagules. Conclusions: Herbaceous vegetation and CWD have an important ecological function in degraded mangroves by retaining tidally dispersed propagules. Here, we show that herbaceous vegetation does not suppress the growth of seedlings but facilitates mangrove recolonization. Due to limited tidal dispersal, regeneration relies on local propagule supply. In addition to hydrological restoration, the observed vegetation patterns suggest that, in the absence of propagule‐retaining vegetation, restoration of high‐intertidal mangroves can be facilitated by establishing nuclei of planted trees and installing secured logs. [ABSTRACT FROM AUTHOR]

The global effort to rehabilitate and restore destroyed mangrove forests is unable to keep up with the high mangrove deforestation rates, which exceed the average pace of global deforestation. Although facilitation theory presents new possibilities for the restoration of heavily degraded mangrove sites, knowledge of tree-tree interactions in stressed mangrove forest ecosystems is too limited to utilize facilitation appropriately. The aim was to determine the mode of local interaction among stressed mangrove trees by investigating the effect of clustering on tree size and crown morphology under contrasting stand densities. The study was conducted in a dwarf Avicennia germinans forest in Northern Brazil, in which tree growth is limited by infrequent inundation and high pore-water salinity. Autoregressive regression, Voronoi tessellation and spatial point pattern statistics were used to address the spatial processes underlying tree interaction. Under low stand density (1.2 trees m−2) dwarf trees which grew in clustered cohorts of A. germinans had a less stunted crown morphology revealing the dominance of a positive neighborhood influence among plants. In contrast, dwarf trees in the denser forest stand (2.7 trees m−2) were interacting competitively as indicated by the more negative effect of neighbors on crown morphology and size. The shift from facilitative to competitive interactions is an important feature of mangrove forest regeneration under harsh environmental conditions. If mangrove trees are unable to regenerate naturally on severely degraded sites, intraspecific facilitation could be used to assist regeneration by planting seedlings in clusters and not evenly spaced. [ABSTRACT FROM AUTHOR]