Climate Change, Arctic Plant Communities and Nutrient Feedbacks Rebecca Hale Biogeochemistry of Northern Ecosystems 20 April 2005

A glimpse of things to come… Global warming (!) has a disproportionate effect on Arctic ecosystems Global warming (!) has a disproportionate effect on Arctic ecosystems Effects of climate change on tundra ecosystems? Effects of climate change on tundra ecosystems? Change in plant community compositionChange in plant community composition Changes in plant physiology, structure, functionChanges in plant physiology, structure, function Effects of plant change? Effects of plant change? A work in progress…thinking about effects on nitrogen cyclingA work in progress…thinking about effects on nitrogen cycling

Climate change in the Arctic! Temperature Temperature 2-3ºC increase in Arctic since 1960’s/70’s2-3ºC increase in Arctic since 1960’s/70’s Direct effect on plantsDirect effect on plants Indirect effectsIndirect effects permafrost thawing, increased active soil depthpermafrost thawing, increased active soil depth extended growing seasonextended growing season soil warming and changes in soil processes (i.e. decomposition, N-mineralization)soil warming and changes in soil processes (i.e. decomposition, N-mineralization)

Changes in N Cycling N deposition N deposition indirect effects due to warming and CO 2 indirect effects due to warming and CO 2 increased N mineralizationincreased N mineralization altered C:N ratios and associated changes in decomposition ratesaltered C:N ratios and associated changes in decomposition rates indirect effects due to plant community and physiology changes indirect effects due to plant community and physiology changes changes in litter decompositionchanges in litter decomposition changes due to altered water regimechanges due to altered water regime

Welcome to the Tundra plant growth is 1° nutrient limited plant growth is 1° nutrient limited most biomass in below ground plant parts (stems, rhizomes, storage tissue) most biomass in below ground plant parts (stems, rhizomes, storage tissue) controls over plant community composition change across environmental gradient controls over plant community composition change across environmental gradient lower tundra - biotic and abiotic controls (higher biomass = more competition)lower tundra - biotic and abiotic controls (higher biomass = more competition) higher tundra - become gradually more abiotic, very little competitionhigher tundra - become gradually more abiotic, very little competition

Arctic Plants tussock tundra tussock tundra

shrub tundra

Methods remote sensing remote sensing different scales spatially and temporally – tell us different thingsdifferent scales spatially and temporally – tell us different things historic aerial photographs – small spatial, large temporal scalehistoric aerial photographs – small spatial, large temporal scale satellites – lots of them, fall all over the spatial/temporal scale spectrumsatellites – lots of them, fall all over the spatial/temporal scale spectrum paleoclimatic records paleoclimatic records global warming in Holocene – what was the change in plant community composition then?global warming in Holocene – what was the change in plant community composition then? Modeling Modeling experimental manipulations experimental manipulations control changes over the past years in plant community compositional changes and physiological changes have often been in agreement with experimental and modeling resultscontrol changes over the past years in plant community compositional changes and physiological changes have often been in agreement with experimental and modeling results

Changes in Plant Community [the abridged version] decreased biodiversity, loss of lichens and mosses decreased biodiversity, loss of lichens and mosses Chapin et al. (1995): % decline in species richness in tussock after 9 yr warming exp. (loss of forbs and mosses)Chapin et al. (1995): % decline in species richness in tussock after 9 yr warming exp. (loss of forbs and mosses) Jonasson et al. (1991): loss of diversity in lichens and mosses with 3 yr fertilizationJonasson et al. (1991): loss of diversity in lichens and mosses with 3 yr fertilization

Shrubs! increase in evergreen and deciduous shrub abundance and biomass with warming and fertilization increase in evergreen and deciduous shrub abundance and biomass with warming and fertilization Betula nana increased from 25% to >90% tussock tundra biomass after 15 years fertilizationBetula nana increased from 25% to >90% tussock tundra biomass after 15 years fertilization Paleoclimatic methods corroborate these results Paleoclimatic methods corroborate these results early Holocene warming – shrub invasions in Alaska arcticearly Holocene warming – shrub invasions in Alaska arctic increased shrub growth and development increased shrub growth and development short term versus long term resultsshort term versus long term results Hartley et al (1999) soil warming increases shoot productionHartley et al (1999) soil warming increases shoot production

Shrubs Part II increased shrub growth and development increased shrub growth and development short term versus long term resultsshort term versus long term results Hartley et al (1999): soil warming increases shoot production after 3 years, but had no effect after 5 yearsHartley et al (1999): soil warming increases shoot production after 3 years, but had no effect after 5 years

Betula nana dwarf birch Arctic willow

Viccinium uliginosum Alpine bilberry Alnus crispa Green alder

Why?!?!? loss of lichen/moss abundance loss of lichen/moss abundance competition with vascular plantscompetition with vascular plants lightlight nitrogennitrogen negative response to N fertilizationnegative response to N fertilization response to acid rain, increased T, decreased snow cover, increased CO 2, altered fire regimes are other possibilities for lichen lossresponse to acid rain, increased T, decreased snow cover, increased CO 2, altered fire regimes are other possibilities for lichen loss

Plant Composition warming warming increased growing season (up to 7 days earlier) is correlated with increased photosynthetically active periodincreased growing season (up to 7 days earlier) is correlated with increased photosynthetically active period modeling results versus field resultsmodeling results versus field results increased N mineralization/soil fertility increased N mineralization/soil fertility fertilization experiments have caused changes in plant community composition – are these experiments realistic?fertilization experiments have caused changes in plant community composition – are these experiments realistic? increased N min has been demonstrated in field control plots, but increases in experimental warming plots have been small and variableincreased N min has been demonstrated in field control plots, but increases in experimental warming plots have been small and variable

Still to come: so what? what are the effects of these compositional changes on ecosystem functions? what are the effects of these compositional changes on ecosystem functions? Nutrient partitioning Nutrient partitioning differentiation in timing, depth and chemical form of N uptake in arctic tundradifferentiation in timing, depth and chemical form of N uptake in arctic tundra dominant species use the most available forms of Ndominant species use the most available forms of N how will this be affected by increased abundance of dominant and loss of rarer species?how will this be affected by increased abundance of dominant and loss of rarer species?

effects of plant communities on soil processes and fertility effects of plant communities on soil processes and fertility lichens/mosses – large role in maintaining soil moisturelichens/mosses – large role in maintaining soil moisture increased transpiration with increased shrub abundanceincreased transpiration with increased shrub abundance changes in litter quality with change in dominant specieschanges in litter quality with change in dominant species