O. Janne Kjønaas
Research Professor
Abstract
Understanding long-term effects of clear-cutting on current soil carbon (C) fluxes in boreal forests is important in the perspective of global C cycling and future forest management decisions. We studied twelve pairs of forest stands in South-Eastern Norway, each comprised of one previously clear-cut stand and one near-natural stand with similar macroclimate, topography and soil properties. We measured aboveground tree litterfall continuously during two consecutive years and soil respiration fluxes monthly during the snow-free period of one year. Ground vegetation litterfall was estimated from destructive biomass sampling. The previously clear-cut stands had on average 12 % higher annual soil respiration rates, 20 % greater tree litterfall, and tended to have greater total aboveground litterfall (12 %), while the near-natural stands had greater litterfall from ground vegetation (45 %). Litterfall from ground vegetation was strongly linked with below-canopy light transmission, but the contribution of this flux to the total aboveground litterfall was minor. Soil respiration rates were related to microclimate, nitrogen concentration in aboveground tree litter and tree basal area. Though, only basal area could be linked to management type differences in soil respiration, that likely has additional unidentified drivers. We found similar temperature sensitivities of soil respiration in the two management types. We emphasise that age of the dominating trees is an integrated part of the differences between these two types of forest stands. Jointly, our results suggest limited differences in the current net soil C balance of near-natural and previously clear-cut stands.
Authors
Lisa Fagerli Lunde Tone Birkemoe Anne Sverdrup-Thygeson Johan Asplund Rune Halvorsen O. Janne Kjønaas Jenni Nordén Sundy Maurice Inger Skrede Line Nybakken Håvard KauserudAbstract
Boreal forests are important carbon sinks and host a diverse array of species that provide important ecosystem functions.Boreal forests have a long history of intensive forestry, in which even-aged management with clear-cutting has been thedominant harvesting practice for the past 50–80 years. As a second cycle of clear-cutting is emerging, there is an urgentneed to examine the effects of repeated clear-cutting events on biodiversity. Clear-cutting has led to reduced numbers ofold and large trees, decreased volumes of dead wood of varied decay stages and diameters, and altered physical andchemical compositions of soils. The old-growth boreal forest has been fragmented and considerably reduced. Here,we review short- and long-term (≥50 years) effects of clear-cutting on boreal forest biodiversity in four key substrates:living trees, dead wood, ground and soil. We then assess landscape-level changes (habitat fragmentation and edge effects)on this biodiversity. There is evidence for long-term community changes af
Authors
Johan Asplund Jenni Nordén O. Janne Kjønaas Rieke Lo Madsen Lisa Fagerli Lunde Tone Birkemoe Eivind Kverme Ronold Milda Norkute Ulrika Jansson Damian Petkovic Karlsen Anne Sverdrup-Thygeson Inger Skrede Ine-Susanne Hopland Methlie Sundy Maurice Ulrik Geiran Botten Regine Jusnes Krok Håvard Kauserud Line NybakkenAbstract
The history of forestry in Fennoscandia spans five centuries, with clear-cutting being the dominant practice since the mid-20th century. This has led to a significant transformation of the forest landscape. In this study we investigated long-term effects of clear-cutting on forest structure and dead wood volumes. We established twelve pairs of spruce forest sites in southeastern Norway, each pair constituting of a mature, previously clear-cut stand and its near-natural counterpart with similar edaphic factors. The near-natural stands had 2.8 times higher volumes of dead wood and a larger proportion of dead wood in late stages of decay. The near-natural stands had on average 36.8 ± 9.1 m3 ha−1 of downed dead wood and 24.1 ± 6.2 m3 ha−1 of standing dead wood. Corresponding numbers for the previously clear-cut stands were 10.2 ± 2.8 m3 ha−1 and 11.9 ± 3.7 m3 ha−1. Forests with lower volumes of dead wood often also had lower connectivity of old spruce forests, which potentially have further negative effects on biodiversity. Furthermore, near-natural stands displayed greater tree size heterogeneity, resulting in a wider variation in light conditions. While no difference was observed in living tree volume, we found only weak evidence for higher basal area in the previously clear-cut stands, which had a higher stem density with more slender stems and shorter crowns. Our findings suggest that managed forests do not develop structures typical of near-natural forests before they become mature for logging. We stress the importance of a thorough site selection for studies of management effects, as forest management history may be confounded with productivity and other edaphic factors. Experimental designs like ours are vital for testing how differences in structure and deadwood volumes, driven by forest management, translate into variations in biodiversity, carbon sequestration and ecosystem functioning in future studies.