Text Carlos P. Carmona
Eucalyptus species are among the most most controversial and frequently used species in forests plantations worldwide. These plantations occupy a huge surface in many countries, with almost 8 millions ha in Brazil alone, where they are generally located in heterogeneous landscapes which also include native forest patches and a variety of other non-forest land uses. Eucalyptus plantations generally receive a high input of fertilizers and are very water demanding. On top of that, forestry practices in these plantations have profound impacts on soil structure. On the other hand, when compared to non-forest uses, these plantations can harbor some native species typical from forests and increase landscape connectivity, facilitating the movements of these species. Therefore, it is unclear what is their impact in diversity, and some studies have shown that there are not more species poor than primary forests.
However, the concept of biological diversity goes beyond the taxonomic aspect. In this sense, it is increasingly clear that the diversity and identity of the traits of organisms is a better indicator of the functioning of ecosystems than species richness per se. Some taxonomic groups are particularly interesting for evaluating the impact of human activities. Ants are one of these groups; ants are involved in a great number of ecological processes, ranging from soil cycling to seed dispersion and decomposition of organic matter, and are also very good indicators of anthropic disturbances. Consequently, studying the functional diversity of ants in Eucalyptus plantations could give us a better idea of the ecological impacts of this land use.
In this study, conducted at the Alto Tietê and Itatinga River basins, in São Paulo, Brazil, we compared the functional trait structure of ant communities in four types of forests: young (7 years old) Eucalyptus plantations currently being managed for wood and cellulose production; old (28 years) Eucalyptus plantations also under intensive ongoing management; abandoned Eucalyptus plantations; and original native rain forest. We sampled ant communities from these forests, capturing individuals of 78 different species of ants, and measured several morphological traits in them (traits like distance between the eyes, head size, eye length, or mandible size, which were related to different processes, such as foraging, thermal and drought resistance, or behavior). In addition to their taxonomic diversity, we used these traits and the species composition of each forest to estimate the functional structure of our ant communities using a novel framework that allows to consider intraspecific variability in trait values (thus acknowledging that not all the individuals of the same species have the same trait values).
Interestingly, whereas the number of species present in managed Eucalyptus plantations was almost half of that found in native forests, abandoned Eucalyptus plantations had as many species as native forests. However, we found that ant communities in Eucalyptus plantations, regardless of their management status, had much lower functional diversity than native forests. This effectively means that Eucalyptus plantations have a great impact on diversity and ecosystem functioning, an impact that does not disappear even after long a long period of abandonment. Moreover, the patches of native forests were also much more different between them than the patches of Eucalyptus forests, which implies that these plantations have a negative impact on diversity at the landscape scale. Altogether, our results imply that many of the species that colonized the abandoned plantations were functionally very similar between them, probably because they share characteristics that allow them to survive in this kind of environment. Our findings support the idea that Eucalyptus plantations can severely affect the taxonomic and functional diversities of ant communities, and that these impacts have long-term effects, even in unmanaged plantations. However, we would not have been able to detect these impacts by merely looking at the taxonomical facet of diversity, which calls for a more comprehensive evaluation of the impacts of human activities on biological communities. On the bright side, and communities from long term abandoned Eucalyptus plantations showed a tendency to converge with the communities from the original forests, which suggests that the implementation of restoration strategies, such as passive restoration between stands of tree plantation, may mitigate some impacts of this land use on ant communities, and on the ecological processes in which these insects are essential.
Citation: Martello, F., de Bello, F., de Castro Morini, M. S., Silva, R. R., de Souza-Campana, D. R., Ribeiro, M. C., & Carmona, C. P. (2018). Homogenization and impoverishment of taxonomic and functional diversity of ants in Eucalyptus plantations. Scientific reports, 8(1), 3266. (link to full text)
Mean and standard deviation of taxonomic (A) and functional (B–D) α diversity indices of ant communities located in native rain forest, 28-year-old unmanaged Eucalyptus plantations, seven-year-old commercial Eucalyptus plantations and 28-year-old Eucalyptus plantations. Different letters associated with the environments represent significant differences in the means assessed by Tukey’s Post-hoc analysis. (Graph from the paper)
Despite its negative impacts on the environment and biodiversity, tree plantations can contribute to biodiversity conservation in fragmented landscapes, as they harbor many native species. In this study, we investigated the impact of Eucalyptus plantations on the taxonomic and functional diversity of ant communities, comparing ant communities sampled in managed and unmanaged (abandoned for 28 years) Eucalyptus plantations, and native Atlantic rain forests. Eucalyptus plantations, both managed and unmanaged, reduced the functional diversity and increased the similarity between ant communities leading to functional homogenization. While communities in managed plantations had the lowest values of both taxonomic and functional ant diversities, ant communities from unmanaged plantations had similar values of species richness, functional redundancy and Rao’s Q compared to ant communities from forest patches (although functional richness was lower). In addition, communities in unmanaged Eucalyptus plantations were taxonomically and functionally more similar to communities located in managed plantations, indicating that Eucalyptus plantations have a severe long-term impact on ant communities. These results indicate that natural regeneration may mitigate the impact of Eucalyptus management, particularly regarding the functional structure of the community (α diversity), although it does not attenuate the effects of long term homogenization in community composition (β diversity).