This is called inosculation: when branches or roots of different trees are in prolonged intimate contact, they often abrade each other, exposing their inner tissues, which may eventually fuse.
It's not so much one tree feeding another as the formation of a new hybrid organism.
In this case, it looks like two beeches (which are partial to inosculation) fused their limbs. Later, the smaller tree's roots/lower trunk were cut away, yet it survived by continuing to exchange water and sugars with its other half. It had already become part of something bigger
Plants have an astounding ability to merge w/ one another & grafting is widely practiced in agriculture. It's very common for a fruit tree to be a hybrid: a fruit-bearing 'scion' (top part) grafted onto a hardy rootstock that grows well in local soil.
White tern
-This is it. This is the nest
-A failure to recognize the fundamental impermanence of being is the source of all suffering
-Taught Marie Kondo everything she knows
Red ovenbird
-Fond of turquoise
-Will challenge you to a contest measured in Scoville heat units
-Have you seen my prize-winning succulents?
-Knows the One True Cornbread recipe
Vogelkop bowerbird
-Apprenticed (read: volunteered) at MOMA one summer
-My favorite artist? You wouldn't know them
-Actually, it's not a "nest"—it's an interactive sculptural platform that uses found objects and corporeal semiotics to interrogate the very essence of intimacy