Evaluating the performance of LoRa in different operating conditions, especially when LoRa is adopted as communication technology for enabling applications in rural environments, is a key challenge. LoRa performance is affected by the values assigned to several parameters, such as the Spreading Factor (SF), the Code Rate (CR), etc. To this purpose, at first, we designed and implemented a flexible, user-friendly, and easy to program Lora packet generator. Then, we investigated the performance of LoRa in light-dense and very-dense forest vegetation environments when the distance between the transmitter and the receiver varies. This study aimed at highlighting how such performance is related to different LoRa settings when operating in the 433 MHz and 868 MHz bands. Focusing on the link quality and transmission performance, we conducted both a theoretical study and a massive measurements campaign in a field trial deployed in an Italian natural park. Results help find the best LoRa configuration parameters when operating in light-dense or very-dense forest environments.