Effect of shrub encroachment on vegetation communities in Brazilian forest-grassland mosaics

Guido, Anaclara; Salengue, Elisa Viana; Dresseno, André Luís Pereira

doi:10.1016/j.pecon.2016.11.002

Cited by 27 publications

(31 citation statements)

References 23 publications

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“…We understand that a native shrubby vegetation, which seems to be a transient alternative state, can be beneficial at some level (see 44 ) and deserves to be protected as well (see [36][37][38] ). However, larger native grassland areas affected by woody encroachment as a result of fire and grazing suppression, can alter grassland communities, especially by reducing native forbs abundance and plant species richness 45 , as well as altering ecosystem functioning 30 . Besides, encroachment by B. uncinella seems to be facilitated by high air temperatures and native grasses 23 and even monocultures 16 .…”

Section: Discussionmentioning

confidence: 99%

Preventing traditional management can cause grassland loss within 30 years in southern Brazil

Sühs

Giehl

Peroni

2020

Sci Rep

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Woody encroachment threatens several ecosystems around the world. In general, management of grasslands includes regulation of fire and grazing regimes. Changes in these two types of disturbances are potential drivers of woody encroachment. Here we assessed how the traditional management carried out by local landholders affects a highland grassland ecosystem in southern Brazil. We hypothesized that grasslands converted to protected areas undergo fast woody encroachment. To reconstruct changes in vegetation, we interviewed former and current landholders and coupled their knowledge with an analysis of aerial and satellite images. During the first 11 years without fire and cattle, woody encroachment in grasslands increased exponentially. Woody encroachment occurred mostly by the replacement of grasslands by shrublands. Meanwhile, grasslands under traditional management remained almost unchanged for the last 40 years. The management of fire by local landholders has been part of their traditional practices for decades. Such management prevents largescale wildfires and maintains natural highland grasslands. The quick pace of shrub encroachment in such grasslands threatens its exclusive diversity, human well-being and regional cultural heritage. Thus, conservation policies are needed to regulate and instruct about the use of fire as a management tool in highland grasslands of southern Brazil. Extensive vegetation change can have important consequences in ecosystem functioning and economy 1. For instance, woody encroachment (or woody plant encroachment), which is the increase in density, cover and biomass of shrubs or woody vegetation in grasslands 2 , has been reported around the world 3. Woody encroachment is caused by several factors such as shifts in climate and biogeochemical cycles, changes in disturbance regimes (e.g. fire and grazing), or modification in ecological succession by introduction of non-native species or predator removal 2-5. Woody encroachment alters fundamental ecological processes of ecosystems, including global carbon balances, reduction of water flow or groundwater recharge and the loss of biodiversity 4,6,7. Because woody encroachment tends to negatively affect herbaceous vegetation, it constitutes a major threat to savanna and grassland ecosystems. Control of woody encroachment is a key concern in rangelands. Woody encroachment reduces forage production, creates habitat for ectoparasites, and hampers animal handling 4. Woody encroachment concerns land managers and methods for control and eradication include either fire, cutting trees, grazing, or a combination of these three methods 8,9. Woody encroachment has been reported all over the world, e.g., southern Ethiopian savanna 8 , North American savanna, shrub-steppe and grasslands ecosystems 10 , southeastern South American savanna 11 ('Campos' 6), and Brazilian savanna ('Cerrado' 12). In highland grasslands of southern Brazil, extensive cattle grazing is part of the traditional management employed for centuries 13. In addition, local ranchers c...

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Section: Discussionmentioning

confidence: 99%

Preventing traditional management can cause grassland loss within 30 years in southern Brazil

Sühs

Giehl

Peroni

2020

Sci Rep

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“…Moreover, sites from the PI area were the only ones that presented a native forest species with relatively high coverage (Dodonaea viscosa; see Table S2 for complete flowering species list and also Table S3 for flowering species list with the largest contribution to each fragment), even though these sites had a high proportion of surrounding grassland cover ( Figure 3C, Table 1). This is a clear indication that the suppression of disturbance for such a long time is promoting not only grassland biodiversity loss, but also the beginning of a shift towards a different system, which starts with the encroachment by ligneous species [78]. Conversely, sites that have been subjected to more frequent disturbances due to their proximity to urban areas presented higher plant species richness in comparison with sites that, although surrounded by natural vegetation, had their disturbance regimes alleviated or completely stopped.…”

Section: Plant Communitymentioning

confidence: 93%

“…In our study, all grassland sites were inserted into protected areas, which should minimize anthropogenic influences, prevent fire events, and ultimately affect the disturbance regime as a whole. When this happens, grassland communities change towards a simplified structure with few dominant species, predominantly tussock grasses and shrubs [76][77][78], coupled with the accumulation of flammable biomass and the colonization of ligneous species [44]. Even though they are all inserted into protected areas, the protection of these sites regarding human intervention was directly linked to their surroundings.…”

Section: Plant Communitymentioning

confidence: 99%

The Influence of Urbanization and Fire Disturbance on Plant-floral Visitor Mutualistic Networks

et al. 2020

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The biodiversity loss resulting from rising levels of human impacts on ecosystems has been extensively discussed over the last years. The expansion of urban areas promotes drastic ecological changes, especially through fragmentation of natural areas. Natural grassland remnants surrounded by an urban matrix are more likely to undergo disturbance events. Since grassland ecosystems are closely related to disturbances such as fire and grazing, grassland plant communities, pollinators, and their interaction networks may be especially sensitive to urban expansion, because it promotes habitat fragmentation and modifies disturbance regimes. This work evaluated the effect of the level of urbanization and recent history of fire disturbance on grassland plants communities and plant-floral visitor mutualistic networks. We sampled plant communities and floral visitors in 12 grassland sites with different levels of urbanization and time since the last fire event. Sites with higher levels of urbanization showed higher values for plant species richness, floral visitor richness, and network asymmetry. All sampled networks were significantly nested (with one exception), asymmetric, and specialized. In addition, all networks presented more modules than expected by chance. The frequency of fire disturbance events increased with the level of urbanization. Since grassland ecosystems depend on disturbances to maintain their structure and diversity, we inferred that the history of fire disturbance was the mechanism behind the relationship between urbanization and our biological descriptors. Our findings highlight the importance of small and isolated grassland remnants as conservation assets within urban areas, and that the disturbance events that such sites are submitted to may in fact be what maintains their diversity on multiple levels.

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“…However, the grassland matrix is a harsher environment compared to neighbouring forests in terms of solar radiation and microclimate, with high frequency of frost events that limit establishment of woody species above the tree line (Rehm & Feeley, ). Therefore, forest expansion over grasslands has been occurring gradually from the edges, sometimes facilitated by other plant species (Blanco et al., ; Duarte et al., ; Guido, Salenque, & Dresseno, ).…”

Section: Introductionmentioning

confidence: 99%

“…Such interventions have reduced the levels of disturbance and stress in these grasslands, causing changes in the interaction dynamics between grasses and woody species. Baccharis uncinella DC (Asteraceae) is a widespread and abundant shrub in these systems that may act as a nurse, triggering the conversion of grasslands into forest (Blanco et al., ; Duarte et al., ; Guido et al., ). B. uncinella encroachment had a significant effect on grassland communities, reducing native plant species richness, and particularly the number of forbs (Guido et al., ).…”

Section: Introductionmentioning

confidence: 99%

Factors controlling shrub encroachment in subtropical montane systems

Dechoum

Peroni

Pugnaire

2018

Applied Vegetation Science

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Aim We aimed to assess the effects of temperature rise and neighbour removal on growth and performance of juvenile individuals of Baccharis uncinella shrubs in a montane grassland. We hypothesized that removal of neighbouring grasses and increased air temperature would enhance B. uncinella growth. Location High‐elevation forest–grassland patches, southern Brazil. Methods An experiment with factorial design was carried out from Aug 2014 to Sept 2015 using air temperature and neighbour removal as factors with two levels each. Air temperature was increased using acrylic open‐top chambers (OTC). For the neighbour removal treatment we removed neighbouring grasses from 30 cm around randomly selected B. uncinella juveniles. Survival, growth and plant physiological status were assessed at the end of the experiment. Results Plants with OTCs grew more than plants without them. Neighbour removal did not have a significant effect on plant growth. These data suggest that an increase in temperature may enhance encroachment of B. uncinella in the studied grasslands, and that neighbour grasses may act as facilitators for B. uncinella shrubs by improving water balance. Conclusions Considering the capacity of B. uncinella to expand from forest edges towards grasslands, it is likely that montane grasslands in southern Brazil will be subject to B. uncinella encroachment within the next decades. The potential synergistic – negative – effects of global warming and habitat loss might jeopardize the high biodiversity of this ecosystem. Specific management actions and conservation public policies are needed to protect this already threatened montane system.

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Effect of shrub encroachment on vegetation communities in Brazilian forest-grassland mosaics

Cited by 27 publications

References 23 publications

Preventing traditional management can cause grassland loss within 30 years in southern Brazil

Preventing traditional management can cause grassland loss within 30 years in southern Brazil

The Influence of Urbanization and Fire Disturbance on Plant-floral Visitor Mutualistic Networks

Factors controlling shrub encroachment in subtropical montane systems

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