Abstract
Variation in reproductive phenology among species is an important mechanism for maintaining species coexistence. In mixed forests, the impact of limiting (biotic and abiotic) factors on tree reproductive success regulates the maintenance of species in balanced proportions or the conversion towards monospecific forests. This study offer a significant first approach to the reproductive phenology of mixed forests, assessing flowering, seeding and loss factors on reproductive success in three forest types (pure deciduous Nothofagus pumilio (Np), evergreen Nothofagus betuloides (Nb) and mixed (M) forests), comparing also between two geographical locations (coast and mountain), during one growing season. Flowering falling started early in Np. Seed fall occurred first and more concentrated in Np, while in Nb, it was progressive during autumn. Phenology in M combined both patterns, but with better reproductive performance of both species. Seed production was greater in Nb (42,900,000 ha−1) than in Np (710,000 ha−1), while M presented intermediate values (31,900,000 ha−1). Abortion was greatest in Np (19% of female flowers and 10% of immature fruits), while fruit predation was low (7–9%) in all forest types. Empty seed was the main loss factor, but with low net values for each species in M. Regarding geographical location, sea proximity generated a quick starting of the growing season in coast compared to mountain sites. However, we detected forest types × location interactions in flowering and seeding patterns (e.g. in male flower production and in empty and viable seeds), with differences in species response according to location. Both deciduous and evergreen species have reproductive advantages in mixed compared to pure forests. However, mixed were more similar to pure evergreen forests in their reproductive traits and the incidence of the limiting factors. The study of only one growing season does not allow us to conclude whether mixed forests are stable communities, but we contribute to understand the roles of reproductive phenology in mixed forest dynamics.
Highlights
Variation in reproductive phenology among species is an important mechanism for maintaining species coexistence
Forest structure Forest structure showed significant differences among forest types and geographical locations, but interactions existed for basal area and direct radiation (Table 1)
M forests did not differ from N. betuloides forests (Nb) forests in density and dominant height, but mean diameter M showed an intermediate situation between N. pumilio forests (Np) and Nb forests
Summary
Variation in reproductive phenology among species is an important mechanism for maintaining species coexistence. In mixed forest, the natural dynamic of recruitment is a function of the completion of the annual reproductive cycle (flowering, seeding and seedling establishment) of tree species and their accomplished phenology and of the interactions with other organisms, climate and natural disturbances (Espelta et al 2009; Schoolmaster 2013; Bergeron et al 2014; Dreiss and Volin 2013). Such interactions might determine a shift from mixed forest to stands dominated only by one or few species (Bergeron et al 2014), as part of the natural succession. There are many ecological features of mixed forest that we ignore, and our understanding of how compositional or structural drivers shape species distribution is still far from complete
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