The Teakettle Experiment1 

Malcolm P. North2 

Abstract 

A critical question in the Sierra Nevada concerns how to use disturbance effectively to 

restore forest ecosystems after nearly a century of fire suppression. With increases in 

stem densities and ladder fuels, many forests require a combination of stand thinning 

and controlled burning to mimic natural fire intensity. In spite of their widespread use, 

the different effects of fire and thinning on fundamental ecological processes have never 

been studied in mixed-conifer forests of the Sierra Nevada. The Teakettle Ecosystem 

Experiment is designed to compare these effects in an old-growth, experimental forest by 

applying fire and thinning manipulations in a factorial design. By using integrated 

sampling methods, coordinated studies will follow vegetation, soil, microclimate, 

invertebrate, and tree response variables before and after treatments on replicated plots. 

These five component studies will provide a core understanding of changes in ecosystem 

allocations of energy, water, and nutrients among plants and first-order consumers. 

Responses of these baseline processes should provide important metrics of fundamental 

changes in ecosystem conditions throughout higher trophic levels. This experiment can 

provide an important contrast of how the type and intensity of disturbance affect forest 

functions and succession. 

A fundamental question concerning forest management in the Sierra Nevada 

of California involves the degree to which selective timber harvesting mimics the 

ecological effects of the natural fire-disturbance regime. If thinning differs from 

burning, what ecosystem functions and processes are being altered, what are the 

consequences of these changes, and how might the effects be mitigated? 

In the Sierra Nevada, fire historically has been the disturbance dynamic driving 

forest ecosystem structure, function, and composition. If forest management is to 

conserve biodiversity and maintain ecosystem functions, the effects of silvicultural 

treatments should approximate the disturbance regime by which the flora and fauna 

of the Sierra have evolved. In the summary section of critical findings, the report 

from the recent Sierra Nevada Ecosystem Project (SNEP 1996, summary p. 4-5) 

emphasized that this essential information was absent: 

Although silvicultural treatments can mimic the effects of fire on structural 

patterns of woody vegetation, virtually no data exist on the ability to mimic 

ecological functions of natural fire. Silvicultural treatments can create 

patterns of woody vegetation that appear similar to those that fire would 

create, but the consequence for nutrient cycling, hydrology, seed 

scarification, nonwoody vegetation response, plant diversity, disease and 

insect infestation, and genetic diversity are mostly unknown. 

Accordingly, the Teakettle Ecosystem Experiment has been designed to 

compare the impacts of fire and timber harvest on key ecosystem functions in 

old-growth, mixed-conifer forest of the Sierra Nevada. 

1 	 An abbreviated version of this 

paper was presented at the 

Symposium on the Kings River 

Sustainable Forest Ecosystems 

Project: Progress and Current 

Status, January 26, 1998, Clovis, 

California. 

2 	 Research Ecologist, Pacific 

Southwest Research Station, 

USDA Forest Service, 2081 E. 

Sierra Ave., Fresno, CA 93710. 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 47 
North 

Figure 1—Teakettle Experimental 

Forest (shaded) abuts the 

southeastern edge of the Kings 

River Sustainable Forest Ecosystems 

Project area. Major water bodies 

are numbered: 1–Shaver Lake; 2– 

Courtright Reservoir; 3–Wishon 

Reservoir; 4–Pine Flat Reservoir. 

48 

The Teakettle Experiment 

Teakettle’s Role in the Kings River 

Administrative Study 

Landscape-level research, such as that in the Kings River Sustainable Forest 

Ecosystems Project (KR Project), is ideal for studying within a watershed such 

large-scale processes as hydrology, geomorphology, large animal movements 

and habitat requirements, and management effects on forest fragmentation. All 

of these processes, however, build on fundamental ecosystem dynamics, many 

of which operate at a much finer scale. Changes in an ecosystem are often the 

cumulative effect of many site-specific alterations in the exchange of energy, 

nutrients, and interactions within the food web. Changes in these stand-level 

processes can cascade through higher trophic levels, fundamentally altering a 

watershed’s ecological dynamics. 

The Teakettle Experimental Forest (Teakettle), located on the southeastern 

edge of the KR Project area (fig. 1), is typical of mixed-conifer forests in this area. 

Teakettle is 1,300 ha of old-growth, mixed-conifer and red fir (Abies magnifica) 

ranging in elevation from 1,980 m along the southern boundary to 2,590 m at the 

top of Patterson Mountain, along the northern boundary. Annual precipitation 

averages 110 cm at 2,100 m, falling mostly as snow between November and May. 

Mean, maximum, and minimum July temperatures are 17o

C, 30oC, and 3oC (Berg 

1990). Teakettle grades from a mix of white fir (Abies concolor), sugar pine (Pinus 

lambertiana), incense-cedar (Calocedrus decurrens), Jeffrey pine (Pinus jeffreyi), and 

red fir at the lower elevations to red fir, lodgepole pine (Pinus contorta), and 

western white pine (Pinus monticola) at higher elevations. Soils are generally 

Xerumbrepts and Xeropsamments typical of the southwestern slopes of the 

Sierra Nevada (Anonymous 1993). 

Research Design 

Ecological research requires a robust experimental design to assure that treatment 

responses can be detected amongst the variability inherent in complex, interactive 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
The Teakettle Experiment 

processes. The Teakettle experiment is a controlled, replicated, manipulation study. 

Baseline data on ecosystem functions will be collected for 2 years on replicated 

treatment and control sites, followed by treatments and 4 years of data collection on 

responses. This design has advantages over chronosequence or comparison studies, 

where often little control is possible over replication or treatment effects. 

Furthermore, conducting multiple studies on the same sites will enable scientists to 

examine the interaction effects among different ecosystem components. 

Selecting a plot size and identifying replicated sites can be difficult in mixedconifer because of its variability. The size of a representative unit or stand of 

Sierra mixed-conifer forest has never been identified. In a new approach, this 

problem was addressed following a three-step process using two data sets 

collected during the 1997 field season. 

In the first step, a field crew established a reference grid 100 by 100 m 

throughout the 1,300 ha of Teakettle using a surveyor’s total station, permanently 

marking each point with Cartesian coordinates, and sampling vegetation. These 

data were analyzed with cluster analysis, and all mixed-conifer association 

points were mapped. In the second step, soils within the mixed-conifer areas 

were surveyed using soil pits and augur extraction. The most common soil was a 

well-drained, mixed, frigid Dystric Xeropsamments, formed from decomposed 

granite typical of many southern Sierra forests (Anonymous 1993). Mixed-conifer 

areas with other soil types were eliminated from further consideration. 

In the final step, a grid 50 by 50 m was established within the selected areas, 

and vegetation was intensively surveyed (20 percent sample of the area). We 

used two methods to determine plot size and how to replicate mixed-conifer’s 

heterogeneity. Plot size was determined by calculating the distance from a fixed 

point required to incorporate the full range of variability in the vegetation data. 

Basal-area-by-species data were converted to linear, univariate values using 

eigenvalue scores from a principal components analyses. A variogram analysis 

(Anonymous 1991) indicated that 58 percent of the data’s variability was present 

even in adjacent points (the relative nugget effect) and that points 180 m apart 

were spatially independent (the sill value) (Bailey and Gatrell 1995). The large 

nugget effect implied that an effort to use a small plot to replicate vegetation 

would be difficult. By using the sill value as a guide, a plot size of 200 by 200 m 

was selected as large enough to include the range of variability within Teakettle’s 

mixed-conifer forest. 

In the second method, vegetation data were analyzed with cluster analysis 

and all 50-by-50-m points were mapped as one of the four identified clusters. The 

relative percentages of each cluster type were calculated (for example 11 percent 

of all points were type 1) and plot windows of 200 by 200 m were moved over the 

grid points until the enclosed set of points contained a representative ratio of the 

four cluster types. Tree density, basal area, and species composition were 

compared with one way ANOVA and 18 plots were selected with no significant 

difference (P > 0.05). 

Treatments 

In forests, many structural components such as litter depth, tree size, shrub cover, 

and snag and log volumes covary. Covariance can make it difficult to isolate and 

identify processes, and multicollinearity among measured variables can significantly 

weaken data analysis (North and Reynolds 1996). Although it is with reservation 

that the experiment proposes manipulating old growth, some perturbation is 

required to tease apart the covariation of components in a forest ecosystem. 

Six stand conditions will be determined by combinations of fire and tree 

removal (table 1). Each of these six conditions will be replicated three times on 4-

ha plots. Burn treatments will have two levels: no burn and a ground fire. The 

burn is designed to mimic the historical disturbance regime by containing the 

North 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 49 
North The Teakettle Experiment 

Table 1—Full factorial design of the Teakettle Experiment 

Thinning level No burn Understory burn 

None Control Burn only 

From below Light thin/No burn Light thin/Burn 

Shelterwood Heavy thin/No burn Heavy thin/Burn 

flames to a ground fire and avoiding overstory crown ignition (Skinner and 

Chang 1996). Ladder fuels—understory trees with tops within 5 m of overstory 

tree crown bases—will be felled and left on the ground prior to burning. 

Thinning treatments will contrast three levels of tree removal: no removal 

(present forest conditions), removal of the understory (thinning from below), 

and removal of the overstory (shelterwood harvest). Understory thinning 

removes all trees with a diameter at breast height (dbh) <76 cm, and overstory 

thinning removes all stems >30 cm in dbh, except 15-18 of the largest trees per ha. 

Understory thinning mimics stem reduction patterns noted in post-wildfire 

studies in the Sierra Nevada, where mortality is associated with a tree’s size and 

canopy position (McKelvey and Johnston 1992, Weatherspoon 1996). Many 

smaller trees are shade-tolerant species with thin bark and a low crown base, so 

they ignite easily. While understory thinning may mimic the tree structure 

produced by a ground fire, the removal of stem wood and increase in litter and 

shrub cover will produce a significantly different effect on carbon pools and 

flows. Sierra National Forest personnel will mark and administer the thinning, 

following current guidelines outlined in the California Spotted Owl (CASPO) 

Report (Verner and others 1992). 

Overstory thinning removes most of the stand’s large structures, leaving 15-18 

widely spaced, dominant trees per ha and regenerating trees with a dbh <30 cm. This 

method is used to mimic stand structure 40 years after an intense wildfire in which 

small-diameter regeneration is filling in the gaps between a few widely spaced, 

“legacy” trees (Skinner and Chang 1996, Stephenson and others 1991). Although a 

less frequent disturbance historically, these types of fire may have provided the large 

openings required for pine regeneration and be important for creating mixedconifer’s combination of shade-tolerant and intolerant species. Overstory thinning 

will produce a distinct tree structure, composition, and distribution from ground fire 

or understory thinning treatments. 

Research Studies 

Multiple-study or “pulse” research at a common site allows scientific 

collaboration across disciplines and can provide insights into ecosystem 

interactions often hidden from single-study experiments. The Teakettle 

Experiment focuses on elemental pathways in a forest ecosystem—nutrients, 

moisture, energy, and food—and their allotment among soil, plants, 

invertebrates, and “higher” animals (fig. 2). 

In each study, conditions will be monitored for 2 years before and 4 years 

after treatments (table 2). Detailed information on sampling protocol is available 

at the Teakettle Experiment website (http://teakettle.ucdavis.edu). 

Post-treatment analyses will examine both treatment-induced changes in the 

pathways, in kind and magnitude, and the dynamic relations among the 

components as the system responds to disturbance. This allows for revision of a 

model’s hypothesized pathways developed from the pretreatment analysis, as 

well as exploration of temporal feedbacks arising from the different disturbances. 

50 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
The Teakettle Experiment North 

Figure 2—Schematic of the 

hypothesized interactions of 

different component studies 

in the Teakettle Experiment. 

Three scales in the 

experiment are: the five 

component studies; 

ecosystem interactions that 

are the pathways within the 

box; and overall ecosystem 

response, which is shown at 

the bottom. C = carbon, N = 

Project Coordination and Data Integration 

A common sampling design was developed with the project’s statistician to 

ensure that component studies collect data at the same mapped sample points. 

The goal of this design is to measure plot-level differences among the six 

treatments as well as to assess spatial variation within a treatment. Mixedconifer forests are highly heterogeneous, and we expect data values within a plot 

to vary in response to small-scale changes in forest conditions, such as canopy 

cover, stem density, and litter depth. To address this variability, one replicate of 

each of the six treatments will be sampled intensively on a seven-by-seven grid 

(points spaced 25 m apart, including a 25-m buffer to the plot boundary). These 

49 within-plot samples serve to determine the scale at which data points for a 

particular measure become independent, using variogram analysis. To 

interpolate among the discrete sample points, a response surface for each plot 

will be calculated using kriging analysis. A three-by-three grid with points 

spaced 50 m apart will be used at the two other replicate plots in each treatment. 

Data from these points will be averaged to calculate a mean plot response. Mean 

plot values from both sampling schemes will allow tests for significant differences 

among replicates. 

We will convert data from the mapped grid locations to layers in a geographic 

information system (GIS), using ARC/INFO and linked to S-Plus, allowing the 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 51 
North The Teakettle Experiment 

use of spatial statistics. Pretreatment analyses will be static examinations across 

space to detect the kinds of pathways and their magnitudes between specific 

components. GIS layers will be examined for patterns of spatial concordance 

among different variables. For example, soil sites with abundant invertebrates 

also may have high nitrogen levels or ceanothus shrubs. Robust data 

visualization tools, and bivariate Ripley’s K analysis will be used (Diggle 1983) to 

test for significant associations among component measures within treatment 

plots. Associations involving nonspatial component measures will be 

investigated using multi-dimensional scaling, canonical correlation analysis, and 

regression techniques appropriate to each data set (Jongman and others 1995). 

Associations will be used to develop hypothetical models of ecosystem pathways. 

Table 2—Research studies, scientists, and their institutional affiliation cooperating in the Teakettle Experiment 

Study Principle Investigator Institution 

Tree pathogens Tom Smith, Dave Rizzo	 University of California, 

Davis 

Fire history and stand Jim Bouldin, Michael University of California, 

reconstruction Barbour Davis 

Small mammal diets, Marc Meyers and Douglas University of California, 

movement, and demography Kelt Davis 

Fire history	 Robert Figener, Michael University of California, 

Barbour, and Malcolm Davis 

North1 

Epiphyte diversity and Thomas Rambo, Malcolm University of California, 

response North1,, and Michael Barbour Davis 

Decomposition Martin Jurgensen	 Michigan Tech. University, 

Houghton 

Microclimate, soil respiration, Siyan Ma and Jiquan Chan Michigan Tech. University, 

and NEP2 Houghton 

Canopy and shrub Timothy Schowalter Oregon State University, 

invertebrates Corvallis 

Tree regeneration and soil Andrew Gray USDA Forest Service, 

moisture Inventory and Monitoring 

Program, Portland, OR 

Soil and CWD3 invertebrates Jim Marra and Robert University of Washington, 

Edmonds Seattle 

Ceanothus, nitrogen, and Brian Oakley, Jerry Franklin, University of Washington, 

Frankia response and Malcolm North1 Seattle 

Mycorrhizal diversity and Antonio Innez and Thomas University of California, 

response Bruns Berkeley 

Soil nutrients Heather Erickson Universidad Metropolitan, 

SanJuan, PR 

Tree/shrub growth, mortality, Malcolm North1 USDA Forest Service, PSW 

and distribution ResearchStation, Fresno, CA 

Truffle abundance and Malcolm North1 USDA Forest Service, PSW 

diversity ResearchStation, Fresno, CA 

Herb diversity and response Malcolm North1	 USDA Forest Service, PSW 

ResearchStation, Fresno, CA 

1Project Coordinator, USDA Forest Service, Pacific Southwest Research Station, Fresno, California.


2 Net Ecosystem Productivity


3 Coarse Woody Debris


52 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 
The Teakettle Experiment 

Importance to Long-term Research and 

Management Issues in the Sierra Nevada 

For millennia, fire has shaped the forests of the Sierra Nevada. The ecological 

linkages among plants, animals, soil, and climate were forged long before modern 

management practices commenced. The last several decades of selectively 

harvesting large pines and suppressing fires does not have a historical precedent. 

Under this condition of deflected succession, ecosystem processes may have 

moved outside their historical range, reducing any options for managers to allow 

the forest to heal itself. Many forests are now thickets of fir and incense cedar, 

which can “ladder” fires into the crowns of the old-growth overstory canopy. 

These stands will eventually suffer catastrophic fire in which all trees will be 

killed and much of the soil will be sterilized. Research should help facilitate 

proactive ecosystem management of the Sierra Nevada by providing information 

on the impacts of forest practices on ecological functions. The central question of 

the Teakettle Ecosystem Experiment is, therefore, one of fundamental importance 

to management in the Sierra Nevada: “How can foresters responsibly mimic the 

natural fire regime?” 

Acknowledgments 

This project has been an interdisciplinary effort with significant assistance 

from the scientists listed in table 2, as well as many Sierra National Forest 

personnel who have been invaluable in planning the treatments for the 

experiment. Joel Reynolds and Bill Laudenslayer provided helpful comments 

on the draft manuscript. 

References 

Anonymous. 1991. GEO-EAS 1.2.1. User’s guide. Las Vegas, NV: Environmental Monitoring System 

Laboratory, U.S. Environmental Protection Agency. EPA/600/8-91/008. 

Anonymous. 1993. Soil survey of Sierra National Forest area, California. Fresno, CA: USDA Soil 

Conservation Service and the Regents of the University of California Agricultural Experiment 

Station. 

Bailey, Trevor C.; Gatrell, Anthony C. 1995. Interactive spatial data analysis. New York, NY: 

Longman Scientific and Technical, John Wiley and Sons, Inc.; 413 p. 

Berg, Neil H., technical coordinator. 1990. Experimental forests and ranges. Field research facilities 

of the Pacific Southwest Research Station. Gen. Tech. Rep. PSW-GTR-119. Albany, CA: Pacific 

Southwest Research Station, Forest Service, U.S. Department of Agriculture; 67 p. 

Diggle, Peter. 1983. Statistical analysis of spatial point patterns. London, England: Academic 

Press; 183 p. 

Jongman, R. H. G.; Ter Braak, C. J. F.; Van Tongeren, O. F. R., eds. 1995. Data analysis in community 

and landscape ecology. New York, NY: Cambridge University Press; 299 p. 

McKelvey, Kevin S.; Johnston, James D. 1992. Historical perspectives on forests of the Sierra 

Nevada and the Transverse Ranges of southern California: forest conditions at the turn of the 

century. In: Verner, Jared; McKelvey, Kevin S.; Noon, Barry R.; Gutiérrez, R. J.; Gould, Gordon, 

I., Jr.; Beck, Thomas W., technical coordinators. The California spotted owl: a technical assessment 

of its current status. Gen. Tech. Rep. PSW-GTR-133. Albany, CA: Pacific Southwest Research 

Station, Forest Service, U.S. Department of Agriculture; 225-246. 

North, Malcolm P.; Reynolds, Joel H. 1996. Microhabitat analysis using radiotelemetry locations 

and polytomous logistic regression. Journal of Wildlife Management 60: 639-653. 

Skinner, Carl N.; Chang, Chi-Ru. 1996. Fire regimes, past and present. In: Sierra Nevada Ecosystem 

Project, final report to Congress. Vol. II. Assessments and scientific basis for management 

options. Davis, CA: University of California, Centers for Water and Wildland Resources; 

Wildland Resources Center Report No. 37; 1,041-1,069. 

SNEP. 1996. Sierra Nevada Ecosystem Project, final report to Congress. Vol. I. Assessment 

summaries and management strategies. Davis, CA: University of California, Centers for Water 

and Wildland Resources; Wildland Resources Center Report No. 37; 209 p. 

North 

USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002. 53 
North The Teakettle Experiment 

Stephenson, Nate L.; Parsons, David J.; Swetnam, Thomas W. 1991. Restoring natural fire to the 

sequoia-mixed conifer forest: should intense fire play a role? Proceedings, tall timber fire 

ecology conference 17: 321-337. 

Verner, Jared; McKelvey, Kevin S.; Noon, Barry, R.; Gutiérrez, R. J.; Gould, Gordon, I., Jr.; Beck, 

Thomas W. 1992. The California spotted owl: a technical assessment of its current status. Gen. 

Tech. Rep. PSW-GTR-133. Berkeley, CA: Pacific Southwest Research Station, Forest Service, U. 

S. Department of Agriculture; 285 p. 

Weatherspoon, C. Phillip. 1996. Fire-silviculture relationships in Sierra forests. In: Sierra Nevada 

Ecosystem Project, final report to Congress. Vol. II. Assessments and scientific basis for 

management options. Davis, CA: University of California, Centers for Water and Wildland 

Resources; Wildland Resources Center Report No. 37; 1167-1176. 

54 USDA Forest Service Gen. Tech. Rep. PSW-GTR-183. 2002.