I donated to Arbor Day Foundation $100 to plant 50 trees in a National Forest. I got a card showing where the trees are planted in honor of us- is this deductible?

Yes, this would be a charitable donation. The Arbor Day Foundation is a 501(c)(3) nonprofit conservation and education organization. Monetary donations are deductible to this charity, but not if you received a tree in return for payment. The card is a nice receipt, but it doesn't mean that you received anything of monetary value in return for your donation.