Growth of juvenile and sapling trees differs with both fire season and understorey type

Trade-offs and transitions out of the fire trap in an Australian savanna

Pat Werner

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    Canopy tree populations in mesic savannas are often bimodal with few saplings but many smaller individuals of indeterminate age that repeatedly suffer topkill and regenerate from underground tissues. Little is known about growth rates or mechanisms that allow subadult trees to reach the canopy. The wooded savannas of northern Australia have high frequencies of dry-season fires. In a 32400-m 2 field experiment, 2405 juveniles (<150-cm height) and saplings (150-499cm) of the eucalypt canopy species were individually marked and measured the year prior to fires set in three different seasons and again at the end of the growing season (without fires) a year later. Trees in unburnt plots served as controls. All fire treatments were repeated in plots dominated by the most common understorey, a native annual grass (sorghum) and in plots dominated by perennial native species; these produce different fuels for fires and competitive regimes for young trees. After early dry-season fires, height growth of larger juveniles and all saplings was significantly enhanced, especially in sorghum. After late dry- or wet-season fires, juvenile trees grew well, but all of the small saplings (150- to 299-cm height) were reduced to 'juveniles' and did not recover pre-fire heights but, instead, produced many new basal (coppice) stems. Late, dry-season fires reduced more than 80% of large saplings (300-499cm) to juvenile size in sorghum, whereas in non-sorghum, 60% of the trees grew to poles (500-999cm). The results demonstrate that juvenile and sapling growth responses to fire and the probability of subadult trees reaching the canopy are related to fire-understorey interactions, and suggest that the mechanisms include morphological and carbohydrate storage dynamics which vary with tree size and life history stage. The key to successful management of a sustainable woody canopy lies in the understorey.

    Original languageEnglish
    Pages (from-to)644-657
    Number of pages14
    JournalAustral Ecology
    Volume37
    Issue number6
    Early online date9 Dec 2011
    DOIs
    Publication statusPublished - Sep 2012

    Fingerprint

    fire season
    sapling
    saplings
    savanna
    understory
    savannas
    traps
    canopy
    dry season
    sorghum
    Sorghum (Poaceae)
    coppice
    growth response
    wet season
    native species
    carbohydrate
    indigenous species
    life history
    growing season

    Cite this

    @article{902927f763134662a09cb2272f45ebac,
    title = "Growth of juvenile and sapling trees differs with both fire season and understorey type: Trade-offs and transitions out of the fire trap in an Australian savanna",
    abstract = "Canopy tree populations in mesic savannas are often bimodal with few saplings but many smaller individuals of indeterminate age that repeatedly suffer topkill and regenerate from underground tissues. Little is known about growth rates or mechanisms that allow subadult trees to reach the canopy. The wooded savannas of northern Australia have high frequencies of dry-season fires. In a 32400-m 2 field experiment, 2405 juveniles (<150-cm height) and saplings (150-499cm) of the eucalypt canopy species were individually marked and measured the year prior to fires set in three different seasons and again at the end of the growing season (without fires) a year later. Trees in unburnt plots served as controls. All fire treatments were repeated in plots dominated by the most common understorey, a native annual grass (sorghum) and in plots dominated by perennial native species; these produce different fuels for fires and competitive regimes for young trees. After early dry-season fires, height growth of larger juveniles and all saplings was significantly enhanced, especially in sorghum. After late dry- or wet-season fires, juvenile trees grew well, but all of the small saplings (150- to 299-cm height) were reduced to 'juveniles' and did not recover pre-fire heights but, instead, produced many new basal (coppice) stems. Late, dry-season fires reduced more than 80{\%} of large saplings (300-499cm) to juvenile size in sorghum, whereas in non-sorghum, 60{\%} of the trees grew to poles (500-999cm). The results demonstrate that juvenile and sapling growth responses to fire and the probability of subadult trees reaching the canopy are related to fire-understorey interactions, and suggest that the mechanisms include morphological and carbohydrate storage dynamics which vary with tree size and life history stage. The key to successful management of a sustainable woody canopy lies in the understorey.",
    keywords = "carbohydrate, coniferous forest, fire behavior, forest canopy, forest management, growth rate, growth response, juvenile, morphology, native species, population dynamics, sapling, savanna, sorghum, trade-off, understory, woodland, Australia, Eucalyptus",
    author = "Pat Werner",
    year = "2012",
    month = "9",
    doi = "10.1111/j.1442-9993.2011.02333.x",
    language = "English",
    volume = "37",
    pages = "644--657",
    journal = "Australian Journal of Ecology",
    issn = "1442-9985",
    publisher = "Blackwell Publishing",
    number = "6",

    }

    Growth of juvenile and sapling trees differs with both fire season and understorey type : Trade-offs and transitions out of the fire trap in an Australian savanna. / Werner, Pat.

    In: Austral Ecology, Vol. 37, No. 6, 09.2012, p. 644-657.

    Research output: Contribution to journalArticleResearchpeer-review

    TY - JOUR

    T1 - Growth of juvenile and sapling trees differs with both fire season and understorey type

    T2 - Trade-offs and transitions out of the fire trap in an Australian savanna

    AU - Werner, Pat

    PY - 2012/9

    Y1 - 2012/9

    N2 - Canopy tree populations in mesic savannas are often bimodal with few saplings but many smaller individuals of indeterminate age that repeatedly suffer topkill and regenerate from underground tissues. Little is known about growth rates or mechanisms that allow subadult trees to reach the canopy. The wooded savannas of northern Australia have high frequencies of dry-season fires. In a 32400-m 2 field experiment, 2405 juveniles (<150-cm height) and saplings (150-499cm) of the eucalypt canopy species were individually marked and measured the year prior to fires set in three different seasons and again at the end of the growing season (without fires) a year later. Trees in unburnt plots served as controls. All fire treatments were repeated in plots dominated by the most common understorey, a native annual grass (sorghum) and in plots dominated by perennial native species; these produce different fuels for fires and competitive regimes for young trees. After early dry-season fires, height growth of larger juveniles and all saplings was significantly enhanced, especially in sorghum. After late dry- or wet-season fires, juvenile trees grew well, but all of the small saplings (150- to 299-cm height) were reduced to 'juveniles' and did not recover pre-fire heights but, instead, produced many new basal (coppice) stems. Late, dry-season fires reduced more than 80% of large saplings (300-499cm) to juvenile size in sorghum, whereas in non-sorghum, 60% of the trees grew to poles (500-999cm). The results demonstrate that juvenile and sapling growth responses to fire and the probability of subadult trees reaching the canopy are related to fire-understorey interactions, and suggest that the mechanisms include morphological and carbohydrate storage dynamics which vary with tree size and life history stage. The key to successful management of a sustainable woody canopy lies in the understorey.

    AB - Canopy tree populations in mesic savannas are often bimodal with few saplings but many smaller individuals of indeterminate age that repeatedly suffer topkill and regenerate from underground tissues. Little is known about growth rates or mechanisms that allow subadult trees to reach the canopy. The wooded savannas of northern Australia have high frequencies of dry-season fires. In a 32400-m 2 field experiment, 2405 juveniles (<150-cm height) and saplings (150-499cm) of the eucalypt canopy species were individually marked and measured the year prior to fires set in three different seasons and again at the end of the growing season (without fires) a year later. Trees in unburnt plots served as controls. All fire treatments were repeated in plots dominated by the most common understorey, a native annual grass (sorghum) and in plots dominated by perennial native species; these produce different fuels for fires and competitive regimes for young trees. After early dry-season fires, height growth of larger juveniles and all saplings was significantly enhanced, especially in sorghum. After late dry- or wet-season fires, juvenile trees grew well, but all of the small saplings (150- to 299-cm height) were reduced to 'juveniles' and did not recover pre-fire heights but, instead, produced many new basal (coppice) stems. Late, dry-season fires reduced more than 80% of large saplings (300-499cm) to juvenile size in sorghum, whereas in non-sorghum, 60% of the trees grew to poles (500-999cm). The results demonstrate that juvenile and sapling growth responses to fire and the probability of subadult trees reaching the canopy are related to fire-understorey interactions, and suggest that the mechanisms include morphological and carbohydrate storage dynamics which vary with tree size and life history stage. The key to successful management of a sustainable woody canopy lies in the understorey.

    KW - carbohydrate

    KW - coniferous forest

    KW - fire behavior

    KW - forest canopy

    KW - forest management

    KW - growth rate

    KW - growth response

    KW - juvenile

    KW - morphology

    KW - native species

    KW - population dynamics

    KW - sapling

    KW - savanna

    KW - sorghum

    KW - trade-off

    KW - understory

    KW - woodland

    KW - Australia

    KW - Eucalyptus

    UR - http://www.scopus.com/inward/record.url?scp=84865599483&partnerID=8YFLogxK

    U2 - 10.1111/j.1442-9993.2011.02333.x

    DO - 10.1111/j.1442-9993.2011.02333.x

    M3 - Article

    VL - 37

    SP - 644

    EP - 657

    JO - Australian Journal of Ecology

    JF - Australian Journal of Ecology

    SN - 1442-9985

    IS - 6

    ER -