Climate Change & Plant Community Dynamics

Climate Change & Plant Community Dynamics

1. Buxton Climate Change Experiment

   • One of the largest climate change experiments in the world, investigates the effects on changing temperature and rainfall on plant communities
   • 1. Methods: Include several climate manipulations that mimic a range of possible climate change scenarios in the UK
     • Summer drought - imposed by automatic rain shelters throughout July and August
     • Enhanced summer rainfall - by additional watering of plots (+20%) during June-September
     • Elevation of winter temperature - (+3°C) imposed by soil warming cables from November - April
     • Elevated winter temperature/ summer drought
     • Elevated winter temperature/ Supplemented summer rainfall
     • Control, and cable control (ambient conditions with unconnected heating cables)
   • Early results - Grime et al 2000: After 5 yrs there were obvious effects on plant phenology:
     • Greening and flowering occurred up to a month earlier in plots experiencing an artificially induced mild winter
       • But, species composition of the treated plots were relatively unaffected by clime manipulations
   • Later results - Grime et al 2008: 13yrs after initial manipulation, reported few differences between plots
     • Similar composition of plant life-forms across treatments, only summer drought being responsive with significantly fewer forbs and more shrubs
       • Chronic summer drought reduced productivity and species number, winter heated plots also had fewer species
         • Over 13yrs, only summer drought caused any variation in species composition
           • Species composition of established grassland at Buxton responded little to drought and winter warming
   • Conclusion: Effects are habitat specific! Some plant communities are born buffered against climate change but others are not.

2. Response of Tundra Vegetation

   • Recent observations has shown changes in some tundra ecosystems appear to be responses to arming climate
     • Several experimental studies have shown that tundra plants and ecosystems can respond strongly to environmental change, including warming; however, most studies were limited to a single site and were ot short duration and based on a variety of experimental designs
       • Walker et al 2006 - So instead used meta-analysis on plant community measurements from standardised warming experiments at 11 locations across the tundra biome.
         • Results: The passive warming treatment increased plant-level air temperature by 1-3°C, the range of predicted and observed warming for tundra regions. Although there was a great variability between sites, some patterns emerged.
           • - Significant increases in canopy height in warmed plots of vascular plants - Increased cover of vascular plants in warmed plots, but a decrease in lichens and mosses - Species richness and diversity decreased with warming Low latitude sites respond most to warming, because of greater water and nutrient availability.
           • Conclusions: the study underscores: the interaction between factors like temperature and precipitation, the need to compare responses across several sites to arrive at general predictions
             • The results predict that warming will cause a decline in biodiversity across a wide variety of tundra, at least in the short term. With plant community behaving differently, it makes it harder to predict responses

3. Mediterranean Vegetation

   • Lloret et al 2009; Prieto et al 2009: Both looked at climate related effects on Mediterrnaean - scrub near Barcelona
     • Methods: 4X5squared plots manipulated for 8 years their treatments were warming and droughts
       • Results: Effects on seedlings - seedling composition affected by drought, reduced seedling recruitment for several species, and warming had little effect on seedlings. Community level: drought reduced species richness, warming had little effect on species number, drought reduced tree and herb abundance but increased shrub abundance
         • Both conclude that plant communities will be severely affected

4. eCO2 at Community-Level

   • Although individual plants often grow better in eCO2 in isolation, Poorter and Nevas (2003) showed that there is little relationship with their performance in mixed communities
     • Similarly, while increased biomass is often seen at the species-level, when plant communities are exposed to eCO2 there is often little effect on total biomass (e.g. Niklaus and Korner 2004)
   • Research now focuses on responses to eCO2 within the plant community
     • Growth responses within a synthesised chalk grassland - Hanley et al 2004
       • Community - eCO2 had no effect on total biomass until nitrogen was added to the microcosms
         • Functional groups - eCO2 increased non-legume forb cover and biomass, grass cover and biomass decreased in eCO2, legume cover and biomass increased in eCO2, but effect lost when extra nutrients added
           • Species: only one of the 6 fobs showed increased cover in eCO2 without extra nutrients
             • Only one species displayed any response to eCO2 when nutrients were added. Thus most of the increase in forb biomass and cover was driven by a single species. Only one of 5 grass species had reduced cover in eCO2 without extra nutrients, most species unaffected
     • Korner 2006 - Examined similar issues
       • Looked at plant community responses across many different grassland ecosystems and notes the general lack of response to eCO2 in late successful grasslands
         • Typically found: - a clear influence of soil moisture. - an overarching effect of few very responsive species. - No instances where legumes as a group were positively affected. - No instances where C4 grasses as a group negatively affect
           • A photosynthesis-only driven CO2 effect seems rare/small in late successional systems. Once CO2- induced moisture effects are accounted for, there remains no direct CO2 effect on growth, and hence the overall effect could have been simulated with a watering treatment alone.
     • BUT - Hanley et al 2004 - Emphasized the importance of Nitrogen addition in eliciting a growth response