Browsing by Subject "CONIFEROUS FORESTS"

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  • Peltoniemi, Mikko; Pulkkinen, Minna; Aurela, Mika; Pumpanen, Jukka; Kolari, Pasi; Makela, Annikki (2015)
    Simple approaches to predicting ecosystem fluxes are useful in large-scale applications because existing data rarely support justified use of complex models. We developed a model of daily ecosystem gross primary production (P), evapotranspiration (E), and soil water content (theta), which only requires standard weather data and information about the fraction of absorbed radiation. We estimated the parameters of the model for two boreal Scots pine eddy-covariance sites (Hyytiala and Sodankyla). The model predicted P and E adequately for Hyytiala for both calibration and additional test years. The model calibrated for Hyytiala slightly overestimated P and E in Sodankyla, but its performance levelled with the model calibrated for Sodankyla in a dry year. Sensitivity analysis of the model implied that drought prediction is sensitive, not only to key E submodel parameters, but also to P submodel parameters. Further improvement and calibrations of the model could benefit from forest sites with varying canopy and different species structures.
  • Vehkaoja, Mia; Nummi, Petri; Rikkinen, Jouko (2017)
    Beavers are ecosystem engineers that modify and maintain a range of special habitat types in boreal forests. They also produce large quantities of deadwood that provide substrate for many lignicolous organisms such as calicioid fungi (Ascomycota). We studied how calicioid diversity differed between boreal riparian forests with and without beaver activity. The results show that calicioid diversity were significantly higher at beaver sites compared to the other two forest site types studied. The large quantity and diverse forms of deadwood produced by beavers clearly promotes calicioid diversity in the boreal landscape. The specific lighting and humidity conditions within beaver wetlands could be the reason why they promote the success of certain calicioid species.
  • Pulliainen, Jouni; Aurela, Mika; Laurila, Tuomas; Aalto, Tuula; Takala, Matias; Salminen, Miia; Kulmala, Markku; Barr, Alan; Heimann, Martin; Lindroth, Anders; Laaksonen, Ari; Derksen, Chris; Mäkelä, Annikki; Markkanen, Tiina; Lemmetyinen, Juha; Susiluoto, Jouni; Dengel, Sigrid; Mammarella, Ivan; Tuovinen, Juha-Pekka; Vesala, Timo (2017)
    We determine the annual timing of spring recovery from space-borne microwave radiometer observations across northern hemisphere boreal evergreen forests for 1979-2014. We find a trend of advanced spring recovery of carbon uptake for this period, with a total average shift of 8.1 d (2.3 d/decade). We use this trend to estimate the corresponding changes in gross primary production (GPP) by applying in situ carbon flux observations. Micrometeoro-logical CO2 measurements at four sites in northern Europe and North America indicate that such an advance in spring recovery would have increased the January-June GPP sum by 29 g.C.m(-2) [8.4 g.C.m(-2) (3.7%)/decade]. We find this sensitivity of the measured springtime GPP to the spring recovery to be in accordance with the corresponding sensitivity derived from simulations with a land ecosystem model coupled to a global circulation model. The model-predicted increase in springtime cumulative GPP was 0.035 Pg/decade [15.5 g.C.m(-2) (6.8%)/decade] for Eurasian forests and 0.017 Pg/decade for forests in North America [9.8 g.C.m(-2) (4.4%)/decade]. This change in the springtime sum of GPP related to the timing of spring snowmelt is quantified here for boreal evergreen forests.
  • Saine, Sonja; Aakala, Tuomas; Purhonen, Jenna; Launis, Annina; Tuovila, Hanna; Kosonen, Timo; Halme, Panu (2018)
    Human-induced fragmentation affects forest continuity, i.e. availability of a suitable habitat for the target species over a time period. The dependence of wood-inhabiting fungi on landscape level continuity has been well demonstrated, but the importance of local continuity has remained controversial. In this study, we explored the effects of local forest continuity (microhabitat and stand level) on the diversity of wood-inhabiting fungi on standing dead trunks of Scots pine (Paws sylvestris L.). We studied species richness and community composition of decomposers and Micarea lichens on 70 trunks in 14 forests in central Finland that differed in their state of continuity. We used dendrochronological methods to assess the detailed history of each study trunk, i.e. the microhabitat continuity. The stand continuity was estimated as dead wood diversity and past management intensity (number of stumps). We recorded 107 species (91 decomposers, 16 Micarea lichens), with a total of 510 occurrences. Using generalized linear mixed models, we found that none of the variables explained decomposer species richness, but that Micarea species richness was positively dependent on the time since tree death. Dead wood diversity was the most important variable determining the composition of decomposer communities. For Micarea lichens, the community composition was best explained by the combined effect of years from death, site and dead wood diversity. However, these effects were rather tentative. The results are in line with those of previous studies suggesting the restricted significance of local forest continuity for wood-inhabiting fungi. However, standing dead pines that have been available continuously over long periods seem to be important for species-rich communities of Micarea lichens. Rare specialists (e.g. on veteran trees) may be more sensitive to local continuity, and should be at the center of future research.
  • Leppälammi-Kujansuu, Jaana; Aro, Lasse; Salemaa, Maija; Hansson, Karna; Kleja, Dan Berggren; Helmisaari, Heljä-Sisko (2014)
  • Kulmala, Liisa; Read, Jesse; Nöjd, Pekka; Rathgeber, Cyrille B.K.; Cuny, Henri E.; Hollmén, Jaakko; Mäkinen, Harri (2017)
    Even though studies monitoring the phenology and seasonal dynamics of the wood formation have accumulated for several conifer species across the Northern Hemisphere, the environmental control of tracheid production and differentiation is still fragmentary. With microcore and environmental data from six stands in Finland and France, we built auto-calibrated data-driven black box models for analyzing the most important factors controlling the tracheid production and maturation in Scots pine stem. In the best models, estimation was accurate to within a fraction of a tracheid per week. We compared the relative results of models built using different predictors, and found that the rate of tracheid production was partly regular but current and previous air temperature had influence on the sites in the middle of the temperature range and photosynthetic production in the coldest ones. The rate of mature cell production was more difficult to relate to the predictors but recent photosynthetic production was included in all successful models.
  • Palmroth, Sari; Bach, Lisbet H.; Lindh, Marie; Kolari, Pasi; Nordin, Annika; Palmqvist, Kristin (2019)
    In boreal forests, carbon (C) uptake by understory may be too large to be ignored and too variable in space to be assumed a constant fraction of the ecosystem gross primary production. To improve estimates of understory production in these ecosystems, we need to better account for its main controls. In this study, we estimated C uptake of field-layer vegetation, dominated by Vaccinium myrtillus, V. vitis-idaea, and Deschampsia flexuosa, in a boreal Picea abies stand in northern Sweden. Nitrogen (N) availability in the stand has been manipulated through annual N additions since 1996 at the rates of 0, 12.5, and 50 kg N ha(-1) yr(-1). To assess the relative importance of N supply, and interannual fluctuations in leaf biomass and weather, in controlling field-layer photosynthetic production, we calculated C uptake over eight growing seasons using a canopy photosynthesis model. Without N additions, tree leaf area index (L) was already high (8.5) and field-layer C uptake was small, 27 g Cm-2 (or similar to 3% of stand C uptake). An increase in tree L with N additions further reduced light availability for the understory, yet the concurrent increase in the relative abundance of the more physiologically active D. flexuosa sustained the contribution of the field-layer to stand photosynthetic production. Based on a literature survey, in which site quality or stand age generated a wide range in L, understory contribution to ecosystem C uptake increases linearly with the fraction of available light reaching the forest floor across high latitude forests. Understory contributes only similar to 5% to ecosystem C uptake where trees intercept similar to 80% of incoming light, increasing to 100% after clearcut tree harvest. While the availability of solar energy, both spatially and temporally, is the primary driver of understory production, our analyses suggest that the predicted increases in drought severity and frequency at high latitudes may affect understory communities more than trees. Future empirical and modeling studies should focus on functional and ecological responses to drought of not only trees but also understory species, which contribute to biodiversity and convert their photosynthates to important non-timber products.
  • Minkkinen, Kari; Ojanen, Paavo; Penttilä, Timo; Aurela, Mika; Laurila, Tuomas; Tuovinen, Juha-Pekka; Lohila, Annalea (2018)
    Drainage of peatlands is expected to turn these ecosystems into carbon sources to the atmosphere. We measured carbon dynamics of a drained forested peatland in southern Finland over 4 years, including one with severe drought during growing season. Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured with the eddy covariance method from a mast above the forest. Soil and forest floor CO2 and methane (CH4) fluxes were measured from the strips and from ditches with closed chambers. Biomass and litter production were sampled, and soil subsidence was measured by repeated levellings of the soil surface. The drained peatland ecosystem was a strong sink of carbon dioxide in all studied years. Soil CO2 balance was estimated by subtracting the carbon sink of the growing tree stand from NEE, and it showed that the soil itself was a carbon sink as well. A drought period in one summer significantly decreased the sink through decreased gross primary production. Drought also decreased ecosystem respiration. The site was a small sink for CH4, even when emissions from ditches were taken into account. Despite the continuous carbon sink, peat surface subsided slightly during the 10-year measurement period, which was probably mainly due to compaction of peat. It is concluded that even 50 years after drainage this peatland site acted as a soil C sink due to relatively small changes in the water table and in plant community structure compared to similar undrained sites, and the significantly increased tree stand growth and litter production. Although the site is currently a soil C sink, simulation studies with process models are needed to test whether such sites could remain C sinks when managed for forestry over several tree-stand rotations.
  • 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.