Browsing by Subject "BLACK SPRUCE"

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  • Palviainen, Marjo; Laurén, Ari; Pumpanen, Jukka; Bergeron, Yves; Bond-Lamberty, Ben; Larjavaara, Markku; Kashian, Daniel; Köster, Kajar; Prokushkin, Anatoly; Chen, Han; Seedre, Meelis; Wardle, David; Gundale, Michael; Nilsson, Marie-Charlotte; Wang, Chuankuan; Berninger, Frank (2020)
    Boreal forests store 30% of the world's terrestrial carbon (C). Consequently, climate change mediated alterations in the boreal forest fire regime can have a significant impact on the global C budget. Here we synthesize the effects of forest fires on the stocks and recovery rates of C in boreal forests using 368 plots from 16 long-term (>= 100 year) fire chronosequences distributed throughout the boreal zone. Forest fires led to a decrease in total C stocks (excluding mineral soil) by an average of 60% (range from 80%), which was primarily a result of C stock declines in the living trees and soil organic layer. Total C stocks increased with time since fire largely following a sigmoidal shape Gompertz function, with an average asymptote of 8.1 kg C m(-2). Total C stocks accumulated at a rate of 2-60 g m(-2) yr(-1)during the first 100 years. Potential evapotranspiration (PET) was identified as a significant driver of C stocks and their post-fire recovery, likely because it integrates temperature, radiation, and the length of the growing season. If the fire return interval shortens to
  • Ribeiro-Kumara, Christine; Pumpanen, Jukka; Heinonsalo, Jussi; Metslaid, Marek; Orumaa, Argo; Jõgiste, Kalev; Berninger, Frank; Köster, Kajar (2020)
    Fire is the most important natural disturbance in boreal forests, and it has a major role regulating the carbon (C) budget of these systems. With the expected increase in fire frequency, the greenhouse gas (GHG) budget of boreal forest soils may change. In order to understand the long-term nature of the soil–atmosphere GHG exchange after fire, we established a fire chronosequence representing successional stages at 8, 19, 34, 65, 76 and 179years following stand-replacing fires in hemiboreal Scots pine forests in Estonia. Changes in extracellular activity, litter decomposition, vegetation biomass, and soil physicochemical properties were assessed in relation to carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. Soil temperature was highest 8years after fire, whereas soil moisture varied through the fire chronosequences without a consistent pattern. Litter decomposition and CO2 efflux were still lower 8years after fire compared with pre-fire levels (179years after fire). Both returned to pre-fire levels before vegetation re-established, and CO2 efflux was only strongly responsive to temperature from 19years after fire onward. Recovery of CO2 efflux in the long term was associated with a moderate effect of fire on enzyme activity, the input of above- and below-ground litter carbon, and the re-establishment of vegetation. Soil acted as a CH4 sink and N2O source similarly in all successional stages. Compared with soil moisture and time after fire, soil temperature was the most important predictor for both GHGs. The re-establishment of overstorey and vegetation cover (mosses and lichens) might have caused an increase in CH4 and N2O effluxes in the studied areas, respectively.
  • Kulha, Niko; Pasanen, Leena; Holmström, Lasse; Grandpre, Louis de; Gauthier, Sylvie; Kuuluvainen, Timo; Aakala, Tuomas (2020)
    Context: Changes in the structure of boreal old-growth forests are typically studied at a specific spatial scale. Consequently, little is known about forest development across different spatial scales. Objectives: We investigated how and at what spatial scales forest structure changed over several decades in three 4 km² boreal old-growth forests landscapes in northeastern Finland and two in Quebec, Canada. Methods: We used canopy cover values visually interpreted to 0.1-ha grid cells from aerial photographs taken at three time points between the years 1959 and 2011, and error distributions quantified for the interpretation. We identified the spatial scales at which canopy cover changed between the time points, and examined the credibility of changes at these scales using the error distributions in Bayesian inference. Results: Canopy cover changed at three to four spatial scales, the number of scales depending on the studied landscape and time interval. At large scales (15.4–321.7 ha), canopy cover increased in Finland during all time intervals. In Quebec, the direction of the large-scale change varied between the studied time intervals, owing to the occurrence of an insect outbreak and a consequent recovery. However, parts of these landscapes also showed canopy cover increase. Superimposed on the large-scale developments, canopy cover changed variably at smaller scales (1.3–2.8-ha and 0.1-ha). Conclusions: Our findings support the idea that the structure of boreal old-growth forests changes at discernible spatial scales. Instead of being driven by gap dynamics, the old-growth forests in the studied regions are currently reacting to large-scale drivers by an increase in canopy cover.