1. Diversity and function of terrestrial ecosystems under global changes
Han Y. H. Chen

2. Research in Chen’s lab Global changes Function Diversity loss
Climate change
Disturbances
Global changes
Function
Biomass & element cycling
Diversity loss
Plants

3. Rockström et al. 2009. A safe operating space for humanity
Rockström et al A safe operating space for humanity. Nature 461:472

4. Barnosky et al. Nature 471, 51-57 (2011) doi:10.1038/nature09678
Relationship between extinction rates and the time interval for mammals
Five mass species extinctions occurred in the past 540 million years
Entering 6th mass species extinction
Barnosky et al. Nature 471, (2011) doi: /nature09678

5. Humans and the extinction crisis
Urbanization
Humans and the extinction crisis
Agriculture
Forestry
Climate change
Pollution

6. Global threats to biodiversity
C. J. Vörösmarty, Global threats to human water security and river biodiversity. Nature  47, 555–561 (2010)

7. Biodiversity (loss) ecological functioning (BEF)
Net primary production
Nutrient cycling
Trophic interactions
Insect and pathogen out breaks

8. The original hypothesis
The presence of a “divergence of characters” reduces competition as a result of different demands for resources, and consequently improves productivity

9. The “First” empirical evidence
Cedar Creek experiment
Tilman et al. (1997) Science 277:

10. Diversity and productivity relationships
Debate persists
Natural vs. planted grasslands
(Adler et al. 2011, Science 333, 1750; Fraser et al. 2015, Science 349, 302)
Evenness
Heterogeneity of life-history traits
Poorly understood for forests

11. Hypotheses . Richness & evenness The extent of life-history variation
Biomes: competitive exclusion vs positive interactions (niche differentiation, facilitation)
Stand origin: planted vs natural systems
Stand age .

12. 13 22 Tropical Boreal Meta-data Temperate 19
Each selected original study was designed to test diversity effects, i.e., similar sites and disturbance history

13. Net diversity effect (ES)
Pij = Productivity in mixtures
j = observation, i = study
= the mean productivity of monocultures of ith study
Evenness
H’ = observed Shannon’s index
S = species richness
Pielou (1969)

14. Variation of life history traits
Contrasting shade tolerance
Yachi & Loreau (2007)
Contrasting nitrogen-fixing
Fast-slow growth

15. Global average effect of diversity
25% productivity increase
Zhang, Chen & Reich, J Ecol 100:742-49

16. Statistical analysis Boosted regression trees De’ath 2007
Elith et al. 2008
Regression trees + boosting
Machine learning
Model averaging

17. Predicted ln(ES) Monotonic Non-monotonic 13% 34% 15% 29% <3% <2%

18. Mechanisms from DPR experiments
Niche differentiation and/or facilitation
Grasslands (Tilman and others)
Algae in fresh water systems (Cardinale BJ, Nature 472, 86-89)
Reduced Janzen–Connell effects
Positive DPRs realized by reduced plant disease (Schnitzer et al. 2011, Ecology 92, )

19. Potential mechanisms are poorly understood in natural environments - Greater resource utilization spatially and temporally due to resource heterogeneity?

20. Fine root biomass
Fine root production

21. Forest
Grassland

23. Multivariate relationship--SEM

24. Plant species mixtures increase microbial biomass and respiration

25. The effect increases with the number of species in mixtures
More pronounced over time

26. Summary-DPR Diversity increases productivity
Both natural and planted systems
Above- and belowground
Strength of DPR increases over time
Mechanisms in natural systems
Increased tree size inequality for aboveground
Increased soil volume filling and nutrient utilization
Plant diversity increases
Soil respiration
Microbial biomass/abundance

27. Research in Chen’s lab Global changes Diversity Function
Climate change
Disturbances
Global changes
Diversity
Plants
Function
Biomass & element cycling

28. IPCC 2014
Rising CO2
Warming

29. IPCC 2014

30. Global drought trends for past 60 years
Sheffied et al Nature 491: 435

31. Importance of understanding climate change impacts on forests
A large and persistent carbon sink in the World’s forests via increasing biomass (Pan et al Science)
Uptake (2.4 Pg C year−1) = 35% of fossil fuel emission (7 Pg C year−1)
Boreal forests account for 49% of global forest carbon (Dixon et al Science)

32. Climate change and forests
Studied 76 old-growth (>200 years old) stands
Implications
Reduced ecosystem function, carbon sink to source
Forest compositional change
Biome shifts

33. Studied 96 old stands (>80 years old)

34. Two underlying assumptions:
Climate change effects are the same in young and old forests
Endogenous effects on tree mortality in old forests are solely attributed to climate change
Connell and Slatyer (1977), Am Nat 104:501-28
"We have found no example of a community of sexually reproducing individuals…… reached a steady-state equilibrium"

35. Others attributed temporal increases in mortality to stand development
Luo & Chen Journal of Ecology 99:
Lutz & Halpern Ecological Monographs 76:
Thorpe & Daniels Canadian Journal of Forest Research 42:
Competition
Negative density dependence
Tree ageing
“Unsuitable statistical methods that marginalize either climate or non-climate drivers for longitudinal data in which these drivers are highly correlated” (Brown et al GCB: 17: 3697)

36. Bayesian models 887 permanent plots Measured from 1958 to 2007
Stand age ranges from 17 to 243 years old
~ a million records
Bayesian models

37. Higher climate change-induced tree mortality in young than old forests
Aging
Competition
NDD

39. Broadleaves
Early-successional
conifers
Late-successional
conifers

40. Broadleaves
Early-successional
conifers
Late-successional
conifers

41. Changes in plant N:P do not only affect the fitness of plants, but also the fitness
and composition of herbivores

42. Global data
1,418 publications
24,770 observations

43. Plant biomass N : P responses to global change
Natural (Controlled)

47. On-going Research in Chen’s lab
Climate change
Disturbances
Global changes
Global patterns
Mechanisms
Mitigation strategies
Diversity
Plants and others
Function
Biomass & element cycling

48. Acknowledgements