Sugarbush Spring, by Marsha Chall. This picture book celebrates the month of the Maple Sugar Moon. It's time to collect sap from the family sugar bush and grandpa invites his youngest granddaughter to help. They collect sap the old way - in buckets - and boil it down in the sugarhouse. A perfect read-aloud before you head out for a walk along Kelsey Road (where they still tap the trees the old way) or wherever your nearest sugarhouse is.
The Maple Sugar Book by Helen & Scott Nearing is aptly subtitled: With remarks on pioneering as a way of living in the twentieth century. Originally published half-a-century ago, it is filled with a history of sugaring from Native American to modern (1950s) time. This book is full of tips on how to tap a tree and boil down the sap. Great for back yard sugaring and the historically curious.
Another fun source is The Salt Book, edited by Pamela Wood. It's a Foxfire type book - a collection of downeast stories of how to make maple syrup, build stone walls, catch lobsters and more. All told in plainspoken language of the Maine coast.
Spring is a great season for tree-watching and Carole Gerber's book, Spring Blossoms
provides a fun introduction. She celebrates trees in verse, with a
story that follows two girls and their dog as they race from red maple
to willow. We learn that crab apple blossoms are white and cherry
blossoms pink, red maple flowers red but redbud blossoms not. She shows
male flowers and female flowers, flowers with showy petals and flowers
with petals so tiny you hardly notice them at all. Here are some book-extending activities for kids of all ages. 
My spring robin by Anne Rockwell shows a young girl who goes out on the first day of spring. She finds forsythia and crocuses, violets and daffodils, a toad, an earthworm and fiddlehead ferns emerging from the soil. But spring isn't spring unless she can find the first robin of the year.