Monitoring and evaluation of forest ecosystem restoration
Laen...
Kuupäev
2014
Kättesaadav alates
Autorid
Laarmann, Diana
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Eesti Maaülikool
Abstrakt
Doktoritöö käsitleb metsaökosüsteemide taastamist Eestis, hõlmates nii kaevandamisega rikutud alade taasmetsastamist kui ka loodusmetsade struktuurikomponentide tekitamist madala loodusväärtusega aladele ning aladele, kus loodusliku taastumise protsess on aeglane. Intensiivne metsade majandamine on põhjustanud metsade struktuuri ja liigilise koosseisu lihtsustumist ning muutnud looduslike häiringute dünaamikat. Metsi oskuslikult majandades saab vähendada majandamisvõtete negatiivset mõju elurikkusele ja säilitada metsaökosüsteemide looduslikke funktsioone. Samuti tuleks eelkõige kaitsealustes metsades jälgida ja taastada metsade looduslikku funktsionaalsust. Ökoloogilise taastamise eesmärk on kiirendada muudetud, rikutud või hävitatud ökosüsteemides loodusliku taastumise protsesse. Doktoritöös käsitletakse ja analüüsitakse metsade taastamise erinevaid aspekte ja komponente ning otsesteks eesmärkideks on: a) uurida puistute looduslikkuse indikaatoreid ning hinnata puistute looduslikkust, b) määrata puistus üksikpuu suremist mõjutavad faktorid, c) analüüsida looduslikkuse taastamise võtete mõju puistu dünaamikale ja elurikkusele, d) analüüsida kaevandamisjärgsel taasmetsastamisel tekkinud ökosüsteemi. Püstitatud eesmärkide täitmiseks viidi läbi välitööd kokku 640 püsiproovitükil. Doktoritöös leiti, et surnud puidu kogus, surnud puude ruumiline paiknemine puistus, samuti suremise kiirus ja põhjused on tihedas seoses puistu looduslikkusega. Surnud puidu maht looduslikus seisundis ja majandatud metsas erinevad üksteisest oluliselt. Puude suremise hindamine võimaldab paremini aru saada metsaökosüsteemi struktuurist ja seal toimivatest protsessidest. Puu ellujäämine sõltub puu suhtelisest suurusest puistus ning puude suremise põhjused erinevat tüüpi puistutes on erinevad. Suremise põhjuste mitmekesisus on suurem looduslikus seisundis puistutes ning samuti on surnud puude paiknemine sellises puistus rohkem hajutatud. Töös väljatöötatud indeksid pakuvad võimalusi paremini hinnata puistu looduslikkust ja seejuures eristada puistus toimunud hiljutisi häiringuid. Looduslikkuse taastamise võtted olid läbi viidud ühetaolistes keskealistes okaspuupuistutes, kus peale taastamisvõtete tegemist puistustruktuur mitmekesistus, näiteks surnud puidu maht suurenes lagupuidu tekitamise võtte korral kuni 67 m3 ha-1. Loodusliku uuenduse arvukus oli kõrgeim pindalalt suuremas häilus ning ülepõletatud häilu korral. Taastamisvõtted avaldasid erinevatele liigirühmadele erinevat mõju: rohttaimede mitmekesisus suurenes enim ülepõletatud häilu korral, sammalde mitmekesisus lagupuidu tekitamise korral, samblike mitmekesisus suurenes enim häilu tekitamisel, ülepõletatud häilu korral mitmekesisus aga vähenes. Kontrollaladest eristus kõige rohkem rohttaimede, sammalde ja samblike puhul häilu ülepõletamise võte. Mardikaliste suurenenud arvukus ja liigiline mitmekesisus on puistu valgustingimuste muutuse ning elupaikade lisandumise otsene tulemus. Võrreldes ühe taastamisvõtte rakendamisega suurendab erinevate taastamisvõtete üheaegne kasutamine puistu heterogeensust ja tänu sellele suureneb ka elurikkus. Kaevandamisjärgse taasmetsastamise eesmärk on taastada ökosüsteemide kaevandamiseelne olukord. Üldjuhul on võimatu taastada minevikus olnud seisundit, sest kaevandamisega on kasvupinnast täielikult muudetud ning tihtipeale areneb seal välja hoopis uudne ökosüsteem. Taastamisedukuse hindamine põhineb mullanäitajate dünaamika, liigilise mitmekesisuse, taimkatte struktuuri ja ökoloogiliste protsesside uurimisel. Endise kaevandamisala mullad erinesid tüüpilistest metsamuldadest ja seetõttu on seal taimestiku arenguks tekkinud teistsugused tingimused. Samuti erinesid sealsed taimekooslused tüüpilistest metsas esinevatest kooslustest. Puistu takseernäitajad olid sarnaseimad sinilille kasvukohatüübi puistute takseernäitajatega. Ala looduslikule arengule jätmine võib taastamisel olla oluline alternatiiv metsaistutamisele, eriti juhul, kui rikutud ala on väike ja ümbritsetud loodusliku taimkattega ning kui alale pole määratud soovitavat eesmärki ning taastumise tähtaega.
This thesis synthesizes several studies of forest ecosystem restoration in Estonia, including afforestation on abandoned oil-shale mining areas and initiating natural processes and fostering natural structures and species composition. Silvicultural systems for timber production have caused changes in ecosystem structure and function associated with anthropogenic alterations of natural disturbance regimes. Increasingly, forest management is based on understanding of processes of natural disturbances, their effects for stand and landscape composition and structure, considering that this enables managers to reduce the negative impacts of timber harvest on biodiversity and thereafter maintain ecological functions. Restoration is activity which can improve conservation efforts in protected areas in order to enhance quality and quantity, to improve connectivity between fragmented areas and create buffer zones between protected and managed forest areas. The objective of ecological restoration is to re-create a self-supporting ecosystem which existed previously and is resilient to contingent damage and to maintain the system in a desirable state or moving away from an undesirable state. The aims of the thesis are: a) to develop naturalness and structural indicators in forest ecosystems; b) to analyze the effects of restoration treatments for biodiversity and stand development in managed forest ecosystems; c) to analyze the success of reclamation on post-mining restoration site; d) to determine factors influencing tree survival/mortality in forest stands. This thesis based on 640 permanent sample plots all over Estonia. Based on the results of this thesis, deadwood quantity and spatial distribution as well as tree mortality rate and causes are reliable indicators of forest naturalness. Deadwood mingling index and diversity index of mortality reasons as new proposed variables improve the assessment of forest naturalness and clarify the effects of recent disturbances. Tree mortality in a stand is caused by specific agents or by the complex effect of several mortality agents and it is different in semi-natural and managed forest. Determining the cause for a tree death is often difficult; therefore it is sensible to use a process-based multiple-reason method for determining the factors of mortality for a single tree. Survival probability of a tree is dependent on the specific mortality agent and relative size of the tree in a stand. Restoration pre-treatment stands are often homogeneous even-aged monocultures on fertile sites; rehabilitation treatments (gap cuttings, overburning and addition of deadwood) increase their structural heterogeneity and promote differentiation of microclimatic conditions and therefore species richness and abundance increase after treatments. In a gap treatment, the ratio between the gap diameter and the surrounding stand height determines the light availability inside the gap; the larger this ratio is, the greater likelihood of seedling recruitment and successful establishment of light demanding species. Species groups respond differently to treatments: understory vegetation diversity increases in gaps with burning, lichen diversity in gaps without burning, and bryophyte diversity with the addition of dead wood. Increased beetle abundance and greater species diversity is a direct effect of changed light conditions inside the canopy. Gaps with overburning have the greatest recruitment of tree seedlings. Multiple treatments create stand heterogeneity and can increase biodiversity more than one homogenous application of a single treatment. It is not possible to restore historical or natural ecosystems on reclaimed mined areas by simple afforestation. Soil formation and properties and the vegetation on reclaimed sites is different from soils and vegetation on common forest sites, hence this leads to development of novel ecosystems. Spontaneous succession should be considered in forest restoration as an alternative to afforestation practice, especially if reclamation sites are small, surrounded by natural vegetation, and there is no specific production goal or time limit for restoration.
This thesis synthesizes several studies of forest ecosystem restoration in Estonia, including afforestation on abandoned oil-shale mining areas and initiating natural processes and fostering natural structures and species composition. Silvicultural systems for timber production have caused changes in ecosystem structure and function associated with anthropogenic alterations of natural disturbance regimes. Increasingly, forest management is based on understanding of processes of natural disturbances, their effects for stand and landscape composition and structure, considering that this enables managers to reduce the negative impacts of timber harvest on biodiversity and thereafter maintain ecological functions. Restoration is activity which can improve conservation efforts in protected areas in order to enhance quality and quantity, to improve connectivity between fragmented areas and create buffer zones between protected and managed forest areas. The objective of ecological restoration is to re-create a self-supporting ecosystem which existed previously and is resilient to contingent damage and to maintain the system in a desirable state or moving away from an undesirable state. The aims of the thesis are: a) to develop naturalness and structural indicators in forest ecosystems; b) to analyze the effects of restoration treatments for biodiversity and stand development in managed forest ecosystems; c) to analyze the success of reclamation on post-mining restoration site; d) to determine factors influencing tree survival/mortality in forest stands. This thesis based on 640 permanent sample plots all over Estonia. Based on the results of this thesis, deadwood quantity and spatial distribution as well as tree mortality rate and causes are reliable indicators of forest naturalness. Deadwood mingling index and diversity index of mortality reasons as new proposed variables improve the assessment of forest naturalness and clarify the effects of recent disturbances. Tree mortality in a stand is caused by specific agents or by the complex effect of several mortality agents and it is different in semi-natural and managed forest. Determining the cause for a tree death is often difficult; therefore it is sensible to use a process-based multiple-reason method for determining the factors of mortality for a single tree. Survival probability of a tree is dependent on the specific mortality agent and relative size of the tree in a stand. Restoration pre-treatment stands are often homogeneous even-aged monocultures on fertile sites; rehabilitation treatments (gap cuttings, overburning and addition of deadwood) increase their structural heterogeneity and promote differentiation of microclimatic conditions and therefore species richness and abundance increase after treatments. In a gap treatment, the ratio between the gap diameter and the surrounding stand height determines the light availability inside the gap; the larger this ratio is, the greater likelihood of seedling recruitment and successful establishment of light demanding species. Species groups respond differently to treatments: understory vegetation diversity increases in gaps with burning, lichen diversity in gaps without burning, and bryophyte diversity with the addition of dead wood. Increased beetle abundance and greater species diversity is a direct effect of changed light conditions inside the canopy. Gaps with overburning have the greatest recruitment of tree seedlings. Multiple treatments create stand heterogeneity and can increase biodiversity more than one homogenous application of a single treatment. It is not possible to restore historical or natural ecosystems on reclaimed mined areas by simple afforestation. Soil formation and properties and the vegetation on reclaimed sites is different from soils and vegetation on common forest sites, hence this leads to development of novel ecosystems. Spontaneous succession should be considered in forest restoration as an alternative to afforestation practice, especially if reclamation sites are small, surrounded by natural vegetation, and there is no specific production goal or time limit for restoration.
Kirjeldus
A Thesis for applying for the degree of Doctor of Philosophy in Forestry
Märksõnad
metsamajandus, metsakasutus, metsaökosüsteemid, seire, metsauuendus, metsakasvatus, Eesti, dissertatsioonid, forestry, forest utilization, forest ecosystems, monitoring, silviculture, Estonia, dissertations