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This study was conducted to improve estimation of concomitant variables for implementation of a stand density management diagram (SDMD) for ponderosa pine (Pinus ponderosa Laws.) in northern California and Oregon. In traditional SDMD, isolines for variables such as stand volume are presented in such a way that uncertainty with estimation is not available. We developed the new top height and stand volume equations, as well as aboveground biomass and percent canopy cover, for building isolines in the SDMD using high-quality data collected from well-managed even-aged stands. The data were selected from the USDA Forest Service’s Pacific Southwest Research Station database. A total of 829 observations (from 113 plots across 15 sites in Oregon and California) were used for model construction. In addition, covariance-variance structures of all of the estimated parameters were provided so that users can evaluate the uncertainty associated with predictions. The model validation results indicated that the predictions made from fixed-effects model forms performed better than the current volume equation of SDMD, as well as those from mixed-effects model forms using the population average effect. The proposed equations provide enhanced predictions and additional useful information about managed ponderosa pine stands, including their uncertainty.

Stand density affects not only structure and growth, but also the health of forests and, subsequently, the functions of forest ecosystems. Here, we integrated dendrochronology and repeated inventories for ponderosa pine research plots to determine whether long-term growth and mortality responded to climate trends and how varying stand density influenced the responses. The plots were established prior to 1975 on existing stands throughout northern California. Although annual temperature increased consistently for the last 65 years, ring-width indices produced by eliminating age and thinning effects failed to detect radial trend regardless of site quality. However, interannual variation for the indices was substantial, reflecting a strong influence of climate on tree growth. Plot-level basal area increments were significantly affected by tree mortality. Stand density index explained most variation of mortality. Lowering stand density enhanced remaining tree growth, reduced mortality, and increased stand resiliency to disturbances and climate change. Besides higher climate moisture indices or lower vapor pressure deficits, any treatments that improve tree vigor and reduce stress will have a similar effect to reducing stand density. Although neither biotic disturbances nor abiotic conditions can be controlled, forest managers can manage stand density appropriately to enhance resilience to climate change and disturbances.

Quaking aspen (Populus tremuloides) is a valued, minor component on northeastern California landscapes. It provides a wide range of ecosystem services and has been in decline throughout the region for the last century. This decline may be explained partially by the lack of fire on the landscape due to heavier fire suppression, as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. However, there is little known about how aspen stand area changes in response to overlapping fire. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 52-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized aerial photos and satellite imagery to delineate aspen stands and assess conifer cover percent. We chose aspen stands in areas where wildfires overlapped (twice-burned), where only a single wildfire burned, and areas that did not burn within the recent 24-year period. We observed these same stands within the first period of fire exclusion for comparison (i.e., 1941–1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting expansion of aspen stand area. Stands with less edge:area ratio also expanded in area more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater loss of area and changes in location (movement) than in the return of fire period, highlighting their vulnerability to loss via succession to conifers in the absence of disturbances that provide adequate growing space for aspen over time.

Quaking aspen (Populus tremuloides) is a valued, minor component on western landscapes. It provides a wide range of ecosystem services and has been in decline throughout the arid west for the last century. This decline may be explained partially by the lack of fire on the landscape as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. Managers are interested in aspen restoration but there is a lack of knowledge about their spatial dynamics in response to fire. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 54-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized aerial photos to delineate aspen stand size, location and succession to conifers. We chose aspen stands in areas where wildfires overlapped (twice-burned), where only a single wildfire burned, and areas that did not burn within the recent 24-year period. We looked at these same stands within the first period of fire exclusion for comparison (i.e., 1941-1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting aspen recovery and expansion. Stands with less edge:area ratio also expanded more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater changes in area and location (movement), highlighting their vulnerability to loss in the absence of disturbances that provide adequate growing space for aspen over time.

Forest inventories based on field surveys can provide quantitative measures of regeneration such as density and stocking proportion. Understanding regeneration dynamics is a key element that supports silvicultural decision-making processes in sustainable forest management. The objectives of this study were to: 1) describe historical regeneration in ponderosa pine dominated forests by species and height class, 2) find associations of regeneration with overstory, soil, and topography variables, 3) describe contemporary regeneration across various management treatments, and 4) compare differences in regeneration between historical and contemporary forests. The study area, a ponderosa pine (Pinus ponderosae Dougl. ex P. and C. Law) dominated forest, is located within the Blacks Mountain Experimental Forest (BMEF) in northeastern California, United States, which was designated as an experimental forest in 1934. We used 1935 and 2018 field surveyed regeneration data containing information about three species&mdash, ponderosa pine, incense-cedar (Calocedrus decurrens (Torr.) Florin) and white fir (Abies concolor (Grod. and Glend)&mdash, and four height classes: class 1: 0&ndash, 0.31 m, class 2: 0.31&ndash, 0.91 m, class 3: 0.91&ndash, 1.83 m, and class 4: &gt, 1.83 m and &lt, 8.9 cm diameter at breast height. We used stocking as proxy for regeneration density in this study. We found that historically, stocking in the BMEF was dominated by shade-intolerant ponderosa pine in height classes 2 and 3. Two variables&mdash, overstory basal area per hectare (m2 ha&minus, 1) and available water capacity at 150 cm, which is the amount of water that is available for plants up to a depth of 150 cm from the soil surface&mdash, were significantly associated with stocking, and a beta regression model fit was found to have a pseudo-R2 of 0.49. We identified significant differences in contemporary stocking among six management scenarios using a Kruskal&ndash, Wallis non-parametric one-way ANOVA. Control compartments had the highest stocking followed by burned compartments. In contemporary forest stands, recent treatments involving a combination of burning and thinning resulted in high stocking in height classes 2 and 3. Overall, the stocking in historical BMEF stands was higher than in contemporary stands and was dominated by ponderosa pine.

Historically, oak woodlands in western North America were maintained by frequent fire that killed competing conifers. Today, these woodlands are often in decline as competition from conifers intensifies. Among oak species affected is the ecologically important California black oak (Quercus kelloggii Newberry). Within its range, large high-severity wildfires have become more common. We examined responses of black oak to two mixed-severity wildfires 12 years apart (2000 Storrie Fire and 2012 Chips Fire reburn). Regeneration was examined in relation to fire severity as measured by the Relative differenced Normalized Burn Ratio (RdNBR). We found that the RdNBR of the Storrie Fire was a useful predictor of the RdNBR of the Chips Fire reburn, suggesting that effects of the Storrie Fire on vegetation influenced fire behavior in the Chips reburn (t 12 = 2.892, P = 0.014, n =14, r = 0.641). After experiencing a second top-kill (complete cambium mortality above the root collar) in the Chips reburn, 95 % (99 of 104) of black oak sprout clumps resprouted. Twelve years after the Storrie Fire, we found lower proportions of sprout clumps produced acorns in places where more overstory trees survived the fire (t 5 = −3.023, P = 0.029, n = 7, r = 0.804). After both fires, the crown volume of entire sprout clumps was lower in areas of higher live overstory tree basal area (Storrie Fire: t 5 = 2.527, P = 0.053, n = 7, r = 0.749; Chips reburn: t 5 = −3.597, P = 0.016, n = 7, r = 0.849). Our finding that most black oak survived successive top-kill from repeat fire suggested that repeated high-severity or mixed-severity fire is not an immediate threat to black oak presence on the landscape. Our findings also suggest that, if high-severity fire is followed by historically normal fire return intervals, rapidly regenerating black oak may be favored over conifers and recover from decline.

Controlling competing vegetation is vital for early plantation establishment and growth. Aboveground biomass (AGB) response to manual grubbing release from shrub competition was compared with no release control in a twelve-year-old ponderosa pine (Pinus ponderosa Lawson &amp, C. Lawson) plantation established after a wildfire in northeastern California. In addition, response to chemical release followed by precommercial thinning in an adjacent plantation was also examined as a growth potential from a more intensively managed regime, where shrub competition was virtually eliminated. We measured AGB in both planted trees and competing woody shrubs to partition the biomass pools in the plantation. The results showed a significant grubbing treatment effect on basal diameter (BD) at 10 cm aboveground (p = 0.02), but not on tree height (p = 0.055). Height and BD were 2.0 m and 7.4 cm in the manual release, respectively, compared to 1.7 m and 5.6 cm in the control. However, chemical release produced much greater rates of tree growth with a height of 3.6 m and BD of 14.7 cm, respectively. Tree AGB was 60% higher with the manual release of shrubs (1.2 Mg ha&minus, 1) than with control (0.7 Mg ha&minus, 1) (p &lt, 0.05). The planted area without shrub competition yielded a much higher green tree biomass (16.0 Mg ha&minus, 1). When woody shrub biomass was included, the total AGB (trees and woody shrubs) appeared slightly higher, but non-significant in the no release control (13.3 Mg ha&minus, 1) than in the manual release (11.9 Mg ha&minus, 1) (p = 0.66), the chemical release had 17.1 Mg ha&minus, 1. Clearly, shrub biomass dominated this young plantation when understory shrubs were not completely controlled. Although the manual release did increase targeted tree growth to some degree, the cost may limit this practice to a smaller scale and the remaining shrub dominance may create long-term reductions in growth and a persistent fuels problem in these fire-prone ecosystems.

Accurate estimates of growth and structural changes are key for forest management tasks such as determination of optimal rotation times, optimal rotation times, site indices and for identifying areas experiencing difficulties to regenerate. Estimation of structural changes, especially for biomass, is also key to quantify greenhouse gas (GHG) emissions/sequestration. We compared two different modeling strategies to estimate changes in V, BA and B, at three different spatial aggregation levels using auxiliary information from two light detection and ranging (LiDAR) flights. The study area is Blacks Mountains Experimental Forest, a ponderosa pine dominated forest in Northern California for which two LiDAR acquisitions separated by six years were available. Analyzed strategies consisted of (1) directly modeling the observed changes as a function of the LiDAR auxiliary information ( δ -modeling method) and (2) modeling V, BA and B at two different points in time, including a term to account for the temporal correlation, and then computing the changes as the difference between the predicted values of V, BA and B for time two and time one. We analyzed predictions and measures of uncertainty at three different level of aggregation (i.e., pixels, stands or compartments and the entire study area). Results showed that changes were very weakly correlated with the LiDAR auxiliary information. Both modeling alternatives provided similar results with a better performance of the δ -modeling for the entire study area; however, this method also showed some inconsistencies and seemed to be very prone to extrapolation problems. The y -modeling method, which seems to be less prone to extrapolation problems, allows obtaining more outputs that are flexible and can outperform the δ -modeling method at the stand level. The weak correlation between changes in structural attributes and LiDAR auxiliary information indicates that pixel-level maps have very large uncertainties and estimation of change clearly requires some degree of spatial aggregation; additionally, in similar environments, it might be necessary to increase the time lapse between LiDAR acquisitions to obtain reliable estimates of change.

The Blacks Mountain Experimental Research Project created two distinct overstory structural classes (highstructural diversity [HiD]; low-structural diversity [LoD]) across 12 stands and subsequently burned half of each stand. We analyzed stand-level growth 10 years after treatment and then modeled individual tree growth to forecast stand-level growth 10 –20 years after treatment. Net stand growth was compared between treatments and with adjacent Research Natural Areas (RNAs). An analysis of variance of growth in total aboveground tree biomass suggested that growth was greatest in unburned stands (P 0.001) and in LoD stands (P 0.039). We formed iteratively annualized nonlinear models to forecast individual tree growth. Modeled diameter growth, height growth, and mortality were used exclusively for forecasting and highlighting growth and mortality trends in the data (i.e., not testing effects). Forecasts of stand board foot volume suggested that HiD and LoD stands may be no different in net growth in the second decade since treatment (P 0.355). Differences between logged and unlogged stands appeared to be much greater: we predict that RNA stands will net 136 board feet ac 1 in the forecast period, whereas HiD and LoD stands are expected to net 627 and 485 board feet of volume per acre. We also tracked the large tree (dbh 23.5 in.) component stand density index (SDI) over the measurement and forecast periods. We found that the unburned HiD treatment had a net positive effect (13% increase over 20 years) on relative density, whereas the burned HiD was not expected to change (P 0.803), and unlogged stands tended to exhibit a declining SDI over time ( 16%).

An experiment designed to evaluate the treatment effects of salvaging merchantable fire-killed trees on surface fuels and regeneration was established after a wildfire in northeastern California. The study was then monitored for 10 years. Surface fuel accumulations were rapid, corresponding with a high rate of snag decay and subsequent breakage or windthrow. Pine snags retained exhibited the fastest rates of breakage and transition to surface fuels, while white fir and incense-cedar were much more stable for the duration of this study. Natural regeneration observed following salvage was scarce and did not appear to be related to treatment. Similarly, artificial regeneration, although highly variable between treatment units, both in terms of growth and survival, was not related to salvage treatment.

The purpose of this article was to determine whether natural regeneration or planted seedlings should be used in group-selection openings. The answer depends on the survival and growth rate of both types of seedlings, and that could depend on the size of the openings and the effect of trees on their edge. In this side-by-side study, the natural pine seedlings originated from the 1988 seed crop and the 1–0 nursery-grown seedlings were outplanted in spring 1989. Openings ranged from 0.01 to 0.65 ha. The plant community consisted of many species of shrubs, forbs, and grasses with manzanita having the highest density and greatest development. After 9 years, manzanita had an average density of 13,870 plants/ha, 2,050 m2/ha of foliar cover, and was 125 cm tall. From 1990 to 1997, planted ponderosa pine seedlings were taller (P < 0.05) than natural seedlings, and from 1995 to 1997, mean stem diameter at 30 cm of planted seedlings was larger than natural counterparts (P < 0.05). Development for 1 year in the nursery apparently gave the planted seedlings a growth advantage over the natural seedlings. For natural seedlings, distance from opening edge had little effect on pine height or diameter growth regardless of opening size. Planted seedlings, however, appeared to increase in height and diameter growth with both opening size and distance from edge.

We evaluated the relationship between crown cover measured with a vertical sight tube and stand basal area per acre in treated (thinned, burned, and thinned and burned) and untreated interior ponderosa pine (Pinus ponderosa P. & C. Lawson) stands in northeastern California. Crown cover was significantly related to basal area at the plot level and stand level. In addition, the relationship was not affected by two extremely different thinning regimes. However, the predicted crown cover was generally lower, for a given level of basal area, in a recently thinned stand than in a stand that had not been recently thinned. Prescribed fire had no detectable effect on the relationship. The maximum measured value of stand level crown cover in untreated stands in this study was about 60 percent. West. J. Appl. For. 20(4): 240–246.

Three solutions are presented for estimating stems per acre when trees are tallied by diameter class with horizontal point sampling. The first solution is based on the arithmetic mean of the diameter-class limits. The second is based on the geometric mean of the diameter-class limits and is unbiased for uniform within-class diameter distributions. The third is a harmonic mean solution; it is derived from the ratio of the geometric mean squared and the arithmetic mean. If the within-class distribution is linear, then the solution based on the geometric mean is preferable. Any of these solutions may be adequate provided diameter-class widths are minimized, particularly for small trees. The geometric-mean solution is the recommended solution in instances where uniformity can be assumed within diameter classes. Observed frequencies in two stands, however, provided inconsistent results. In estimating tree frequency, errors resulting from grouping become smaller as tree diameter increases. For large trees, estimation of frequency can be obtained with much wider diameter limits than with small trees for a fixed level of grouping error. Rather than fixing diameter-class width, it may be advantageous to consider a narrower class width or exact measurement for trees in smaller diameter classes. West. J. Appl. For. 12(4):108-114.

Forest managers need accurate biomass equations to plan thinning for fuel reduction or energy production. Estimates of carbon sequestration also rely upon such equations. The current allometric equations for ponderosa pine (Pinus ponderosa) commonly employed for California forests were developed elsewhere, and are often applied without consideration potential for spatial or temporal variability. Individual-tree aboveground biomass allometric equations are presented from an analysis of 79 felled trees from four separate management units at Blacks Mountain Experimental Forest: one unthinned and three separate thinned units. A simultaneous set of allometric equations for foliage, branch and bole biomass were developed as well as branch-level equations for wood and foliage. Foliage biomass relationships varied substantially between units while branch and bole biomass estimates were more stable across a range of stand conditions. Trees of a given breast height diameter and crown ratio in thinned stands had more foliage biomass, but slightly less branch biomass than those in an unthinned stand. The observed variability in biomass relationships within Blacks Mountain Experimental Forest suggests that users should consider how well the data used to develop a selected model relate to the conditions in any given application.

In the past, researchers from the Pacific Southwest Research Station (PSW) undertook forest growth studies to evaluate how best to manage timber resources. However, historical and future data collected at PSW growth plots also have the potential to increase our understanding of the ecological processes occurring in our forests and shed light on national issues of importance. This report provides information on the history, geography, plant species studied, installation, and measurement interval of each plot along with a list of publications arising from data gathered at these plots. This will enable current and future researchers to reidentify these plots and continue research at these locations.