#' @name oakwoods
#' @title Oak Woodlands in the Willamette Valley, Oregon, USA
#' @aliases oakwoods
#' @docType data
#' @description
#' Vascular plants in oak forests of the Willamette Valley from the PhD
#' dissertation of John F. Thilenius at Oregon State University.
#'
#' @format A list of 5 data.frames:
#'
#' - \code{spe} species abundance matrix: 47 observations of 103 vascular
#' plant species. Abundances were relativized by species maximum. This is
#' a subset of all species, where all singletons and doubletons were removed
#' from the `raw` matrix below.
#'
#' - \code{env} environmental matrix: 47 observations of 30 environmental
#' variables. Environmental variables, described in detail below, include
#' topographic, geographic and soils variables, and indicators of stand
#' history. We also provide some community summary variables, including
#' species richness, groups derived from cluster analysis, and community
#' types as originally designated by Thilenius.
#'
#' - \code{tra} traits matrix: 103 vascular plant species scored for each of 6
#' traits. The traits are simply growth forms and are scored as binary 0/1
#' (no/yes).
#'
#' - \code{xy} spatial matrix: 47 observations of 2 spatial coordinates.
#'
#' - \code{raw} raw species abundances: 47 observations of 189 vascular plant
#' species. The raw species abundances are before any modifications. The
#' values are basal areas (ft^2^/acre) for trees and percentage cover for
#' lower strata, based on 60, 0.2 m^2^ quadrats/stand. “Trace” was
#' converted to 0.5\%. A check on the field data sheet was converted
#' to 0.2\%. Be careful! Any use of these raw data must recognize that the
#' columns representing the tree stratum differ in units from the lower
#' strata; hence, use of a relativized matrix in \code{spe}.
#'
#' @details
#'
#' This documentation is nearly verbatim from PC-ORD (McCune and Mefford 2017).
#'
#' @section Overview:
#'
#' In 1961 and 1962 John F. Thilenius sampled vascular plants in oak forests in
#' the Willamette Valley for his Ph.D. at Oregon State University
#' (Thilenius 1963, 1968). The data came from a fairly narrow range of habitats
#' – all of the stands were closed forests dominated by \emph{Quercus garryana}.
#' This resulted in a data set with fairly low beta diversity. The environmental
#' differences among the sites are rather modest. Much of the variation in
#' species composition presumably is derived from the particular histories of
#' each stand, such as episodes of grazing, logging, and fire. Of course we have
#' limited information on those histories, so you will see that much of the
#' variation in the plant communities is not readily explained by the measured
#' environmental and historical variables. Nevertheless a definite environmental
#' gradient emerges from the analysis.
#'
#' The abstract from Thilenius (1968) is reproduced below:
#'
#' “\emph{Quercus garryana} forests, prominent at low elevations throughout the
#' Willamette Valley, Oregon, have developed from oak savanna subsequent to
#' settlement of the valley in the mid-nineteenth century. Interruption of the
#' ground fires that were common in the pre-settlement environment probably
#' caused the change. The understory of the oak forest is dominated by shrubs,
#' and well-defined strata are present. Four plant communities occur: (1)
#' \emph{Quercus garryana/Corylus cornuta var. californica/Polystichum munitum}
#' (most mesic); (2) \emph{Quercus garryana/Prunus avium/Symphoricarpos albus};
#' (3) \emph{Quercus garryana/Amelanchier alnifolia}; (4) \emph{Quercus
#' garryana/Rhus diversiloba} (most xeric). All are in seral condition because
#' of their relatively recent development and because they have been disturbed
#' throughout their existence by man`s activities. The soils supporting the oak
#' forest are generally deep and well drained and have developed profiles with
#' illuvial horizons and acidic reaction. They are derived from sedimentary and
#' basic igneous rocks and old valley-filling alluvium. Seven established soil
#' series are present: Steiwer, Carlton, Peavine, Nekia, Dixonville, Olympic,
#' and Amity. The Steiwer series and its catenary associate, Carlton, are the
#' most common soils.”
#'
#' Thilenius’ goals were to describe “the floristic composition, stand
#' structure, physical environment, and successional status of plant
#' communities where \emph{Quercus garryana} is the major component of the overstory.”
#' Although quantitative data were carefully recorded, Thilenius had few
#' possibilities for multivariate analysis. His primary analyses were first
#' arranging his data “according to similarities in species composition,
#' importance ranks, and environmental attributes.” He then tabulated
#' averages for species and environmental variables within the four groups.
#' Here is an interesting challenge for modern community analysts: what
#' can you add to his account (Thilenius 1968) based on a more sophisticated
#' quantitative analysis of the data? I mentioned above that a single strong
#' environmental gradient emerges from the analysis, but this is only hinted
#' in Thilenius’ abstract. What is that gradient?
#'
#' After a listing of the files and variables contained in the files, three
#' example procedures are given. The first demonstrates modification of the raw
#' data into a form suitable for analysis. The second is an ordination with
#' nonmetric multidimensional scaling. The third compares groups of sample
#' units, as defined by landform.
#'
#' @section Methods from Thilenius (1968):
#'
#' “Investigations were confined to closed-canopy stands 4 ha or more in area
#' where \emph{Quercus garryana} was the major component of the overstory. Basal area,
#' frequency, and density of overstory trees were determined on twenty 0.004-ha
#' circular plots spaced at 9-m intervals in four rows parallel to the slope
#' contour. Density was recorded in four classes: saplings (< 10 cm dbh);
#' poles (11-40 cm dbh); mature (41-100 cm dbh) and relict (> 100 cm dbh).
#' The maximum height of trees on each plot was measured with an optical
#' rangefinder.”
#'
#' “Frequency and percentage crown coverage of shrub and herbaceous species
#' were recorded on sixty 0.2 m2 quadrats spaced at 3-m intervals in four
#' rows coincident with the rows of 0.004-ha plots. Very low crown coverage
#' was recorded as trace and arbitrarily assigned a value of 0.5\% for
#' calculation purposes. Above trace, the intervals were 1\% and 5\%. Coverage
#' greater than 5% was estimated to the nearest 10\%.”
#'
#' @section Coding for variables in the second matrix:
#'
#' \emph{Topographic and geographic variables}
#'
#' Elev,m = elevation above sea level in meters.\cr
#' LatAppx = approximate latitude, decimal degrees, based on automated
#' conversion of Township/Range/Section, using the program TRS2LL.exe.\cr
#' LongAppx = approximate longitude, decimal degrees, based on automated
#' conversion of Township/Range/Section, using the program TRS2LL.exe.\cr
#' SlopeDeg = slope in degrees (originally recorded in percentages)\cr
#' AspClass = aspect class, 1=SW, 2=S or W, 3=SE or NW, 4=N or E, 5=NE.\cr
#' AspDeg = aspect in degrees E of N\cr
#' PDIR = Potential annual direct incident radiation, MJ/cm2/yr, calculated
#' according to McCune and Keon (2002) Eq. 3.\cr
#' HeatLoad = Heat load index, calculated according to McCune and Keon (2002)\cr
#' Landform: 1=valley bottom, 2=draw or slope of draw, 3=slope, 4=ridge\cr
#' TopoClas = Topographic position class: adapted from scales used by
#' Whittaker & Kessell (Kessell 1979)\cr
#'
#' \emph{Soil variables}
#'
#' Drainage: 1=poor, 2=moderate, 3=good, 4=well\cr
#' Soil series: 1=Steiwer, 2=Peavine, 3=Dixonville, 4=Nekia, 5=Carlton,
#' 6=Olympia, 7=Amity\cr
#' SoilGrp: 1=sedimentary, 2=basic igneous, 3=alluvial\cr
#' A-horiz = thickness of A horizon, cm\cr
#' B1-horiz = thickness of B1 horizon, cm\cr
#' B2-horiz = thickness of B2 horizon, cm\cr
#' B3-horiz = thickness of B3 horizon, cm (if profile truncated, e.g.
#' “44+ inches”, add 20 inches)\cr
#' B-horiz = sum of B1+B2+B3, cm\cr
#'
#' \emph{Indicators of stand history}
#'
#' GrazCurr = signs of current grazing recorded on field data sheet
#' (0=no,1=yes)\cr
#' GrazCurrC = same as above but provided as text-based categorical variable
#' (ungrazed, grazed)\cr
#' GrazPast = signs of past grazing recorded on field data sheet
#' (0=no, 1=yes, must be 1 if GrazCurr=1)\cr
#' GrazPastC = same as above but provided as text-based categorical variable
#' (ungrazedpast, grazedpast)\cr
#' NotLogged = NPL recorded under “Influences” on data sheet. I guessed this
#' means “no past logging”, i.e. no signs of past logging
#' (0=logged, 1=not logged)\cr
#' NotLoggedC = same as above but provided as text-based categorical
#' variable (logged, notlogged)\cr
#' Que>60cm = number of \emph{Quercus garryana} recorded in the 60 cm (24 inch)
#' size class and larger (no stands had large Pseudotsuga; one stand (Stand05)
#' had a large Acer macrophyllum and one stand (Stand07) had two large Arbutus
#' menziesii).\cr
#' LogQ>60 = log of (x+1) where x is the number of \emph{Quercus garryana} recorded
#' in the 60 cm (24 inch) size class and larger (i.e. x = “LogQ>60”).\cr
#' TreeHtM = maximum height of \emph{Quercus garryana} in meters.\cr
#'
#' \emph{Community summary variables derived from the species matrix}
#'
#' SppRich = species richness, calculated from OakRaw.wk1, counting each
#' species x layer combination as a separate species.\cr
#' ThilType = vegetation types from Thilenius (1968)\cr
#' - 1 = Quercus/Corylus/Polystichum\cr
#' - 2 = Quercus/Prunus/Symphoricarpos\cr
#' - 3 = Quercus/Amelanchier/Symphoricarpos\cr
#' - 4 = Quercus/Rhus\cr
#' FlxB-.25 = community types defined at the 4-group level from hierarchical
#' cluster analysis, Flexible beta method, Sørensen distance, beta= -0.25.\cr
#'
#' @section List of species codes:
#'
#' Note: because woody species may occur in more than one stratum, a suffix
#' (-s, -t) is used to indicate a given species in the shrub or tree stratum.
#'
#' Abgr‑s Abies grandis SHRUB
#' Abgr-t Abies grandis
#' Acar Actea arguta
#' Acgld Acer glabrum var. douglasii
#' Acma‑s Acer macrophyllum shrub
#' Acma-t Acer macrophyllum
#' Acmi Achillea millefolium
#' Adbi Adenocaulon bicolor
#' Agha Agrostis hallii
#' Agre Agropyron repens
#' AGRO Agrostis sp?
#' Agse Agrostis semiverticullata (subsecundum)
#' Agte Agrostis tenuis
#' Aica Aira caryophyllea
#' ALL Allium sp.
#' Alpr Alopecurus pratensis
#' Amal‑s Amelanchier alnifolia shrub
#' Amal-t Amelanchier alnifolia
#' Apan Apocynum androsaemifolium
#' Aqfo Aquilegia formosa
#' Arel Arrhenatherum elatius
#' Arme‑s Arbutus menziesii SHRUB
#' Arme-t Arbutus menziesii
#' Avfa Avena fatua
#' Beaq Berberis aquifolium
#' Brpu Brodiaea pulchella
#' Brco Bromus commutatus
#' Brla Bromus laevipes
#' Brri Bromus rigidus
#' Brse Bromus secalinus
#' Brst Bromus sterilis
#' Brvu Bromus vulgeris
#' Caqu Camassia quamash
#' CAR Carex sp.
#' Cato Calochortus tolmiei
#' Cear Cerastium arenses
#' Ceum Centaurium umbellatum
#' Ceve Ceanothus velutinus
#' Cipa Circaea pacifica
#' Civu Cirsium vulgare
#' Coco‑s Corylus cornuta shrub
#' Coco-t Corylus cornuta
#' Cogr Collomia grandiflora
#' Conu‑S Cornus nuttallii SHRUB
#' Conu-t Cornus nuttallii
#' CORY Corylus sp.
#' Cost Corallorhiza striata
#' Crca Crepis capillaris
#' Crdo‑t Crataegus douglasii
#' Crdo‑s Crataegus douglasii
#' Crox Crataegus oxyacantha
#' Cyec Cynosurus echinatus
#' Cyfo Cystopteris fragilis
#' Cygr Cynoglossum grande
#' Daca Danthonia californica
#' Dacar Daucus carota
#' Dagl Dactylus glomerata
#' Deel Deschampsia elongata
#' Diar Dianthus armeria
#' Doel Downingia elegans
#' Drar Drysopterus arguta
#' Drar Dryopteris arguta
#' Elgl Elymus glaucus
#' Erla Eriophyllum lanatum
#' Erog Erythronium oregonum
#' Eucr Euphorbia crenulata
#' Feca Festuca californica
#' Fede Festuca dertonenses
#' Feel Festuca elatior var. arendmaceae
#' Feme Festuca megalura
#' Feoc Festuca occidentalis
#' Feru Festuca rubra
#' Frbr Fragaria bracteata (vesca)
#' Frcu Fragaria cuneifolia
#' Frla‑s Fraxinus latifolia shrub
#' Frla-t Fraxinus latifolia
#' Frvi Fragaria virginiana
#' GAL Galium sp.
#' Gema Geum macrophyllum
#' Geog Geranium oreganum (incisum)
#' Gepu Geranium pusillum
#' Haob Habenaria orbiculata
#' Haun Habenaria unalacensis
#' Hehe Hedera helix
#' Hemi Heuchera micrantha
#' Hodi Holodiscus discolor
#' Hola Holcus lanatus
#' Hyoc Hydrophyllum occidentale
#' Hype Hypericum perforatum
#' Hyra Hypochaeris radicata
#' Irte Iris tenax
#' JUNC Juncus sp.
#' Kocr Koeleria cristata
#' Laco Lapsana comunis
#' Lapo Lathyrus polyphyllus
#' Lasa Lathyrus sativus (Pisum sativum)
#' Liap Ligusticum apiifolium
#' Libu Lithophragma bulbifera
#' Lico Lilium columbianum
#' Lide-t Libocedrus deccurens
#' Lide‑s Libocedrus deccurens
#' LILI Lilium sp.
#' Loci Lonicera ciliosa
#' Lope Lolium perenne
#' LOT Lotus sp.
#' Lotr Lomatium triternatum
#' Lumu Luzula multiflora
#' Maex Madia exigua
#' MAL Malvaceae sp.
#' Maor Marah oreganus
#' Mebu Melica bulbosa
#' Mila Microseris laciniata
#' Mope Montia perfoliata
#' Mosi Montia sibirica
#' Nepa Nemophylla parviflora
#' ONGR Onagraceae sp.
#' Osce‑t Osmaronia cerasiformis tree
#' Osce-s Osmaronia cerasiformis
#' Osch Osmorhiza chilensis
#' Osnu Osmorhiza nuda (chilensis)
#' Phca Physocarpus capitatus
#' Phle Philadelphus lewisii
#' Phpr Phleum pratense
#' Phvi Phoradendron villosum
#' Pipo‑s Pinus ponderosa
#' Pipo Pinus ponderosa
#' Plla Plantago lanceolata
#' Poco Poa compressa
#' Pogl Potentilla glandulosa
#' Pogr Potentilla gracilus
#' Pogr Potentilla gracilis
#' Pomu Polystichum munitum
#' Popr Poa pratensis
#' Povu Polypodium vulgare
#' Prav‑s Prunus avium shrub
#' Prav-t Prunus avium
#' Prde-t Prunus virginiana var. demissa
#' Prde‑s Prunus virginiana var. demissa shrub
#' Prvu Prunella vulgeris
#' Psme‑s Pseudotsuga menziesii shrub
#' Psme-t Pseudotsuga menziesii
#' Ptan Pterospora andromedia
#' Ptaq Pteridium aquilinum var. lanuginosum
#' Pyco‑s Pyrus communis shrub
#' Pyco Pyrus communis
#' Pyfu‑s Pyrus fusca SHRUB
#' Pyfu-t Pyrus fusca
#' Quga-s Quercus garryana shrub
#' Quga Quercus garryana
#' Raoc Ranunculus occidentalis
#' Rhdi Rhus diversiloba
#' Rhpu‑s Rhamnus purshiana shrub
#' Rhpu Rhamnus purshiana
#' Risa Ribes sanguinius
#' Rodu Rosa???
#' Roeg Rosa eglanteria
#' Rogy Rosa gymnocarpa
#' Ronu Rosa nutkana
#' Ropi Rosa pisocarpa
#' Ropi Rosa pisocarpa
#' Ruac Rumex acetosella
#' Rula Rubus laciniatus
#' Rule Rubus leucodermus
#' Rupa Rubus parvifloris
#' Rupr Rubus procerus
#' Ruur Rubus ursinus
#' S‑2 Carex sp2.
#' S‑1 Carex sp1.
#' Sacr Sanicula crassicaulis
#' Sado Satureja douglasii
#' Sagr Sanicula graveolens
#' Seja Senecio jacobaea
#' Siho Silene hookeri
#' Smra Smilacina racemosa
#' Smse Smilacina sessilifolia
#' Syal Symphoricarpus albus
#' Taas Taeniatherum asperum
#' Taof Taraxacum officinale
#' Tegr Tellima grandiflora
#' Thoc Thalictrum occidentale
#' Toar Torilis arvensis
#' Trca Trisetum canescens
#' TRIF Trifolium sp
#' Trla Trientalis latifolia
#' Trov Trillium ovatum
#' Trpr Trifolium procumbens
#' V1 Vicia sp.
#' Valo Valerianella locusta
#' Viam Vicia americana
#' Viel Viburnum ellipticum
#' Vinu Viola nuttallii
#' VIOL Viola sp
#' Zice Zygadenus venosus
#'
#' @source Bruce McCune collected this dataset for PC-ORD (McCune and Mefford
#' 2017). The original raw data cards from Thilenius study in 1963
#' (data collected in 1961 and 1962) were obtained from John Thilenius
#' via Bob Frenkel. Thanks to John Thilenius for granting permission to
#' distribute his data. Bill Daly did the initial data entry. Bibit Traut
#' added more variables and resolved numerous nomenclatural questions
#' regarding the species codes used by Thilenius.
#'
#' @references
#' Kessell, S. R. 1979. Gradient Modeling: Resource and Fire Management.
#' Springer-Verlag, New York. 432 pp.
#'
#' McCune, B. and D. Keon. 2002. Equations for potential annual direct
#' incident radiation and heat load. Journal of Vegetation Science
#' 13:603-606.
#'
#' McCune, B., and M. J. Mefford. 2017. PC-ORD. Multivariate Analysis
#' of Ecological Data. Version 7. MjM Software Design, Gleneden
#' Beach, OR.
#'
#' Thilenius, J. F. 1963. Synecology of the white-oak (\emph{Quercus garryana}
#' Douglas) woodlands of the Willamette Valley, Oregon. PhD Dissertation.
#' Oregon State University, Department of Botany and Plant Pathology,
#' Corvallis. 151 pages.
#'
#' Thilenius, J. F. 1968. The \emph{Quercus garryana} forests of the Willamette
#' Valley, Oregon. Ecology 49:1124-1133.
#'
#' @examples
#' # split into two data.frames
#' data(oakwoods)
#' spe <- oakwoods$spe
#' env <- oakwoods$env
#' tra <- oakwoods$tra
#' raw <- oakwoods$raw
#'
#' @keywords datasets
"oakwoods"
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