The interaction of climate and land-use changes leads to synergistic effects that drive the decline of biodiversity and ecosystem services (Brook et al., 2008; He et al., 2019). Synergistic effects are factors that interact and increase the extinction risk of a species (Brook et al., 2008). Because rapid climate change may hamper adaptive responses in many species, sufficient dispersal is often the only mechanism preventing extinction (Garcia et al., 2014; Loarie et al., 2009; Parmesan, 2006). However, species dispersal ability in response to climate change may be compromised by habitat loss and fragmentation, which impose barriers for many species (Brook et al., 2008; He et al., 2019; Sales et al., 2019). Among plants, species with abiotically-dispersed seeds which establish viable populations reaching reproductive maturity in a relatively short time (Cramer et al., 2007; Di Musciano et al., 2020; Tabarelli and Peres, 2002), may be able to persist in the face of current habitat loss and fragmentation. On the other hand, species with large zoochoric fruits and seeds have slower dispersal rates, are less likely to cope with environmental changes and, consequently, are more prone to extinction (Cramer et al., 2007; Tabarelli and Peres, 2002). Therefore, it is important to consider the potential synergies of climate and land-use changes, especially for species with limited dispersal, which can be done by modeling the distribution of species (Lemes and Loyola, 2015) and assessing the effectiveness of protected areas (PAs) in the face of those threats.

A major strategy in conservation has been implementing PAs, which seek to maintain biodiversity and ecosystem functioning through time (Margules and Pressey, 2000). PAs may not protect resident species that change their distribution in response to climate change (McDonald et al., 2019), especially in a country like Brazil, where PAs are unevenly distributed across biomes (Overbeck et al., 2015b; Vieira et al., 2019). A few studies have recently analyzed the impact of future climate change and habitat loss on the distribution of different organisms in an integrative way, including woody plants from the Atlantic Forest (Zwiener et al., 2017), plants from the Cerrado (Velazco et al., 2019), and monkeys from the Amazon (Sales et al., 2019). While these biomes are usually at the core of the conservation agenda, other biomes like Pantanal, Caatinga, and Pampa are usually neglected (Vieira et al., 2019). Specifically, open native ecosystems such as the South Brazilian grasslands are severely threatened, poorly known, and receive insufficient attention in the conservation agenda (Overbeck et al., 2007, 2015b).

South Brazilian grasslands are natural open ecosystems occurring under subtropical climate in the Pampa and Atlantic Forest biomes in Brazil's southern states (Overbeck et al., 2015a). These grasslands are threatened due to conversion for agriculture and silviculture (Overbeck et al., 2007; Vélez-Martin et al., 2015), and by climate change (Costa et al., 2018). Paleopalynological studies showed that the grassland-dominated landscape of southern Brazil has started to be subject to forest expansion promoted by increased temperature and humidity in the late Holocene (Behling, 2002), evidencing that grasslands are relictual ecosystems in the region. The potential for forest expansion over grassland is expected to be maintained along the 21st century (Anadón et al., 2014; Salazar et al., 2007). To understand the effects of climate and land-use changes in the South Brazilian grasslands, we can use typical species of these ecosystems as ecological indicators and project their modeled distribution into future climate change scenarios.

In the South Brazilian grasslands, several palms are part of the relictual vegetation and play a fundamental ecological role as food resources for the local fauna (De Lourdes et al., 2007; Pintaud et al., 2008; Sosinski et al., 2019). Although the distribution of palm species (Arecaceae) is predominantly pantropical, species of genera such as Allagoptera, Butia, and Trithrinax have established in the grassland ecosystems of South America (Pintaud et al., 2008), where the combination of climatic, edaphic, and historical factors promoted their diversification (Bjorholm et al., 2006a,b). Palm species of these genera are distributed throughout the South Brazilian grasslands (Soares et al., 2014) and these palms may be considered as ecological indicators for these ecosystems. Understanding how these palms could respond to future climate and land-use changes may help us predict the future of the South Brazilian grasslands and provide informed conservation strategies. We addressed the following questions: (1) what are the impacts of climate and land-use changes on the geographical distribution of palm species in the South Brazilian grasslands given two dispersal scenarios: without dispersal (hereafter, “no-dispersal”) or with dispersal (hereafter, “dispersal”)?, and (2) to what extent are these species encompassed by the current network of protected areas in present and future distribution? We hypothesized that (1) in the dispersal scenario the distribution area of palm species will increase because the synergistic effects of climate and land-use changes will not be sufficient to prevent species dispersal to new areas, (2) in the no-dispersal scenario, the distribution area of palm species will decrease due to synergistic effects of climate and land-use changes, because barriers resulting from these changes will prevent species dispersal to new areas, and (3) the studied palm species will be poorly covered by PAs in the present and future due to the small total area of the PA network in South Brazilian grasslands.

Overall, models presented a good performance, with average AUC and Boyce's index of 0.87 and 0.70, respectively (Table S6). The change in distribution area varied between dispersal scenarios and species groups (Table S7). Our future projection shows that all palm species would lose distribution area under the no-dispersal scenario and that such reduction would be greater for the associated species (Fig. 2, Figs. S3 and S4). Considering the dispersal scenario, both typical and associated species could increase their area (Fig. 2, Figs. S3 and S4).

Fig. 2.

Percentage of remaining distribution area for the typical and associated palm species of South Brazilian grasslands, based on their current distribution (100%), considering environment and land-use changes under different emission scenarios (RCPs 4.5 and 8.5) and dispersal scenarios for 2050. The outlier within the group of typical species corresponds to Butia lallemantii because the gain in area for this species is much higher than the average gain for the other species.

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Under the current environment and land-use conditions, the highest values for richness of palm species were found in the Campos Gerais, Planalto Médio, Campos das Missões, and Serra do Sudeste (for more details about regions of South Brazilian grasslands, see Appendix S5). We predicted a reduction of species richness in areas that currently have the highest species richness in the future no-dispersal scenario. On the other hand, in the dispersal scenario, the species richness would increase in these same areas (Fig. 3, Fig. S5).

Fig. 3.

Species richness of palm species in the South Brazilian grasslands under current conditions and the different future emissions (RCPs 4.5 and 8.5) and dispersal scenarios for 2050 obtained from the ESM models. A: Campos Gerais, B: Planalto Médio, C: Campos das Missões, D: Serra do Sudeste.

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Our results indicated that the current protection degree is low, and most of the species have less than 2% of their distribution protected within strictly protected areas (SPs) and sustainable use areas (SUs), except for B. pubispatha, A. campestris and B. microspadix, which currently have, respectively, 100%, 25% and 22% of their distribution within SUs (Table 1). The results also shown that two species are gap species, i.e. they are not represented in PAs: B. witeckiiand B. paraguayensis. Considering the future dispersal scenarios, a slight increase in the protection degree of B. microspadix, B. odorata and T. acanthocoma within SUs is expected. However, the protection degree is expected to be constant in the future under both dispersal and no-dispersal scenarios for the other species (Table 1).

The synergistic effects of climate and land-use changes under the no-dispersal scenario might reduce the future geographical distribution of palms in southern Brazilian grassland. It is important to clarify that the decrease in the distribution area of associated palm species within the study area does not necessarily mean a decrease in the total area of these species, because they also occur in other areas such as the Cerrado, mixed Araucaria forests, rocky outcrops of the Pampa biome and riparian forest edges (Cano et al., 2013; Morais, 1996; Flora do Brasil 2020 em construção). On the other hand, the scenarios with dispersal show that it is possible species distributions will increase. A similar pattern of decrease in area when constraining the dispersal and increase under a dispersal scenario was also observed for palm species in Africa (Blach-Overgaard et al., 2015), monkeys in the Amazon (Sales et al., 2019), and Neotropical palms (Velazco et al., 2020). Based on our results, we confirm our first and second hypothesis. It is important to clarify the meaning of the no-dispersal and dispersal scenarios used here: the no-dispersal scenario seems feasible for all studied species, considering the past and current trends of habitat loss they are experiencing (Table S1). The no-dispersal scenario seems especially feasible for Butia exilata, which, in landscapes under severe land use change, is increasingly confined to roadsides, i.e. to the very last remnants of natural grasslands (authors’ observ.). Regarding the scenario with dispersal, we used the only information currently available (to our knowledge) on dispersal rates of palms, which was done for African species (Blach-Overgaard et al., 2015), thus our scenario with a dispersal of 1kmyr−1 might be optimistic. However, geometrically speaking, the more a species is able to disperse, the more its range will increase. Then, if we generated a new scenario of intermediate dispersal (e.g. 500myr−1), the increase in the range would lay somewhere in between the no-dispersal and the dispersal scenarios. The most important point to make about the implications of these scenarios is that factors such as habitat loss, defaunation and overexploitation contribute to a result closer to the no-dispersal scenario, while the creation of PAs and improvement of grassland management and conservation contribute to the dispersal scenario. Recent findings indicate that, among rare species confined to particular microhabitats, dispersal distance can play a fundamental role in species persistence (Di Musciano et al., 2020), so it will be important to obtain real estimates of species dispersal abilities in future studies.

The gain in distribution area under the dispersal scenario is overly optimistic because it would mean the expansion of species distribution to new territories. Actually, this is unlikely to happen, because the ability of palm species to disperse and occupy new areas depend on other factors, such as (i) the capacity of pollination and seed dispersal agents, such as birds and mammals (Nascimento et al., 2020), to positively respond to climate change; (ii) the negative biotic interactions of the resident community with the newcomers (Corlett, 2016), such as competitive exclusion, predation, and parasitism; and (iii) on land management (e.g. grazing pressure) (Sosinski et al., 2019). There is evidence that, as the defaunation increases in fragmented landscapes, the recruitment and regeneration of palm populations decrease (Galetti et al., 2006), and that long-term homogenization of genetic pools of palm populations may occur (Carvalho et al., 2016). Moreover, the dispersal scenario assumes that future landscape will follow the projections made by Soares-Filho et al. (2016), i.e. land occupation complying with the environmental law – an unlikely situation considering Brazil's economic expansion policies (Loyola, 2014) and current setbacks in national environmental legislation enforcement (Abessa et al., 2019).

Our results highlight the low protection degree of most palm species regarding their distribution in the current PA network, thereby partly corroborating our third hypothesis, and reflecting the negligence in protecting the South Brazilian grasslands (Overbeck et al., 2015b, 2007). A similar result was found for Neotropical palms, under different dispersal scenarios, in which the existing PA network had a poor performance in protecting the phylogenetic diversity of palms under current and future climates (Velazco et al., 2020). A clear implication of the low protection degree of studied palm species can be seen for B. witeckii and B. paraguayensis, considered as gap species because they are not represented in any PAs. It is also noteworthy that the occurrences of palm species also depend on the management grasslands are subject to. Since most of the protection of species is on PAs of SU, palm conservation should be carefully planned to avoid lack of regeneration under high grazing pressures, as these PAs allow sustainable management and use of natural resources. For example, appropriate livestock management rotation in butiazal1 ecosystems enabled the establishment and growth of seedlings of B. odorata (Sosinski et al., 2019). Such management consisted in selecting butiazal areas to exclude from grazing during the winter and allow low density herds to graze beneath the palm grove during the other seasons (Sosinski et al., 2019; Rivas, 2005). In an opposite, drastic situation, the only known population of B. pubispatha is 100% encompassed by the Environmental Protected Area of Escarpa Devoniana (a SU). However, this unique population is mostly covered by a recent plantation of Pinus sp. (authors’ observ.), which can lead the species to extinction if no urgent actions are taken, e.g., the formation of seed banks, live collections, and assisted migration. Furthermore, although B. microspadix has 22% of its distribution within SUs, care must be taken because this species is endemic to the Campos Gerais region (Fig. S5), where it is considered vulnerable because of increasing habitat loss.

Moreover, the lack of management in most of the strictly protected areas in South Brazilian grasslands (Overbeck et al., 2007) also seems to threaten palm species typical of grassland environments. The population of B. exilata, which is found in the State Park of Papagaio-Charão (a SP) in the Planalto Médio region (Fig. S5), seems to be in decline due to forest expansion over grassland habitats of this species (authors’ observ.). Forest expansion over grasslands has been observed throughout southern Brazil (Behling, 2002; Oliveira and Pillar, 2004; Quadros and Pillar, 2001), therefore grazing and fire management can be a double-edged sword for Butia palm groves because the prevention of forest expansion is balanced by the possible negative effect of higher grazing pressure or intensive fire use on palm recruitment (Sosinski et al., 2019). Further research is needed to understand the ecological relationship of South Brazilian grasslands with fire and grazing (Overbeck et al., 2015a) and implement adequate management that promotes palm species persistence.

Studying the combined effect of climate and land-use changes in the distribution of palm species under different dispersal scenarios enabled exploring a wide range of future possibilities for these plants. We observed that if palm species are able to disperse, the synergistic effects of climate and land-use changes may not be bad for them. However, as we did not consider other factors in the dispersal scenario, such as local adaptation of palm species to non-climatic conditions (e.g. like relief, slope, soil chemical characteristics), and the responses of pollinators and seed dispersers to global changes, it is unlikely that palm species will disperse in the assumed dispersal rates. For this reason, the no-dispersal scenario seems to be more plausible, which points to the necessity of the implementation of urgent conservation actions, as these species are mostly endangered due to habitat loss. Most of the studied species are restricted to South Brazilian grasslands, where they are also economically important as they are used as raw material in handicrafts, food production, and as ornamental plants (Büttow et al., 2009; De Lourdes et al., 2007; Sosinski et al., 2019), which could increase the pressure on their populations, or alternately stimulate their protection through public awareness. Besides the impacts on the palm populations per se and on the associated fauna, species loss might also impact the regional economy. Our analyses revealed that PAs provide low protection to palm species and highlighted which of them are gap species, which can inform the formulation of conservation policies and support the creation of new PAs in the study region. Further research is needed to expand the knowledge on the distribution and biology of palm species, especially B. pubispatha,B. witeckii and B. exilata, which have only a few known populations and need more information to properly plan for their conservation.

Finally, we suggest some actions that can be taken to protect palm species of the South Brazilian grasslands. In-situ actions that could be taken involve the development of policies aiming to reduce the conversion of the South Brazilian grasslands, the expansion of the current PA network, adequate grazing and fire management allowing the recruitment of palm species, restoration of palm groves through the introduction of new seedlings (Sosinski et al., 2019), and the incentive of sustainable use of fruits and leaves. Regarding adequate management, we suggest initiatives to train and support landowners to maintain and properly manage palm groves in their legal reserves, with which private lands must comply (Brancalion et al., 2016). Ex-situ actions important to consider include the formation of seed banks, cryopreservation, live collections, and assisted migration (Corlett, 2016), especially for rare and geographically restricted species, which might increase the availability of seedlings available to restore palm groves. Putting these actions in practice is necessary to ensure the persistence of these palm species and their ecosystem in the future.

This study presented the first evaluation of the impact of climate and land-use changes on the geographical distribution of palm species in the South Brazilian grasslands and assessed the protection degree of these species in the current network of PAs considering present and future species distributions. We show that the scenario where species will be unable to migrate to new areas (no-dispersal) is unfortunately the more plausible scenario under increasing rates of land use changes. Furthermore, new protected areas should be created to increase protection to palm species in the future. Our findings reflect the state of conservation of South Brazilian grasslands and invite stakeholders to develop actions towards the protection of palm species and their ecosystems.

This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001, under a master's scholarship to LFCT and EMG, and a post-doctoral fellowship to FTB (PNPD/CAPES, process number 88882.306081/2018-1). Financial support was also obtained from a postdoctoral fellowship by Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET/Argentina) to SJEV, a doctoral scholarship by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq/Brazil) to PMH (#141137/2020-7), and a grant by the Fundação Grupo Boticário de Proteção à Natureza (project #1124_20181).