Mudanças climática vão favorecer gramíneas exóticas sobre espécies engenheiras nativas em áreas úmidas da Amazônia.

PROGRAMA DE PÓS GRADUAÇÃO EM ECOLOGIA

MUDANÇAS CLIMÁTICAS VÃO FAVORECER GRAMÍNEAS EXÓTICAS SOBRE ESPÉCIES ENGENHEIRAS NATIVAS EM

ÁREAS ÚMIDAS DA AMAZÔNIA

GIULIETTE BARBOSA MANO

Manaus, Amazonas Agosto, 2022

GIULIETTE BARBOSA MANO

MUDANÇAS CLIMÁTICAS VÃO FAVORECER GRAMÍNEAS EXÓTICAS SOBRE ESPÉCIES ENGENHEIRAS NATIVAS EM

ÁREAS ÚMIDAS DA AMAZÔNIA

MARIA TERESA FERNANDEZ PIEDADE Aline Lopes

Manaus, Amazonas Agosto, 2022

Dissertação apresentada ao Instituto Nacional de Pesquisas da Amazônia como parte dos requisitos para obtenção do título de Mestre em Biologia (Ecologia).

FICHA CATALOGRÁFICA

Sinopse: Estudou-se as áreas de adequabilidade de duas espécies engenheiras, Echinochloa polystachya e Paspalum fasciculatum e duas exóticas invasoras Urochloa brizantha e Urochloa decumbens frente a cenário de mudanças

climáticas para a Bacia Amazônica. Utilizou-se de ferramentas de modelagem de nicho ecológico, investigando a resposta das quatro plantas a diferentes cenários e anos.

Palavras-chave: adequabilidade; aquecimento global; nicho ecológico;

herbáceas aquáticas; várzea amazônica; biodiversidade.

Palavras-chave:

AGRADECIMENTOS

Agradeço à minha família, motivadores incansáveis de todos os meus sonhos e presentes em todos os momentos. Mãe, pai, Cesco e Carol, sem vocês, nada disso seria possível.

Agradeço imensamente minhas orientadoras Maitê e Aline, primeiro por terem topado essa orientação e segundo por serem tão presentes e terem me ensinado tanto. Espero fazer muita ciência ainda com vocês!

Agradeço aos amigos, que mesmo em tempos pandêmicos fortaleceram os laços e se fizeram presentes da maneira que foi possível, Marinas, Babi, Maria, Bia, Jean, Arthur, gratidão!

Agradeço a Sara, que se fez presente em todos os momentos, dando apoio, ombro amigo e torcida. Conseguimos!

Agradeço à turma do mestrado Eco 2020, infelizmente o tempo pré-pandemia foi curto para estreitarmos os laços, mas admiro cada um e desejo sucesso na jornada!

A todos os membros do grupo MAUA, meu muito obrigado por todas as trocas e aprendizados durante as reuniões das terças-feiras.

Agradeço à FAPEAM pela bolsa concedida e ao programa de pós-graduação em Ecologia por todo apoio.

Agradeço ao Programa Uso Sustentável do Instituto Humanine pelo auxílio emergencial concedido.

Por fim, meu muito obrigado a todos que de alguma forma ou outra, contribuíram para a realização deste trabalho.

RESUMO

A Bacia Amazônica vem sofrendo diversos impactos antrópicos, como desmatamento, queimadas, abertura de estradas e barragens. Esses fatores, em sinergia com as mudanças climáticas, vêm resultando no aumento de eventos extremos, como alagamentos e secas severas. Ao longo dos grandes rios amazônicos as herbáceas aquáticas, principalmente da família Poaceae, possuem alta abundância e produzem uma quantidade de biomassa até três vezes maior que a floresta alagável. Algumas espécies como Echinochloa polystachya (Kunth) Hitchc e Paspalum fasciculatum Willd. ex Fluggé são espécies-chave devido ao elevado aporte de carbono para o ecossistema de várzea, sendo consideradas espécies engenheiras dado seu papel estruturante nos primeiros estágios sucessionais desses ambientes. Nas últimas décadas gramíneas invasoras como Urochloa brizantha (A. Rich.) R. D. Webster e Urochloa decumbens (Stapf) R. D. Webster se espalharam pelos Neotrópicos e estão colonizando gradativamente a Amazônia, principalmente a partir do arco- do-desmatamento. Essas espécies invasoras muitas vezes atingem alta cobertura, suprimem outras espécies e se tornam dominantes em habitats perturbados e pristinos. Este trabalho teve como objetivo analisar o padrão de distribuição de duas espécies nativas engenheiras e duas espécies invasoras na Bacia Amazônica. Além disso, foi avaliado o efeito de diferentes cenários de mudanças climáticas nas áreas potencialmente adequadas para a ocorrência das mesmas. Para a projeção das áreas de adequabilidade foram escolhidos cinco cenários, sendo eles: atual, SSP1 2.6, SSP2 4.5, SSP3 7.0 e SSP5 8.5 para os anos de 2040, 2060, 2080 e 2100. A criação dos modelos foi realizada no programa R, utilizando 8 algoritmos, disponibilizados pelo pacote ‗biomod2‘.

Foram utilizadas 19 camadas bioclimáticas disponíveis na plataforma Wordclim para o período atual; o modelo de circulação global - CNRM CM6 foi utilizado para projetar os cenários futuros. As espécies apresentaram um baixo número de registros únicos (E. polystachya, 69, P. fasciculatum 69, U. brizantha 79, U.

decumbens 97) na Bacia Amazônica na resolução de 10 km². As atuais áreas climaticamente adequadas para as espécies engenheiras foi estimada em 22%

da Bacia Amazônica, enquanto que as invasoras possuem 23% de áreas potencialmente adequadas. Foi observada uma diminuição nas áreas de adequabilidade das duas espécies engenheiras em quase todos os cenários e anos, com perda de até 5,4% de área em cenário de alta emissão (SSP 8.5) para as duas espécies em conjunto. Por outro lado, as espécies invasoras, demonstraram um aumento nas áreas de adequabilidade, com ganho de área de até 5,2% em cenário de alta emissão (SSP 8.5). Estes resultados levantam uma preocupação quanto a invasão de gramíneas com alto potencial agressivo que poderá resultar na exclusão de espécies nativas engenheiras.

Palavras-chave: adequabilidade; aquecimento global; nicho ecológico;

herbáceas aquáticas; várzeas amazônicas; biodiversidade.

ABSTRACT

Climate change will favor exotic grasses over native engineer species in Amazonian wetlands

The Amazon Basin has suffered several anthropic impacts, such as deforestation, fires, and construction of roads and dams. These factors in synergy with climate change lead to an increase in extreme events, such as floods and severe droughts. Along the Amazonian rivers, aquatic herbaceous plants, mainly from the Poaceae family, are very abundant and produce up to three times more biomass than the flooded forest. Some species such as Echinochloa polystachya (Kunth) Hitchc and Paspalum fasciculatum Willd. ex Fluggé are key species due to the high carbon contribution to the floodplain ecosystem, being considered engineers given its structuring role in the early stages of succession of these environments. In the last decades, invasive grasses such as Urochloa brizantha (A. Rich.) R. D. Webster and Urochloa decumbens (Stapf) R. D. Webster have spread through the Neotropics and are gradually entering the Amazon through the arc of deforestation. These invasive species often reach high coverage, suppress other species, and become dominant in disturbed and, pristine habitats. This work aimed to analyze the pattern of distribution of two native engineer species and two invasive species in the Amazon Basin. In addition, the effect of different climate change scenarios on areas potentially suitable for their occurrence was evaluated. Five scenarios were chosen, current, SSP1 2.6, SSP2 4.5, SSP3 7.0 and SSP5 8.5 for the years 2040, 2060, 2080 and 2100 to project the suitable areas. The modeling to create the consensus model, using eight algorithms, was performed in the R program using the ‗biomod2‘ package. It was used 19 bioclimatic layers available in the Wordclim website for the current period, and the global circulation model - CNRM CM6 was used to project the future scenarios. The species presented a low number of unique records (E. polystachya, 69, P.

fasciculatum 69, U. brizantha 79, U. decumbens 97) in the Amazon Basin at a 10 km² resolution. The current climatically suitable areas for the engineer species was estimated at 22% of the Amazon Basin, while the invasive ones have 23% of potentially suitable areas. A decrease in the areas of suitability of the two engineer species was observed in almost every scenario and year, with losses of up to 5,4% of area in a high emission scenario (SSP 8.5) for the two species combined. On the other hand, invasive species showed an increase in suitable areas, with an area gain of up to 5.2% in a high emission scenario (SSP 8.5). These results raise a concern about the invasion of grasses with high aggressive potential that could result in the exclusion of native engineer species.

Keywords: suitability; global warming; ecological niche; aquatic grasses;

Amazonian várzeas; biodiversity.

SUMÁRIO

AGRADECIMENTOS ... IV RESUMO... V ABSTRACT ... VII SUMÁRIO... VIII

INTRODUÇÃO GERAL ... 9

OBJETIVO... 14

Capitulo único ... 15

1. INTRODUCTION ... 16

2. MATERIAL AND METHODS ... 18

2.1 Study area ... 18

2.2 Species ... 19

2.3 Occurrence data ... 20

2.4 Environmental data ... 21

2.5 Potential Distribution Range - PDR ... 21

3. RESULTS ... 24

4. DISCUSSION ... 27

5. CONCLUSION ... 31

CONCLUSÃO GERAL ... 31

REFERÊNCIAS BIBLIOGRÁFICAS ... 33

INTRODUÇÃO GERAL

As plantas aquáticas constituem um grande grupo ecológico que cresce em ambientes aquáticos e de transição (terrestre/aquático), e são consideradas uma das comunidades mais produtivas do mundo (Dhir 2015). Plantas aquáticas têm um papel vital quando se trata da preservação e diversidade de ambientes aquáticos (Hossain et al. 2017), devido às múltiplas funções que desempenham nesses sistemas. Dentre essas funções, podem ser destacadas: importantes produtores primários na cadeia trófica; participam da ciclagem de nutrientes no ambiente; influenciam na dinâmica de sedimentação nos ecossistemas de água doce, podem servir como fonte de refúgio e moradia para diversos outros organismos (desde perifíton, zooplâncton, até invertebrados e vertebrados), pois aumentam a complexidade e heterogeneidade do ambiente e influenciam o microclima e os processos hidromecânicos das zonas litorâneas (Dhir 2015; Hossain et al. 2017; Piedade et al. 2019).

O papel exercido pelas plantas aquáticas na estruturação, funcionamento e oferta de serviços ecossistêmicos para o meio aquático é fundamental (O‘Hare et al. 2018). Nas áreas alagáveis amazônicas as plantas aquáticas são capazes de influenciar tanto a hidrologia, quanto a geomorfologia dos ecossistemas aquáticos, além de influenciar processos físicos como o transporte de solutos, deposição de sedimentos, penetração de luz na água, entre outros (Junk & Piedade 1997; Piedade & Junk 2000). Em contrapartida, essas plantas respondem a variáveis físicas do ambiente, como a velocidade e turbulência da água e sua oscilação de nível, e por isso também são consideradas bio-indicadoras devido a sua forte ligação com fatores ambientais (Hossain et al. 2017; O‘Hare et al. 2018).

Ao longo dos grandes rios da Bacia Amazônica são periodicamente formadas extensas áreas alagáveis, com inundações que podem exceder mais de 200 dias, e uma coluna de água que chega ao redor de 10 m de altura na Amazônia Central (Junk et al. 1989). Estas áreas cobrem mais de 750.000 km², dos quais 450.000 km² correspondem a áreas de várzea e 300.000 km² a áreas de igapó (Wittmann & Junk 2016). Nas várzeas, onde a fertilidade é maior,

cerca de 400 espécies de herbáceas aquáticas foram descritas (Junk &

Piedade 1993); nos igapós, onde a pobreza nutricional e a acidez são limitantes, apenas cerca de 10% do número de plantas aquáticas é encontrado em relação à várzea (Piedade et al. 2019). Espécies de herbáceas aquáticas são particularmente fundamentais nas várzeas por criarem condições favoráveis para o estabelecimento das primeiras espécies arbóreas na sucessão dos processos de colonização (Worbes et al. 1992).

Diversas atividades antrópicas vêm causando mudanças notáveis nos ecossistemas naturais ao redor do mundo. Construções de estradas, hidroelétricas, desmatamento e mineração são algumas das atividades que modificam os ambientes naturais e causam grandes impactos na biodiversidade de plantas e animais, em escalas regionais e globais (Piedade et al. 2014; Hossain et al. 2017). Um dos maiores efeitos dos impactos antrópicos na modificação de ambientes naturais é a mudança climática. De fato, o clima tem mudado significantemente ao longo dos anos, e apesar de alterações climáticas já terem ocorrido no passado, a magnitude, o ritmo acelerado e as projeções futuras dessas mudanças não têm precedentes (Hossain et al. 2017). O quinto relatório Painel Intergovernamental sobre Mudanças Climáticas AR5 (IPCC 2013) corrobora esse cenário, ao concluir que o aquecimento global é inequívoco, e que a influência humana é clara nas mudanças climáticas. Além disso, é provável que ações humanas como a queima de combustíveis fósseis e o desmatamento sejam a grande causa do aquecimento global que vem sendo observado desde meados do século XX (Marengo & Souza Jr. 2018). Nas duas últimas décadas foi notado o aumento de gás carbônico na atmosfera de 280 para 650 ppm, o que por si só contribuiu para a elevação de 0.6 ºC na temperatura da Terra (Dhir 2015).

Entre os anos de 1949 a 2017, foi observado na Amazônia um aumento de 0,6 a 0,7 ºC, sendo o ano de 2017 considerado o mais quente desde meados do século XX. Através de complexos modelos climáticos apresentados pelo IPCC (2013), é projetado um aumento superior a 4ºC na temperatura média do ar na Amazônia até o final do século XXI, além de uma redução de até 40% nas chuvas (Marengo & Souza Jr 2018). Diversos estudos têm demonstrado o aumento na frequência de eventos extremos ao longo da Bacia

Amazônica, como o aumento ou a falta de chuvas, nas últimas décadas (Nobre et al. 2007; 2016; Marengo et al. 2008; 2010; 2013; Espinoza et al 2009a;

2009b; 2014; Aleixo et al. 2019). Os impactos decorrentes do aumento na frequência desses eventos podem ir desde o aumento do risco de incêndios, o aumento extremo da temperatura, bem como enchentes e inundações, causando grandes impactos tanto para as comunidades humanas quanto para a flora e fauna locais (Nobre et al. 2007; Piedade et al. 2013; Marengo &

Espinoza 2016).

De fato, as secas na Amazônia dos anos 2005 e 2010 foram tão intensas que, devido ao stress hídrico, árvores de grande porte morreram, havendo também um aumento no número de focos de incêndios florestais, além da liberação de grandes somas de carbono na atmosfera (Marengo &

Espinoza 2016; Nobre et al. 2016; Barichivich et al. 2018). Dados de nível dos rios em 2005 e 2010, mostraram os números mais baixos dos últimos 40 anos (Marengo et al. 2013). Já nos anos de 2012, 2014, 2015 e 2021 o intenso aumento das chuvas, causou grandes enchentes em diversos estados, como Acre, Rondônia e Manaus alagando cidades, estradas e fazendas, causando diversos danos nas residências e para a subsistência da população (Marengo et al. 2013; Chevuturi et al. 2022; Espinoza et al. 2021). Dados hidrológicos mostram uma tendência de aumento de eventos extremos na região amazônica, fato este consistente com modelos desenvolvidos pelo IPCC, que demostram tendências semelhantes para o futuro (Nobre et al 2007; Marengo

& Espinoza 2016; Marengo & Souza Jr 2018).

O aumento da temperatura, da concentração de CO2 e a alteração na precipitação têm um efeito direto em comunidades de plantas terrestres e aquáticas, tanto no crescimento e na produtividade, como em suas distribuições (Dhir 2015; Hossain et al. 2017). Os ecossistemas aquáticos estão entre os mais vulneráveis frente às mudanças climáticas, sendo esperado aumento da temperatura dos rios, como consequência do aumento da temperatura do ar e do equilíbrio entre esses dois meios (Hossain et al. 2017).

Tais alterações no clima trazem reflexos diretos nas características dos sistemas de água doce de várias formas, principalmente alterando o regime

hidrológico, causando, assim, mudanças na estrutura e no funcionamento das comunidades de plantas aquáticas (Dhir 2015; Hossain et al. 2017).

Devido às evidentes mudanças climáticas, estudos que modelam as respostas de organismos frente a elas vêm sendo cada vez mais desenvolvidos (Jones & Cheung 2015; Lopes et al. 2015; House et al. 2017; Cordeiro et al.

2020). O estudo em microcosmo realizado por Lopes e colabores (2015), por exemplo, evidenciou a influência que uma alta concentração de CO2 (600-900 ppm) em conjunto com o aumento na temperatura (28 a 30 ºC) exercem no crescimento inicial de Montrichardia arborescens, uma planta aquática de ampla distribuição e grande porte. Nos últimos 20 anos, diversos métodos foram desenvolvidos para investigar possíveis áreas de ocorrência de espécies, com base nas ocorrências conhecidas em correlação com as variáveis ambientais (Peterson & Soberón 2012).

A modelagem de nicho ecológico (MDE) nos ajuda a prever as potenciais áreas nas quais uma espécie poderia ocorrer em circunstâncias ambientais variáveis, de acordo com suas necessidades ecológicas, tanto bióticas quanto abióticas (Peterson & Soberón 2012). O entendimento dos fatores que controlam a área de distribuição das espécies desde escalas locais até regionais é de suma importância para predizer a resposta dos organismos frente às mudanças climáticas, e determinar as áreas de destruição das espécies é o primeiro passo para isto (Lopes et al. 2017; Cordeiro et al. 2020).

Ecossistemas aquáticos abrigam uma elevada biodiversidade, e espécies exóticas invasoras representam uma grande ameaça às plantas aquáticas nativas, devido ao seu comportamento agressivo caracterizado por uma intensa reprodução e dispersão além do seu ponto de introdução, ocupando nichos semelhantes aos das espécies nativas, contribuindo para a diminuição da diversidade local (Villa & Weiner 2004; Ferreira et al. 2016;

Cordeiro et al. 2020). As espécies do gênero Urochloa são plantas nativas da África que se destacam fortemente entre as espécies invasoras reconhecidas nas áreas alagáveis amazônicas. Segundo a Lista de espécies da Flora do Brasil (Flora e Funga do Brasil 2022), oito espécies do gênero são registradas para a região amazônica. Por se tratarem de gramíneas (Poaceae) frequentemente usadas para alimentação de gado, sua distribuição se

expandiu ao longo da Bacia Amazônica, podendo tornar essas espécies uma ameaça para as espécies nativas, mudando a composição, diversidade e produtividade do ambiente (Fares et al. 2020).

Nas várzeas amazônicas, duas gramíneas endêmicas Echinochloa polystachya (Kunth) Hitchc e Paspalum fasciculatum Willd. ex Fluggé desempenham o papel de engenheiras ecossistêmicas (Heaton et al. 2004).

Organismos engenheiros ecossistêmicos são aqueles que disponibilizam recursos para outros taxa pela transformação do ambiente (e.g. castores que constroem barragens, modulando a distribuição de água, sedimentos e nutrientes para o ambiente), e não por meio da provisão direta de recursos para outros organismos (Jones et al. 1994). Embora algumas espécies exóticas invasoras poderem apresentar a capacidade de ―engenheiras do ecossistema‖, a modificação que estas são capazes de exercer no ambiente são geralmente negativas. Por exemplo, elas alteram a composição da comunidade local pela diminuição da complexidade estrutural, aumentam a erosão do ambiente e a turbidez da agua, e modificam o regime de fluxo da agua, o que culmina na alteração da biodiversidade associada ao ambiente no qual ingressaram (Emery-Butcher et al. 2020). As espécies nativas, por sua vez, especificamente E. polystachya e P. fasciculatum, apresentam altos valores de produtividade primária, e são provedoras de alimento e abrigo para diversas espécies de animais aquáticos (Conserva & Piedade 2001; Piedade et al. 2014). Devido à predominância da propagação vegetativa, por meio de rebrotamento na camada superior do solo, essas duas gramíneas auxiliam os processos de sedimentação, ajudando a estabilizar o substrato e prevenindo a erosão causada na época de baixa do rio, além de abrirem caminho para as primeiras etapas do processo de sucessão arbórea das áreas de várzea da Bacia Amazônica (Worbes et al. 1992; Piedade et al. 2010b).

Embora ainda pouco se saiba sobre os efeitos das espécies exóticas invasoras para a várzea amazônica, especialmente em cenários de mudanças climáticas, os impactos que essas espécies podem causar ao ecossistema e às plantas nativas engenheiras merecem avaliação pois podem ser desastrosos (Silva & Silva-Forsberg 2015), tanto no ponto de vista dos estoques de carbono desses ambientes, quanto na integridade das florestas alagáveis. Frente a isso,

este estudo, constituído por um único capítulo, visa entender o comportamento e predizer as áreas de distribuição das gramíneas aquáticas engenheiras e invasoras frente às mudanças climáticas, aspecto de grande importância para prognosticar a integridade, mitigar efeitos de invasões biológicas e para o desenvolvimento de planos de conservação e manejo dos ambientes aquáticos e sua biodiversidade.

OBJETIVO

Investigar o impacto de diferentes cenários de mudanças climáticas nas áreas de adequabilidade de duas espécies de gramíneas nativas engenheiras ecossistêmicas, E. polystachya e P. Fasciculatum, e de duas espécies de gramíneas invasoras Urochloa brizantha (A. Rich.) R. D. Webster e Urochloa decumbens (Stapf) R. D. Webster ao longo da Bacia Amazônica.

Single Chapter

___________________

Mano, G.B.; Lopes, A. & Piedade, M.T.F. 2022.

Climate change will favor exotic grasses over native

engineer species in Amazonian wetlands. Submetido ao jornal Ecological Informatics.

1. INTRODUCTION

One of the biggest threats to native species is invasive alien species.

Invasive species have the potential to modify ecosystems, influencing the structure and functioning of local communities, thus being a concern worldwide (Fares et al. 2020). African grasses, for example the Poaceae genus Urochloa, have been introduced in Brazil for forage purposes, and have spread beyond the introduction site and invaded natural ecosystems (Martins et al. 2004).

Grass species of this genus have already shown great invasive potential and are already a source of concern in different environments, such as in the Pantanal wetland, where they can reduce plant diversity in the dry season (Bao et al. 2015). These plants have similar requirements in terms of water use and tolerance to high temperatures as those of aquatic native grasses endemic to the Amazon Basin and, therefore, they can pose a threat due to their resistance to stress, great competitive power and widespread distribution, reducing the native biodiversity (Martins et al. 2004; Fares et al. 2020).

Ecosystem engineer species play an extremely important role in the ecosystem by, modulating the environment and providing resources for different organisms. They act to ―directly or indirectly modulate the availability of resources to other species by causing physical state changes in biotic or abiotic materials‖ (Jones et al. 1994). Although some alien species may play the role of ecosystem engineers, most often the changes they bring about in ecosystems have a negative impact, as they can alter the structure and function of the community to achieve optimal abiotic conditions that suit them (Emery - Butcher et al. al. 2020). Differently, two native grasses Echinochloa polystachya (Kunth) Hitchc and Paspalum fasciculatum Willd. ex Fluggé are considered ecosystem engineers in the Amazonian floodplain. Both native species have high values of primary productivity and provide food and shelter for several species of aquatic animals (Conserva & Piedade 2001; Piedade et al. 2014). Due to the predominance of vegetative propagation and through regrowth in the upper layer of the soil, E. polystachya and P. fasciculatum help in the sedimentation processes, facilitating soil stabilization and preventing erosion caused during the river‘s low season. Additionally, they clear the way for the first stages of the

succession process of the várzea (white-water river floodplains) areas of the Amazon Basin (Worbes et al. 1992; Piedade et al. 2010).

An increase over 4º C in the average air temperature in the Amazon is predicted by the end of the 21st century, combined with a reduction in precipitation due to climate change (Marengo & Souza Jr 2018; Castellanos et al. in press). An increase in extreme events, such as heat waves, floods and droughts, resulting from global warming is already perceived (Huber & Gulledge 2011; Chevuturi et al. 2022). Over the last three decades‘ extreme drought and flood events have been observed more frequently along the basin, causing severe impacts on the entire region (Marengo et al. 2008, 2010, 2013; Espinoza et al 2009a; 2009b; 2014; Barichivich et al. 2018; Aleixo et al. al. 2019). Several studies have already shown that the intensification of these events is related to human activities that have been accelerating the processes of climate change observed around the world (Silva et al. 2018; Ribeiro Neto et al. 2021; Espinoza et al. 2021).

Climate change can modify the structure and functionality of ecosystems, in addition to regional changes in climate and in the frequency of extreme events (Ribeiro Neto et al. 2021). In wetlands, the potential impacts will be mainly on water regime changes, flood and drought-related disturbances and also on the tolerance of species that inhabit these areas (Dang et al. 2021;

Salimi et al. 2021). For plants, it is already known that climate changes will strongly affect areas suitable for their distribution, modifying their range of occurrence and diversity (Zhao et al. 2021). It was observed that projected increases in temperature and decrease in precipitation at high latitudes in South America lead to an increase in the suitability areas for invasive African grasses (Barbosa 2016), thus suggesting the potential migration and colonization of new areas by these species. However, another study highlighted the negative impact on growth and survival of two Amazonian native aquatic macrophytes resulting from increase in temperature and CO2 concentration(Souza et al. 2020). Native species may, therefore, be at great risk in the face of climate change and biological invasions.

Understanding the factors that control the areas of distribution of species from local to regional scales is of paramount importance to predict the response

of organisms to climate change and determining the areas of species distribution is the first step towards this (Lopes et al. 2017; Cordeiro et al. 2020).

Ecological niche modeling is one of the tools that has been most used in recent years to estimate the areas of best suitability for native and invasive species in the face of climate change (Moraes et al. 2020). Several approaches can be used to choose the best algorithms that fit data and the methodology used for modeling (Ahmad et al. 2019; Moura-Júnior et al. 2021). The consensus models approach is one of the most used methods because, several algorithms are used to take into account the uncertainty of each model, and increase their predictive power (Thuiller et al. 2009; Castro et al. 2019; Lopes et al. 2021;

Moura-Júnior et al. 2021).

The ongoing deforestation along the Amazon Basin for agriculture and pasture purposes is followed by the introduction of invasive alien species for forage, a potential threat to native species. Thus, the present study aimed to investigate the current distribution and the impact of different climate change scenarios on the suitability areas of two native engineer grasses, Echinochloa polystachya and Paspalum fasciculatum, and of two invasive grasses Urochloa brizantha (A. Rich.) RD Webster and Urochloa decumbens (Stapf) RD Webster along the Amazon Basin. We hypothesize that the invasive species will be favored by climate change because of their high reproduction and dispersion rate, having a broader ecological niche, while native engineer species will have a reduction in suitable areas due to their specific relationship with the floodplains and the threats that the area is under the impacts of climate change.

2. MATERIAL AND METHODS

2.1 Study area

The Amazon Basin is, located between coordinates 5'N and 20'S, covers 8 countries (Brazil, Bolivia, Colombia, Ecuador, Guyana, Peru, Suriname and Venezuela) and has an estimated area of 6,915 million Km², wich approximately 5 million Km² belong to Brazil (Zhong et al. 2021). The basin is limited in the west by the Andes Mountains, with an elevation up to 6,000 meters, in the north by the Guiana Plateau, with mountains up to 3,000 meters, in the south by the

Central Plateau, with typical altitudes of 1,200 meters, and in the east by the Atlantic Ocean, so that all the water captured by the basin flows into the sea (Fisch et al. 1998).

The seasonal thermal amplitude of the region is of the order of 1 to 2 ºC, with average values of 24 and 26 ºC. The mean temperature in the coldest month is ≥ 18 °C and in the warmest month approximately 35 °C (Zhong et al.

2021). The Amazon Basin is one of the regions with the highest precipitation in the world (Espinoza et al. 2009a), with a mean of 2,050 mm.year ^-1 , and highest annual value of 3,500 mm on the border between Brazil, Colombia and Venezuela (Gloor et al. 2015).

2.2 Species

Echinochloa polystachya (Poaceae), popularly known as canarana, is an emerging aquatic grass, native to the Americas, with tropical and subtropical distribution. Similarly, Paspalum fasciculatum is a native species with distribution in several biomes of the country, it is popularly known as capim-mori and murim. It is an aquatic herb that occurs in tropical and subtropical regions and, together with E. polystachya, stands out in the Amazonian floodplain, due to its wide distribution and biomass production (Ferreira et al. 2010; Piedade et al. 1991). Both species tolerate large floods and, while E. polystachya grows mainly during the aquatic phase (Piedade et al. 1991), P. fasciculatum synchronizes its growth with the terrestrial phase (Conserva & Piedade 2001;

Piedade et al. 2019).

Urochloa brizantha (Poaceae), originally from Africa, is a very common species in Brazil, easily found in pastures, roadside, vacant lots and even in protect areas. It has fast and aggressive growth, and can reach up to 1.8 m in height. Its seeds are produced in high quantity and have a high germination capacity (Filgueiras et al. 2012). Urochloa decumbens is also native to Africa and is easily found in pastures, roadside and abandoned lands. A little less aggressive than U. brizantha, but with the same invasive potential, U.

decumbens can reach from 40 to 60 cm, has a slender habit and is typically decumbent (Filgueiras et al. 2012).

Although the four selected species are perennial C4 grasses, they differ in the annual productivity. While U decumbens and U. brizantha may produce 15 and 18 t/ha/year, respectively, E. polystachya and P. fasciculatum may reach 100 and 70 t/ha/year, respectively. Much of the big difference between the productivity of exotic and native species is due to the production of vigorous stems and roots by Amazonian species, which favor their attachment to the substrate and retention of sediments, that is, their role as ecosystem engineers.

2.3 Occurrence data

The database was constructed based on the points of species occurrence obtained from the online platforms: Global Biodiversity Information Facility – GBIF (https://www.gbif.org/) and SpeciesLink (https://specieslink.net/).

To obtain the points of occurrence of invasive species in Brazil, the data platform of the Instituto Hórus de Desenvolvimento e Conservação Ambiental (https://institutohorus.org.br/) was consulted. Additionally, data from scientific articles were collected through the Google Scholar platform, using the keywords

―Echinochloa polystachya Amazon basin‖; ―Paspalum fasciculatum Amazon basin‖; ―Urochloa brizantha Amazon basin‖; ―Urochloa decumbens Amazon basin‖; ―Brachiaria brizantha Amazon basin‖; ―Brachiaria decumbens Amazon basin‖. Subsequently, the data set was standardized, and the duplicates (repeated occurrences/occurrences in the same pixel) were excluded. After this procedure, the total number of species occurrence obtained was 69 for E.

polystachya, 69 for P. fasciculatum, 79 for U. brizantha and 97 for U.

decumbens (Fig. 1).

Figure 1. Spatial distribution of the species Echinochloa polystachya, Paspalum fasciculatum, Urochloa brizantha and Urochloa decumbens in the Amazon Basin (data obtained from scientific papers and from the on-line platforms - Global Biodiversity Information Facility -GBIF, SpeciesLink and Institute Horus).

2.4 Environmental data

To build the current climate scenario, 19 bioclimatic variables were obtained at a resolution of 5 arc-min (~ 10 km), extracted from the Worldclim platform (https://www.worldclim.org/). All layers were cut to the extent of the Amazon Basin, using the ‗raster‘ package in the R software. This extension was chosen because the invasive plants are already naturalized in the Amazon Basin (Flora and Funga do Brasil 2022) and the records in the region of origin, Africa, present many inconsistencies due to changes in the separation of the genera Brachiaria, Panicum and Urochloa (Sánchez-Ken 2011). To avoid multicollinearity between the environmental variables a principal component analysis (PCA) was performed using the ‗rasterPCA‘ package in the R software (Dormann et al. 2013). The axis that added up to 90% of the total variation were retained and used on further analysis. This process was performed for each model.

Four Shared Socioeconomic Pathways (SSPs) of the CMIP6 scenarios were considered for the years 2040, 2060, 2080 and 2100, extracted from the

WordClim plataform. The SSPs are complementary of the RCPs (pathways for greenhouse gas concentrations) and take into account how socioeconomic factors may change over the next century. They are as followed: SSP1 - 2.6

―Sustainability – taking the green road‖, a world focused on sustainability growth and equality (low greenhouse gases (GHG) emission scenario, with an estimated long-term temperature increase around 1.7-1.8 °C), SSP2 - 4.5

―Middle of the road‖, slow progress into achieving sustainable development goals (average GHG emission scenario, with long-term temperature rise estimate around 2.5-2.7 °C), SSP3 - 7.0 ―Regional rivalry – a rocky road‖, a world of ever-increasing inequality high GHG emission scenario, with long-term temperature rise estimate around 3.8-4.2 °C) and SSP5 - 8.5 ―Fossil-fueled development – taking the highway‖, the catastrophic scenario, where a world of rapid growth in economic output and energy use is perceived (high GHG emission scenario, with long-term temperature rise estimate around 5.1 °C) (O'neill et al. 2017; Riahi et al. 2017). These scenarios were simulated with the global circulation model - CNRM CM6. The layers were cut to the extent of the Amazon Basin using the crop feature in the R environment. This model was chosen because it has a good seasonal and interannual representation for most Brazilian basins (Silveira et al. 2013; 2019).

2.5 Potential Distribution Range - PDR

The current and future potential distribution models of the species were constructed using nine algorithms offered by the 'biomod2' package (Thuiller et al. 2014) of the R program, namely: Generalized Linear Models (GLM);

(McCullagh & Nelder 1989); Artificial Neural Networks (ANN); (Hopfield 1982), Generalized Boosted Models (GBM); (Friedman et al. 2000), Generalized Additive Model (GAM); (Hastie & Tibshirani 1987), Maximum Entropy ( MaxEnt ); (Phillips et al. 2006), Random Forest (RF); (Breiman 1999), Classification Tree Analysis (CTA); (Breiman et al. 1984), Flexible Discriminant Analysis (FDA); (Hastie et al. 1994), Surface-range Envelope (SER); (Jiguet et al. 2011).

All algorithms were used with the default configuration of the 'biomod2' package.

Because the database is created only on species occurrence records, pseudo-absence points (background) were created for the study area as

specified in Barbet-Massin et al. (2012). Therefore, for the CTA, RF and GBM algorithms, the number of pseudo-absence points generated was equal to the existing points for each species. For the ANN, SRE, FDA, GLM, GAM and MaxEnt algorithms, 1,000 pseudo-absence points were created. For the best accuracy of the models, through the cross-validation method, the data were randomly selected between 70% training (assessing model accuracy) and 30%

testing (model fitting) (Huberty 1994). This procedure was repeated 10 times for each climate scenario and for each species.

The final model was build based on the TSS (true skill statistic) mean values of the 10 repetitions. The values vary from -1 to 1, where negative values or values close to 0 indicate that the model does not differ by chance.

Models with values close to 1 are considered to have great predictive power (Allouche et al. 2006). Therefore, models with a TSS value ≥ 0.4 were selected to produce the consensus map for each scenario (Araujo & New 2007). The consensus map consists of the union of the binary maps generated with a mean threshold of the retained each chosen algorithm, where the areas of greatest suitability for the occurrence of species will be those that most models indicate as suitable (Giannini et al. 2012). A global wetlands shape (Lehner and Döll 2004) was cut to the extent of the Amazon Basin and overlapped on the binary maps and suitable areas for the four species within the wetlands were estimated.

In addition, the mean, standard deviation and uncertainty coefficient of the ROC (receiver operating characteristics), was used to quantify the uncertainty between the different models and the consensus model. These metrics show the sensitivity-probability that a test result will have to be positive when the species is present (Thuiller et al. 2019). Therefore, the consensus model for each species was classified based on the average of the ROC sensitivity values and the sensitivity of the ROC standard deviation (SD). The best performing models have a sensitivity close to 100. Based on Ochoa-Ochoa et al. (2016) the models were classified into four reliability categories: poor (sensitivity ≤50 or SD ≥ 50), medium (sensitivity ≥50 with SD ≤ 45), good (sensitivity ≥70 with SD ≤ 30) and great (sensitivity ≥ 90 with SD ≤ 30). All models were performed in the R 4.2.0 program (R Core Development Team

2020) following the script developed by Eiseinloh 2020 (https://github.com/pedroeisenlohr/niche_modelling).

Finally, maps of the potential distribution area of species (PDR) were created using the software ArcGIS 10.2. The consensus maps were reclassified by the Reclassify tool into 4 suitability classes: > 60 ―high potential‖ of suitability for the occurrence of the species, 40-60 ―good potential‖, 20-40 ―moderate potential‖ and < 20 ―unlikely potential‖ for suitability. The percentage in the area of suitability (SA) was calculated from the difference between the numbers of pixels of each class (0 = not suitable; 1 = suitable, Lopes et al. 2021). For that, binary maps of suitability/non-suitability areas were created, by counting the pixels of gain and loss of area and applying the following equation:

1) 𝑆𝐴 % = number of pixels in a suitable area for the species

to tal number of pixels × 100 2) Δ SA % = SA future – SA actual

3. RESULTS

The mean values (± standard deviation) of ROC sensitivity ranged from 75.36 (± 1.07) to 85.82 (± 7.06), demonstrating a good performance for all analyzed models (supplementary material). The SRE algorithm was not included in any consensus model, as it did not reach a TSS value >0.4 for any of the scenarios. The CTA, FDA, GLM and MaxEnt algorithms, were discarded from some models of the E. polystachya, P. fasciculatum, U. brizantha and U.

decumbens species, due to their low TSS. The combination of SSPs, years and models generated 16 future projections for each species, totalizing 64 projections of suitability areas.

According to the current consensus model, the engineer E. polystachya has an area of suitability of approximately 16% of the total area and 34.87% of wetlands. Parts of Brazil, Colombia and Ecuador can be highlighted as the largest areas of suitability for the species (Fig. 2A). The engineer P.

fasciculatum has an area of ~11% in the Amazon basil and 33.4% in the wetlands, with the greatest suitability concentrated in the Brazilian and Guiana shield portion of the basin and some parts of Peru and Bolivia (Fig. 2B). The

invasive species, U. brizantha exhibited an area of ~19% in the Amazon basin and 14.5% of wetlands, demonstrating greater suitability in southeastern Bolivia and a large portion of Brazil (Fig. 2C). The species U. decumbens showed the smallest area with potential suitability for the current consensus model with

~11% in the Amazon Basin and 3.0% of the wetlands, with areas of suitability found in the southern and southeastern portions of Bolivia, Ecuador, Colombia and southern of the Brazilian Amazon Basin (Fig. 2D). While the engineer species have a distribution more related to the várzea areas, concentrated along the Solimões and Amazonas river, the invasive species were more concentrated in the southern portion of the basin, in the arc of deforestation.

Figure 2 Consensus map of current projection of suitability area for the four species studied in the Amazon Basin. (A) Echinochloa polystachya (B) Paspalum fasciculatum (C) Urochloa brizantha (D) Urochloa decumbens.

The native engineer species demonstrated loss of suitability area in most scenarios as a response to climate change (Table 1). Even though E.

polystachya showed a slight increase in the area of suitability for the highest impact scenarios (SSP3 - 7.0 and SSP5 - 8.5) for the year 2060, the species lost area in all other scenarios and years. The greatest loss was concentrated in the Colombian and Ecuadorian areas of the basin. The species P. fasciculatum

showed an increase in its suitability area for almost every year in the lowest impact scenario (SSP1 - 2.6) (Table 1), but had a reduction in suitability for all other scenarios and years.

Table 1. Percentage of suitability area for two native species (E. polystachya and P. fasciculatum) and two exotic species (U. brizantha and U. decumbens) in the Amazon Basin, in current and future climate change scenarios.

2040 species current SSP1 SSP2 SSP3 SSP5 Δ SSP1 Δ SSP2 Δ SSP3 Δ SSP5 Echinochloa polystachya 16.4% 14.0% 14.3% 14.2% 14.4% -2.5% -2.2% -2.2% -2.0%

Paspalum fasciculatum 11.0% 11.9% 11.2% 10.8% 10.4% 0.9% 0.2% -0.1% -0.6%

2 species together 21.7% 14.4% 18.5% 18.1% 19.1% -7.3% -3.3% -3.6% -2.7%

Urochloa brizantha 19.4% 15.1% 17.1% 17.3% 16.2% -4.2% -2.3% -2.0% -3.2%

Urochloa decumbens 10.9% 13.9% 11.2% 12.3% 16.3% 3.0% 0.3% 1.4% 5.4%

2 species together 22.9% 21.8% 20.9% 21.9% 23.9% -1.1% -2.1% -1.0% 0.9%

2060 species current SSP1 SSP2 SSP3 SSP5 Δ SSP1 Δ SSP2 Δ SSP3 Δ SSP5 Echinochloa polystachya 16.4% 14.0% 13.2% 16.6% 16.8% -2.5% -3.3% 0.2% 0.4%

Paspalum fasciculatum 11.0% 12.0% 10.5% 10.8% 10.1% 1.0% -0.5% -0.2% -0.9%

2 species together 21.7% 18.72% 17.24% 20.22% 20.35% -3.0% -4.5% -1.5% -1.4%

Urochloa brizantha 19.4% 16.5% 16.0% 15.1% 14.6% -2.9% -3.3% -4.2% -4.8%

Urochloa decumbens 10.9% 15.4% 11.0% 11.2% 16.1% 4.5% 0.1% 0.3% 5.2%

2 species together 22.9% 23.5% 20.9% 19.4% 22.7% 0.5% -2.0% -3.5% -0.3%

2080 species current SSP1 SSP2 SSP3 SSP5 Δ SSP1 Δ SSP2 Δ SSP3 Δ SSP5 Echinochloa polystachya 16.4% 17.6% 15.2% 15.7% 13.6% 1.2% -1.3% -0.8% -2.9%

Paspalum fasciculatum 11.0% 12.2% 9.5% 9.3% 8.2% 1.2% -1.5% -1.7% -2.7%

2 species together 21.7% 21.2% 18.1% 18.7% 16.3% -0.5% -3.6% -3.0% -5.4%

Urochloa brizantha 19.4% 15.1% 15.0% 20.3% 18.0% -4.2% -4.3% 0.9% -1.4%

Urochloa decumbens 10.9% 13.4% 14.9% 15.2% 13.3% 2.5% 4.0% 4.3% 2.4%

2 species together 22.9% 21.7% 21.0% 25.3% 22.6% -1.2% -1.9% 2.4% -0.3%

2100 species current SSP1 SSP2 SSP3 SSP5 Δ SSP1 Δ SSP2 Δ SSP3 Δ SSP5 Echinochloa polystachya 16.4% 16.8% 13.6% 14.0% 13.8% 0.3% -2.8% -2.4% -2.7%

Paspalum fasciculatum 11.0% 12.7% 10.8% 12.3% 7.9% 1.7% -0.2% 1.3% -3.1%

2 species together 21.7% 20.87% 17.85% 19.35% 16.65% -0.9% -3.9% -2.4% -5.1%

Urochloa brizantha 19.4% 16.5% 13.8% 18.8% 19.7% -2.8% -5.5% -0.6% 0.3%

Urochloa decumbens 10.9% 16.5% 20.7% 24.5% 14.6% 5.6% 9.8% 13.6% 3.7%

2 species together 22.9% 24.55% 20.71% 24.48% 24.76% 1.6% -2.2% 1.6% 1.8%

The two invasive species showed an increase in the suitable area in the most extreme scenarios of climate change. The species U. brizantha had an increase in its area of suitability for the years 2080 (SSP3 - 7.0) and 2100 (SSP5 - 8.5) for the highest impact scenarios showing a loss of suitable area in all other scenarios and years (Table 1). The species U. decumbens, on the other hand, showed an increase in its suitability area for all years and scenarios, with a more expressive (13.6%) for the year 2100 in the SSP3 - 7.0 scenario.

4. DISCUSSION

This study evaluated the potential impact of climate change in the current and future areas of suitability of two engineer herbaceous species, E.

polystachya and P. fasciculatum, and two invasive grass species, U. brizantha and U. decumbens, for the Amazon Basin. The results obtained point to a significant loss of suitability area in future scenarios for E. polystachya and P.

fasciculatum, thus corroborating with studies carried out around the world (eg.

South America, Asia, Europe) that predict loss of suitable areas for several native plants against climate change scenarios (Hossain et al. 2017; Silva et al.

2018; Castro et al. 2019; Zhao et al. 2021; Glad & Mallard 2022). On the other hand, an expansion of the suitability areas of U. brizantha and U. decumbens was observed, a result that is similar to studies carried out with invasive plants in different environments (eg. Tropical (Puga et al. 2016); Subtropical (Ahmad et al. 2019); Temperate (Fang et al. 2021)), which demonstrate the importance of actions to mitigate the environmental interventions that favor the spread of these invasive species and their associated impacts.

The species Echinochloa polystachya and Paspalum fasciculatum presented, together, a loss of up to ~5.4% in suitability area in the high emission scenario (SSP5 - 8.5). But a loss of suitability area was also observed in the short term (2040) and in the most optimistic scenario (SSP1 - 2.6) for both species. These results show the impact that climate change can have in short- and long-term periods on these species. Contrary to the native species, U. brizantha and U. decumbens showed gains in areas of high and moderate

suitability in almost all scenarios and years analyzed. The species U.

decumbens showed a gain of up to 13.6% in areas of suitability for the year 2100 in the Amazon Basin and 18% on the SSP3 – 7.0 scenario for the wetland in 2100. Studies developed with invasive exotic grasses around the world demonstrate the same trend of an increase in suitable area under the effects of climate change (Gillard et al. 2017; Damasceno et al. 2018; Fulgêncio-Lima et al. 2021). The Amazon basin has been under increased anthropogenic pressure, for example land-use change, which can heighten the dispersal of invasive species and have direct impact in the loss of habitat and diversity in the ecosystem (Fares et al. 2020). It is well known that invasive species, such as African grasses, can affect the function of ecosystems, altering the productivity or the trophic structure, increasing the frequency and intensity of fire and compromising the stability of the ecosystem (Williams & Baruch 2000). Thus, the loss of suitability area for E. polystachya and P. fasciculatum and the gain for U. brizantha and U. decumbens predicted in future scenarios can have great impact on the Amazon floodplains. When considering only the wetlands, where the native species are better adapted, the loss of suitable area is lower but still relevant in the most extreme scenarios, mainly for P. fasciculatum (loss of 10.3% in the SSP5 - 8.5 2100 scenario).

It is also important to highlight the loss of suitability area for the two native species along the Amazon River channel for the year 2080 (Fig. 3). The species E. polystachya and P. fasciculatum play an important role in the Amazonian floodplains, increasing habitat complexity by creating large monospecific stands that retain sediments in the receding waters of the river, thus facilitating the establishment of tree species from the first successional stages of the várzea floodplain, such as the species Salix humboldtiana (Worbes et al. 1992). Furthermore, a primary production of 99 Mg/ha is recorded for E. polystachya (Piedade et al. 1991), and this high value is directly related to nutrient cycling (Piedade et al. 1997) and carbon input in the várzea floodplains. (Morison et al. 2000). When taken into perspective the importance of the native species for the ecological processes in the basin, the gain of suitability area for the invasive U. decumbens can be very harmful, since the latter is known for producing a dense layer in the soils thereafter reducing the

light incidence, which can prevent the germination processes and recruitment of native species from seed banks (Ferreira et al. 2016). Therefore, it is essential that policies for the control of the exotic species should be established, to preserve the integrity of the floodplain.

Figure 3. Map of potential suitability area for the species E. polystachya and P. fasciculatum for the 2080s and 2100s based on consensus model, classified into 4 classes: > 60 “high potential” suitability, 40-60

“good potential”, 20-40 “potential” moderate” and < 20 “unlikely potential”. Left image: A) current; YEAR 2080: (B) SSP1 2.6 (C) SSP2 4.5 (D) SSP3 7.0 (E) SSP5 8.5; YEAR 2100: (F) SSP1 2.6 (G) SSP2 4.5 (H) SSP3 7.0 (I) SSP5 8.5. Right image: (A) current; YEAR 2080: (B) SSP1 2.6 (C) SSP2 4.5 (D) SSP3 7.0 (E) SSP5 8.5; YEAR 2100: (F) SSP1 2.6 (G) SSP2 4.5 (H) SSP3 7.0 (I) SSP5 8.5.

The expansion of the suitability area of U. brizantha and U. decumbens is particularly noticeable in several areas in Bolivia. According to data from the SPA (Science Panel for the Amazon 2021), the Santa Cruz region is considered the largest area of deforestation in the Amazon nowadays. Deforestation for the establishment of pasture areas is one of the biggest causes of climate change and biological invasions of exotic grass species. In the Brazilian Amazon, it is estimated that 80% of the deforested area is used for pasture (Ministério do Meio Ambiente 2018). Fares et al. (2020) recorded the occurrence of Urochloa arrecta in several lakes in Pará, along anthropized areas, such as pastures,

crops and, urban areas. The authors suggested that, the species probably managed to disperse across the border of the State of Maranhão, facilitated by the deforested areas for agriculture that are expanding in Brazil. In this sense, U. arrecta, that belong to the same genus, may be favored by the high rates of deforestation and soil transformation that have been occurring along the Amazon Basin, which in 2022 already concentrated 3.988 km² of deforested area, 80% higher than the same period in 2018 (Ipam 2022).

Several studies have already been carried out with African grasses in the Cerrado (Williams & Baruch 2000; Damasceno et al. 2018; Zenni et al. 2020), but little is known about the impact of these species on the Amazon biome.

Compared with the current distribution models of the two invasive species, the future models demonstrate a displacement of areas of suitability for the two invasive species through the Cerrado/Amazon transition zone, known as the arc of deforestation (Fig. 4). This region is the most devastated area in the Amazon, and the place where several invasive exotic species occur. Approximately 44,600,743 hectares of forests have already been converted to pasture in the Amazon Basin (MapBiomas Project 2022), the projections of areas of suitability for the species of this study demonstrate the urgent need for prevent the increase of the dispersion of these species, through the Amazon basin.

Figure 4 Consensus map of potential suitability area for U. brizantha and U. decumbens for the 2080s and 2100s classified into 4 classes: > 60 “high potential” suitability, 40-60 “good potential”, 20-40 “potential”

moderate” and < 20 “unlikely potential”. Right image: (A) current; YEAR 2080: (B) SSP1 2.6 (C) SSP2 4.5 (D) SSP3 7.0 (E) SSP5 8.5; YEAR 2100: (F) SSP1 2.6 (G) SSP2 4.5 (H) SSP3 7.0 (I) SSP5 8.5. Left image: (A) current; YEAR 2080: (B) SSP1 2.6 (C) SSP2 4.5 (D) SSP3 7.0 (E) SSP5 8.5; YEAR 2100: (F) SSP1 2.6 (G) SSP2 4.5 (H) SSP3 7.0 (I) SSP5 8.5.

5. CONCLUSION

The hypothesis raised in this study, that the invasive species, for having a broader ecological niche, will be favored by climate change was confirmed.

Likewise, the engineer species, will experience a reduction in suitable areas.

These results indicate a threat to the biological diversity of the Amazonian floodplain, with potential change in the succession patterns of the várzea floodplain and the flow of energy, nutrient and water, compromising these ecosystems and their processes.

CONCLUSÃO GERAL

Embora pouco contemplada em estudos pretéritos, a questão das invasões de plantas exóticas na Bacia Amazônica, em particular em áreas alagáveis de várzea, merece atenção. A introdução de pastagens exóticas, bem como o aporte acidental de propágulos podem comprometer a biodiversidade nativa. Sendo constituídas por sedimentos oriundos da região andina e pré-andina, mal compactados e de fácil remoção pelas correntes dos rios, as áreas de várzea se consolidam e são ocupadas por florestas alagáveis, a partir do papel de engenheiras ambientais de algumas gramíneas de rápido e vigoroso crescimento. Nesse sentido, se destacam as Poaceae Echinochloa polystachya e Paspalum fasciculatum, que com seus compridos talos e sistemas de raízes retêm os sedimentos e favorecem o aparecimento das espécies colonizadoras arbóreas desses ambientes. O presente estudo buscou testar se as espécies invasoras, detentoras de um nicho ecológico mais amplo, serão favorecidas pelas mudanças climáticas prognosticadas. Essa hipótese foi confirmada, indicando que as espécies engenheiras ecossistêmicas, que são estruturais nos estágios sucessionais iniciais das várzeas, e bem adaptadas às áreas úmidas, terão uma redução das áreas adequadas. Esses resultados indicam uma potencial mudança dos padrões de sucessão da várzea, podendo comprometer a integridade desses ecossistemas. Os dados obtidos servem também de base para projetos visando mitigar os efeitos de invasões biológicas e para o desenvolvimento de planos de conservação e manejo dos ambientes de áreas alagáveis, sua biodiversidade e múltiplos serviços ambientais.

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