Aspects of the ecology of Sarcopoterium spinosum in the Maltese islands

Abstract

The main aim of this study was to observe the size and spatial distribution of Sarcopoterium spinosum in Pembroke, Malta, and eventually create a population model based on the population-level data gathered during its reproductive cycle, that is, the number of inflorescence, fruiting rate, seeding rate, germination and seedling survival. The foundation of this study required a preliminary survey of the Pembroke Special Area of Conservation, in order to locate all the shrubs that make up the S. spinosum population. The survey was also required to determine what other plant species were present and define their life-form accordingly, so as to understand any interspecific competition that ensues. In total, eight shrubs were located and their size parameters and spatial distribution were measured. One of the shrubs (Cluster C), which had the largest parameters, was assumed to be made up of various individuals. Its central position within the population indicated that this particular cluster is perhaps the parent plant, and the other shrubs were all established seedlings that resulted through seed dispersal. Every individual showed successful flowering and fruiting, which ultimately led to the production of a great number of seeds. Germination of S. spinosum seeds occurred at 15˚C in conjunction with 12 hours of irradiance. The average germination rate was 20%, with germination being higher in those seeds that had their spongy tissue removed. Moreover, no relationship between seed size and germination was found. The germinated seeds were transferred to pots in hopes of establishing seedlings, however all samples died within a week. A population model was created using the flowering rate, fruiting rate, seeding rate and germination. The seed mortality and recruitment values were not known, nonetheless, in an ideal scenario, 30,784 new plants would be recruited after each reproductive cycle. Noticeably, this number is very high, however, the fact that no seedlings were recorded in this study also indicates that a factor must be restricting seedling establishment. S. spinosum is able to reproduce vegetatively by producing ramets, and this might be the reason why it still persists in Malta. In conclusion, this study has significantly contributed to quantifying and describing the Maltese S. spinosum population, but the population model may only be used qualitatively to describe and understand the pathway to seedling recruitment.