Semeadura direta de espécies arbóreas nativas de Cerrado: diferenças entre espécies e efeitos da matocompetição
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Data
2018-08-20
Autores
Passaretti, Raquel Aparecida
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Universidade Estadual Paulista (Unesp)
Resumo
Face à expressiva degradação a que o Cerrado brasileiro vem sendo submetido, é de grande importância a investigação e o desenvolvimento de métodos para a sua restauração. Atualmente, há obstáculos ecológicos e tecnológicos para a restauração da vegetação de cerrado, tais como a presença de espécies exóticas invasoras, a estação seca prolongada, a dificuldade para obtenção de mudas de espécies nativas em viveiros e a falta de conhecimento para a escolha de espécies adequadas para cada técnica de restauração. O entendimento acerca do desempenho de diferentes espécies arbóreas nativas semeadas diretamente em campo e dos efeitos da matocompetição sobre o desempenho dessas espécies é altamente relevante para a superação dos obstáculos mencionados. Os objetivos deste estudo foram: (i) comparar o desempenho de espécies arbóreas nativas por meio de semeadura direta, em busca de padrões funcionais que expliquem esse desempenho, (ii) verificar se o desempenho das espécies é comprometido pela matocompetição e (iii) verificar se a semeadura consorciada com gramíneas nativas pode inibir o estabelecimento da matocompetição. Instalamos um experimento fatorial em blocos (5 blocos) com os seguintes fatores: 1) espécies nativas arbóreas (11); 2) controle de matocompetição (sim ou não) e 3) consorciação com um mix de seis gramíneas nativas (sim ou não). O experimento totalizou 110 parcelas de 4 m2 cada, distribuídas nos 5 blocos. Em cada parcela semeamos 100 sementes de uma espécie arbórea aleatoriamente definida, em linhas, com 20 cm entre sementes. Contamos a quantidade de indivíduos arbóreos emergidos e mortos aos 10, 20 e 30 dias após a semeadura e, posteriormente, ao término das estações seca e chuvosa. Após um ano, medimos a altura e o diâmetro do caule dos indivíduos sobreviventes e estimamos a porcentagem de cobertura do terreno por gramíneas nativas e por matocompetição em cada parcela. Adicionalmente, medimos o comprimento e quantificamos a biomassa seca da parte aérea e da parte subterrânea de 11 indivíduos de cada espécie arbórea e apresentamos uma estimativa de custos da semeadura direta. Observamos diferença no desempenho entre tratamentos para algumas espécies que foram prejudicadas pela matocompetição. As espécies Dipteryx alata, Hymenaea stigonocarpa e Plathymenia reticulata apresentaram os maiores valores médios de taxa de sobrevivência (superiores a 60%) e as duas espécies do gênero Stryphnodendron apresentaram os piores desempenhos (ao redor de 20%). A presença de gramíneas nativas não beneficiou nenhuma espécie arbórea nem inibiu a colonização e o desenvolvimento da matocompetição. A interação entre as variáveis massa das sementes, biomassa raiz:parte aérea e comprimento do sistema radicular explicou 93% da variação na sobrevivência das plântulas em campo. Conclui-se que a semeadura direta de espécies arbóreas em cerrado pode ser bem sucedida, especialmente para espécies com sementes grandes, raízes profundas e que investem mais em sistema subterrâneo do que em parte aérea, que são atributos funcionais relacionados com a capacidade de sobreviver em condições de déficit hídrico. Embora algumas espécies possam ter sucesso sob matocompetição, o controle de gramíneas exóticas e ervas ruderais pode viabilizar a semeadura direta para um conjunto maior de espécies.
In view of the vast and fast degradation to which Brazilian Cerrado has been submitted, it is of great importance to find adequate restoration techniques to be widely applied. There are currently ecological and technological challenges for the restoration of the cerrado vegetation, such as the presence of invasive alien species, the prolonged dry season, the difficulty to obtain seedlings of native species in nurseries and the lack of knowledge to choose suitable species for each restoration technique. Understanding the performance of different tree species in direct seeding and the interactions between weeds and native grasses is highly relevant to overcome the mentioned obstacles. The objectives of this study were: (i) to evaluate the performance of native tree species in direct sowing, in search for functional patterns related to this performance, (ii) to verify if the consortium of native grasses with tree seeds can help in weed control, positively influencing the performance of tree species, and (iii) to verify if the native grasses are able to inhibit weeds colonization and development (competition). We set up a factorial experiment in blocks with the following levels of variation: 1) species (11); 2) weed control (yes or no) and 3) consortium with a mix of six native grasses (yes or no). The experiment totalled 110 plots of 4 m2 each, distributed in the 5 blocks. In each plot we sowed 100 seeds of an arboreal species, in rows, with 20 cm between seeds. We counted the number of arboreal individuals emerged and dead at 10, 20 and 30 days after sowing; and then at the end of both the dry season and the rainy season. After one year from sowing, we measured stem height and diameter of the surviving individuals, and estimated the percentage of ground cover by native grasses and weeds per plot. In addition, we measured the length and quantified the dry aerial and belowground biomass of 11 individuals of each tree species and we estimated the costs for direct seeding. We observed a difference in performance among treatments for some species that were adversely affected by weed competition. The species Dipteryx alata, Hymenaea stigonocarpa and Plathymenia reticulata had the highest average survival rates (over 60%) and the two species of the genus Stryphnodendron had the worst performances (around 20%). The presence of native grasses did not benefit any tree species nor inhibit colonization and development of weed competition. The interaction of the attributes seed mass, root: shoot ratio and root length, explained 93% of the variation in seedling survival in the field. We concluded that direct seeding of tree species in Cerrado regions can be successful, especially for species with large seeds, deep roots and that invest more in underground structures than in aerial parts, which are functional attributes related to the capacity to survive in conditions of water deficit. Although some species may succeed under weed competition, the control of exotic grasses and ruderal forbs may enable direct seeding for a larger set of species.
In view of the vast and fast degradation to which Brazilian Cerrado has been submitted, it is of great importance to find adequate restoration techniques to be widely applied. There are currently ecological and technological challenges for the restoration of the cerrado vegetation, such as the presence of invasive alien species, the prolonged dry season, the difficulty to obtain seedlings of native species in nurseries and the lack of knowledge to choose suitable species for each restoration technique. Understanding the performance of different tree species in direct seeding and the interactions between weeds and native grasses is highly relevant to overcome the mentioned obstacles. The objectives of this study were: (i) to evaluate the performance of native tree species in direct sowing, in search for functional patterns related to this performance, (ii) to verify if the consortium of native grasses with tree seeds can help in weed control, positively influencing the performance of tree species, and (iii) to verify if the native grasses are able to inhibit weeds colonization and development (competition). We set up a factorial experiment in blocks with the following levels of variation: 1) species (11); 2) weed control (yes or no) and 3) consortium with a mix of six native grasses (yes or no). The experiment totalled 110 plots of 4 m2 each, distributed in the 5 blocks. In each plot we sowed 100 seeds of an arboreal species, in rows, with 20 cm between seeds. We counted the number of arboreal individuals emerged and dead at 10, 20 and 30 days after sowing; and then at the end of both the dry season and the rainy season. After one year from sowing, we measured stem height and diameter of the surviving individuals, and estimated the percentage of ground cover by native grasses and weeds per plot. In addition, we measured the length and quantified the dry aerial and belowground biomass of 11 individuals of each tree species and we estimated the costs for direct seeding. We observed a difference in performance among treatments for some species that were adversely affected by weed competition. The species Dipteryx alata, Hymenaea stigonocarpa and Plathymenia reticulata had the highest average survival rates (over 60%) and the two species of the genus Stryphnodendron had the worst performances (around 20%). The presence of native grasses did not benefit any tree species nor inhibit colonization and development of weed competition. The interaction of the attributes seed mass, root: shoot ratio and root length, explained 93% of the variation in seedling survival in the field. We concluded that direct seeding of tree species in Cerrado regions can be successful, especially for species with large seeds, deep roots and that invest more in underground structures than in aerial parts, which are functional attributes related to the capacity to survive in conditions of water deficit. Although some species may succeed under weed competition, the control of exotic grasses and ruderal forbs may enable direct seeding for a larger set of species.
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Palavras-chave
Restauração ecológica, Cerrado, Sementes, Árvores, Gramíneas nativas, Competição, Atributos funcionais, Ecological restoration, Cerrado, Seeds, Trees, Native grasses, Weed competition, Functional traits