Background
Plant invasions of natural ecosystems can seriously threaten native biodiversity and the subsistence of indigenous peoples [
1‐
4]. Invasive plants can cause a number of environmental impacts, such as loss of native species, alterations in the structure and composition of invaded habitats, and their capacity to provide ecosystem goods and services, resulting in fewer available natural resources essential for the survival of local populations [
1,
5,
6]. Invasive species, however, are often important for generating local income in many different parts of the world, as well as providing food resources, medicines, and socio-culturally significant items [
7‐
10]. These contradictory views about invasive plants require detailed studies of the Local Ecological Knowledge (LEK) of the human populations coexisting with them in order to comprehend the equilibrium between positive and negative impacts.
Although scientists have investigated the effects of invasive plants in various parts of the world and the phases of the invasion process [
11], there is still a need for more detailed information about LEK and how the propagation of invasive plants impacts the well-being of traditional and/or indigenous populations. Berkes [
12] defined LEK as: “the accumulated body of knowledge, practices, and beliefs concerning the evolving relationships between humans and their environment and how that information is culturally transmitted through generations.” Using this approach in ecological research can provide useful perspectives for managing biological invasions and invaded ecosystems [
2,
13]. As such, the present study sought to analyze indigenous knowledge concerning the invasion by
Acacia mangium of indigenous lands in Roraima, Brazil, and to determine how to contribute to mitigating the environmental damage caused by these trees.
The spontaneous propagation of
A. mangium within indigenous lands is considered an injustice imposed on those communities and has been discussed in numerous community meetings. During these discussions, in addition to doubts about how these plants propagated themselves, community members voiced their concerns about future threats to their socio-biodiversity, guarantees of food security, and the physical and cultural continuity of their indigenous lifestyles [
12]. In light of these concerns, community members have taken into their own hands the eradication of invasive plants, principally during the preparation of farm plots for planting, when invasive trees are cut and burned (although the trunks are left in the fields, as their removal is quite labor intensive).
The concerns of the indigenous peoples have been ignored by the administrators of the commercial tree farms ever since they were first planted, even though there are records of formal complaints citing impacts to the local environment. Only a few limited initiatives have been carried out by the administrators (such as the removal of easily accessible acacia trees near the communities)—measures that have not solved the problem. We believe that the negative impacts of these non-native trees will only be minimized after evaluating, together with members of these communities, the factors that aid their propagation. These plans would take into consideration the specificity of the social and natural environment and incorporate efficient proactive components (the inclusion of scientific information concerning the ecology of the invasive species, continuous monitoring to control its propagation, and eradication of adult plants). These actions would reduce seed dispersal, while investments were made in scientific studies of their natural enemies for control purposes.
Researchers examining the perceptions of human societies in relation to the impacts of invasive plants have approached the subject from different angles, with some finding that these plants can take on positive roles [
2,
8], while others have focused on their negative impacts on local social dynamics [
7]. Based on these studies, there appear to be various schools of thought that support the exploitation of invasive species that cause ecological and social-environmental impacts, and it must be recognized that some invasive species actually assume positive roles in the lives and subsistence activities of rural communities due to their utility and the opportunity of generating extra income and promoting cultural continuity [
8]. The species
Acacia delbata, for example, offers valuable contributions to the subsistence of rural populations in Madagascar, who exploit its wood for fuel in their homes, as well as commercially for railway construction; it also provides shade along roads and avenues. Similarly,
Acacia mearnsii is sold by rural communities in South Africa for its wood and is used in traditional ceremonies and cultural rituals [
7]. Although invasive species are occasionally used to fulfill subsistence necessities, the communities that use them are well aware of the environmental and social problems they generate. In Kenya, where invasion by
Prosopis juliflora is most advanced, few people recognize any benefits from the plant, while most recognize its many problems, including making agricultural activities more difficult, draining water resources, displacing native trees, and creating obstacles to their movement and transportation needs [
14].
Numerous studies have reported serious negative impacts on the food security and cultural resources of indigenous populations, as well as restrictions on free access to previously used resources due to the arrival of those non-native plants [
2,
7]. Other studies have noted that these plants produce landscape alterations that upset the natural equilibrium of the regional fauna [
2,
14] and put local traditional knowledge of regional biodiversity at risk [
2].
One example of an invasive plant with both positive and negative attributes is the tree species
Acacia mangium Willdenow (Fabaceae), a member of the group known as the “Australian acacias,” which are native to Queensland in Northern Australia, Papua New Guinea, and Indonesia [
15]. This species demonstrates vigorous and competitive growth, and rapid adaptation to a wide variety of edapho-climatic conditions [
16]. This adaptability favors the silviculture of
A. mangium for commercial exploitation of its wood and related products (such as cellulose, honey, beeswax, tannins, and charcoal); it can also be used to recuperate degraded soils [
16,
17]. Initial interest in producing cellulose and lumber in Roraima resulted in the planting of 30,000 ha of
A. mangium in natural savanna ecosystems (“Lavrado”) during the early 1990s, near the lands of the Wapichana and Macuxi Amerindians. “Lavrado” is the regional designation for the local savanna eco-region [
18]. According to Barbosa et al. [
18], savanna ecosystems are principally characterized by phytophysiognomies with grassy substrates and low densities of trees and shrubs that do not form a continuous canopy layer. This type of ecosystem supports many animal and plant species essential to native human populations that have been managed based on traditional knowledge, guaranteeing the continuity of these material and cultural resources.
The Wapichana and Macuxi people have had more than two decades of contact with
A. mangium (often called the “foreign plant”), which has favored the accumulation of local ecological knowledge about this non-native species as it spread through their lands in Roraima State, Brazil [
2]. The interactions between this invasive species and other plants in their farm plots have been discussed in community meetings—as shown in the quote that opens the introduction of this text.
The Wapichana and Macuxi have attempted to defend their territory by publicizing the invasions of their farm plots by
A. mangium, as well as the alterations in the color of the water; the lowering of water levels in rivers, wetlands, and hand-dug wells; losses of crop production; and the exaggerated abundance of highly aggressive Africanized bees
Apis mellifera scutellata, another invasive species that is adapted to inhospitable environments and demonstrates a higher reproductive capacity and a shorter life cycle than other subspecies in Brazil [
19]. According to their local ecological knowledge, the cultivation of
A. mangium threatens the cultural and material continuity of the Wapichana and Macuxi in the region [
2].
Local ecological knowledge concerning the impacts of invasive plants on the survival of traditional populations is a recent focus of research. Siges [
9] analyzed the different uses of the invasive species
Piper aduncum according to the ages of members of rural communities in Africa, as well as the different perceptions of men and women and older and younger people concerning that plant. Older people demonstrated significant concerns about the loss of forest products following the invasion by
P. aduncum, and men cited the substitution of other food plants by sweet potatoes (which grow well in the presence of the invader). For men, the presence of
P. aduncum made the plots easier to tend by women, although the women noted the disappearance of mushrooms that were previously encountered in the forest edges. The authors also noted divergence among the informants in terms of the effects of
P. aduncum on food production: with some residents complaining of losses of tuber production and others stating the exact opposite. Another study focusing on the invasive plant
Piper juliflora in Kenya indicated that its effects on subsistence production were not significant in terms of local perceptions [
14]. While rural communities in Nepal use the invasive species
Mikania micrantha in subsistence activities, they evaluated it as an ecological evil—suggesting that local perceptions can vary over time according to different intensities of invasion. Local populations observed decreases in the production rates of forest products, but many were not able to accurately evaluate production over the last 5 years and felt that there was actually an increase in resource availability [
20]. The rapid dissemination of the invasive species
Lantana camara can be attributed to its prolific fruit production, the ample dispersal of its seeds, changes in fire management practices, and the traditional harvesting of grass and bamboo; younger members of the local population mentioned that
Lantana promptly re-sprouts after burning [
2].
In light of the fact that indigenous communities in Roraima have experienced severe social-environmental impacts due to the rapid spread of
A. mangium [
3], we undertook an analysis of this invasive species considering the specific natural and social environments of these communities to identify the causes of the dissemination of the plant and its effects and to produce information that could be used to better administer the situation. We initiated our studies considering the existence of variations in the perceptions of individual community members concerning the socio-ecological impacts of the dispersal of
A. mangium onto indigenous lands. As such, we examined various human aspects (gender, age, leadership functions, and the time of residency in the community), assuming that certain roles within the indigenous communities would favor greater or lesser contact with this invasive species and therefore influence the acquisition of knowledge concerning it.
The records presented here of indigenous local ecological knowledge concerning the invasion of the Moskow and Malacacheta communities by A. mangium were based on informant responses to the following questions: (1) what are the principal problems that the Wapichana and Macuxi communities attribute to the invasion by acacias? (2) What are the uses/importance of these trees to these indigenous populations? (3) Are there relationships between perceived problems and human factors, such as gender, age, leadership roles, and residence time? (4) How do the indigenous communities explain the dispersal of the acacias in terms of their LEK?
Results
The principal problems identified by the informants
The context of invasions by acacia trees is described by a community leader in São Domingos during field research activities related to the social mapping of PNCSA in 2012:
We live on an island surrounded by acacia plants! Before, we hunted and fished, now we have bees that attack us and acacia plants that invade our farm plots as soon as we clear (burn) them, and they grow even stronger. I’ve killed rattlesnakes there that are attracted by the rats, and there have been more foxes and opossums, which damage the buriti palms. There are no more electric eels, and the water is rusty. You can’t drink the water in the Manoá igarapé, and even our wells are drying up. The ingá trees have stopped producing fruit since the acacia appeared. Parrots used to make nests in São Domingo, but now the bees have taken over. Rolinha doves used to wake us up and tell us when it was going to rain; now those birds don’t exist here anymore.
Among the community members consulted during the research phase, most (89%) expressed their perception of changes in IL community routines after invasion by
A. mangium. Only 11% of the interviewees did not identify the acacia plants as causing any problems. For most of the informants, the invasive plants resulted in scarcities of essential natural resources for the community and caused numerous social-environmental problems. The interviewees cited an average of two problems (varying from zero problems cited to a maximum of five). The most frequent citations referred to the degradation of water resources (71.3%), farming losses (60.6%), increased labor necessary to prepare and maintain their crop fields (41.5%), and disturbances of the local fauna (52.1%—principally caused by increases in bee populations that impede access to natural resources through their threatened or real attacks) (Table
2).
Table 2
Problems caused by the invasion of A. mangium that has altered the routines of the indigenous residents of the Moskow and São Domingos communities in the Moskow and Malacacheta Indigenous Lands, in the Serra da Lua region, Roraima State, Brazil
Alterations of water resources | 67 | 71.3 |
Prejudicial to cultivation | 57 | 60.6 |
Disequilibrium of the fauna | 49 | 52.1 |
Well and river water drying more rapidly | 44 | 46.8 |
Altered water color | 44 | 46.8 |
Increased presence of bees | 39 | 41.5 |
Increased work for farm plot preparation | 39 | 41.5 |
Restricted access to surrounding lands | 22 | 23.4 |
No problems with the water | 14 | 14.9 |
No problems cited | 10 | 10.6 |
Increased presence of snakes | 8 | 8.5 |
Increased presence of rats | 7 | 7.4 |
Well water salty | 3 | 3.2 |
Both direct and indirect problems were cited in relation to water resources: diminishing water volumes (in wetlands, rivers, and wells); alterations in water color (turbidity); well water becoming salty; and wells having reduced volumes or even drying up (Table
2). Among the arguments used by indigenous interviewees to support their negative evaluations of acacia plants, the most important was the fact that they “suck” the water from rivers and wells that serve their communities. This factor was cited as the most important effect of those plants on the environment—especially as the interviewees associated the low water levels in the rivers with their proximity to commercial plantations of acacia; in their eyes, acacia trees have deep roots and remove large quantities of water from the soil. There were likewise common complaints that acacias were making the water “
bad,” “
dirty,” “
red,” or “
rust-colored,” degrading its quality for community consumption. These indigenous populations fear that the situation will become much worse in the future, for it has become increasingly difficult to draw water from their wells: “
now we have to dig deeper wells to find water.” These reports of changes in water quality and availability make investigations of current environmental risks imperative, especially in relation to threats to water resources that are used for diverse daily activities.
In the category related to the disequilibrium of the regional fauna are problems related to the increased presence of bees, snakes, and rats and diminishing quantities of fish because of the problems with water. According to the informants, transformations affecting the natural ecosystem include the appearance of large rats, apparently seeking food resources no longer encountered in acacia plantations. Similarly, increases in the numbers of snakes have been reported due to the greater accumulation of leaf litter in commercial acacia plantations. Another serious problem attributed to the acacia is the proliferation of Africanized bees. These bees make travel to fishing spots, or areas with buriti palms (to collect material used in making handicrafts), and hunting much more difficult; numerous bee attacks on people and animals have been reported. Additionally, the bees are thought to drain the floral resources of cultivated plants (maize, beans, squash, and bananas) and suppress their development.
Our food plots used to produce many fruits, like bananas and pineapples, but now nothing grows well.
The acacias are attracting many noxious creatures to our lands, and we don’t have much maize because of the bees, because when the maize begins to flower the bees drain them.
We are surrounded by acacia, but those plants don’t yield any fruits that we can eat, and those plants are creating many problems because of the bees that chase away the little jandaíra bees that gave us their honey we used to make medicines for our children, syrups, and other remedies.
According to the interviewees, invasive plants can appear at any time in the farm plots, where they grow very rapidly and compete with the cultivated plants—making it imperative to remove them to permit the healthy development of the plot. The local residents complained that removing those invasive plants significantly increased the maintenance efforts needed for farming. This perception varied from 25% among the inhabitants of Malacacheta to 70% in Moskow and 80% in São Domingos.
There are reports from the São Domingos community of the necessity of removing acacia trees from old farm plot localities. The trees are generally burnt, but their remains are left on the ground (because removing them demands excessive effort and energy). After burning the vegetation at the beginning of the rainy season, new seedlings germinate and must be removed. The most efficient way to remove them is to pull them out by their roots; only that will guarantee that they will not re-sprout. If the seedlings are allowed to grow they will be more difficult to remove in the future and will be prejudicial to the cultivated plants because their roots take up a great deal of the soil moisture and leave it too dry for root crops (such as sweet potato and sweet and bitter manioc) and they will not develop well. The following statements are illustrative of this situation:
The acacias are the first things to germinate in farm plots, they germinate real pretty, better than the manioc. If I could live off the acacia I wouldn’t even need to plant anything. The acacias stunt the manioc plants, which stay small, tiny, and the roots also stay small.
I weed out the acacia first thing because they form many roots quickly, and if you just cut them they’ll grow right back. You can’t let them grow, or they’ll produce more seeds.
Abandoned farm plots (“capoeira” or fallow) are frequently visited to collect fruits and roots (pineapples, bananas, papaya, sweet potatoes, yams, and manioc stems for planting), but they are increasingly dominated by the rapidly proliferating acacia trees. This is extremely vexing, as the farmers will have to remove the trees to clean the land when the plots are replanted (after lying fallow). There are reports of people giving up planting a plot due to the excessive work required to remove all of the acacia trees, as explained by a resident of São Domingos: “I just didn’t want to plant there again, I was going to just use a machine to clear the area, but the acacias are very nasty plants.”
Approximately 49% of the interviewees stated that acacia plants are very different from the native species they are familiar with. They noted significant differences in the development of the acacias, and likewise attributed impacts to the cultivated garden plants to these invaders:
The acacias grow more rapidly than garden plants, they ruin the garden plots, after three months you have to rip the acacias out again.
Acacias grow very fast. Where that fellow M. had his farm plot in São Domingos is pure acacia now.
Acacia grows green and pretty, and the leaves don’t fall.
Acacia grows more rapidly than manioc or the other plants cultivated in our gardens. After it flowers, lots of seeds are produced, they germinate and grow even in the dry season, with nice green leaves; the leaves don’t fall, and the leaves are different – long and thick when it starts growing and then they change.
Descriptions of the problems caused by acacias were reinforced by the statements of a community leader (“
tuxaua”) from the Moskow IL, who has a large family and a large farm plot with manioc, squash, watermelons, beans, maize, sweet potatoes, papaya, green peppers, taioba, and peanuts) 13 km from a commercial acacia grove. He stated that:
The farm plot used to grow really nice bitter manioc, beautiful sweet manioc, now it’s pure acacia. The rivers had lots of fish in those days and we caught lots of them. Now we have acacia damaging our plants. Our community here is being seriously hurt by the acacias.
Many of the indigenous residents manifested their discontent with the restrictions being imposed on movements within their own lands. In some places, they now have to ask permission from the owners of the commercial acacia plantations to go through them; quite frequently they are stopped at the entrances to the plantations to explain where they are going and why.
The uses and importance of acacias
On being asked about the uses and importance of acacias, most of the informants (89%) stated that they could think of no uses at all for these invasive plants. For these people, acacias had no positive importance for the communities, and they categorically stated that they had no future expectation of ever being able to use the acacias for any beneficial purpose: “acacia wood isn’t good for anything, it’s too soft.” As an informant from São Domingos noted: “to me they are just a pest that has fallen upon our community.” There are some reports of uses for these invasive trees as firewood for drying manioc flour or for supplying fibers (“envira”) for binding wood and manioc; it is also said that the trees are useful for their copious shade. These positive citations are only occasional, however, and the useful practices cited are apparently quite sporadic.
Sentiments of revulsion and fear were quite perceptible among the interviewees in terms of the futures of their communities. In general, A. mangium was viewed as a pest species that did not, and never would, bring any benefits at all to the community and would never become an important product in the local economy—a plant that would only generate difficulties, such as those described in relation to farming practices and decreasing productivity, with grave consequences for community subsistence. Some interviewees, however, considered that they lacked more information about the possibility of acacias generating benefits for their community.
Gender and leadership
The invasive A. mangium has altered the routines of the indigenous communities in Roraima, generating problems that affect their subsistence. As such, acacias were considered prejudicial by 89% of the members of the Malacacheta, Moskow, and São Domingos indigenous communities. A more detailed analysis of the information gathered indicated the lack of significant differences between the opinions of men and women (χ2 = 0.99; p = 0.753) and leaders and nonleaders (χ2 = 0.180; p = 0.671) in terms of their perceptions of alterations in their routines attributable to the occurrence of acacia plants in the ILs. Similarly, there were no significant differences in terms of the types of environmental impacts cited by men or women (χ2 = 5; p = 0.691) or by leaders and nonleaders (χ2 = 5; p = 0.46).
The Mann–Whitney test, however, indicated that the local community leaders (tuxauas) could more precisely describe the types of problems encountered than could nonleaders (Z = − 0.2078; p = 0.038). The same test did not demonstrate significant differences between men and women in terms of the numbers of environmental alterations cited (Z = − 0.217; p = 0.828). It is important to note that the community leaders tended to report all of the problems that occurred in the communities. To be a community leader means occupying the highest position in the social hierarchy of an ethnic group, a person who represents their community in all local and external events, and who must always conduct themselves in a manner that guarantees the well-being of their people. The leaders had sought the support of the PNCSA-Roraima Nucleus to publicly express their perceptions and concerns about the propagation of acacias throughout the ILs based on collective opinions and decisions.
Age and residence time in the community
There was a positive correlation between age and the numbers of citations contributed by an informant (rho = − 0.275;
p = 0.007), indicating that older people mentioned more types of environmental alterations attributable to invasive plants. Individuals that had lived for longer periods of time in the communities were not only the most emphatic in their affirmations that there were palpable alterations in the routines of the community members due to the invasion by acacia trees, but they also provided more supporting information (Z = − 1.965;
p = 0.049). This type of knowledge can be seen in a section of a statement provided by one of the leaders who helped found the São Domingos community and lived on the IL before there were acacia plantations:
[…] it wasn’t like that before, after burning for clearing now, only acacia seedlings germinate, and when you’re ready to plant – there she is again, the seedlings germinate before the grasses and grow rapidly; and the rains help, acacias really like water […].
Local ecological knowledge concerning acacia dispersal in the ILs
In terms of the LEK of the indigenous populations concerning the dispersal of acacias within the Moskow and Malacacheta ILs, 37% of the interviewees stated that their dispersal was intermediated by birds, by wind (10%), or by bats (6%). However, 46% of the interviewees stated that they had no explanation for the rapid dissemination of those invasive plants to localities distant from the commercial plots. The following statement expressed their views on dispersal:
[…] There is an area in the Malacacheta reserve that has only acacias, they also grow near the neighbor’s house, even 4 or 5 km in from the border of Malacacheta there are acacia plants, so you ask yourself, how did those acacias get there? Their seeds are very light, and the wind and birds will take them, and wherever they fall an acacia will germinate […].
According to the interviewees, burning the vegetation (67%) and rainfall (70%) intensified germination—creating concern among community members in relation to the rapid advance of acacias in secondary vegetation and invading fallow plots (“roça velha”). During the interviews, many of the interviewees expressed in their answers worries and lamentations about A. mangium:
What is our future going to be like? I already know, the acacias suck all the water from the soil and leave it really dry, I have to pull the maniac roots from the hard clay, it’s tiring work.
My fear is that in the future we’re going to be without any water if we can’t control the acacias. Who’s going to cut the acacia trees in the future, my sons?
We’re going to have a lot more trouble in the future because of the acacias. I’m worried about the fact that they could take over everything, because they’re already just about everywhere: the forest, our farm plots, the banks of the rivers – I’m worried that if in the future our children have any way to live, everything will just turn into acacia, my worry is that they will do away with the native plants.
Some of the indigenous residents felt that the acacias were unknown plants, as they did not know where they came from or what they were used for—even though there are so many commercial stands of acacia. It became very clear from the interviews that the local inhabitants knew very little about the commercial uses of acacia trees and even less about their benefits— “the trees that do not produce fruits” that could be seen rapidly changing the lives of the people in the surrounding communities.