What better reason to talk about syrup than this here pie?
There are two syrups in here - maple syrup in the crust, and barley malt syrup in the filling.
Sap runs through a variety of trees, but maple is the sweetest source - every year the tree moves its stores of sugar from the previous season from its trunk to its cambium, the layer of vessels just inside the bark where the tree gets tapped.
According to Harold McGee, before Europeans brought the common honeybee over the ocean, the American Indians were doing just fine maple sugaring for their sweets. They would cut a gash in a tree and freeze the liquid that poured out in sheets of bark overnight, after which they could easily remove the ice crystals from the surface of the concentrated sap. Sugar does not freeze, so a few nights of skimming the ice crystals from the barkful of liquid yielded brown, sweet water.
Using what they had learned from the American Indians, the early colonists began refining their concentrated sap into sugar-loafs - the tall, white conical predecessor to the sugar cube - to mimic the expensive, highly taxed, imported sugar cane of the West Indies and feign salon-style sophistication with the natural resources available to them in the wilds of the Northeast. The goal was to get the syrup as clear and the sugar as white as possible. By the beginning of the 20th century, market shelves were filled with maple syrup diluted with corn and glucose to ensure translucency and delicate flavor. The Pure Food and Drug Act forced truth in labeling, and these syrups were reclassified as "pancake syrups", which have but scant amounts of actual maple syrup in them and command American taste buds to this very day.
The recipes I use tend to primarily call for maple syrup as a whole food, unrefined sweetener. Pure maple syrup, that is, not Aunt Jemima. Pure maple syrup is expensive, but sweeter than sugar, so you do end up using less. The recipe for this cranberry pecan pie likely called for maple syrup because of it's warm, autumnal flavor notes and appropriate viscosity for the crust.
The filling, on the other hand, is gooey and thick - the perfect job for barley malt syrup. Be careful: this sweetener has an intense malty flavor edged with bitterness. Though it needs to be refrigerated after opening, it is much easier to use if you let the jar drop to room temperature again before attempting to measure out what you need. Malt syrup has an even richer history than maple syrup - the Chinese were using it as their main sweetener as early as 1000 BCE. As this syrup is simply malted from whole grains, it was much cheaper to transform household staples than to import sugar cane.
Malting: the grain, in this case barley, is soaked until it is ready to sprout, or germinate. Activating the sprouting process causes the grain to shed the dormant enzymes in its outer layer and produce new enzymes. These new enzymes go to work breaking down the grain's network of proteins and carbs, disassembling the packets of starch particles hiding out in the inner layer, the endosperm, in order to repurpose them as sugary fuel for the grain's growth spurt. At this point, the maltster (those who malt!) halts the germination process by drying the grain. These malted grains are mixed with water and additional cooked grains, and the malted enzymes digest the cooked grains, yielding a sugary slush that is then boiled down into the barley malt syrup we know and love!