Seed dispersal limitation causes negative legacy effect on restoration of grassland plant diversity on ski slopes

Past forest use often has a long-term negative impact on the recovery of the original plant composition of semi-natural grasslands, which is known as a legacy effect. This study investigates the impact of seed dispersal limitations on the restoration of grassland plant diversity on ski slopes with past forest use, highlighting the negative legacy effect on biodiversity recovery. Focusing on ski areas, our research contrasts the vegetation on ski slopes originally created on semi-natural grasslands such as pasture (pasture slopes) and constructed by clearing secondary forests or conifer plantations (forest slopes). We examined species richness and diversity, considering seed dispersal modes, grassland management history, and seed source proximity. We reveal that the proximity to species-rich grassland sources is pivotal for the restoration of native grassland vegetation. Particularly, wind-dispersed species show significant recovery on slopes with sustained management for more than 70 years and those with neighboring species-rich grasslands, suggesting that both the duration of management and the proximity to seed sources are critical for overcoming the legacy effects of past forest use. Meanwhile, gravity-dispersed species failed to recover their richness and diversity regardless of both the duration of management and the proximity to seed source grasslands, which their diversity recovered where seed sources neighbored. Our findings emphasize the importance of considering seed dispersal limitation and management history in the restoration and conservation of grasslands and their biodiversity, particularly in landscapes experiencing past human intervention.

Abandoned Croplands: Drivers and Secondary Succession Trajectories under Livestock Grazing in Communal Areas of South Africa

Cropland abandonment has been happening in different parts of the world and is being driven by socio-economic, ecological, edaphic, and environmental factors. Most of the research focusing on drivers of cropland abandonment, succession trajectories, and responses to active restoration initiatives has been conducted in the republic of Nepal and regions such as Europe and America. In South Africa, the impact of cropland abandonment on household livelihoods, changes in vegetation and soil properties, and soil seed bank statuses have been conducted mainly in the Eastern Cape Province. The drivers of cropland abandonment in South Africa are like those observed in other countries, except for a few, which are country-specific such as poor support of communal farmers compared to their counterparts in the highly mechanised commercial farming sector. There is also a shift from low input cropping in the distant fields to high input cultivation in homestead gardens. Research results elsewhere suggest a woody growth suppressive effect of grazing, particularly average grazing intensities, being crucial in suppressing woody proliferation while high grazing intensities are detrimental to herbaceous species’ richness and promote woody species’ encroachment. A combination of fire and grazing alters the natural succession trajectory by promoting fire-tolerant species and arresting woody species. Similar to other countries, cropland abandonment is associated with colonisation by alien invasive species which are favoured by cropping legacies, such as altered soil levels of pH, Nitrogen, and phosphorus. Furthermore, limited moisture in semi-arid areas promotes the encroachment of indigenous woody species. Secondary succession in abandoned croplands can be manipulated for the benefit of livestock production in communal areas by introducing management strategies that will discourage encroachment by both invasive and indigenous woody species which lowers the grazing capacity. Furthermore, active restorative practices, such as reseeding with indigenous mid succession perennial grasses and legumes, will improve forage quality in abandoned croplands. Our understanding of succession trajectories under various unique disturbance regimes experienced in South Africa, such as communal grazing of abandoned croplands, compared to situations in other parts of the world is limited. Furthermore, the influence of other factors such as fire, soil fertility, and moisture needs to be understood.

Large sample area and size are needed for forest soil seed bank studies to ensure low discrepancy with standing vegetation

A large number of small-sized samples invariably shows that woody species are absent from forest soil seed banks, leading to a large discrepancy with the seedling bank on the forest floor. We ask: 1) Does this conventional sampling strategy limit the detection of seeds of woody species? 2) Are large sample areas and sample sizes needed for higher recovery of seeds of woody species? We collected 100 samples that were 10 cm (length) × 10 cm (width) × 10 cm (depth), referred to as larger number of small-sized samples (LNSS) in a 1 ha forest plot, and placed them to germinate in a greenhouse, and collected 30 samples that were 1 m × 1 m × 10 cm, referred to as small number of large-sized samples (SNLS) and placed them (10 each) in a nearby secondary forest, shrub land and grass land. Only 15.7% of woody plant species of the forest stand were detected by the 100 LNSS, contrasting with 22.9%, 37.3% and 20.5% woody plant species being detected by SNLS in the secondary forest, shrub land and grassland, respectively. The increased number of species vs. sampled areas confirmed power-law relationships for forest stand, the LNSS and SNLS at all three recipient sites. Our results, although based on one forest, indicate that conventional LNSS did not yield a high percentage of detection for woody species, but SNLS strategy yielded a higher percentage of detection for woody species in the seed bank if samples were exposed to a better field germination environment. A 4 m2 minimum sample area derived from power equations is larger than the sampled area in most studies in the literature. Increased sample size also is needed to obtain an increased sample area if the number of samples is to remain relatively low.