The direct and indirect effects of management on boreal forest structure and field layer vegetation
Date
2012-11-02
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Abstract
Viimastel aastakümnetel on hakatud metsade elurikkuse säilimise pärast järjest rohkem muret tundma. Ühe lahendusena nähakse ökoloogiliste võrgustike loomist, kus majandamisest kõrvale jäetavate metsade vahel paiknevad looduslähedaselt majandatud metsad. Selleks, et määratleda praktikas metsade looduslähedust, kasutatakse indikaato¬reid. Käesolevate teeside eesmärgiks oli uurida, millised Eesti boreaalsete metsade struktuursed ja koosseisulised tunnused on majandamisest enim mõjutatud. Koos-seisulistest tunnustest uurisime detailsemalt puude järelkasvu ning puhma- ja rohurinde koosseisu tundlikkust majandamisest tingitud muu¬tustele.
Majandamine mõjutas negatiivselt järgmisi metsa karakteristikuid: suurediameetriliste puude arv, diameetriklasside arv, kuuse ja lehtpuude osakaal puistus, erinevas laguastmes lamapuidu kogus ning puistu erinevate rinnete liituvus. Loodus¬lähedasi metsi ennustas kõige paremini tunnustekompleks, kuhu kuulusid: seisva surnud puidu kogus, lehtpuude osakaal mustika kasvukohatüübi metsades, erilise võrakujuga puude hulk, rähnide tegevusjälgede esinemine ning negatiivse tunnusena jäi mudelisse Melampyrum praten¬sise ohtruse suurenemine. Alustaimestikku mõjutas majandamine kaudselt, eelkõige puistu vertikaalse struktuuri ja liigilise koosseisu kaudu. Valgus¬tingi¬musi kujundavate faktorite kompleks oli domineeriv alustaimestiku koos¬seisu muutuste selgitamisel kõige madalama ja kõrgema produktiivsusega kasvukohatüüpides. Optimaalsete valgustingimustega keskmise produktiivsusega pohla ja mustika kasvukohatüübis olid kõige olulisemateks alustaimestiku koosseisu määravateks tunnusteks kõdu- ja huumushorisondi paksus.
Eesti nõmme- ja palumetsades peab puistu tasandil pöörama rohkem tähelepanu surnud puidu, vanade puude ja lehtpuude säilitamisele. Alustaimestiku mitmekesisuse säilita¬miseks peab erinevates kasvukohatüüpides kasutama majandamis¬võtteid, mis suurendavad puistute ruumilist varieeruvust. Maastiku tasandil peab säilitama looduslike häiringute järgseid suktsessioonifaase.
The biodiversity of boreal forests has been reported to be increasingly endangered. The main reasons for this are related to the intensification of silvicultural practices and the loss of old-growth forests. One way to respond is to establish conservation areas and change manage¬ment practices in commercial forests to maintain or restore the elements characteristic to natural forests. In order to identify the degree of naturalness we need indicators. The purpose of current thesis is to define which structural and compositional characteristics of Estonian boreal forests are sensitive to forest management and useful as indicators. From compositional aspects we studied the effects of management on forest regeneration and field layer composition. Forest characteristics negatively affected by management were: number of large-diameter trees and diameter classes, the proportion of spruce and deciduous trees, the amount of dead wood of various decay stages, canopy closure and the coverage of lower canopy layers. Only a fraction of forest characteristics was statistically significant for predicting the naturalness of forests. The set of significant indicators were: the amount of standing dead wood, the proportion of deciduous trees in the Myrtillus site type, the presence of specially shaped trees, signs of woodpeckers and as negative indicator the abundance of herb Melampyrum pratense. Indirect forest management mainly affected tree regeneration and field layer composition through manipulated canopy structure and composition. Light conditions represented the dominant factor complex explaining the compositional variation of the field layer in site types with low and high productivity. Soil and ground layer were the most important determinants of field layer composition in site types of intermediate productivity. Sustainable forest management in Estonian boreal forests should focus at the stand scale on the maintenance of structural features like dead wood, old trees and deciduous tree species. To enhance the diversity of the field layer, management should be site type specific in diversifying stand structure. At the landscape scale, forest management should begin to emphasize the importance of successional phases after stand-replacing disturbances.
The biodiversity of boreal forests has been reported to be increasingly endangered. The main reasons for this are related to the intensification of silvicultural practices and the loss of old-growth forests. One way to respond is to establish conservation areas and change manage¬ment practices in commercial forests to maintain or restore the elements characteristic to natural forests. In order to identify the degree of naturalness we need indicators. The purpose of current thesis is to define which structural and compositional characteristics of Estonian boreal forests are sensitive to forest management and useful as indicators. From compositional aspects we studied the effects of management on forest regeneration and field layer composition. Forest characteristics negatively affected by management were: number of large-diameter trees and diameter classes, the proportion of spruce and deciduous trees, the amount of dead wood of various decay stages, canopy closure and the coverage of lower canopy layers. Only a fraction of forest characteristics was statistically significant for predicting the naturalness of forests. The set of significant indicators were: the amount of standing dead wood, the proportion of deciduous trees in the Myrtillus site type, the presence of specially shaped trees, signs of woodpeckers and as negative indicator the abundance of herb Melampyrum pratense. Indirect forest management mainly affected tree regeneration and field layer composition through manipulated canopy structure and composition. Light conditions represented the dominant factor complex explaining the compositional variation of the field layer in site types with low and high productivity. Soil and ground layer were the most important determinants of field layer composition in site types of intermediate productivity. Sustainable forest management in Estonian boreal forests should focus at the stand scale on the maintenance of structural features like dead wood, old trees and deciduous tree species. To enhance the diversity of the field layer, management should be site type specific in diversifying stand structure. At the landscape scale, forest management should begin to emphasize the importance of successional phases after stand-replacing disturbances.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
metsad, koosluste struktuur, metsamajandus, alustaimestu, liigirikkus, forests, community structure, forest economics, ground cover, species richness