In your mind, how does dropping leaves harm the shrubs? Wouldn't it allow for more light to pass down to the forest floor? It feels like the tree's response to shrubs was "grow taller to maximize sun exposure"
I feel like the conventional wisdom that this is a response to environment(conserve energy/lower wind resistance) make more sense than "offensive deterrent for competing plants" even more so when you consider that every leaf dropped is biomass that the tree had already taken in and utilized, but now it's giving it up. Maybe a pro-symbiotic move whereby dropping the leaves provides shelter/biomass for beneficial insects that could provide root aeration or soil enrichment would be another reason?
I feel like the conventional wisdom that this is a response to environment(conserve energy/lower wind resistance) make more sense than "offensive deterrent for competing plants" even more so when you consider that every leaf dropped is biomass that the tree had already taken in and utilized, but now it's giving it up. Maybe a pro-symbiotic move whereby dropping the leaves provides shelter/biomass for beneficial insects that could provide root aeration or soil enrichment would be another reason?