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

Abstract

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.

Response of plant diversity and soil physicochemical properties to different gap sizes in a Pinus massoniana plantation

“…Gap formation also contributes to the dynamic growth of woody plants. Large-area gaps form mosaic patches with different sizes of tree species, structures and ages ( Runkle, 1981 ; Nygaard, Strand & Stuanes, 2018 ; Keram et al, 2019 ). Forest soil, an essential part of the ecosystem in which nutrients are recycled and many organisms live, is also influenced by forest canopy gaps ( Yang et al, 2017 ).…”

Spontaneous development of early successional vegetation improves Norway spruce forest soil after clear-cutting and renewal failure: a case study at a sandy-soil site

“…These processes can also be affected by warming up of surface humus and upper soil layers as reported by Dymov, Startsev (2016) in taiga spruce forest after clear-cutting. Increased concentration of plant-available calcium in gaps formed in old-growth spruce-pine-birch forest with bilberry Nygaard et al (2017). Also logging residues left at the site after clear-cut-ting can contribute to additional inputs of nutrients (Siebers, Kruse 2019).…”

“…Early successional species can however improve upper soil properties compared to target species (Martiník et al 2017). Different tree species life span and tolerance to lower subcanopy light levels are the reasons why the long dominance of late successional species such as spruce can even exclude the shade intolerant birch from a forest stand (Nygaard et al 2017).…”

Water balance in boreal forests: the role of season-specific responses in a warming climate

“…Additionally, this suggests that enhanced tree T observed during recent drought years, is not necessarily linked to a higher tree growth, but rather as a response to increasing temperatures and VPD. Additionally, while boreal forests can change in stand structure decades or centuries after establishment [43][44][45] , our site is a 120-year-old, relatively unmanaged boreal forest with prior limited selective cutting. Additionally, long-term tree BAI trends in our sites peaked in 1970's (Figure 3), and under such conditions, growth dynamics are not primarily linked to stand establishment, but rather to the interaction between resource availability and environmental variables.…”