Historical and Contemporary Lessons From Ponderosa Pine Genetic Studies at the Fort Valley Experimental Forest, Arizona

Forest management will protect genetic integrity of tree species only if their genetic diversity is understood and considered in decision-making. Genetic knowledge is particularly important for species such as ponderosa pine (Pinus ponderosa Dougl. ex Laws.) that are distributed across wide geographic distances and types of climates. A ponderosa pine study initiated in 1910 at the Fort Valley Experimental Forest is among the earliest ponderosa pine genetic research efforts in the United States. This study contributed to the description of ponderosa pine’s varietal differences, genetic diversity and adaptation patterns, and helped confirm the importance of using local seed sources. The role this and other pioneer studies had in improving forest management of ponderosa pine was, and still is critical. These early studies have long-term value because they improve our knowledge of responses to climate change and our understanding of genetic variability in physiology and pest resistance in older trees. More recently, studies of natural ponderosa pine stands at Fort Valley using molecular markers have shown the importance of stand structure and disturbance regimes to genetic composition and structural patterns. This knowledge is important to ensure ecological restoration efforts in ponderosa pine forests will also restore and protect genetic integrity into the future. Highlights of these historical and contemporary studies at Fort Valley are summarized and their applications to management of ponderosa pine forests are described. Most of the seedlings used to establish the Fort Valley provenance test were grown by G. A. “Gus” Pearson in a nursery at Fort Valley. The nursery-grown seedlings were transplanted into the test site located west of the Experimental Forest Headquarters at 7,300 feet elevation. The seedlings were hand-planted at a 6-foot spacing, in rows oriented east-west. Each row represented one seed source and varied in length up to 660 feet. Survival was monitored annually until 1919, and then in 1928, 1951, 1964, and 1995. Heights were measured in 1928, and both height and diameter were measured in 1964 and 1995-1996. It is noteworthy that the 1995-1996 data were collected by Roy Silen, who was a retired project leader for genetics research, USFS Pacific Northwest Forest Research Station in Corvallis, Oregon. Roy Silen (who is now deceased) spent his personal time and resources during his retirement to measure this historical test because of his strong belief in the long-term value of such studies. Although some results of the Fort Valley test are summarized by Pearson in a variety of reports (e.g., Pearson 1950), the first full analysis of the provenance test was not published until 1966 in a USFS Research Note written by M. M. Larson,