Decadal time-scale vegetation changes at high latitudes:responses to climatic and non-climatic drivers

• Main Author: Maliniemi, T. (Tuija)
• Other Authors: Virtanen, R. (Risto), Oksanen, J. (Jari), Hjort, J. (Jan)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Oulun yliopisto 2018
• Subjects: boreal forests; bryophytes; climate change; community ecology; lichens; long-term studies; plant communities; plant diversity; reindeer grazing; treeless heaths; tundra; vascular plants; vegetation dynamics; vegetation resurvey; boreaaliset metsät; diversiteetti; ilmastonmuutos; jäkälät; kasvillisuuden dynamiikka; kasviyhteisöt; laidunnus; pitkäaikaistutkimukset; putkilokasvit; puuttomat kankaat; sammalet; uudelleenkartoitus; uudelleenotanta; yhteisöekologia; Arctic; Climate change; Empetrum nigrum; Fennoscandia; Tundra
• Online Access: http://urn.fi/urn:isbn:9789526220123

Abstract Boreal and arctic plant communities are responding to anthropogenic climate change that has been exceptionally rapid during the recent decades. General responses include increased productivity, range expansions and biodiversity changes, all of which affect ecosystem functions. Vegetation dynamics are however controlled by multiple drivers, and the outcomes under the changing climate are not yet fully clear. As high latitude areas often lack long-term monitoring of vegetation, alternative methods are required to observe and understand vegetation changes and dynamics. Recently, resurveying historical vegetation data has become a valuable method of studying vegetation changes over the past few decades. In this thesis, I studied multidecadal (23–60 years) vegetation changes in forest and treeless heath and tundra plant communities along a latitudinal gradient in northern Fennoscandia using both vegetation resurveys and long-term experimental data. In addition to examining climate-driven vegetation changes, I related changes in plant communities to key local drivers of each context including mesotopography, grazing, soil moisture and soil fertility. General trends among the resurveyed treeless heath sites were the pronounced increase of the dwarf shrub Empetrum nigrum ssp. hermaphroditum in snow-protected habitats and the decrease of lichens throughout. Southernmost heath communities showed strong responses to multidriver effects and had shifted towards new community states. The long-term experiment in the tundra confirmed that depending on driver combinations, tundra communities evolve towards divergent alternative states, highlighting the importance of local drivers in modifying tundra vegetation over time. Communities in fertile forest sites experienced greater temporal turnover compared to infertile forest sites, suggesting that the soil fertility level is a key predictor of vegetation changes under climate change. This particularly important finding previously relied mainly on experimental evidence. ...