The coexistence of grasses, herbs, shrubs and trees characterizes savannas; therefore, to restore such ecosystems one should consider reintroducing all these growth forms. Currently, little is known about field establishment of most ''Cerrado'' (Brazilian savanna) species that could be used for restoration purposes. Most knowledge on restoration is focused on planting seedlings of tree species from forest physiognomies. Alternatively, direct seeding can be an appropriate method to reintroduce plants of different life forms to restore savannas. We evaluated the initial establishment success under field conditions of 75 ''Cerrado'' native species (50 trees, 13 shrubs, and 12 grasses) in direct seeding experiments in four sites in Central Brazil for 2.5 years. For that, we tagged and measured tree and larger shrub species and estimated ground cover by small shrub and grass species. Sixty-two species became established (42 trees, 11 shrubs and 9 grasses) under field conditions. Thirty-eight of the 48 tagged species had relatively high emergence rates ([10%) and 41 had high seedling survival ([60%) in the first year. Among grasses and small shrub species, Andropogon fastigiatus Sw., Aristida riparia Trin., Schizachyrium sanguineum (Retz.) Alston, Lepidaploa aurea (Mart. ex DC.) H.Rob., Stylosanthes capitata Vogel, S. macrocephala M.B.Ferreira & Sousa Costa, Achyrocline satureioides (Lam.) DC. and Trachypogon spicatus (L.f.) Kuntze had the greatest initial establishment success (up to 30% soil cover). The data on harvesting period, processing mode and field establishment for these 75 species can be readily used in restoration efforts in the ''Cerrado''.
Defining the reference system for restoration projects in regions characterized by complex vegetation mosaics is challenging.Here we use the Cerrado region of Brazil as an example of the importance of clearly defining multiple natural and anthropogenically altered states in grassland-savanna-forest mosaics. We define three main, natural vegetation types-grassland, savanna, and scleromorphic (cerradão) forest-to (1) distinguish between original and degraded states and (2) set appropriate targets for and guide restoration. We contend that the differences in Cerrado vegetation composition originally were driven by soil conditions and secondarily by fire frequency and precipitation patterns that differ from the core to the edge of the Cerrado region. Grasslands are found on the shallowest, least fertile soils and/or in waterlogged soils; scleromorphic forests are generally located on deeper, more fertile soils; and savannas occupy an intermediate position. In recent decades, this biophysical template has been overlain by a range of human land-use intensities that strongly affect resilience, resulting in alternative anthropogenic states. For example, areas that were originally scleromorphic forest are likely to regenerate naturally following low-or medium-intensity land use due to extensive resprouting of woody plants, whereas grassland restoration requires reintroduction of grass and forb species that do not tolerate soil disturbance and exotic grass competition. Planting trees into historic grasslands results in inappropriate restoration targets and often restoration failure. Correctly identifying original vegetation types is critical to most effectively allocate scarce restoration funding. Implications for Practice• Land managers and scientists should collaborate to identify the range of natural and anthropogenic states in grassland-savanna-forest mosaics to choose appropriate targets for restoration. • Identifying natural and anthropogenic factors influencing these vegetation types and their degraded states can help guide selection of the most suitable and cost-effective restoration techniques. • The resprouting ability of woody species allows for high resilience under low-intensity disturbance regimes; however, herbaceous native species rarely recover naturally following extensive soil disturbance and exotic grass invasion. • There is an urgent need to improve evidence-based restoration techniques in the Cerrado grassland-savannaforest complex, especially how to control invasive grasses, reestablish soil conditions, and manage fire, since techniques applicable at a large scale are necessary to achieve restoration commitments and targets.The following information may be found in the online version of this article: Figure S1. Map of Brazilian biomes. The Cerrado region (light green) is in central Brazil and borders four different biomes. Figure S2. Photos of the three main Cerrado vegetation types: (A) grassland; (B) savanna, and (C) cerradão (scleromorphic forest). Photos: Bruno M. T. Walter.
Aims:Indicators that can provide information during the early stages of restoration are very useful for predicting restoration outcomes. We posed the following questions: Can savanna restoration outcomes be affected by the initial functional-group composition? Are there functional groups that, when established early, can prevent colonization by invasive grasses, trigger a successful restoration trajectory, and be used as early indicators of restoration success? Methods:We established 110 plots spanning a naturally occurring range of species composition in savanna areas that had been restored through direct seeding. We looked for different initial compositions of the following functional groups: perennial grasses, annual grasses, short-lived shrubs, and invasive grasses. We measured vegetation cover over two years and evaluated the effects of the initial functional composition on the successional trajectory of the plots. Results:The initial dominant functional group determined the assembly trajectory.Short-lived and fast-growing species were replaced by perennial species, indicating a fast species turnover. Invasive grass cover remained stable over time, demonstrating that once they establish and dominate an area, an alternative stable state is achieved. Conclusions:Our results demonstrate the importance of introducing a mixture of functional groups when restoring savannas in severely disturbed areas. Fast-growing and short-lived species are important for quickly covering the ground, creating the conditions for the establishment of perennial grasses that naturally dominate the herbaceous layer of savannas. Trees are also characteristic of the savanna structure and must be introduced. Our results indicate that invasive grasses must be eliminated and/or constantly controlled before native species are introduced. K E Y W O R D Sassembly trajectory, cerrado, direct seeding, functional group, invasive grasses, priority effects, savanna restoration, species turnover, succession 62 |
Seed processing and dormancy break treatments are recommended for rendering seeds restoration-ready. Conversely, fruit structures and seed coats may protect seeds from environmental harm in the field. We evaluated the effects of seed processing (by either keeping fruit structures or extracting seeds) and/or scarification (of physically dormant seeds) on the seedling emergence and establishment of 10 legume tree species from tropical forests and savannas of Central Brazil. We sowed seeds in a greenhouse for reference and in a field experiment conducted in tilled ready-to-seed sites. We monitored seedling emergence and survival for a year. We calculated the costs of harvesting, processing, and pretreating seeds, and considered the final cost of a 1-year-old seedling. Seed extraction resulted in lower emergence for most species in the greenhouse and in the field. It also accelerated emergence of three and four species in the greenhouse and the field, respectively. Scarification resulted in lower seedling emergence in the field for half of the species, while it increased emergence of three species in the greenhouse. Most species presented accelerated emergence both in the greenhouse and the field. The seedling cost was 1.6 to 74.6 times higher when seeds were processed, and 1.3 to 6.0 times when seeds were scarified, except for one species. Keeping fruit structures and seed coats reduced the costs of seeds and increased the success of direct seeding.
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