TY - JOUR
T1 - Gap expansion is the dominant driver of canopy openings in a temperate mountain forest landscape
AU - Krüger, Kirsten
AU - Senf, Cornelius
AU - Jucker, Tommaso
AU - Pflugmacher, Dirk
AU - Seidl, Rupert
N1 - Publisher Copyright:
© 2024 The Authors. Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.
PY - 2024/7
Y1 - 2024/7
N2 - Natural disturbances are important drivers of forest dynamics, and canopy gaps are their fingerprints in forest ecosystems. Gaps form and persist because of the interplay of tree mortality and regeneration. They can have long-lasting impacts on ecosystems, yet the temporal dynamics of gap formation and closure remains poorly quantified. We analysed 11,331 canopy gaps and their changes through time across 3999 ha of unmanaged temperate mountain forests at Berchtesgaden National Park (Germany). We assessed gap formation and closure using three repeat lidar acquisitions between 2009 and 2021, analysing canopy height changes at 1 m horizontal resolution. Our objective was to determine the dominant mode of gap formation, distinguishing the creation of new gaps from the expansion of existing ones. Additionally, we studied the rate of gap closure, considering closure from tree regeneration and lateral crown expansion. Gap formation was primarily driven by gap expansion rather than the initiation of new gaps. Gap expansion accounted for 81.3% of gap formation, although new gaps were on average twice as large as gap expansions. Only 1.4% of gaps did not expand over the 12-year study period, and Norway spruce forests had the highest rate of gap expansion. Overall, gap closure rate (0.74 ha 100 ha−1 year−1) was higher than gap formation (0.58 ha 100 ha−1 year−1) in our study system. Ingrowth of the regenerating tree cohort was the primary mode of gap closure, with lateral crown expansion accounting for 20% of all gap area closed. Mixed-species stands had the highest rate of gap closure, and gaps <0.1 ha closed faster than larger gaps. Synthesis. While canopy openings are generally small in the European Alps, we show that they keep growing over multiple years, underlining that gap expansion is an important driver of temperate forest dynamics. Canopy gaps closed faster than they were created, highlighting the resilience of European mountain forests to natural disturbances. However, as disturbances are projected to increase under climate change, this resilience might be challenged in the future, requiring a continuous monitoring of gap dynamics as an important early warning indicator of forest change.
AB - Natural disturbances are important drivers of forest dynamics, and canopy gaps are their fingerprints in forest ecosystems. Gaps form and persist because of the interplay of tree mortality and regeneration. They can have long-lasting impacts on ecosystems, yet the temporal dynamics of gap formation and closure remains poorly quantified. We analysed 11,331 canopy gaps and their changes through time across 3999 ha of unmanaged temperate mountain forests at Berchtesgaden National Park (Germany). We assessed gap formation and closure using three repeat lidar acquisitions between 2009 and 2021, analysing canopy height changes at 1 m horizontal resolution. Our objective was to determine the dominant mode of gap formation, distinguishing the creation of new gaps from the expansion of existing ones. Additionally, we studied the rate of gap closure, considering closure from tree regeneration and lateral crown expansion. Gap formation was primarily driven by gap expansion rather than the initiation of new gaps. Gap expansion accounted for 81.3% of gap formation, although new gaps were on average twice as large as gap expansions. Only 1.4% of gaps did not expand over the 12-year study period, and Norway spruce forests had the highest rate of gap expansion. Overall, gap closure rate (0.74 ha 100 ha−1 year−1) was higher than gap formation (0.58 ha 100 ha−1 year−1) in our study system. Ingrowth of the regenerating tree cohort was the primary mode of gap closure, with lateral crown expansion accounting for 20% of all gap area closed. Mixed-species stands had the highest rate of gap closure, and gaps <0.1 ha closed faster than larger gaps. Synthesis. While canopy openings are generally small in the European Alps, we show that they keep growing over multiple years, underlining that gap expansion is an important driver of temperate forest dynamics. Canopy gaps closed faster than they were created, highlighting the resilience of European mountain forests to natural disturbances. However, as disturbances are projected to increase under climate change, this resilience might be challenged in the future, requiring a continuous monitoring of gap dynamics as an important early warning indicator of forest change.
KW - forest disturbance
KW - gap dynamics
KW - gap formation and closure
KW - gap-phase regeneration
KW - landscape ecology
KW - lidar
KW - temperate mountain forest
UR - http://www.scopus.com/inward/record.url?scp=85192063046&partnerID=8YFLogxK
U2 - 10.1111/1365-2745.14320
DO - 10.1111/1365-2745.14320
M3 - Article
AN - SCOPUS:85192063046
SN - 0022-0477
VL - 112
SP - 1501
EP - 1515
JO - Journal of Ecology
JF - Journal of Ecology
IS - 7
ER -