Final answer:
Douglas fir trees thrive beneath the taller lodgepole trees due to increased shade, protection from harsh weather, and a steady supply of nutrients from the lodgepole's fallen needles.
Step-by-step explanation:
Douglas fir trees thrive beneath the umbrella of taller lodgepole trees because they benefit from increased shade and protection from harsh weather conditions. This allows the Douglas fir trees to grow and develop more successfully. Additionally, the lodgepole trees provide a steady supply of nutrients to the Douglas fir trees through their fallen needles, giving them an advantage in accessing important resources. Therefore, option A and B are correct: A) Benefiting from increased shade and protection from harsh weather conditions, and B) Receiving a steady supply of nutrients from the lodgepole's fallen needles.