Santa Fe Forest Coalition

Colorado State Forestry Service publishes a document called "Piñon-Juniper Management", and in the document it recommends against thinning piñon trees during the growing season (spring to early fall) to avoid attracting Ips (bark) beetles.

Key quotes:

• In drought years, it is best to thin and prune during the late fall and winter months (the dormant season) to avoid attracting Ips beetles.

• If thinning and pruning occurs in the spring and/or summer, it is important to properly dispose of slash within three weeks. This is to prevent a generation of Ips from infesting slash piles and producing offspring that may infest healthy trees.

• Slash that is chipped in spring or summer should not be placed or piled near the base of standing trees because it may attract Ips.

Here's the full document:

• Piñon-Juniper Management, Colorado State Forestry Service