Plant traits survey
Every two months, from June 2010 to April 2011, we measured two morphological traits known to potentially affect arthropod plant-interactions in B. cordata : leaf thickness and water content (Agren et al. 1999).  Leaf thickness was measured with a Vernier on five leaves per tree. Water content was measured in five leaves per plant, controlling for leaf age and size. Water content proportion was obtained as:
Water content = (fresh weight-dry weight) / fresh weight
We also recorded herbivory rate as it is known to be related to plant defense and it is by itself a record of plant-herbivore interactions (Kersch-Becker et al. 2017). Herbivory rate depends on many traits such as secondary compound concentration, nutrient content, and trichomes abundance, and it is thus a proxy for herbivore’s plant preference and performance. Every two months, we marked six young undamaged leaves per plant. Three weeks later, herbivory was estimated on those leaves as follows:
HR= CLA/TLA
Where CLA is the consumed leaf area and TLA is the total leaf area. The unit is leaf-area consumed for 21 days. Additionally, B. cordatasex-ratio was measured because differences in this trait may indicate differences in the survival rate between sexes (Cornelissen and Stiling 2005, Barrett and Hough 2013, Sargent and McKeough 2022) and therefore differences in reproduction investment (Sinclair et al. 2012).