Article

Ten-year responses of ponderosa pine growth, vigor, and recruitment to restoration treatments in the Bitterroot Mountains, Montana, USA

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Abstract

Little is known about ponderosa pine forest ecosystem responses to restoration practices in the Northern Rocky Mountains, USA. In this study, restoration treatments aimed at approximating historical forest structure and disturbances included modified single-tree selection cutting, with and without prescribed burning. We compared the effectiveness of restoration treatments on growth, vigor, and composition of recruitment responses with untreated controls. We used a randomized block design to detect treatment differences in mean individual tree basal area increment (BAInc10), growth efficiency (GE), and recruitment abundance between two restoration treatments (Cut-only and Cut-burn) and a Control. We further examined treatment effects by tree age-class (Young, Mature, Presettlement) using a spatial ANOVA model that incorporates the spatial autocorrelation among trees within experimental units. Ten years after implementing restoration treatments, mean individual tree BAInc10 and GE were significantly higher for treated units relative to Control units; all three age-classes benefited similarly from restoration treatments relative to the Control, with the greatest response in the Cut-only and moderate response in the Cut-burn. When treated units were compared, Cut-burn negatively affected BAInc10 and GE relative to Cut-only. Presettlement trees responded positively to treatment relative to the Control, particularly for BAInc10, demonstrating the potential of these old trees to respond to reduced competition. The Cut-burn treatment, in contrast, negatively affected the BAInc10 and GE response of postsettlement trees when compared to Cut-only. Restoration treatments did not reduce the amount of Douglas-fir recruits. In addition, the recruitment of both ponderosa pine and Douglas-fir species was associated with the proximate cover of woody debris in Cut-only and Control treatments. Finally, special consideration needs to be taken for spring Cut-burn treatments, which appeared to dampen growth and vigor, relative to Cut-only, particularly for Young and Mature trees, and increased recruitment of ponderosa pine and particularly Douglas-fir.

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... A general pattern of increased regeneration 11 − 20 years following all treatments was observed. This is consistent with research that shows ponderosa pine seedling established 10 years post disturbance (Bonnet et al. 2005;Fajardo et al. 2007;Haire and McGarigal 2010). In studies where time since treatment was greater than 20 years, there was a trend in decreased regeneration compared to untreated stands, as some long-term studies reported that stands return to pre-treatment density and forest floor duff levels without subsequent maintenance treatments applied every 2-10 years (McDonald and Reynolds 1999;Ffolliott et al. 2009;Clyatt et al. 2017). ...
... Bailey and Covington (2002) observed 18-41 seedlings ha −1 in thinned areas and only 12 seedlings ha −1 on thin plus burn sites. However, a study in Montana showed that at ten years post-treatment, ponderosa pine had higher recruitment in the thin-only and thin plus burn treatments relative to controls, with the highest recruitment on thin plus burn sites (Fajardo et al. 2007). Thinning and thinning plus burning also increased the amount of regeneration and were effective at facilitating new cohorts of ponderosa pine in New Mexico (Thomas and Waring 2015). ...
... Several studies of ponderosa regeneration patterns after thinning in Montana (Fajardo et al. 2007), New Mexico (Thomas and Waring 2015), Colorado (Shepperd et al. 2006), and Arizona (Bailey and Covington 2002;Puhlick et al. 2012;Flathers et al. 2016) reported significantly greater regeneration densities in thinned stands versus unthinned stands (e.g., Fig. 2). Mechanical thinning and thinning plus prescribed fire increased seedling density over time but there was high variability among sites (Schwilk et al. 2009). ...
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Understanding naturally occurring pine regeneration dynamics in response to thinning and burning treatments is necessary not only to measure the longevity of the restoration or fuels treatment, but also to assess how well regeneration meets forest sustainability guidelines and whether natural regeneration is sufficient for maintaining a sustainable forest structure and composition. A synthesis review was carried out on the effects of mechanical thinning and prescribed burn treatments on natural pine regeneration response in frequent-fire ponderosa pine forests across the western United States. The focus was on site-specific variability in pine regeneration dynamics, temporal trends in regeneration presence and abundance, and response to treatment as described in the current literature using 29 studies that met our evidence-based review protocols. Data showed that the effects of thinning and burning treatments on regeneration depended on time since treatment. Mechanical thinning, prescribed burning, and thinning plus burn treatments all increased seedling density, but there was high variability among sites and studies. There were mixed results in the short-term (< 10 years) with both increasing and decreasing regeneration, and a general increase in regeneration 11 − 20 years post-treatment. Some long-term studies (> 20 years) concluded that stands can return to pre-treatment densities in terms of total trees per hectare and forest floor duff levels when there are no maintenance treatments applied. Several studies showed the average ponderosa pine seedling presence, survival and growth found in today’s forests to be at a high density; this combined with missed fire cycles could contribute to future fire risk and reduce the efficacy of maintaining fuel reduction goals.
... For non-serotinous species, large surviving trees are critical to post-fire resilience, providing seed source and maintaining patches of forest cover (Franklin et al., 2007). However, surviving trees are not all equivalent, as varying fire damage impairs vigour and admits pathogens in more injured stems, resulting in delayed mortality for years after a fire (Busse et al., 2000;Fajardo et al., 2007;Van Mantgem et al., 2011), with cascading effects on regeneration (Franklin et al., 2007). Likewise, climate change may cause greater post-fire stress and delayed mortality, as post-fire survivorship and fecundity is highly sensitive to environmental and climate conditions (Allen et al., 2015;Harvey et al., 2016a;Kolb et al., 2019;Littlefield, 2019). ...
... Our 19-year study has found the P. occidentalis forests of the Cordillera Central were resilient (sensu Pimm, 1984) to an unusually large and severe fire, despite a severe multi-year drought after the fire and ongoing climate change. Trees that initially survived the fire had a large pulse of delayed mortality in both lowand moderate-severity burns, a common pattern caused by severe stem char, crown scorch and fine root damage that weaken the tree and increase pathogen susceptibility (Busse et al., 2000;Fajardo et al., 2007;Hood et al., 2018;Slack et al., 2016;Varner et al., 2009Varner et al., , 2021Woolley et al., 2012). Yet, 13 years post fire, pine regeneration was evident across all fire severities, and recruitment of new pine trees (i.e. ...
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Higher temperatures, declining precipitation, changing cloud cover and increased wildfires threaten tropical montane pine forests by overriding the environmental heterogeneity that typically buffers these systems from catastrophic fires. Severe fires threaten to overwhelm forest resilience and tip this biome into alternate vegetation states. This study focused on long‐term dynamics of montane Pinus occidentalis forests in the Cordillera Central, Dominican Republic after a ~1000 km² fire in 2005, the largest since 1965. We used long‐term records to investigate climate before and after the fire, and 19‐year dataset of pre‐ and post‐fire vegetation change from a network of 55 permanent plots (20 small 0.05 ha plots and 35 large 0.1 ha plots) established in 1999 to model overstorey and understorey vegetation dynamics. The 2005 fire was synchronized with the most extreme drought in the region in over 60 years. The fire burned from <1600 to >3000 m a.s.l. in elevation across windward and leeward slopes, creating a mosaic of low‐, moderate‐ and high‐severity patches. Lower elevations, leeward slopes and stands with a higher proportion of smaller pine trees all burned at higher severities. Growth rates of trees that survived the fire remained lower than pre‐fire rates 13 years after the fire. The highest post‐fire mortality rates were soon after the fire and in the census immediately following subsequent post‐fire droughts. Post‐fire pine seedling abundance was significantly greater in stands with higher basal area of live canopy trees and significantly reduced by increased shrub abundance in the understorey. Understorey composition recovered rapidly to pre‐fire states in sites affected by low‐ and moderate‐severity fires, but sites affected by high‐severity fires remained dissimilar to pre‐fire composition 13 years after the fire. Even though high‐severity patches had persistently low pine regeneration, 100% of small plots and 96% of large plots had at least one pine sapling or canopy tree recruit by 2018. Shrub taxa survived the fire in higher numbers and recovered to pre‐fire densities much faster than the pine, especially in high‐severity burns. Synthesis. Climate change has increased the likelihood of wildfires in tropical montane pine forests, with long‐lasting effects on vegetation dynamics. However, this biome may prove resilient to increasingly severe fires in the near future, given the ongoing recovery of Pinus occidentalis forests in Hispaniola despite repeated severe droughts. Nevertheless, highly drought‐ and fire‐resistant taxa (e.g. shrubs) may form alternate stable states in drier portions of tropical montane landscapes in the future as droughts and high‐severity fires become more common.
... There is extensive evidence that prescribed fire can dramatically alter the structure of forested ecosystems by reducing tree densities, altering species composition, and reducing fuel loads (e.g., Thomas and Agee, 1986;Fajardo et al., 2007;Knapp et al., 2015). In addition, several studies have investigated the potential impacts of prescribed fire on individual tree growth and vigor caused by cambial injury, crown scorch, altered nutrient and water status of the soil, and modified competitive environment following burning (e.g., Van Wagner, 1963;Monleon and Cromack, 1996). ...
... For example, burning experiments in oak forests and woodlands (Peterson and Reich, 2001;Hutchinson et al., 2005;Knapp et al., 2015), southeastern USA pine forests (Waldrop et al., 1992;Brockway and Lewis, 1997;Varner et al., 2005), and western USA ponderosa pine (Pinus ponderosa Dougl.) forests (Thomas and Agee, 1986;Sackett et al., 1994;Sackett and Haase, 1998;Fajardo et al., 2007) have found that repeated burning reduces the density of the overstory by reducing numbers of small diameter and thin barked trees. The resultant stands typically display changes to the distribution of tree sizes with diameter distributions shifting from negative exponential forms in unburned controls to Gaussian forms in repeatedly burned treatments (Peterson and Reich, 2001;Knapp et al., 2015). ...
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Prescribed fire is increasingly viewed as a valuable tool for reversing ecological consequences of fire suppression within fire-adapted forests. While the use of burning treatments in northern temperate conifer forests has received considerable attention, the long-term (>10 year) effects on understory composition and dynamics have not been quantified. We describe the persistence of prescribed fire effects on the woody and herbaceous understory in a mature red pine (Pinus resinosa Ait.) forest in northern Minnesota, USA, over a ∼50-year period, as well as the relative roles of fire season and frequency in affecting vegetation responses. Burning treatments were applied from 1960 to 1970 on 0.4 ha experimental units and crossed fire season and frequency in a randomized block design. Burning altered shrub layer dynamics and composition in both the short and long terms and was influenced by both fire season and frequency, with frequent summer season burns having the largest impact, including greatest control of hazel (Corylus spp.). The application of fire facilitated regeneration of pine; however, recruitment into the overstory was limited. Additionally, community composition of the herbaceous understory diverged 40+ years following burning. This study highlights the importance of continued burning in affecting vegetation responses and the potential of fire as a long-lasting vegetation management tool in these forests.
... There is extensive evidence that prescribed fire can dramatically alter the structure of forested ecosystems by reducing tree densities, altering species composition, and reducing fuel loads (e.g., Thomas and Agee, 1986;Fajardo et al., 2007;Knapp et al., 2015). In addition, several studies have investigated the potential impacts of prescribed fire on individual tree growth and vigor caused by cambial injury, crown scorch, altered nutrient and water status of the soil, and modified competitive environment following burning (e.g., Van Wagner, 1963;Monleon and Cromack, 1996). ...
... For example, burning experiments in oak forests and woodlands (Peterson and Reich, 2001;Hutchinson et al., 2005;Knapp et al., 2015), southeastern USA pine forests (Waldrop et al., 1992;Brockway and Lewis, 1997;Varner et al., 2005), and western USA ponderosa pine (Pinus ponderosa Dougl.) forests (Thomas and Agee, 1986;Sackett et al., 1994;Sackett and Haase, 1998;Fajardo et al., 2007) have found that repeated burning reduces the density of the overstory by reducing numbers of small diameter and thin barked trees. The resultant stands typically display changes to the distribution of tree sizes with diameter distributions shifting from negative exponential forms in unburned controls to Gaussian forms in repeatedly burned treatments (Peterson and Reich, 2001;Knapp et al., 2015). ...
... Radial growth ceased in the control by early July, but continued until mid to late August in a treatment thinned to nearly the same density as the thinning treatments in this study. Numerous investigators (McDowell et al. 2003, Skov et al. 2004, Fajardo et al. 2007) have reported ponderosa pine growth responses to thinning. Increased BAI has also been observed in large old trees (Feeney et al. 1998, Stone et al. 1999, Fiedler 2000a), with increases persisting up to 25 years in one Oregon study (Latham and Tappeiner (2002). ...
... For example, Fiedler (2000) found similar and large positive growth responses in thin-only and thin-burn treatments relative to a control. Yet Fajardo et al. (2007) found no differences in BAI between a thin-burn and a control, despite a significant growth response in a thin-only treatment at the same reserve density. Landsberg et al. (1984) reported 16 –28% reductions in BAI after burning in central Oregon. ...
Article
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Crown fires that burned thousands of ha of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests in recent years attest to the hazardous conditions extant on the western landscape. Managers have responded with broad-scale implementation of fuel reduction treatments; however. because threats to pine forests extend beyond fire, so too must the approaches to address them. This western Montana study evaluated four treatments in a randomized complete block experiment for their effects on stand structural characteristics, growth increment, and crown fire potential. Evaluation of control, burn-only, thin-only, and thin-burn treatments showed that the combined thin-burn treatment had the greatest number of desired effects, the burn-only had the fewest, and the thin-only was intermediate. The thin-burn significantly reduced stand density, canopy cover, torching hazard, and crowning hazard and increased average diameter, height-to live-crown, and basal area increment; the thin-only reduced stand density, canopy cover, and crowning hazard and increased average diameter and basal area increment; and the burn-only reduced torching hazard and increased height-to-live crown. These structural and growth effects are related to or influence numerous stand/ecosystem properties at our site, including diameter distributions, species composition, large-tree development potential, overall tree vigor, potential for shade-intolerant tree regeneration, and resiliency to fire. Results demonstrate that well-designed restoration treatments can promote key short-term stand and ecosystem responses while significantly reducing crown fire potential.
... Several papers have analyzed the change in potential fire behavior resulting from initial fuels treatments using empirical field studies (Kilgore and Sando, 1975;Covington et al., 1997;Omi and Martinson, 2004;North et al., 2007;Stephens et al., 2009;Fiedler et al., 2010) or simulations with or without the aid of field data (Keane et al., 1990;van Wagtendonk, 1996;Stephens, 1998). Far fewer studies have investigated how forests that have received fuel treatments change over time (Peterson et al., 1994;Sackett and Haase, 1998;Fulé et al., 2005Fulé et al., , 2007Fajardo et al., 2007) and most of these studies have occurred in relatively xeric Rocky Mountain ponderosa pine (Pinus ponderosa) forests. ...
... Working in ponderosa pine forests in the Northern Rocky Mountains, Fajardo et al. (2007) found delayed mortality in ponderosa pine after their mechanical plus fire treatment. They concluded 'Special consideration needs to be taken on the cut-burn treatments (relative to cut-only), which appeared to dampen response in terms of growth and vigor, particularly for mature and young trees.' ...
Article
Understanding the longevity of fuel treatments in terms of their ability to maintain fire behavior and effects within a desired range is an important question. The objective of this study was to determine how fuels, forest structure, and predicted fire behavior changed 7-years after initial treatments. Three different treatments: mechanical only, mechanical plus fire, and prescribed fire only, as well as untreated control, were each randomly applied to 3 of 12 experimental units. Many aspects of the initial fuel treatments changed in 7 years. The overall hazard of the control units increased significantly indicating continued passive management has further increased already high fire hazards. Mechanical only fire hazard decreased after 7 years and are now similar to the two fire treatments, which both maintained low hazards throughout the study. Tree density declined significantly 7 years after the initial fire only treatments, while basal area in both fire treatments was unchanged relative to immediate post-treatment conditions. Our findings indicating reduced fire hazard over time in mechanical only treatments might provide an opportunity for a staggered treatment schedule that included prescribed fire which could increase overall treatment longevity to approximately 20 years. Changes in our mixed conifer forests after fuel treatment were generally larger than those reported from ponderosa pine forests in the Rocky Mountains.
... We predicted that savanna restoration -mechanical removal of woody encroachment -would result in elevated growth rates of relict Q. alba overstory trees, relative to growth rates of Q. alba trees in encroached savannas. Reductions in overstory density normally result in accelerated growth rates of residual trees across a variety of forested ecosystems, including oak forests (e.g., Schlesinger, 1978;Cutter et al., 1991;Abrams and Nowacki, 1992;Nowacki and Abrams, 1997;Feeney et al., 1998;Bebber et al., 2004;Devine and Harrington, 2006;Fajardo et al., 2007;Götmark, 2009), and we predict that this pattern will be evident in our savanna system. ...
... These results corroborate substantial evidence for residual tree release, from a variety of silvicultural settings (Schlesinger, 1978;Cutter et al., 1991;Abrams and Nowacki, 1992;Nowacki and Abrams, 1997;Bebber et al., 2004;Devine and Harrington, 2006). Our results also add to a growing body of evidence for overstory release in restoration contexts (e.g., Feeney et al., 1998;Fulé et al., 2005;Fajardo et al., 2007;Götmark, 2009). Further, our work provides some of the first evidence for release of savanna overstory trees during restoration. ...
Article
Midwestern savannas historically covered >10Mha in central North America, but are now rare due to agricultural conversion and anthropogenic modifications to disturbance regimes – particularly fire suppression. Throughout this range, Midwestern savannas are characterized by scattered overstory trees; however, with fire suppression, these systems are invaded by non-savanna trees. Restoration of encroached savannas involves removal of invading trees, yet little is known about the impacts of encroachment or encroachment removal on the relict savanna overstory trees, which define these systems. Here, we use tree ring analysis to investigate savanna tree growth rates in encroached, non-encroached, and experimentally restored Midwestern oak savannas in central Iowa. We found that woody encroachment led to pronounced declines in growth rate (ring width) of relict overstory white oak (Quercus alba), relative to Q. alba trees in competition-free, open-grown conditions, or in an encroachment-free remnant woodland. To further understand effects of encroachment removal on relict Q. alba savanna trees, we conducted a large-scale restoration experiment, where encroaching trees were mechanically removed from four encroached savannas, with an additional four savannas retained as encroached controls. Restoration led to elevated tree growth rates, with these changes generally persistent through 7years post-restoration (2003–2009). Over the course of this post-restoration study period, ring width, basal area increment, and relative basal area increased by 49%, 59%, and 55%, respectively, in trees from restored sites, relative to trees from encroached, control sites. These results suggest that woody encroachment has strong influence on overstory savanna trees, through increased competitive dynamics; however, woody encroachment removal may help to restore relict savanna tree growth rates, even after prolonged periods of encroachment (>40years). To restore the oak savannas at our sites, and perhaps elsewhere, we advocate a three step process: (1) mechanical woody encroachment removal, (2) maintenance of the encroachment-free state through prescribed fire, and (3) promotion of a diverse understory layer, characteristic of oak savanna in our region. While promoting oak regeneration will be important for the long-term maintenance of these sites as oak savanna, relict savanna trees appear responsive to restoration and should maintain overstory conditions through the near-term.
... InTable 3 . Summary of type 3 tests of fixed effects for periodic annual increment (PAI) and mean annual increment (MAI) for repeatedly thinned red pine stands on the Cutfoot Sioux Experimental Forest, Chippewa National Forest, Minnesota, from addition, the positive post-thinning growth responses (based on PAI) we observed for red pine within higher stockinglevels treatments after thinnings applied at age 138 years are consistent with a growing body of literature that has demonstrated the responsiveness of several North American conifer species to density reductions at advanced ages (Youngblood 1991; Latham and Tappeiner 2002; Fajardo et al. 2007). Collectively, these findings highlight the potential for using repeated thinning treatments and extended rotations beyond stand ages of 120 years to simultaneously meet ecological and economic goals within red pine forests. ...
... The largely asymptotic density–growth relationships observed in this study are important in the context of restoring late-successional structural attributes to red pine systems , as a greater range of flexibility may exist for choosing stocking levels that promote structural development (see Discussion above) and maintain a high level of stand productivity. Thinning treatments are increasingly being applied to older forest stands in attempts to increase residual tree vigor, reduce fuel loads, and promote and maintain structural characteristics of old-growth stands in forests managed for wood (e.g., Latham and Tappeiner 2002; Fajardo et al. 2007; Kolb et al. 2007). A surprising result of recent studies examining the response of older trees to various density manipulations has been the positive growth response of older trees to these treatments (Latham and Tappeiner 2002; Bebber et al. 2004; Powers et al. 2009 ). ...
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Extended rotations are increasingly used to meet ecological objectives on forestland however, information about long-term growth and yield of these systems is lacking for most forests in North America. Additionally, long-term growth responses to repeated thinnings in older stands have received little attention. We addressed these needs by examining the growth and yield of red pine (Pinus resinosa Ait.) in a growing stock experiment in northern Minnesota. Stands were 85years old at the onset of this experiment and were repeatedly thinned to five levels of basal area (13.8, 18.4, 23.0, 27.5, and 32.1m²ha¹) over 58years. Cumulative volume production and volume growth were lowest within the lowest stocking treatment and similar across other stocking levels. Late-successional structural attributes, such as the density of treeswith 40cm diameter at breast height, was similar across stocking levels. The mean annual volume growth culminated between 130 and 140years. Additionally, positive growth responses were observed within the highest stocking-level treatments after thinning at 138 years, demonstrating the ability of older red pine to respond to reductions in competition. These results illustrate that extended rotations with repeated thinnings in red pine help achieve ecological goals, including the restoration of old-forest structure, while also maintaining high levels of stand productivity.
... Together with another long-term fuel treatment study in western Montana, Lick Creek, the Lubrecht FFS site includes crossed thinning and prescribed burning treatments. At both study sites, treatment effects on vegetation and fuel dynamics (Crotteau et al., 2018Fajardo et al., 2007;Fiedler et al., 2010;Hood et al., 2020), understory diversity (Dodson et al., 2007;Jang et al., 2021;Metlen & Fiedler, 2006), aboveground ecosystem biomass and C stocks (Clyatt et al., 2017), tree physiology (Peters & Sala, 2008;Sala et al., 2005), soil nutrient cycling (DeLuca & Zouhar, 2000;Ganzlin et al., 2016;Gundale et al., 2005), forage quality (Ayers et al., 1999), and resilience to drought stress and bark beetles Hood et al., 2016;Six & Skov, 2009;Tepley et al., 2020) have been studied extensively. Research from these two study areas forms most of the current and comprehensive body of knowledge of longterm restoration fuel treatment effects in the region. ...
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Fuel and restoration treatments seeking to mitigate the likelihood of uncharacteristic high‐severity wildfires in forests with historically frequent, low‐severity fire regimes are increasingly common, but long‐term treatment effects on fuels, aboveground carbon, plant community structure, ecosystem resilience, and other ecosystem attributes are understudied. We present 20‐year responses to thinning and prescribed burning treatments commonly used in dry, low‐elevation forests of the western United States from a long‐term study site in the Northern Rockies that is part of the National Fire and Fire Surrogate Study. We provide a comprehensive synthesis of short‐term (<4 years) and mid‐term (<14 years) results from previous findings. We then place these results in the context of a mountain pine beetle (MPB; Dendroctonus ponderosae) outbreak that impacted the site 5–10 years post‐treatment and describe 20‐year responses to assess the longevity of restoration and fuel reduction treatments in light of the MPB outbreak. Thinning treatments had persistently lower forest density and higher tree growth, but effects were more pronounced when thinning was combined with prescribed fire. The thinning+prescribed fire treatment had the additional benefit of maintaining the highest proportion of ponderosa pine (Pinus ponderosa) for overstory and regeneration. No differences in understory native plant cover and richness or exotic species cover remained after 20 years, but exotic species richness, while low relative to native species, was still higher in the thinning+prescribed fire treatment than the control. Aboveground live carbon stocks in thinning treatments recovered to near control and prescribed fire treatment levels by 20 years. The prescribed fire treatment and control had higher fuel loads than thinning treatments due to interactions with the MPB outbreak. The MPB‐induced changes to forest structure and fuels increased the fire hazard 20 years post‐treatment in the control and prescribed fire treatment. Should a wildfire occur now, the thinning+prescribed fire treatment would likely have the lowest intensity fire and highest tree survival and stable carbon stocks. Our findings show broad support that thinning and prescribed fire increase ponderosa pine forest resilience to both wildfire and bark beetles for up to 20 years, but efficacy is waning and additional fuel treatments are needed to maintain resilience.
... Although growth efficiency is not a direct resistance metric, Waring [4] identified that it is a "sensitive indicator to environmental stresses" and that increased growth efficiency is associated with decreased tree stress and increased resistance to disease and insect attack. Our models corroborate that thinning, even as a restoration treatment, results in greater growth efficiency in ponderosa pine ( [40,55]; but results vary by index in [56]). Furthermore, only 5% of trees in thinned treatments (versus 38% in unthinned treatments) had growth efficiency less than 100 g m −2 yr −1 , which Larsson et al. [40] identified as a threshold for successful mountain pine beetle attack. ...
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Research Highlights: This study provides much needed insight into the development of resistance to disturbance and growth dynamics of overstory trees in response to restoration-based fuel reduction, and will be useful to scientists and managers attempting to better grasp the relative merits of restoration treatment types. Background and Objectives: Restoration-based fuel reduction treatments are common in dry, fire-prone forests of the western United States. The primary objective of such treatments is to immediately reduce a stand’s crown fire hazard. However, the impact of these treatments on residual trees is relevant to assess their longevity and resistance to future disturbances. In this study, we evaluate the effects of restoration on retained overstory ponderosa pine (Pinus ponderosa Lawson & C. Lawson) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees in western Montana, where treatments were experimentally implemented 13 years prior as part of the national Fire and Fire Surrogate study. Materials and Methods: We examined tree attributes in response to the following replicated treatments: thin-only, burn-only, thin + burn, and a no-action control. We analyzed three different tree attributes that confer resistance to common disturbances: height-to-diameter ratio (resistance to wind), bark thickness (resistance to surface fire), and growth efficiency (resistance to bark beetles). Results: Our models suggest that thinning (with or without burning) alters tree attributes relative to the control in a manner that may increase tree resistance to wind and snow breakage, surface fire, and biotic agents such as bark beetles. Further analysis of annual growth of ponderosa pine and Douglas-fir varied by treatment type: thinning-based restoration (thin-only and thin + burn) increased diameter growth for both species, crown length and width in ponderosa pine, and crown length in Douglas-fir relative to unthinned treatments. Burning (burn-only and thin + burn) did not significantly affect tree growth relative to unburned treatments. Conclusions: While low-severity prescribed burning treatments are often used for restoration and have various ecosystem benefits, this study demonstrates that thinning (alone or in addition to burning) produces more measureable, beneficial results to overstory tree disturbance resistance metrics and growth.
... Results of vegetative sheltering of ponderosa pine have been mixed (reviewed in Korb et al., 2019), but survival through drought conditions has been shown to increase dramatically when not in direct competition with surrounding vegetation due to increased soil moisture availability (e.g., Pinto et al., 2012). Our results are also consistent more generally with documented positive relationships of regeneration survival or densities with woody debris in environments likely to have high abiotic stress after high-impact disturbance events like intensive harvesting (Alexander, 1966;Fajardo et al., 2007) and severe fire (Keyes et al., 2007) and demonstrate this effect persists for ponderosa pine in a putatively more mesic forest relative to its typical regional altitudinal range. ...
Article
Warming climate in U.S. forests may limit future viability of dominant high-elevation species at their lower elevation range limits but favor more drought-adapted sympatric species, potentially contributing to species distribution changes. Adaptive management may address future uncertainty in species distributions by facilitating regeneration of multiple species with contrasting silvics. However, the success of this approach will depend on suitable microsite conditions, the effects of which are not well understood across species and forest types. These concerns are present in the southern Rocky Mountain region, where current and future climate may restrict Engelmann spruce regeneration but benefit sympatric species like ponderosa pine. We used a planting experiment to systematically evaluate microsite conditions which support critical first-season survival and root growth of these contrasting species in a low-elevation spruce forest during a droughty 2018 growing season. Our assessment targeted species responses to variation in canopy cover generated by different silvicultural regeneration treatments, with and without additional shelter from coarse woody debris. We also considered microsite variables of seedling size, vegetation and litter cover, soil moisture and depth, and competition from established tree regeneration. Survival of ponderosa pine was nearly twice that of Engelmann spruce, but the relative effects of microsite variables were similar. Coarse woody debris shelter improved the probability of survival by approximately 357%, though the effect was stronger for spruce. Influences of canopy cover were minimal and opposite our expectations; spruce was marginally inhibited by canopy cover, while pine was positively influenced by more dense canopy. Smaller seedling heights improved the probability of survival for both species by 179% compared to mean seedling heights. Pine root growth was 150% greater in open versus dense canopy microsites and limited in coarse woody debris shelter. We discuss likely site and physiological factors underlying these results. This study provides insight into the factors which define suitable microsites for first-season establishment for these species in rapidly changing low-elevation spruce forests, especially during drought conditions. We discuss implications for adaptive management and silviculture, concluding that regeneration efforts which seek to improve forest resilience to climate-related changes in species viability could consider more drought-adapted, sympatric species as viable supplements to moisture-dependent species at their current lower range limits.
... These approaches are often centered on increasing disturbance resistance (remaining unchanged in the face of disturbance) and resilience (forest recovery to pre-disturbance composition or structure). Tree vigor is under management control to a limited degree, inasmuch as growth of residual trees may be modified following treatments that regulate stand density (e.g., mechanical thinning, prescribed fire, or both; Wenger 1984, Fajardo et al. 2007, Valor et al. 2015. A recent meta-analysis suggests that thinning treatments may encourage resilience to drought in terms of growth, particularly for dry coniferous forests (Sohn et al. 2016). ...
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Tree mortality is an important outcome of many forest fires. Extensive tree injuries from fire may lead directly to mortality, but environmental and biological stressors may also contribute to tree death. However, there is little evidence showing how the combined effects of two common stressors, drought and competition, influence post-fire mortality. Geographically broad observations of three common western coniferous trees subjected to prescribed fire showed the likelihood of post-fire mortality was related to intermediate-term (10 yr) pre-fire average radial growth, an important component of tree vigor. Path analysis showed that indices of competition and drought stress prior to fire can be described in terms of joint effects on growth, indirectly affecting post-fire mortality. Our results suggest that the conditions that govern the relationship between growth and mortality in unburned stands may also apply to post-fire environments. Thus, biotic and abiotic changes that affect growth negatively (e.g., drought stress) or positively (e.g., growth releases following thinning treatments) prior to fire may influence expressed fire severity, independent of fire intensity (e.g., heat flux, residence time). These relationships suggest that tree mortality may increase under stressful climatic or stand conditions even if fire behavior remains constant.
... GE can be expressed in stem wood production (volume or weight) per unit leaf surface area [43] or stem wood production per unit leaf surface area (e.g. [42,44,45]). For this study, the estimation of periodic stem wood production would have required additional previous measurement of tree heights and bark thicknesses, which did not exist. ...
Article
To investigate the long-term impacts of biomass harvesting on site productivity, we remeasured trees in the 1974 Forest Residues Utilization Research and Development Program at Coram Experimental Forest in western Montana. Three levels (high, medium, and low) of biomass removal intensity combined with broadcast burning treatment were assigned after clearcut in western larch (Larix occidentalis Nutt.) stands in 1974. From 1976 to 79, twenty five 2 + 0 bare root seedlings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were consecutively planted in rows. In 2013, tree height, dbh (diameter at breast height), foliar N and C concentrations were measured. From cross-sectional sapwood area, growth efficiency (the ratio of 5-year-basal area increment to total leaf area) was calculated. Previous measurements from 1980, 1987, 1992, and 2001 were used for dbh and height growth analyses. At this site, none of the response variables were affected by biomass removal level. Only seedling planting year contributed significantly to affect tree mean height, dbh, volume. Growth efficiency was not affected by any treatment. These results indicate no apparent effect of biomass removal on site productivity for the range of biomass harvest levels performed.
... Franco), ponderosa pine, and sugar pine (Pinus lambertiana Douglas) from 5 to 25 years, with the greatest growth 20 to 25 years post-treatment. In contrast, old ponderosa pine in Arizona (Feeney et al. 1998;Kolb et al. 2007;Erickson & Waring 2014), Montana (Fajardo et al. 2007), and Oregon (McDowell et al. 2003) increased radial growth within 1-4 years of density reduction treatments. Although Skov et al. (2005) found no change in radial growth of pre-settlement ponderosa pine following thinning, responses were only tracked for 3 years. ...
Article
Full-text available
Restoration efforts to improve vigor of large, old trees and decrease risk to high-intensity wildland fire and drought-mediated insect mortality often include reductions in stand density. We examined 15-year growth response of old ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi) trees in northeastern California, U.S.A. to two levels of thinning treatments compared to an untreated (control) area. Density reductions involved radial thinning (thinning 9.1 m around individual trees) and stand thinning. Annual tree growth in the stand thinning increased immediately following treatment and was sustained over the 15 years. In contrast, radial thinning did not increase growth, but slowed decline compared to control trees. Available soil moisture was higher in the stand thinning than the control for 5 years post-treatment and likely extended seasonal tree growth. Our results show that large, old trees can respond to restoration thinning treatments, but that the level of thinning impacts this response. Stand thinning must be sufficiently intensive to improve old tree growth and health, in part due to increasing available soil moisture. Importantly, focusing stand density reductions around the immediate neighborhood of legacy trees was insufficient to elicit a growth response, calling into question treatments attempting to increase vigor of legacy trees while still maintaining closed canopies in dry, coniferous forest types. Although radial thinning did not affect tree growth rates, this treatment may still achieve other resource objectives not studied here, such as protecting wildlife habitat, reducing the risk of severe fire injury, and decreasing susceptibility to bark beetle attacks.
... GE represents stem volume production per unit leaf area; thus, it is generally expressed as the ratio of a periodic volume growth to total surface leaf area (Waring 1983). In practice, BA increment is a common replacement for stem volume growth in GE (e.g., Waring et al. 1980, O'Hara 1988, Fajardo et al. 2007. In this study, GE was expressed as the ratio of 5-year BA increment to total leaf area (unit: cm 2 m Ϫ2 ). ...
Article
Full-text available
Classic regeneration cuttings retaining trees at harvest (shelterwood with reserves, group selection) can be analyzed as analogs of variable-retention harvesting. A 1974 silvicultural experiment in the northern Rocky Mountains was analyzed at 38 years to evaluate the long-term effects of retention harvests on stand development, with a focus on both regeneration and retention tree responses. The postharvest understory treatments (understory removed and broadcast burned) effects were also evaluated. Results indicate that overstory retention results in relatively long-term regeneration growth reduction. Compared with the overstory-free condition (clearcut), the shelterwood with reserves and group selection overstories both reduced the regenerated cohort’s basal area, 63 and 44%, respectively. Postharvest burning increased regeneration stem density and also decreased mean regenerated tree size; consequently, these treatment effects were somewhat offsetting, as they produced a zero net difference in regenerated cohort basal area. Considerable regeneration growth reduction associated with retained overstory trees in the shelterwood with reserves was partially mitigated by understory vegetation protection measures that conserved advance regeneration. We conclude that both retention treatments somewhat suppressed regenerated cohort development, but that these impacts were lessened when overstory trees were aggregated and cuttings were in groups, rather than regularly dispersed through the cutting unit.
... Consequently, management treatments that retain large diameter pines and stands containing relatively high densities of large pines will be important for promoting cone crops and arthropods. Treatments that reduce stand densities while retaining larger pines can enhance cone crop production (Krannitz andDuralia 2004, Peters andSala 2008), while decreasing the risk of tree mortality due to wildfires and beetle outbreaks (McDowell et al. 2003, Fajardo et al. 2007, Fettig et al. 2007, Zhang et al. 2008, Hayes et al. 2009). Treatments that create patchy, open canopy conditions can promote heterogeneity across landscapes (cf. ...
Thesis
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The white-headed woodpecker (Picoides albolarvatus) is a species of conservation concern that is strongly associated with ponderosa pine (Pinus ponderosa)-dominated forests in the Inland Northwest. More information on home range size and habitat selection patterns is needed to inform conservation of the white-headed woodpecker, a focal management species for dry-forest restoration treatments. We examined whether home range size was associated with food resources and if fine-scale habitat characteristics influenced selection of foraging sites. During the post-fledging periods of 2014 and 2015, we radio-tracked 11 white-headed woodpeckers in forests of west-central Idaho. These forests were historically managed for timber harvest, resulting in removal of large-diameter, cone-producing ponderosa pine trees. We hypothesized that ponderosa pine cones would be a highly-valued food resource providing seeds and arthropods. We expected smaller home ranges to be associated with a greater availability of cones for foraging and that cone foraging would be concentrated in core use areas. We used foraging behavior to test this hypothesis, specifically, the proportion of time foraging on cones as an index of cone availability. Home range sizes ranged from 24 to 169 ha (90% fixed-kernel estimates). Consistent with our hypothesis, individuals with relatively small home ranges spent a greater proportion of foraging time on cones (β_1[SE] = 2.48[1.32], P = 0.096; β_2[SE] = -5.00[1.61], P = 0.014). Cone foraging was also higher in core use areas compared to home range peripheries for individuals exhibiting at least moderate cone foraging. We also expected foraging woodpeckers to favor larger diameter pines in sites with moderate to high canopy closure. To test this hypothesis, we analyzed foraging-site selection by comparing habitat characteristics between foraging trees and available trees, which provided support for our foraging site prediction (β_TreeDiameter[SE] = 3.50[0.43], P <0.001; β_Canopy[SE] = 1.74[0.41], P <0.001; β_Species[SE] = 1.43[0.33], P <0.001). Our results suggest that large diameter pines provide important foraging resources, and that landscapes with more productive cone crops could support greater numbers of white-headed woodpeckers. We recommend restoration treatments that retain high-density patches of large diameter pines while promoting mosaics of open and closed canopies at larger spatial scales.
... GE represents stem volume production per unit leaf area; thus, it is generally expressed as the ratio of a periodic volume growth to total surface leaf area (Waring 1983). In practice, BA increment is a common replacement for stem volume growth in GE (e.g., Waring et al. 1980, O'Hara 1988, Fajardo et al. 2007. In this study, GE was expressed as the ratio of 5-year BA increment to total leaf area (unit: cm 2 m Ϫ2 ). ...
Article
Full-text available
Classic regeneration cuttings retaining trees at harvest (shelterwood with reserves, group selection) can be analyzed as analogs of variable-retention harvesting. A 1974 silvicultural experiment in the northern Rocky Mountains was analyzed at 38 years to evaluate the long-term effects of retention harvests on stand development, with a focus on both regeneration and retention tree responses. The postharvest understory treatments (understory removed and broadcast burned) effects were also evaluated. Results indicate that overstory retention results in relatively long-term regeneration growth reduction. Compared with the overstory-free condition (clearcut), the shelterwood with reserves and group selection overstories both reduced the regenerated cohort's basal area, 63 and 44%, respectively. Postharvest burning increased regeneration stem density and also decreased mean regenerated tree size; consequently, these treatment effects were somewhat offsetting, as they produced a zero net difference in regenerated cohort basal area. Considerable regeneration growth reduction associated with retained overstory trees in the shelterwood with reserves was partially mitigated by understory vegetation protection measures that conserved advance regeneration. We conclude that both retention treatments somewhat suppressed regenerated cohort development, but that these impacts were lessened when overstory trees were aggregated and cuttings were in groups, rather than regularly dispersed through the cutting unit.
... Ponderosa pine has episodic regeneration patterns throughout its range (Cooper, 1960;Bailey and Covington, 2002;Shepperd et al., 2006) and there were no years during the time period of our study with the combinations of high cone production and adequate precipitation patterns that facilitate establishment of seedlings (Shepperd et al., 2006;Flathers et al., 2016). Other studies of ponderosa regeneration patterns after forest thinning in Colorado (Shepperd et al., 2006;Ertl, 2015), as well as in Arizona (Bailey and Covington, 2002;Puhlick et al., 2012), Montana (Fajardo et al., 2007), and New Mexico (Thomas and Waring, 2014), have found significantly greater densities in thinned stands versus unthinned stands. However, these studies occurred later post-treatment than our study, providing more time for trees to respond to changes in growing conditions. ...
Article
Ecological restoration treatments are being implemented at an increasing rate in ponderosa pine and other dry conifer forests across the western United States, via the USDA Forest Service’s Collaborative Forest Landscape Restoration (CFLR) program. In this program, collaborative stakeholder groups work with National Forests (NFs) to adaptively implement and monitor ecological restoration treatments intended to offset the effects of many decades of anthropogenic stressors. We initiated a novel study to expand the scope of treatment effectiveness monitoring efforts in one of the first CFLR landscapes, Colorado’s Front Range. We used a Before/After/Control/Impact framework to evaluate the short-term consequences of treatments on numerous ecological properties. We collected pre-treatment and one year post-treatment data on NF and partner agencies’ lands, in 66 plots distributed across seven treatment units and nearby untreated areas. Our results reflected progress toward several treatment objectives: treated areas had lower tree density and basal area, greater openness, no increase in exotic understory plants, no decrease in native understory plants, and no decrease in use by tree squirrels and ungulates. However, some findings suggested the need for adaptive modification of both treatment prescriptions and monitoring protocols: treatments did not promote heterogeneity of stand structure, and monitoring methods may not have been robust enough to detect changes in surface fuels. Our study highlights both the effective aspects of these restoration treatments, and the importance of initiating and continuing collaborative science-based monitoring to improve the outcomes of broad-scale forest restoration efforts.
... Thinning dense stands reduces competition for resources among trees and fosters increased growth and vigor of residual trees. Although the response of increased growth, basal area increment, and growth efficiency after thinning is well documented (Myers 1958, 1963, Markstrom et al. 1983, Skov et al. 2005, Fajardo et al. 2007), how quickly trees can respond to increased growing space is variable and can take one (Hood et al. 2016) to several years (Oliver 1979, Yang 1998). In the case of ponderosa pine, the response may not be evident for at least 10 years postthinning (Oliver and Edminster 1988). ...
Article
Full-text available
Mountain pine beetle ( Dendroctonus ponderosae Hopkins) (MPB), can cause extensive ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) mortality in the Black Hills of South Dakota and Wyoming, USA. Lower tree densities have been associated with reduced MPB-caused tree mortality, but few studies have reported on large-scale thinning and most data come from small plots that may not be representative of a large area. We quantified MPB-caused tree mortality in 21 pairs of commercially thinned and unthinned stands across the Black Hills. Both pre- and postoutbreak, unthinned stands had higher ponderosa pine basal area, tree density, and stand density index. Quadratic mean diameter was larger in thinned stands, both pre- and postoutbreak. Percent ponderosa pine basal area and tree density killed by MPB in unthinned stands were 38.2 ± 7.0 and 34.4 ± 6.9% compared with 3.9 ± 3.2 and 3.6 ± 2.9% in thinned stands, respectively. All stands were thinned within 2 years of exposure to MPB, suggesting a rapid effect from thinning treatments in mitigating tree mortality attributed to MPB. Stand density reductions through silviculture across a large geographical area can abate MPB-caused tree mortality.
... GE represents stem volume production per unit leaf area; thus, it is generally expressed as the ratio of a periodic volume growth to total surface leaf area (Waring 1983). In practice, BA increment is a common replacement for stem volume growth in GE (e.g., Waring et al. 1980, O'Hara 1988, Fajardo et al. 2007. In this study, GE was expressed as the ratio of 5-year BA increment to total leaf area (unit: cm 2 m Ϫ2 ). ...
Article
Full-text available
Classic regeneration cuttings retaining trees at harvest (shelterwood with reserves, group selection) can be analyzed as analogs of variable-retention harvesting. A 1974 silvicultural experiment in the northern Rocky Mountains was analyzed at 38 years to evaluate the long-term effects of retention harvests on stand development, with a focus on both regeneration and retention tree responses. The postharvest understory treatments (understory removed and broadcast burned) effects were also evaluated. Results indicate that overstory retention results in relatively long-term regeneration growth reduction. Compared with the overstory-free condition (clearcut), the shelterwood with reserves and group selection overstories both reduced the regenerated cohort?s basal area, 63 and 44%, respectively. Postharvest burning increased regeneration stem density and also decreased mean regenerated tree size; consequently, these treatment effects were somewhat offsetting, as they produced a zero net difference in regenerated cohort basal area. Considerable regeneration growth reduction associated with retained overstory trees in the shelterwood with reserves was partially mitigated by understory vegetation protection measures that conserved advance regeneration. We conclude that both retention treatments somewhat suppressed regenerated cohort development, but that these impacts were lessened when overstory trees were aggregated and cuttings were in groups, rather than regularly dispersed through the cutting unit.
... For example, in central Arizona, basal area increment has been observed to both decrease (Sutherland et al. 1991) and increase (Feeney et al. 1998) relative to control trees ,1-2 years post-fire. Likewise, in the Bitterroot Mountains in western Montana, radial wood growth has been observed to increase (Fajardo et al. 2007) or not be significantly different (Sala et al. 2005) relative to control trees ,9-10 years post-fire. Variability in growth metrics could be due to differences in water availability and other environmental factors between studies. ...
Article
Full-text available
Recent studies have highlighted the potential of linking fire behaviour to plant ecophysiology as an improved route to characterising severity, but research to date has been limited to laboratory-scale investigations. Fine-scale fire behaviour during prescribed fires has been identified as a strong predictor of post-fire tree recovery and growth, but most studies report these metrics averaged over the entire fire. Previous research has found inconsistent effects of low-intensity fire on mature Pinus ponderosa growth. In this study, fire behaviour was quantified at the tree scale and compared with post-fire radial growth and axial resin duct defences. Results show a clear dose–response relationship between peak fire radiative power per unit area (W m–2) and post-fire Pinus ponderosa radial growth. Unlike in previous laboratory research on seedlings, there was no dose–response relationship observed between fire radiative energy per unit area (J m–2) and post-fire mature tree growth in the surviving trees. These results may suggest that post-fire impacts on growth of surviving seedlings and mature trees require other modes of heat transfer to impact plant canopies. This study demonstrates that increased resin duct defence is induced regardless of fire intensity, which may decrease Pinus ponderosa vulnerability to secondary mortality agents.
... Decreased plant uptake and increases in soil temperature and moisture due to the actions of thinning and/or burning have also been shown to stimulate net N mineralization and nitrification rates, often creating a delayed pulse of nitrate (NO − 3 ) (e.g., White 1986, Kaye and Hart 1998, Gundale et al. 2005. Thinning alone has been shown to increase plant growth due to enhanced soil water availability in ponderosa pine forests (Feeney et al. 1998, Skov et al. 2004, Kaye et al. 2005, Sala et al. 2005, Fajardo et al. 2007. By contrast, thinning has been shown to suppress nutrient cycling rates due to its addition of high C:N ratio woody substrates (i.e., logging residues). ...
Article
Decades of fire suppression following extensive timber harvesting have left much of the forest in the intermountain western United States exceedingly dense, and forest restoration techniques (i.e., thinning and prescribed fire) are increasingly being used in an attempt to mitigate the effects of severe wildfire, to enhance tree growth and regeneration, and to stimulate soil nutrient cycling. While many of the short-term effects of forest restoration have been established, the long-term effects on soil biogeochemical and ecosystem processes are largely unknown. We assessed the effects of commonly used forest restoration treatments (thinning, burning, and thinning + burning) on nutrient cycling and other ecosystem processes 11 yr after restoration treatments were implemented in a ponderosa pine (Pinus ponderosa var. scopulorum)/Douglas fir (Pseudotsuga menziesii var. glauca) forest at the Lubrecht Fire and Fire Surrogates Study (FFS) site in western Montana, USA. Despite short-term (<3 yr) increases in soil inorganic nitrogen (N) pools and N cycling rates following prescribed fire, long-term soil N pools and N mineralization rates showed only subtle differences from untreated control plots. Similarly, despite a persistent positive correlation between fuels consumed in prescribed burns and several metrics of N cycling, variability in inorganic N pools decreased significantly since treatments were implemented, indicating a decline in N spatial heterogeneity through time. However, rates of net nitrification remain significantly higher in a thin + burn treatment relative to other treatments. Short-term declines in forest floor carbon (C) pools have persisted in the thin + burn treatment, but there were no significant long-term differences among treatments in extractable soil phosphorus (P). Finally, despite some short-term differences, long-term foliar nutrient concentrations, litter decomposition rates, and rates of free-living N fixation in the experimental plots were not different from control plots, suggesting nutrient cycles and ecosystem processes in temperate coniferous forests are resilient to disturbance following long periods of fire suppression. Overall, this study provides forest managers and policymakers valuable information showing that the effects of these commonly used restoration prescriptions on soil nutrient cycling are ephemeral and that use of repeated treatments (i.e., frequent fire) will be necessary to ensure continued restoration success.
... temperature and moisture due to the actions of thinning and/or burning have also been shown to stimulate net N mineralization and nitrification rates, often creating a delayed pulse of nitrate (NO 3 -) (e.g., White 1986, Kaye and Hart 1998, Gundale et al. 2005. Thinning alone has been shown to increase plant growth due to enhanced soil water availability in ponderosa pine forests (Feeney et al. 1998, Kaye et al. 2005, Sala et al. 2005, Skov et al. 2004, Fajardo et al. 2007). By contrast, thinning has been shown to suppress nutrient cycling rates due to its addition of high C:N ratio woody substrates (i.e., logging residues). ...
... Other researchers have found more seedlings germinated in burned treatments than in unburned treatments (Sackett and Haase 1998). Fajardo et al. (2007) noted that regeneration rates for Douglas-r and ponderosa pine in Montana were higher ten years a er cut-and-burn and cut-only treatments than they were in control plots. In ponderosa pine-Gambel oak forests on the South Rim of the Grand Canyon, Fulé et al. (2005) monitored the results ve years a er areas were treated with thinning and prescribed burning (full restoration), minimal thinning around old trees and prescribed burning (minimum restoration), and burning alone. ...
Technical Report
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Fuel treatments are common and are generally regarded as beneficial for reducing fire behavior, as well as for ecological reasons such as increasing understory diversity and reducing competition among trees for nutrients and water. What remains unclear is how long such fuel treatments are effective in reducing undesirable fire behavior. This working paper addresses the following management questions regarding fuel treatment longevity: What factors influence fuel treatment longevity? How long will fuel treatments last before sites need to be retreated? Do some types of treatments last longer than others?
... ed for species such as ponderosa pine. In northern Arizona, higher-intensity treatments were found to have twice the number of ponderosa pine seedlings as low-intensity restoration treatments (Bailey and Covington 2002). Other researchers have found more seedlings germinated in burned treatments than in unburned treatments (Sackett and Haase 1998). Fajardo et al. (2007) noted that regeneration rates for Douglas--r and ponderosa pine in Montana were higher ten years aer cut-and-burn and cut-only treatments than they were in control plots. In ponderosa pine-Gambel oak forests on the South Rim of the Grand Canyon, Fulé et al. (2005) monitored the results ve years aer areas were treated with thinning and p ...
Research
Dry forests of the western United States have been altered by long-term fire exclusion, resulting in a more dense forest structure and an increased risk of crown fire. Recently, thinning and prescribed fire treatments have been implemented in these forests for two main reasons: ecological restoration and fire hazard reduction. Ecological restoration is a holistic endeavor that focuses on restoring ecological patterns, processes, and functions. Ecological restoration goals often include restoring the process of fire to forested ecosystems and changing forest structure to fall within the historical range of variability as indicated by reference information. While fire hazard reduction is often a goal or an outcome of ecological restoration, not all treatments specifically designed to reduce fuels also restore ecosystem patterns, processes, and functions (Reinhardt et al. 2008). Fire hazard reduction treatments are designed specifically to reduce fire intensity, reduce fire severity, and increase the ability of firefighters to control wildfires (Table 1). Fuel treatments are common and are generally regarded as beneficial for reducing fire behavior, as well as for ecological reasons such as increasing understory diversity and reducing competition among trees for nutrients and water. What remains unclear is how long such fuel treatments are effective in reducing undesirable fire behavior. This working paper addresses the following management questions regarding fuel treatment longevity: What factors influence fuel treatment longevity? How long will fuel treatments last before sites need to be retreated? Do some types of treatments last longer than others?
... In forests that evolved with frequent, low-severity fire, stands that are relatively open with low fuel loads are more likely to be resilient to disturbances under future climate conditions than those that have high tree density and fuel loads (Fulé, 2008). In recent decades, managers have implemented a variety of restoration and fuels treatments in degraded forests to restore ecological integrity and increase resilience to disturbances, such as highseverity crown fires and insect outbreaks Lynch et al., 2000;Youngblood et al., 2006;Fajardo et al., 2007;Stephens et al., 2009;Roccaforte et al., 2010). Fuels reduction and restoration treatments found to be effective include manipulations to individual trees, such as raking and pruning (Schmidt and Wakimoto, 1988), treatments focused on protecting old/large trees (Fulé et al., 2006), mechanical thinning without burning (Agee and Skinner, 2005), and strategic placement of fuelbreaks (Agee et al., 2000;Finney, 2001). ...
... Treatment timing can also be important. Although cut-burn treatment combinations have consistently been found to be most effective at restoring dry forests, it has also been shown that burning too soon after thinning can result in delayed tree mortality (Fajardo et al. 2007). [A consistent management implication from many of the dry-forest restoration studies is that direct reduction of overstory density (thinning), in combination with renewal of nutrient cycling mechanisms (burning), yields the greatest increases in undergrowth plant and overstory tree vigor.] Figure 47 -Fenced clone of quaking aspen located along the 5316 road on the North Fork John Day Ranger District (aspen is short and has yellow foliage). ...
... Interestingly, only under the CNRM-A2 scenario did the thin-only live tree C approximate the control C by the end of the mid-century simulation period (Fig. 5). This was surprising given the common observation of tree growth-release following forest thinning (Latham and Tappeiner, 2002;McDowell et al., 2006;Fajardo et al., 2007). The growth-and-yield model, FVS, is the principal tool used by many forest managers to project forest growth because it effectively captures stand-level growth response to forest management practices, such as density reduction from fuels treatments. ...
... and/or electronic compass are still rare even in temperate forest ecology (Kalliovirta et al. 2005, Fajardo et al. 2007), while there are virtually no such studies from the tropical forest ecosystems. Aim of this paper is to introduce the application of the above mentioned measuring technology in a tropical forest inventory. ...
Article
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This paper describes a new technique for inventory of permanent plots in tropical forests and presents the results of its application in a 1 ha permanent plot in a lowland dipterocarp forest at Kuala Belalong, Ulu Temburong National Park, Brunei Darussalam. The technique is based on mapping of positions of tree individuals in three-dimensional space with a high accuracy. Measuring set consists of a distance measuring device (laser rangefinder) and a electronic compass supplying data to a field computer with specialized software (FieldMap®). This method is faster and more exact than methods based on Cartesian grids established in the field. As an example, inventories from 2000 and 2007 of the plot mentioned are compared ≥ 5 cm. The structural and diversity properties of the forest show similar patterns to the other two permanent plots in Kuala Belalong. In 2007, 1 318 trees were found, out of 2000). Total basal area was 39.18 m2 (0.2 m2 were dead individuals). Growth dynamics has distinct spatial patterns: about half of the plot shows fast dbh increment in 2000-2007 and appearance of numerous new trees; the other half displays stagnation. This is probably due to topographic conditions and partly to the gap dynamics (several dominant trees have fallen there since 2000). Concerning the taxonomic composition, 47 families were recorded, the dominant ones in terms of basal area being Dipterocar paceae, Myrtaceae, Euphorbiaceae, Lauraceae, Sapotaceae and Burseraceae (sorted in decreasing order). The Dipterocarp family accounts for about 40 % of the total dbh. The most frequent ones were trees of Euphorbiaceae, Dipterocarpaceae, Myrtaceae, Burseraceae and Anacardiaceae. However, this census concerns mainly trees with dbh ≥ 10 cm, while the rest (dbh 5-10 cm) remained partly undetermined until 2007.
... Changes in fire regime and forest structure have increased the vulnerability of ponderosa pine forests to large, stand-replacing crown fires (Allen et al. 2002). Ecological restoration provides an opportunity to restore the natural structure and function of these fire-adapted ecosystems consistent with their evolutionary environment ) and has been applied throughout the western United States (Youngblood et al. 2006;Fajardo et al. 2007). Similar concerns about severe wildfires in uncharacteristically dense forests have been the focus of restoration efforts in pine-oak ecosystems of Europe (Pausas et al. 2004) and Mexico (Rodríguez-Trejo & Fulé 2003). ...
Article
We evaluated landscape-scale forest restoration treatment implementation and effectiveness in meeting objectives in a ponderosa pine forest at Mt. Trumbull, Arizona, U.S.A. The goal of the project was to alter forest structure by thinning and burning to more closely resemble forest conditions prior to Euro-American settlement in 1870. We measured 117 permanent plots before (1996/1997) and after (2003) treatments. The plots were evenly distributed across the landscape (approximately 1,200 ha), about half of which was an untreated control. We evaluated treatment implementation and effectiveness based on 1870 structure and/or goals outlined by managers. The success of treatment implementation varied: about 94% of the area originally planned for restoration was treated in some manner by 2003, but only 70% received the full planned treatment (thin and burn). Although density of ponderosa pines >2.5 cm was reduced significantly by 66% from approximately 429 pines/ha to approximately 146 pines/ha in the treated area, the targeted residual density was exceeded by 111–256% (all plots) or 10–85% (thinned and burned plots). Thirteen percent of the pre-settlement pines died in the treated area by 2003, but 9% percent also died in the control, indicating that pre-settlement pines in untreated areas were nearly as vulnerable as those exposed to restoration treatments. Large snags increased 45%, and 65% of logs >50 cm were retained, achieving implementation goals. Although restoration treatments were not implemented totally to specifications, they were effective in attaining the overall project goal of restoring more open forest structure while preserving more than 75% of the pre-settlement pines. Canopy fuel loads were substantially reduced, allowing for the reintroduction of surface fires.
... Such low densities are feasible in other regions where ponderosa pine grows. For instance, ponderosa pine regeneration 10 years post-treatment in the Bitterroot Mountains of Montana ranged between 33 and 87 seedlings ha À1 (Fajardo et al., 2007). In northern Arizona, ponderosa pine regeneration after prescribed fire or thinning ranged between 12 and 41 seedlings ha À1 (Bailey and Covington, 2002), although the coincidence of a banner seed year and a very wet summer can produce several thousand ponderosa pine seedlings ha À1 in northern Arizona (Sackett and Haase, 1998). ...
Article
Full-text available
We determine the time frame after initial fuel treatment when prescribed fire will be likely to produce high enough mortality rates in ponderosa pine (Pinus ponderosa var. scopulorum Dougl. ex Laws.) regeneration to be successful in maintaining treatment effectiveness in the Black Hills of South Dakota. We measured pine regeneration in disturbed stands and young pine growth rates to estimate the susceptibility of pine regeneration to prescribed fire with time since initial treatment. We also determined surface fuel accumulation rates for stands after prescribed fire to help estimate likely fire behavior in maintenance prescribed fire. Given our estimates of regeneration density and tree size, and likely fire behavior, we then used small pine tree mortality—fire effect relations to estimate the effects of prescribed fire on developing understory pine at specific times since initial treatments.
... The decreased density of tree-and bole-foraging species suggests that these species emigrate from these areas since the larger trees do not reestablish in this short time frame. The increased density of the tassel-eared squirrel over a 10-year time period, however, may be due to increased growth and vigor of large pine trees (Fajardo et al., 2007) on which they depend (Patton and Green, 1970). ...
Article
Full-text available
After a century of fire suppression, conifer forests in the western United States have dramatically departed from conditions that existed prior to Euro-American settlement, with heavy fuel loads and an increased incidence of wildfire. To reduce this threat and improve overall forest health, land managers are designing landscape-scale treatments that strategically locate thinning and burning treatments to disrupt fuel continuity, allowing managed wildfires to burn the remaining area. A necessary step in designing and evaluating these treatments is understanding their ecological effects on wildlife. We used meta-analysis to compare effects of small-diameter removal (thinnings and shelterwoods) and burning treatments, selective harvesting, overstory removal (including clearcutting), and wildfire on wildlife species in southwestern conifer forests. We hypothesized that small-diameter removal and burning treatments would have minimal effects on wildlife compared to other treatments. We found 33 studies that met our criteria by (1) comparing density or reproductive output for wildlife species, (2) using forest management or wildfire treatments, (3) implementing control-impact or before-after control-impact design using unmanaged stands as controls, and (4) occurring in Arizona or New Mexico ponderosa pine (Pinus ponderosa) or mixed conifer (Abies/Picea/Pinus) forest. The 22 studies suitable for meta-analysis occurred ≤20 years post-treatment on sites <400 ha. Small-diameter harvest and burning treatments had positive effects but thin/burn and selective harvest treatments had no detectable effect on most small mammals and passerine bird species reported in studies; overstory removal and wildfire resulted in an overall negative response. We examined foraging guild responses to treatments; ground-foraging birds and rodents had no strong response. Aerial-, tree-, and bole-foraging birds had positive or neutral responses to the small-diameter removal and burning treatments, but negative responses to overstory removal and wildfire. Small-diameter removal and burning treatments as currently being implemented in the Southwest do not negatively impact most of the wildlife species in the studies we examined in the short-term (≤10 years). We believe a combination of treatments in a patchy arrangement across the landscape will result in the highest diversity and density. We recommend that managers implement thinning and burning treatments, but that future research efforts focus on long-term responses of species at larger spatial scales, use reproductive output as a more informative response variable, and target species for which there is a paucity of data.
... Several of these modeled C values (burn only, understory thin and burn, overstory thin) likely represent conservative estimates because the percent change in large tree carbon was lower than the control. Previous research on tree removal suggests that growth release in large leave trees may be delayed anywhere between 5 and 20 years after thinning (North et al., 1996;Latham and Tappeiner, 2002;McDowell et al., 2006;Fajardo et al., 2007). ...
Article
Sequestered forest carbon can provide a climate change mitigation benefit, but in dry temperate forests, wildfire poses a reversal risk to carbon offset projects. Reducing wildfire risk requires a reduction in and redistribution of carbon stocks, the benefit of which is only realized when wildfire occurs. To estimate the time needed to recover carbon removed and emitted during treatment, we compared the 7-year post-treatment carbon stocks for mechanical thinning and prescribed fire fuels reduction treatments in Sierra Nevada mixed-conifer forest and modeled annual carbon accumulation rates. Within our 7-year re-sample period, the burn only and understory thin treatments sequestered more carbon than had been removed or emitted during treatment. The understory thin and burn, overstory thin, and overstory thin and burn continued to have net negative carbon stocks when emissions associated with treatment were subtracted from 7-year carbon stock gains. However, the size of the carbon deficit in the understory thin and burn 7 years post-treatment and the live tree growth rates suggest that the remaining trees may sequester treatment emissions within several more years of growth. Overstory tree thinning treatments resulted in a large carbon deficit and removed many of the largest trees that accumulate the most carbon annually, thereby increasing carbon stock recovery time. Our results indicate that while there is an initial carbon stock reduction associated with fuels treatments, treated forests can quickly recover carbon stocks if treatments do not remove large, fire-resistant overstory trees.
... However, no decline in growth increment was detected following the low-severity repeated burns in 2002, which was well after the Pandora moth infestation had subsided. Therefore, we suggest that low-to moderate-intensity burning in central Oregon does not have a major effect on tree vigor, which differs from findings in other western forests (Fajardo et al. 2007). Unlike burning, fertilizing with N, P, and S led to sizeable increases in vegetation growth (Fig. 9D). ...
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Thinning and prescribed burning are common management practices for reducing fuel buildup in ponderosa pine forests. However, it is not well understood if their combined use is required to lower wildfire risk and to help restore natural ecological function. We compared 16 treatment combinations of thinning, prescribed fire, and slash retention for two decades across a site quality gradient of second-growth pine stands, measuring changes in forest vegetation growth, structure, and composition. Thinning alone doubled the diameter growth increment of ponderosa pine, moderately stimulated shrub production, and resulted in lower tree mortality compared with unthinned plots. In contrast, repeated fire alone did not substantially alter stand structure or increase tree vigor, herbaceous production, or plant diversity. The combined use of thinning and repeated burning reduced shrub cover, yet produced no changes in herbaceous production, plant diversity, stand structure, or tree vigor compared with thin-only treatments. Additional findings identified (1) inconsequential effects of thinning residues on site productivity, (2) the need for multiple entries of prescribed fire if the abatement of shrubs is required, (3) the ineffectiveness of repeated burning to stimulate plant growth, and (4) that the thinning treatment served as an effective surrogate to fire for managing central Oregon forest vegetation.
... Although the initial treatment may reduce crown fire risk in the short term, the long-term outcome of these treatments is unknown. For instance, retention of a low-density mature overstorey coupled with ground disturbance can create ideal conditions for prolific regeneration (Oliver and Ryker 1990;Shepperd and Battaglia 2002) and produce rapid growth of new or existing pine regeneration (Fajardo et al. 2007). Ladder fuels and increased canopy density created over time by growth of these trees and the existing overstorey lead to increased potential for crown fire behavior. ...
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Reduction of crown fire hazard in Pinus ponderosa forests in the Black Hills, SD, often focuses on the removal of overstorey trees to reduce crown bulk density. Dense ponderosa pine regeneration establishes several years after treatment and eventually increases crown fire risk if allowed to grow. Using prescribed fire to control this regeneration is hampered by the limited knowledge of fire-related mortality threshold values for seedlings (<1.4 m tall) and saplings (0.25 to 10 cm diameter at breast height). The present study was initiated to assess fire-related mortality of ponderosa pine seedlings and saplings on prescribed burns across the Black Hills. We established plots in several burn units after the first post-fire growing season to measure crown volume scorch, crown volume consumption, basal scorch, and ground char for ponderosa pine seedlings and saplings. Logistic regression was used to model the probability of mortality based on tree size, flame length, and direct fire effects. Tree size, flame length, crown damage, ground char, and basal char severity were all important factors in the prediction of mortality. Observed mortality was >70% for seedlings but was only 18 to 46% for sapling-sized trees. The differences in mortality thresholds for ponderosa pine seedlings and saplings highlight their susceptibility to different damage pathways and give managers several options when designing burn prescriptions.
... Thinning studies in loblolly pine (Pinus taeda L.), lodgepole pine (Pinus contorta Dougl. ex Loud.), and ponderosa pine that involved similar or larger basal area reductions when expressed as a percentage of pretreatment values report either post-thinning GE increases similar to those found in our study (Sword Sayer et al. 2004;Blevins et al. 2005;Fajardo et al. 2007), or decreases in GE as thinning intensity increased, depending on how GE was calculated (McDowell et al. 2007). The %GC we observed varies from similar to (in northeastern quadrants that received understory release treatments) to much lower than (in southeastern quadrants) the diameter increment changes of 40%-50% reported for naturally regenerated red pine, lodgepole pine, and ponderosa pine following thinning of similar or greater intensity (Cooley 1970;Blevins et al. 2005;Sala et al. 2005). ...
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Variable retention harvest systems are encouraged to promote complexity in managed forests, and aggregated retention has been suggested as a means of reducing moisture stress in residual trees. We studied the impacts of within-aggregate position on growth and foliar physiology to better understand the spatial dynamics of residual-tree responses to aggregated retention harvests in even-aged Pinus resinosa Ait. stands. Distance from edge and edge aspect influenced radial growth, volume increment, and growth efficiency, but only edge aspect affected foliar nitrogen content. Spatial variables had no significant relationships with foliar carbon isotope ratios (¹³C). Increases in radial growth, volume increment, and growth efficiency following harvesting were greatest near edges and in the northeastern quadrants of aggregates that received mechanical understory release treatments, and lowest in the southeastern quadrant of aggregates and near aggregate centers. Foliar nitrogen content was highest in the southwestern quadrants of aggregates that received understory release treatments, and lowest in the northwestern quadrants of aggregates. Our results suggest spatial relationships are important determinants of residual-tree responses to aggregated retention harvests.
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Little is known about the relationship between anatomical and physiological characteristics of live trees and woodpecker foraging behavior, despite some woodpecker species foraging on live trees more often than dead trees. We assessed whether excavation of prey by insectivorous bark-foraging woodpeckers was associated with five characteristics (phloem thickness, oleoresin exudation, oleoresin viscosity, and bark thickness and hardness) of ponderosa pine (Pinus ponderosa) trees, and whether those characteristics, and the abundance of woodpecker foraging excavations, differed between trees growing on geologically older fine soils vs. coarser, volcanically derived, younger cinder soils in northern Arizona. We hypothesized that trees experienced greater water and nutrient stress on cinder soils and that stress would lead to differences in tree traits that affect woodpecker foraging. We found that trees growing on fine soils were >10 times less likely to be used by woodpeckers than were trees growing on cinder soils. Tree use by both woodpeckers and their wood-borer prey was negatively associated with bark thickness and hardness, but was not associated with other tree characteristics. The negative relationship with bark characteristics was stronger for woodpeckers than wood-borers, and woodpecker predation rates on wood-borers were negatively associated with bark hardness, suggesting that woodpeckers were responding to bark hardness independent of wood-borer presence. Tree traits we examined did not explain the 10-fold difference in tree use by woodpeckers across soil types, suggesting there were other variables we did not measure affecting this pattern. Wood-borers like those feeding on live trees we studied typically do not kill trees and remain part of the landscape without destroying forests, suggesting forests on cinder soils could act as important woodpecker foraging habitat without experiencing expansive forest losses typical of more irruptive beetle species. Poco se sabe acerca de la relación entre las características anatómicas y fisiológicas de los árboles vivos y el comportamiento de alimentación de los pájaros carpinteros, a pesar de que algunas especies de pájaros carpinteros se alimentan de árboles vivos con más frecuencia que de árboles muertos. Evaluamos si la excavación de presas por pájaros carpinteros insectívoros que buscan debajo de la corteza fue asociada con cinco características (grosor del floema, exudación de oleorresina, viscosidad de oleorresina y grosor y dureza de la corteza) de los árboles de pino ponderosa (Pinus ponderosa), y si esas características y la abundancia de las excavaciones de alimentación por pájaros carpinteros, difirieron entre árboles que crecían en suelos finos geológicamente más antiguos contra suelos de ceniza más jóvenes, más gruesos, derivados de volcanes en el norte de Arizona. Hipotetizamos que los árboles experimentaron un mayor estrés hídrico y de nutrientes en los suelos de ceniza y que el estrés conduciría a diferencias en las características de los árboles que afectan la alimentación por los pájaros carpinteros. Descubrimos que los árboles que crecen en suelos finos tenían >10 veces menos probabilidades de ser utilizados por los pájaros carpinteros que los árboles que crecen en suelos de ceniza. El uso de árboles tanto por los pájaros carpinteros como por sus presas, los barrenadores de la madera, se asoció negativamente con el grosor y la dureza de la corteza, pero no se asoció con otras características de los árboles. La relación negativa con las características de la corteza fue más fuerte para los pájaros carpinteros que para los barrenadores, y las tasas de depredación de los pájaros carpinteros sobre los barrenadores se asociaron negativamente con la dureza de la corteza, lo que sugiere que los pájaros carpinteros respondían a la dureza de la corteza independientemente de la presencia del barrenador. Las características de los árboles que examinamos no explicaron la diferencia de 10 veces en el uso de los árboles por parte de los pájaros carpinteros en todos los tipos de suelo, lo que sugiere que hubo otras variables que no medimos que afectaron este patrón. Los barrenadores de madera como los que se alimentan de árboles vivos que estudiamos normalmente no matan árboles y siguen siendo parte del paisaje sin destruir bosques, lo que sugiere que los bosques en suelos de ceniza podrían actuar como un importante hábitat de alimentación para pájaros carpinteros sin experimentar pérdidas forestales expansivas típicas de especies de escarabajos más irruptivos.
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Disturbances play a fundamental role in shaping forest communities. It is therefore important to accurately quantify their frequency and magnitude in forest ecosystems. Tree-ring series are commonly used for relatively accurate detection of past disturbances. Currently, several dendroecological techniques exist that enable the detection of disturbances in tree-ring series. In this study, increment cores (n = 312) were collected from trees that were deliberately retained in harvested gaps of two natural-disturbance-based silvicultural systems in the Acadian Forest of Maine, USA. These systems were designed to approximate the gap-based natural disturbance regime of the region. Since the specific harvest dates and severities were known, we compared the efficacy of three predominant disturbance detection techniques in accurately detecting disturbance within two years of the harvest date across five common, yet ecologically distinct species-Acer rubrum, Picea rubens, Pinus strobus, Thuja occidentalis, and Tsuga canadensis-and the length of elapsed time prior to when maximum growth responses were experienced. We tested the growth-averaging method, the boundary-line method, and the combination of the growth-averaging and boundary-line methods (Splechtna method) using the TRADER R package. We found little variation among detection techniques in their-relatively high success-rate of detecting disturbance within two years of the harvest date (growth-averaging method: 69.9%, Splechtna method: 68.6%, and boundary-line method: 64.1%). We most frequently found negative correlations with pre-treatment growth rates and detection rates among detection techniques. Our estimates of disturbance severity did not influence the probability of detecting the year-of-harvest. Of the species tested, Tsuga canadensis (73.7% − 85.5%) and Thuja occidentalis (78.4% − 83.7%) had the greatest detection rates across the techniques while Pinus strobus was consistently the lowest (51%). Time-lags-defined as the number of years post-harvest before a tree reaches its peak growth rate-were also analyzed. Pre-disturbance basal area increment and crown ratio were marginally negatively correlated with the length of time-lags in response to harvest and Thuja occidentalis (7.2 ± 0.4) and Tsuga canadensis (6.8 ± 0.3) had significantly longer time-lags than Acer rubrum (5.4 ± 0.3). Overall, all techniques demonstrated relatively high detection rates (>60%), given the range of sizes and ages of the species tested and reduced two-year time window for detection. Absent from all models were variables that measured disturbance severity, which suggests tree responses to disturbance were more sensitive to tree-level attributes and local changes to the growing environment.
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The effective use of functional traits to explain species coexistence has been hindered by the scarce use of demographic variables, such as growth, with the association between functional traits and growth often assumed rather than tested. In this study, using spatial point‐pattern analyses, we spatially related three functional traits linked to plant competitive ability (maximum tree height [HMAX], leaf mass per area [LMA] and wood density [WD]) to tree growth rates (basal area increment [BAI10] and growth efficiency [GE]) in a stem‐mapped plot of a temperate rainforest in southern Chile. With this, we tested the competition‐trait similarity and the competition‐trait hierarchy hypotheses, and further assessed the relationship between functional trait values' spatial distribution and growth rate. We used spatial point‐pattern analyses, in particular, pair‐wise spatial association patterns, the Schlather's I index and mark variograms associated to specific null models to infer spatial correlations among individuals of several species with different traits and growth values. First, we found spatial similarity in trees' functional traits on a fine‐scale, a result supporting the competition‐trait hierarchy hypothesis. Second, while the HMAX and LMA specific values of the focal tree were spatially positively correlated with their neighbours' growth rates, the WD of the focal tree had a negative spatial correlation with its neighbours' growth rates. We also found a positive spatial autocorrelation among HMAX, LMA and WD at a fine‐scale; neighbouring trees tended to have similar values. In agreement with our a priori statements, we infer that HMAX and LMA provide a competitive tolerance, while WD of the focal tree has a competitive effect on its immediate neighbours. As such, we have demonstrated that functional traits mediate species interactions, which is a step forward in predictive community ecology, thus we can further our understanding regarding how traits mediate community assembly and species coexistence.
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California's high density, fire-excluded forests experienced an extreme drought accompanied by warmer than normal temperatures from 2012 to 2015, resulting in the deaths of millions of trees. We examined tree mortality and growth of mixed-conifer stands that had been experimentally treated between 2011 and 2013 with two different thinning treatments, one with more structural variability (HighV) and one with less structural variability (LowV), applied alone or in combination with prescribed burning. Tree mortality between 2014 and 2018 varied by species ranging from 42% of white fir (Abies concolor) to 18% of sugar pine (Pinus lambertiana), 12% of incense cedar (Calocedrus decurrens) and 10% of yellow pine (P. ponderosa and P. jeffreyi). Lower overall tree mortality rates at this location relative to drier locations in the southern Sierra Nevada suggested that drought effects may have been ameliorated by lower water deficits due to our site's more northerly location and deep, productive soils in combination with reductions in tree competition following thinning and burning. Averaged across burn treatments, thinning reduced the overall mortality rate between 2014 and 2018 from 34% to 11%. A total of 23% of the basal area was lost in the unthinned control treatments during this time period, while basal area was unchanged in the thinned treatments, with growth offsetting mortality. There was no significant difference in mortality or basal area change between LowV and HighV, suggesting that leaving trees at variable spacing may not compromise growth or resilience of the stand during a drought. Overall tree mortality was greater in the prescribed burn treatments, most pronounced in the smaller tree size classes, and varied by species, with burning having a significant effect on incense cedar and all pines, but not white fir. Trees with greater competition (Hegyi index) were more likely to die, particularly when also burned. Burning, however, consumed surface fuels and lowered fire hazard. With predictions of warmer droughts and greater weather variability, reducing forest density (basal area) and keeping surface fuel loads low will be important for building greater resilience to future drought stress and wildfire.
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One goal of fuels treatments is to limit potential fire behavior by reducing overstory tree density, but this may precipitate regeneration, which contributes to increasing potential fire behavior over time. To understand factors that influence tree regeneration in treated stands, we compared abundance of advance and post treatment regeneration in 5–14-year-old thinning and mastication treatments covering approximately 2600 ha within two National Forests in Colorado, U.S.A. The study sites were dominated by two species with complimentary regeneration niches. Ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) is less shade tolerant, but more fire and drought resistant than Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). We considered three critical features of the post treatment environment: species composition, forest structure (especially density), and site characteristics. Regeneration densities at the plot level varied considerably: 37% of the plots had no regeneration, while 15% had more than double the average density. High-density areas tended to occur in moist sites, mostly on north aspects that were dominated by Douglas-fir in the overstory. These areas are where wildfire mitigation benefits will likely deteriorate most rapidly. The vast majority (69%) of all regeneration was Douglas-fir. 31% of all regeneration occurred post treatment. In this group, ponderosa pine abundance was positively related to time since treatment but Douglas-fir was not, suggesting a stronger positive effect of treatment for ponderosa pine, although Douglas-fir was still more abundant. This is likely because treatments reduced the seed source for Douglas-fir more than for ponderosa pine while reducing total overstory density to create conditions that met the regeneration requirements of this shade intolerant species. Advanced regeneration was common throughout the study area, consisting of nearly 80% Douglas-fir and only 13% ponderosa pine. Although the abundance of advance regeneration decreased over time since treatment, likely due to mortality given that we encountered few sapling-sized trees, surviving trees reduce treatment longevity and have the potential for subsequent growth release and contribution to fuel hazard development. Conifer regeneration did not vary between mastication and thinning treatments. The impact of regeneration on treatment longevity was highly variable at smaller-than-stand scales. On the Colorado Front Range, moist sites with low overstory density and mature Douglas-fir to provide a seed source are where treatment effectiveness is likely to degrade most rapidly. These areas with abundant regeneration may be best left untreated, or managers should anticipate the need to re-treat them more frequently.
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Hazardous fuels reduction treatments often reduce the likelihood of undesirable fire behavior (e.g. crown fire) through some combination of tree thinning and surface fuel reduction. However, fuels treatment effectiveness declines over time as fuels re-accumulate and new tree cohorts of trees establish and grow. Fuels treatment longevity therefore depends in part on post treatment tree regeneration rates, which vary depending on characteristics of sites and treatments as well as on stand composition. We used a chronosequence of 3–12 year old fuels treatments to investigate the impact of site (“wet” north aspects versus “dry” south aspects), treatment type (thinning with and without follow up slash burning), and stand composition on conifer regeneration following treatments in stands of ponderosa pine (Pinus ponderosa Lawson & C. Lawson) and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco var. glauca [Beissn.] Franco) in Colorado, USA. We found conifer regeneration density was >500 trees ha⁻¹ on average by 10 years post treatment. While stands on north aspects had twice the regeneration density of those on south aspects, the rate of increase since treatment was similar. Instead, there was significantly more regeneration on north aspects because these stands contained a considerable amount of Douglas-fir, which was largely absent on south aspects. Ponderosa pine regeneration density increased with time since treatment, while Douglas-fir regeneration density did not, which suggests that treatments promoted reproduction of ponderosa pine. Conversely, Douglas-fir regeneration density was related to the amount of Douglas-fir basal area in stands, which was not the case for ponderosa pine, probably because all stands had ample amounts of ponderosa pine basal area. There was no difference in regeneration density between burned and unburned stands. Our results highlight the influence of stand composition and site characteristics on tree regeneration following fuels treatments. In this study, fuels treatments acted much like shelterwood regeneration treatments for ponderosa pine, pairing favorable establishment environments for this species with a seed source. This resulted in ponderosa pine trees establishing even on relatively dry south aspects, while Douglas-fir regeneration may have been inhibited by seed availability and was largely confined to wetter north aspects. Despite similar tree regeneration rates across aspects, fuels treatment effects may nonetheless deteriorate more quickly on north aspects because of this Douglas-fir regeneration, much of which predated treatments. Indeed, advance regeneration was common in all of our stands, suggesting the longevity of fuels treatment effects will depend substantially on whether these trees are eventually able to release.
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This report synthesizes the literature and current state of knowledge pertaining to reintroducing fire in stands where it has been excluded for long periods and the impact of these introductory fires on overstory tree injury and mortality. Only forested ecosystems in the United States that are adapted to survive frequent fire are included. Treatment options that minimize large-diameter and old tree injury and mortality in areas with deep duff and methods to manage and reduce duff accumulations are discussed. Pertinent background information on tree physiology, properties of duff, and historical versus current disturbance regimes are also discussed.
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QuestionsDo landscape-scale thin and burn restoration treatments have a long-term, landscape-scale impact on old Pinus ponderosa growth? Is there a relationship between old P. ponderosa growth and climatic factors, in particular, drought, before and after restoration treatments? LocationNorthwestern Arizona, USA. Methods We looked at old P. ponderosa growth across the landscape in both an area ‘treated’ by thin and burn restoration treatments, and a neighbouring untreated area. We re-visited each old P. ponderosa located on permanent 0.1-ha plots installed across the landscape prior to treatment implementation and recorded tree status, diameter, aspect, slope and competition from neighbouring trees. Growth was analysed from shallow increment cores taken from each tree at breast height (1.37 m). Comparisons of growth between the treated and untreated areas were carried out using regional proxy and instrumental Palmer drought severity index values and instrument precipitation data. ResultsWe found significant differences in precipitation and temperature between the treated and untreated areas, indicating a drier, less advantageous climate in the untreated area. Old trees in the treated area responded less negatively in diameter growth to treatments; both treatment and abiotic site factors were important in predicting post-treatment growth. All old trees grew slowly during drought years; however, old trees in the treated area grew better after three recent drought years than old trees in the untreated area. Conclusions Old P. ponderosa diameter growth increased following restoration, though not immediately. Old trees in the treated area also grew better in the years after drought than old trees in the untreated area. Restoration, or similar treatments removing small, neighbouring trees may be critical in maintaining old P. ponderosa in the landscape, particularly under future climate change and increasing drought frequency in the western USA.
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We carried out a systematic review and meta-analysis of the effects of forest thinning and burning treatments on restoring fire behavior attributes in western USA pine forests. Ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi), with co-occurring species, are adapted to a disturbance regime of frequent surface fires, but extended fire exclusion and other factors have led to historically uncharacteristically dense stands and high fuel loadings, supporting high-severity fires. Treatments to begin to reverse these changes and reduce fuel hazards have been tested experimentally and observations of wildfire behavior in treated stands have also been reported. Using a systematic review methodology, we found 54 studies with quantitative data suitable for meta-analysis. Combined treatments (thinning + burning) tended to have the greatest effect on reducing surface fuels and stand density, and raising modeled crowning and torching indices, as compared to burning or thinning alone. However, changes in canopy base height and canopy bulk density were not consistently related to treatment intensity, as measured by basal area reduction. There are a number of qualifications to the findings. First, because it is not feasible to subject treated areas to severe fire experimentally, inferences about potential fire behavior rely on imperfect modeling techniques. Second, research has not been carried uniformly over the ranges of the pine forests, although we found no significant differences in treatment effects between regions or forest types. Overall, however, meta-analysis of the literature to date strongly indicates that thinning and/or burning treatments do have effects consistent with the restoration of low-severity fire behavior.
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Thinnings using cut-to-length or whole-tree harvesting systems followed by underburning were evaluated for their effects on seedling and sapling demography in a pure, uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf.) stand containing a minor component of California white fir (Abies concolor var. lowiana [Gord.] Lemm.). Depression of seedling counts due to forest floor disturbance associated with thinning was followed by a recovery largely confined to Jeffrey pine in the whole-tree treatment where final seedling counts exceeded those found initially. The postburn substrate was more favorable for establishment of Jeffrey pine than white fir seedlings, and the largest increase in seedling counts between the initial and final inventories occurred in the burned portion of the whole-tree treatment. Live sapling losses from thinning were greatest in the cut-to-length treatment, while underburning induced complete sapling mortality. Absent treatment, several stand and site variables influenced seedling and sapling abundance, prominent among them a propensity for mahala mat (Ceanothus prostratus Benth.) to elevate counts of white fir within both size classes. These results provide land managers insight into the impacts of six combinations of thinning and burning treatment on natural regeneration in eastern Sierra Nevada Jeffrey pine and similar dry site forest types.
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U The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of multiple use management of the Nation’s forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, cooperation with the States and private forest owners, and management of the National Forests and National Grasslands, it strives—as directed by Congress—to provide increasingly greater service to a growing Nation. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720–2600 (voice and TDD). To fi le a complaint of discrimination, write
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We examined the cumulative effects of 20 years of two-year interval prescription burning on available nitrogen (N) and total N and phosphorus (P) pools in the upper 15 cm of mineral soil of a southwestern ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forest over a complete two-year burn cycle. Repeated burning reduced anaerobically mineralizable N up to 25%. However, burned and control plots had similar monthly ammonium and nitrate pool sizes in the mineral soil during both years of the two-year burn cycle. Mineral soil total N in the upper 15 cm was reduced by 110 kg N/ha (about a 7% reduction) after 20 years of prescription burning at this site. This estimate, coupled with a calculated 470 kg/ha loss of N from the forest floor, indicates repeated burning has substantially depleted soil N stocks at this site. In contrast to N, mineral soil total P in burned plots was similar to control plots. Our results suggest that repeated prescription burning at two-year intervals may have deleterious long-term effects on N cycling in southwestern ponderosa pine forests.
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Heavy livestock grazing, logging, and fire exclusion associated with Euro-American settlement has brought about substantial changes in forest conditions in western forests. Thus, old-growth definitions based on current forest conditions may not be compatible with the natural conditions prevalent throughout the evolutionary history of western forest types. Detailed analysis of data from two study areas in the southwestern ponderosa pine type suggests that average tree densities have increased from as few as 23 trees per acre in presettlement times to as many as 851 trees per acre today. Associated with these increases in tree density are increases in canopy closure, vertical fuel continuity, and surface fuel loadings resulting in fire hazards over large areas never reached before settlement. In addition, fire exclusion and increased tree density has likely decreased tree vigor (increasing mortality from disease, insect, drought, etc.), herbaceous and shrub production, aesthetic values, water availability and runoff, and nutrient availability, and also changed soil characteristics and altered wildlife habitat. To remedy these problems and restore these forest ecosystems to more nearly natural conditions, and maintain a viable cohort of old age-class trees, it will be necessary to thin out most of the postsettlement trees, manually remove heavy fuels from the base of large, old trees, and reintroduce periodic burning.
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Intertree competition indices and effects were examined in 14 uneven-aged ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) stands in eastern Montana. Location, height, diameter at breast height (DBH), basal area in- crement, crown ratio, and sapwood area were determined for each tree (DBH >3.8 cm) on one stem-mapped plot (0.2- 0.4 ha) in each sample stand. Based on tree locations, various competition indices were derived for each sample tree and correlated with its growth efficiency by diameter class. In addition, trends in individual tree attributes by diameter class and level of surrounding competition were determined. For trees with a DBH
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The age structure in 1876, the last year of the natural frequent-fire regime, of an unharvested ponderosa pine forest in northern Arizona was reconstructed from living and dead dendrochronological samples. Approximately 20% of the trees were .200 yr old in 1876 with ages ranging to 540 yr. If dead trees had not been included in the reconstruction, the distribution would have been biased toward younger trees and a 40% shorter age range. The presettlement age distribution was multimodal with broad peaks of establishment, consistent with the model of regeneration in ''safe sites'' where herbaceous competition and fire thinning are reduced. Although fire disturbance regimes and climatic conditions varied over the centuries before 1876, a clear relationship between these variations and tree establishment was not observed. Due to fire exclusion, reduced grass competition, and favorable climatic events, high levels of regeneration in the 20th century raised forest density from 60 trees/ha in 1876 to .3000 trees/ha in 1992. An ecological restoration experiment initiated in 1993 conserved all living presettlement trees and reduced the density of young trees to near-presettlement levels. Two important components for evaluating the restoration treatment effects are monitoring of old-tree persistence and patterns of future regeneration in the context of the presettlement reference age structure.
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Ecological restoration is the process of reestablishing the structure and func- tion of native ecosystems and developing mutually beneficial human-wildland interactions that are compatible with the evolutionary history of those systems. Restoration is based on an ecosystem's reference conditions (or natural range of variability); the difference between reference conditions and contemporary conditions is used to assess the need for restorative treatments and to evaluate their success. Since ecosystems are highly complex and dynamic, it is not possible to describe comprehensively all possible attributes of ref- erence conditions. Instead, ecosystem characteristics with essential roles in the evolutionary environment are chosen for detailed study. Key characteristics of structure, function, and disturbance—especially fire regimes in ponderosa pine ecosystems—are quantified as far as possible through dendroecological and paleoecological studies, historical evidence, and comparison to undisrupted sites. Ecological restoration treatments are designed to reverse recent, human-caused ecological degradation. Testing of restoration treatments at four sites in northern Arizona, USA, has shown promise, but the diverse context of management goals and constraints for Southwestern forest ecosystems means that appropriate applica- tions of restoration techniques will probably differ in various settings.
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This study assessed the effects of restoration treatments on growth, leaf physiology, and insect resistance characteristics of presettlement-age ponderosa pines (Pinus ponderosa Dougl. ex Laws.) at the Gus Pearson Natural Area in northern Arizona. Treatments (C, control; T thinned from below; TB, thinned and prescribed burned) were designed to restore stand structure and disturbance regime to a pre-Euro-American settlement reference condition. Tree growth and some physiological characteristics differed between wet (1995) and dry (1996) years. Soil water content was greater in both thinned treatments than in the control. Compared with the control: trees in both thinned treatments had greater leaf nitrogen content (C = 1.44, T = 1.57, TB = 1.59 g.m(-2)), leaf toughness (C = 65.1, T = 71.3, TB = 69.3 g), and basal area increment (C = 14.3, T = 19.9, TB = 20.7 cm(2)). Resin flow was greater in the thinned and burned treatment (12.2 mL.day(-1)) than in the thinned treatment (4.3 mL.day(-1)) and control (3.6 mL.day(-1)). Treatment differences in predawn water potential and net photosynthetic rate varied among sample dates, with the largest differences during a period of drought (C < T and TB). Our results suggest that restoration treatments improved resource uptake, growth, and insect resistance capabilities of presettlement ponderosa pines.
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This review is intended to introduce an outline of the results of community metabolism studies on various forest ecosystems of the Western Pacific area made by Japanese investigators in these past ten years. In 1955,SATOO opened this line of research by publishing his first report(65)on the productivity of artificial plantations in this country. A few years later, in 1957 and 1958,four groups of ecologists and forest scientists including ourselves began almost simultaneously to follow him, and the fields of study were expanded to include various types of natural and artificial vegetation ranging from subarctic conifer forests of Hokkaido to the tropical jungle of Southeast Asia. Since that time, more than one hundred stands belonging to some forty different forest types have been investigated, of course mostly within Japan Proper, but also in the Ryukyus(40), Thailand(21,22,24,42,44-47,93,100)and Cambodia(23). Steady progress has been made in the methodology for analysing the metabolism of forest community. These studies were, therefore, not always based on one and the same method, making it difficult to compare the results obtained by different authors. Thus the contents of this review are more or less tentative ; yet we hope, this may well be a useful starting point for more advanced studies to be made under the framework of the International Biological Programme.
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This chapter demonstrates two structural properties of plant communities—canopy leaf area and growth efficiency. It develops four basic premises that (1) canopy leaf area can be related to competition for light, (2) growth efficiency is responsive to canopy leaf area and other identified environmental factors, (3) potential productivity or site capability can be estimated from knowing maximum canopy leaf area, and (4) canopy leaf areas for trees or stands can be nondestructively estimated by determining sapwood cross-sectional area at a convenient reference height. Canopy leaf area and its vertical distribution can be accurately estimated through correlations with conducting sapwood area throughout the crown. Species within the same genera have widely differing ratios of leaf area to sapwood area. To estimate the canopy leaf area on large trees, the linear taper in sapwood area from breast height (1.37 m) to the base of the crown must be determined.
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Southwestern ponderosa pine forests were dramatically altered by fire regime disruption that accompanied Euro-American settlement in the 1800s. Major changes include increased tree density, diminished herbaceous cover, and a shift from a frequent low- intensity fire regime to a stand-replacing fire regime. Ecological restoration via thinning and prescribed burning is being widely applied to return forests to the pre-settlement condition, but the effects of restoration on ecosystem function are unknown. We measured carbon (C), nitrogen (N), and phosphorus (P) fluxes during the first two years after the implementation of a replicated field experiment comparing thinning and composite (thin- ning, forest floor fuel reduction, and prescribed burning) restoration treatments to untreated controls in a ponderosa pine forest in northern Arizona, USA. Total net primary productivity (260 g C·m 22 ·yr 21 ) was similar among treatments because a 30-50% decrease in pine foliage and fine-root production in restored ecosystems was balanced by greater wood, coarse root, and herbaceous production. Herbaceous plants accounted for ,20% of total plant C, N, and P uptake in the controls but from 25% to 70% in restored plots. Total plant N uptake was ;3 g N·m 22 ·yr 21 in all treatments, but net N mineralization was just one-half and two- thirds of this value in the control and composite restoration, respectively. Element flux rates in controls generally declined more in a drought year than rates in restoration treat- ments. In this ponderosa pine forest, ecological restoration that emulated pre-settlement stand structure and fire characteristics had a small effect on plant C, N, and P fluxes at the whole ecosystem level because lower pine foliage and fine-root fluxes in treated plots (compared to controls) were approximately balanced by higher fluxes in wood and her-
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The impact of fire damage on the shoot growth potential of 36 branches on each of nine ponderosa pine (Pinusponderosa Laws.) trees was evaluated after a fall season prescribed surface fire. In the first season after burning, mean fascicle lengths and bud sizes (length and diameter) were greater on trees which received underburning treatment than on unburned trees. No treatment effect was observed on shoot lengths, needle numbers, or fascicle numbers, characters determined in the season of bud formation.