Phenological observations provide a method to investigate the relationship between climate variation and plant development as well as data for the development and testing of growth and development models. Temperature driven heat unit accumulation has a big influence on plant growth and development and therefore phenological observations of natural plant species can potentially be used to characterize climate. The objectives of this paper are (1) to present 10 years of phenological data for nine natural species growing in a Mediterranean-type climate, (2) to present threshold temperatures that were derived for the computation of growing degree-days (GDD), and (3) to evaluate the sensitivity of the nine natural species to weather variability. The study was conducted at the Phenological Research Garden of Oristano, Sardinia, Italy, during the period 1986-96. The observations were made on five typical species of a Mediterranean-type ecosystem (Pistacia lentiscus, Olea europea, Myrtus communis, Quercus ilex, Spartium junceum) and four species typical of higher latitude. We reported the mean annual pattern of phenological events and the GDD accumulated from 1 January for each development stage. Temperature thresholds were evaluated by comparing the standard deviation in days from the mean number of days for each species. The analysis showed that a complex relationship exists between the timing of phenophase occurrence and environmental conditions, such as temperature and water availability.