Zalika Črepinšek

Impact of Climate Change on Developmental Dynamics of Thrips tabaci (Thysanoptera: Thripidae): Can It Be Quantified?

Abstract We attempt to quantify the impact of future climate change on the developmental dynamics of onion thrips in Slovenia. Monthly averaged results of simulations of future climate from four different general circulation models (GCMs) were projected to local scale by empirical downscaling. The GCM simulations were based on two emission scenarios (IPCC SRES A2 and B2). Local estimates of monthly averaged air temperatures for five locations in Slovenia were adjusted for an additional four emission scenarios (SRES A1T, A1F1, A1B, and B1) using a pattern scaling technique. They were further transferred to a daily scale using a first-order autoregressive model. A simple degree-day model, based on data reported in the literature, was used to relate the development of onion thrips to temperature. Potential changes in the period with favorable developmental conditions for onion thrips (i.e., temperatures above the lower developmental threshold) and in the number of generations per season were estimated with regard to the expected future climate change in Slovenia. The changes are influenced by the magnitude of temperature increase, its asymmetry within the year, and present climate conditions. Using this approach, one can obtain quantitative estimates of the impact of climate change on the developmental dynamics of an insect pest, but one must be fully cognizant of all the assumptions made in the procedure, which introduce uncertainties in the final results. Further research is needed to evaluate the plausibility of such simplified projections.

Shifts in walnut (Juglans regia L.) phenology due to increasing temperatures in Slovenia.

Summary Bud-breaking date (BBD) is one of the most important traits in walnut cultivars for commercial cultivation. In regions with frequent late-Spring frost injuries, BBD affects the stability, quantity, and quality of walnut yield. Due to global warming, shifts in walnut phenology are expected in the future, and the suitability of some cultivars for certain climatic regions may be affected. In the present study, the influence of increasing Winter and Spring air temperatures on BBD was analysed. The late BBD cultivar ‘Franquette’ and the medium BBD cultivar ‘G-139’ were observed over two timeperiods: 1984 – 1990 (P1), and 2000 – 2006 (P2). During P1, the mean air temperature from January to April was 3.7ºC, and the average BBDs were 23 April and 5 May for ‘G-139’ and ‘Franquette’, respectively. During P2, the mean air temperature from January to April increased by 0.9ºC and the BBDs were 3 days (d) earlier for ‘G-139’ and 7 d earlier for ‘Franquette’. Phenological models showed that the mean air temperatures in the preceding 1 – 2 months (TMar and TApr) were important for predicting BBD and, due to increasing temperatures in Winter and early-Spring, BBDs will be shifted to earlier in the year. Depending on walnut cultivar, the average BBD could be advanced by as much as 4 weeks by 2060. Consequently, the frost hazard will probably increase.

Do variations in leaf phenology affect radial growth variations in Fagus sylvatica

We used a dendrochronological and leaf phenology network of European beech (Fagus sylvatica) in Slovenia, a transitional area between Mediterranean, Alpine and continental climatic regimes, for the period 1955–2007 to test whether year to year variations in leaf unfolding and canopy duration (i.e. time between leaf unfolding and colouring) influence radial growth (annual xylem production and tree ring widths) and if such influences are more pronounced at higher altitudes. We showed that variability in leaf phenology has no significant effect on variations in radial growth. The results are consistent in the entire region, irrespective of the climatic regime or altitude, although previous studies have shown that leaf phenology and tree ring variation depend on altitude. The lack of relationship between year to year variability in leaf phenology and radial growth may suggest that earlier leaf unfolding—as observed in a previous study—probably does not cause increased tree growth rates in beech in Slovenia.