Physical site characteristics including aspect, elevation, and slope were recorded for each study plot and spatial coordinates were obtained from a global positioning system. Stand height was determined by averaging the heights of the first live woody individual encountered along each 10 m subplot in mechanically masticated plots as well as in the adjacent controls. Unfortunately height data was not collected from postfire plots in the prior study. The age of the stand prior to each mechanical disturbance was obtained from stem samples collected from the first two obligate seeding individuals encountered within controls and ranged from seven to sixty-four years across all mechanically masticated fuel treatments. The stand ages of postfire plots, on the other hand, were obtained from stem samples collected from nearby unburned vegetation or estimated from burned skeletons of obligate seeding species collected within the burn area. These sites ranged in age from twenty-four to fifty-one years old at the time of the 2003 wildfires. All data from mechanically treated study sites, including both treatment and control, were collected in the spring and summer of 2011 and 2012. The postfire data from the local case study were also collected in the spring and summer of 2011 and 2012 whereas the postfire data used in the regional comparison were collected in the spring and summer of 2005. The age of each plot at the time of sampling was determined by subtracting the year of the disturbance from the year of data collection.

Physical site characteristics including aspect, elevation, and slope were recorded for each study plot and spatial coordinates were obtained from a global positioning system. Stand height was determined by averaging the heights of the first live woody individual encountered along each 10 m subplot in mechanically masticated plots as well as in the adjacent controls. Unfortunately height data was not collected from postfire plots in the prior study. The age of the stand prior to each mechanical disturbance was obtained from stem samples collected from the first two obligate seeding individuals encountered within controls and ranged from seven to sixty-four years across all mechanically masticated fuel treatments. The stand ages of postfire plots, on the other hand, were obtained from stem samples collected from nearby unburned vegetation or estimated from burned skeletons of obligate seeding species collected within the burn area. These sites ranged in age from twenty-four to fifty-one years old at the time of the 2003 wildfires. All data from mechanically treated study sites, including both treatment and control, were collected in the spring and summer of 2011 and 2012. The postfire data from the local case study were also collected in the spring and summer of 2011 and 2012 whereas the postfire data used in the regional comparison were collected in the spring and summer of 2005. The age of each plot at the time of sampling was determined by subtracting the year of the disturbance from the year of data collection.

The sampling design at each of the 149 mechanically masticated fuel treatment study sites consisted of a 10 x 100 m plot established within the treated area at the random point generated in ArcGIS and an adjacent 10 x 100 m control plot placed one meter inside the edge of untreated vegetation to avoid edge affects. Each study plot was further subdivided into 10 100-m2 subplots with a nested 1-m2 quadrat placed along the top edge of the measurement tape. Postfire study sites consisted of a 20 x 50 m plot that was equal in area to a fuel treatment study plot and was also further subdivided into 10 100-m2 subplots with a nested 1-m2 quadrat placed along the outer top and bottom edges of the plot. Cover and density were recorded for each species within 1-m2 quadrats and a list of additional species present within the rest of the 100-m2 subplot was compiled. Ocular estimates of cover were made and density was either counted, or estimated when there were more than 30 individuals in a quadrat. First year seedlings were recorded separately from mature and resprouting individuals. Comprehensive surveys for additional species were conducted in subplots of mechanical treatments and postfire plots; whereas controls were more limited and as such total species richness in these plots was potentially underrepresented.

The sampling design at each of the 149 mechanically masticated fuel treatment study sites consisted of a 10 x 100 m plot established within the treated area at the random point generated in ArcGIS and an adjacent 10 x 100 m control plot placed one meter inside the edge of untreated vegetation to avoid edge affects. Each study plot was further subdivided into 10 100-m2 subplots with a nested 1-m2 quadrat placed along the top edge of the measurement tape. Postfire study sites consisted of a 20 x 50 m plot that was equal in area to a fuel treatment study plot and was also further subdivided into 10 100-m2 subplots with a nested 1-m2 quadrat placed along the outer top and bottom edges of the plot. Cover and density were recorded for each species within 1-m2 quadrats and a list of additional species present within the rest of the 100-m2 subplot was compiled. Ocular estimates of cover were made and density was either counted, or estimated when there were more than 30 individuals in a quadrat. First year seedlings were recorded separately from mature and resprouting individuals. Comprehensive surveys for additional species were conducted in subplots of mechanical treatments and postfire plots; whereas controls were more limited and as such total species richness in these plots was potentially underrepresented.

The sampling design at each of the 149 mechanically masticated fuel treatment study sites consisted of a 10 x 100 m plot established within the treated area at the random point generated in ArcGIS and an adjacent 10 x 100 m control plot placed one meter inside the edge of untreated vegetation to avoid edge affects. Each study plot was further subdivided into 10 100-m2 subplots with a nested 1-m2 quadrat placed along the top edge of the measurement tape. Postfire study sites consisted of a 20 x 50 m plot that was equal in area to a fuel treatment study plot and was also further subdivided into 10 100-m2 subplots with a nested 1-m2 quadrat placed along the outer top and bottom edges of the plot. Cover and density were recorded for each species within 1-m2 quadrats and a list of additional species present within the rest of the 100-m2 subplot was compiled. Ocular estimates of cover were made and density was either counted, or estimated when there were more than 30 individuals in a quadrat. First year seedlings were recorded separately from mature and resprouting individuals. Comprehensive surveys for additional species were conducted in subplots of mechanical treatments and postfire plots; whereas controls were more limited and as such total species richness in these plots was potentially underrepresented.

All plant species were identified down to finest taxa when possible. Each plant code used in the survey data is paired to a plant code on this species list which provides the full scientific name of each species, the plant family the species belongs to, the native or non-native status of species, and the life history of the plant. Plant nomenclature follows: Baldwin B.G., D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken, editors. 2012. The Jepson Manual: vascular plants of California. Second edition. University of California Press, Berkeley, USA.

All plant species were identified down to finest taxa when possible. Each plant code used in the survey data is paired to a plant code on this species list which provides the full scientific name of each species, the plant family the species belongs to, the native or non-native status of species, and the life history of the plant. Plant nomenclature follows: Baldwin B.G., D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken, editors. 2012. The Jepson Manual: vascular plants of California. Second edition. University of California Press, Berkeley, USA.

All plant species were identified down to finest taxa when possible. Each plant code used in the survey data is paired to a plant code on this species list which provides the full scientific name of each species, the plant family the species belongs to, the native or non-native status of species, and the life history of the plant. Plant nomenclature follows: Baldwin B.G., D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken, editors. 2012. The Jepson Manual: vascular plants of California. Second edition. University of California Press, Berkeley, USA.

Mechanical fuel treatments are a primary pre-fire strategy for potentially mitigating the threat of wildland fire, yet there is limited information on how they impact shrubland ecosystems. This publication contains data related to vegetation structure and composition in mechanically masticated chaparral communities used to assess the impact of these fuel treatments on shrubland vegetation and to determine the extent to which they emulate postfire succession. Data were collected from within chaparral dominated communities on the Angeles, Cleveland, Los Padres, and San Bernardino national forests of southern California. The climate of the region is Mediterranean with mild, wet winters and hot, dry summers and the topography is rugged and steep with elevations from near sea level to over 3500 m in the Transverse and Peninsular ranges. The rocky and shallow soils of the area are predominantly granitic and support a wide range of shrubland communities that include stands dominated by a single species (>50% cover) such as Adenostoma fasciculatum (chamise), Arctostaphylos spp. (manzanita), Ceanothus spp. (wild lilac) and Quercus spp. (oak) and mixed stands without a single dominant. The mechanically masticated fuel treatments utilized for this study were identified using the USGS Southern California Fuel Treatment Data Set (http://www.calfiresci.org) and were limited to single-entry mastication treatments with no follow-up treatment of burning or re-mastication. The size and shape of available treatments were highly variable and thus a random sampling design was used to maximize the number of study sites. This was accomplished by selecting sites from within treatment boundaries using the random-point generator in ArcGIS and a buffer of at least 400 m between points. The final sample size of accessible locations included 149 mechanically masticated study sites, each with a treatment plot and a control. All treatments were completed between 2004 and 2011 using a variety of masticating equipment and ranged in size from less than a hectare to large-scale treatments spanning thousands of hectares across entire ridgelines. The timing of mastication treatments extended across all seasons and ranged in completion time from several days to several years depending on their size. In order to evaluate the differences between mechanically masticated and early successional postfire vegetation two comparisons were made. The first was a single site case study on the Cleveland National Forest where a spark from a masticator ignited the 39 acre Long Canyon Wildfire on September 23rd, 2010 that burned next to the mechanical treatment being implemented and comprised similar pre-disturbance vegetation. This comparison consisted of four study plots in the masticated treatment and four study plots in the adjacent burned area that were monitored for the first two years following the disturbances. The second was a regionally broad comparison of two-year old mechanically masticated study plots from this fuel treatment study (n = 25) to a subset of two-year-old postfire plots (n = 56) from a regional study of early postfire succession in southern California chaparral published in an earlier paper (Keeley et al. 2008). This study investigated factors determining fire severity and ecosystem responses in 250 randomly selected study plots within the 2003 Cedar, Grand Prix, Old, and Paradise fire perimeters. The subset of 56 plots chosen from the original 250 plots were based on the criteria that the site was located within one of the four southern California national forests, was in chaparral vegetation, and had a pre-disturbance stand age and elevation within the same range as the two-year-old masticated sites used in the regional comparison. These data support the following publication: Brennan, Teresa J., Keeley, J.E. In Press. Response of chaparral shrubland vegetation to mechanical mastication fuel treatments. Regional postfire data were extracted from this

Mechanical fuel treatments are a primary pre-fire strategy for potentially mitigating the threat of wildland fire, yet there is limited information on how they impact shrubland ecosystems. This publication contains data related to vegetation structure and composition in mechanically masticated chaparral communities used to assess the impact of these fuel treatments on shrubland vegetation and to determine the extent to which they emulate postfire succession. Data were collected from within chaparral dominated communities on the Angeles, Cleveland, Los Padres, and San Bernardino national forests of southern California. The climate of the region is Mediterranean with mild, wet winters and hot, dry summers and the topography is rugged and steep with elevations from near sea level to over 3500 m in the Transverse and Peninsular ranges. The rocky and shallow soils of the area are predominantly granitic and support a wide range of shrubland communities that include stands dominated by a single species (>50% cover) such as Adenostoma fasciculatum (chamise), Arctostaphylos spp. (manzanita), Ceanothus spp. (wild lilac) and Quercus spp. (oak) and mixed stands without a single dominant. The mechanically masticated fuel treatments utilized for this study were identified using the USGS Southern California Fuel Treatment Data Set (http://www.calfiresci.org) and were limited to single-entry mastication treatments with no follow-up treatment of burning or re-mastication. The size and shape of available treatments were highly variable and thus a random sampling design was used to maximize the number of study sites. This was accomplished by selecting sites from within treatment boundaries using the random-point generator in ArcGIS and a buffer of at least 400 m between points. The final sample size of accessible locations included 149 mechanically masticated study sites, each with a treatment plot and a control. All treatments were completed between 2004 and 2011 using a variety of masticating equipment and ranged in size from less than a hectare to large-scale treatments spanning thousands of hectares across entire ridgelines. The timing of mastication treatments extended across all seasons and ranged in completion time from several days to several years depending on their size. In order to evaluate the differences between mechanically masticated and early successional postfire vegetation two comparisons were made. The first was a single site case study on the Cleveland National Forest where a spark from a masticator ignited the 39 acre Long Canyon Wildfire on September 23rd, 2010 that burned next to the mechanical treatment being implemented and comprised similar pre-disturbance vegetation. This comparison consisted of four study plots in the masticated treatment and four study plots in the adjacent burned area that were monitored for the first two years following the disturbances. The second was a regionally broad comparison of two-year old mechanically masticated study plots from this fuel treatment study (n = 25) to a subset of two-year-old postfire plots (n = 56) from a regional study of early postfire succession in southern California chaparral published in an earlier paper (Keeley et al. 2008). This study investigated factors determining fire severity and ecosystem responses in 250 randomly selected study plots within the 2003 Cedar, Grand Prix, Old, and Paradise fire perimeters. The subset of 56 plots chosen from the original 250 plots were based on the criteria that the site was located within one of the four southern California national forests, was in chaparral vegetation, and had a pre-disturbance stand age and elevation within the same range as the two-year-old masticated sites used in the regional comparison. These data support the following publication: Brennan, Teresa J., Keeley, J.E. In Press. Response of chaparral shrubland vegetation to mechanical mastication fuel treatments. Regional postfire data were extracted from this