Regeneration of trees - influence of climate, disturbance and ecological factors

How is plant establishment affected by the bottom layer. This is one of the topics studied in the project. Photo Mats Hannerz.

The research is structured along the following themes:

1. Interactive effects of feather mosses and dwarf shrubs on tree seedlings following disturbance.
   This project specifically focuses at addressing questions that improve the knowledge about how conifer and broadleaved trees respond to abiotic and biotic factors in forests of different disturbance history including those of a changed climate. Much of this work is focused on the role of feather mosses to provide nitrogen input to soils and in mediating climate change effects on tree growth. This will in turn be useful in predicting in which sites and under what conditions mosses and dwarf shrubs are most likely to be influenced by forestry operations and under what conditions understory (mosses in particular) will impact regeneration of different forest species.
2. Effects of fire on the regeneration of native and exotic tree species and soil properties.
   The work in this project is directed to study how tree seedlings respond to orders of fire severity and different charcoal types produced from prescribed burning on soils of varying productivity. Part of this work is also directed to better understand how biochar from forest residues impact on tree growth and biogeo­chemical cycling of boreal forest ecosystems.As such we expect this work will provide fundamental knowledge that should enhance our understanding of the mechanisms underpinning the effect of fire on forest recruitment, and yield new insights as to how forest management practices can improve natural regeneration and growth of desired tree species.
3. The role of soil biotic interactions in regulating growth of exotic tree species.
   This project explores the role of soil biota in influencing the growth of the non-native Pinus contorta introduced to Swedish plantations. This work will provide new understanding of the mechanisms for why some exotic tree species can function so well in their new environment, and will provide useful insight of help for production forestry dealing with exotic species.
4. The effects of atmospheric N deposition on ecosystem C balance and tree growth.
   The aim of this work is to understand how environmental nitrogen pollution via atmospheric N deposition lead to changes in the net carbon balance of boreal forest ecosystems. We seek to do this by understanding how aboveground biomass pools change in response to simulated atmospheric N inputs. We subsequently investigate how C sequestration in the soil changes, due to a variety of mechanisms including changes in the quantity and quality of litter inputs, as well as changes in microbial community composition, and decomposition rates. This work will provide advanced understanding of how aboveground biomass production by trees will respond to global change.

Major research achievements

• Discovering that accumulation of C in boreal forests in the long term absence of fire arises primarily from mycorrhizal fungal residues, rather than from plant litter as per previous dogma. These findings were published in Science and profiled in commentaries in both Science and Nature as well as in the worldwide media.
• Biologically fixed N₂ by cyanobacteria associated with boreal feather mosses was found to be transferred to moss tissues, providing undisputed evidence of the role of feather mosses in contributing to boreal forest nutrition. This discovery was published in New Phytologist as a ‘Rapid report’ and profiled by a commentary article in the same volume.
• The impacts of a secondary stressor (i.e. herbivory) on Scots pine seedlings were shown to both increase or reduce the effects of a primary stressor (i.e. drought). This study also revealed for the first time that the relative intensities of multiple stressors are critical in determining the direction and magnitude of their impacts on establishing seedlings. This work was published in Tree Physiology and featured by a front cover and commentary article in the same volume.
• Discovery that interactions with soil biota shift from negative to positive when Pinus contorta (a North American conifer) is planted in Sweden compared to its native range.  This was a key finding of a unique greenhouse experiment using Canadian and Swedish soils, where soils were sterilized and re-innoculated with soil biota.  The results have substantial implications for understory the high level of productivity this species achieves in Sweden, and will start a new line of work looking at the net effect of soil biotic communities on tree growth in Swedish forestry.  The results are in review with the journal New Phytologist as a ‘Rapid report’ and profiled by a commentary article in the same volume.
• Discovery that anthropogenic nitrogen deposition causes a minor quantity of carbon to be sequestered into boreal ecosystems.  It has been proposed that as much as 450 parts of C are sequestered for every unit of N deposition in the boreal region, which would account for almost 1/3 of annual anthropogenic C emissions.  Our study published in Global Change Biology (2014) shows that only 16 parts C are sequestered for every unit of N, indicating that N deposition in boreal forests plays only a minor role in the global C cycle.

Field experimental sites

• A long-term forest island fire chronosequence in Arjeplog spanning over 6000 years since last fire disturbance.
• A forest fire chronosequence in Arvidsjaur ranging over the last 45 to 350 years after wildfire.
• A clear-cut chronosequence consisting of forest sites owned by Sveaskog in Arvidsjaur involving sites that were recently clear-cut (0-6 years ago), sites that were cut 12-19 years ago (pre-commercial thinning stands), those that were cut 26-42 years ago (thinning stands) and those that have not been cut over the last 100 years (mature forest).
• An experimental burning sites at a clear-cut and intact forest at Gammnybränna, the Unit for Field-based Research in Vindeln.
• An experimental site for biochar application at the Unit for Field-based Research in Vindeln.
• An 18-year running stand scale experimental simulated N deposition experiment at the Unit for Field-based Research in Vindeln.   

Selected publications:

2014

Pluchon N, MJ Gundale, M-C Nilsson, P Kardol, and DA Wardle (2014) Stimulation of boreal tree seedling growth by wood-derived charcoal: effects of charcoal properties, seedling species, and soil fertility. Functional Ecology (in press). doi: 10.1111/1365-2435.12221

Gundale MJ, Kardol P, Nilsson M-C, Nilsson U, Lucas RW and DA Wardle (2014) Interactions with soil biota shift from negative to positive when a tree species is moved outside its native range. New Phytologist (Rapid report) (in press) DOI: 10.1111/nph.12699

Bokhorst, S., D.A. Wardle, M-C. Nilsson, and M.J. Gundale (2014) The effect of plant species and functional group removal on soil arthropod communities along a boreal forest chronosequence.  Plant and Soil: In Press.

Gundale, M.J., F. From, L. Back-Holmen, and A. Nordin (2014) Nitrogen deposition in boreal forests has a minor impact on the global carbon cycle. Global Change Biology: 20:276-286. 

Gundale M.J., A. Pauchard, B. Langdon, D.A. Peltzer, B.D. Maxwell, and M.A. Nunez (2014) Can model species advance the field of invasion ecology? Biological Invasions (in press).

Jeffery, S., Bezemer, T., Cornelissen, G., Kuyper, T., Lehmann, J., Mommer, L., Sohi, S., van de Voorde, T., Wardle, D. A. and van Groenigen, J. W (2014). The way forward in biochar research: targeting trade-offs between the potential wins. Global Change Biology – Bioenergy (in press).

McLauchlan, K , Higuera, P. E., Gavin, D. G., Perakis, S. S., Mack, M. C., Alexander, H.,  Battles, J., Biondi, F., Buma, B., Colombaroli, D., Enders, S., Engstrom, D. R., Hu, F. S.,  Marlon, R. R., Marshall, J., McGlone, M., Morris, J. J., Nave, L. E., Shuman, B. N., Smithwick, E., Urrego, D. H., Wardle, D. A., Williams, C. J. and Williams, J. J. (2014) Reconstructing disturbances and their biogeochemical consequences over multiple timescales. BioScience (in press).

DeLuca, T.H., M.J. Gundale, M.D. MacKenzie, and D.L. Jones (2014) Bio-char effects on soil nutrient transformation. 2^nd Edition. Chapter 14. In: Lehmann, J. and Joseph, S. (eds). Biochar for Environmental Management: Science and Technology. Earthscan Publications Ltd, London. (in press)

2013

Lindo Z, M-C Nilsson, and MJ Gundale (2013) Bryophyte-cyanobacteria associations as regulators of the northern latitude carbon balance in response to global change.  Global Change Biology: 19: 2022-2035.

Bansal S, Hallsby G, Lofvenius MO, and Nilsson M-C (2013) Synergistic, additive and antagonistic impacts of drought and herbivory on Pinus sylvestris: leaf, tissue and whole-plant responses and recovery. Tree Physiology 33: 451-463.

Bay, G., Nahar, N., Oubre, M., Whitehouse, M., Wardle, D. A., Zackrisson, O., Nilsson, M.-C. and Rasmussen, U. (2013) Boreal feather mosses secrete chemical signals to gain nitrogen. New Phytologist (Rapid Report) 200: 54-60.

Clemmensen, K. E., Bahr, A., Ovaskainen, O., Dahlberg, A., Ekblad, A., Wallander, H.,  Stenlid, J., Finlay, R. D., Wardle, D. A. and Lindahl, B. D. (2013) Roots and associated fungi drive long-term carbon sequestration in boreal forest. Science 339: 904-919.

Hyodo, F., Kusaka, S., Wardle, D. A. and Nilsson, M.-C. (2013) Changes in stable nitrogen and carbon isotope ratios of plants and soil across a boreal forest fire chronosequence. Plant and Soil 367: 111-119.

Jackson, B. G., Nilsson, M.-C. and Wardle, D. A. (2013) The effects of the moss layer on the decomposition of intercepted vascular plant litter across a post-fire boreal forest chronosequence. Plant and Soil 367: 119-214.

Simberloff, D., Martin, J.-L., Genovesi, P., Maris, V., Wardle, D. A., Aronson, J., Courchamp, F., Galil, B., García-Berthou, E., Pascal, M., Pyšek, P., Sousa, R., Tabacchi, E., and Vilà, M. (2013) Impacts of biological invasions - what’s what and the way forward. Trends in Ecology and Evolution 28: 58-66.

Wik Persson, L (2013) Nitrogen fixation among boreal feather mosses along a clear-cut chronosequence . Second cycle, A2E. Umeå: SLU, Dept. of Forest Ecology and Management.

Gundale, M.J., L. Back-Holmen, and A. Nordin (2013) The impact of simulated chronic nitrogen deposition on the biomass and N2-fixation activity of two boreal feather moss-cyanobacteria associations.  Biology Letters 9: 20130797.

2012

Bansal, S., Nilsson, M.-C. and Wardle, D. A. (2012) Response of photosynthetic carbon gain to ecosystem retrogression of vascular plants and mosses in the boreal forest. Oecologia 169: 661-672.

Gundale, M. J., Hyodo, M., Nilsson, M.-C. & Wardle, D. A. (2012) Nitrogen niches revealed through species and functional group removal in a boreal shrub community. Ecology 93: 1695-1704.

Gundale, M. J., Wardle, D. A. and Nilsson, M.-C. (2012) The effect of altered macroclimate on N-fixation by boreal feather mosses. Biology Letters 8: 805-808.

Gundale, M.J., Nilsson, M., Bansal, S., Jäderlund, A. (2012) The interactive effects of temperature and light on biological nitrogen fixation in boreal forests. New Phytologist 194:454-463. 

McIntosh, A.C.S., Macdonald, S.E. and Gundale, M.J. (2012).  Tree species versus regional controls on ecosystem properties and processes: an example using introduced Pinus contorta in Swedish boreal forests.  Canadian Journal of Forest Research. 42:1228-1238.

2011

Jackson, B. G., Martin, P., Nilsson, M.-C. and Wardle, D. A. (2011) Response of feather moss-associated nitrogen fixation and litter decomposition to variations in simulated rainfall intensity and frequency. Oikos 120: 170-180.

Gundale, M. J., Fajardo, A., Lucas, R. W., Nilsson, M.-C. and Wardle, D. A. (2011) Resource heterogeneity does not explain the productivity-diversity relationship across a boreal island fertility gradient. Ecography 34: 887-896. 

Gundale MJ, T.H. DeLuca, and A. Nordin (2011) Bryophytes attenuate anthropogenic nitrogen inputs in boreal forests. Global Change Biology: 17:2743-2753.