Browsing by Subject "BOREAL"

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  • White, Joanne C.; Saarinen, Ninni; Wulder, Michael A.; Kankare, Ville; Hermosilla, Txomin; Coops, Nicholas C.; Holopainen, Markus; Hyyppä, Juha; Vastaranta, Mikko (2019)
    Information regarding the nature and rate of forest recovery is required to inform forest management, monitoring, and reporting activities. Delayed establishment or return of forests has implications to harvest rotations and carbon uptake, among others, creating a need for spatially-explicit, large-area, characterizations of forest recovery. Landsat time series (LTS) has been demonstrated as a means to quantitatively relate forest recovery, noting that there are gaps in our understanding of the linkage between spectral measures of forest recovery and manifestations of forest structure and composition. Field plots provide a means to better understand the linkage between forest characteristics and spectral recovery indices. As such, from a large set of existing field plots, we considered the conditions present for the year in which the co-located pixel was considered spectrally recovered using the Years to Recovery (Y2R) metric. Y2R is a long-term metric of spectral recovery that indicates the number of years required for a pixel to return to 80% of its pre-disturbance Normalized Burn Ratio value. Absolute and relative metrics of recovery at 5 years post-disturbance were also considered. We used these three spectral recovery metrics to predict the stand development class assigned by the field crew for 284 seedling plots with an overall accuracy of 73.59%, with advanced seedling stands more accurately discriminated (omission error, OE = 15.74%) than young seedling stands (OE = 49.84%). We then used field-measured attributes (e.g. height, stem density, dominant species) from the seedling plots to classify the plots into three spectral recovery groups, which were defined using the Y2R metric: spectral recovery in (1) 1–5 years, (2) 6–10 years, or (3) 11–15 years. Overall accuracy for spectral recovery groups was 61.06%. Recovery groups 1 and 3 were discriminated with greater accuracy (producer’s and user’s accuracies > 66%) than recovery group 2 (<50%). The top field-measured predictors of spectral recovery were mean height, dominant species, and percentage of stems in the plot that were deciduous. Variability in stand establishment and condition make it challenging to accurately discriminate among recovery rates within 10 years post-harvest. Our results indicate that the long-term metric Y2R relates to forest structure and composition attributes measured in the field and that spectral development post-disturbance corresponds with expectations of structural development, particularly height, for different species, site types, and deciduous abundance. These results confirm the utility of spectral recovery measures derived from LTS data to augment landscape-level assessments of post-disturbance recovery.
  • Lundell, Robin; Hänninen, Heikki; Saarinen, Timo; Åström, Helena; Zhang, Rui (2020)
    Bud dormancy of plants has traditionally been explained either by physiological growth arresting conditions in the bud or by unfavourable environmental conditions, such as non-growth-promoting low air temperatures. This conceptual dichotomy has provided the framework also for developing process-based plant phenology models. Here, we propose a novel model that in addition to covering the classical dichotomy as a special case also allows the quantification of an interaction of physiological and environmental factors. According to this plant-environment interaction suggested conceptually decades ago, rather than being unambiguous, the concept of "non-growth-promoting low air temperature" depends on the dormancy status of the plant. We parameterized the model with experimental results of growth onset for seven boreal plant species and found that based on the strength of the interaction, the species can be classified into three dormancy types, only one of which represents the traditional dichotomy. We also tested the model with four species in an independent experiment. Our study suggests that interaction of environmental and physiological factors may be involved in many such phenomena that have until now been considered simply as plant traits without any considerations of effects of the environmental factors.
  • Ylivinkka, Ilona; Kaupinmäki, Santeri; Virman, Meri; Peltola, Maija; Taipale, Ditte; Petäjä, Tuukka; Kerminen, Veli-Matti; Kulmala, Markku; Ezhova, Ekaterina (2020)
    We developed a simple algorithm to classify clouds based on global radiation and cloud base height measured by pyranometer and ceilometer, respectively. We separated clouds into seven different classes (stratus, stratocumulus, cumulus, nimbostratus, altocumulus + altostratus, cirrus + cirrocumulus + cirrostratus and clear sky + cirrus). We also included classes for cumulus and cirrus clouds causing global radiation enhancement, and we classified multilayered clouds, when captured by the ceilometer, based on their height and characteristics (transmittance, patchiness and uniformity). The overall performance of the algorithm was nearly 70% when compared with classification by an observer using total-sky images. The performance was best for clouds having well-distinguishable effects on solar radiation: nimbostratus clouds were classified correctly in 100% of the cases. The worst performance corresponds to cirriform clouds (50 %). Although the overall performance of the algorithm was good, it is likely to miss the occurrences of high and multilayered clouds. This is due to the technical limits of the instrumentation: the vertical detection range of the ceilometer and occultation of the laser pulse by the lowest cloud layer. We examined the use of clearness index, which is defined as a ratio between measured global radiation and modeled radiation at the top of the atmosphere, as an indicator of clear-sky conditions. Our results show that cumulus, altocumulus, altostratus and cirriform clouds can be present when the index indicates clear-sky conditions. Those conditions have previously been associated with enhanced aerosol formation under clear skies. This is an important finding especially in the case of low clouds coupled to the surface, which can influence aerosol population via aerosol-cloud interactions. Overall, caution is required when the clearness index is used in the analysis of processes affected by partitioning of radiation by clouds.
  • Dawson, Samantha K.; Berglund, Håkan; Ovaskainen, Otso; Snäll, Tord; Jonsson, Bengt G.; Jönsson, Mari (2020)
    Setting aside small remnant patches of high biodiversity forest within managed forest landscapes is often used as conservation measure to provide a refuge and future source population of forest biodiversity, including wood-inhabiting fungal communities. Yet little is known about the long-term fungal community assembly, how these small, isolated patches change through time and how forest management in the surrounding landscape impacts traits and community functionality housed within. We applied a joint species distribution model to compare how fungal traits and communities changed over two survey periods undertaken similar to 20 years apart in boreal forest set-aside and natural patches. Natural patches in naturally fragmented landscapes were considered reference forests for small, remnant, near-natural forest patches in intensively managed forest landscapes. We found the majority of fungal traits converged over time between set-aside and natural patches, without changes in overall species richness. Red-listed species occurrence was initially lower in set-aside patches, but reached a comparable level of natural patches over time as a result of opposing changes in both patch types. Functional trait changes were larger in set-aside patches, but convergence was also related to opposing changes in natural patches. This is the first study to directly measure and test wood fungal community trait-environment relationships over time in small, high-conservation value forest patches. The long-term functional trait and red-listed species values of set-asides, coupled with their capacity for old-growth recovery, make them valuable focal areas for conservation.
  • Kuttim, Martin; Hofsommer, Maaike L.; Robroek, Bjorn J. M.; Signarbieux, Constant; Jassey, Vincent E. J.; Laine, Anna M.; Lamentowicz, Mariusz; Buttler, Alexandre; Ilomets, Mati; Mills, Robert T. E. (2017)
    Decreasing snow cover in winter resulting from climate warming increases the incidence of freeze-thaw cycles (FTCs) in many ecosystems, including peatlands. As peatland ecosystems form a globally significant long-term carbon storage, understanding the effects of changing conditions in winter on carbon dynamics is essential. We studied how FTCs affect peatland carbon cycling by conducting mesocosm experiments with Sphagnum. Our results indicate an overall impeding effect of FTCs on Sphagnum photosynthesis, chlorophyll content, ecosystem respiration and enzymatic processes. A threefold reduction in photosynthesis in the FTC treatment was related to a decrease in chlorophyll content, showing that Sphagnum physiologically suffers from repeated FTCs. In the FTC treatment beta-glucosidase and phosphatase enzymatic activities decreased by 50% and 30%, respectively, whilst alanine remained unaffected, indicating that in peat soils short-term FTCs affect the carbon and phosphorus cycles, but not the nitrogen cycle. Long-term effects of FTCs deserve further studies.
  • Juurola, Eija; Korhonen, Janne F. J.; Kulmala, Liisa; Kolari, Pasi; Taipale, Ulla; Rasinmaki, Jussi; Ruuskanen, Taina; Haapoja, Terike; Back, Jaana; Levula, Janne; Riuttanen, Laura; Kyro, Ella-Maria; Dzhedzhev, Ivaylo; Nikinmaa, Eero; Vesala, Timo; Kulmala, Markku (2014)
  • De Marco, Anna; Esposito, Fabrizio; Berg, Björn; Zarrelli, Armando; De Santo, Amalia Virzo (2018)
    Research Highlights: Plant cover drives the activity of the microbial decomposer community and affects carbon (C) sequestration in the soil. Despite the relationship between microbial activity and C sequestration in the soil, potential inhibition of soil microbial activity by plant cover has received little attention to date. Background and Objectives: Differences in soil microbial activity between two paired stands on soil at a very early stage of formation and a common story until afforestation, can be traced back to the plant cover. We hypothesized that in a black locust (Robinia pseudoacacia L.) stand the high-quality leaf litter of the tree, and that of the blackberry (Rubus fruticosus L.) understory had an inhibitory effect on soil microbial community resulting in lower mineralization of soil organic matter compared to the paired black pine (Pinus nigra Arn.) stand. Materials and Methods: We estimated potential mineralization rates (MR), microbial (MB), and active fungal biomass (AFB) of newly-shed litter, forest floor, and mineral soil. We tested the effects of litters' water extracts on soil MR, MB, AFB and its catabolic response profile (CRP). Results: Newly-shed litter of black locust had higher MR than that of blackberry and black pine; MR, MB, and AFB were higher in forest floor and in mineral soil under black pine than under black locust. Water extracts of black locust and blackberry litter had a negative effect on the amount, activity of microorganisms, and CRP. Conclusions: The results demonstrate the potential for black locust and blackberry litter to have a marked inhibitory effect on decomposer microorganisms that, in turn, reduce organic matter mineralization with possible consequences at the ecosystem level, by increasing C sequestration in mineral soil.
  • Kuuluvainen, Timo; Lindberg, Henrik; Vanha-Majamaa, Ilkka; Keto-Tokoi, Petri; Punttila, Pekka (2019)
    In managed forests, leaving retention trees during final harvesting has globally become a common approach to reconciling the often conflicting goals of timber production and safeguarding biodiversity and delivery of several ecosystem services. In Finland, the dominant certification scheme requires leaving low levels of retention that can benefit some specific species. However, species responses are dependent on the level of retention and the current low amounts of retention clearly do not provide the habitat quality and continuity needed for declining and red-listed forest species which are dependent on old living trees and coarse woody debris. Several factors contribute to this situation. First, the ecological benefits of the current low retention levels are further diminished by monotonous standwise use of retention, resulting in low variability of retention habitat at the landscape scale. Second, the prevailing timber-oriented management thinking may regard retention trees as an external cost to be minimized, rather than as part of an integrated approach to managing the ecosystem for specific goals. Third, the main obstacles of development may still be institutional and policy-related. The development of retention practices in Finland indicates that the aim has not been to use ecological understanding to attain specific ecological sustainability goals, but rather to define the lowest level of retention that still allows access to the market. We conclude that prevailing retention practices in Finland currently lack ecological credibility in safeguarding biodiversity and they should urgently be developed based on current scientific knowledge to meet ecological sustainability goals.
  • Stendahl, Johan; Berg, Björn; Lindahl, Björn D. (2017)
    Carbon sequestration below ground depends on organic matter input and decomposition, but regulatory bottlenecks remain unclear. The relative importance of plant production, climate and edaphic factors has to be elucidated to better predict carbon storage in forests. In Swedish forest soil inventory data from across the entire boreal latitudinal range (n = 2378), the concentration of exchangeable manganese was singled out as the strongest predictor (R-2 = 0.26) of carbon storage in the extensive organic horizon (mor layer), which accounts for one third of the total below ground carbon. In comparison, established ecosystem models applied on the same data have failed to predict carbon stocks (R-2 <0.05), and in our study manganese availability overshadowed both litter production and climatic factors. We also identified exchangeable potassium as an additional strong predictor, however strongly correlated with manganese. The negative correlation between manganese and carbon highlights the importance of Mn-peroxidases in oxidative decomposition of recalcitrant organic matter. The results support the idea that the fungus-driven decomposition could be a critical factor regulating humus carbon accumulation in boreal forests, as Mn-peroxidases are specifically produced by basidiomycetes.
  • Pakkala, Timo; Tiainen, Juha; Piha, Markus; Kouki, Jari (2018)
    The Three-toed Woodpecker Picoides tridactylus is a mature and old-growth forest specialist but how the species uses trees for nesting in its breeding sites and whether cavity trees are a critical habitat feature is poorly known. We studied the nest tree characteristics of the species in a 170-km(2) area in southern Finland during 1987-2016. The data included 538 nest trees of eight different species and 665 nest cavities in 86 territory areas. Norway spruce Picea abler was the predominant nest tree comprising 71% of all nest trees. Proportionally, deciduous nest trees were more common in moist forests on mineral soils and conifer nest trees more common in spruce swamps. The majority of nest trees (85%) were dead or decaying trees; higher numbers of dead deciduous nest trees were recorded than dead conifer trees. The mean diameter of a nest tree at diameter at breast height (DBH) was 29.4 cm and the mean height of a cavity hole was 5.1 m; size and height were significantly positively correlated. The proportion of deciduous nest trees was significantly higher (45%) in natural forests compared with other areas subjected to variable amounts of forest management, where the respective proportion was only 9-17%. In addition, cavity holes were significantly higher in natural forests than in managed ones. In general, the results highlight the substantial flexibility in nest tree use but also the importance of large dead and decaying trees (including deciduous trees) as nest cavity sites for the species. Spruce swamps can be considered as key nesting habitats in managed forest landscapes.
  • Alekseychik, Pavel; Mammarella, Ivan; Karpov, Dmitry; Dengel, Sigrid; Terentieva, Irina; Sabrekov, Alexander; Glagolev, Mikhail; Lapshina, Elena (2017)
    Very few studies of ecosystem-atmosphere exchange involving eddy covariance data have been conducted in Siberia, with none in the western Siberian middle taiga. This work provides the first estimates of carbon dioxide (CO2) and energy budgets in a typical bog of the western Siberian middle taiga based on May-August measurements in 2015. The footprint of measured fluxes consisted of a homogeneous mixture of tree-covered ridges and hollows with the vegetation represented by typical sedges and shrubs. Generally, the surface exchange rates resembled those of pinecovered bogs elsewhere. The surface energy balance closure approached 100 %. Net CO2 uptake was comparatively high, summing up to CO2 gCm(-2) for the four measurement months, while the Bowen ratio was seasonally stable at 28 %. The ecosystem turned into a net CO2 source during several front passage events in June and July. The periods of heavy rain helped keep the water table at a sustainably high level, preventing a usual drawdown in summer. However, because of the cloudy and rainy weather, the observed fluxes might rather represent the special weather conditions of 2015 than their typical magnitudes.
  • Hui, Nan; Liu, Xinxin; Jumpponen, Ari; Setälä, Heikki; Kotze, D. Johan; Biktasheva, Liliya; Romantschuk, Martin (2018)
    Although soil-inhabiting fungi can affect tree health and biomass production in managed and pristine forests, little is known about the sensitivity of the plant-fungal associations to long-term changes in land use. We aimed to investigate how reforestation of farmlands change soil characteristics and affected the recovery of soil fungal functional guilds. We examined edaphic conditions and fungal communities (Illumina Sequencing) in three land-use types: primary forests (PF), secondary forests (SF, established over two decades ago) and active farmlands during May, July and September in Wuying, China. Edaphic conditions and general fungal communities varied with land-use. Interestingly, overall fungal diversity was higher in soils at the farmland than at the forested sites, possibly as a result of recurring disturbances (tilling) allowing competitive release as described by the intermediate disturbance hypothesis. Although ectomycorrhizal fungal diversity and richness were marginally higher in PF than in SF, the latter still hosted surprisingly diverse and abundant ectomycorrhizal fungal communities. Reforestation largely restored fungal communities that were still in transition, as their composition in SF was distinct from that in PF. Our results highlight the ability of fungi grown in previously strongly managed agricultural land to rapidly respond to reforestation and thus provide support for forest trees.
  • Ryhti, Kira; Kulmala, Liisa; Pumpanen, Jukka; Isotalo, Jarkko; Pihlatie, Mari; Helmisaari, Heljä-Sisko; Leppälammi-Kujansuu, Jaana; Kieloaho, Antti-Jussi; Bäck, Jaana; Heinonsalo, Jussi (2021)
    Changes in the climate may have unpredictable effects on belowground carbon processes and thus, the carbon balance of boreal forests. To understand the interactions of these processes in soil and to quantify the potential changes in the carbon cycle, partitioning of forest floor respiration is crucial. For this purpose, we used nine different treatments to separate the sources of forest floor carbon dioxide (CO2) emissions in a mature Scots pine (Pinus sylvestris L.) stand in southern Finland. To partition the belowground CO2 emissions, we used two different trenching methods: 1) to exclude roots and mycorrhizal fungal mycelia (mesh with 1-mu m pores) and 2) to exclude roots, but not mycorrhizal hyphae (mesh with 50-mu m pores). Additionally, we used 3) a control treatment that included roots and fungal hyphae. To partition the CO2 emissions from the forest floor vegetation, we 1) removed it, 2) left only the dwarf shrubs, or 3) left the vegetation intact. The forest floor CO2 emissions were regularly measured with a flux chamber throughout the growing seasons in 2013-2015. The total forest floor respiration was partitioned into respiration of tree roots (contributing 48%), heterotrophic soil respiration (30%) and respiration of ground vegetation other than shrubs (10%), dwarf shrubs (8%), and hyphae of mycorrhizal fungi (4%). Heterotrophic respiration increased in the trenched treatments without ground vegetation over time, due to the so-called 'Gadgil effect'. In the absence of tree mots, but when hyphal access was allowed, respiration in the dwarf shrub treatment increased throughout the experiment. This indicated that dwarf shrubs had fungal connections to outside the experimental plots via their ericoid mycorrhiza. At the same time, other ground vegetation, such as mosses, suppressed the dwarf shrub respiration in trenched treatments. Our results show that competition on the forest floor is intense between plant roots and soil microbes.
  • Piilo, Sanna; Zhang, Hui; Garneau, Michelle; Gallego-Sala, Angela V.; Amesbury, Matthew; Väliranta, Minna (2019)
    Peatland ecosystems are important carbon sinks, but also release carbon back to the atmosphere as carbon dioxide and methane. Peatlands therefore play an essential role in the global carbon cycle. However, the response of high-latitude peatlands to ongoing climate change is still not fully understood. In this study, we used plant macrofossils and peat property analyses as proxies to document changes in vegetation and peat and carbon accumulation after the Little Ice Age. Results from 12 peat monoliths collected in high-boreal and low-subarctic regions in northwestern Quebec, Canada, suggest high carbon accumulation rates for the recent past (post AD 1970s). Successional changes in plant assemblages were asynchronous within the cores in the southernmost region, but more consistent in the northern region. Average apparent recent carbon accumulation rates varied between 50.7 and 149.1 g C m(-2) yr(-1) with the northernmost study region showing higher values. The variation in vegetation records and peat properties found within samples taken from the same sites and amongst cores taken from different regions highlights the need to investigate multiple records from each peatland, but also from different peatlands within one region.
  • Matkala, Laura; Salemaa, Maija; Bäck, Jaana (2020)
    The relationship of the community composition of forest vegetation and soil nutrients were studied near the Sokli phosphate ore deposit in northern Finland. Simultaneously, the effects of the dominant species and the age of trees, rock parent material and soil layer on these nutrients were examined. For this purpose, 16 study plots were established at different distances from the phosphate ore along four transects. Phosphate mining may take place in Sokli in the future, and the vegetation surveys and soil sampling conducted at the plots can be used as a baseline status for following the possible changes that the mining may cause in the surrounding ecosystem. The total phosphorus (P) and nitrogen (N) contents of the soil humus layer were positively related with species number and abundance of the understorey vegetation, and the correlation was slightly higher with P than N. This is interesting, as N usually has the most important growth-limiting role in boreal ecosystems. The spatial variation in the content of soil elements was high both between and within plots, emphasizing the heterogeneity of the soil. Dominant tree species and the soil layer were the most important environmental variables affecting soil nutrient content. High contents of P in the humus layer (maximum 2.60 g kg(-1)) were measured from the birch-dominated plots. As the P contents of birch leaves and leaf litter were also rather high (2.58 and 1.28 g kg(-1), respectively), this may imply that the leaf litter of birch forms an important source of P for the soil. The possible mining effects, together with climate change, can have an influence on the release of nutrients to plants, which may lead to alterations in the vegetation community composition in the study region.
  • Pavelka, Marian; Acosta, Manuel; Kiese, Ralf; Altimir, Nuria; Bruemmer, Christian; Crill, Patrick; Darenova, Eva; Fuss, Roland; Gielen, Bert; Graf, Alexander; Klemedtsson, Leif; Lohila, Annalea; Longdoz, Bernhard; Lindroth, Anders; Nilsson, Mats; Jimenez, Sara Maranon; Merbold, Lutz; Montagnani, Leonardo; Peichl, Matthias; Pihlatie, Mari; Pumpanen, Jukka; Ortiz, Penelope Serrano; Silvennoinen, Hanna; Skiba, Ute; Vestin, Patrik; Weslien, Per; Janous, Dalibor; Kutsch, Werner (2018)
    Chamber measurements of trace gas fluxes between the land surface and the atmosphere have been conducted for almost a century. Different chamber techniques, including static and dynamic, have been used with varying degrees of success in estimating greenhouse gases (CO2, CH4, N2O) fluxes. However, all of these have certain disadvantages which have either prevented them from providing an adequate estimate of greenhouse gas exchange or restricted them to be used under limited conditions. Generally, chamber methods are relatively low in cost and simple to operate. In combination with the appropriate sample allocations, chamber methods are adaptable for a wide variety of studies from local to global spatial scales, and they are particularly well suited for in situ and laboratory-based studies. Consequently, chamber measurements will play an important role in the portfolio of the Pan-European long-term research infrastructure Integrated Carbon Observation System. The respective working group of the Integrated Carbon Observation System Ecosystem Monitoring Station Assembly has decided to ascertain standards and quality checks for automated and manual chamber systems instead of defining one or several standard systems provided by commercial manufacturers in order to define minimum requirements for chamber measurements. The defined requirements and recommendations related to chamber measurements are described here.
  • Fraixedas, Sara; Linden, Andreas; Meller, Kalle; Lindström, Åke; Keiss, Oskars; Kålås, John Atle; Husby, Magne; Leivits, Agu; Leivits, Meelis; Lehikoinen, Aleksi (2017)
    Northern European peatlands are important habitats for biological conservation because they support rich biodiversity and unique species compositions. However, historical management of peatland habitats has had negative consequences for biodiversity and their degradation remains a major conservation concern. Despite increasing awareness of the conservation value of peatlands, the statuses and ecological requirements of peat land species have remained largely understudied. Here, we first analysed temporal trends of Northern European peatland birds to document the status of their populations using bird data from five different countries. Second, we used Finnish monitoring data to assess habitat preferences of peatland bird species, hence helping to target conservation to the most relevant habitat types. There was a general decline of 40% in Northern European peatland bird population sizes in 1981-2014 (speed of decline 1.5%/year) largely driven by Finland, where populations declined almost 50% (2.0% annual decline). In Sweden and Norway, peatland bird populations declined by 20% during 1997-2014 (1.0% annual decline). In contrast, southern populations in Estonia and Latvia, where the majority of open peatlands are protected, showed a 40% increase during 1981-2014 (1.0% annual increase). The most important habitat characteristics preferred by common peatland species in Finland were openness and low tree height, while wetness proved to be an important feature for waders. Drainage of peatlands had clear negative effects on the densities of many species, with the only exception of rustic bunting, which specializes on edge habitats. Our findings call for more effective conservation actions in Northern European peatland habitats, especially in Finland where peatland drainage represents a major threat to biodiversity.
  • Ding, Yiyang; Schiestl-Aalto, Pauliina; Helmisaari, Heljä-Sisko; Makita, Naoki; Ryhti, Kira; Kulmala, Liisa (2020)
    Scots pine (Pinus sylvestris L.) is one of the most important conifers in northern Europe. In boreal forests, over one-third of net primary production is allocated to roots. Pioneer roots expand the horizontal and vertical root systems and transport nutrients and water from belowground to aboveground. Fibrous roots, often colonized by mycorrhiza, emerge from the pioneer roots and absorb water and nutrients from the soil. In this study, we installed three flatbed scanners to detect the daily growth of both pioneer and fibrous roots of Scots pine during the growing season of 2018, a year with an unexpected summer drought in southern Finland. The growth rate of both types of roots had a positive relationship with temperature. However, the relations between root elongation rate and soil moisture differed significantly between scanners and between root types indicating spatial heterogeneity in soil moisture. The pioneer roots were more tolerance to severe environmental conditions than fibrous roots. The pioneer roots initiated elongation earlier and ceased it later than the fibrous roots. Elongation ended when the temperature dropped below the threshold temperature of 4°C for pioneer roots and 6°C for fibrous roots. During the summer drought, the fibrous roots halted root surface area growth at the beginning of the drought, but there was no drought effect on the pioneer roots over the same period. To compare the timing of root production and the aboveground organs’ production, we used the CASSIA model, which estimates the aboveground tree carbon dynamics. In this study, root growth started and ceased later than growth of aboveground organs. Pioneer roots accounted for 87% of total root productivity. We suggest that future carbon allocation models should separate the roots by root types (pioneer and fibrous), as their growth patterns are different and they have different reactions to changes in the soil environment.
  • Kaarlejarvi, Elina; Salemaa, Maija; Tonteri, Tiina; Merila, Paivi; Laine, Anna-Liisa (2021)
    Aim The diversity and composition of natural communities are rapidly changing due to anthropogenic disturbances. Magnitude of this compositional reorganization varies across the globe, but reasons behind the variation remain largely unknown. Disturbances induce temporal turnover by stimulating species colonizations, causing local extinctions, altering dominance structure, or all of these. We test which of these processes drive temporal community changes, and whether they are constrained by natural environmental gradients. Moreover, we assess to what degree identity shifts translate to changes in dominance structure. Location Finland. Time period Observations 1985-2006, disturbance history > 140 years. Major taxa studied Vascular plants. Methods We investigated temporal turnover of boreal forest understorey in response to disturbance, here forest management, along a soil fertility gradient. We disentangle the roles of species gains, losses and abundance changes in driving temporal turnover in response to and after disturbance by comparing turnover rates in different forest age categories along a fertility gradient. We quantify temporal turnover using richness-based complement of Jaccard's similarity index and proportional-abundance based dissimilarity index. We also test whether disturbance history or fertility influence the relationship between identity shifts and dominance structure. Results We found that the impact of disturbance on temporal turnover depends on soil fertility. The greatest turnover occurred in the most fertile forests immediately after disturbance. There, species gains and losses strongly altered dominance structure leading to high turnover, whereas undisturbed old forests and nutrient-poor habitats were characterized by stable dominant species even when the majority of species shifted their identity. Main conclusions Our results suggest that human impacts on temporal biodiversity change vary along environmental gradients. In boreal forests, the fertile habitats have a higher probability than nutrient-poor sites of changing their composition in response to anthropogenic disturbances. Resource availability and disturbance history may thus influence consequences of temporal turnover for ecosystem functioning.