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

Direct seeding as a recruitment alternative for the threatened tropical palm Syagrus coronata (Mart.) Beccari in Brazilian dry forest

Habitat loss reduces biodiversity and threatens ecological services. The use of techniques for vegetation restoration such as direct seeding seems promising, mainly because it reduces costs and labor. The aim of this study was to investigate which are the main ecological filters that can inhibit the success of direct seeding, using Syagrus coronata (Mart.) Beccari (Arecaceae), a species that has great ecological and extractive importance for the Brazilian semi-arid region, and is found in habitats with different management intensities. The following hypotheses were tested: (1) managed habitat (pasture) and natural habitat (caatinga vegetation) show differences in seed fate; and (2) defleshed fruits will have greater seed germination success compared to not defleshed. Seed fate was evaluated for two consecutive years, year I (2016-2017) and year II (2017-2018). Within these years, 800 mature fruits were buried along 300 m transects, half with defleshing treatment, and monitored during 240 days. The highest seed survival occurred in year II, this result may be associated with higher rainfall recorded during the experiment, considering that there was no difference in seed germination between habitats. Defleshing facilitated germination and reduced insect predation, likely by removing invertebrate larvae before they have reached the seed. Desiccation was the major cause of mortality in the entire study and was higher in the managed habitat. Water insufficiency may have caused the deactivation of antioxidant mechanisms and affected the embryo. Although defleshing may favor germination, this procedure would not be indicated for pastures as it favors desiccation. The study showed how habitat management and fruit defleshing can affect seed fate. More studies on ecological relationships need to be carried out to increase understanding of how habitat modification affects the functioning of arid ecosystems.

Restoring Mexican Tropical Dry Forests: A National Review

Deforestation is the dominant threat to tropical dry forests (TDFs) in Mexico. Its causes include agriculture, tourism, and mining. In some cases, unassisted forest regeneration is sufficient to return diverse forest cover to a site, but in other cases, changes in land use are so severe that active restoration is required to reintroduce tree cover. The ecological and social constraints on TDF restoration in Mexico are poorly understood. To address this knowledge gap, we synthesized relevant restoration literature for Mexico published between January 1990 and February 2020. We examined 43 unique articles about TDF restoration practices in Mexico to identify (1) the national distribution of TDF restoration projects, (2) restoration objectives, and (3) factors contributing to TDF restoration success or failure. The largest number of restoration sites were in the Yucatan Peninsula, and the most common objective was to restore dry forest vegetation on lands that had been used for agriculture or impacted by fires. Planting seedlings was the most widely reported restoration strategy, and plant survival was the most frequently monitored response variable. Maximum annual temperature and the Lang Aridity Index were the best predictors of plant survival, which ranged from 15% to 78%. This synthesis highlights how national restoration inventories can facilitate the development of a restoration evaluation framework to increase the efficacy of restoration investments.

Early establishment and survival of the neotropical dry deciduous forest treeLysiloma microphyllumfrom mountainous Bajio Queretano, Mexico

The tropical dry deciduous forest (TDF) of the semi-arid region of Bajio in Mexico is dominated by successional communities, in whichLysiloma microphyllumis irregularly distributed, however the environmental factors influencing its establishment have been poorly studied. We conducted field experiments to isolate the impact of three factors on the early life-history stages of this tree. Over a 2-y period, we monitored the effects of (1) predation, (2) understorey light and (3) aspect on germination, seed-to-seedling transition (establishment) and seedling survival, and we found that open space negatively affected germination (14.9 ± 1.5% vs 96 ± 1.5% in shade; mean ± SE), while shade increased seedling establishment and survival (36.9 ± 8.2% vs 4.7 ± 3.8% in open sites). Predation decreased survival and was strongest in open conditions (0 vs 62.7 ± 9.4% in shaded exclosures). In contrast, aspect had little influence on germination and survival. The results suggest that shaded microsites positively affect the early life stages ofL. microphyllum, a key process in TDF recovery.