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Field Trials to Assess the Growth, Survival, and Stomatal Densities of Five Mexican Pine Species and Their Hybrids under Common Plantation Conditions

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Forests
Authors:
Ricardo Silas Sánchez-Hernández at Juarez University of the State of Durango
Ricardo Silas Sánchez-Hernández
Carmen Zulema Quiñones-Pérez
Carmen Zulema Quiñones-Pérez
Carmen Zulema Quiñones-Pérez
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Jose Ciro Hernandez-Díaz at Juarez University of the State of Durango
Jose Ciro Hernandez-Díaz
José Ángel Prieto-Ruiz at UJED Universidad Juárez del Estado de Durango
José Ángel Prieto-Ruiz
  • UJED Universidad Juárez del Estado de Durango
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Abstract and Figures

Understanding hybridization is important for practical reasons, as the presence of hybrid trees in seed stands can influence the success of natural regeneration and reforestation. Hybridization creates new gene combinations, which can promote or enhance adaptation to new or changing environments. In the present research, we aimed, for the first time, to evaluate and compare the growth and survival of 541 putative hybrid seedlings and 455 seedlings of the pure parental trees of Pinus arizonica, P. durangensis, P. engelmannii, P. leiophylla, and P. teocote, in two reciprocal trials of duration 27 months in the Sierra Madre Occidental (SMO), Durango, Mexico. We also examined the possible correlation between needle stomatal density and seedling growth and survival. The overall analysis of the data showed that the mean height to the apical bud was slightly higher in the hybrids than in the pure trees. Considering both trials, the survival rate of P. arizonica (p = 0.002) and P. durangensis (p = 0.01) hybrids was significantly higher than that of the pure trees. The growth parameters were significantly correlated with the mean stomatal density (p < 0.01). Stomatal density and survival at the seed stand level were significantly and positively correlated in the hybrids, but not in the pure trees. In summary, Pinus hybrids generally exhibited the same ability as the pure species (or sometimes a greater ability) to withstand weather conditions, survive, and grow effectively in both growth trials. The systematic use of natural pine hybrids in Mexico could therefore be considered a possible option for sustainable management and as a component of adaptive silviculture.
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Forests2022,13,1791.https://doi.org/10.3390/f13111791www.mdpi.com/journal/forests
Article
FieldTrialstoAssesstheGrowth,Survival,andStomatal
DensitiesofFiveMexicanPineSpeciesandTheirHybrids
underCommonPlantationConditions
RicardoSilasSánchez‐Hernández
1
,CarmenZulemaQuiñones‐Pérez
2
,JoséCiroHernández‐Díaz
3
,
JoséÁngelPrieto‐Ruíz
4
andChristianWehenkel
3,
*
1
MaestríaInstitucionalenCienciasAgropecuariasyForestales(MICAF),UniversidadJuárezdelEstadode
Durango(UJED),Durango34120,Mexico
2
TecnológicoNacionaldeMéxicoCampusValledelGuadiana(TecNM‐ITVG),VillaMontemorelos,
Durango34371,Mexico
3
InstitutodeSilviculturaeIndustriadelaMadera(ISIMA),UniversidadJuárezdelEstadodeDurango
(UJED),Durango34120,Mexico
4
FacultaddeCienciasForestalesyAmbientales(FCFA),UniversidadJuárezdelEstadodeDurango(UJED),
Durango34120,Mexico
*Correspondence:wehenkel@ujed.mx
Abstract:Understandinghybridizationisimportantforpracticalreasons,asthepresenceofhybrid
treesinseedstandscaninfluencethesuccessofnaturalregenerationandreforestation.Hybridiza‐
tioncreatesnewgenecombinations,whichcanpromoteorenhanceadaptationtoneworchanging
environments.Inthepresentresearch,weaimed,forthefirsttime,toevaluateandcomparethe
growthandsurvivalof541putativehybridseedlingsand455seedlingsofthepureparentaltrees
ofPinusarizonica,P.durangensis,P.engelmannii,P.leiophylla,andP.teocote,intworeciprocaltrials
ofduration27monthsintheSierraMadreOccidental(SMO),Durango,Mexico.Wealsoexamined
thepossiblecorrelationbetweenneedlestomataldensityandseedlinggrowthandsurvival.The
overallanalysisofthedatashowedthatthemeanheighttotheapicalbudwassignificantlyhigher
(p=0.01)inthehybridsthaninthepuretrees.Consideringbothtrials,thesurvivalrateofP.arizonica
(p=0.002)andP.durangensis(p=0.01)hybridswassignificantlyhigherthanthatofthepuretrees.
Thegrowthparametersweresignificantlycorrelatedwiththemeanstomataldensity(p<0.01).Sto‐
mataldensityandsurvivalattheseedstandlevelweresignificantlyandpositivelycorrelatedinthe
hybrids,butnotinthepuretrees.Insummary,Pinus
hybridsgenerallyexhibitedthesameability
asthepurespecies(orsometimesagreaterability)towithstandweatherconditions,survive,and
groweffectivelyinbothgrowthtrials.ThesystematicuseofnaturalpinehybridsinMexicocould
thereforebeconsideredapossibleoptionforsustainablemanagementandasacomponentofadap‐
tivesilviculture.
Keywords:naturalhybridization;Pinusarizonica;Pinusdurangensis;Pinusengelmannii;Pinus
leiophylla;Pinusteocote
1.Introduction
Naturalhybridizationisacommonphenomenoninplants[1],asmorethan25%of
plantshybridizenaturally[2].Interspecificgenetransferoccursduringhybridization,
whichmayintroducemoredifferentgeneticmaterialthanthatgenerateddirectlybymu‐
tations[3].Understandinghybridizationisimportantforpracticalreasons,asthepres‐
enceofhybridsinseedstandscaninfluencethesuccessofnaturalregenerationandrefor‐
estation[4,5].Inthesamegenerationofhybrids,viability,fertility,andvigorcanvary
widelyacrossindividuals,withsomeofthemhavingthesamevalues,lowervalues,or
Citation:Sánchez‐Hernández,R.S.;
Quiñones‐Pérez,C.Z.;
Hernández‐Díaz,J.C.;
Prieto‐Ruíz,J.Á.;Wehenkel,C.
FieldTrialstoAssesstheGrowth,
Survival,andStomatalDensitiesof
FiveMexicanPineSpeciesandTheir
HybridsunderCommonPlantation
Conditions.Forests2022,13,1791.
https://doi.org/10.3390/f13111791
AcademicEditor:MichaelP.Strager
Received:25August2022
Accepted:24October2022
Published:28October2022
Publisher’sNote:MDPIstaysneu‐
tralwithregardtojurisdictional
claimsinpublishedmapsandinstitu‐
tionalaffiliations.
Copyright:©2022bytheauthors.Li‐
censeeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsandcon‐
ditionsoftheCreativeCommonsAt‐
tribution(CCBY)license(https://cre‐
ativecommons.org/licenses/by/4.0/).
Forests2022,13,17912of14
evenhighervaluesthantheirparents[4].DifferentcasesofnaturalhybridizationofMex‐
icanpinespecieshavebeenobserved[6].
Hernández‐Velascoetal.[7]detectedsignificantdifferencesinthesurvival,diame‐
ter,andheightbetweenseedlingsofthepureparentaltreesandputativehybridseedlings
offiveveryimportanttimberspeciesinMexico,i.e.,Pinusarizonica,P.durangensis,P.engel‐
mannii,P.leiophylla,andP.teocote[8],whichweregrownfor15monthsinnurserycondi‐
tions.Theseedofthespecieswascollectedfromseedstandsinthemunicipalitiesof
Tepehuanes,Otáez,andSantiagoPapasquiaro,inthestateofDurango,Mexico.Because
thecontrolledconditionsinnurseriesarecompletelydifferentfromthoseinnaturalfield
environments,thesameauthors[7]recommendedfurtherstudiestodeterminetheper‐
formanceofeachhybridinfieldconditions,particularlyinregionswhereslowergrowing
parentaltreesarefound,aswellasinextremeenvironments.Thisisbecausehybridization
createsnewgenecombinationsthatcanpromoteorenhanceadaptationtoneworchang‐
ingenvironments[9].
Provenancetrialsareusefulfordetectingassociationsbetweengenetic,geographic,
andclimaticfactors[10].However,thesetrialsaretime‐consumingandusuallyonlyallow
forthemeasurementofphenotypicdifferencesbetweenindividualsandpopulationsun‐
dercommonconditions.Onlyreciprocaltrialsallowforthecontributionofphenotypic
plasticityandtheinteractionsbetweengenotypeandenvironmenttoberevealed[11,12].
Someforestplantspecieshavewidedistributionranges,astheypossessadaptive
strategiesthatallowthemtosurviveandgrowinecologicallydifferentareas[13].Oneof
thesestrategiesisthemorphologicalalterationofleaves,asaconsequenceofstress‐related
effects[14].Thestomataaremicroscopicstructurespresentonthesurfaceofleaves.Inthe
caseofconifers,thestomatahaveaprotectivefunctionastheysurroundacentralpore
andlimitaccesstomesophyllcells.Environmentalfactorssuchaslightintensity,atmos‐
phericCO2concentration,andinternalcontrolsystemsregulatethedevelopmentofthe
stomata[15].Plantscanaltertheopeningofthestomatalpores,moderatinggasexchange
betweentheleafinteriorandtheatmosphere[16].Themorphologyanddistributionof
stomatavaryinresponsetoenvironmentalchangesandareprimarilydirectedbygenetic
traitsandphenotypicplasticity,representinglong‐termadaptationsofplantspecies
[15,17].Characteristicsofthestomata,suchassize,density,andresponsivenesstoenvi‐
ronmentalfactorsarekeycomponentsinfluencingplantgrowth[18].
Thepresentresearchaimed,forthefirsttime,toevaluateandcomparethegrowth
andsurvivalofputativehybridseedlingsandseedlingsofthepureparentalspeciesof
Pinusarizonica,P.durangensis,P.engelmannii,P.leiophylla,andP.teocote,intworeciprocal
trialsintheSierraMadreOccidental(SMO),inthestateofDurango,Mexico.Thestudy
alsoaimedtoexaminethepossiblecorrelationbetweenthestomataldensityoftheneedles
andthegrowthandsurvivaloftheseedlings.Thegrowthofbothtypesofseedlingsmay
notbestatisticallydifferent[19];however,theremaybesignificantdifferencesbetween
thegrowthofputativehybridseedlingsandseedlingsofthepureparentaltreesinthe
fieldintermsofeitherhybridvigor[20]orhybriddepression[5].Inaddition,stomatal
densitymayalsoinfluencepineseedlinggrowthandsurvival[17].
2.MaterialsandMethods
2.1.StudySite
Twofieldtrials(1hectareeach)wereestablishedinJuly2018tocomparethegrowth
ofputativehybridseedlingsandseedlingsofthepureparentaltreesinthefield(referred
toashybridseedlingsandpureseedlings).Theplantingdistancebetweentheseedlings
was2×2m.Regardlessofthespeciesandthetypeofplant(hybridorpure),eachplant
wasrandomlyincludedinbothtrials.Thetrialareaswereclearedoftreevegetationand
protectedbya1.8mhighwirefence,beforetheseedlingswereplanted.Thetrialsincluded
atotalof2552seedlings,whichwereproduced,evaluated,andclassifiedeitherashybrids
Forests2022,13,17913of14
(1297,mostlyconsistingofbackcrosses,withsmallernumbersofF2andsubsequenthy‐
bridgenerations,butnoF1hybrids)orpurespecies(1255).Theseedlingswerefirstgrown
togetherfor15monthsinthenursery[7]andthenfor27monthsinthefield.
ThefirsttrialwasestablishedintheCiénegadeSalpicaelAguaejido,inthearea
knownasLaMesaAlta,atanelevationof2710m(25.06N,−105.77W).Theothertrialwas
establishedintheLagunadeLaChaparraejido,intheareaknownasLaMesaSeca,atan
elevationof2610m(25.12N,−105.70W).Bothsitesarelocatedwithinthemunicipalityof
SantiagoPapasquiaro,stateofDurango,Mexico(Figure1).
Figure1.Locationofthetwostudysiteswheretheseedlingsofinterestwereplantedandare
growing.
Bothsitesarecomposedofpine–oakforests.Thetopographyoftheareaconsistsof
highandlowmountainranges.Duringtheperiod1961–1990,themeanannualtempera‐
turewas10.5°CinMesaSecaand9.6°CinMesaAlta;themeanannualprecipitationwas
803mminMesaSecaand903mminMesaAlta.Thesoilcharacteristicsdifferlittlebe‐
tweenthetwosites(Table1).ThepresenceofPappogeomyscastanopsBaird,arodentthat
consumesplantsorpartsofplants[21],wasdetectedinbothsites.

m
m
Forests2022,13,17914of14
Table1.SoilcharacteristicsinbothreciprocaltrialsinthemunicipalityofSantiagoPapasquiaro,
stateofDurango,Mexico.
CharacteristicMesaAltaMesaSeca
TexturalclassSandyclayloamLoam
Organicmatter(OM,%)4.64High1.94Median
Nitrogen(N‐NO3
,
kg/ha)12.327.39
Phosphorus(ppm)9.667.39
Potassium(ppm)220116
Magnesium(ppm)198114
Zinc(ppm)2.064.12
pH1:2water5.885.25
CaCO3(ppm)1698774
CEC(meq/100g)10.995.35
CEC=cationexchangecapacity.
InOctober2020,seedlingsurvivalwascalculatedforeachpurespeciesandhybrid
andpertrial,asapercentageofthetotalnumberofindividualsplantedinbothtrialsin
July2018(Table2).
Table2.Descriptivestatisticsofthebasaldiameter(mm)ofthesurvivingseedlingsofthefivepure
Pinusspeciesandtheirhybrids,ineachseparatetrialandbothtrialstogether,after27monthsinthe
field.
SpeciesMesaAltaMesaSecaBothTrialsTogether
NMedianMeanSdNMedianMeanSdNMedianMeanSd
PA‐H513.1ab13.10.8521.5ab21.55.21013.6ab15.94.9
PA‐P39.6b9.60.6411.0b11.01.4710.3ab10.31.0
PD‐H1810.6b11.43.65814.8b15.15.57613.2b14.25.3
PD‐P1411.6b11.52.72014.6b15.35.23412.6ab13.74.7
PE‐H5619.9a19.49.021124.4a24.67.426723.6a23.58.0
PE‐P7820.1a20.27.821823.3a23.67.129622.5a22.67.4
PL‐H717.3ab19.35.91820.3ab20.16.72520.0b19.96.4
PL‐P422.1a22.55.81314.6b17.36.91718.7b18.56.9
PT‐H4916.2ab15.96.411416.7b16.96.316316.6b16.66.3
PT‐P2415.3ab15.95.47715.3b16.85.910115.3b16.65.7
H13515.4a15.85.140619.5a19.66.254117.4a18.06.2
P12315.7a15.94.533215.8a16.85.345515.9a16.35.2
Sd=standarddeviation,N=numberofPinusseedlings,PA‐P=Pinusarizonica,PD‐P=P.durangen‐
sis,PE‐P=P.engelmannii,PL‐P=P.leiophyllaandPT‐P=P.teocote.PA‐H=hybridsofPinusarizonica
×P.durangensisgeneticallymoresimilartoP.arizonica;PD‐H=hybridsofP.durangensis×P.arizonica
geneticallymoresimilartoP.durangensisandP.durangensis×P.engelmanniigeneticallymoresimilar
toP.durangensisPE‐H=hybridsofP.engelmannii×P.arizonicageneticallymoresimilartoP.engel‐
mannii;PL‐H=hybridsofP.leiophylla×P.teocotegeneticallymoresimilartoP.leiophylla;PT‐H=P.
leiophylla×P.teocotegeneticallymoresimilartoP.teocote;differentlettersindicatesignificantdiffer‐
ences(α=0.025).
2.2.EvaluationofDifferencesintheDevelopmentofHybrid/PureIndividualsintheField
Intotal,541hybridseedlingsand455pureseedlingsofthefivespeciesunderstudy
wereanalyzed(258fromMesaAltaand738fromMesaSeca)(Table2).Thebasaldiameter
(atplantcollar)wasmeasuredusingadigitalVernierscale,witharesolutionoftenthsof
amillimeter(AVEDISTANT,LCD6);plantheightattheapicalgrowthbudandmaximum
needleheight(fromthebasetothetopoftheneedles)weremeasuredusingaflexometer,
witharesolutionofmillimeters(UlineAccu‐Lock,H‐1766)(Tables2–4).Needlelengthin
Forests2022,13,17915of14
youngseedlingsisconsideredagoodindicatoroffuturegrowth[22].AccordingtoSquil‐
lanceandSilen[23],pineneedlelengthispositivelycorrelatedwithheightgrowthand
thuswithproductivity.
Table3.Descriptivestatisticsofheighttotheapicalbud(cm)ofPinusseedlingsperspeciesand
theirhybrids,ineachtrialandbothtrialstogether,aftergrowingfor27monthsinthefield.
SpeciesMesaAltaMesaSecaBothTrialsTogether
N
MedianMeanSd
N
MedianMeanSd
N
MedianMeanSd
PA‐H522.2ab22.25.9516.0ab16.05.11018.0ab20.15.5
PA‐P330.0a30.07.6418.3ab18.38.8724.2ab24.28.3
PD‐H1833.2a34.614.15831.3a32.712.27631.5a33.212.6
PD‐P1431.3a31.410.52035.6a36.914.73432.8a34.613.2
PE‐H5614.2b16.512.721115.9b16.66.726715.2b16.78.4
PE‐P7814.2b15.16.221815.8b17.68.329615.3b16.97.8
PL‐H730.0a30.87.41834.1a33.39.12531.2a32.68.6
PL‐P443.3a40.813.31333.0a34.48.21737.0a35.99.6
PT‐H4933.7a35.212.611430.0a31.310.916332.0a32.511.5
PT‐P2434.5a36.114.77734.7a36.017.210134.5a36.016.6
H13526.7a27.910.540625.5a26.08.854122.0a24.612.9
P12330.7b30.710.533227.5a28.611.445519.5b23.314.1
Sd=standarddeviation,N=numberofPinusseedlings,PA‐P=Pinusarizonica,PD‐P=P.durangen‐
sis,PE‐P=P.engelmannii,PL‐P=P.leiophyllaandPT‐P=P.teocote.PA‐H=hybridsofPinusarizonica
×P.durangensisgeneticallymoresimilartoP.arizonica;PD‐H=hybridsofP.durangensis×P.arizonica
geneticallymoresimilartoP.durangensisandP.durangensis×P.engelmanniigeneticallymoresimilar
toP.durangensis;PE‐H=hybridsofP.engelmannii×P.arizonicageneticallymoresimilartoP.engel‐
mannii;PL‐H=hybridsofP.leiophylla×P.teocotegeneticallymoresimilartoP.leiophylla;PT‐H=P.
leiophylla×P.teocotegeneticallymoresimilartoP.teocote;differentlettersindicatesignificantdiffer‐
ences(α=0.025).
Table4.Descriptivestatisticsofthemaximumheighttothetopoftheneedles(cm)ofPinusseed‐
lingsperspeciesandtheirhybrids,ineachtrialandbothtrialstogether,aftergrowingfor27months
inthefield.
SpeciesMesaAltaMesaSecaOverall,BothTrials
N
MedianMeanSd
N
MedianMeanSd
N
MedianMeanSd
PA‐H531.4b31.45.9523.0ab23.06.91027.2ab28.66.4
PA‐P331.6b31.63.6427.7ab27.72.2729.7ab29.72.8
PD‐H1844.5a46.413.45842.0a43.912.97642.0a44.513.0
PD‐P1442.1a40.413.72046.0a47.714.23442.9a44.714.2
PE‐H5632.8b32.98.821133.0b34.38.526733.0b34.08.6
PE‐P7832.0b32.49.221833.2b34.69.629633.0b34.09.5
PL‐H734.0a36.89.31838.7a39.310.32538.4ab38.69.9
PL‐P446.6a44.716.11342.0a40.18.81743.0ab41.210.5
PT‐H4940.2a40.312.311436.2a37.410.416336.0a37.010.8
PT‐P2439.6a41.513.97739.5a42.116.710135.1a36.912.4
H13536.6a37.59.940634.6a35.69.754135.3a36.59.7
P12338.4a38.111.333237.7a38.410.445536.7a37.39.9
Sd=standarddeviation,N=numberofPinusseedlings,PA‐P=Pinusarizonica,PD‐P=P.durangen‐
sis,PE‐P=P.engelmannii,PL‐P=P.leiophyllaandPT‐P=P.teocote.PA‐H=hybridsofPinusarizonica
×P.durangensisgeneticallymoresimilartoP.arizonica;PD‐H=hybridsofP.durangensis×P.arizonica
geneticallymoresimilartoP.durangensisandP.durangensis×P.engelmanniigeneticallymoresimilar
toP.durangensis;PE‐H=hybridsofP.engelmannii×P.arizonicageneticallymoresimilartoP.engel‐
mannii;PL‐H=hybridsofP.leiophylla×P.teocotegeneticallymoresimilartoP.leiophylla;PT‐H=P.
Forests2022,13,17916of14
leiophylla×P.teocotegeneticallymoresimilartoP.teocote;differentlettersindicatesignificantdiffer‐
ences(α=0.025).
2.3.CalculationofStomatalDensityinNeedles
Inbothstudysites,twoneedlesperseedlingwerecollectedfrom245individuals
(randomlychosen)ofthethreemostfrequentspecies(P.engelmannii,P.durangensis,and
P.teocote)ofthefiveinitiallyconsideredspecies(astherequirednumberofreplicateswas
notobtainedfortheothertwospecies).Theneedlesampleswereexaminedunderabin‐
ocularstereoscope(EUROMEX:ED‐1402‐S)tocalculatethestomataldensity.Therowsof
stomataandthenumberofstomatawithinanareaofonesquaremillimeterwerecounted
onboththeabaxialandadaxialsidesoftheneedles.Thestomataldensityofeachfacewas
calculatedbymultiplyingthenumberofstomatapermm2bythenumberofrows.These
valuesweresummedtoobtainthedensityperneedle.Werepeatedthisprocesswitha
secondneedleandthencalculatedthemeandensity.Thevaluesofcentraltendencyand
dispersionofthestomataldensitywereestimated(Table4).
2.4.StatisticalAnalysis
Multiplemediancomparisonsofthebasaldiameter,heightattheapicalbud,maxi‐
mumheighttothetopoftheneedlesandsurvivalweremade,andtherespectivepvalues
werecalculatedforhybridandpurespeciesseedlings(TablesS1–S3).Thecomparisons
wereconductedusingNemenyitests(posthoc.kruskal.nemenyi.test)andthePMCMR
packageoftheRsoftwareversion1.4.1103[24](α=0.025).
Spearman’sanalysiswasusedtoexaminethepossiblecorrelation(rs)betweenthe
stomataldensityandseedlingdiameter,height,andsurvivalinbothtrialsofhybridand
pureseedlings.Correlationvaluesandtheirsignificance(p)wereestimatedconsidering
α=0.025.
Theaveragesurvival(%)oftheseedlingsperseedstandwascomputed.Significant
differencesinthesurvivalofthepureandhybridseedlingswerecheckedusingtheDelta
index(δ)andthecorrespondingpvalue(TableS4).Aδvalueofzeroindicatestwocollec‐
tivesofindividualswithidenticalsurvivalrates,andaδvalueofoneindicatescompletely
differentsurvivalrate(0vs.100%survival)[25,26].Thecorrelationsbetweensurvivaland
stomataldensityandthecorrespondingpvalueswerealsocalculated.
3.Results
3.1.GrowthParametersandSurvival
Consideringbothtrialstogetherandeachtrialseparately,nosignificantdifference
betweenthebasaldiameterofthehybridandpureseedlingswasdetected.Comparison
ofthediameterofthedifferentspeciesrevealedthatPinusengelmanniiseedlingsweresig‐
nificantlylargerthantheP.durangensis,P.leiophyilla,andP.teocoteseedlings(Table2).
Consideringbothtrialstogetherandseparately,nosignificantdifferencesinthe
heightstotheapicalbudbetweenhybridandpureindividualsofthecorrespondingspe‐
cieswereobserved.Overall,forbothtrials,themedianheighttotheapicalbudofthe
hybridindividualswassignificantlylargerthanthatofthepureseedlings(Table3).
Consideringbothtrialstogetherandseparately,comparisonofthemedianvaluesfor
thehybridandpurespeciesseedlingsofP.engelmanniirevealedsignificantlylowervalues
ofthemaximumheighttothetopoftheneedlesofthisspeciesrelativetothehybridand
pureP.durangensisandP.teocoteseedlings.Ontheotherhand,therewasnosignificant
differencebetweenhybridsandpureseedlingsofeachspeciesinmaximumheighttothe
topoftheneedles(Table4).
Consideringbothtrialstogether,weobservedsignificantdifferencesinsurvival(δ)
betweenhybridandpurespeciesindividualsofP.arizonicaandP.durangensis(45%vs.
12%and40%vs.27%).However,wedidnotobserveanysignificantdifferencesinthe
Forests2022,13,17917of14
analysisoftheoverallsurvivalofhybridandpureseedlings(δ=0.23,p=0.99).Consider‐
ingthetrialsseparately,themeansurvivalrateoftheP.arizonicahybridswassignificantly
higherthanthatofthepureindividuals,butthemeansurvivalofthehybridP.durangensis
wasonlyhigherintheMesaSecatrial.Overallinbothtrials,purePinusarizonicaseedlings
exhibitedthelowestsurvivalinthefield(12%),andtheδwassignificantrelativetothe
otherhybridsandpureseedlings.PureP.durangensisseedlingspresentedsignificantδ
relativetothehybridsandpureseedlingsofP.engelmannii(26%,46%,and42%).Individ‐
ualsofpureP.teocote(34%)andhybridsofP.engelmannii(46%)alsopresentedsignificant
δ(Table5).
Table5.NumberofPinusseedlings(N)growinginthefieldinbothprovenancetrials,betweenJuly
2018andOctober2020(classifiedashybridsandpurespecies).Differentlettersineachsurvival
columnindicatesignificantdifferencesinthesurvivalrate.
Species
MesaAltaMesaSecaMeanSurvival
(%)
N2018N2020Survival
(%)N2018N2020Survival
(%)2020
PA‐H11545a11545b45ab
PA‐P29310b29414d12c
PD‐H941819b945861ab40a
PD‐P661421b652030c26b
PE‐H2945619b29321172a46a
PE‐P3547822b35721861ab42a
PL‐H35720b341852b36ab
PL‐P27415b281347b31ab
PT‐H2164923b21511452b38a
PT‐P1502416b1507751b34ab
H64913521a64940663a42a
P62812320a62733253a36a
PA‐P=Pinusarizonica,PD‐P=P.durangensis,PE‐P=P.engelmannii,PL‐P=P.leiophyllaandPT‐P=
P.teocote;PA‐H=hybridsofPinusarizonica×PinusdurangensisgeneticallymoresimilartoP.arizon‐
ica;PD‐H=hybridsofP.durangensis×P.arizonicageneticallymoresimilartoP.durangensis(13live
individuals)andP.durangensis×P.engelmanniigeneticallymoresimilartoP.durangensis(63live
individuals);PE‐H=hybridsofP.engelmannii×P.arizonicageneticallymoresimilartoP.engel‐
mannii;PL‐H=hybridsofP.leiophylla×P.teocotegeneticallymoresimilartoP.leiophylla;PT‐H=P.
leiophylla×P.teocotegeneticallymoresimilartoP.teocote;differentlettersindicatesignificantdiffer‐
ences(α=0.025).
3.2.StomatalDensityandGrowthintheField
Consideringbothtrialstogether,thestomataldensitydidnotdiffersignificantlybe‐
tweentheseedlingsofthesamepurespeciesandtherespectivehybrids.However,sto‐
mataldensitywassignificantlyhigherinthehybridandpureindividualsofP.engelmannii
(145.7inhybridsand146.6inpureindividuals)thanintheothertwospecies(p<0.001)
(Table6).

Forests2022,13,17918of14
Table6.Descriptivestatisticsoftheestimatedstomataldensity(stomata/mm2)foreachpurespecies
analyzedandthehybridsinbothprovenancetrials.
SpeciesN
MesaAlta
N
MesaSecaTotalNMedianMeanSd
PD‐H12162894.0b94.617.1
PD‐P1061696.5b97.724.6
PE‐H272956144.3a145.733.6
PE‐P303565142.0a146.635.6
PT‐H232447109.5b111.324.2
PT‐P151833108.0b112.230.3
H6269131119.7a122.434.6
P5559114127.0a129.638.0
Sd=standarddeviation,N=numberofPinusseedlings,PD‐P=Pinusdurangensis,PE‐P=P.engel‐
mannii,PT‐P=P.teocote;PD‐H=hybridsofP.durangensis×P.arizonicageneticallymoresimilarto
P.durangensisandP.durangensis×P.engelmanniigeneticallymoresimilartoP.durangensis;PE‐H=
hybridsofP.engelmannii×P.arizonicageneticallymoresimilartoP.engelmannii;PT‐H=P.leiophylla
×P.teocotegeneticallymoresimilartoP.teocote.N=numberofindividuals;differentlettersindicate
significantdifferencesinthemedianstomatadensity(α=0.025).
Inallthreespecies,themeanstomataldensitywassignificantlycorrelatedwiththe
basaldiameter,heighttotheapicalbud,maximumheighttothetopoftheneedles,and
survival(p<0.01).Stomataldensitywassignificantlypositivelycorrelatedwiththebasal
diameter,butnegativelycorrelatedwithbothheightsinthethreespecies.Inthehybrid
seedlings,stomataldensitywassignificantlypositivelycorrelatedwithsurvivalatthe
seedstandlevel.Incontrast,therewasnosignificantcorrelationbetweenthesetwovari‐
ablesinthepureseedlings.However,forthepureseedlings,aparabolic‐likefunctionwith
anegativequadraticcoefficientofthesurvivalratewithstomataldensitywasobserved
(withmaximumsurvivalrateatabout120stomata/mm2).Thesetwovariableswerenot
significantlycorrelatedinthepureseedlings.Consequently,verylowandveryhighsto‐
mataldensitycorrespondtolowersurvivalofthepureseedlings(Figure2andTable7).
Wedidnotdetectasignificantrelationshipbetweenstomataldensityandseedlinggrowth
orsurvivalwithinanyofthethreespeciesortheirhybrids.
rs=0.34
rs=−0.36
Forests2022,13,17919of14
Figure2.Correlationsbetweenstomataldensity(N/mm2)andbasaldiameter(mm),heighttoapical
bud(cm),maximumheighttothetopoftheneedles(cm)perindividual,andsurvivalbyseedstand
inindividualsofthethreeselectedpurespecies(Pinusdurangensis,P.engelmannii,andP.teocote)and
theirhybrids(P.durangensis×P.arizonica,P.durangensis×P.engelmannii,P.engelmannii×P.arizonica,
andP.tecote×P.leiophylla).Meanvalues(cyanandredlines)andthe95%confidencelevelintervals
forpredictions(greyarea)arebasedongeneralizedadditivemodels(GAM).
Table7.Spearman’scorrelation(rs)(andp‐value)betweenthestomataldensityandthebasaldiam‐
eter,heighttotheapicalbud,andmaximumheighttothetopoftheneedlesperseedling.Inaddi‐
tion,Spearman’scorrelations(rs)(andp‐value)betweenthestomataldensityandsurvivalinseed‐
lingsofthethreeselectedpurepinespecies(Pinusdurangensis,P.engelmannii,andP.teocote)and
theirhybrids(P.durangensis×P.arizonica,P.durangensis×P.engelmannii,P.engelmannii×P.arizonica,
andP.teocote×P.leiophylla)(α=0.025)areshownforeachtrial.
Variablersp‐Value
Basaldiameter+0.343×10⁻⁷
Heighttoapicalbud−0.365×10⁻⁸
Maximumheighttothetopoftheneedles−0.230.0006
Survival(hybridseedlings)+0.4910⁻⁸
Survival(pureseedlings)−0.0020.98
4.Discussion
4.1.SeedlingGrowthandSurvival
Weobservedsignificantdifferencesinthegrowthoftheheightandbasaldiameter
andahighersurvivalrateinPinusengelmanniirelativetotheotherspecies.Thesediffer‐
encescanbeattributedtothefactthatatthefirststageofdevelopment,P.engelmannii,as
apioneerspecies,rapidlyincreasesindiameterandneedles,andtoalesserextentin
height,anddisplaysacespitosegrowthhabit[27,28].Thegreatersurvivalofthisspecies
isalsoduetoitsresistancetodrought(meanannualprecipitationfrom670to830mm[9])
andtothefactthatitusuallygrowsonplateaus,slopes,valleys,andterraces,atelevations
ofbetween1500and2700m[29,30].Thesameappliestothemoredrought‐resistantspe‐
ciesofP.leiophyllaandP.teocote[9],whichareoftenassociatedwithP.engelmannii[8].
AlthoughP.arizonicaisoneofthemostimportanttimberspeciesintheSMO[31],survival
oftheseseedlingswaslowerthanthatofotherspeciesinbothtrials(Table5).Thisspecies
hasspecificgrowthrequirements,includingapHof4.9±0.3[32],densetreecover[33,34],
andameanannualprecipitationofbetween870and1200mm[9].Theseconditionsdid
notoccurinthestudyarea,astreecoverissparseinbothsites,andthelevelofprecipita‐
tionwaslowintheyearpriortodatacollection.
rs=−0.23rs(Hybrid)=0.49
rs(Pure)=−0.002
Forests2022,13,179110of14
Ingeneral,thegrowthofhybridseedlingswassimilartothatofthepureseedlings
inthetrials(Tables2–4).Onlytheoverallmedianheighttotheapicalbudofhybridseed‐
lingswasslightly,butsignificantly,greaterthanthemedianheightofthepureseedlings
(Table3).Thishasalsobeenobservedinhybridsofotherspecies,suchasPinusoocarpa×
P.pringei[19]andP.arizonica×P.engelmannii[29],andadulthybridtreesofPinusluzmariae
×P.herrerae,whichweretallerthanpureP.luzmariaetrees[35].However,hybridsgenerally
showintermediatevaluesofheightanddiameterrelativetothe(pure)parents[36].
Inaddition,thesurvivalofhybridsofP.arizonicaandofP.durangensiswassignifi‐
cantlyhigherthanthatofthepurespecies(Table5),whichmayindicatehybridvigor
(heterosis).Intheory,heterosisoccursfordifferentreasons:heterozygousindividualsdis‐
playhigherlevelsoffitnessthanhomozygousindividuals,thusfavoringthesurvivalof
hybrids[37].Individualswithhigherindividualheterozygosityshowmorestablegrowth,
beinglessaffectedbyenvironmentalfactors[20],becausehybridshavegreatergeneticvar‐
iability,whichallowsthemtoadapttoagreaternumberofecosystemsandconditions[5].
Anotherreasonforhybridvigorisoverdominance,whichoccurswhenheterozygous
individualsaremorevigorousthanhomozygousindividuals,givingrisetosuperiorhy‐
brids[37,38].Dominanceoccurswhenlesshomozygousindividualshave,bydefinition,
lowervaluesofinbreedingandlowerinbreedingdepression[39–41].
However,themostlikelycauseofhybridvigoristhattheenvironmentalconditions,
inbothtrials,weremoresuitableforthehybridswithP.engelmanniigenes(P.arizonica×
P.engelmannii,P.durangensis×P.engelmannii)(Table5).
Finally,aftergrowingfor27monthsinthefield,themeansurvivalrateofseedlings
was35%(Table2).ThisislowerthantheratedeterminedbyMejíaetal.[42],whostudied
seedlingsofPinusofdifferentspeciesandagesintheSMO,whereonlyplantingstrees
olderthaneightyearshadasurvivalrateoflessthan60%.Thisisalsolowerthantherate
reportedbyBenítez[43],whocalculatedameansurvivalof60%inPinusengelmanniiplan‐
tationsinDurango,Mexico.However,itwassimilartothatintheplantationsstudiedby
TorresRojo[44],withameansurvivalrateof38%,andtosomeofthePinusengelmannii
plantationsstudiedbyPrietoRuízetal.[45].Possiblecausesoflowsurvivalintheplant‐
ingsites(bothtrials)includethepresenceofPappogeomyscastanopsBairdandlowrainfall
during2019(429mm),theyearpriortodatacollection[46].
4.2.StomatalDensity
Stomataldensitywasthehighestinthedrought‐tolerantP.engelmannii[26,30](Table
7).Thisfindingisconsistentwiththoseofotherstudiesthathavereportedahighersto‐
mataldensityand/ornumberofstomatalrowsinP.ponderosa[47]andinsomeMediter‐
raneanpinesunderdroughtconditions[48–50].AccordingtoAfasetal.[51]andShu[47],
ahigherstomataldensitycouldenableincreasedleafgasexchangeduringshort,favorable
periodsandgreatercontrolofwaterlossandgasexchangeunderdroughtstressinharsh
dryconditions.Stomataldensitydependsondifferentenvironmentalfactors,suchaswa‐
terstress[52]andchangesinambientCO2concentration[53].Despitetheinfluenceof
environmentalfactors,stomataldensityisstronglycontrolledbygeneticfactors[54].
Thestomataldensitywaspositivelyandsignificantlycorrelatedwiththebasaldiam‐
eterandnegativelycorrelatedwithheightinthepinespeciesanalyzed(Table7,Figure2).
InastudyofanF1hybridbetweenQuercusroburandQ.robursubsp.Slavonica,Gailinget
al.[55]alsoobservedapositive,significantcorrelationbetweenthestomataldensityand
basaldiameter;however,thecorrelationbetweenstomataldensityandheightwasalso
positive.Weobtainedtheoppositeresultregardingheight,whichcanbeexplainedbythe
lowerheightgrowthofP.engelmanniithanofP.durangensisandP.teocote(Tables3and
4).However,P.engelmanniihasthehigheststomataldensity(Table6).Thesameauthors
[55]alsostatedthat(i)stomataldevelopmentisregulatedbydifferentgeneticandenvi‐
ronmentalsignalsand(ii)inQ.robur,thealleleofaparticularquantitativetraitlocusas‐
sociatedwithhigherstomataldensitywasgenerallycorrelatedwithtallerplantsandan
Forests2022,13,179111of14
increaseinsize,indicatingpleiotropicgeneeffectsoraclosegeneticlinkage,asalsore‐
portedbyChebibandGuillaume[56].
Inthepresentstudy,inadditiontoinfluencinggrowth,stomataldensitywasalso
positivelycorrelatedwiththesurvivalofthehybridseedlings.However,forthepure
seedlings,plottingthesurvivalrateagainstthestomataldensityyieldedaparabolic‐like
curve(Figure2andTable7).Thus,onaverage,hybridswithahighstomataldensitysur‐
vivedbetterthanpureseedlingswithasimilarhighstomataldensity,whichcouldbe
explainedbydifferencesinothertraitsnotstudiedhere.Theseothertraitscouldhave
contributedtoenhancingtheadaptivecapacityofthehybridsbyenablingthemtocope
withenvironmentalconditionsinbothtrialsmoresuccessfullythanthepureindividuals.
Significantvariationinstomataldensityhasbeendetectedbetweenclonesandhybridsof
Populusspecies,anditsrespectivecorrelationwithbiomassproduction[57]andlightcon‐
ductance[58],indicatingthatstomataldensitymayvaryamongclonesorpurespecies,as
wellasamonghybrids;suchvariationwillenablethetreestoadapttothesurrounding
environmentalconditions.
5.Conclusions
Thebasaldiameter,heighttotheapicalbud,andmaximumheighttothetopofthe
needlesvariedweaklybetweenhybridandpureseedlingsofdifferentpinespecies.A
greaterheighttotheapicalbudandsurvivalofhybridsweredetectedinPinusarizonica
andP.durangensisthaninthepurespecies.Aftergrowingfor27monthsinthefield,the
hybridsgenerallydisplayedthesamecapacityasthepureseedlings(andinsomecasesa
greatercapacity)towithstandweatherconditions,survive,andgroweffectively.These
differencesareexpectedtoincreaseovertimeinthefield.Thus,thereisnoreasontoex‐
cludethesehybridsfromtheforestmanagementplans.
Werecommendcontinuingtomonitorthesetrialsinordertodeterminethelong‐
termviabilityofthehybridandpureseedlings.Becauseofthespatialandtemporallimi‐
tationsofthestudy,wealsosuggestreplicatingthistypeoftrialwithotherspeciesandin
othersites,asthereisawidevariationinthechancesofdetectinghybridvigor.
Theresultsofthisresearchwillhelpforestmanagerstoselectthemostappropriate
speciesandtheirhybridsforreforestationorplantations,thuscontributingtosustainable
forestprotection,conservation,andmanagement,includingadaptivesilviculture,andto
satisfyingthegrowingdemandforwoodintheforestrysector.
SupplementaryMaterials:Thefollowingsupportinginformationcanbedownloadedat:
https://www.mdpi.com/article/10.3390/f13111791/s1,SupplementaryTableS1:Differencebetween
basaldiametersmediansofPinusspeciesinmillimetersandp‐valuescalculatedinKruskal‐Wallis
multipletesting(bothtrials);α=0.025.;TableS2:Differencesbetweenthemedianheighttotheapical
budofPinusspeciesincentimeters,andthecorrespondingp‐values,calculatedinKruskal‐Wallis
multipletests(overallforbothtrials);α=0.025;TableS3:Differencebetweenthemediansofthemax‐
imumheighttothetopoftheneedlesofPinusspecies,incentimeters,andp‐valuescalculatedinKrus‐
kal‐Wallismultipletests(overallforbothtrials);α=0.025;TableS4:Deltaindex(δ)andcorresponding
p‐valuesindeltatestsforthesurvivalofPinusspecies(bothtrialscombined),α=0.025.
AuthorContributions:Conceptualization,C.W.;formalanalysis,R.S.S.‐H.;investigation,R.S.S.‐H.;
methodology;supervision,C.W.;writingoftheoriginaldraft,R.S.S.‐H.andC.W.;writing—review‐
ingandediting,C.W.,C.Z.Q.‐P.,J.C.H.‐D.,andJ.Á.P.‐R.Allauthorshavereadandagreedtothe
publishedversionofthemanuscript.
Funding:ThisstudywassupportedbytheCouncilofScienceandTechnologyofthestateofDu‐
rango(COCYTED);FinanceCode21571/2020.WewouldliketothanktheScienceandTechnology
Council(CONACYT)forapostgraduatescholarship,whichactedasanincentivetocarryoutthe
study.Thefundingbodieshadnoroleinthestudydesign,datacollectionandanalysis,decisionto
publish,orpreparationofthemanuscript.
Forests2022,13,179112of14
Acknowledgments:WearethankfultotheadministrationoftheejidosCiénegadeSalpicaelAgua
yLagunadelaChaparra,municipalityofSantiagoPapasquiaro,stateofDurango,México(1005)
(EngineerFernandoSalazarJiménez)fortheirhelpfulassistance.
ConflictsofInterest:Theauthorsdeclarenoconflictofinterest.
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Effect of seedling size on post-planting growth and survival of five Mexican Pinus species and their hybrids
Article
Full-text available
  • Dec 2024
Background: Seedling growth and survival depend on seedling quality. However, there is no experimental evidence showing that the seedling dimensions of the abundant, economically important and widely distributed tree species Pinus arizonica, P. durangensis, P. engelmannii, P. leiophylla, and P. teocote and their hybrids effectively improve survival and growth in reforestations and plantations in Mexico. Therefore, the aim was to evaluate the influence of initial morphological parameters of 2,007 nursery seedlings of these species and their hybrids on their growth and survival 44 months after planting in the Sierra Madre Occidental, Mexico. Methods: Spearman’s coefficient (rs) and the unbiased conditional pseudo coefficient of determination (R2c) between each specific predictor and each response variable and their 95% confidence interval (CI95%) were determined using Random Forest, generalized linear model, and bootstrapping. By bootstrapping, the potential environmental heterogeneity inside the trial fields and its impact on the results were also quantified. Results: Among the studied species and their hybrids moderate correlations were observed between the nursery seedling dimensions and the plant dimensions 44 months after planting. However, only weak significant correlations were found between survival rate (SR) and height (H) (rs = 0.10) and between SR and robustness index (HRCD) both before planting (rs = 0.06). Also, weak significant R2c values of the seedlings RCD, H and HRCD were detected with respect to the corresponding RCD, H and SR 44 months after planting, respectively. Furthermore, the predictor variable “seed provenance” (with 23 provenances) significantly explained the variation in the post-planting RCD, H and SR of the seedlings, with R2c values ranging from 0.10 to 0.15. The low width of the CI95% shows that the environmental conditions in the trial fields were quite homogeneous. Discussion: The results also show that the inclusion of “confounding” variables in the statistical analysis of the study was crucial. Important factors to explain this low association could be the strong damage observed caused by pocket gopher, the typically low winter-spring precipitation in both field trials and adaptation factors. The study findings provide preliminary insights and information aimed at helping to design more appropriate standards for nurseries.
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Pleiotropy or linkage? Their relative contributions to the genetic correlation of quantitative traits and detection by multi-trait GWA studies
Article
Full-text available
  • Sep 2021
  • GENETICS
Genetic correlations between traits may cause correlated responses to selection. Previous models described the conditions under which genetic correlations are expected to be maintained. Selection, mutation and migration are all proposed to affect genetic correlations, regardless of whether the underlying genetic architecture consists of pleiotropic or tightly linked loci affecting the traits. Here, we investigate the conditions under which pleiotropy and linkage have different effects on the genetic correlations between traits by explicitly modeling multiple genetic architectures to look at the effects of selection strength, degree of correlational selection, mutation rate, mutational variance, recombination rate, and migration rate. We show that at mutation-selection(-migration) balance, mutation rates differentially affect the equilibrium levels of genetic correlation when architectures are composed of pairs of physically linked loci compared to architectures of pleiotropic loci. Even when there is perfect linkage (no recombination within pairs of linked loci), a lower genetic correlation is maintained than with pleiotropy, with a lower mutation rate leading to a larger decrease. These results imply that the detection of causal loci in multi-trait association studies will be affected by the type of underlying architectures, whereby pleiotropic variants are more likely to be underlying multiple detected associations. We also confirm that tighter linkage between non-pleiotropic causal loci maintains higher genetic correlations at the traits and leads to a greater proportion of false positives in association analyses.
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Natural hybridization in seed stands of seven Mexican Pinus species
Article
Full-text available
  • May 2022
  • NEW FOREST
Natural hybridization can manifest different evolutionary results, such as accelerating differentiation and facilitating speciation through the rapid origin of new biochemical compounds, physiological or morphological phenotypes that allow hybrid species to occupy new habitats, which for parental species would be inaccessible. However, these expectations are not always fulfilled, because natural hybridization between divergent populations can lead to inadequate or unviable hybrids and, therefore, lower forest stability and productivity. Using pure species Pinus arizonica, P. cembroides, P. durangensis, P. engelmannii, P. leiophylla, P. lumholtzii and P. teocote trees and their natural hybrids, this study aims to determine for the first time: (i) morphological differences between pure pine trees and their hybrids molecularly detected, (ii) differences in vigor between 1970 seeds from trees of pure pine species and their hybrid trees (hereinafter called pure and hybrid parents), (iii) differences in vigor between 3465 seedlings from 1421 pure and hybrid parents, and (iv) whether growth of seedlings of hybrid parents is differently associated to parent tree’s environmental conditions, than growth of seedlings of pure parents. The seedlings grew under equal nursery conditions. Our results show some significant differences in morphological traits between the seed trees of pure species and their respective putative hybrid seed trees, and in seed and seedling fitness indices. In contrast to the mean growth of seedlings of hybrid parents, the mean growth of seedlings from pure parents was significantly associated with the parent tree’s bioclimatic conditions studied (R2 = 0.70 vs 0.83). There were only some individuals that presented hybrid superiority.
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Modelling Shifts and Contraction of Seed Zones in Two Mexican Pine Species by Using Molecular Markers
Article
Full-text available
  • May 2021
A seed zone or provenance region is an area within which plants can be moved with little risk of maladaptation, because of the low environmental variation. Delineation of seed zones is of great importance for commercial plantations, reforestation and restoration programs. In this study, we used AFLP markers associated with environmental variation for locating and delimiting seed zones for two widespread and economically important Mexican pine species (Pinus arizonica Engelm. and P. durangensis Martínez), both based on recent climate conditions and under a predicted climate scenario for 2030 (Representative Concentration Pathway of ~4.5 Wm-2). We expected to observe: i) associations between seed zones and local climate, soil and geographical factors, and ii) a meaning latitudinal shift of seed zones, along with a contraction of species distributions for the period 1990 - 2030 in a northward direction. Some AFLP outliers were significantly associated with spring and winter precipitation, and with phosphorus concentration in the soil. According to the scenario for 2030, the estimated species and seed zone distributions will change both in size and position. Our modeling of seed zones could contribute to reduce the probabilities of maladaptation of reforestations and plantations with the pine species studied.
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Factores ambientales y físicos que afectan la supervivencia de siete especies forestales en el Estado de México
Article
Full-text available
  • Feb 2021
Esta investigación tuvo como objetivo evaluar el efecto de diferentes variables ambientales y físicas sobre la supervivencia de las siete especies más usadas para la reforestación en el Estado de México, durante el periodo 1997-2003. La evaluación se realizó a través de un muestreo de dos etapas de 757 plantaciones. En la primera, se seleccionaron aleatoriamente las plantaciones bajo un diseño completamente al azar. La segunda fase consistió en levantar sitios de muestreo de 100 m2 elegidos de manera sistemática en cada una de las plantaciones seleccionadas, con una intensidad de muestreo de 5 % del área plantada. En los sitios se evaluó la supervivencia y un conjunto de variables de sitio. El análisis se realizó mediante un modelo Probit, en el cual se probaron todas las combinaciones de diferentes subconjuntos de variables de sitio y climáticas como variables de control. Los resultados mostraron que las plantaciones tienen una baja supervivencia (38 %), atribuible a la poca protección de las plantaciones, la rápida conversión a terreno agropecuario, así como a la desvinculación entre los requerimientos de cada especie y las características de los sitios de plantación. Se analiza y discute el efecto de las variables evaluadas por especie y se proporcionan recomendaciones de registro de información para las plantaciones.
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Tall Pinus luzmariae trees with genes from P. herrerae
Article
Full-text available
  • Feb 2020
Context: Pinus herrerae and P. luzmariae are endemic to western Mexico, where they cover an area of more than 1 million hectares. Pinus herrerae is also cultivated in field trials in South Africa and South America, because of its considerable economic importance as a source of timber and resin. Seed quality, afforestation success and desirable traits may all be influenced by the presence of hybrid trees in seed stands. Aims: We aimed to determine the degree of hybridization between P. herrerae and P. luzmariae in seed stands of each species located in the Sierra Madre Occidental, Durango, Mexico. Methods: AFLP molecular markers from samples of 171 trees across five populations were analyzed with STRUCTURE and NewHybrids software to determine the degree of introgressive hybridization. The accuracy of STRUCTURE and NewHybrids in detecting hybrids was quantified using the software Hybridlab 1.0. Morphological analysis of 131 samples from two populations of P. herrerae and two populations of P. luzmariae was also conducted by Random Forest. The data were compared by Principal Coordinate Analysis (PCoA) in GenAlex 6.501. Results: Hybridization between Pinus herrerae and P. luzmariae was observed in all seed stands under study and resulted in enhancement of desirable silvicultural traits in the latter species. In P. luzmariae, only about 16% of molecularly detected hybrids correspond to those identified on a morphological basis. However, the morphology of P. herrerae is not consistent with the molecularly identified hybrids from one population and is only consistent with 3% of those from the other population. Conclusions: This is the first report of hybrid vigour (heterosis) in Mexican pines. Information about hybridization and introgression is essential for developing effective future breeding programs, successful establishment of plantations and management of natural forest stands. Understanding how natural hybridization may influence the evolution and adaptation of pines to climate change is a cornerstone to sustainable forest management including adaptive silviculture.
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Supervivencia y crecimiento de dos especies forestales, con base en la morfología inicial al plantarse
Article
Full-text available
  • May 2018
Las reforestaciones exitosas dependen de varios factores, la calidad de planta es uno de ellos, ya que es determinante para su establecimiento después de plantada. El objetivo del ensayo fue evaluar el efecto de dos condiciones morfológicas de planta, basadas en la altura, diámetro al cuello, la supervivencia y crecimiento inicial de Pinus cooperi y Pinus engelmannii en Agua Zarca, Otinapa, Durango. La planta se distribuyó bajo un diseño experimental de bloques al azar, con cuatro repeticiones por tratamiento. Después de 13 meses, en Pinus engelmannii solo se determinaron diferencias significativas (p<0.05) en la supervivencia y la altura, con los mejores resultados en los individuos con la condición morfológica alta. Las diferencias en supervivencia, entre tratamientos, fueron de 50 %, mientras que en la altura de 3.37 cm y en el diámetro de 4.87 mm. En Pinus cooperi, únicamente, existieron diferencias significativas (p<0.05) en la altura, con una separación entre valores de 6.7 cm, y en la supervivencia fue de 2.5 %, con más de 90 % de supervivencia en ambas calidades; en el diámetro, las diferencias fueron menores a 1.0 mm; en todos los casos, la planta con los atributos morfológicos más altos registró los valores mayores. Con relación a la supervivencia entre especies, sin considerar la condición morfológica de la planta, las diferencias finales fueron de 51.2 %, con los porcentajes más altos para P. cooperi, especie que mejor se adaptó a las condiciones del sitio de plantación.
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Multi-locus phylogenetics, lineage sorting, and reticulation in Pinus subsection Australes
Article
Full-text available
  • Apr 2018
Premise of the Study Both incomplete lineage sorting and reticulation have been proposed as causes of phylogenetic incongruence. Disentangling these factors may be most difficult in long‐lived, wind‐pollinated plants with large population sizes and weak reproductive barriers. Methods We used solution hybridization for targeted enrichment and massive parallel sequencing to characterize low‐copy‐number nuclear genes and high‐copy‐number plastomes (Hyb‐Seq) in 74 individuals of Pinus subsection Australes, a group of ~30 New World pine species of exceptional ecological and economic importance. We inferred relationships using methods that account for both incomplete lineage sorting and reticulation. Key Results Concatenation‐ and coalescent‐based trees inferred from nuclear genes mainly agreed with one another, but they contradicted the plastid DNA tree in recovering the Attenuatae (the California closed‐cone pines) and Oocarpae (the egg‐cone pines of Mexico and Central America) as monophyletic and the Australes sensu stricto (the southern yellow pines) as paraphyletic to the Oocarpae. The plastid tree featured some relationships that were discordant with morphological and geographic evidence and species limits. Incorporating gene flow into the coalescent analyses better fit the data, but evidence supporting the hypothesis that hybridization explains the non‐monophyly of the Attenuatae in the plastid tree was equivocal. Conclusions Our analyses document cytonuclear discordance in Pinus subsection Australes. We attribute this discordance to ancient and recent introgression and present a phylogenetic hypothesis in which mostly hierarchical relationships are overlain by gene flow.
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The Ecology Of Elevational Positions In Plants: Drought Resistance In Five Montane Pine Species In Southeastern Arizona
Article
Full-text available
  • Jan 1993
We subjected seedlings of five pine species from the Chiricahua Mountains, Arizona to drought in the greenhouse to assess the relationships among elevational position, drought resistance, and biomass allocation. In comparison with upper elevation species, lower elevation species survived longer and experienced less depression of photosynthesis in response to the imposed drought. During the last week of the 29-d drought, internal water potential decreased little in lower elevation species but dropped precipitously in upper elevation species. Thus, relative drought resistance and elevational position of these pines seem associated with the ability of seedlings to survive drought by maintaining favorable plant water potential. Lower elevation and more drought-resistant species allocated less biomass to roots than did other species, a fact suggesting, contrary to assumptions of recent plant community models, that biomass allocation was unimportant in species differences in drought resistance.
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Spatial Genetic Structure in Seed Stands of Pinus arizonica Engelm. and Pinus cooperi Blanco in the State of Durango, Mexico
Article
Full-text available
  • Apr 2018
Spatial genetic structure (SGS) characterizes the geographical distribution of genetic variation. Pinus arizonica and P. cooperi are two of the most important timber tree species in Mexico. Certified seed stands of these species are needed to increase productivity and recover degraded areas. In the present study, we analyzed neutral and putatively adaptive AFLPs toexamine the SGS in 12 natural seed stands of P. arizonica and P. cooperi at local (within the seed stands) and large scales (among the seed stands). Since these pine species are wind-pollinated, widespread and often occur at high population densities, we did not expect to find any SGS at the fine scale or significant differences in the SGS of the two species. At the fine-scale, we observed highly significant spatial genetic autocorrelation for both species in only two of the 12 seed stands. At the large scale, we observed significant spatial structure, which may be the result of isolation by distance. We recommend establishing a fine-meshed network of seed stands, with maximal distances of 9 - 18 km between them to prevent greater loss of local genetic structure.
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