Did historical tree removal promote woody plant encroachment in Australian woodlands?

Karen Ross, Ian Lunt, Ross A. Bradstock, Michael Bedward, Murray V. Ellis

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Question: Woody plants have increased in density in many ecosystems, but the factors promoting encroachment are often debated. Since European colonization, Callitris glaucophylla has recruited abundantly in many Eucalyptus-Callitris woodlands in eastern Australia following changes to disturbance regimes analogous to changes in many other ecosystems globally. We used a dynamic stand model to disentangle effects of disturbances on Callitris encroachment and asked, to what extent was Callitris encroachment enhanced by historical removal of pre-settlement trees and subsequent thinning of regrowth? Location: Woodlands dominated by Eucalyptus species and Callitris glaucophylla, which originally occupied approximately 100,000 km2 in eastern Australia. Methods: We used a process-driven stand simulation model to simulate tree demography, with growth, survival and recruitment mediated by annual rainfall, competition and disturbance. Following parameter calibration and model testing, we orthogonally manipulated historical removal of pre-settlement trees and thinning of regrowth to identify how both processes may have influenced structural changes over 120 years of European settlement.Results: Removal of pre-settlement trees had little effect on modelled encroachment, as trees increased to comparable densities whether pre-settlement trees were retained or removed. In unthinned scenarios, Callitris regeneration formed 'locked' stands of high density but low basal area.Thinning promoted growth of retained Callitris, increased total stand basal area, and together with direct removal of large pre-settlement Eucalyptus and thinning of Eucalyptus regrowth, transformed stands from Eucalyptus to Callitris dominance.Conclusions: Removal of pre-settlement trees does not appear to have been a necessary precursor to modelled encroachment in Eucalyptus-Callitris woodlands in eastern Australia, perhaps because initial tree cover was low and Callitris can regenerate beneath isolated trees. Manual thinning was required to effect major structural change because Callitris self-thins extremely slowly; thinning will be less important in other ecosystems that self-thin more rapidly. More generally, the impact of historical tree removal on encroachment is likely to vary according to initial tree cover, with greatest impacts in dense ecosystems with high tree cover. These results highlight the value of simulation models for disentangling the effects of multiple disturbances on tree encroachment and other ecosystem dynamics.
Original languageEnglish
Pages (from-to)304-312
Number of pages9
JournalJournal of Vegetation Science
Volume23
Issue number2
DOIs
Publication statusPublished - Apr 2012

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Callitris
woody plant
woody plants
woodlands
woodland
thinning (plants)
Eucalyptus
thinning
Callitris glaucophylla
regrowth
ecosystems
disturbance
ecosystem
basal area
structural change
removal
simulation models
stand dynamics
ecosystem dynamics
demography

Cite this

Ross, Karen ; Lunt, Ian ; Bradstock, Ross A. ; Bedward, Michael ; Ellis, Murray V. / Did historical tree removal promote woody plant encroachment in Australian woodlands?. In: Journal of Vegetation Science. 2012 ; Vol. 23, No. 2. pp. 304-312.
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title = "Did historical tree removal promote woody plant encroachment in Australian woodlands?",
abstract = "Question: Woody plants have increased in density in many ecosystems, but the factors promoting encroachment are often debated. Since European colonization, Callitris glaucophylla has recruited abundantly in many Eucalyptus-Callitris woodlands in eastern Australia following changes to disturbance regimes analogous to changes in many other ecosystems globally. We used a dynamic stand model to disentangle effects of disturbances on Callitris encroachment and asked, to what extent was Callitris encroachment enhanced by historical removal of pre-settlement trees and subsequent thinning of regrowth? Location: Woodlands dominated by Eucalyptus species and Callitris glaucophylla, which originally occupied approximately 100,000 km2 in eastern Australia. Methods: We used a process-driven stand simulation model to simulate tree demography, with growth, survival and recruitment mediated by annual rainfall, competition and disturbance. Following parameter calibration and model testing, we orthogonally manipulated historical removal of pre-settlement trees and thinning of regrowth to identify how both processes may have influenced structural changes over 120 years of European settlement.Results: Removal of pre-settlement trees had little effect on modelled encroachment, as trees increased to comparable densities whether pre-settlement trees were retained or removed. In unthinned scenarios, Callitris regeneration formed 'locked' stands of high density but low basal area.Thinning promoted growth of retained Callitris, increased total stand basal area, and together with direct removal of large pre-settlement Eucalyptus and thinning of Eucalyptus regrowth, transformed stands from Eucalyptus to Callitris dominance.Conclusions: Removal of pre-settlement trees does not appear to have been a necessary precursor to modelled encroachment in Eucalyptus-Callitris woodlands in eastern Australia, perhaps because initial tree cover was low and Callitris can regenerate beneath isolated trees. Manual thinning was required to effect major structural change because Callitris self-thins extremely slowly; thinning will be less important in other ecosystems that self-thin more rapidly. More generally, the impact of historical tree removal on encroachment is likely to vary according to initial tree cover, with greatest impacts in dense ecosystems with high tree cover. These results highlight the value of simulation models for disentangling the effects of multiple disturbances on tree encroachment and other ecosystem dynamics.",
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Did historical tree removal promote woody plant encroachment in Australian woodlands? / Ross, Karen; Lunt, Ian; Bradstock, Ross A.; Bedward, Michael; Ellis, Murray V.

In: Journal of Vegetation Science, Vol. 23, No. 2, 04.2012, p. 304-312.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Did historical tree removal promote woody plant encroachment in Australian woodlands?

AU - Ross, Karen

AU - Lunt, Ian

AU - Bradstock, Ross A.

AU - Bedward, Michael

AU - Ellis, Murray V.

N1 - Imported on 12 Apr 2017 - DigiTool details were: month (773h) = April; Journal title (773t) = Journal of Vegetation Science. ISSNs: 1654-1103;

PY - 2012/4

Y1 - 2012/4

N2 - Question: Woody plants have increased in density in many ecosystems, but the factors promoting encroachment are often debated. Since European colonization, Callitris glaucophylla has recruited abundantly in many Eucalyptus-Callitris woodlands in eastern Australia following changes to disturbance regimes analogous to changes in many other ecosystems globally. We used a dynamic stand model to disentangle effects of disturbances on Callitris encroachment and asked, to what extent was Callitris encroachment enhanced by historical removal of pre-settlement trees and subsequent thinning of regrowth? Location: Woodlands dominated by Eucalyptus species and Callitris glaucophylla, which originally occupied approximately 100,000 km2 in eastern Australia. Methods: We used a process-driven stand simulation model to simulate tree demography, with growth, survival and recruitment mediated by annual rainfall, competition and disturbance. Following parameter calibration and model testing, we orthogonally manipulated historical removal of pre-settlement trees and thinning of regrowth to identify how both processes may have influenced structural changes over 120 years of European settlement.Results: Removal of pre-settlement trees had little effect on modelled encroachment, as trees increased to comparable densities whether pre-settlement trees were retained or removed. In unthinned scenarios, Callitris regeneration formed 'locked' stands of high density but low basal area.Thinning promoted growth of retained Callitris, increased total stand basal area, and together with direct removal of large pre-settlement Eucalyptus and thinning of Eucalyptus regrowth, transformed stands from Eucalyptus to Callitris dominance.Conclusions: Removal of pre-settlement trees does not appear to have been a necessary precursor to modelled encroachment in Eucalyptus-Callitris woodlands in eastern Australia, perhaps because initial tree cover was low and Callitris can regenerate beneath isolated trees. Manual thinning was required to effect major structural change because Callitris self-thins extremely slowly; thinning will be less important in other ecosystems that self-thin more rapidly. More generally, the impact of historical tree removal on encroachment is likely to vary according to initial tree cover, with greatest impacts in dense ecosystems with high tree cover. These results highlight the value of simulation models for disentangling the effects of multiple disturbances on tree encroachment and other ecosystem dynamics.

AB - Question: Woody plants have increased in density in many ecosystems, but the factors promoting encroachment are often debated. Since European colonization, Callitris glaucophylla has recruited abundantly in many Eucalyptus-Callitris woodlands in eastern Australia following changes to disturbance regimes analogous to changes in many other ecosystems globally. We used a dynamic stand model to disentangle effects of disturbances on Callitris encroachment and asked, to what extent was Callitris encroachment enhanced by historical removal of pre-settlement trees and subsequent thinning of regrowth? Location: Woodlands dominated by Eucalyptus species and Callitris glaucophylla, which originally occupied approximately 100,000 km2 in eastern Australia. Methods: We used a process-driven stand simulation model to simulate tree demography, with growth, survival and recruitment mediated by annual rainfall, competition and disturbance. Following parameter calibration and model testing, we orthogonally manipulated historical removal of pre-settlement trees and thinning of regrowth to identify how both processes may have influenced structural changes over 120 years of European settlement.Results: Removal of pre-settlement trees had little effect on modelled encroachment, as trees increased to comparable densities whether pre-settlement trees were retained or removed. In unthinned scenarios, Callitris regeneration formed 'locked' stands of high density but low basal area.Thinning promoted growth of retained Callitris, increased total stand basal area, and together with direct removal of large pre-settlement Eucalyptus and thinning of Eucalyptus regrowth, transformed stands from Eucalyptus to Callitris dominance.Conclusions: Removal of pre-settlement trees does not appear to have been a necessary precursor to modelled encroachment in Eucalyptus-Callitris woodlands in eastern Australia, perhaps because initial tree cover was low and Callitris can regenerate beneath isolated trees. Manual thinning was required to effect major structural change because Callitris self-thins extremely slowly; thinning will be less important in other ecosystems that self-thin more rapidly. More generally, the impact of historical tree removal on encroachment is likely to vary according to initial tree cover, with greatest impacts in dense ecosystems with high tree cover. These results highlight the value of simulation models for disentangling the effects of multiple disturbances on tree encroachment and other ecosystem dynamics.

KW - Callitris glaucophylla

KW - Eucalyptus

KW - Forest dynamics

KW - Logging

KW - Pinus ponderosa

KW - Silviculture

KW - Stand simulation modelling

KW - Timber harvesting

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DO - 10.1111/j.1654-1103.2011.01356.x

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SP - 304

EP - 312

JO - Journal of Vegetation Science

JF - Journal of Vegetation Science

SN - 1100-9233

IS - 2

ER -