Site conditions for regeneration of climax species, the key for restoring moist deciduous tropical forest in Southern Vietnam

Abstract

Understanding the requirements and tolerances of the seedlings of climax species is fundamental for tropical forest restoration. This study investigates how the presence and abundance of seedlings of a previously dominant, now threatened species (Dipterocapus dyeri Pierre), varies across a range of environmental conditions. Dipterocapus dyeri seedling abundance and site characteristics were recorded at 122 observation points (4 m 2) at nine clusters from two sites. Seedling presence (p = 0.065) and abundance varied significantly (p = 0.001) between the two sites, and was strongly correlated with adult D. dyeri dominance and lower soil pH, and weakly correlated with canopy openness and total stand basal area. Dipterocarpus dyeri seedlings were also grown in shade houses with three light levels on two soils. Seedling survival was significantly lower at the lowest light level (<10% full irradiance) at 13% for the forest soil and 25% for degraded soil. At higher irradiance the seedling survival rates were greater than 99%. Moisture levels remained high at the lowest light level and many seedlings died from fungal infection. We concluded that secondary forests which contain adequate numbers of adult D. dyeri as seed sources, light availability, soil pH of < 5.0, and good drainage strongly favour survival and growth of D. dyeri seedlings. Historically, D. dyeri was dominant in moist deciduous tropical forest across southeastern Vietnam, but today it is rare. Active management of these recovering forests is essential in order to recover this high-value, climax forest species.

Regeneration failure and seedling growth of Dipterocarpus gracilis, a vulnerable dipterocarp in a tropical monsoon forest in Central Java, Indonesia

“…The D. gracilis is also a large-seeded tropical climax species with recalcitrant seeds, indicating that it is shade-tolerant. Furthermore, our finding also supported a previous study that concluded that the Dipterocarpus with latesuccessional tropical seedlings is the most shade-tolerant genus in Dipterocarpaceae family (Do et al 2020).…”

“…Inbreeding depression can occur in Dipterocarpaceae at all stages of development, including seed formation and germination, seedling development, and sapling establishment (Tsumura 2011). On the other hand, the dry soil, high temperature, and increased water loss through extensive leaf areas of the seedling of particular species are likely to be disadvantageous in wide canopy gaps (O'Brien et al 2013;Do et al 2020), as also indicated in this study. Furthermore, being intolerant to water stress, Dipterocarpus spp., a C3 plant (Raes et al 2014), has low photosynthetic efficiency.…”

“…Plants require water, nutrients, and light to grow and survive (Do et al 2020). Previous research by Queenborough et al (2009) showed that the natural regeneration of plant community is influenced by a variety of environmental factors.…”

Floristic composition and diversity at Keruing (Dipterocarpus spp.) habitat in Tangkahan, Gunung Leuser National Park, Indonesia

“…The heavy, dense canopy and lack of parent trees are thought to be the cause of the small number of this keruing in the seedling stage. Do et al (2020) found substantial mortality for D. kerii seedlings at low light intensity. Another study on D. alatus conducted by Dongsansuk et al (2020) showed the high survival of seedlings on 50% light intensity compared to 10%, 30%, and 100%.…”

“…According to Steur et al (2020), the presence of local light variation may influence the growth and abundance of herbaceous layers, young trees, and seedlings. Furthermore, Do et al (2020) also stated that the forest canopy density influences the availability of forest floor light and varies over time as the forest develops. In old-growth tropical forests, light competition significantly impacts seedling's recruitment (Born et al 2015).…”