Critical factors affecting seed dispersal and germination of invasive alien 𝘙𝘰𝘴𝘢 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 in the eastern Free State

𝘙𝘰𝘴𝘢 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 L. (Rosaceae) is a common woody plant invader in the grassland biome of South Africa. It is originally from Eurasia and is classified as a category 1b invader in South Africa under the National Environmental Management: Biodiversity Act, 2004. This act prohibits the planting or harvesting of this species in South Africa. However, the impacts of 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 on the environment and economy are complex, with both positive and negative effects that warrant further investigation. The objectives of this study were to investigate (1) various aspects of the reproductive ecology of 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢, including fruit and seed production, the abundance and viability/longevity of seeds in the soil seed bank, and the importance of cold stratification for seed germination; (2) the impact of the seed predator 𝘔𝘦𝘨𝘢𝘴𝘵𝘪𝘨𝘮𝘶𝘴 𝘢𝘤𝘶𝘭𝘦𝘢𝘵𝘶𝘴 wederus (Hymenoptera: Torymidae) on 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 seeds; and (3) the potential for 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 to facilitate woody invasions into the grassland biome of South Africa. This study showed that for invading populations of 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 on farms outside Clarens in the Free State of South Africa, seed germination successis low. An overall percentage of 1.25% of seeds exposed to cold stratification were observed to germinate within 24 months, while no seeds germinated from the control treatment (seeds stored at ambient temperature for the same amount of time) or from seeds collected every two weeks from the field. Seeds buried in material bags and having been exposed to soil ambient temperature in the soil, however, showed high levels of viability (90%), decreasing to only 83% after being buried in the soil for 17 months. Significantly more seeds were found in the soil under the 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 canopy, compared to 2 and 8 m away from the parent shrub. The maximum number of fruits produced per shrub was 1 950 fruits on a shrub with a volume of 78 m³‏, while the minimum number of fruits produced was 118 fruits by a shrub with a volume of 5 m³. On average, 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 shrubs in the studied populations had an average (± standard error) volume of 25 ± 3 m³, produced an average of 480 ± 57 fruits per shrub, and fruits produced an average of 18 seeds per fruit. The potential of 𝘔𝘦𝘨𝘢𝘴𝘵𝘪𝘨𝘮𝘶𝘴 𝘢𝘤𝘶𝘭𝘦𝘢𝘵𝘶𝘴 to limit the spread of 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢, and the proportion of seeds predated by the wasp was assessed. One hundred rosehips were randomly collected every month from March until September 2021. Only a total of 148 𝘔. 𝘢𝘤𝘶𝘭𝘦𝘢𝘵𝘶𝘴 emerged from some of the 700 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 fruits, giving an overall percentage of 1.28% of seeds predated. This showed that the seed predator 𝘔. 𝘢𝘤𝘶𝘭𝘦𝘢𝘵𝘶𝘴 does not have a large impact on the number of seeds entering the environment, produced by 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 shrubs. Differences in woody plant (> 10 cm height) diversity and abundance were assessed under three treatments: 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 canopy, 𝘓𝘦𝘶𝘤𝘰𝘴𝘪𝘥𝘦𝘢 𝘴𝘦𝘳𝘪𝘤𝘦𝘢 Eckl. & Zeyh. (native) canopy, and open plots of herbaceous grassland (control), to assess if 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 acts as a nurse plant and facilitates the recruitment of woody plant species. This study showed that 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 had a more significant nurse plant effect compared to both 𝘓. 𝘴𝘦𝘳𝘪𝘤𝘦𝘢 and open grassland (control), facilitating the establishment of both native and invasive species. There were significantly more native species than invasive species under all three treatments. Furthermore, more invasive species (13 species) were recorded growing under 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 compared to both 𝘓. 𝘴𝘦𝘳𝘪𝘤𝘦𝘢 (11 species) and in the control plots (11 species). Shrub size also affected the number of plant species recorded underneath each focal species with larger shrubs having more woody plant species underneath. To investigate if 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 is creating a different microclimate under its canopy, two temperature and light loggers were placed under 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 shrubs and in open grassland. This showed that plants under 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 experienced both lower average temperatures and light intensity (14.6 ºC, 3940.5 lux respectively) while open grassland sites experienced both a higher average temperature and more light (17.7 ºC, 17544.36 lux respectively). Thus 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 created a different microclimate compared to open grassland. This study provides valuable insights into the reproductive ecology of 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢, a species that has significant impacts on the environment and economy in South Africa. This study showed that cold stratification is needed for 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 seeds to germinate and 𝘔. 𝘢𝘤𝘶𝘭𝘦𝘢𝘵𝘶𝘴 has a poor limiting potential on 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢. Furthermore, 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 shrubs have been shown to produce many fruits, each of which have many seeds and these seeds can stay viable in the soil for a long time. 𝘙𝘰𝘴𝘢 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 is demonstrated to act as a nurse plant to both native and invasive species when compared to both native 𝘓. 𝘴𝘦𝘳𝘪𝘤𝘦𝘢 and control sites, since it accommodates more seedlings of native species than invasive species when compared to both treatments. However, more research is needed to fully understand the complex relationships between 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 and other plant species and investigate more effective potential biocontrol agents to further slow the spread of 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 in South Africa. The experiments conducted here will add to the current knowledge of 𝘙. 𝘳𝘶𝘣𝘪𝘨𝘪𝘯𝘰𝘴𝘢 here in South Africa, aiding in determining the stage that is most feasible for their management.