{"id":{"repo_id":"ag-u-iceland","oai_identifier":"oai:skemman.is:1946/50562"},"canonical_url":"https://search.dev.ndltd.org/etd/ag-u-iceland/oai:skemman.is:1946/50562","repository":{"repo_id":"ag-u-iceland","name":"Agricultural University of Iceland","base_url":"https://skemman.is/oai/request"},"display":{"title":"Trapped? Evidence of changes in relative plant abundance after long-term grazing exclosure across the Tundra.","abstract":"Herbivores alter plant communities through the effects of selective grazing based on plant palatability. There has also been a perceived link between the relative palatability of plants and ecosystem functions. By changing the relative abundance of certain plant species, prolonged or intense grazing can affect ecosystem processes and lead to land degradation. Management interventions such as grazing exclusion can help an ecosystem recover from degraded states. However, a recent study from a degraded area in Iceland showed no significant change in plant community composition after decades of grazing cessation. This lack of response to the removal of the presumed driver of degradation could indicate the ecosystems being ‘trapped’ in a degraded state. Yet, we do not know how widespread this lack of response to long-term grazing exclusion is across the tundra biome. This thesis aims to review the current grazing literature to identify if similar situations are happening elsewhere in the tundra. I reviewed articles that experimentally excluded large and medium herbivores for ten or more years. The literature search yielded 12 articles; none of which mentioned previous degradation, making them unsuitable to assess whether the ecosystems were actually trapped in a degraded state. Moreover, the coarsest taxonomical resolution reported in the available literature was based on plant growth forms, which is too broad to characterise the plant communities in terms of their relative palatability to grazers. However, by assessing studies looking at change in relative abundance for the available growth form groups I found that most groups showed no changes after the exclosure period suggesting that gazing cessation does not necessarily impact the abundance of all growth form groups.","abstract_html":"Herbivores alter plant communities through the effects of selective grazing based on plant palatability. There has also been a perceived link between the relative palatability of plants and ecosystem functions. By changing the relative abundance of certain plant species, prolonged or intense grazing can affect ecosystem processes and lead to land degradation. Management interventions such as grazing exclusion can help an ecosystem recover from degraded states. However, a recent study from a degraded area in Iceland showed no significant change in plant community composition after decades of grazing cessation. This lack of response to the removal of the presumed driver of degradation could indicate the ecosystems being ‘trapped’ in a degraded state. Yet, we do not know how widespread this lack of response to long-term grazing exclusion is across the tundra biome. This thesis aims to review the current grazing literature to identify if similar situations are happening elsewhere in the tundra. I reviewed articles that experimentally excluded large and medium herbivores for ten or more years. The literature search yielded 12 articles; none of which mentioned previous degradation, making them unsuitable to assess whether the ecosystems were actually trapped in a degraded state. Moreover, the coarsest taxonomical resolution reported in the available literature was based on plant growth forms, which is too broad to characterise the plant communities in terms of their relative palatability to grazers. However, by assessing studies looking at change in relative abundance for the available growth form groups I found that most groups showed no changes after the exclosure period suggesting that gazing cessation does not necessarily impact the abundance of all growth form groups.","abstract_has_math":false,"creators":["Snæbjörn Helgi Arnarsson Jack 1996-"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Landbúnaðarháskóli Íslands"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-06-11T10:15:16Z","date_published":"2025-06-11T10:15:16Z","updated_at":"2026-07-27T18:42:25Z","subjects":["Náttúru- og umhverfisfræði","State-and-transition models","Land degradation","Plant growth form","Tundra","Grazing exclosure","Grazing ecology"],"languages":["en"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1946/50562","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Landbúnaðarháskóli Íslands"]},{"key":"dc:creator","label":"Author","values":["Snæbjörn Helgi Arnarsson Jack 1996-"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2025-06-11T10:15:15Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2025-06-11T10:15:15Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-06-11T10:15:16Z"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Náttúru- og umhverfisfræði","State-and-transition models","Land degradation","Plant growth form","Tundra","Grazing exclosure","Grazing ecology"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/1946/50562"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Herbivores alter plant communities through the effects of selective grazing based on plant palatability. There has also been a perceived link between the relative palatability of plants and ecosystem functions. By changing the relative abundance of certain plant species, prolonged or intense grazing can affect ecosystem processes and lead to land degradation. Management interventions such as grazing exclusion can help an ecosystem recover from degraded states. However, a recent study from a degraded area in Iceland showed no significant change in plant community composition after decades of grazing cessation. This lack of response to the removal of the presumed driver of degradation could indicate the ecosystems being ‘trapped’ in a degraded state. Yet, we do not know how widespread this lack of response to long-term grazing exclusion is across the tundra biome. This thesis aims to review the current grazing literature to identify if similar situations are happening elsewhere in the tundra. I reviewed articles that experimentally excluded large and medium herbivores for ten or more years. The literature search yielded 12 articles; none of which mentioned previous degradation, making them unsuitable to assess whether the ecosystems were actually trapped in a degraded state. Moreover, the coarsest taxonomical resolution reported in the available literature was based on plant growth forms, which is too broad to characterise the plant communities in terms of their relative palatability to grazers. However, by assessing studies looking at change in relative abundance for the available growth form groups I found that most groups showed no changes after the exclosure period suggesting that gazing cessation does not necessarily impact the abundance of all growth form groups.","Fæðuval jurtaæta ræðst af lostæti plantna og hefur þannig val dýranna á æti einkennandi áhrif á plöntusamfélög. Einnig má að gæta sambands hlutfallslegs lostætis plöntu og virkni hennar innan vistkerfa. Með því að breyta hlutfallslegri mergð ákveðinna plöntutegunda getur þannig þung eða langvarandi beit breytt vistkerfisstarfsemi svæðis og jafnvel leitt til landhnignunar. Aðgerðir beitarstýringar (t.d. beitarfriðun) geta hjálpað vistkerfum að ná bata eftir hnignun í virkni. Á Íslandi hafa hins vegar nýlegar rannsóknir sýnt að engar marktækar breytingar urðu á samsetningu plöntusamfélaga eftir áratugalanga beitarfriðun. Þetta viðbragðaleysi við fjarlægingu meints drifkrafts hnignunarinnar gæti bent til þess að vistkerfin sem um ræðir séu ‚föst‘ í hnignuðu ástandi. Ekki er þó vitað hversu útbreidd slík ‚fangavistkerfi‘ gætu leynst innan túndrunnar. Mitt verkefni er að taka saman heimildir sem lýsa svipuðum kringumstæðum í þeirri von að fleiri dæmi geti bætt skilning okkar á þessu vistkerfa fyrirbæri. Nánar tiltekið leitaði ég eftir tilraunum þar sem útilokun stórra og meðalstórra jurtaæta fór fram í áratug eða lengur. Leitin skilaði 12 greinum en engin þeirra minntist á fyrra ástand vistkerfanna sem hnignum. Það gerir greinarnar óhentugar til að meta hvort vistkerfin séu þá í raun föst í hnignuðu ástandi. Þar að auki var grófasta flokkunarfræðilega upplausn greinanna á plöntuvirknihópum byggða á vaxtarformum, sem eru of víðtækir hópar til að lýsa plöntusamfélögunum út frá lostætisstýrðri virkni. Þó með því að skoða breytingar á mergð þeirra eins og hægt var, komst ég að því að flestar samanburðarmælingar bentu til engra breytinga eftir beitarfriðunarskeiðið. Það bendir til þess að beitarfriðun hafi ekki endilega haft áhrif á mergð allra plöntuvirknihópanna."]},{"key":"dc:title","label":"Title","values":["Trapped? Evidence of changes in relative plant abundance after long-term grazing exclosure across the Tundra.","Festistu? Ummerki breytinga í mergð plantna eftir langtíma beitarfriðun í trúndrunni"]}]}],"canonical_facts":{"dc:contributor":["Landbúnaðarháskóli Íslands"],"dc:creator":["Snæbjörn Helgi Arnarsson Jack 1996-"],"dc:date.accessioned":["2025-06-11T10:15:15Z"],"dc:date.available":["2025-06-11T10:15:15Z"],"dc:date.issued":["2025-06-11T10:15:16Z"],"dc:description.abstract":["Herbivores alter plant communities through the effects of selective grazing based on plant palatability. There has also been a perceived link between the relative palatability of plants and ecosystem functions. By changing the relative abundance of certain plant species, prolonged or intense grazing can affect ecosystem processes and lead to land degradation. Management interventions such as grazing exclusion can help an ecosystem recover from degraded states. However, a recent study from a degraded area in Iceland showed no significant change in plant community composition after decades of grazing cessation. This lack of response to the removal of the presumed driver of degradation could indicate the ecosystems being ‘trapped’ in a degraded state. Yet, we do not know how widespread this lack of response to long-term grazing exclusion is across the tundra biome. This thesis aims to review the current grazing literature to identify if similar situations are happening elsewhere in the tundra. I reviewed articles that experimentally excluded large and medium herbivores for ten or more years. The literature search yielded 12 articles; none of which mentioned previous degradation, making them unsuitable to assess whether the ecosystems were actually trapped in a degraded state. Moreover, the coarsest taxonomical resolution reported in the available literature was based on plant growth forms, which is too broad to characterise the plant communities in terms of their relative palatability to grazers. However, by assessing studies looking at change in relative abundance for the available growth form groups I found that most groups showed no changes after the exclosure period suggesting that gazing cessation does not necessarily impact the abundance of all growth form groups.","Fæðuval jurtaæta ræðst af lostæti plantna og hefur þannig val dýranna á æti einkennandi áhrif á plöntusamfélög. Einnig má að gæta sambands hlutfallslegs lostætis plöntu og virkni hennar innan vistkerfa. Með því að breyta hlutfallslegri mergð ákveðinna plöntutegunda getur þannig þung eða langvarandi beit breytt vistkerfisstarfsemi svæðis og jafnvel leitt til landhnignunar. Aðgerðir beitarstýringar (t.d. beitarfriðun) geta hjálpað vistkerfum að ná bata eftir hnignun í virkni. Á Íslandi hafa hins vegar nýlegar rannsóknir sýnt að engar marktækar breytingar urðu á samsetningu plöntusamfélaga eftir áratugalanga beitarfriðun. Þetta viðbragðaleysi við fjarlægingu meints drifkrafts hnignunarinnar gæti bent til þess að vistkerfin sem um ræðir séu ‚föst‘ í hnignuðu ástandi. Ekki er þó vitað hversu útbreidd slík ‚fangavistkerfi‘ gætu leynst innan túndrunnar. Mitt verkefni er að taka saman heimildir sem lýsa svipuðum kringumstæðum í þeirri von að fleiri dæmi geti bætt skilning okkar á þessu vistkerfa fyrirbæri. Nánar tiltekið leitaði ég eftir tilraunum þar sem útilokun stórra og meðalstórra jurtaæta fór fram í áratug eða lengur. Leitin skilaði 12 greinum en engin þeirra minntist á fyrra ástand vistkerfanna sem hnignum. Það gerir greinarnar óhentugar til að meta hvort vistkerfin séu þá í raun föst í hnignuðu ástandi. Þar að auki var grófasta flokkunarfræðilega upplausn greinanna á plöntuvirknihópum byggða á vaxtarformum, sem eru of víðtækir hópar til að lýsa plöntusamfélögunum út frá lostætisstýrðri virkni. Þó með því að skoða breytingar á mergð þeirra eins og hægt var, komst ég að því að flestar samanburðarmælingar bentu til engra breytinga eftir beitarfriðunarskeiðið. Það bendir til þess að beitarfriðun hafi ekki endilega haft áhrif á mergð allra plöntuvirknihópanna."],"dc:identifier.uri":["https://hdl.handle.net/1946/50562"],"dc:language.iso":["en"],"dc:subject":["Náttúru- og umhverfisfræði","State-and-transition models","Land degradation","Plant growth form","Tundra","Grazing exclosure","Grazing ecology"],"dc:title":["Trapped? Evidence of changes in relative plant abundance after long-term grazing exclosure across the Tundra.","Festistu? Ummerki breytinga í mergð plantna eftir langtíma beitarfriðun í trúndrunni"],"dc:type":["Thesis"]},"updated_at":"2026-07-27T18:42:25Z"}