Effectiveness of passive restoration on density and diversity of regenerating tree species in mixed Dipterocarp forests of Nepal

Abstract

In many developing countries, the only affordable approach to recover ecosystem structure and function is through passive restoration. We conducted a 3 year study of passive restoration in mixed Dipterocarp forests dominated by Shorea robusta to examine the effectiveness of exclusion (fencing and fire suppression) on diversity, density, and richness of regenerating tree seedlings and saplings. We analyzed excluded and disturbed paired sites. We observed exclusion was effective in increasing seedling richness and occurrence of S. robusta and Syzygium cumini. A significant improvement in sapling strata (diversity, density, and richness) from excluding the disturbances was observed. Mean sapling density estimated was about 500% higher in excluded compared to disturbed sites. Probability of occurrence of S. robusta and Dalbergia latifolia saplings increased due to exclusion. That said, presence of exotic species Chromolaena odorata was higher in excluded sites reflecting the need for assisted natural regeneration in forests. This study has demonstrated passive restoration as an effective approach for improving natural regeneration in mixed Dipterocarp forest ecosystems and possibly other similar forest types, and will serve as a reference document for future restoration interventions. Implications for Practice• Passive restoration can be a suitable strategy to reestablish health and integrity of degraded Dipterocarp-dominated forests which have supported biodiversity and livelihood of millions of households in many south and southeast Asian countries. • Seedling to sapling development transition in Shorea robusta mixed forests can be crossed within a short period of regulating livestock and suppressing surface fire. • Without assistance to natural regeneration, undesirable weeds and exotic species can create a problem in growth and development of mixed Dipterocarp forests.

Impacts of Livestock Grazing on Vegetation and Soil in Lowland Grassland Ecosystem of Nepal

“…Calleja et al, (2019) reported that livestock grazing had very low impact on shrub encroachment as it was observed that the cattle prefer herbaceous plants to woody species. Similarly, consistent with the results of Sapkota and Stahl (2018), invasive species richness was found higher at low grazed area despite having no significant difference in species diversity with high grazed area (Fig. 4 and Fig.…”

Participatory active restoration of communal forests in temperate Himalaya, India

“…Failure of natural regeneration of planted species other than bamboo in the trial area likely reflects dispersal and soil propagule bank limitations and the lack of safe sites in shallow soils on steep and dissected slopes, with long histories of anthropogenic disturbances (Adnan & Holscher 2011; Semwal et al 2013). A 20‐year period of restoration may be too short to catalyze passive restoration of economic species in temperate Himalaya, unlike tropical Himalayan foothills (Sapkota & Stahl 2019) and other eco‐regions (Meli et al 2017 a ). Active restoration is expensive, but may be a necessity for securing the participation of people desiring early material benefits and high income (Nguyen et al 2015; Holmes et al 2017; Wang et al 2019).…”