There are at least 20 species of tree that can be tapped for their edible sap. And in many cases, once the sap has been reduced, a syrup can be produced. Trees in the maple (Acer spp.) family can be tapped from January to March – as long as the nights are cold and the days crisp and sunny. Birch trees (Betula spp.) however only run for a very short period of 2 to 3 weeks in mid- to end of March once the coming of Spring starts the sap flowing. Walnut trees (Juglans spp.) like a freezing cold winter and spring. Some walnut species can be tapped from autumn right through until spring.
Climate change is affecting sap production. Although some of this is hearsay, there is certainly recorded evidence that maple sap yields in southern states are dropping and that the season is starting earlier, often in December, and not lasting as long. It also affects the quality of the syrup. Higher temperatures are linked to maple syrup with higher levels of phenolics which makes the syrup darker. Phenolics are secondary metabolite defense compounds that influence the flavour of the sap.