Скачать или смотреть Using phenology for long-term ecological observations (SAEON Seminar, Dec 2023)

Presenter: Wynand Calitz (Arid Lands Node)

Title: Using phenology for long-term ecological observations: a case study
from the Karoo.

Abstract:
The importance of climatic conditions on influencing vegetation has been well documented and understanding these effects allow us to make predictions and prepare for future harsh conditions. South Africa is considered to be a mostly arid country but despite its arid status there is still much to learn about species responses to these conditions. The Karoo, which covers 30% of South Africa, is a great place to investigate plant responses to aridity as it experiences severe drought conditions and irregular rainfall. Phenological studies have been used for centuries, particularly in agriculture, and are useful to determine species-level responses to climate among other long-term variations. A previous study of phenology at the Tierberg Karoo Research Centre (now Tierberg Long-Term Ecological Research), focussed on how life form and landscape location influenced growth and flowering. In 2017 SAEON started a new phenological study to investigate the long-term phenology of five plant species (Ruschia spinosa, Osteospermum sinuatum, Pteronia pallens, Drosanthemum praecultum, and Galenia fruticosa). Ten plots with five replicates of each species (250 individuals in total) were observed at least once a month. Over the course of 6 years, including a significant dry period, 35% of individuals had died. The most notable species results were that R. spinosa had no fatalities and that G. fruticosa suffered 86% mortality. We also show the influence of rainfall seasonality on plant phenology. All species showed considerable growth and flowering after good rains irrespective of season, however there are still clear trends in the phenology. All of the observed species flowered in spring with fruits forming near the end of spring and being ripe in summer. There were cases where individuals flowered after rain events, but the flowers would often wilt if the rain was not substantial or was followed by high temperatures. Growth for R. spinosa occurred in small amounts throughout the year but the strongest growth was seen during winter months, particularly when there were good rain. Pteronia pallens had highest growth during the autumn months and D. praecultum during late summer. Galenia fruticosa showed highest growth only after really good rainfall. The O. sinuatum showed the greatest variability in growth, strongly correlated to rainfall events, and even seemingly dead individuals would resprout after rain events. These data are valuable in determining which species are drought-resistant as adult plants, however as no seedling emergence data were collected during the phenology study it cannot inform population ecology of the study species.