The size of bonsai trees is primarily a result of environmental factors, specifically the care and techniques used in their cultivation. Bonsai is the art of growing miniature trees by carefully managing their growth through pruning, root reduction, potting, and controlled watering. These practices are learned skills passed down through generations of bonsai artisans and require significant knowledge and experience.
While there are intrinsic genetic traits that may influence how a particular species of tree grows, in the context of bonsai, it is the cultivation techniques and environmental conditions—such as light, temperature, and soil—that predominantly shape the final size and appearance of the trees. Therefore, understanding bonsai highlights the importance of learned and environmental factors in shaping a trait like size, making this option the most accurate.