Perhaps that white fleece/row cover.

Row cover holds in heat in many applications. One consideration. If you put up a teepee with enough bamboo, you might not need other shade for a young tree. When you mention pine trees, are you wondering about permanent shade? I think pines are often shallow-rooted and could interfere with the pawpaw's roots.

No -- I wasn't very clear on that -- I'm not thinking of a live pine tree. I was thinking of cutting some branches off a pine tree and using them for shade. I've used tree branches several times before for temporary shade for new plantings, but for pawpaws the problem would be that most tree species only hold their leaves for a week or so after being cut off. I'm wondering what I might use for shade like a tree branch that won't wither up and stop providing shade so quickly. Does anyone use anything organic (as in live or formerly alive) for shade structures (like for pawpaws)?