Between 1925 and 1936, the Fort Valley Experimental Forest (FVEF) scientists initiated a study to examine a series of forest thinning experiments in second growth ponderosa pine stands in Arizona and New Mexico. These early thinning plots furnished much of the early background for the development of methods used in forest management in the Southwest. The plots ranged from 0.1 ac to 5 ac (0.04 ha to 2.02 ha) in size and many of the thinning plots and control plots were remeasured at 2 to 10-year intervals until the 1940s. The first thinning plots in the Southwest, called the White Spar plots, were established in 1925 on the Prescott National Forest. The residual trees on the thinned White Spar plots maintained higher growth rates than the control until the mid 1970s. The results from these early stand thinning experiments led G.A. Pearson, Director of FVEF, and others to largely abandon uniform thinning treatments and adopt the crop-tree thinning method as an improved method for thinning southwestern ponderosa pine stands

De Blois, Benjamin P.

Finkral, Alex J.

Moore, Margaret M.

Sanchez-Meador, Andrew J.

OpenKnowledge@NAU

USDA Forest Service RMRS-P-53CD.  2008. 197In: Olberding, Susan D., and Moore, Margaret M., tech coords. 2008. Fort Valley Experimental Forest—A Century of Research 1908-2008. Proceedings RMRS-P-53CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 408 p.Early Thinning Experiments Established by the Fort Valley Experimental ForestBenjamin P. De Blois, School of Forestry, Northern Arizona University, Flagstaff, AZ; Alex. J. Finkral, School of Forestry, Northern Arizona University, Flagstaff, AZ; Andrew J. Sánchez Meador, USFS, Forest Management Service Center, Fort Collins, CO; and Margaret M. Moore, School of Forestry, Northern Arizona University, Flagstaff, AZAbstract—Between 1925 and 1936, the Fort Valley Experimental Forest (FVEF) sci-entists initiated a study to examine a series of forest thinning experiments in second growth ponderosa pine stands in Arizona and New Mexico. These early thinning plots furnished much of the early background for the development of methods used in forest management in the Southwest. The plots ranged from 0.1 ac to 5 ac (0.04 ha to 2.02 ha) in size and many of the thinning plots and control plots were remeasured at 2 to 10-year intervals until the 1940s. The first thinning plots in the Southwest, called the White Spar plots, were established in 1925 on the Prescott National Forest. The residual trees on the thinned White Spar plots maintained higher growth rates than the control until the mid 1970s. The results from these early stand thinning ex-periments led G.A. Pearson, Director of FVEF, and others to largely abandon uniform thinning treatments and adopt the crop-tree thinning method as an improved method for thinning southwestern ponderosa pine stands.IntroductionIn 1908, the Fort Valley Experiment Forest (FVEF) was established with a pri-mary purpose of solving forest management problems in the Southwest (Pearson 1942). One issue of particular importance was how to manage densely stocked young stands of ponderosa pine (Pinus ponderosa Laws. var. scopulorum Engelm.), which were numerous throughout the Southwest by the early 1920s. This prompted G.A. Pearson, Director of the Station, to initiate the first thinning experiments in the Southwest.198 USDA Forest Service RMRS-P-53CD.  2008.Between 1925 and 1936, a series of seven forest thinning sites were established in second growth ponderosa pine stands in Arizona and New Mexico (Gaines and Kotok 1954). The objectives of these original thinning were to: 1) convert an es-sentially even-aged stand of second-growth ponderosa pine to a more uneven-aged structure through periodic partial cuttings, often referred to as crop tree thinnings (Krauch 1949); 2) shorten the rotation period required to produce crop trees of saw-log size; and 3) determine the volume of wood that could be periodically harvested in both thinned and unthinned stands. The crop tree method involved selecting 60 to 120 trees per acre as crop trees. If a designated crop tree held a dominant position in the canopy, then little to no release was prescribed. If the crop tree did not hold a dominant position in the canopy, then the crown was freed on at least three sides (Gaines and Kotok 1954). In this paper, we list the location, size, and establish-ment date for all of the original thinning studies established by the FVEF between 1925-1936, and we describe the earliest thinning study site, the White Spar site, in detail.Study SitesStand thinning plots were located in a variety of locations and stand conditions, with the unifying factor being an overstory dominated by naturally regenerated ponderosa pine. Table 1 provides an overview of each study site. The majority of the plots was located in pole-sized stands of ponderosa pine of various ages while the Decker Wash and Corey Pasture plots were established in stands of sapling-sized ponderosa pine (12-20 years old) that established in 1914 (Gaines and Kotok 1954).Table 1. Overview of each series of experimental sites and plots established in the Southwest between 1925-1936 (information from Gaines and Kotok 1954). Site Number Acreage (ac) Establishment  Last Historical  Elevation (ft) Forest Name of Plots (ha) Date Re-measurement (m)Apache Sitgreaves Decker Wash 5 0.12 to 0.14 1926 1948 7,000   (0.12 to 0.05)   (2,133)Coconino Ft. Valley- Ranger 7 0.04 to 0.15 1927 1946 7,600   (0.02 to 0.06)   (2,316) Ft. Valley- Sec. 19 8 0.27-0.50 1936 1947 7,600   (0.11 to 0.20)   (2,316) Ft. Valley- Corey Pasture 4 0.12 1934 1947 7,350   (0.05)   (2,240)Gila Redstone 16 0.1-0.25 1933 1948 7,300   (0.04 to 0.10)   (2,225)Prescott Copper Basin 3 0.6 1933 1948 6,400   (0.24)   (1,951) White Spar-A 4 0.24-4.2 1925 1946 5,500   (0.10 to 1.70)   (1,676)USDA Forest Service RMRS-P-53CD.  2008. 199The White Spar plots were the earliest plots established, and are the only ones that have been re-measured since the late 1940s. These plots are located on the Prescott National Forest in central Arizona. The plots are located at an elevation of 5,800 ft (1,768 m) and receive approximately 19 inches (50 cm) of precipitation per year (Fogarty and Staudenmaier 2007). The soils are derived from granite and are fairly shallow (Pearson 1936).MethodsUpon plot establishment, trees were tagged and their height and diameter at breast height were measured and recorded. After each thinning treatment, plots were re-measured at 2 to10-year intervals up until the late 1940s. The White Spar site consisted of two control plots, plots B and D, and one treated plot, plot A.To remeasure the White Spar plots, we used the same survey and inventory methods that were used at plot establishment in 1925. Measurements were taken in English units and later converted into metric units. The original plot corners were destroyed, so we relocated trees with historical tags and then reestablished a plot perimeter that captured all tagged trees. If the original tree tag still existed, we measured the diameter at the location of the original nail and tag. Otherwise, diameters were measured to the nearest tenth of an inch at breast height (4.5 ft or 1.37 m above ground) using a diameter tape. All living trees, which were left as the result of thinning in 1925, were cored to determine age and decadal growth rates from 1925-2005.Increment core samples were mounted, sanded, and cross-dated with a tree ring chronology from a research site near Granite Mountain on the Prescott National Forest (PIPO-ITRDB AZ036; NOAA 2006). After crossdating many cores, we adapted the Granite Mountain chronology data and created a chronology list for the White Spar plots. After each core was crossdated and inspected, radial decadal growth increments were measured.To quantify radial growth, we converted the radial growth (from pith to last tree ring) measurements into 10-year basal area increments (BAI). A BAI is a mea-sure of tree growth over a given period of time. This conversion was performed to account for the fact that distance between growth rings may decrease as the tree increases in size even if actual growth rates remain the same (Thomas and Parresol 1989).ResultsThe current status of each original thinning study site is summarized in Table 2. Many sites have yet to be relocated and a portion of those that have been relocated are no longer in a condition that can be re-measured.The White Spar site was relocated and the plots were remeasured during the summer of 2005 (Figure 1a,b). The thinned plot had a higher BAI until the 1970s. Control plot B never surpassed the growth rates of either the thinned plot or control plot D. Control plot D had the highest BAI from the 1980s until 2005 (Figure 2).200 USDA Forest Service RMRS-P-53CD.  2008.Table 2. Overview of each series of experimental sites and plots established in the Southwest between 1925-1936 (information from Gaines and Kotok 1954).Forest Site Name Re-located Condition of PlotApache-Sitgreaves Decker Wash  No UnknownCoconino Ft. Valley- Ranger No Unknown Ft. Valley- Sec. 19 No Unknown Ft. Valley- Corey Pasture No UnknownGila Redstone 8 of 16 Variable, but mostly intactPrescott Copper Basin Yes Rendered useless by road and insects White Spar Yes Intact and Re-measuredFigure 1a, b. Photographs of White Spar site taken in 1925 (top) as well as a photograph taken in 2005 (bottom). (Source: 1925 photo, Fort Valley Archives Image #20539, 2005 photograph by Ben De Blois).USDA Forest Service RMRS-P-53CD.  2008. 201Discussion and ConclusionsThese studies were the first to demonstrate the effects of thinning ponderosa pine forests in the Southwest. All seven study sites demonstrated that diameter growth of crop trees was increased when competition was decreased (Gaines and Kotok 1954). Although this does not seem surprising to foresters today, the spacing guide-lines and potential tree growth for ponderosa pine stands were largely unknown when these studies were established.Ultimately, the results from these early stand thinning experiments led Pearson and others to abandon uniform thinning treatments and adopt the crop-tree method as a more general thinning guide in southwestern ponderosa pine stands (Pearson 1950). The findings of these studies were directly applied to timber stand im-provement guidelines throughout the Southwest (Gaines and Kotok 1954, Pearson 1940).The White Spar plots demonstrate that the crop tree thinning method allowed the residual trees on the thinned plots to maintain higher growth rates for about 50 years. Such findings are consistent with that of earlier studies performed on the White Spar plots (Gaines and Kotok 1954, Krauch 1949, Pearson 1936). Our data also suggest that an additional thinning occurred in the early to mid 1970s, because there is a notable increase in radial growth, especially in control plot D. More de-tails about the pre-treatment stocking levels would be useful and may have shown why the thinned plot had a higher net basal area before the thinning treatment Figure 2. Comparison of the basal area growth increments (BAI), after converting radial growth into basal area growth per tree per year averaged over each ten year period, for the thinned and unthinned White Spar plots.0510152025301920 1930 1940 1950 1960 1970 1980 1990 2000Decadal Measurements (Years)BA Growth (cm_)Thinned PlotControl BControl D 202 USDA Forest Service RMRS-P-53CD.  2008.occurred. For example, Krauch (1949) states that many of the pine stands were nearly clear-cut 40 years prior to the establishment of the White Spar study site. Such information on the stand history is critical in determining conditions prior to thinning and suggests other factors that might influence tree growth.The rigor of experimental design in forestry studies has changed significantly since these early thinning trials in the Southwest. The study sites were not randomly located or thoroughly replicated. Microsite differences may have had a dispropor-tionate affect on the results for the White Spar study site and possibly the other thinning studies. However, these original thinning plots, established by the Fort Valley Experimental Forest in the 1920s and 1930s, furnished much of the ear-ly background for the development of methods used in forest management in the Southwest today.AcknowledgmentsWe thank Jonathan D. Bakker and Thomas E. Kolb for reviewing earlier versions of this paper. The 2005 resurvey of the White Spar thinning plot was supported by USDA Cooperative State Research, Education and Extension Service grant 2003-35101-12919. Additional funding and personnel support was provided by the Ecological Restoration Institute (ERI) at Northern Arizona University and a NAU Hooper Undergraduate Research award granted to B. De Blois. We are grateful to Jonathan Bakker, Jacob Dyer, Dave Bell, Don Normandin and numerous people from the ERI who provided field, laboratory, data entry assistance, and logistical support. We thank the Prescott National Forest for permission to conduct sam-pling. We also thank Susan Olberding, archivist and historian, RMRS Fort Valley Experimental Forest Archives, Flagstaff, AZ, who helped us locate historical maps, photos and ledger data. Finally, we are indebted to G.A. Pearson, who had the fore-sight to establish these permanent thinning plots in 1925 to advance the knowledge of southwestern ponderosa pine management today.ReferencesFogarty, B.; Staudenmaier, M. 2007. NOAA Technical Memorandum NWS WR-274. http://www.wrh.noaa.gov/wrh/techMemos/TM-274.pdfFort Valley Archives, USFS Rocky Mountain Research Station, Flagstaff, AZ. http://www.rms.nau.edu/imagedb/viewrec.shtml?id=19038&colid=fvGaines, E.M.; Kotok, E.S. 1954. Thinning ponderosa pine in the Southwest. Sta. Pap. 17. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 20 p.Krauch, H. 1949. Results of thinning experiment in ponderosa pine pole stands in Central Arizona. Journal of Forestry. 47: 466-469.NOAA, Contributors of the International Tree-Ring Data Bank, IGBP PAGES/World Data Center for Paleoclimatology, NOAA/NGDC Paleoclimatology Program, Boulder, Colorado, U.S.A. 2006. http://www.ngdc.noaa.-gov/paleo/treering.htmlUSDA Forest Service RMRS-P-53CD.  2008. 203Pearson, G.A. 1936. A thinning experiment applied to timber stand improvement. Journal of Forestry. 34: 855-861.Pearson, G.A. 1940. Timber stand improvement in the Southwest. Forestry Pub. 6. Southwest Forest and Range Experiment Station. 12 p.Pearson, G.A. 1942. The Fort Valley Experiment Station. Tucson, AZ. USDA Forest Service. 25 p.Pearson, G.A. 1950. Management of ponderosa pine in the Southwest. Agriculture Monograph 6. USDA Forest Service, Government Printing Office. Washington, DC.Thomas, C.E.; Parresol, B.R. 1989. Comparing basal area growth rates in repeated inventories: Simpson’s Paradox in forestry. Forest Science. 35: 4.The content of this paper reflects the views of the author(s), who are responsible for the facts and accuracy of the information presented herein.

Early thinning experiments established by the Fort Valley Experimental Forest

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Early thinning experiments established by the Fort Valley Experimental Forest

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