MEXICO CITY (AP) — Researchers in Mexico say illegal logging has practically been eliminated in the wintering grounds of the Monarch butterfly.

It is the first time that logging has not been found in detectable amounts since the area was declared a nature reserve in 2000.

Omar Vidal of the environmental group WWF says the battle hasn't been won, since climate change now appears to be affecting the mountain reserve west of Mexico City.

The report released Wednesday says pests and drought caused a combined loss of almost 52 acres (21 hectares) of pine and fir forest.

The area has been hit by bark beetles.

Logging was once considered the main threat to the reserve, where millions of butterflies spend the winter after migrating from the United States and Canada each year.