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Physical disturbance determines effects from nitrogen addition on ground vegetation in boreal coniferous forests
Author(s) -
Strengbom Joachim,
Nordin Annika
Publication year - 2012
Publication title -
journal of vegetation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 115
eISSN - 1654-1103
pISSN - 1100-9233
DOI - 10.1111/j.1654-1103.2011.01359.x
Subject(s) - disturbance (geology) , plant community , vegetation (pathology) , taiga , ecology , transect , intermediate disturbance hypothesis , abundance (ecology) , species diversity , environmental science , boreal , vascular plant , biology , ecological succession , species richness , medicine , paleontology , pathology
Questions 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? Location Boreal coniferous forest, B ispgården (63 °00′N, 16 °40′E), central S weden. Methods 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. Results 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. Conclusions 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.