Abstract ID: 3.8734 | Accepted as Talk | Talk/Oral | TBA | TBA

Global warming has a significant impact on the vitality and resilience of mountain forests, with trees showing reduced vitality in response to prolonged heatwaves and decreased soil water availability. This decline in vitality increases the risk of pathogen infestations and recurrent episodes of heat and drought have already led to a higher incidence of tree mortality. Two primary physiological mechanisms that contribute to tree mortality are persistent carbon deficiency and hydraulic failure. The phloem, which is hydraulically connected to the xylem in higher plants, plays critical roles in carbon allocation, signal transduction, and pathogen defense. When phloem formation is impaired, these essential processes are disrupted, leading to reversible or permanent inactivity of the cambium. Consequently, tree vitality declines, increasing the risk of mortality. The objective of this study is to examine the growth dynamics associated with tree vitality in the xylem, and cambium of Scots pine (Pinus sylvestris) and juniper (Juniperus communis) at a dry-mesic site on the Mieminger Plateau (980 m a.s.l., Tyrol, Austria). The study area is characterized by shallow soils with low water holding capacity, which provides ideal conditions for observing trees subjected to recurrent heat and drought episodes. Histological analyses of the xylem formation throughout the growing season offer a high-resolution perspective on cell differentiation. The present study contributes to our understanding of the different sensitivity of radial stem growth in coexisting tree and shrub species under drought, which enables the formulation of future dieback rates, and hence stand development.