Modeling the potential impact of climate change on the distribution of Western Corn Rootworm in Europe

The Western Corn Rootworm (WCR), Diabrotica virgifera virgifera, is an important insect pest of corn, which has been introduced into Europe from Northern America in 1980s. Since then, its distributional range is continuously expanding over the Central and South-Eastern Europe. This study assessed the potential effect of increased temperatures on the timing of WCR generation development and on the WCR distributional range in 2011-2100. An impact model, describing a linear relationship between temperature and thermal requirements for the complete development of adult WCR, was forced by an ensemble of climate model data from three regional climate models, representing two different future forcing scenarios. The impact model simulations showed the fulfillment of temperature requirements in earlier date and over the extended area, covering continental Europe, large parts of British Isles and Scandinavia, in 2011-2100 in comparison with 1981-2005. In addition, the impact model projections display an increase in frequencies of years in which the temperature requirements of the WCR are fulfilled in central, eastern and northern parts of Europe, thereby indicating a future northward extension of area suitable for the establishment of a permanent WCR population. Policymakers are needed be informed about possible risks of the WCR spread in order to adjust pest management practices.The climate system has been instrumentally observing since the mid-19th century, providing evidence of temperature increase. The process is very likely caused by an increase in anthropogenic emissions of greenhouse gases. A warmer climate may affect complex interaction, which exist between environment, insect pest and host plant. The possible responses of insect to climate change should be understood to develop relevant strategies in pest management. This study focuses on the Western Corn Rootworm (WCR), Diabrotica virgifera virgifera, an important insect pest of maize. It significantly reduces maize yield by damaging maize roots. Yield losses may reach up to 40%. The WCR has been introduced into Europe from Northern America in 1980s. Since then, the insect has been spread to large parts of Central and South-Eastern Europe. Temperature influences the development of insects, which happens within specific temperature ranges. Therefore, the data of future temperature, produced by climate models, can be used to analyse temperature suitability for insect in a particular geographical region. For this purpose a mathematical model describing the temperature requirements of the WCR has been developed. The model simulations showed that favorable temperature conditions for the development of adult insect may occur earlier it the year and over a larger area in 2011-2100 in comparison with present day. The progression is dependent on current and future emission of greenhouse gasses. The abovementioned area includes continental Europe, considerable parts of British Isles and Scandinavia. In addition, the percentage of years with appropriate temperatures may increase, allowing the WCR to migrate into the northern European regions and establish a permanent population. Interested parties are needed be informed about possible risks of the WCR spread to be able to adapt pest management practices, including crop rotation and monitoring of areas potentially suitable for the insect

Understanding the environmental regulation of tree phenology

In temperate and boreal climates, trees synchronise their annual growth cycles with seasonal changes in daylength and temperature. Understanding how environmental cues regulate tree phenology is important to our ability to capture the potential responses of trees to climate change, with implications for forest productivity.In this thesis, we demonstrated that different research methods can be applied to study the regulation of tree phenology and that this knowledge can be used to generate climate change impact assessments. The knowledge gaps identifiedby summarising recent advances on the molecular regulation of growth cessation and bud set were addressed by modelling. Modelling autumnal bud development showed that both photoperiod and temperature help to predict thetiming of bud set in non-stressful conditions, while additional regulatory mechanisms may be involved under stressful conditions.The differences in phenological response to environmental signals between populations and provenances were accounted for via the values of model parameters. The provenance specific temperature sum requirements for bud burst for Norway spruce were used to calculate the risk of spring frost damage under current climate conditions and future climate scenario. The timing of bud burst will occur earlier in future and will be associated with an increased risk ofspring frost damage due to the increased frequency and severity of spring frost events. The information on the provenance specific frost risk will facilitate forest management decisions on choosing suitable plant material for regeneration.The ecosystem model was used to assess the effect of phenology parameterisation on simulating carbon uptake. Model simulations with calibrated phenology parameterization predicted enhanced forest productivity by the end of the century due to earlier timing of bud burst. However, uncertainty remains whether reduced winter chilling may slow down future bud burst advancement and forest productivity increase, highlighting the need for a mechanistic understanding of environmental regulation of dormancy release and bud burst.Further progress towards a better understanding of regulation of tree phenology can be achieved through integrating molecular and modelling approaches, by incorporating knowledge on molecular pathways of environmental control ofstages of the annual growth cycle into phenological models

Model analysis of temperature impact on the Norway spruce provenance specific bud burst and associated risk of frost damage

The annual growth cycle of boreal trees is synchronized with seasonal changes in photoperiod and temperature. A warmer climate can lead to an earlier bud burst and increased risk of frost damage caused by temperature backlashes. In this study we analysed site- and provenance specific responses to interannual variation in temperature, using data from 18 Swedish and East-European provenances of Norway spruce (Picea abies), grown in three different sites in southern Sweden. The temperature sum requirements for bud burst, estimated from the provenance trials, were correlated with the provenance specific place of origin, in terms of latitudinal and longitudinal gradients. Frost damage had a significant effect on tree height development. Earlier timing of bud burst was linked to a higher risk of frost damage, with one of the sites being more prone to spring frost than the other two. The estimated provenance specific temperature sum requirements for bud burst were used to parametrize a temperature sum model of bud burst timing, which was then used together with the ensemble of gridded climate model data (RCP8.5) to assess the climate change impact on bud burst and associated risk of frost damage. In this respect, the simulated timing of bud burst and occurrence of frost events for the periods 2021-2050 and 2071-2100 were compared with 1989-2018. In response to a warmer climate, the total number of frost events in southern Sweden will decrease, while the number of frost events after bud burst will increase due to earlier bud burst timing. The provenance specific assessments of frost risk under climate change can be used for a selection of seed sources in Swedish forestry. In terms of selecting suitable provenances, knowledge on local climate conditions is of importance, as the gridded climate data may differ from local temperature conditions. A comparison with temperature logger data from ten different sites indicated that the gridded temperature data were a good proxy for the daily mean temperatures, but the gridded daily minimum temperatures tended to underestimate the local risk of frost events, in particular at the measurements 0.5 m above ground representing the height of newly established seedlings

Exploring Populus phenological response to climate change using observational data and ecosystem modelling

The length of the growing season for deciduous trees in temperate and boreal forests is determined by the timing of bud burst and autumn senescence. It is generally assumed that a warmer climate leads to a longer growing season due to earlier bud burst and delayed autumn senescence and thereby increased gross primary production (GPP) of forests. In this study, we analysed past (1873–1951) and current (2008–2020) phenological observations on bud burst and senescence from aspen trees (Populus tremula) grown in Sweden. The observations indicated a reduction in temperature sensitivity of bud burst between the time periods, likely associated with warmer winters and reduced exposure to chilling. The phenological observations were used in the evaluation of an ecosystem model. Biases in modelling spring and autumn leaf cover development influenced the seasonal and annual GPP estimates. The overestimation of the modelled GPP was more pronounced in spring than in autumn, reflecting the GPP limitations by leaf cover development in spring, and by daylength and temperature conditions in autumn. Calibration of the spring phenology parameters, using the accumulated temperature sums and chilling days at the observed timing of bud burst, significantly improved model performance compared to the original parameterisation. The calibrated ecosystem model projections representing RCP8.5 suggested 15 days earlier timing of bud burst and enhanced mean annual GPP by the end of the century compared with current climate conditions in Sweden

Modelling Populus autumn phenology : The importance of temperature and photoperiod

In late summer-early autumn, trees undergo growth cessation culminating in bud set. For a wide range of plants, including Populus, photoperiod is considered as the primary environmental cue determining timing of growth cessation and shoot to bud transition. However, studies on Populus have revealed temperature influence on seasonal growth cessation and bud set. In this study we examine the role of temperature in regulating the transition between phenological stages of bud development, from a growing apex to a closed bud. We test different model structures incorporating cues from both temperature and photoperiod (M1 and M2) as compared to the previously established model based on photoperiod only (M0, null hypothesis). All models simulate the date of bud set forPopulustrees from 12 latitudinal populations grown in the common garden of Sävar. For two of the three years (2005 and 2007) M1 and M2 models outperformed the null model in predicting bud set date. Poor predictions for 2006 were related to stressful weather conditions. This indicates that under non-stressful conditions temperature can be a factor modifying the photoperiod response, while other regulatory mechanisms can be at play during stressful conditions. A phenological model of bud development has to account for both types of responses. Thus, our study highlights the importance of temperature as a factor that should be considered in addition to the well-established photoperiodic signal in studies on autumnal bud set under natural conditions

Photoperiod- and temperature-mediated control of phenology in trees – a molecular perspective

(Table presented.). Summary: Trees growing in boreal and temperate regions synchronize their growth with seasonal climatic changes in adaptive responses that are essential for their survival. These trees cease growth before the winter and establish a dormant state during which growth cessation is maintained by repression of responses to growth-promotive signals. Reactivation of growth in the spring follows the release from dormancy promoted by prolonged exposure to low temperature during the winter. The timing of the key events and regulation of the molecular programs associated with the key stages of the annual growth cycle are controlled by two main environmental cues: photoperiod and temperature. Recently, key components mediating photoperiodic control of growth cessation and bud set have been identified, and striking similarities have been observed in signaling pathways controlling growth cessation in trees and floral transition in Arabidopsis. Although less well understood, the regulation of bud dormancy and bud burst may involve cell–cell communication and chromatin remodeling. Here, we discuss current knowledge of the molecular-level regulation of the annual growth cycle of woody trees in temperate and boreal regions, and identify key questions that need to be addressed in the future