30th Anniversary Edition

Aspect of Wolf

Enchant creature
Enchanted creature gets +X/+Y, where X is half the number of Forests you control, rounded down, and Y is half the number of Forests you control, rounded up.

Treasure Chest

Fifth Edition

Enchanted creature gets +*/+*, where * is equal to half the number of forests you control, rounded down for power and up for toughness.

Fourth Edition

Increase target creature's power and toughness by half the number of forests you control, rounding down for power and up for toughness.

Fourth Edition Foreign Black Border

Summer Magic / Edgar

Revised Edition

Target creature's power and toughness are increased by half the number of forests you have in play, rounding down for power and up for toughness.