Ecology of seed and seedling growth for conservation and restoration of tropical dry forest : a review

Abstract

Dry forests are among the most threatened ecosystems and have been extensively converted into grasslands, secondary forest, savanna or agricultural land. Knowledge of seed germination and seedling establishment is required for the success of efforts on restoration of these forests. This review focuses on the ecological requirements at seed and seedling stages, and collates the current knowledge of seed viability, dormancy, germination pattern and seedling behaviour of dry tropical tree species. The spatio-temporal variations within the tropical dry forest biome in soil moisture, light, temperature, nutrients and intensity of predation, significantly affect the seed and seedling traits of component species. The majority of dry tropical species possess orthodox seeds which are characterized by dormancy, while a few have recalcitrant seeds which possess little or no dormancy. Seed coat dormancy, which can be overcome by mechanical or acid scarification or sometimes by transit through animal guts, is most prevalent in the dry tropical forest species. Persistent species dominating the undisturbed portions of the forest have bigger seeds compared to those that mostly occur in disturbed regions and require shade for the survival of their seedlings. Shade demand is associated with drought endurance, and may be absolute in species such as Guettarda parviflora and Coccoloba microstachya, or facultative as in Plumeria alba and Bursera simaruba. The fluctuation in temperature significantly affects seed germination in several species of dry Afromontane forest trees of Ethiopia. Seedling mortality is primarily a function of moisture stress during the dry period. Adaptive responses of seedlings to drought stress include increased chlorophyll content, for example in Acacia catechu, and root biomass, as in several dry forest species (for example Drypetes parvifolia, Teclia verdoornia) of Ghana. Mulching, application of fertilizers, interplanting of leguminous species and mycorrhizal inoculation are useful tools for promoting seedling establishment in nutrient-poor dry tropical soils. Periodic forest fires, and predation affect recruitment and seedling development according to their intensity. Many species experiencing frequent fires have evolved thick seed coats, produce fire-hardy seedlings, or escape the effect by temporal separation of seed dispersal and fire events. Predation may result in abortion of fruits or may enhance germination and recruitment by scarification and dispersal, as in most species of the Guanacaste dry forest. Exposure to elevated CO 2 has increased relative growth rate, total leaf area and water use efficiency in most of the dry tropical seedlings tested, but the magnitude of the effect has varied markedly among species. Due to the availability of a large source of energy, large seeds show higher germination percentage, greater seedling survival and increased growth. Seeds originating from different provenances exhibit differences in germination and seedling growth (for example Prosopis cineraria, Albizia...

Germination of <i>Cola anomala</i> (K. Shum.) Shott and Endl seeds: effects of provenance, substrate and dehydration

“…Some of this variation has been suggested to be of genetic origin (Bischoff et al, 2006), but much of it is known to be phenotypic, caused by the local conditions under which the seed matured (Cedan et al, 2013). Indeed, germination characteristics are not only affected by the current environmental conditions but also by conditions experienced by the mother plants in the previous generation (Khurana and Singh, 2001;Fenner and Thompson, 2005). Nevertheless, it cannot be concluded from the present study which factor (topographic or climatic characteristics of locations or genetic characteristics of mother trees) caused the provenance-related variation in Cola anomala seeds germination.…”

Environmental Factors Influencing Tree Species Regeneration in Different Forest Stands Growing on a Limestone Hill in Phrae Province, Northern Thailand

“…Light and soil moisture jointly regulate seed germination, seedling establishment, and seedling survival in tropical forests (Khurana and Singh 2001). Soil moisture availability is influenced directly by rainfall, which is highly seasonal in dry tropical forest ecosystems (McLaren and McDonald 2003).…”

“…Soil moisture availability is influenced directly by rainfall, which is highly seasonal in dry tropical forest ecosystems (McLaren and McDonald 2003). This pronounced seasonality affects the patterns of seed production, germination, and seedling survival and development (Khurana and Singh 2001). Light is often the primary limiting factor for seedling regeneration in tropical lowland rainforests (Gustafsson et al 2016).…”

“…However, dense bedrock in karst landforms enhances the surface soil moisture in the epikarst, thereby contributing positively to the colonization process of tree species and vegetation development in the area (Li et al 2014). Soil moisture likely regulates both seedling establishment and survival, and is a key factor in the initial process of seedling recruitment (Khurana and Singh 2001;McLaren and McDonald 2003). Trejo-torres and Ackerman (2002) indicated that the soil humidity regime, which is related to topography, was more important than geography in promoting floristic links among limestone vegetation communities of the Caribbean.…”

“…Light and soil moisture variables are important for tree species regeneration in tropical forests (Marques and Oliveira 2008). Soil moisture availability is a key factor influencing the growth and survival of plant communities in tropical dry forests (Khurana and Singh 2001). This factor is often the most important among those affecting plant establishment and growth following a disturbance (Yang et al 2011).…”