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| 2. |
- Stuiver, Babs, et al.
(författare)
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Nitrogen fixation rates associated with the feather mosses Pleurozium schreberi and Hylocomium splendens during forest stand development following clear-cutting
- 2015
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 347, s. 130-139
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Tidskriftsartikel (refereegranskat)abstract
- Pleurocarpous feather mosses host di-nitrogen (N-2) fixing cyanobacteria, and this association serves as an important source of N input to late-successional natural boreal forests. However, little is known about how forest management affects feather mosses and their associated N-2-fixation rates, or how these rates change during post-logging stand development. We established a chronosequence of 32 forest stands used for commercial wood production to better understand how stand development after clear-cutting drives changes in biomass and N-2-fixation rates of the two dominant feather mosses, Pleurozium schreberi and Hylocomium splendens. These stands included eight replicate stands of each of four stand types: (1) recently clear-cut and newly planted stands (CC, 4 years); (2) pre-commercial thinning stands (PCT, 16 years); (3) first thinning stands (T1, 34 years); and (4) mature uncut forest (MF, 123 years), all dominated by Pinus sylvestris. We found that clear-cutting did not reduce moss biomass relative to the uncut forest. Further, biomass of P. schreberi (but not of H. splendens) increased twofold from CC stands to PCT stands, and remained high throughout the T1 stands. Di-nitrogen fixation capacity, determined as the amount of N fixed per unit moss mass, was ca. six and three times larger in PCT stands compared to the other stand types for P. schreberi and H. splendens respectively. Correlation analyses showed that N-2-fixation capacity associated with both moss species increased with increasing Empetrum hermaphroditum biomass, and that N-2-fixation capacity of P. schreberi declined with increasing NH4+ availability. Further, correlation analysis showed that N-2-fixation capacity of H. splendens declined with increasing tree biomass and decreasing light transmission. The total amount of N fixed at the stand level was highest in the PCT stands (1.0 kg ha(-1) year(-1) of N), and was associated with both high moss biomass and high N-2-fixation capacity. The contribution of N-2-fixation to total N accrual per hectare during stand development was ca. 9%, and across the chronosequence N-2 was fixed on average at rates of 0.4 kg ha-1 year-1. Our results show that N-2-fixation rates in feather moss communities were promoted by the conditions at the PCT stands approximately 16 years after clear-cutting, while N-2-fixation rates were lowest under conditions at the newly clear-cut and mature stands. Further, it suggests that mosses and associated N-2-fixation can be important in maintaining a long-term N balance, and that this source of N input should be accounted for when modeling N balance in N-limited managed boreal forests. (C) 2015 Elsevier B.V. All rights reserved.
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| 3. |
- Stuiver, Babs, et al.
(författare)
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Seedling responses to changes in canopy and soil properties during stand development following clear-cutting
- 2016
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 378, s. 31-43
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Tidskriftsartikel (refereegranskat)abstract
- The role of natural regeneration in silvicultural systems is attracting increasing interest, but much is unknown about how stand development after clear-cutting affects seedling regeneration. We looked at the impact of tree canopy and ground layer vegetation (i.e., 'stand type') as well as soil properties (i.e., 'soil origin' or stand from which soil originated) on survival and growth of Pinus sylvestris and Picea abies seedlings at three forest developmental stages, i.e., 4, 16 and 34 years after clear-cutting. To do this we transplanted soil cores between stands of different stages to separate the effects of soil properties versus canopy closure on seedling performance. We found that seedling survival of both species was highest when planted in the oldest stands independent of soil origin. P. sylvestris seedling growth responded to stand type but not soil origin, and biomass was highest at the youngest stand likely because of greater light availability. Meanwhile, although P. abies seedling root biomass responded to stand type, this species was mostly responsive to soil origin, with shoot and total biomass being greatest when seedlings were grown in soil originating from the oldest stands. These findings have implications for our understanding of tree regeneration of species that differ in their responsiveness to light and soil characteristics. The results can further inform forest managers about how to optimize survival and growth of seedlings by means of canopy regulation as well as provide information to assist the regeneration and development of multi-storied forest stands. (C) 2016 Elsevier B.V. All rights reserved.
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| 4. |
- Stuiver, Babs
(författare)
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Stand development effects on N₂-fixation and seedling performance in northern boreal forests
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For large parts of the Swedish boreal forests, stand development starts with clear-cutting. Still, much is unknown about how stand development affects ecosystem processes and how these processes are driven by changes in vegetation and soil properties that occur during stand development. In this thesis, the processes of feather moss associated N₂-fixation and tree seedling regeneration are examined along a post clear-cut chronosequence which consisted of 32 stands; eight in each of four development stages with mean ages of 4, 16, 34, and 123 years. Stand development had statistically significant effects on the total amount of N fixed at the stand level. The N₂-fixation rates initially increased after clear-cutting and peaked in the 16-year old stands at rates of 1.0 kg N ha-1 yr-1, after which the rates declined and remained at levels similar to those found in young clear-cut stands even when stands had reached maturity. This pattern was associated with high moss biomass and positive effects of local conditions on N fixed per kg moss mass in the 16-year old stands. The cumulative contribution of N₂-fixation to the total accrual of N per ha in the aboveground vegetation and humus layer during one stand rotation was about 9%. Stand development had negative effects on the growth of Pinus sylvestris seedlings as a consequence of changes in the canopy. In contrast, the effect of stand development on Picea abies seedling growth was mainly driven by soil properties, and seedlings performed best when grown in soils originating from the 34-year old stands. Seedling mortality decreased with stand age for both P. sylvestris and P. abies seedlings, which was mainly caused by a positive effect of the canopy. The effect of several moss species on P. sylvestris seedling growth was further explored in a greenhouse mesocosm experiment. Seedling growth was most negatively affected by Hylocomium splendens and in pots with high moss biomass, likely driven by differences in moss depth related to moss species and moss biomass. This thesis shows that stand development has strong effects on N₂-fixation rates and the performance of P. sylvestris and P. abies seedlings in production forests. However, these effects and their drivers do not necessarily respond linearly to stand development and can differ between moss and tree species with potential long-term consequences for the functioning of boreal forests.
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| 5. |
- Stuiver, Babs, et al.
(författare)
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The Impact of Moss Species and Biomass on the Growth of Pinus sylvestris Tree Seedlings at Different Precipitation Frequencies
- 2014
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 5, s. 1931-1951
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Tidskriftsartikel (refereegranskat)abstract
- Boreal forests are characterized by an extensive moss layer, which may have both competitive and facilitative effects on forest regeneration. We conducted a greenhouse experiment to investigate how variation in moss species and biomass, in combination with precipitation frequency, affect Pinus sylvestris seedling growth. We found that moss species differed in their effects on seedling growth, and moss biomass had negative effects on seedlings, primarily when it reached maximal levels. When moss biomass was maximal, seedling biomass decreased, whereas height and above-relative to below-ground mass increased, due to competition for light. The effect that moss biomass had on seedling performance differed among the moss species. Hylocomium splendens and Polytrichum commune reduced seedling growth the most, likely because of their taller growth form. Seedlings were not adversely affected by Sphagnum girgensohnii and Pleurozium schreberi, possibly because they were not tall enough to compete for light and improved soil resource availability. Reduced precipitation frequency decreased the growth of all moss species, except P. commune, while it impaired the growth of seedlings only when they were grown with P. commune. Our findings suggest that changes in moss species and biomass, which can be altered by disturbance or climate change, can influence forest regeneration.
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