Species functional traits and the response of populations to disturbance govern the rate and trajectory of succession, and the functioning of high latitude ecosystems. Consequently, climate change will alter successional dynamics and ecosystem function primarily through its effects on disturbance regime and on those species that govern successional/ecosystem processes.

Actinorhizal plants 25 genera 220 perennial dicotyledonous plants (mostly woody) within 8 families: (Betulaceae, Casuarinaceae, Coriariaceae, Datiscaceae, Elaeagnaceae, Myricaceae, Rhamnaceae, Rosaceae) Associated with the filamentous actinomycete: Frankia

Thin-leaf alder (Alnus incana subsp. tenuifolia) Green alder (Alnus viridis subsp. fruticosa)

Autoregulation The down-regulation of nodule production and nitrogenase activity via a N-sensitive, phloem-transported signal inhibitor Factors that influence plant growth and plant demand for N, also influence N fixation rates Climate (temperature, ppt.) Resource supply (light, water, nutrients) Phenology & ontogeny Disturbance (herbivory) Plant Growth Rate Plant N Demand (N:P ratio) Nodule production and growth Nitrogenase activity Whole-plant N 2 -fixation rate Ecosystem N Inputs Plant density Nodule biomass/plant

Alnus incana subsp. tenuifolia (Uliassi and Ruess 2002) Mitchell and Ruess (in prep) Alnus viridis subsp. fruticosa N Fixation =  (julian day, soil temperature, soil moisture)

Alnus incana subsp. tenuifolia (Uliassi and Ruess 2002)

Ruess et al. (submitted) Woolly alder sawfly, Eriocampa ovata

Anderson et al. (in prep) Effects of Frankia genetic structure on N fixation rates Early Successional Stands White Spruce Stands RF Pattern

Phylogeography of Frankia

How will alder expansion in the arctic (Sturm et al. 2001) affect ecosystem function?? pictures stolen from Ken Tape

Increase in Alnus pollen percentages from 10% to 70% circa BP. Hu et al. (2001)

Mack et al. (2004)

Mitchell and Ruess (in prep)

So what's the quick and dirty way to assess N fixation inputs at the ecosystem scale?? Anderson et al. (2004) Ruess et al. (submitted)

Research/Monitoring Tasks: 1)Establish long-term vegetation monitoring plan for tracking the expansion of alder (low-level aerial photography). 2)Among landscapes where alder is know to be expanding, can we model/predict hot-spots for N fixation? (e.g. climate, soil P, pH, soil  15 N) 3)What are the long-term consequences of N inputs to ecosystem structure and function in landscapes where alder is expanding? (changes in vegetation composition, NPP and forage quality; soil C and N stocks; watershed biogeochemistry). 4)Monitor outbreaks of herbivorous insects and plant pathogens.