Environmental and demographic correlates of tree recruitment and mortality in north Australian savannas

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    Tropical savannas cover approximately 20% of the earth's land area, and therefore represent an important carbon store. Under scenarios of future climate change it is thus important to understand the demographic processes determining tree cover, namely tree recruitment, growth and mortality. This study measured tree recruitment and mortality in 123 (0.08 h) plots in Kakadu, Nitmiluk and Litchfield National Parks, in the Australian monsoonal tropics, over two consecutive 5-year intervals. Plots were located in two important habitats, both dominated by eucalyptus-lowland savanna and savanna growing on sandstone plateaux. All trees with diameter at breast height (DBH) ?5 cm were tagged and identified. Recruitment was calculated as the proportion of tagged trees present at the end of an interval that were not present at the beginning. There were a total of 6666 and 6571 tree-intervals for mortality and recruitment, respectively. We used Akaike Information Criterion (AIC)-based model selection and multi-model inference to relate tree mortality and recruitment to fire frequency, mean annual rainfall (MAR), stand basal area, tree density and eco-taxonomic group. Recruitment decreased with tree density in both savanna types, and in lowland savanna, with the frequency of fires. In sandstone savanna, recruitment increased with MAR. Effects of fire on recruitment were better explained by season than severity of fire, while fire severity had a stronger influence on mortality. Mortality decreased with tree size up to about 25 cm DBH, but increased sharply when DBH exceeded 50 cm. Mortality increased with stand basal area, and increased with the frequency of late dry season fires in lowland savanna only. There was little evidence that mortality was affected by the frequency of early dry season fires or MAR. Both recruitment and mortality rates were higher for Acacia and Proteaceae species than for pantropical or Myrtaceae (including Eucalyptus) species. We identified several negative feedbacks, mediated by changes in tree density and stand basal area that help confer long-term stability to savanna tree cover. Nonetheless, changes such as a long-term increase in MAR or an increase in frequency or severity of fires are likely to result in changes in tree density, stand basal area and therefore carbon storage potential of savannas. � 2008 Elsevier B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)66-74
    Number of pages9
    JournalForest Ecology and Management
    Volume257
    Issue number1
    Publication statusPublished - 2009

    Fingerprint

    savanna
    savannas
    demographic statistics
    mortality
    fire severity
    basal area
    tree and stand measurements
    rain
    lowlands
    rainfall
    sandstone
    Eucalyptus
    dry season
    Proteaceae
    tree mortality
    Myrtaceae
    stand density
    Akaike information criterion
    Acacia
    carbon sequestration

    Cite this

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    title = "Environmental and demographic correlates of tree recruitment and mortality in north Australian savannas",
    abstract = "Tropical savannas cover approximately 20{\%} of the earth's land area, and therefore represent an important carbon store. Under scenarios of future climate change it is thus important to understand the demographic processes determining tree cover, namely tree recruitment, growth and mortality. This study measured tree recruitment and mortality in 123 (0.08 h) plots in Kakadu, Nitmiluk and Litchfield National Parks, in the Australian monsoonal tropics, over two consecutive 5-year intervals. Plots were located in two important habitats, both dominated by eucalyptus-lowland savanna and savanna growing on sandstone plateaux. All trees with diameter at breast height (DBH) ?5 cm were tagged and identified. Recruitment was calculated as the proportion of tagged trees present at the end of an interval that were not present at the beginning. There were a total of 6666 and 6571 tree-intervals for mortality and recruitment, respectively. We used Akaike Information Criterion (AIC)-based model selection and multi-model inference to relate tree mortality and recruitment to fire frequency, mean annual rainfall (MAR), stand basal area, tree density and eco-taxonomic group. Recruitment decreased with tree density in both savanna types, and in lowland savanna, with the frequency of fires. In sandstone savanna, recruitment increased with MAR. Effects of fire on recruitment were better explained by season than severity of fire, while fire severity had a stronger influence on mortality. Mortality decreased with tree size up to about 25 cm DBH, but increased sharply when DBH exceeded 50 cm. Mortality increased with stand basal area, and increased with the frequency of late dry season fires in lowland savanna only. There was little evidence that mortality was affected by the frequency of early dry season fires or MAR. Both recruitment and mortality rates were higher for Acacia and Proteaceae species than for pantropical or Myrtaceae (including Eucalyptus) species. We identified several negative feedbacks, mediated by changes in tree density and stand basal area that help confer long-term stability to savanna tree cover. Nonetheless, changes such as a long-term increase in MAR or an increase in frequency or severity of fires are likely to result in changes in tree density, stand basal area and therefore carbon storage potential of savannas. � 2008 Elsevier B.V. All rights reserved.",
    keywords = "Climate change, Climatology, Control theory, Curing, Disasters, Drought, Employment, Feedback, Fires, Parks, Patient monitoring, Sandstone, Fire ecology, Fire frequency, Mesic savanna, Season of fire, Stand basal area, Tree survival, Forestry, carbon sequestration, demographic trend, ecosystem modeling, forest fire, lowland environment, mortality, recruitment (population dynamics), savanna, survival, Carbon, Ecology, Growth, Meteorology, Pollution Control, Trees, Australasia, Australia, Kakadu National Park, Litchfield National Park, Nitmiluk National Park, Northern Territory, Acacia, Eucalyptus, Myrtaceae, Proteaceae",
    author = "Lynda Prior and Brett Murphy and Jeremy Russell-Smith",
    year = "2009",
    language = "English",
    volume = "257",
    pages = "66--74",
    journal = "Forest Ecology and Management",
    issn = "0378-1127",
    publisher = "Elsevier",
    number = "1",

    }

    Environmental and demographic correlates of tree recruitment and mortality in north Australian savannas. / Prior, Lynda; Murphy, Brett; Russell-Smith, Jeremy.

    In: Forest Ecology and Management, Vol. 257, No. 1, 2009, p. 66-74.

    Research output: Contribution to journalArticleResearchpeer-review

    TY - JOUR

    T1 - Environmental and demographic correlates of tree recruitment and mortality in north Australian savannas

    AU - Prior, Lynda

    AU - Murphy, Brett

    AU - Russell-Smith, Jeremy

    PY - 2009

    Y1 - 2009

    N2 - Tropical savannas cover approximately 20% of the earth's land area, and therefore represent an important carbon store. Under scenarios of future climate change it is thus important to understand the demographic processes determining tree cover, namely tree recruitment, growth and mortality. This study measured tree recruitment and mortality in 123 (0.08 h) plots in Kakadu, Nitmiluk and Litchfield National Parks, in the Australian monsoonal tropics, over two consecutive 5-year intervals. Plots were located in two important habitats, both dominated by eucalyptus-lowland savanna and savanna growing on sandstone plateaux. All trees with diameter at breast height (DBH) ?5 cm were tagged and identified. Recruitment was calculated as the proportion of tagged trees present at the end of an interval that were not present at the beginning. There were a total of 6666 and 6571 tree-intervals for mortality and recruitment, respectively. We used Akaike Information Criterion (AIC)-based model selection and multi-model inference to relate tree mortality and recruitment to fire frequency, mean annual rainfall (MAR), stand basal area, tree density and eco-taxonomic group. Recruitment decreased with tree density in both savanna types, and in lowland savanna, with the frequency of fires. In sandstone savanna, recruitment increased with MAR. Effects of fire on recruitment were better explained by season than severity of fire, while fire severity had a stronger influence on mortality. Mortality decreased with tree size up to about 25 cm DBH, but increased sharply when DBH exceeded 50 cm. Mortality increased with stand basal area, and increased with the frequency of late dry season fires in lowland savanna only. There was little evidence that mortality was affected by the frequency of early dry season fires or MAR. Both recruitment and mortality rates were higher for Acacia and Proteaceae species than for pantropical or Myrtaceae (including Eucalyptus) species. We identified several negative feedbacks, mediated by changes in tree density and stand basal area that help confer long-term stability to savanna tree cover. Nonetheless, changes such as a long-term increase in MAR or an increase in frequency or severity of fires are likely to result in changes in tree density, stand basal area and therefore carbon storage potential of savannas. � 2008 Elsevier B.V. All rights reserved.

    AB - Tropical savannas cover approximately 20% of the earth's land area, and therefore represent an important carbon store. Under scenarios of future climate change it is thus important to understand the demographic processes determining tree cover, namely tree recruitment, growth and mortality. This study measured tree recruitment and mortality in 123 (0.08 h) plots in Kakadu, Nitmiluk and Litchfield National Parks, in the Australian monsoonal tropics, over two consecutive 5-year intervals. Plots were located in two important habitats, both dominated by eucalyptus-lowland savanna and savanna growing on sandstone plateaux. All trees with diameter at breast height (DBH) ?5 cm were tagged and identified. Recruitment was calculated as the proportion of tagged trees present at the end of an interval that were not present at the beginning. There were a total of 6666 and 6571 tree-intervals for mortality and recruitment, respectively. We used Akaike Information Criterion (AIC)-based model selection and multi-model inference to relate tree mortality and recruitment to fire frequency, mean annual rainfall (MAR), stand basal area, tree density and eco-taxonomic group. Recruitment decreased with tree density in both savanna types, and in lowland savanna, with the frequency of fires. In sandstone savanna, recruitment increased with MAR. Effects of fire on recruitment were better explained by season than severity of fire, while fire severity had a stronger influence on mortality. Mortality decreased with tree size up to about 25 cm DBH, but increased sharply when DBH exceeded 50 cm. Mortality increased with stand basal area, and increased with the frequency of late dry season fires in lowland savanna only. There was little evidence that mortality was affected by the frequency of early dry season fires or MAR. Both recruitment and mortality rates were higher for Acacia and Proteaceae species than for pantropical or Myrtaceae (including Eucalyptus) species. We identified several negative feedbacks, mediated by changes in tree density and stand basal area that help confer long-term stability to savanna tree cover. Nonetheless, changes such as a long-term increase in MAR or an increase in frequency or severity of fires are likely to result in changes in tree density, stand basal area and therefore carbon storage potential of savannas. � 2008 Elsevier B.V. All rights reserved.

    KW - Climate change

    KW - Climatology

    KW - Control theory

    KW - Curing

    KW - Disasters

    KW - Drought

    KW - Employment

    KW - Feedback

    KW - Fires

    KW - Parks

    KW - Patient monitoring

    KW - Sandstone

    KW - Fire ecology

    KW - Fire frequency

    KW - Mesic savanna

    KW - Season of fire

    KW - Stand basal area

    KW - Tree survival

    KW - Forestry

    KW - carbon sequestration

    KW - demographic trend

    KW - ecosystem modeling

    KW - forest fire

    KW - lowland environment

    KW - mortality

    KW - recruitment (population dynamics)

    KW - savanna

    KW - survival

    KW - Carbon

    KW - Ecology

    KW - Growth

    KW - Meteorology

    KW - Pollution Control

    KW - Trees

    KW - Australasia

    KW - Australia

    KW - Kakadu National Park

    KW - Litchfield National Park

    KW - Nitmiluk National Park

    KW - Northern Territory

    KW - Acacia

    KW - Eucalyptus

    KW - Myrtaceae

    KW - Proteaceae

    M3 - Article

    VL - 257

    SP - 66

    EP - 74

    JO - Forest Ecology and Management

    JF - Forest Ecology and Management

    SN - 0378-1127

    IS - 1

    ER -