Dendrology

Abstract: Summary Attempts at explaining range limits of temperate tree species still rest on correlations with climatic data that lack a physiological justification. Here, we present a synthesis of a multidisciplinary project that offers mechanistic explanations. Employing climatology, biogeography, dendrology, population and reproduction biology, stress physiology and phenology, we combine results from in situ elevational (Swiss Alps) and latitudinal (Alps vs. Scandinavia) comparisons, from reciprocal common garden and phytotron studies for eight European broadleaf tree species. We show that unlike for low-stature plants, tree canopy temperatures can be predicted from weather station data, and that low-temperature extremes in winter do not explain range limits. At the current low-temperature range limit, all species recruit well. Transplants revealed that the local environment rather than elevation of seed origin dominates growth and phenology. Tree ring width at the range limit is not related to season length, but to growing season temperature, with no evidence of carbon shortage. Bud break and leaf emergence in adults trees are timed in such a way that the probability of freezing damage is almost zero, with a uniform safety margin across elevations and taxa. More freezing-resistant species flush earlier than less resistant species. Synthesis: we conclude that the range limits of the examined tree species are set by the interactive influence of freezing resistance in spring, phenology settings, and the time required to mature tissue. Microevolution of spring phenology compromises between demands set by freezing resistance of young, immature tissue and season length requirements related to autumnal tissue maturation.

Abstract: The brown marmorated stink bug, Halyomorpha halys (Stal) (Hemiptera: Pentatomidae) is an invasive plant-feeding insect native to eastern Asia. This herbivore is highly polyphagous, feeding on and damaging diverse plants, including field crops, vegetables, tree fruits, and ornamentals. Woody ornamental plants provide early- and late-season resources for adults emerging from and returning to overwintering sites, as well as feeding and breeding sites for H. halys throughout the growing season. In this study, we quantify the use of diverse plants by H. halys in two commercial nurseries in Maryland, recording data on the abundance of egg masses, early and late instar nymphs, and adults over a three-year study period. Our specific goals were to provide a quantitative comparison of the use of diverse plant species and cultivated varieties, identify non-hosts that could be used to create landscapes refractory to H. halys, and determine whether the use of plants varied across life stages of H. halys or the taxonomic status of plants. We found broad use of diverse plants in this study, identifying 88 host plants used by all life stages of H. halys. We also highlight the 43 plant taxa that did not support any life stage of H. halys and are thus classified as non-hosts. Interestingly, some of these plants were congeners of highly-used plants, underscoring high intrageneric and intraspecific variation in the use of plants by this polyphagous herbivore. We discuss how the selective planting of non-hosts, especially gymnosperms, may aid in reducing the agricultural and nuisance pest status of this invasive insect.