Less is more: Little seed processing required for direct seeding in seasonal tropics

Abstract

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.

Direct seeding versus seedling planting: survival, biomass, growth, and cost up to 6 years for four tropical seasonal tree species

“…The survival of species planted via DS was relatively high when compared with SP. Other studies conducted in the seasonal tropics have shown high survival rates of DS (Pellizzaro et al 2017; Silva & Vieira 2017; Correia et al 2022) as well as of SP (Navarro‐Cerrillo et al 2011; Scaloppi & de Souza 2020). The lower survival in SP of As.…”

“…Mortality was very low in the DS (7%) when compared to other studies conducted in the seasonal tropics (33% in Silva & Vieira 2017; 23% in Pellizzaro et al 2017; 55% in Souza & Engel 2018). This high survival rate can be explained by the careful measures taken for seeding (Shaw et al 2020; Correia et al 2022), and by managing the invasive plant incidence since the start of the experiment. Overall DS survival rate was 29% higher in plots where exotic grasses were eliminated, when compared to control, for 10 species of savanna (Passaretti et al 2020), and 44% higher for 7 species (Pereira et al 2013).…”

“…Seed batches with low viability, the loss of seeds to desiccation, or the low survival of newly emerged seedlings can result in a low efficiency of the method (Meli et al 2018; Souza & Engel 2018). These issues can, nevertheless, be avoided by storing the seeds in adequate conditions, performing good soil preparation, seeding at times when soil moisture conditions are favorable, avoiding laboratory pretreatments of seeds, which may expose them to extreme field conditions, laying the seeds at adequate depths, and by managing invasive plants after planting (Sampaio et al 2019; Shaw et al 2020; Correia et al 2022). Following these guidelines, DS was the most cost‐effective alternative for three of the four studied species.…”

“…Seeds can suffer especially in the emergence phase, due to predation, desiccation, or laying in inappropriate microsites or times (Woods & Elliott 2004; Doust et al 2006). In recent years, the DS method has been enhanced to overcome bottlenecks in the emergence phase, for example, studies have investigated the ideal seeding depth (Doust et al 2006; Shaw et al 2020); others have shown that many species are negatively affected by pregerminative treatments (Ten Brink et al 2020; Correia et al 2022). Recent research has also investigated the application of mulch to attenuate temperature and moisture oscillations (Silva & Vieira 2017), and developed protocols for seeding at optimum times to ensure adequate soil moisture (Grossnickle & Ivetić 2017; Shaw et al 2020).…”

Physical seed damage, not rodent's saliva, accelerates seed germination of trees in a subtropical forest

“…Larger seeds typically have more stored energy and water, which can lead to higher germination rates and faster emergence (Baskin & Baskin, 2014). Seeds with low moisture content and those with protective coats are more likely to germinate successfully due to their ability to avoid dehydration in hot and dry seeding sites (Correia et al., 2022; Dias Laumann et al., 2023). Thick seed coats can protect seeds from harsh environmental conditions but can also impede water uptake and gas exchange, potentially delaying or preventing germination (Bewley & Black, 2013).…”