Direct seeding of dry forest tree species in abandoned pastures: effects of grass canopy and seed burial on germination

Abstract

Natural tree regeneration in abandoned pastures can be hampered by various biotic and abiotic filters, including seed removal and predation. We tested the effects of maintenance and removal of grass and seed deposition (buried and unburied) on seed germination of 12 tree species in dry forest pastures. We obtained evidence supporting the hypothesis that seeds attain higher germination under a grass canopy than on bare ground. For most species, grass cover provides safety from seed predators and facilitates germination by providing a suitable microclimate with soil humidity similar to the forest. The hypothesis that buried seeds attain higher germination was not supported by our data. Predation and removal of unburied seeds ranged from 0 to 77 % and, alone or together, were the major causes of non‐germination. Direct seeding is a promising technique for revegetation of recently abandoned pastures in areas originally covered by tropical dry forests. The high germination rate of seeds deposited on the ground and under grass reduces costs during initial restoration stages, potentially facilitating the spread and use of this technique.

Evidence on the Adaptive Recruitment of Chinese Cork Oak (Quercus variabilis Bl.): Influence on Repeated Germination and Constraint Germination by Food-Hoarding Animals

“…However, seedling recruitment and forest restoration are highly affected by some abiotic and biotic factors such as high predation on seeds by animals, periodic drought, soil degradation and lack of seed dispersal [3,4]. The key factors vary greatly among different species and areas [5].…”

“…Many forest seeds are sensitive to desiccation and temperature [7][8][9]. The low soil moisture is responsible for the drought stress in seed germination and also affects the seedling survival [3,10]. Burying the seeds in soil conserves their selected and kept in PVC buckets, and then covered with trace-moisture sand to prevent acorns from dehydration and deterioration.…”

Effects of Clear Polymer Film on Emergence and Survival of Direct Sown Native Vegetation

“…The low rates of emergence irrespective of treatment (range 0-47%, mean 3·6%) are similar to results reported in other direct seeding trials (Ray & Brown, 1995;Madsen & Löff, 2005;Ceccon et al, 2016) and may reflect seed foraging. For example, seed predation of 12 native tree species in Brazil accounted for up to 77% removal of seed in direct seeding experiments in abandoned pastures (Guarino & Scariot, 2014), and vertebrate exclusion treatments increased emergence of some eucalypt species by up to 15-fold (Stoneman, 1993). An experiment performed on the same site found that treating seed with insecticide dramatically increased emergence compared to a control treatment (T. Bailey, unpublished data), suggesting that foraging may have been partially responsible for the poor emergence.…”

“…Improving our understanding for the reasons for low emergence rates is critical to reducing direct seeding costs. Other studies point to seed foraging as a major cause of low emergence following direct seeding (Andersen, 1989;Florentine et al, 2013;Guarino & Scariot, 2014). Better understanding critical temperature and moisture thresholds for target species will also help explain low emergence rates.…”

“…Some of the factors contributing to direct seeding failure may include seed foraging, insufficient soil water availability to support germination and survival, unfavourable germination temperatures and low relative humidity (Andersen, 1989;Banerjee et al, 2006;Guarino & Scariot, 2014). All of these factors are difficult to control in a field situation.…”