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80 Years of Change in a Ponderosa Pine Forest

p13_1909_250tall_thumb80 Years of Change in a Ponderosa Pine Forest

Living things change constantly, as do communities of living things. In a forest, where individual trees can live for centuries and new plants replace old plants, it is not easy to visualize the changes that occur over time.

Luckily, we have some records and photos that illustrate how forests change. This poster shows how one stand of ponderosa pine (Pinus ponderosa), located in the Lick Creek drainage of the Bitterroot National Forest, Montana,  changed throughout the 1900s. The initial photo was taken in 1909 to document a timber sale, the first large harvest of ponderosa pine from the northern Rocky Mountains. Sadly, there is no photo of the stand before that first harvest, which removed about half of the large pines on the site. Afterwards, however, photos were taken periodically from exactly the same spot. Now, nearly a century later, the photo series illustrates both immediate and long-term changes on the site. Especially noticeable are increases in tree density and a shift from ponderosa pine to Douglas-fir (Pseudotsuga menziesii) dominance. This kind of change took place in both logged and unlogged ponderosa pine forests of the northern Rockies during the 1900s.

Details about "80 Years of Change in a Ponderosa Pine Forest"

Before the First Photo:

In the 1900s, this was an open forest of Ponderosa pine (Pinus ponderosa), typical of millions of acres of forest in the western United States. The forest contained scattered large trees and patches of young trees. Fires had burned through the grass and pine litter on the forest floor every seven years, on average, since before 1600. These fires had little impact on large trees but killed many of the young trees, although some survived. The original forest had about 50 trees per acre and plenty of grass and lupine, an early summer wildflower that supplies nitrogen to the soil. Each time a fire burned through, it would kill the tops of the grasses and flowers, but they resprouted from underground stems, sometimes within weeks. There were few tall shrubs but many low-growing ones, because frequent fires killed the tops of many shrubs and they had to resprout from their roots after every fire.

About the Six Photos on the Poster:

Please click on each image to see a larger version.



Here we see “cleanup” operations after loggers used horses to harvest about half of the trees on the site. They left half as “reserve” timber for a second cut and to provide seed for a new generation of trees. Most of the Douglas-firs (Pseudotsuga menziesii) were harvested, even though they were of lower economic value, to keep a native parasitic plant, Western dwarf mistletoe (Arceuthobium campylopodum), from spreading through the stand.


The reserve trees grew quite well for 40 years, especially during the first decade after logging and during a period of high rainfall about 30 years later. Some trees were blown down shortly after logging, but few others died. Young ponderosa pine and Douglas-fir became established. These young trees grew about one inch in diameter every three to four years.


To make room for the young trees to grow well, most of the undamaged Douglas-firs over 14 inches in diameter were harvested in the 1950s. Loggers also cut dead-topped and lightning-damaged trees, slow-growing old trees, trees with decay near the base, and trees leaning more than 20 degrees.


In 1962, some large trees were cut and patches of smaller trees were thinned. The most striking result captured in these photos is the proliferation of ponderosa pine seedlings. Ponderosa pine seedlings originate sporadically, in years after the trees produce abundant cones, and grow well in open spaces and on bare soil.


Lots of young Douglas-fir seedlings are growing among the pines. Douglas-fir tolerates shade and dense forest conditions better than pine, so its seedlings can grow even when the site is partly occupied by taller trees and is quite shady.


Ponderosa pine and Douglas-fir seedlings have developed into a dense understory. Tree branches are almost continuous from the ground into the tops of the tallest trees, so wildfires are not likely to stay in the grass and shrubs on the forest floor. Instead, they are likely to burn up into the tree crowns by way of the “ladder fuels” provided by saplings and young trees. Eighty years ago, wildfires changed the forest very little. Now they are likely to kill even the oldest, tallest trees on the site.


Related Materials

Print the poster ( 8.5" x 11" or 16" x 24").pdf_icon


Most of the information here, and much more information on forest ecology and management in the Lick Creek area, comes from the following publication:

Smith, Helen Y.; Arno, Stephen F., eds. 1999. Eighty-eight years of change in a managed ponderosa pine forest. Gen. Tech. Rep. RMRS-GTR-23. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 55 p.