SEIWA  Kenji

SUYAMA  Yoshihisa

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SEIWA, Kenji

SUYAMA, Yoshihisa

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Recent Research Topics in Ecological andGenetic Approaches for Sustainable ForestManagement著者 SEIWA  Kenji, SUYAMA  Yoshihisajournal orpublication titleTohoku journal of agricultural researchvolume 60number 1-2page range 59-62year 2009-12URL http://hdl.handle.net/10097/41181Tohoku Joumalof AgriculturalResearchVol. 60 Ⅳ0. 1-2, December 2009Pn'nted in JapanRecent Research Topics in Ecolo色ical and GeneticApproaches for Sustainable Forest Mana色ementKenji SEIWA and Yoshihisa StTYAMALabwatory of Forest Ecology, GVaduate School of Agricultural Sbience, Tohoku University(Received, October 20, 2009)Summaryln forests, maintainbg and/Or increasing biodiversity has become Anincreas-lngly important management goaltx) provide a broad array of ecosystem servicesthat directly or indirectly benefit human endeavors･ Althoughdegradation ofbiodiversity is a worldwide conoem on bothglobaland localscales, relatively littleevidence is available on the mechanisms of biodiversity. We focus on studies ofmechamims maintaining biodiversity (i･e･, speOies diversity, genetic diversity) andecosystem functioning.Mechamisms of Species Diversity in Temperate Forestsln temperate forests, it was thought that species diversity is mainly createdby abiotic factors, such aB heterogeneity of light, water, and nutrients, each ofwhich is closely related to topographyand canopy gaps (Nagamatsu et al., 2002 ;Seiwa et al･, 2006)･ However, increasing evidence indicates the effects of bioticfactors such as pathogensand herbivores, both of which have an important role inmaintaining species diversity in tropicalforests･ We testcd the two most impor-tant hypotheses explaining species diversity of tropical forests in txtmperateforest8.Janzen and Connell hypothesized that seed dispersal enhances the probabil-ity of survivalby distanclng Offspring from adults, because host-specific natllralenemies reduce recruitment near conspecific adults in a density-dependent and/Ordistance-dependent manner, thereby freeing space for other plant species andgenerating species diversitywithin plant communities･ Our community-levelstudies show that distance- and/or density-dependent juvenile mortality causedby pathogens and by invertebrate and vertebrate herbivores occur in most treespecies c0-0ccurringwithin a forest (Tomita et al., 2002 ; Yamazaki et al., 2009).These traits strongly suggest recIPrOCal replacement of tree species c0-occurringwithin forest communities･ We also found that death and growth redllCtion in a5960 K. Seiwa et al.distance-dependent manner occur throughout the juvenile stages, from current-year seedlings to large saplings (height ～3 m) in Prunus grayana, probably dueto severe attack by a leaf pathogen on JuVenilesI Because this leaf pathogencauses leaf-Spot symptoⅡ旭and subsequent leaf shedding in the early growlngseason, the photosymthetic ability of juveniles is strongly reduoed, particularlybeneath the adults (Seiwa et al･, 2008)･ The leaf pathogen was identified asPhaeoi'sariopsw pnmも-grayanae Sawada, which infects many more seedlings of P･grayana than seedlings of the two other tree species testcd in inoculation experi-ments, suggesting selective host preference･ If pathogens attackal1 juvenilessimilarly, Juvenile mortality of the fooalspecieswill occur even beneathheterospecific adults whenthe totaljuvenile density is high, suggesting no benefitof long-range dispersal from conspeoific adult8. Thus, for Janzen-Connell mecha-nisms, species-specific pathogens are more important than generalist pathogens･This evidence strongly suggests that the Janzen-Connell hypothesis is valid evenin temperate forests.In spatial1y heterogeneous environments, a trade-off between seedling sur-vivalin the forest understory and relative growth rate in gaps promotes thecoexistence of plant species (trade-off hypothesis). In temperate forests, however,little support for this hypothesis has been found underfield conditions, as compar-ed to shadehouse experiments･Anexperiment over a large resource gradient ina temperate hardwood forest strongly supportedthe idea of light gradient par-titioning (i･e･, species coexistence ; Seiwa, 2007).We also foundthat shade-tolerant species allocate more carbon to defense andstorage and less to growth compared to shade-intolerant species (lmajiand Seiwa,in press)･ The ratio of condensed tannins to TNC pool sizes was usually higherin shade-tolerant species than in shade-intolerant species･ Hence, shade-tolerantspecies preferentially Invest more Carbon in defense thanin storage･ Such adefense-biased carbonallocation patternwould be advantageous for a shade-tolerant species,allowlng Such a species to persist in the forest understory evenwhere damage from herbivores and pathogens is costly･ In contrast, Shade-intolerant species preferentially invest more carbon in growth rather than defense,and invest similaramounts of carbon in storage as shade-tolerant species, ensunngestablishment success in gaps, where there is severe competition for lightamongneighboring plants･ These contrasting carbonallocation pattems may contributeto species coexistence across light gradients.Mechanisms Maintaimin色Genetic Diversity in Temperate ForestsThe availability of hyper-variablemicrosatellite DNA markers has greatlyextended the possibility of analysis of genetic diversity, gene 丘ow, and/or parent-age鮎Slgnment in naturalforests･ In a pnmary beeoh forest, current-year seed-Recent Research物ぬin Ecob画and Gmet血Appnaehes fw Sustainabk Fwest Management　611ings and adult trees of Fagus crmata were sampled formiCrosatellitc analysis,andthe spatialpattems of seedand pollen dispersalWere investigated based onparentage assignment analysis･ Seeds are dispersed near their matemal trees(average distance : ll m), but the average pollen dispersaldistanoe is greater thanthe seed dispersaldistance ( > 33 m)･ Larger trees tend to produce more seedlingsfor bothmaternaland patemalparents･ The analysts revealed not only the basicpattem of gene flow at a localscale, butalsothe relativeferbility of individualtreesand txBmporalchanges in spatialgenetic structure inthe forest･Forest fragmentation can cause reduced seed production and genetic erosionin future generations･ To evaluatxt the effects of forest fragmentation on pollen且ow, the seed set and genetic diversity of the resulting seeds were comparedamongF･ crmata trees looatedwithin various localpollen donor densities. Althoughtheseed-set data suggested pol.len limitation, pollenflow over a long distance waseffective in the low-pollen-donor-density populations of F･ mnata in the studyplot･ The results draw attention to the potentialreproductive ability of frag-mented or low-density populations as core populations for future generations･Reforestationwith non-localseed sources may result in genetic disturbanceand maladaptation to localenvironments･ Therefore, it is important to use alocalseed sourcewithin a seed transfer zone delineated by the phylogeography ofthe species being reforested･ To determine the localphylogeographic pattem(genetic structure) of F･ crmata in MiyagiPrefecture, the variation in chloroplastI)NA and nuclearmicrosatellites was investigatxBd for naturaland planted popula-tions･ Furthermore, CPDNA haplotypes and growth performance were investigat-ed in a planted population of the species to demonstrate the fitness advantages oflocalgenotypes･ As a result, at leastthree seed zones (conservation units) wereindicated for F･ crmata in Miyagi･ Furthermore, the CPDNA haplotypes of theplanted trees showed that half of the plantations were non-localand that someplantations have a higherrisk of causlng genetic disturbance to adjacent naturalforests･ Afitness advantage of local haplotype plants (home-site advantage) wasdemonstrated inthe planted population ofmiⅩed origin by comparlng growthperformance between localand nonllocalplants･ Our results indicate that theestablishment of conservationunits is necessary to conserve localgenetic resourcesin this species.In conclusion,althoughgeneflow via seed is limited to a small area, long-distance pollen Bow could be effective to maintain localgenetic diversity, even ina fragmented forest･ It is important to conserve remnant forests in each region tx)promote the fitness of localspecies while avoiding the transplantation of non-localspecies that may devastate local populations･62 K. Seiwa et al.Refe rence slmaji, A･ and Seiwa, K･ Carbonallocation to defense, storage, and growthinseedlings of two temperatx! broad-leaved tree species. Oecolo如(inpress).Nagamatm, D･, Seiwa, K and Sakai, A. Seedling establishment of decid110uStrees in various tx)pographl/c positions. JmLrnal of Yegetalion Sbi-ence 13 : 35-44, 2002.Seiwa, K., Kiknzawa, K., Kadowaki, T., Aknshkn, S. and Ueno, N. Shoot lifespan in relation to successionalstatus in deciduous broad-leaved treespeci飴in a tx!mperatc forest. NeuJ Phytologist 169 : 537-548, 2006.Seiwa, KI Tradel0ffs between seedling growth and survival in deciduousbroad-leaved trees in a bmperate forest. Annals of Botany 99 :537-544, 2007.Seiwa, K., Miwa, YりSahashi, NりKanno, H., Tomita, M., Ueno, N. and Yamaza-ki, MI Pathogen aitack and spatial pattx,ms of juvenile mortalityand growthin a bmperate tree, PmLnuS grayana. Canadian Journalof Forest Resewch 38 : 2445-2454, 2008.Tomita, M･, Eirabuki, and Seiwa, KI Post-dispersalchanges in the spatialdistribution of Eagws crenata seeds. Ecology 83 : 1560-1565, 2002.Yamazaki, M･, IwamotD,and Seiwa, K Distance-and density-dependent seed-lmg mortality caused by severalfungal diseases for eight tree speciesc0-0ccumng ln a bmPerateforest. Plant Ecology 201 : 181-196,2009.

Recent Research Topics in Ecological and Genetic Approaches for Sustainable Forest Management

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Recent Research Topics in Ecological and Genetic Approaches for Sustainable Forest Management

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