Physical resistance of woody plants to browsing: resistance of aspen browse to shearing. Dockrill, Craig, Bailey, Arthur^*,, Blenis, Peter, King, Jane,

ABSTRACT- Aspen is an important forage for cattle browsing in logged clear-cuts of central Alberta. There is potential for cattle browsing to negatively affect tree regeneration. It was suspected that stem hardening in mid-summer was a major factor affecting cattle browsing of aspen. In this study aspen stems were collected for 2 years throughout the growing season and partitioned into 3 stem portions (current, 1 year-old growth, 2 year-old growth). Each section was sheared using a custom attachment on an Instron 1000, and the force required to shear the shoot was recorded. Less force was found to be required to shear current annual growth than either 1 year-old or 2 year-old growth of aspen. In spring less force was required to shear all 3 stem portions than in fall. Seasonal changes in shear strengh from spring to fall helped explain field observation of cattle browsing.

KEY WORDS: browse, aspen, shearing, resistance