In recent years, the forest has been used as a protective structure to reduce rockfall propagation. When a rock propagates down a forested slope, it hits trees and these interactions modify its trajectory. This paper focuses on the dynamic behavior of small-diameter live trees impacted by a rock To better understand the protective effect of forests against rockfalls, a finite element (FE) model of a live stem subjected to a local dynamic loading is proposed. Large displacements and material nonlinearities are taken into account. The numerical simulations are calibrated based on laboratory tests (free oscillation tests and impact tests). The displacement field measured by a high-speed camera is correctly reproduced by the FE model for both kinds of tests. For impact tests, the analysis of the impactor-stem interaction identified three main regimes of the stem's response (quasi-static/intermediate/impulsive). These depend on the impactor's and stem's mechanical and geometrical features (relative mass and stiffness). Finally, we attempt to predict the regime response of the stem as a function of its diameter and the impactor mass.