The struggling history of the trees whose roots had been severed

The aims of this study were: 1) to evaluate the effect of two levels of root severance on tree growth and physiology of two shade tree species supposed to differ in tolerance to root manipulation; 2) to evaluate the effects of root damage on tree stability by theoretical calculations and pull test. The root system of 48 established Aesculus hippocastanum (25-30 cm circumference) and 48 Tilia x europaea (25-30 cm circumference) growing in a loamy soil was damaged according to the following treatments: 1) roots were severed only on one side of the tree by excavating a trench (70 cm deep and 50 cm wide) 40 cm apart from the root flare (Moderate Damage); 2) roots were severed at two opposed sides of the tree by excavating two trenches (both 70 cm deep and 50 cm wide) 40 cm apart from the root flare (Severe Damage); 3) roots were not damaged (control). Shoot and stem diameter growth, leaf gas exchange, chlorophyll fluorescence and water relations were assessed for the 4 years following the damage. Roots were dug with Airspade a few months and 4 years after the damage to assess the size of the root plate and to calculate the uprooting resistance index according to standard methodology. The pull test was performed immediately after the severance and after 4 year using Orebla analysis software. Effects of root severance on tree stability (both directly measured using pull test and calculated from the size of the root plate and of the crown) and recover from root damage of the two species in the 4 years after severance will be discussed in the presentation. Also, the impact of root loss on growth, leaf gas exchange and water relation will be described and the potential for recovery of the two species will be evaluated.