By Washington Ferreira Junior and Ulysses Albuquerque

The study highlights interesting elements from a discussion about the forest resources sustainability. In fact, one cannot discuss biodiversity without taking into account the great diversity of uses that people make of these resources. One goal of this paper is to present a practical tool to access the diversity and utilitarian redundancy of plant species. However, a practical discussion about these aspects cannot be separated from a theoretical scenario that allows properly accessing the premises which are put into evaluation.
The idea of utilitarian redundancy was first presented in the literature by one of us [1] as an analogy to the idea of functional redundancy. The utilitarian redundancy has been defined as the overlap degree of species with utilitarian analogy, ie, the set of species used for the same purpose by a human population would define the level of redundancy of a given utilitarian category. Albuquerque and Oliveira [1] proposed a utilitarian redundancy model which deals with the use pressure on useful species and on the resilience of systems involving the resources use by human populations. This model presents two situations, considering the plants use for a hypothetical human population: (1) the highest number of species within a utilitarian category (high redundancy) decreases the individual use pressure on species present in this category. However, this situation would be valid if there was no preference for some species in this utilitarian category. In this case, the model suggests a second situation (2) where the presence of species preferred by the population would shift the use pressure for these species, even within a highly redundant category. Regarding the system resilience, the use system of plant species by a human population with highly redundant categories might be more resilient than a system with several low redundancy categories, where these categories would have little resilience to disruption, if there being local extinction of some species, for example [1]. The utilitarian redundancy model has been used by our group in recent publications [see 2,3].
The authors of this paper, in turn, used the utilitarian redundancy to assess the status of the utilitarian potential of forest fragments for rural communities located in southeastern Madagascar. Although this perspective is very interesting, we consider the following questions about the paper of Brown and colleagues (2011).
1. If we limit the concept of utilitarian redundancy only for the forest fragments potential, we can access only a portion of the status of redundancy and resilience of the system involving the use of plants by a human population. For example, exotic plant species can be found in yards near houses, cultivated by people themselves, or can also be obtained in traditional markets in nearby communities to meet the low redundancy of fragments and increase the category redundancy within the local system and can also increase local resilience of the system.

2. The authors deal with utilitarian redundancy in many analyses. In much of the analyses, the checking for utilitarian redundancy is made overall for each fragment, without considering the levels of redundancy for each category or utilitarian property. From our investigations, we found that levels of redundancy vary by utilitarian property or use category [1,2]. In this sense, it would be interesting to make the analyses and present the levels of redundancy for each utilitarian property in order to observe different behaviors among the different use categories.
3. With regard to the text excerpt: "From a human livelihoods perspective, low utilitarian redundancy could indicate how threatened certain services may be for local people." We do not necessarily believe that low redundancy would indicate how much plant resources could be threatened for local people. There may be a clear preference for certain resources, or species specialized for a particular type of use [see 3]. The threat lies not only in the overlap degree (in quantitative terms), but the quality perceived by the people of each resource.
4. The authors state that, from the set of analyses carried out, changes in fragments’ utilitarian redundancy probably occurred as a result of the extraction patterns of local residents. We would also point out that redundancy is not necessarily a consequence of different extraction patterns, but as a consequence of how the human population appropriates and perceive the natural resources. High or low overlap may be the result of different variables:
a. historical uses of resource as a result of different extraction patterns.
b. perceived qualities of resources that place them into a category of high or low redundancy. Furthermore, utilitarian redundancy is strongly tied to the type of specific use made of the resource. Each type of resource use has a dynamic extraction. For example, a study recently developed in a rural community in northeastern Brazil showed that medicinal plants used as anti-inflammatory are grouped into inflammatory subcategories more and less redundant depending on their "effectiveness" locally perceived [2]. In addition, a second study showed that there are some plants preferred for anti-inflammatory use, where stem bark extraction by local population is directed for these species, compared to less preferred species [3]. This information could indicate that for each type of use or utilitarian property the preferred species could be different, leading to differences in the dynamics of extraction in the medicinal use.

References

1. Albuquerque UP, Oliveira RF (2007) Is the use-impact on native caatinga species in Brazil reduced by the high species richness of medicinal plants? Journal of Ethnopharmacology 113: 156-170.
2. Ferreira Júnior WS, Ladio AH, Albuquerque UP (2011) Resilience and adaptation in the use of medicinal plants with suspected anti-inflammatory activity in the Brazilian Northeast. Journal of Ethnopharmacology 138: 238-252.
3. Ferreira Júnior WS, Siqueira CFQ, Albuquerque UP (2012) Plant stem bark extractivism in the Northeast semi-arid region of Brazil: a new aport to utilitarian redundancy model. Evidence-Based Complementary and Alternative Medicine. Special Issue in Medical Ethnobiology and Ethnopharmacology in Latin America.