Plantation areas of Japanese cedar (Cryptomeria japonica) have often been recognized as low-quality habitats for Japanese monkeys (Macaca fuscata) due to the lack of food resources, although empirical studies on this are few, especially in cool-temperate forests. For monkeys, winter is the bottleneck season for food availability. Hence, we evaluated the monkeys' selectivity of winter food tree species by counting their feeding traces in 2008 and 2009; we then compared the number and variety of winter food resources among several forest sites comprising differently aged cedar plantations—with primary beech forests as a control area—in heavy snow regions of the northeastern Shirakami Mountains. We noted that (1) monkeys tended to prefer shade-intolerant trees as food resources; (2) the stem density and variety of such trees in plantations commonly decreased with increasing forest age; (3) dominant cedar tree thinning effectively increased the preferable food resources for monkeys; and (4) the stem density and variety of food resources in the plantations were greater than those in primary beech forests. These results indicated that cedar plantation areas are not always low-quality habitats for monkeys in cool-temperate forests, as long as appropriate cedar tree thinning for timber production is implemented.