Increased inputs of reactive forms of nitrogen (N) are a major threat to biodiversity in all part of the world. Although many of the negative effects are well studies, interactive effects with climate change, and how effects varies depending on choice of management strategy is largely unknown. Moreover, the knowledge is largely restricted to effects on species diversity, while effects on ecosystem functions and services are poorly known.
Effects of environmental changes often tend to be context dependent, so that the effect of one type of change will differ depending on other factors such as climatic conditions, plant community diversity, damage from herbivores and plant pathogens, or on type of management imposed. For example, high plant species diversity may mitigate the effect that elevated [CO2] and increased N input have on plant-herbivore/pathogen interactions, so that effects on plant damage levels will depend on species richness of the plant community (Strengbom et al. 2008; Lau et al. 2008). Consequently, if we lack understanding of such complex interactions, it will limit our possibilities to understand and predict effects of environmental changes at the community and ecosystem level.
I address how increased N input, either as N deposits or due to forest fertilization influence forest ground vegetation and associated ecosystem functions/services, and how such effects are modified by climate, forest structure, and choice of management. In ongoing work I have found that climate and N effects on the ground vegetation are highly dependent on forest structure and management. For example the net effect and the longevity of N effects on ground vegetation are dependent on disturbance imposed by clear-felling and replanting (Strengbom & Nordin 2008; Strengbom & Nordin 2011).
The second leg in my research focuses on effectiveness of the conservational measure of tree retention during clear-cutting. Despite that retention of trees for conservational purposes has been in practice for 15-20 years and millions of trees are retained every year, the knowledge of its effectiveness is limited. So far, the research has been biased towards effects on species richness, while effects on plant community resilience/stability and effects on ecosystem function and services are largely unknown. Hence, important aims in my research are to examine how tree retention influence plant community resilience and how it influence ecosystem services such as pollination and berry production.
Strengbom, J. & Nordin, A. 2011. Physical disturbance determines effects from nitrogen addition on ground vegetation in boreal coniferous forests. Journal of Vegetation Science, accepted for publication.
Granath, G., Strengbom, J. & Rydin, H. 2010. Rapid ecosystem shifts in peatlands: linking plant physiology and succession. Ecology 91, 3047-3056
Strengbom, J., Reich, P.B. & Ritchie, M.E. 2008. High plant species diversity indirectly mitigates CO2- and N-induced effects on grasshopper growth. Acta Oecologica 34, 194-201.
Strengbom, J. & Nordin, A. 2008. Commercial forest fertilization causes long-term residual effects in ground vegetation of boreal forests. Forest Ecology and Management 256, 2175-2181.
Lau, J., Strengbom, J., Stone, L.R., Reich, P.B. & Tiffin, P. 2008. Direct and indirect effects of CO2 enrichment, N fertilization, and community diversity on plant-enemy interactions. Ecology.89, 226-236.