Preheat oven to 425 degrees. In a large mixing bowl, stir together the flour, brown sugar, baking powder, cinnamon, salt, ginger, and allspice. Add the shortening and cut in with 2 knives or hands until crumbly. In another bowl combine sweet potatoes, cream and pecans. Make well in dry ingredients and add potato-cream mixture. Mix to combine. Turn the dough out onto a lightly floured surface. Roll out the dough to 1 1/2 inches thick. Cut out with a 2-inch floured biscuit cutter. Place biscuits 1-inch apart on ungreased baking sheets. Bake for 5 minutes, then turn down temperature to 375 and bake for another 10 to 15 minutes until golden brown. Serve warm or let cool on a wire rack until room temperature.