A B S T R A C TDirect seeding is a potential technique to restore forests; however, further studies are needed before its application on a large scale. We carried out a field experiment in a deforested area in southern Brazil to test the technical and economic feasibility of a direct seeding system with high tree species diversity to restore the tropical seasonal forest. We also compared species performances and tested the effects of seed size and successional group on tree seedling emergence and development. The trial was established at two different sowing times using 31 tree species. For two years after sowing we evaluated seedling emergence, establishment, survival and early growth of tree species, weed competition and costs for plantation establishment and early maintenance. Most species had low seedling emergence and establishment, but high survival rates, implying that low seedling emergence is the main barrier to community assembly that must be overcome. The most successful species had larger seeds, belonged to non-pioneer categories and had slower growth rates. Final costs after two years were lower than has been reported in the literature for most restoration planting using seedlings both in Brazil and elsewhere; however, seedling density was low. Although direct seeding may be a feasible alternative to decrease planting costs, the poor species performances and low seedling density may reduce its applicability. Thus, we recommend direct seeding only in association with the planting of pioneer species seedlings.
O conhecimento da incerteza de uma medida é crucial para obter conclusões a partir de resultados experimentais. Erros aleatórios, comuns em experimentos, produzem uma distribuição dos valores medidos que segue o formato gaussiano. Neste trabalho desenvolvemos uma montagem baseada no fenômeno de queda livre para auxiliar na ilustração do conceito de incerteza em medidas. Os tempos de queda de um objeto foram obtidos automaticamente pela placa Arduino e exibidos na forma de um histograma na tela do computador. A visualização do histograma foi feita em tempo real e permitiu verificar o aparecimento do aspecto gaussiano à medida que repetições do experimento eram realizadas.
Direct seeding has been suggested to be a highly cost‐efficient system for forest restoration but is still not applied on a large scale worldwide. Thus, to improve the knowledge surrounding the application of this system, I conducted a global bibliometric analysis about forest restoration by direct seeding. Based on a literature search of three online databases (Web of Science, Scopus, and Google Scholar), I found 81 peer‐reviewed articles related to field experiments testing direct seeding for forest restoration. Each article was analyzed according to the following aspects: publication years, countries, continents, forest types, stages of restoration, journals, and authors. The results showed an increase in the number of articles published in recent years but a still low number of studies conducted to test the application of the system. These included field studies from a number of tropical and temperate countries worldwide, with a concentration of studies in Brazil and United States. Monitoring forests established by direct seeding is rare. A few researchers have paid special attention to the development of the field, and a few journals have published three or more articles on this topic. Overall, this study concludes that the application of direct seeding for forest restoration is a promising area for research, as the field is still little studied and has great potential to help achieve restoration goals. Furthermore, the results show trends and gaps that should be considered in future research to improve the application of direct seeding around the world.
Although direct tree seeding may be a potentially useful restoration practice, many biotic and abiotic barriers prevent seedling emergence and early development, reducing its success and applicability. To overcome these barriers, we undertook a field experiment to test the effects of using green manure and hydrogel alone, or in combination, on seedling performances of 14 native tree species that were planted by direct seeding in a deforested tropical seasonal forest area in southern Brazil and to examine how green manure affected the initial weed coverage in the study plots. We evaluated competing vegetation coverage and tree seedling emergence and early development for 2 years after sowing. Weed infestation was significantly higher in the experimental plots with no green manure; however, neither green manure nor hydrogel improved tree seedling emergence and early development at any time of measurement. Our results suggest that the use of green manure and hydrogel alone, or in combination, were not effective in guaranteeing direct seeding success; however, green manure can be an effective method to reduce weed infestation. Direct seeding techniques for tree species still need to be improved in order to restore tropical seasonal forests on a larger scale.
Testing techniques to reduce weed infestation is a crucial step in developing direct tree seeding systems. The use of pre-emergence herbicides may be an alternative to manual weeding techniques, but so far, information on how they affect the seeds of native tree species is scarce. We established a greenhouse experiment to evaluate the effects of four preemergence herbicides (atrazine, diuron, isoxaflutole and oxyfluorfen) on weed suppression and seedling emergence and early growth of seven tropical forest tree species (Annona coriacea Mart., Citharexylum myrianthum Cham., Cordia ecalyculata Vell., Peltophorum dubium (Spreng.) Taub., Psidium guajava L., Pterogyne nitens Tul. and Schinus terebinthifolia Raddi). The experimental design was a randomized complete block design with five treatments and five replicates. The treatments consisted of a single dose of each pre-emergence herbicide and a control. Throughout the 60 days after sowing we evaluated weed cover and seedling emergence and early growth of tree species. Overall, our results suggest that all tested herbicides reduced weed cover; however, they also negatively affected tree species seedling emergence. Of the four herbicides tested, atrazine and diuron showed the greatest effects on tree seedling emergence, oxyfluorfen was least aggressive towards native species and isoxaflutole was most effective in weed control. Native tree species varied in their responses to herbicides, indicating that future experiments should increase the number of species tested as well as investigate how seed traits can affect the species responses to different herbicides.
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