Avaliando a influência da diversidade e facilitação na disponibilidade de flores e frutos em comunidades arbóreas restauradas

Abstract

Given the current state of degradation of the Caatinga Biome, ecological restoration strategies are of the utmost importance, not only to halt this degradation process, but also to restore the affected communities, making them stable and productive over time. Caatinga restoration programs that seek out new ecological restoration technologies have shown themselves to be promising alternatives for combating the desertification process. This study was carried out in a large-scale, long-term Caatinga restoration experiment (BrazilDry) implemented in 2016. This experiment is linked to the international Tree Div Net, which includes 29 experiments in 20 countries that test the influence of tree species diversity on the functioning of planted forests. The difference is that we have added the facilitation factor that influences the performance of restored plant communities and thus measured their potential in seasonally dry tropical forests. This study is divided into two chapters, both carried out in the BrazilDry Experiment, and aims to understand how diversity and facilitation mechanisms influence the flowering and fruiting patterns of restored communities. In the first chapter, the main objective is to test whether the diversity of tree plants in restored communities and their facilitation potential influence the number of reproductive individuals in the first 7 years of restoration, and thus answer: I - How many individuals and of which plant species in the restored communities have managed to reproduce in the last 7 years of restoration? II - Is there an effect of diversity and/or facilitation on the presence or absence of flowering and fruiting patterns? As a result, we observed that the diversity of trees planted did not influence the flowering capacity of the species. However, there was a positive effect of facilitation on the flowering capacity of species in the first 7 years of restoration. Diversity and facilitation did not influence fruiting patterns. This may have been due to low rainfall causing many flowers to abort, as well as fruit abscission, which may also be produced in smaller quantities when under great water stress. The second chapter assesses how the diversity of species that make up the restored communities affects the phenophases of the species Piptadenia retusa, popularly known as jurema-branca, in terms of the quantity and synchronization of fruit, flower and leaf production by this species. With the specific objectives of: I - Test whether the diversity of trees in the restored community influences the number and timing of flower and fruit production by the P. retusa species, and which months produce these food resources for the fauna; II - Test whether the diversity of species in the restored tree communities influences the maximum production capacity of flowers, fruit and leaves produced by Piptadenia retusa over the course of a year. As a result, we observed flowering peaks in the wettest months between March and June, while fruiting also occurred in the first half of the dry season between June and November. The production of floral resources (buds and flowers) and seed production (ripe and immature fruit) differed not only in relation to the months, but also increased significantly with the increase in the diversity of trees making up the restored community. In terms of maximum production capacity expressed by the Fournier index, only the explanatory variable, time, had a significant influence. All the variables showed maximum production in the wetter months, with the exception of the production of ripe fruit, which occurred more intensely in the drier months. Leaf production was, on average, 75% of its production capacity in the wettest months, but still maintained 25% of its production capacity during the driest months. This work indicates that restoration models with the presence of nurse or facilitator species should be implemented, given the potential of these species to increase the reproductive capacity of neighboring trees The results also show that the diversity of trees planted in restoration programs can increase the reproductive capacity of some species, promoting the replacement of individuals in the community and the availability of food for the pollinator fauna