Are there many big trees in Oregon?

Because I’m a forester, people often ask me: “Are there very many big trees in Oregon, and are they protected?” That’s a reasonable question, and it reflects genuine public concern about harvesting trees for wood products. And I had a gut feeling about the answer, but frankly, I didn’t know it.

Fortunately, this is just the sort of question the LEMMA project was set up to answer. LEMMA is the Landscape Ecology, Modeling, Mapping and Analysis project, which is a collaborative effort of the Pacific Northwest Research Station of the US Forest Service, the OSU Department of Forest Ecosystems and Society, and the Oregon Department of Forestry.

The LEMMA project uses data from permanent inventory plots and satellite imagery to create Gradient Nearest Neighbor (GNN) maps and tables. This data can be analyzed to determine area and percent of Oregon forestland by tree size classes, as shown in Table 1.

Table 1: Area and Percent of Oregon Forestland by Average Tree Size Class

ClassSize ClassAverage Tree SizeAcreagePercent

1Shrub/seeding<1" dbh964,1963.1%

2Sapling/pole1-10" dbh10,418,67833.6%

3Small tree10-15" dbh9,543,41430.7%

4Medium tree15-20" dbh5,057,48016.3%

5Large tree20-30" dbh3,809,68712.3%

6Giant tree>30" dbh1,244,2954.0%

 TOTAL 31,037,750100.0%

dbh=diameter at breast height    

 

If we consider “big” trees to be those of 20”+ dbh, then the data in Table 1 shows that we have a bit over 5 million acres of big trees, and this totals about 16 percent of Oregon’s forestland.

In terms of protection for the big trees, people generally think of trees being protected if they’re in some sort of a reserve, such as a National Park, Wilderness Area or Late Successional Reserve. Table 2 shows the types and extent of reserved forest areas in Oregon. It also shows acres of large trees included in those reserve areas. Each of these types of Reserved Forest Areas is a bit different. However, they all have in common that little or no timber harvest is allowed within their boundaries. Big trees in Reserved Forest Areas are not likely to be harvested.

 

Table 2: Oregon Forested Area - Reserved Forest Areas and Large Trees

Reserve ClassAcres in 
Large TreesPercent of 
Large TreesAcres in 
Medium TreesForested AcresPercent of Forest

Adaptive Management Areas167,3923.3%78,615524,9281.7%

Administratively Withdrawn140,8132.8%96,286525,3441.7%

National Parks, Monuments & Wildlife Refuges56,0191.1%41,527303,3101.0%

Late Successional Reserves1,393,58427.6%549,0963,525,94311.4%

Wilderness Areas519,53710.3%435,5991,998,5406.4%

Key Watersheds outside other Reserves368,9597.3%216,1821,502,2914.8%

Total Reserved Areas2,646,30352.4%1,417,3048,380,35727.0%

      

Total Non-Reserved Areas2,407,67947.6%3,640,17622,657,39373.0%

Total Area5,053,982100.0%5,057,48031,037,750100.0%

 

Table 2 shows that Reserved Forest Areas total over 8.3 million acres, or about 27 percent of Oregon forestland. These reserves contain about 2.6 million acres, or about 52 percent of the large-tree acres. So, to answer our question, there are over 5 million acres of big trees in Oregon, and about 2.6 million acres of these are protected.

The graphic at the top of the blog shows the 31 million acres of forestland in Oregon as arrayed along a ruler. The green area on the left represents the 22.6 million acres of non-reserved forest, while the blue area to the right represents the 8.4 million acres of Reserve Forest Areas. The 5 million acres of large trees is shown as a purple band that crosses the blue-green boundary, with 2.4 million acres of non-reserved large trees shown in green with purple overlay and 2.6 million acres of reserved large trees shown in blue with purple overlay.

After examining LEMMA data on tree size classes and data on Reserved Forest Areas, I conclude that there are lots of big trees left in Oregon; about one half are protected in reserved forest areas. Over time, there will be more big trees, and most will be protected in reserved forest areas. For a more complete discussion of big trees and reserved areas, including maps, read the Featured Story on the OFRI website.

For the Forest,
Mike Cloughesy, 
Director of Forestry