Tree growth on hillsides primarily remains vertical due to the combined effects of gravitropism and phototropism. Gravitropism, influenced by gravity, dictates the upward direction of growth, while phototropism allows plants to orient themselves towards light, often resulting in angled growth when light sources are uneven. Plant hormones, particularly auxins, play a crucial role in these responses. Environmental conditions can also significantly affect tree growth patterns, leading to phenomena like krummholz and flag trees, which are adaptations to harsh climates. Specific cases, such as the peculiar growth patterns observed in certain forests, may be attributed to past environmental stresses like heavy snowfall or even genetic mutations, as seen in Saskatchewan's Crooked Bush. Overall, the interplay of gravity, light, and environmental factors shapes how trees grow, even in challenging conditions.