DOI: 10.5061/dryad.2bvq83bx1
title: Data from: Thinning and prescribed burning increase shade-tolerant conifer regeneration in a fire excluded mixed-conifer forest

description: Fire exclusion and past management have altered the composition,
 structure, and function of frequent-fire forests throughout western North
 America. In mixed-conifer forests of the California Sierra Nevada, fire
 exclusion has exacerbated the effects of drought and endemic bark beetles,
 resulting in extensive mortality of fire-adapted pine species. Thinning
 and prescribed fire are widely used in these forests to reduce fuels,
 moderate fire behavior, and restore ecosystems. Tree regeneration
 influences future forest composition and structure, and therefore future
 resilience to disturbances, but long-term effects of thinning and
 prescribed burning on tree regeneration after prolonged fire exclusion are
 poorly understood. We measured tree regeneration one year prior to, and
 periodically for 16 years following thinning and prescribed burning in a
 mixed-conifer forest in the Sierra Nevada, California, USA. We asked three
 questions. How did the composition and density of tree regeneration change
 after thinning and prescribed burning? Did pretreatment vegetation types
 influence conifer regeneration density after treatments? Did planting
 after overstory thinning increase regeneration density of native pine
 species? Sixteen years after treatments, combined natural regeneration of
 shade-tolerant white fir (Abies concolor) and incense-cedar (Calocedrus
 decurrens) averaged 2,032 trees per hectare (tph) after understory
 thinning, and 7,745 tph after understory thinning combined with prescribed
 burning, increases of 37% and 146% from pretreatment densities. In
 contrast, combined natural regeneration of white fir and incense-cedar
 averaged 497 tph after overstory thinning, 780 tph after overstory
 thinning with prescribed burning, 113 tph after prescribed burning alone,
 and 807 tph in untreated controls, all of which were declines from
 pretreatment densities. Natural regeneration of white fir and
 incense-cedar was consistently an order of magnitude greater than Jeffrey
 pine (Pinus jeffreyi) and sugar pine (Pinus lambertiana), whose combined
 densities 16 years after treatments averaged 37 tph across treatments and
 did not significantly respond to thinning and/or prescribed burning.
 Natural conifer regeneration after treatments varied by pre-treatment
 vegetation type (closed canopy, Ceanothus cordulatus shrub-dominated, and
 open sparse), with large increases of natural regeneration after
 understory thinning in closed canopy and Ceanothus shrub vegetation types.
 Planting increased sugar pine regeneration density after overstory
 thinning, marginally increased Jeffrey pine regeneration after overstory
 thinning combined with prescribed burning, and increased white fir
 regeneration after overstory thinning with and without burning. No
 treatments reduced white fir and incense-cedar natural regeneration while
 simultaneously increasing natural pine regeneration, suggesting new
 thinning, burning, and planting approaches may be required to meet
 regeneration restoration objectives.
description: See methods section of Zald et al. 2024. Thinning and prescribed
 burning increase shade-tolerant conifer regeneration in a fire excluded
 mixed-conifer forest. <em>Forest Ecology and Management, 551(1)
 121531. https://doi.org/10.1016/j.foreco.2023.121531</em>
description: This README file was generated on 2023-11-20 by Harold Zald. GENERAL
 INFORMATION 1. Title of Dataset: Thinning and prescribed burning increase
 shade-tolerant conifer regeneration in a fire excluded mixed-conifer
 forest 2. Author Information A. Principal Investigator Contact Information
 Name: Harold Zald Institution: USDA Forest Service, Pacific Northwest
 Service Station Address: Corvallis, OR USA Email: harold.zald@usda.gov B.
 Associate or Co-investigator Contact Information Name: Andrew Gray
 Institution: USDA Forest Service, Pacific Northwest Research Station
 Address: Corvallis, OR USA Email: andrew.gray@usda.gov 3. Date of data
 collection (multiple dates, range): 2000-2021 4. Geographic location of
 data collection: Teakettle Experimental Forest, California, USA 36°58′N,
 119°02′W 5. Information about funding sources that supported the
 collection of the data: USDI Joint Fire Science Program (Project ID
 15-1-07-6, 10-1-10-14, 01-3-2-02), California Department of Forestry and
 Fire Protection as part of the California Climate Investments Program
 (Grant #8GG14803, #8GG14804), and the USDA Forest Service Pacific
 Northwest and Pacific Southwest Research Stations SHARING/ACCESS
 INFORMATION 1. Licenses/restrictions placed on the data: CC0 1.0 Universal
 (CC0 1.0) Public Domain 2. Links to publications that cite or use the
 data: Zald, H. S. J., May, C. J., Gray, A. N., North, M. P., Hurteau, M.
 D. (2024). Thinning and prescribed burning increase shade-tolerant conifer
 regeneration in a fire excluded mixed-conifer forest. Forest Ecology and
 Management 551(1): 121531. https://doi.org/10.1016/j.foreco.2023.121531 3.
 Links to other publicly accessible locations of the data: None 4.
 Links/relationships to ancillary data sets: None 5. Was data derived from
 another source? No A. If yes, list source(s): NA 6. Recommended citation
 for this dataset: Zald, H. S. J., May, C. J., Gray, A. N., North, M. P.,
 Hurteau, M. D. (2023). Data from: Thinning and prescribed burning increase
 shade-tolerant conifer regeneration in a fire excluded mixed-conifer
 forest. Dryad Digital Repository. https://doi.org/10.5061/dryad.2bvq83bx1
 DATA & FILE OVERVIEW 1. Data frame List: All data files are data
 frame objects within the R data file TEF\_regeneration.RData A)
 gridpt.count B) gridpt.envars 2. Relationship between files, if important:
 Both data files have a common variable gridpt 3. Additional related data
 collected that was not included in the current data package: None 4. Are
 there multiple versions of the dataset? No A. If yes, name of file(s) that
 was updated: NA i. Why was the file updated? NA ii. When was the file
 updated? NA
 #########################################################################
 DATA-SPECIFIC INFORMATION FOR: gridpt.count 1. Number of variables: 15 2.
 Number of cases/rows: 14670 3. Variable List: * trt: Treatment combination
 of prescribed burning and mechanical thinning. Categorical variable with
 six levels (UN = unburned, not thinned control, UC = unburned, understory
 CASPO thinning, US = unburned, overstory shelterwood thinning, BN =
 burned, not thinned control, BC = burned, understory CASPO thinning, BS =
 burned, overstory shelterwood thinning). CASPO refers understory thinning
 following guidelines in the California spotted owl report (Verner et al.
 1992. https://doi.org/10.2737/PSW-GTR-133), removing intermediate sized
 trees 25–76 cm diameter at breast height (DBH, 1.37 m) while retaining at
 least 40 % canopy cover, retaining 40 % basal area, or no harvest of trees
 greater than 76 cm DBH, whichever constraint was most restrictive. * plot:
 4 hectare plot identification code. Categorical variable with 16 levels.
 There are 3 replicate plots for each level of treatment combination in the
 trt variable. * gridpt: Gridpoint identification code. Categorical
 variable with 402 levels, with first three characters denoting which plot
 a gridpoint is in, followed by a numeric identifier ranging from 01 to 49.
 For each treatment combination, two replicate plots each have nine
 gridpoints (01-09) positioned in a regular grid with 50 m x 50 m spacing.
 For the third replicate plot in each treatment combination there are 49
 gridpoints on regular grid with 25 m x 25 m spacing. * quad: Quadrat of
 3.5 m radius tree regeneration microplots centered on gridpoints.
 Categorical variable with 4 levels (NE = Northeast, SE = Southeast, SW =
 Southwest, NW = Northwest) * species: Tree species code. Categorical
 variable with eight levels (ABCO = White fir, Abies concolor, ABMA = Red
 fir, Abies magnifica, CADE = Incense-cedar, Calocedrus decurrens, PIJE =
 Jeffrey pine, Pinus Jeffreyii, PILA = Sugar pine, Pinus lambertiana, PREM
 = Bitter cherry, Prunus emarginata, QUCH = Canyon live oak, Quercus
 chrysolepis, QUKE = California black oak, Quercus kelloggii). * origin:
 Origin of tree regeneration. Categorical variable with two levels (N =
 natural regeneration, P = planted regeneration). Planted regeneration was
 2 year old bare root stock, planted in 2002, in only the overtstory
 thinned treatments (trt = US or trt = BS). * year: Year of regeneration
 measurement. Numeric variable with values 2000, 2002, 2003, 2004, 2005,
 2011, 2016, 2017, 2018, 2019, 2021. * szcl: Tree regeneration size class\.
 Categorical variable with four levels \(A = height greater or equal than 5
 cm and less than 50 cm\, B = height greater or equal to 50 cm and less
 than 137 cm\, C = height greater or equal to 137 cm and diameter at 137 cm
 height less than 5 cm\, D = height greater or equal to 137 and diameter at
 137 cm height greater or equal then 5 cm\)\. Note that during first
 measurement year \(year = 2000\) tree regeneration was only tallied for
 regeneration less than 5 cm in diameter \(szcl = A \| B \|C\)\. Inclusion
 of szcl = D was in subsequent measurement years to account for
 regeneration that grew greater than 5 cm diameter\. * count: Count of
 regeneration for a given gridpt, quad, species, origin, and szcl. Numeric
 variable from 0 to 327. * azi: Azimuth from gridpoint center to planted
 tree regeneration. Numeric variable from 1-359. Azimuth assumes magnetic
 declination of 14 degree east. * dist: Distance in meters from gridpoint
 center to planted tree regeneration. Numeric variable from 0.1 to 3.5 m. *
 dia: Tree regeneration diameter in cm. Numeric variable from 0.1 to 15.2
 cm. * len: Length/height of tree regeneration in cm. Numeric variable from
 6 to 480 cm.• comments: qualitative field observation comments. Text
 variable * Data.Corrections: Data corrections that derivate from original
 field data sheets. Text variable 4. Missing data codes: NA 5. Specialized
 formats or other abbreviations used: None
 #########################################################################
 DATA-SPECIFIC INFORMATION FOR: gridpt.envars 1. Number of variables: 17 2.
 Number of cases/rows: 402 3. Variable List: * gridpt: Gridpoint
 identification code. Categorical variable with 402 levels, with first
 three characters denoting which plot a gridpoint is in, followed by a
 numeric identifier ranging from 01 to 49. For each treatment combination,
 two replicate plots each have nine gridpoints (01-09) positioned in a
 regular grid with 50 m x 50 m spacing. For the third replicate plot in
 each treatment combination there are 49 gridpoints on regular grid with 25
 m x 25 m spacing. * canopy: Pretreatment percent canopy cover above
 gridpoints. Numeric variable from 0 to 100 percent, estimated using
 digital hemispherical photography taken during the pretreatment summer of
 2000. For details see Gray et al. (2005)
 https://doi.org/10.1093/forestscience/51.3.198. * litter: Percent cover of
 litter within 1.78 m radius microplot centered on each grid point,
 measured during the pretreatment summers of 1998–1999. Numeric variable
 from 0 to 20 percent. * bare: Percent cover of bare ground within 1.78 m
 radius microplot centered on each grid point, measured during the
 pretreatment summers of 1998–1999. Numeric variable from 0 to 95 percent.
 * rock: Percent cover of rock within 1.78 m radius microplot centered on
 each grid point, measured during the pretreatment summers of 1998–1999.
 Numeric variable from 0 to 100 percent. * cwd: Percent cover of coarse
 woody debris (woody pieces greater or equal than 20 cm diameter) within
 1.78 m radius microplot centered on each grid point, measured during the
 pretreatment summers of 1998–1999. Numeric variable from 0 to 84 percent.
 * sticks: Percent cover of sticks (woody pieces less than 20 cm diameter,
 excluding litter) within 1.78 m radius microplot centered on each grid
 point, measured during the pretreatment summers of 1998–1999. Numeric
 variable from 0 to 85 percent. * arpa: Percent cover of shrub
 Arctostaphylos patula within 1.78 m radius microplot centered on each grid
 point, measured during the pretreatment summers of 1998–1999. Numeric
 variable from 0 to 95 percent. * ceco: Percent cover of shrub Ceanothus
 cordulatus within 1.78 m radius microplot centered on each grid point,
 measured during the pretreatment summers of 1998–1999. Numeric variable
 from 0 to 100 percent. * syro: Percent cover of shrub Symphoricarpos
 mollis within 1.78 m radius microplot centered on each grid point,
 measured during the pretreatment summers of 1998–1999. Numeric variable
 from 0 to 55 percent. * prem: Percent cover of shrub/small tree Prunus
 emarginata within 1.78 m radius microplot centered on each grid point,
 measured during the pretreatment summers of 1998–1999. Numeric variable
 from 0 to 55 percent. * riro: Percent cover of shrub Ribes roezlii within
 1.78 m radius microplot centered on each grid point, measured during the
 pretreatment summers of 1998–1999. Numeric variable from 0 to 40 percent.
 * patch: Vegetation patch type classification. Categorical variable with
 three levels (CECO dominated, closed canopy, open). * h2o.oct.1998:
 Volumetric percent soil water content in the upper 15 cm of soil measured
 in mid-Oct. 1998. Numeric variable from 1.72 to 48.3 percent. Soil
 moisture measured using time domain reflectometry. For details, see Zald
 et al. 2008. https://doi.org/10.1016/j.foreco.2008.04.022. * h2o.may.1999:
 Volumetric percent soil water content in the upper 15 cm of soil measured
 in mid-May. 1999. Numeric variable from 3.8 to 50 percent. * soil.depth:
 Soil depth to bedrock in cm. Numeric variable from 0 to 257 cm. 4. Missing
 data codes: NA 5. Specialized formats or other abbreviations used: None