Mixed-severity natural disturbance regime dominates in an old-growth Norway spruce forest of northwest Russia

Questions: What were the long-term disturbance rates (including variability) and agents in pristine Norway spruce-dominated (Picea abies (L.) Karst.) forests? Have soil moisture conditions influenced disturbance rates across this boreal spruce-dominated forest? Were the temporal recruitment patterns of canopy dominants associated with past disturbance periods? Location: Interfluvial region of Northern Dvina and Pinega rivers, Arkhangelsk, northwest Russia. Methods: We linked dendrochronological data with tree spatial data (n trees=1659) to reconstruct the temporal and spatial patterns of canopy gaps in a 1.8-ha area from 1831-2008, and to develop a growth-release chronology from 1775-2008. Results: No evidence of stand-replacing disturbances was found within selected forest stands over the studied period. Forest dynamics were driven by small- to moderate-scale canopy disturbances, which maintained a multi-cohort age structure. Disturbance peaks were observed in the 1820s, 1920s, 1970s and 2000s, with decadal rates reaching 32% of the stand area disturbed. Conclusions: The overall mean decadal rate was 8.3% canopy area disturbed, which suggests a canopy turnover time of 122yr, with a 95% confidence envelop of 91-186yr. Bark beetle outbreaks (possibly exacerbated by droughts) and wind-storms emerged as the principal disturbance agents. Recruitment of both Norway spruce and downy birch was associated with periods of increased canopy disturbance. Moisture conditions (moist vs mesic stands) were not significantly related to long-term disturbance rates. The studied spruce-dominated boreal forests of this region apparently exhibited long-term forest continuity under this mixed-severity disturbance regime. These disturbances caused considerable structural alterations to forest canopies, but apparently did not result in a pronounced successional shifts in tree species composition, rather occasional minor enrichments of birch in these heavily spruce-dominated stands

Emissions of forest floor and mineral soil carbon, nitrogen and mercury pools and relationships with fire severity for the Pagami Creek Fire in the Boreal Forest of northern Minnesota

Forest fires cause large emissions of C (carbon), N (nitrogen) and Hg (mercury) to the atmosphere and thus have important implications for global warming (e.g. via CO2 and N2O emissions), anthropogenic fertilisation of natural ecosystems (e.g. via N deposition), and bioaccumulation of harmful metals in aquatic and terrestrial systems (e.g. via Hg deposition). Research indicates that fires are becoming more severe over much of North America, thus increasing element emissions during fire. However, there has been little research relating forest floor and mineral soil losses of C, N and Hg to on-the-ground indices of fire severity that enable scaling up those losses for larger-scale accounting of fire-level emissions. We investigated the relationships between forest floor and mineral soil elemental pools across a range of soil-level fire severities following the 2011 Pagami Creek wildfire in northern Minnesota, USA. We were able to statistically differentiate losses of forest floor C, N and Hg among a five-class soil-level fire severity classification system. Regression relationships using soil fire severity class were able to predict remaining forest floor C, N and Hg pools with 82–96% confidence. We correlated National Aeronautics and Space Administration Airborne Visible and Infrared Imaging Spectrometer-Classic imagery to ground-based plot-scale estimates of soil fire severity to upscale emissions of C, N and Hg to the fire level. We estimate that 468 000 Mg C, 11 000 Mg of N and over 122 g of Hg were emitted from the forest floor during the burning of the 28 310 ha upland area of the Pagami Creek fire

Salvage logging effects on regulating and supporting ecosystem services. A systematic map

Wildfires, insect outbreaks, and windstorms are increasingly common forest disturbances.Post-disturbance management often involves salvage logging, i.e. the felling and removal of the affected trees. However, this practice may represent an additional disturbance witheffects on ecosystem processes and services. We developed a systematic map to provide an overview of the primary studies on this topic, and created a database with information on the characteristics of the retrieved publications, including information on stands, disturbance, intervention, measured outcomes, and study design. Of 4341 retrieved publications, 90 were retained in the systematic map. These publications represented 49 studies, predominantly from North America and Europe. Salvage logging after wildfire was addressed more frequently than after insect outbreaks or windstorms. Most studies addressed logging after a single disturbance event, and replication of salvaged stands rarely exceeded 10. The most frequent response variables were tree regeneration, ground cover, and deadwood characteristics.Junta de AndalucíaREMEDINA

Patterns and drivers of recent disturbances across the temperate forest biome

Increasing evidence indicates that forest disturbances are changing in response to global change, yet local variability in disturbance remains high. We quantified this considerable variability and analyzed whether recent disturbance episodes around the globe were consistently driven by climate, and if human influence modulates patterns of forest disturbance. We combined remote sensing data on recent (2001-2014) disturbances with in-depth local information for 50 protected landscapes and their surroundings across the temperate biome. Disturbance patterns are highly variable, and shaped by variation in disturbance agents and traits of prevailing tree species. However, high disturbance activity is consistently linked to warmer and drier than average conditions across the globe. Disturbances in protected areas are smaller and more complex in shape compared to their surroundings affected by human land use. This signal disappears in areas with high recent natural disturbance activity, underlining the potential of climate-mediated disturbance to transform forest landscapes.A.S. and R.S. acknowledge support from the Austrian Science Fund (FWF) through START grant Y895-B25. C.S. acknowledges funding from the German Academic Exchange Service (DAAD) with funds from the German Federal Ministry of Education and Research (BMBF) and the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007–2013) under REA grant agreement Nr. 605728 (P.R.I.M.E.—Postdoctoral Researchers International Mobility Experience). T. D. acknowledges funding from the Fonds institutionnel de recherche de l’Universitédu Quebec en Abitibi-Te ́ miscamingue, the Natural Sciences and Engineering Research ́ Council of Canada (NSERC), Tembec, and EACOM Timber Corporation. Á.G.G. was supported by FONDECYT 11150835. S.J.H. and T.T.V. acknowledge NSF Award 1262687. A.H. was partially supported by NSF (award #1738104). D.K. acknowledges support from the US NSF. D.L. was supported by an Australian Research Council Laureate Fellowship. A.S.M. was supported by the Environment Research and Technology Development Fund (S-14) of the Japanese Ministry of the Environment and by the Grants-in-Aid for Scientific Research of the Japan Society for the Promotion of Science (15KK0022). G.L.W.P. acknowledges support from a Royal Society of New Zealand Marsden Fund grant. S.L.S. acknowledges funds from the US Joint Fire Sciences Program (project number 14-1-06-22) and UC ANR competitive grants. M.S. and T.H. acknowledges support from the institutional project MSMT CZ.02.1.01/0.0/0.0/16_019/ 0000803. M.G.T. acknowledges funding from the University of Wisconsin-Madison Vilas Trust and the US Joint Fire Science Program (project numbers 09-1-06-3, 12-3-01-3, and 16-3-01-4). The study used data from the TRY initiative on plant traits (http://www.trydb.org). The TRY initiative and database is hosted, developed and maintained by J. Kattge and G. Boenisch (Max Planck Institute for Biogeochemistry, Jena, Germany). TRY is currently supported by Future Earth/bioDISCOVERY and the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzi

Post-fire comparisons of forest floor and soil carbon, nitrogen, and mercury pools with fire severity indices

Forest fires are important contributors of C, N, and Hg to the atmosphere. In the fall of 2011, a large wildfire occurred in northern Minnesota and we were able to quickly access the area to sample the forest floor and mineral soil for C, N, and Hg pools. When compared with unburned reference soils, the mean loss of C resulting from fire in the forest floor and the upper 20 cm of mineral soil was 19.3 Mg ha−1, for N the mean loss was 0.17 Mg ha−1, and for Hg the mean loss was 9.3 g ha−1. To assess the influence of fire severity on the forest floor and mineral soils, we used an established method that included a soil burn severity index and a tree burn severity index with a gradient of severity classes. It was apparent that the unburned reference class had greater forest floor C, N, and Hg pools and higher C/N ratios than the burned classes. The C/N ratios of the 0- to 10- and 10- to 20-cm mineral soils in the unburned reference class were also greater than in the burned classes, indicating that a small amount of C was lost and/or N was gained, potentially through leaching unburned forest floor material. However, with a couple of exceptions, the severity classes were unable to differentiate the forest floor and mineral soil impacts among soil burn and tree burn severity indices. Developing burn severity indices that are reflective of soil elemental impacts is an important first step in scaling ecosystem impacts both within and across fire events

Spatial and Temporal Patterns of Natural Disturbance in Old-Growth Forests of Northern Maine, USA

I linked methods of dendroecology with spatial analyses to investigate the patterns of natural disturbance in a ca. 2000-ha old-growth landscape of northern Maine. I randomly placed 38 plots among five community types throughout the landscape and reconstructed a history of disturbance (a chronology) for each. I found no evidence of stand replacing disturbance during the period covered by this investigation (back to the mid 1700s). The disturbance rates were generally low (mean of 9.6% canopy destruction per decade), yet fluctuated markedly through time. Minor peaks in disturbance were synchronized among plots, albeit weakly, suggesting landscape-wide pulses of tree recruitment, canopy openness, and deadwood abundance. However, I found no evidence of spatial patterning of disturbance: no correlation between disturbance patterns and the physical distance between plots, and no evidence of disturbance patch structure. Matrix correlation indicated that species composition best explained the variability in temporal patterns of disturbance. Neither landform nor aspect influenced rates or patterns or disturbance. The disturbance dynamic appears to have two components: pulses of moderate severity disturbances caused by host-specific disturbance agents (primarily the spruce budworm) interposed upon a background of scattered small-scale canopy gaps. The relatively low rates of canopy disturbance, coupled with the abundance of advance regeneration, have maintained canopy dominance by shade-tolerant species. Peaks of low- to moderate-severity disturbance may admit mid-tolerant tree species; however, they are insufficient to admit shade-intolerant species. I developed an alternative method of detecting growth releases fiom tree-ring series, based on absolute increases in radial growth. The method has convenient mathematical properties that overcome several shortcomings in the commonly used percent-increase method. By intensively sampling and mapping three red spruce (Picea rubens) plots, I determined the locations and sizes of former canopy gaps back to 1920. Gaps were generally small (median 25.3 m2). Red spruce trees clearly benefit fiom these gaps: 80.6% of trees showed one or more releases before canopy accession. Several measures of canopy structure provided strong supporting evidence for historical disturbance patterns revealed by dendroecological methods

The Conic-Paraboloid Formulae for Coarse Woody Material Volume and Taper, and Their Approximation

The conic-paraboloid volume equation is receiving increased use with downed coarse woody material (CWM), but the consequences for taper have not been identified mathematically. Requiring that subdivision of a conic-paraboloid yields two smaller conic-paraboloids, leads to an exact taper equation intermediate between those of cones and second-order paraboloids. This exact taper equation does not have an explicit inverse, however. An alternative, naive approach does have an explicit inverse, but subdivision does not yield two conic-paraboloids. The exact conic-paraboloid is closely approximated by Fermatâ s paraboloid with exponent 7/5. The exact and naive conic-paraboloids match in volume; differences in taper areThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Effects of blowdown, salvage logging, and wildfire on regeneration and fuel characteristics in Minnesota’s forests

The patchiness resulting from a sequence of recent disturbances – blowdown, salvage logging, and wildfire – provided an excellent opportunity to assess the impacts of these disturbances, singly and in combination, on (1) wildfire severity (2) post-disturbance vegetation responses, (3) ecosystem carbon stocks, and (4) soil mercury (Hg) accumulation or loss in jack pine (P. banksiana) forests of northern Minnesota. Considering issue 1, our results suggest that salvage logging reduced the intensity (heat released) of the subsequent fire. However, its effect on severity (impact to the system) differed between the tree crowns and forest floor. Considering issue 2, our results suggest that disturbance combinations (blowdown and fire with and without salvage logging) resulted in similar woody plant communities, largely dominated by trembling aspen (Populus tremuloides). By comparison, areas experiencing solely fire were dominated by jack pine regeneration, and areas experiencing solely blowdown were dominated by regeneration from shade-tolerant conifer species. Considering issue 3, our results suggest that various disturbances cause dramatic shifts in the proportion of carbon in different pools, suggesting that potential increases in multiple disturbance events may represent a challenge for sustaining ecosystem carbon stocks. Considering issue 4, our results suggest that when disturbance combinations are considered in addition to singular disturbances, unexpected consequences in atmospheric Hg emission, soil Hg accumulation, and risk to aquatic biota may result. Taken together, these results lend themselves to improved forest management strategies, particularly regarding post-disturbance harvesting prescriptions