Ecologically, when you're within the latitudes of 23.5 degrees, you'd find yourself in rainforests rich in diversity but poor in nutrition. The forest floor is a barren mess simply because the canopy is so thick that one to two percent of sunlight ever breaks through it into the floor. As a result, you'd consider yourself lucky if you ever felt a breeze on the forest floor.
In this alternate Earth, if we are to clump together the plants that make up the jungles of South America, Africa and sub-Himalayan Asia for the last four million years, it might look a little like this:
Note here that bamboo makes up the vast majority of modern jungle plants.
Before I ask you my question, let me answer a question that you might be asking--how could this jungle have such a low diversity?
Marked in red is the extent in which the Köppen climate type Af, tropical rainforests, could have spread 144 million years ago. The MC Extinction Event 66 million years ago was merely a temporary disruption. 45 million years ago, the Antarctic Circumpolar Current had finally gotten Antarctica surrounded, icing it. This icing disrupted the global climate to the extent that the global grip of the rainforests was weakening. Marked in pink was the rainforests' extent before five million years ago, when the gradually descending global temperature suddenly spiked down at a faster pace, creating a mass extinction that resulted in the loss of half of all terrestrial species and two-thirds of all marine species. In this extinction event, the plants and animals of the tropics bore the brunt of it, thus resulting in the low diversity that now you see on the pie chart.
Bamboo seems to have an advantage over regular trees in that the stem is uniformly narrow and the leaves are too sparse to create a canopy. So in a tropical rainforest that is predominately bamboo, would this have changed the character of the forest floor in any way?