Potential of Soil Seed Bank and Ungulate-mediated Endozoochory in Old Field Restoration

Soil seed bank plays a key role in old field restoration because it provides information about plant species that may regenerate (Hopfensperger 2007). Most studies on old field restoration have concentrated on floristic similarities between soil seed bank and standing vegetation (Török et al. 2018). However, investigating the effects of proximity to natural/old field edge (habitat fragmentation border) on soil seed bank could yield better recovery predictions. Proximity to natural/old field edge may favour recruitment of a different plant community than that found in the old field interior. This due to favorable abiotic (e.g., soil moisture) and biotic (e.g., seed dispersal) microenvironments created near the edge. On the other hand, ungulate-mediated endozoochory has been shown to potentially facilitate ecological restoration in degraded systems, given that ungulates disperse diaspores across different landscapes (Baltzinger et al. 2019). However, ungulate-mediated endozoochory dispersal in degraded old fields is affected by several factors that include availability of nearby natural perches that attract dispersers, structural vegetation complexities, presence of food especially fruits, and feeding regimes (Baltzinger et al. 2019).

Table 1.

Comparison of seedling density, diversity and richness at various distance from the natural/old field edge. Data are means and ANOVA results are shown. Means with different letter superscripts are significantly different at p < 0.05. OF indicates Old Fields (positive transect direction from edge) and NA indicates Natural Areas (negative transect direction from edge).

This study examined the role of soil seed bank and ungulate-mediated endozoochory on seedling emergency, diversity, and composition in old fields targeted for ecological restoration. The study predicts that: i) proximity to natural/old field edge, which has favourable biotic and abiotic microenvironments, facilitates increased soil seed bank emergence and diversity compared to areas far from the edge into the old field, ii) basic functional traits (feeding regime) facilitate old field seed dispersal by ungulates, meaning seedlings of trees and shrubs will dominate dung of browsers as compared to seedlings of grasses and forbs which are edible by most ungulates. The study is motivated by the need to find an effective old field restoration initiative at Lapalala Wilderness to restore bushveld ecosystem structure and function.

The soil seed bank and ungulate dung were collected in old fields located at Lapalala Wilderness in Limpopo province, South Africa. Vegetation in the reserve is classified as Waterberg Mountain Bushveld, and soils are predominantly sandy (Mucina and Rutherford 2006). Most rain falls in summer (September to April), and temperatures are mild in winter and hot in summer. The old fields where the study was conducted were previously used for tobacco farming 35 years ago but are currently used for wild animal grazing. Three old fields, that share a farm road boundary with adjacent natural areas, were identified in the reserve. The farm road that separated the areas acted as the edge (fragmentation border) for both the natural area and old field. At each of the above-mentioned three sites, five line transects which extended 50 m from the edge into both the natural area (referred to as negative direction [–NA]) and old field area (referred to as positive direction [+OF]), with the edge being zero, were set up. The total number of transects were 30 (five transects × six sites, i.e. three in natural and three in old field area). At each transect, plots measuring 10 × 10 m were set up at distances of 10, 30, and 50 m from the edge into the old fields and at 10 and 50 m from the edge into the natural areas. The expectation was that there would be no marked soil seed bank variation in natural areas to warrant plots at 30 m distance. Within each plot, four soil cores (10-cm diameter × 10-cm depth) were collected from each corner. The four soils were mixed together to form a sample per plot, before being sieved using a 2-mm diameter sieve to remove debris and placed into plastic germination trays measuring 20-cm wide × 20-cm long × 10-cm...