Gap formation and dynamics after long‐term steady state in an old‐growth Picea abies stand in Norway: Above‐ and belowground interactions

• Published in: Ecology and evolution Vol. 8; no. 1; pp. 462 - 476
• Main Authors: Nygaard, Per Holm, Strand, Line Tau, Stuanes, Arne Oddvar
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.01.2018; John Wiley and Sons Inc; Wiley
• Subjects: Bark; Beetles; biomass decline; Canopy gaps; Carbon sequestration; Dissolved organic carbon; Disturbance; Forest floor; Forests; gap initiation; Heterogeneity; late‐successional dynamics; long‐term permanent plots; Moisture content; Nutrients; Original Research; Picea abies; Pine trees; Soil properties; Soil water; Steady state; Treefall; Trees; gap initiation; biomass decline; late‐successional dynamics; long‐term permanent plots; nutrients
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3643

Stand dynamics and the gap initiation prior to gap formation are not well‐understood because of its long‐term nature and the scarcity of late‐successional stands. Reconstruction of such disturbance is normally based on historical records and dendroecological methods. We investigated gap initiation and formation at the fine‐scale stand level in the old‐growth reserve of Karlshaugen in Norway. Given its long‐term conservation history, and thorough mapping in permanent marked plots with spatially referenced trees, it provides an opportunity to present stand development before, during, and after gap formation. Late‐successional decline in biomass was recorded after more than 50 years of close to steady state. Gaps in the canopy were mainly created by large old trees that had been killed by spruce bark beetles. Snapping by wind was the main reason for treefall. Long‐term dominance of Norway spruce excluded downy birch and Scots pine from the stand. Comparisons of the forest floor soil properties between the gap and nongap area showed significantly higher concentrations of plant available Ca within the gap area. Plant root simulator (PRS™) probes showed significantly higher supply rates for Ca and Mg, but significantly lower K for the gap compared to the nongap area. Soil water from the gap area had significantly higher C:N ratios compared to the nongap area. Fine‐scale variation with increasing distance to logs indicated that CWD is important for leaking of DOC and Ca. Our long‐term study from Karlshaugen documents gap dynamics after more than 50 years of steady state and a multiscale disturbance regime in an old‐growth forest. The observed disturbance dynamic caused higher aboveground and belowground heterogeneity in plots, coarse woody debris, and nutrients. Our study of the nutrient levels of the forest floor suggest that natural gaps of old‐growth forest provide a long‐lasting biogeochemical feedback system particularly with respect to Ca and probably also N. Norway spruce trees near the gap edge responded with high plasticity to reduced competition, showing the importance of the edge zone as hot spots for establishing heterogeneity, but also the potential for carbon sequestration in old‐growth forest. Long monitoring with permanent plots documents gap dynamics after and a multiscale disturbance regime in an old‐growth forest. The observed disturbance dynamic caused higher aboveground and belowground heterogeneity in habitats, coarse woody debris but also spatial and temporal gradients in Ca supply. Norway spruce trees near the gap edge responded with high plasticity to reduced competition, showing the importance of the edge zone as hot spots for establishing heterogeneity, but also the potential for carbon sequestration in old‐growth forest.