Reproductive Ecology of the Invasive Alien Shrub Pyracantha angustifolia in the Grassland Biome, South Africa

Lehlohonolo D Adams; Dino Giovannoni; Vincent R Clark; Sandy-Lynn Steenhuisen; Grant D Martin

doi:10.3390/plants12061308

Reproductive Ecology of the Invasive Alien Shrub Pyracantha angustifolia in the Grassland Biome, South Africa

Plants (Basel). 2023 Mar 14;12(6):1308. doi: 10.3390/plants12061308.

Authors

Lehlohonolo D Adams^{1

2

3}, Dino Giovannoni⁴, Vincent R Clark⁵, Sandy-Lynn Steenhuisen², Grant D Martin^{6

7}

Affiliations

¹ South African National Biodiversity Institute, Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Pietermaritzburg 3209, South Africa.
² Afromontane Research Unit & Department of Plant Sciences, University of the Free State, Phuthaditjhaba 9866, South Africa.
³ Centre for Invasion Biology, Department of Plant Sciences, University of the Free State, Phuthaditjhaba 9866, South Africa.
⁴ Department of Physics, Rhodes University, Makhanda (Grahamstown) 6139, South Africa.
⁵ Afromontane Research Unit & Department of Geography, University of the Free State, Phuthaditjhaba 9866, South Africa.
⁶ Afromontane Research Unit & Department of Zoology and Entomology, University of the Free State, Phuthaditjhaba 9866, South Africa.
⁷ Centre for Biological Control, Department of Entomology and Zoology, Rhodes University, Makhanda (Grahamstown) 6139, South Africa.

Abstract

Knowledge on reproductive traits of problematic invasive alien plants, such as the woody invasive shrub Pyracantha angustifolia of temperate Chinese origin, can help better manage invasive species. To determine factors contributing to its invasion, we investigated floral visitors and pollen loads, self-compatibility, seed set, seed rain, soil seed banks, and seed longevity in the soil. Generalist insects were recorded visiting flowers and all carried pollen loads of high purity (>70%). Floral visitor exclusion experiments showed that P. angustifolia can set seed (66%) without pollen vectors, although natural pollination resulted in higher fruit set (91%). Fruit count surveys and seed set showed an exponentially increased relationship between seed set and plant size with high natural seed yield (±2 million seeds m^-2). Soil core samples revealed a high seed density of 46,400 ± (SE) 8934 m^-2 under shrubs, decreasing with distance away from the shrub. Bowl traps stationed under trees and fences confirmed that seeds were efficiently dispersed by animals. Buried seeds survived for less than six months in the soil. Due to high seed production, self-compatibility augmented by generalist pollen vectors, and effective seed dispersal by local frugivores, it is difficult to manage the spread manually. Management of this species should focus on the short life span of seeds.

Keywords: austral temperate grasslands; insect pollination; non-native shrub; plant reproduction; seed biology.

Grants and funding

The Afromontane Research Unit, University of the Free State, supported Lehlohonolo Adams and Sandy-Lynn Steenhuisen with a master’s bursary and running costs for this project, respectively. The South African Department of Forestry, Fisheries and the Environment (DFFE) is thanked for funding, noting that this publication does not necessarily represent the views or opinions of DFFE or its employees. National Research Foundation—German Academic Exchange Service (DAAD) is acknowledged for Lehlohonolo Adams bursary (Fund number: 117648). The South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation of South Africa provided additional funding. Additional running costs provided by DSI–NRF Centre of Excellence for Invasion Biology (CIB) are acknowledged. Any opinion, finding, conclusion, or recommendation expressed in this material is that of the authors, and the National Research Foundation does not accept any liability in this regard.