Background and Objectives
One of the key challenges to sustainable forest management in the 21st century is to understand how climate change may amplify the spread of invasive species that undermine native biodiversity and ecosystem services. As temperate climates continue to experience new extremes of heat and drought, the relative competitive abilities of native and invasive species in relation to their stress tolerance are likely to play an important role in the assembly of novel forest assemblages. New theory in plant functional ecology based on growth-stress tradeoffs (Fig. 1) may provide a predictive framework for invasion-climate interactions, but its relevance to biological invasions remains untested in light of anticipated climate extremes.
For trees, a key recent advance in defining growth-stress tradeoffs is the availability of high-resolution measurements of secondary growth. Using automated point dendrometers, we now understand that conditions supporting tree growth through cell division involve the simultaneous occurrence of adequate hydration (turgor) and warm temperatures conducive to mitotic division. In this way, the capacity for growth under typical field conditions may have as much to do with diurnal stress avoidance (e.g., stomatal control, rooting depth) than traits typically associated with high growth capacity in controlled environments (e.g., maximum photosynthetic rate). Micrometer-resolution stem radial data allow for growth analyses at the scale of hours and minutes to capture key environmental thresholds. Because they also track the extent of stem shrinkage with turgor loss, they provide a mechanistic link between water availability and cell division that can be translated to ancillary measurements of leaf water potential and stomatal behaviors.
The PhD project will make use of existing forest plots to track real-time growth and stress responses in native and non-native invasive trees, and test the hypothesis that invaders are less constrained by stressors (drought, heat, cold) that reduce the competitive ability of native species. Moisture- and temperature-based growth thresholds of each species identified from this analysis will then be used in physiologically-informed species distribution models to predict how anticipated climate shifts will impact the climate suitability of native and non-native invasive tree species across Europe.
Specific objectives of the PhD project include 1) estimating the temperature and moisture thresholds of growth (cell division) in native and non-native invasive trees, using automated point dendrometers and microclimate sensors; 2) using accompanying gas exchange measurements to model how growth constraints drive leaf-level photosynthetic dynamics across species; and 3) with physiologically-informed species distribution models, predict how climate change might alter competitive dynamics and spatial distributions of native and non-native invasive trees.
Research Environment
The project will be conducted at the EDYSAN research unit (Ecologie et Dynamique des Systèmes Anthropisés, UMR 7058 CNRS-UPJV), Jules Verne University of Picardie – Amiens (France).
Field measurements will be conducted in existing forest monitoring networks in France, including the RENECOR network managed by the “Office National des Forêts” (ONF). The project will combine field sampling with statistical modeling, under the supervision of EDYSAN’s researchers. In addition, the student may develop new microclimate sensing technology with support from the EDYSAN staff.
The candidate will work within an international and interdisciplinary research environment at the interface of ecophysiology, forest microclimatology, invasion ecology, and species distribution modeling.
Methodological Approach
The PhD student will make use of existing networks of forest plots containing native and non-native invasive tree species across temperate Europe, focusing on Hauts-de-France. Selected trees in each plot would be equipped with point dendrometers, allowing high resolution analysis of water use and cell growth. Microclimate sensors monitoring soil moisture and air temperature and humidity, combined with repeated samples of leaf water potential, stomatal conductance, and photosynthetic rate, will allow the student to establish growth-tolerance curves for each species in relation to heat, drought, and cold constraints. The student will integrate dendrometer, weather, and physiological data into mechanistic models that translate dendrometer signals to carbon gain and water use responses. For a final component the student will use species distribution models to predict impacts of climate change on demographic outcomes (growth, survival) of the studied native and invasive focal trees.
Candidate Profile
The successful candidate should hold a Master’s degree (or equivalent) in plant biology, ecology, ecophysiology, environmental sciences, or a closely related field.
Required qualifications:
– Strong background in plant physiology and ecology
– Strong quantitative and statistical skills (experience with R or similar software)
– Excellent organizational skills and scientific rigor
– Good written and oral communication skills in English
– Evidence of successful field-based research outcomes
Desirable skills
– Expertise in species distribution modeling
– Experience with plant gas exchange and water relations measurements
– Experience working in the forests of France / central Europe
The candidate should demonstrate autonomy, curiosity, and the ability to work both independently and collaboratively within an international research environment.
Practical Information
Contract: 3-year doctoral contract
Location: Amiens, France
Expected start date: September/October 2026
Application deadline: May 1, 2026
Application should include:
– CV
– Motivation letter
– Contact details of two referees
Interested candidates are encouraged to contact the supervisors for further information and to submit their application materials to: Jason Fridley (jdfridley@gmail.com) and Jonathan Lenoir (jonathan.lenoir@u-picardie.fr)
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