“Wetlands are ecosystems at the interface between aquatic and terrestrial environments; they may be continental or coastal, natural or artificial, permanently or periodically inundated by shallow water or consist of waterlogged soils. Their waters may be fresh, or highly or mildly saline. Wetlands are home to specific plant and animal communities adapted to their hydrological dynamics” (Junk et al., 2013). Wetlands, given their utmost importance for the provision of ecosystem services, have been considered as “the kidneys of the landscape” or “ecological supermarkets”, which places them as a global priority for conservation and restoration (Mitsch and Gosselink, 2011). Their degradation, thus, can lead to the collapse of entire ecological and socioeconomic systems. In addition, wetlands harbour high biodiversity, containing rare or threatened species unique to these environments (MEA, 2005). Numerous species of aquatic and terrestrial animals, including pollinating agents, depend on wetlands for food, shelter and/or reproduction (Gibbs, 2000).

In many countries, the concept of wetland is well understood, and their fragile ecosystems receive due attention, visibility, clear delimitation and legal protection (e.g., http://wetlands.org; https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/national/water/wetlands). The relevance of wetlands was consolidated worldwide with the Convention on Wetlands of International Importance, known as the Ramsar Convention, established in 1971 in the Iranian city of Ramsar (Matthews, 2013). Brazil is a signatory to the Ramsar Convention, which was incorporated into its legal framework in May 1996. In Brazil, however, the term wetland is rarely mentioned in environmental policies, legislation, academia and media, reflecting the lack of understanding of these relevant ecosystems. Wetlands have received different legal treatment and degrees of protection in Brazil depending on the vegetation types occupying them, and their treatment also varies between States and even between sectors within the same organization (Maltchik et al., 2018). Recent efforts have been devoted to categorizing wetland types in Brazil and demonstrating their importance and the urgent need for public policies aiming at their conservation (e.g., Junk et al., 2013; Cunha et al., 2015). However, the multiplicity of vegetation types occupying wetlands in Brazil and the incompleteness of the literature about wetland ecology and conservation require additional efforts to fill the gaps. As a consequence, the environmental laws also remain incomplete when referring to wetlands in Brazil (Grasel et al., 2019).

We here focus on the Cerrado wetlands because: (i) Cerrado is the largest among the Neotropical savannas, covering 22% of the Brazilian territory, and harbouring the headwaters of most watersheds in the country (Lima and Silva, 2007); (ii) recent land-use changes at a large scale in this biome have increased wetland degradation to a level unparalleled in other Brazilian biomes (Latrubesse et al., 2019); (iii) Cerrado wetlands are poorly understood relative to other wetlands in the country, such as the Pantanal or the Amazon River floodplain (Silva et al., 2000; Pott and Pott, 2004; Junk et al., 2018); and (iv) the existing legislation fails in clearly and adequately protecting all types of Cerrado wetlands (see Box 1 for the legal aspects and Table 1 for the vegetation types).

Forests in Cerrado wetlands are not adequately treated by environmental laws, being only partially protected by a narrow strip of Permanent Preservation Area (PPA) around springs or along the banks of watercourses. Because the width of this strip is measured from the stream margin in the dry season (the “smaller width”, according to Art. 4º (I), Law 12,651, May 2012), extensive areas of seasonally or permanently waterlogged forests remain outside the PPA. In addition, isolated patches of wetlands which are not associated with water bodies are entirely unprotected. Equally inadequate is the legal delimitation of PPA around veredas, based on the horizontal distance starting from the permanently waterlogged area. In fact, the narrow strip of PPA includes only a small part of the seasonally waterlogged portions of a vereda, which can often extend far beyond the PPA and should not be separately treated or disregarded. Grassy wetlands located on the margins of water bodies in the Cerrado are often misinterpreted as “deforested land” by environmental agencies and professionals working on prosecution and adjudication of environmental offenses. These wetlands are then considered as environmental liability, and the landowners are inadvertently obliged to plant tree species where they never existed, under the equivocal pretence of “riparian forest restoration”. Afforestation in wetlands causes heavy losses in the rich herbaceous-shrubby flora and associated fauna, along with hydrological impacts.

Among the primary ecosystem services provided by wetlands (MEA, 2005), two are especially noteworthy in the Cerrado: (i) they function as filters and freshwater reservoirs, directly feeding most first-order streams in 8 of the 12 large Brazilian hydrographic regions (Lima and Silva, 2007), ensuring water quality and perennial rivers in the dry season; and (ii) store impressive amounts of carbon in organic soils (exceeding 200 Mg C ha−1) (Wantzen et al., 2012; França and Paiva, 2015). Furthermore, these ecosystems play a fundamental role in the local socio-economy, serving as a livelihood for several traditional human communities (Schmidt et al., 2011; Junk et al., 2013; Borges et al., 2016). Despite their undeniable importance for biodiversity conservation and provisioning of ecosystem services, the critical reality is that, without proper legal protection, Cerrado wetlands remain vulnerable and can be freely converted (drained or not) to any land use, no matter how disastrous this may be (Moreira et al., 2015; Pott et al., 2019; Brasil et al., 2021). Examples of these uses have been sand mining, crops, forestry with exotics (Pinus and Eucalyptus), pastures with African grasses adapted to waterlogged soils (e.g., Urochloa humidicola) and even urbanization. Impounding water or digging wells for livestock watering, irrigation, fish farming, landscape design and recreational purposes can cause the direct loss of wetlands and compromise their natural hydrological pulses.

Different vegetation types occupy wetlands within the Cerrado biome, ranging from forests to grasslands (main types described in Table 1, shown in Fig. 1), often forming complex landscape mosaics. The differences pointed out by phytogeographers, botanists and ecologists between vegetation types occupying Cerrado wetlands result in a broad number of concepts and denominations, not easy to recognize in loco even by specialists, which hampers the interpretation of the current law provisioning. In addition, transitional gradients exist within the wetland mosaics, and the whole mosaics are dynamic over time. The many terms used to refer to herbaceous vegetation include campo úmido, campo alagado, campo com/de murundus, várzea, brejo, and those referring to woody vegetation include vereda, buritizal, palmeiral, floresta higrófila, floresta pantanosa, mata de brejo, mata de galeria inundável, floresta alagável, mata paludosa, mata úmida or mata alagada. These terms often describe systems with only subtle differences, sometimes mixtures of concepts or also mere synonymy, with much redundancy and minor conflicts.

Fig. 1.

Main vegetation types occupying wetlands in the Cerrado (see also Table 1 for detailed information).

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Hydrological functioning is the most critical factor determining wetland characteristics and is the principal descriptor when differentiating wetland types (Junk et al., 2013). Vegetation structure and composition within wetlands are strongly dependent on hydrological processes. The water that characterizes most wetlands in the Cerrado comes from the shallow or superficial water table, in contrast to wetlands in Pantanal or floodplain forests in the Amazon, where flooding results from rivers’ overflow during the rainy season (Silva et al., 2000; Pott and Pott, 2004; Junk et al., 2018; Cunha et al., 2015). Generally, as they are not subject to surface flooding and sediment input from river waters, the Cerrado wetlands have highly stable substrates.

The water table of a Cerrado wetland is fed by rainwater infiltration across the entire watershed. Surface runoff is rare in the Cerrado, restricted to hilly relief or drainage impediment; it is almost nonexistent in the flat areas with sandy and deep soils that comprise the majority of Cerrado land. Part of the rain falling on the vegetation evaporates before reaching the ground, but most infiltrates into the soil; the infiltrated water that exceeds the uptake by plant roots slowly percolates and accumulates at the bottom of the valleys. Because Cerrado rainfall is characterized by a marked seasonality, the hydrological pulses conditioning wetlands are also seasonal and predictable. The maximum elevation of the water table and annual variation in water table depth vary considerably within and between sites (due to edaphic and topographic factors), and between years (due to changes in rain volume and distribution).

Given the slow movement of infiltrated rainwater (Swarowsky et al., 2011), the maximum water table elevation in the Cerrado is usually recorded between April and May, when rainfall has already decreased (Manzione, 2018). Conversely, the lowest levels of the water table occur at the beginning of the rainy season (October–November). Plants quickly use the first rains and, only after this demand is met, the surplus recharges the water table (Oliveira et al., 2017). Part of this water goes further down, feeding deep aquifers. The remainder feeds surface water sources, which, due to these recharge processes, are perennial, in contrast to other extensive savannas on the planet (Tooth, 2000). In some Cerrado wetlands, impediment layers (rocks, laterite, soil textural differentiation) hamper drainage, restricting rain infiltration to deep reserves and, proportionally, increasing the recharge of surface water bodies. Wetlands resulting from impediment layers can occur even in plateaus or slopes, in regions where the geomorphology allows it.

Despite differences in texture (from sandy to clayish) and genesis (sedimentary, residual or organic), wetland soils in the Cerrado are generally very acidic, with poor nutrient availability and high contents of organic matter. They are all subject to water saturation, and thus anaerobic conditions, at least temporarily. The accumulation and slow decomposition of organic matter resulting from permanent water saturation form dark organic soils which may exceed 1 m in depth, often forming peatlands, with impressive carbon storage (Wantzen et al., 2012; França and Paiva, 2015). Such edaphic conditions result in highly specialized flora (Justin and Armstrong, 1987; Rossatto et al., 2012; Villalobos-Vega et al., 2014; Silva et al., 2017).

Although some types of Cerrado wetlands are permanently waterlogged, in many cases plants need to be adapted to hyperseasonality, due to a large water table fluctuation over the year. There is water saturation especially at the end of the rainy season in such ecosystems, but the soil remains extremely dry and the water table very deep over long periods, making it particularly difficult to recognize these seasonal wetland types (Junk et al., 2013). The larger the variation within a wetland in the range of water table fluctuation and level of waterlogging, the higher will be its floristic diversity. These factors generally differ between the edges and the bottom of Cerrado wetlands, leading to associated floristic gradients (Meirelles et al., 2002; Oliveira et al., 2009).

The maximum water table elevation (minimum water table depth) is the main factor limiting the colonization of Cerrado wetlands by species from surrounding dry areas (Ribeiro et al., 2021). In all areas where the water table depth is less than 50 cm, at least during the period of its maximum elevation, sites will support specialized wetland flora and species sensitive to waterlogging will be unable to colonize (Pilon, 2016; Ribeiro, 2020). If this rhythm of annual elevation is changed by natural or anthropogenic factors, the limits of the wetland ecosystem also change, as discussed ahead.

Of the nearly 12,600 plant species in the Cerrado, around 20% are associated with vegetation types characteristic of wetlands (Mendonça et al., 2008). There are entire families whose species occur predominantly or exclusively in wetlands, slightly differing between vegetation types (examples in Table 1 and Fig. 2). These species are often considered indicators of these environments. Such specialization results in high degrees of endemism and many rare and endangered species (e.g. Eriocaulon burchellii, Microlicia ordinata, Mesosetum alatum, Polygala bevilacquai, Xyris goyazensis, X. paradisiaca) (Martinelli et al., 2014).

Fig. 2.

Some examples of Cerrado wetland indicator species. Species were selected based on their absence in well-drained surrounding ecosystems, broad geographical distribution (data from the Species Link database, and Flora do Brasil 2020), and also by their easy identification in the field.

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The absence or rarity of taxa that are otherwise abundant and species-rich in well-drained areas of Cerrado, such as Fabaceae (Leguminosae), also contributes to the floristic distinctiveness of wetlands in this biome. Also notable is the absence of some invasive exotic grasses (e.g., Urochloa decumbens, U. brizantha), which do not survive in waterlogged terrain.

The ecosystem functioning in Cerrado wetlands is heavily dependent on natural hydrological pulses. Consequently, any factor that modifies the water table fluctuation regime will lead to ecosystem degradation, loss of diversity and ecosystem services, primarily by reducing soil carbon stocks and changing water yield. Wetland drainage directly modifies the hydrological regime with immediate impacts. As such, the conservation of wetlands and their functions depends on rigorously controlling changes in land use across the entire watershed, not just within the water-saturated zones.

Changes to vegetation can have large effects on runoff. Evidence from paired catchments shows that increases or decreases in aboveground biomass in more than 20% area of a watershed will cause, respectively, a decrease or increase in runoff (annual watershed flow) (Bosch and Hewlett, 1982; Brown et al., 2005). The greater the rain interception by tree canopies and the greater the transpiration, the less water will recharge the groundwater reserves, springs and rivers (Honda and Durigan, 2016). Therefore, silviculture, crop-forestry-livestock systems based on fast-growing tree species, and even high-density plantations of native trees where the former native vegetation was grassland or savanna will inevitably lower the water table in wetlands (Jackson et al., 2005; Ferraz et al., 2019). The opening and overexploitation of wells in the interfluvial zones, whether for crop irrigation or human supply, also lead to lowering the water table, putting its ecological functions at risk (Salem et al., 2017; Sun et al., 2019). Surface impermeabilization by infrastructure and urbanization, and inadequate management practices in agriculture and livestock lead to soil compaction, reducing infiltration and groundwater recharge and causing flow peaks and even floods during the rainy season (Honda and Durigan, 2017), likely resulting in environmental and economic damage. Unfortunately, the legal instruments which could prevent lowering the water table (e.g., Municipal Master Plan or Ecological-Economic Zoning) have not been effective.

Indirect damages to ecosystems resulting from the lowering of the water table in wetlands are rarely perceived. For instance, under natural conditions in grassy wetlands, a fire event eliminates only aboveground biomass (Schmidt et al., 2017) that immediately recovers by regrowth, followed by intense flowering (Araújo et al., 2013). If, however, the fire was preceded by lowering the water table, then extreme weather conditions can allow accumulated organic matter to burn for months (Maillard et al., 2009), severely compromising the ecosystem resilience. This degradation process is aggravated because burning organic soils results in high methane emissions (Turetsky et al., 2011), a greenhouse gas that is more harmful than CO2 normally emitted by burning aboveground biomass. Lowering the water table can also trigger biological invasions. Formerly waterlogged areas are prone to colonization by aggressive grasses which are widely disseminated in the Cerrado as weeds or invaders (e.g., Andropogon gayanus, Hyparrhenia rufa, Melinis minutiflora, M. repens, Urochloa brizantha, U. decumbens), as these species do not tolerate high water saturation (Tannus and Assis, 2004; Oliveira et al., 2009). Another example of a negative consequence of lowering the water table is increased colonization of grassy wetlands by native shrub and tree species adapted to well-drained environments, an example of woody encroachment (Giotto, 2015; Gonçalves et al., 2021). Despite leading to remarkable transformations in plant communities and the broader landscape, this increase in woody vegetation has been misinterpreted by many as an ecosystem “improvement”. Naturally, all changes mentioned also impact the native fauna inhabiting or using the resources provided by wetlands in the Cerrado (Stanton et al., 2018).

This array of threats, which is now well delineated, stems from the history of wetlands in the Cerrado, which have been the target of predatory and environmentally unsustainable public policies in recent decades. For example, the Provárzeas program (National Program for the Use of Irrigable Floodlands) was developed in the 1970s and 1980s and launched nationally in 1981 (Decree 86,146) to stimulate agricultural production in flooded lands, despite violating the guidelines of the Forest Code of 1965. To this end, the program encouraged the landowners, with financial, technical and administrative support from the government, to drain and cultivate floodplains on their land. The first initiatives in the Cerrado were implemented in Minas Gerais state, and what was understood as “floodplains” were precisely the Cerrado wetlands described here, particularly the grassy veredas and campos úmidos. Such ecosystems, in contrast to true floodplains fed by rivers, are not subject to fertilization pulses by annual floods, and their highly acidic, nutrient-poor and erodible soils are unsuitable for cultivation. Catastrophic occupation of wetlands has expanded to other Cerrado regions, widely replicating the officially stimulated degradation of these fragile ecosystems and severely hampering their biodiversity and ecosystem services.

Brazil has been a Ramsar Convention signatory for a quarter of a century, but this has not contributed to clarifying and disseminating the concept of wetlands, nor to value them in the Cerrado, a biome known as the “cradle of water” or the “water tank of Brazil”. Of the 27 official Ramsar sites in the country, only two (Parque Nacional do Araguaia/TO and APA Carste de Lagoa Santa/MG) are in the Cerrado biome, and both are located on its borders (MMA, 2021), with no sites recognized in the core area of ​the biome. Decision makers and people in general do not perceive that campos com murundus, campos úmidos with or without buritis, or even matas de brejo, among the many denominations presented here Table 1), fit perfectly into the internationally accepted concept of wetlands and should not be treated separately by law or by conservation policies. These vegetation types occupy a large area of ​the Cerrado and are rarely mapped when they do not have tree cover. In the Federal District of Brazil, wetlands were estimated to cover 3.4% of the territory (França et al., 2008). At the Serra Geral do Tocantins Ecological Station, they correspond to 4.8% (Cristo et al., 2016). Similar proportions are likely common within the whole Cerrado biome. Bozelli et al. (2018) estimated that wetlands occupy about 20% of Brazil. Although the Ramsar Convention mandated that signatory countries map their wetlands, this has not yet been achieved in Brazil, especially for small patches (Bozelli et al., 2018) such as those that make up the majority of wetlands in the Cerrado.

Concerning the legal framework, it is crucial to clearly define wetlands and facilitate their identification and delimitation in rural properties and urban areas. It must be recognized that the Native Vegetation Protection Law (12,651/2012) attempted to protect wetlands. However, the law’s application became imprecise, incomplete, and ineffective by poorly defining wetlands, treating the different vegetation types with distinct rules or simply ignoring some of them.

The fact that wetlands in Brazil are not mapped by governmental organizations (e.g. Environmental Ministry or state Secretaries), except when they occupy large areas, aggravates their vulnerability. That is even worse in the Cerrado, where much of the native vegetation in wetlands lacks tree cover. Surveys that map the remaining natural Cerrado vegetation (e.g., Sano et al., 2010, Beuchle et al., 2015) do not detail wetlands and rarely map vegetation types with less than 50% tree cover. Thus, the losses of Cerrado vegetation types with naturally low tree cover, particularly wetlands, are not even quantified. A recent study quantified 25% of palm swamps in the Cerrado as degraded over 34 years (Brasil et al., 2021). The inexistence of maps that allow identifying non-forest wetlands, and even open grasslands and savannas in interfluvial zones, has facilitated degradation and hampered legal inspection and possible penalties. This situation is improving, as the MapBiomas platform (2020) recently made available maps of Cerrado wetlands, grouped in a single legend class – ID 11: Wetlands. Such maps can be the basis for unified public policies to avoid land conversion and prevent land degradation of all wetland types within the Cerrado. That includes revising the provisions of the Native Vegetation Protection Law and aligning it with State laws.

The protection of wetlands requires action in several domains, among which we highlight the need for adequate legal framework and mapping with objective criteria. In addition, we present recommendations related to public policies, planning, communication, technical assistance, training, sustainable management and restoration.

(a) Identification and mapping at a local scale using objective criteria: flora, soils and depth of the water table

Regardless of the type of native vegetation, the recognition of a wetland ought to be based on the distinctive flora (species, genera or families of indicator plants), on hydromorphic soils, and the highest elevation (minimum depth) of the water table over the year. In remote sensing images, wetlands stand out from adjacent dry areas due to their different colour provided by the specialized flora and the organic and moist soils. Although these characteristics make it easy to map even small areas, the exact delimitation of wet, marshy or waterlogged space can only be carried out on site. Considering that the specialized flora occupies areas where the depth of the water table at the end of the rainy season (usually April–May in the Cerrado) is less than 50 cm (Giotto, 2015; Pilon, 2016; Ribeiro 2020), we propose that the delimitation of the wetland in loco is made at that period, adopting this depth as a criterion. Areas where the water table rises above 50 cm in depth at any time of the year cannot be converted for other uses. Without interventions that artificially lower the water table, these areas are not suitable for cultivation given the waterlogged soils which most cultivated plants cannot survive. According to the Natural Resources Conservation Service (USDA-SCS, 1972), the classic recommendation adopted in different regions of the world, and Brazil, is that soils should not be cultivated where the water table can rise above 60 cm depth, even if this elevation is seasonal. Therefore, delimiting the Cerrado wetlands based on a depth of 50 cm at the peak of the water table rise would not imply a loss of productive area.

In addition to the general maps delimiting wetlands as a whole for law compliance verification, maps at detailed scale that differentiate vegetation types and hydrological functioning (see Table 1, Fig. 1) are crucial to driving restoration planning and sustainable use practices. At the state and federal levels, the Brazilian agricultural research and development agencies should provide subsidies and instructions to restrict the use of wetlands for agricultural purposes, along with offering alternatives of ecologically sustainable use practices compatible with each wetland type and property size.

(b) Including unprotected wetlands in Legal Reserves

Although we argue that all Cerrado wetlands should be under the same legal status, this unification requires changes in the text of the current law. While waiting for these changes, we indicated (Box 1) how the Cerrado wetlands can be protected under the current law. However, we also explained that this protection is incomplete, with many areas or wetland types remaining unprotected. If not protected as PPA, any wetland, with or without arboreal vegetation, must be a priority to be included into the Legal Reserve (LR) within the property or to compensate for other properties (servidão ambiental). This recommendation is already included as one of the criteria for delimiting LR (art.14 of federal law 12,651):

Art. 14. The location of the LR within a rural property must take into account the following studies and criteria: (I) the hydrographic basin plan; (II) Ecological-Economic Zoning; (III) the formation of ecological corridors with other LRs, PPAs, Conservation Unities, or with any other legally protected area; (IV) the areas of highest importance for biodiversity conservation; and (V) the areas of critical environmental fragility.