Physical disturbance determines effects from nitrogen addition on ground vegetation in boreal coniferous forests
Article first published online: 31 OCT 2011
© 2011 International Association for Vegetation Science
Journal of Vegetation Science
Volume 23, Issue 2, pages 361–371, April 2012
How to Cite
Strengbom, J., Nordin, A. (2012), Physical disturbance determines effects from nitrogen addition on ground vegetation in boreal coniferous forests. Journal of Vegetation Science, 23: 361–371. doi: 10.1111/j.1654-1103.2011.01359.x
- Issue published online: 14 MAR 2012
- Article first published online: 31 OCT 2011
- Manuscript Accepted: 26 SEP 2011
- Manuscript Received: 23 NOV 2010
- Erik Rönnbergs Fond
- Oscar och Lily Lamms Minne
- Swedish Research Council for Environment
- Agricultural Sciences and Spatial Planning
- Carl Tryggers Stiftelse för Vetenskaplig Forskning
- Ground vegetation;
- Multiple perturbations;
- Nitrogen enrichment;
Nitrogen (N) enrichment often appears in combination with land-use related disturbances. Are there interactive effects between N addition and physical disturbances where N addition increases plant community sensitivity to disturbance?
Boreal coniferous forest, Bispgården (63 °00′N, 16 °40′E), central Sweden.
We tested potential interactive effects between N addition and disturbance by evaluating effects of N fertilization on community composition of forest floor vegetation in clear-cut (disturbed) and mature (undisturbed) forests. We analysed species composition in 63 forests stands (16 clear-cut and N-fertilized, 14 clear-cut and unfertilized, 17 mature and N fertilized, and 16 mature and unfertilized). Species composition was scored by the point-intercept method at 200 random points along a 45-m transect in each stand.
The N effect on plant community composition was strongly dependent on disturbance caused by clear-cutting. In undisturbed forests, there were small or no effects on community composition from N addition. In contrast, effects were large in forests first exposed to N addition and subsequently disturbed by clear-cutting. Effects of N addition differed among plant functional groups. Abundance of graminoids increased (+232%) and abundance of dwarf shrubs decreased (−44%) following disturbance in N-fertilized stands. For vascular plants, the two perturbations had contrasting effects on α- (within stand) and β- (among stands) diversity: in disturbed stands, N addition reduced α-diversity, while β-diversity increased. For bryophytes, effects of disturbance on α-diversity were smaller under N addition than ambient N, while neither N addition nor disturbance had any effect on β-diversity.
Effects of N addition on plant communities may be small, short-lived or even absent until exposure to a disturbance implements full effects of N, highlighting the importance of considering interactive effects with disturbance when evaluating effects of N enrichment on plant community composition and biodiversity.