Hi Mike, 

Thanks for your question.  How tall is the ponderosa pine tree?  Is the pine tree well established or recently planted?

As a general principal, avoid pruning more than 25% percent of the canopy in a given year (unless there are dead/broken/hazardous branches).  As far as timing, if you need to prune conifers, now is a good time to to avoid attracting the sequoia pitch moth to fresh pruning cuts.  

Lisa Cowan

Outreach Program Coordinator – Community Horticulture Program

Oregon State University

OSU Extension Service – Deschutes, Crook, Jefferson Counties

3800 SW Airport Way, Bldg #4

Redmond, OR 97756

Tel.:<personal data hidden> (direct line) I<personal data hidden> (x79590 - main line)

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Hi Mike,

Jenna Deibel, Central Oregon Extension Forester here, and I hope I can offer you some guidance. 

In general, it is recommended to start pruning once the tree is well-established, or approximately 2-3 years old. By the sound of it, your trees are far past that age threshold, so you can absolutely prune them. 

Like Lisa said, there are some important considerations to keep in mind though: 1) Make sure to only prune your pines between Oct - Feb to avoid attracting native pests like sequoia pitch moth and ips bark beetle, and 2) Do not prune more than 25% of the tree crowns at a given time. In general, we like to see trees with at least a 40% crown-to-full tree height ratio. Once those trees have reached approximately 18-feet tall, you can prune to 6-feet. Important to note, ponderosa pines are somewhat self-pruning and drop their lower branches as they grow, an adaptation they've taken on in a fire frequent landscape. 

All that being said, based on the details and goals you've shared, I'm inclined to recommend you explore thinning as an additional option to reach your wildfire resiliency goals, if you haven't already done so. Ponderosa growth after a wildfire can be quite prolific, which can result in some dense thickets if left untended. Thinning will help reduce horizontal vegetative continuity, making the remaining trees more fire- and pest-resilient. 

For your reference, I have attached a useful table that breaks down the recommended trees-per-acre (TPA) for an even-age ponderosa pine stand based on the average diameter at breast height (DBH) and site index of your stand. This table is part of a larger OSU Extension publication: Ecology and Management of Eastern Oregon Forests, of which a free downloadable PDF can be found here. On page 34, you will find details on how to determine your site index, Chapter 3 is all about managing ponderosa pine forests, and you may find other chapters helpful as well. 

If you have any additional questions or would like some assistance determining your site index and associated TPA, please feel free to reach out to me directly at: <personal data hidden>

Thank you for reaching out to Extension!

Best,

Jenna

Hi Mike,

To answer your last question first, ponderosa pines are somewhat self-pruning and drop their lower branches as they grow, an adaptation they've taken on in a fire frequent landscape. Getting into the biology of it, if pines sense that their lower branches are not providing much photosynthetic benefit due to lack of light, the tree will divert resources from that branch to vertical growth or other, more light-soaked branches. In turn, the lower branch dies and falls off. 

If your property is in Central Oregon, or east of the Cascades generally, I would not recommend leaving many pruned pine branches on the forest floor. Because we live in the arid high desert, things hardly decompose at all, which can lead to a build up of hazardous fuels. 

Leaving some is absolutely fine and natural in a forest ecosystem. However, in a historically fire frequent landscape, those dropped branches were burned away before there was a chance for substantial fuel buildup. In the absence of frequent fire, those branches on the forest floor may remain for decades and become fuel for more severe wildfire down the line. Additionally, if still-green branches are left in piles, they can become breeding grounds for ips bark beetles, which can in turn infest nearby standing trees at great enough numbers. 

Most landowners in Central Oregon opt to burn their 'slash' (i.e. branches, forest debris) in the late fall or winter as a management strategy. If you take this approach, make sure to check with your local fire district for their particular rules regarding pile burning first. Generally they just want a 'heads-up' call before you burn, but some districts have additional requirements. Alternatively, you can chip your pruned branches. 

Hope this helps!

Best,

Jenna