USDA Forest Service

Pacific Southwest Research Station

 
Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Forest Management

Methods of Cutting Studies, Stanislaus-Tuolumne Experimental Forest

black and white photo of forest in the background
Old-growth forest near Pinecrest in 1929, showing groups of trees of varying age and size, intermixed with small gaps. (U.S. Forest Service/Duncan Dunning)

Background and project overview

Early in the history of US Forest Service research program, studies of outcomes from different harvest methods were set up on various national forests in Region 5, as well as other states. Trees were typically mapped in plots ranging from 5 to 25 acres (2 to 10 ha) in size (some on the Modoc National Forest were larger), and tree regeneration and growth followed over time. Between 1909 and 1930, twelve of these plots were established on the Stanislaus National Forest, of which four lie fully or mostly within what later (in 1943) became the Stanislaus-Tuolumne Experimental Forest. Stanislaus Method of Cutting plots 8 through 11 (hereafter MC8-11) were mapped and measured in 1928 and 1929, logged shortly thereafter, and due to their location on an experimental forest, have been relatively undisturbed since. These are among the oldest intact USFS research plots known to still exist in California.

Duncan Dunning, who headed the division of forest management research for the USFS California Forest and Range Experiment Station at the time, and a lead figure in the establishment these plots wrote in a 1930 report that the objective of MC8 was "to determine the growth rate and net growth of the residual stand after a heavy Forest Service cutting in an all-aged forest of the sugar pine-white fir type under optimum conditions, and the effects of cutting, logging, and slash disposal upon the survival and growth of advance reproduction, the rate of restocking, and changes in the composition of timber species and other vegetation." Dunning further wrote that "one special object of this experiment is to determine whether the proportion of sugar pine can be increased in a stand where the natural replacement by white fir is in progress." In a progress report, Hasel et al. (1934) described the objective of the study for plots MC9-11 as "to determine the growth rate and net growth, and to determine the rate of restocking after a light, a moderate, and a heavy selection cutting."

Study area

The study is located in the Stanislaus-Tuolumne Experimental Forest, a 1700 acre (518 ha) area of the Stanislaus National Forest, near Pinecrest, CA, set aside for research purposes. The experimental forest was formally established in 1943 to represent high site quality mid-elevation (5200 and 6400 ft, or 1585 to 1951 m) mixed conifer forest, but scientists have been doing research in this area since shortly after the US Forest Service was established in 1905. A fire history study of fire scars in the tree rings shows that this site historically burned approximately every 6 years. The last fire occurred in 1889.

Methods

black and white photo of forest in the backgroundblack and white photo of forest in the background
Illustration of forest change in one acre of mixed conifer forest from 1929 to 2008. From – 'Methods of Cutting' study, Stanislaus-Tuolumne Experimental Forest, Stanislaus NF. Large trees were logged later in 1929, and the forest recovered in the absence of fire.

MC plots were initially mapped by dividing them into a two-chain (one chain = 66 ft or 20 m) grid. Within the grid, tree locations were mapped using a transit and measuring tape and individually tagged with metal tags hand stamped with a unique number. Cover of shrubs, rock, patches of regeneration, and downed logs (this latter variable only on MC9-11) were also mapped (See illustration).

Tree diameters were measured with a diameter tape and tree height with a hypsometer. Measurements were first made in the pre-logging old growth condition. Plots were logged in the fall of 1928 (MC8) or summer of 1929 (MC9-11) and the remaining trees remeasured in the spring of 1929 (MC8) or late summer and early fall of 1929 (MC9-11). Tree measurements were repeated in 1934 and 1939. More intensive data on tree regeneration, shrub, and herbaceous species were collected along transects of milacre (0.001 ac or ~4m2) quadrats that traversed each plot and periodically remeasured until 1947. Data were used in numerous early publications, including tree volume and growth tables (Dunning 1942) as well as a study of post-harvest stand development (Fowells and Shubert 1951).

Much of the original data were found in the National Archives in San Bruno, CA. These data and maps provide a detailed view of the density, species composition, size distribution and structure of productive old-growth mixed conifer forest in 1929. Plots were re-located around 2006. Many of the original metal tags were still visible. Plots were remapped and remeasured in 2007/2008 (MC9-11) and 2016 (MC8) to quantify forest change over time as the forest recovered from logging in the absence of fire. Ingrowth was tagged and tree locations were mapped using a laser rangefinder mounted on tripod placed at points where coordinates had been determined with a Trimble GeoXT global positioning system. Tree diameter measurements were taken as before, but height measured on only a subset of trees in order to develop diameter to height relationships for each species.

black and white photo of forest in the background
MC9 showing abundance and location of canopy gaps (yellow) in 1929 and 2008. The purple is a buffer around plot edge. Tree species: ABCO = white fir, CADE = incense cedar, PILA = sugar pine, PIPO = ponderosa pine.

Results - highlights

Key findings from this investigation of forest change – from old growth in 1929 to the contemporary condition:

  • The historical old growth forest consisted of groups of trees, individual large trees, and small gaps. This structure made crown fire uncommon and contributed to the resilience of the forest to wildfire.
  • Plots in 2007/08 were 2.4 times denser (299 trees per ac or 739 per ha) than the same plots in the old-growth condition in 1929 (127 trees per ac or 314 per ha).
  • Understory shrubs covered 29% of the forest floor in 1929 and only 2% of the forest floor in 2008. Much of this change was likely due to the loss of higher light environments.
  • One of the most striking changes was the decline of forest gaps, which in the absence of fire filled with trees. The contemporary forest also lacks the largest most fire resistant trees that were found in historical forests.
  • Tree species composition shifted to a higher proportion of white fir and incense cedar, and less pine. Very few small pines were found. In the absence of fire, species such as pines that grow best in high light environments do not regenerate well.
  • Over 9 times more standing snags were noted in 2008 and many more logs were found on the forest floor in 2012 than were present in 1929. Contemporary snags and downed logs are generally smaller in size and much of this wood is quite rotten. More numerous, smaller diameter, and more heavily decayed wood potentially further increases the fire hazard.

These changes are similar to those that have occurred in formerly frequent fire forests throughout the western U.S. Many of the changes can be attributed to the removal of fire from the system. The added fuels increases their susceptibility to stand replacing wildfire, helping to explain the behavior of recent fires such as the Rim Fire, which burned through similar forests just south of the Stanislaus-Tuolumne Experimental Forest. Forest densification also contributed to the recent drought-related tree mortality event that peaked in the central and southern Sierra Nevada, killing over 147 million trees. Loss of forests to disturbance events such as wildfire and drought highlights the need for restoring more resilient conditions.

Last Modified: Jun 26, 2020 06:05:03 PM