Causes of tree line stability: stem growth, recruitment and mortality rates over 15 years at New Zealand Nothofagus tree lines

Melanie Harsch, Rowan Buxton, Richard Duncan, Philip Hulme, Peter Wardle, Janet Wilmshurst

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

Aim Abrupt tree lines are relatively rare world-wide and are poorly understood. We studied demographic processes at abrupt tree lines to better understand the factors governing their dynamics. Location Five Nothofagus-dominated tree line sites across the South Island, New Zealand. Methods All Nothofagus stems at or above the tree line were tagged and their spatial locations and heights recorded on three occasions over 15 years at each site. We estimated rates of stem height growth, recruitment and mortality, and used these data to evelop a demographic model to project stem numbers into the future. Results Stem numbers had increased above the tree line at most sites over the last 15 years, but with little evidence of tree line advance. Growth, mortality and recruitment rates, modelled as a function of stem size, showed variation through time and among sites. Using a demographic model to project the numbers of stems above tree line 15 years into the future suggests that stem number will continue to increase, but that these tree lines are unlikely to advance at the rate predicted by recent climate warming. Across sites, variation in the rate of change in the number of stems above the tree line was most strongly related to variation in recruitment rates. Main conclusions Forest expansion at the abrupt Nothofagus tree line in New Zealand appears to be limited primarily by a lack of recruitment of new stems, which may be due to a paucity of suitable sheltered microsites for seedling establishment. Based on past demographic rates, our results suggest that these tree lines are relatively unresponsive to recent climate warming and are unlikely to show substantial upslope movement if past demographic trends continue.
Original languageEnglish
Pages (from-to)2061-2071
Number of pages11
JournalJournal of Biogeography
Volume39
DOIs
Publication statusPublished - 2012
Externally publishedYes

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Nothofagus
treeline
stem elongation
stem
mortality
stems
demographic statistics
global warming
warming
demographic trend
seedling establishment
climate
rate

Cite this

Harsch, Melanie ; Buxton, Rowan ; Duncan, Richard ; Hulme, Philip ; Wardle, Peter ; Wilmshurst, Janet. / Causes of tree line stability: stem growth, recruitment and mortality rates over 15 years at New Zealand Nothofagus tree lines. In: Journal of Biogeography. 2012 ; Vol. 39. pp. 2061-2071.
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title = "Causes of tree line stability: stem growth, recruitment and mortality rates over 15 years at New Zealand Nothofagus tree lines",
abstract = "Aim Abrupt tree lines are relatively rare world-wide and are poorly understood. We studied demographic processes at abrupt tree lines to better understand the factors governing their dynamics. Location Five Nothofagus-dominated tree line sites across the South Island, New Zealand. Methods All Nothofagus stems at or above the tree line were tagged and their spatial locations and heights recorded on three occasions over 15 years at each site. We estimated rates of stem height growth, recruitment and mortality, and used these data to evelop a demographic model to project stem numbers into the future. Results Stem numbers had increased above the tree line at most sites over the last 15 years, but with little evidence of tree line advance. Growth, mortality and recruitment rates, modelled as a function of stem size, showed variation through time and among sites. Using a demographic model to project the numbers of stems above tree line 15 years into the future suggests that stem number will continue to increase, but that these tree lines are unlikely to advance at the rate predicted by recent climate warming. Across sites, variation in the rate of change in the number of stems above the tree line was most strongly related to variation in recruitment rates. Main conclusions Forest expansion at the abrupt Nothofagus tree line in New Zealand appears to be limited primarily by a lack of recruitment of new stems, which may be due to a paucity of suitable sheltered microsites for seedling establishment. Based on past demographic rates, our results suggest that these tree lines are relatively unresponsive to recent climate warming and are unlikely to show substantial upslope movement if past demographic trends continue.",
keywords = "Climate change, demographic model, dispersal, growth, mortality, Nothofagus menziesii, Nothofagus solandri, recruitment, Southern Alps, tree line.",
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Causes of tree line stability: stem growth, recruitment and mortality rates over 15 years at New Zealand Nothofagus tree lines. / Harsch, Melanie; Buxton, Rowan; Duncan, Richard; Hulme, Philip; Wardle, Peter; Wilmshurst, Janet.

In: Journal of Biogeography, Vol. 39, 2012, p. 2061-2071.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Causes of tree line stability: stem growth, recruitment and mortality rates over 15 years at New Zealand Nothofagus tree lines

AU - Harsch, Melanie

AU - Buxton, Rowan

AU - Duncan, Richard

AU - Hulme, Philip

AU - Wardle, Peter

AU - Wilmshurst, Janet

PY - 2012

Y1 - 2012

N2 - Aim Abrupt tree lines are relatively rare world-wide and are poorly understood. We studied demographic processes at abrupt tree lines to better understand the factors governing their dynamics. Location Five Nothofagus-dominated tree line sites across the South Island, New Zealand. Methods All Nothofagus stems at or above the tree line were tagged and their spatial locations and heights recorded on three occasions over 15 years at each site. We estimated rates of stem height growth, recruitment and mortality, and used these data to evelop a demographic model to project stem numbers into the future. Results Stem numbers had increased above the tree line at most sites over the last 15 years, but with little evidence of tree line advance. Growth, mortality and recruitment rates, modelled as a function of stem size, showed variation through time and among sites. Using a demographic model to project the numbers of stems above tree line 15 years into the future suggests that stem number will continue to increase, but that these tree lines are unlikely to advance at the rate predicted by recent climate warming. Across sites, variation in the rate of change in the number of stems above the tree line was most strongly related to variation in recruitment rates. Main conclusions Forest expansion at the abrupt Nothofagus tree line in New Zealand appears to be limited primarily by a lack of recruitment of new stems, which may be due to a paucity of suitable sheltered microsites for seedling establishment. Based on past demographic rates, our results suggest that these tree lines are relatively unresponsive to recent climate warming and are unlikely to show substantial upslope movement if past demographic trends continue.

AB - Aim Abrupt tree lines are relatively rare world-wide and are poorly understood. We studied demographic processes at abrupt tree lines to better understand the factors governing their dynamics. Location Five Nothofagus-dominated tree line sites across the South Island, New Zealand. Methods All Nothofagus stems at or above the tree line were tagged and their spatial locations and heights recorded on three occasions over 15 years at each site. We estimated rates of stem height growth, recruitment and mortality, and used these data to evelop a demographic model to project stem numbers into the future. Results Stem numbers had increased above the tree line at most sites over the last 15 years, but with little evidence of tree line advance. Growth, mortality and recruitment rates, modelled as a function of stem size, showed variation through time and among sites. Using a demographic model to project the numbers of stems above tree line 15 years into the future suggests that stem number will continue to increase, but that these tree lines are unlikely to advance at the rate predicted by recent climate warming. Across sites, variation in the rate of change in the number of stems above the tree line was most strongly related to variation in recruitment rates. Main conclusions Forest expansion at the abrupt Nothofagus tree line in New Zealand appears to be limited primarily by a lack of recruitment of new stems, which may be due to a paucity of suitable sheltered microsites for seedling establishment. Based on past demographic rates, our results suggest that these tree lines are relatively unresponsive to recent climate warming and are unlikely to show substantial upslope movement if past demographic trends continue.

KW - Climate change

KW - demographic model

KW - dispersal

KW - growth

KW - mortality

KW - Nothofagus menziesii

KW - Nothofagus solandri

KW - recruitment

KW - Southern Alps

KW - tree line.

U2 - 10.1111/j.1365-2699.2012.02763.x

DO - 10.1111/j.1365-2699.2012.02763.x

M3 - Article

VL - 39

SP - 2061

EP - 2071

JO - Journal of Biogeography

JF - Journal of Biogeography

SN - 0305-0270

ER -