Reduced ecosystem functions associated with species loss and climate

change

Han Y. H. Chen

Faculty of Natural Resources ManagementLakehead University

Research in Chen’s lab

FunctionBiomass (C), production, Nutrients

DynamicsSuccession, disturbance regimes

DiversityWhy plants co-exist

Disturbance

Species interaction

Climate change

Why understanding diversity function relationships is important?

Continuous loss of biodiversity at the global scale “Earth loses more than three-quarters of its species in a

geologically short interval (1k years), as has happened only five times in the past 540 million years… a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia” Barnosky et al. 2011, Nature 471:51-57

Agriculture Forestry

UrbanizationDrought

Fundamental question in BEF

• How might loss of the world's biodiversity alter ecological function?

• Net primary production• Nutrient cycling• Outbreaks of insects and diseases?

The original hypothesis

Darwin’s (1859): the presence of a “divergence of characters” is essential for reduced interspecific competition as a result of different demands for resources, and in turn, improves productivity

Tilman et al. (1997) Science 277:1300-1302

Diversity and productivity relationships

• Despite being the most published topic in ecology• Debate persists about diversity effects in natural vs. planted

grasslands (Adler et al. 2011, Science 333, 1750-1753)

• Evenness• Heterogeneity of life-history traits

• The impacts of these factors on DPRs in forest

ecosystems are more poorly understood

.

HypothesesRichness & evenness

The extent of life-history variation

Biomes

Stand origin

Stand age

Methods

Each selected original study was designed to test diversity effects, i.e., similar sites and disturbance history

Net diversity effect, effect size (ES)Pij = the observed productivity of

the jth observation in the ith study

= the mean productivity of monocultures

i

ijij M

PES

iM

Evenness)ln(

''

S

HJ H’ = observed Shannon’s index

S = species richness

Pielou (1969)

10

Contrasting shade tolerance

Contrasting nitrogen-fixing

Fast-slow growth

Boosted regression treesDe’ath 2007Elith et al. 2008Regression trees + boosting

Machine learningModel averaging

Statistical analysis

Global average effect of diversityLn(ES) = 0.213ES = 1.24At a global scale, the polycultures have 24%

higher productivity than monocultures

Predicted ln(ES)

Evenness

0.2 0.4 0.6 0.8 1.0

Pre

dict

ed ln

(ES

)

0.0

0.1

0.2

0.3

Richness

0 2 4 6 8 10 12 14 160.0

0.1

0.2

0.3

Stand age (years)

0 20 40 60 80 100 1200.0

0.1

0.2

0.3

Contrasting shade tolerance

Absence Presence

Pre

dict

ed ln

(ES

)

-0.1

0.0

0.1

0.2

0.3

Contrasting N-fixation

Absence Presence0.0

0.1

0.2

0.3

Contrasting growth habit

Absence Presence0.0

0.1

0.2

0.3

Biome

Bo Te Tr

Pre

dict

ed ln

(ES

)

0.0

0.1

0.2

0.3

Stand origin

N P0.0

0.1

0.2

0.3

ba

ed

c

h

f

g

34%13% 15%

29%

<3% <2%

<2% <2%

Zhang et al. 2012. J Ecol

Niche differentiation/partitioning and/or facilitationGrasslands (Tilman and many others) Algae in fresh water systems

(Cardinale BJ, 2011. Biodiversity improves water quality through niche partitioning, Nature 472, 86-89)

Reduced Janzen–Connell effects Positive diversity effects on

productivity are realized by reduced plant disease (Schnitzer et al. 2011, Ecology 92, 296-303)

Known mechanisms for positive DPRs

Diversity effects in belowgroundFew studies examined diversity effects on

belowground productivity of forest ecosystems (although belowground accounts for ≈ 50% of total NPP; fine roots, <2 mm in diameter alone accounts for 33% of total NPP)

Potential mechanisms are poorly understood in natural environmentGreater soil volume filling in natural environments?

Methods

Pb+Late-successional Picea mariana, Picea glauca, and Abies balsamea (LSC)=Pb+LSC

Pinus banksiana (Pb)

Populus tremuloides (Pt)

Pb + Ptgymnosperm vs. angiosperm

Seasonal biomass variation

May

June Ju

ly

Augus

t

Septe

mbe

r

Octobe

r

Fin

e ro

ot b

iom

ass

(Mg

ha-1

)

0

1

2

3

4

5

PbPtPb+LSCPb+Pt

Brassard et al. 2013. J. Ecol.

Fin

e ro

ot p

rodu

ctio

n (M

g ha

-1 y

ear-1

)

0

1

2

3

4Pb +LSCPb Pt Pb+Pt

0.160

0.035

0.047

0.075

MatrixIngrowth

0.116

0.144

0.1810.104

MaxMin MaxMin

Fine root production

• 19% to 83% higher in mixed-species stands than single-species stands

0

1

2

2D Graph 1

0

1

2

3Pb and Pb+LSCPb, Pt and Pb+Pt

Ann

ual f

ine

root

pro

duct

ion

(Mg

ha-1

yea

r-1)

MaxMin

Ann

ual f

ine

root

pro

duct

ion

(Mg

ha-1

yea

r-1)

0

1

2

3

4 Pb+LSCPb Pt Pb+Pt

0.160

0.035

0.047

0.075

MatrixIngrowth

0.116

0.144

0.1810.104

MaxMin

a

b c

d e

0

1

2

Tree species richness

2 3 4 50

1

2

Tree species evenness

0.0 0.2 0.4 0.6 0.8 1.0

f g

h i

MS2

MS1

FF

MS2

MS1

FF

MS2

MS1

FF

MS2

MS1

FF

MS2

MS1

FF

Necromass

0 1 2 3

Pinus banksiana

Fine root biomass and necromass (Mg ha-1)

0 1 2 3

Populus tremuloides and Betula papyrifera

0 1 2 3

MS2

MS1

FF

Non-tree

0 1 2 3

Picea spp. and Abies balsamea

Pb+LSC Pb Pt Pb+Pt

Vertical distribution of fine roots

May

June

July

Aug

Sept

Oct

Seasonal biomass heterogeneity

Fin

e r

oot n

ecro

mass

(M

g h

a-1

)

0

1

2

3

4

5

Vert

ica

l hete

roge

neity

0.0

0.5

1.0

1.5

Ho

rizo

nta

l hete

roge

neity

0.0

0.5

1.0

1.5

2.0

Fin

e r

oot b

iom

ass (

Mg h

a-1)

0

1

2

3

4

5

PbPtPb+LSCPb+Pt

a

c d

b

Summer

Summer Summer

Summer

Sampling date

1 SD of biomass among 3 layers1 SD of biomass among 7 cores

Relationships between fine root biomass and heterogeneity

PbPtPb+LSCPb+Pt

Vertical heterogeneity

0.0 0.3 0.6 0.9 1.2 1.51

2

3

4

5

Horizontal heterogeneity

0.4 0.6 0.8 1.0 1.2 1.4 1.6

Fin

e r

oo

t b

iom

ass

(M

g h

a-1)

1

2

3

4

5

May June July August September October

a b

ConclusionEvenness and trait

diversity increase productivity both above- and belowground

Exploiting resources more completely in space and time

ImplicationsConserving species and

trait diversity Diversity effects are

more pronounced in old forests

Research in Chen’s lab

FunctionBiomass (C), production, N & P resorption

DynamicsSuccession, disturbance regimes

DiversityPlants

Disturbance

Species interaction

Climate change

Climate change and forest dynamics

Biome shiftReduced ecosystem function, NPP, carbon

sink to sourceForest compositional change

Studied 76 old-growth (>200 years old) stands

Assume an equilibrium state, thus all changes in mortality are exogenous (climate change)

Widespread temporal increases in tree mortality have been attributed to climate change

Studied 96 old stands (>80 years old)

Two underlying assumptions:

1. Endogenous effects on tree mortality in old forests are weak, and thus temporal variation in tree mortality can be solely attributed to climate change

2. Climate change effects are the same in young and old forests

Connell and Slatyer (1977):

"We have found no example of a community of sexually reproducing individuals…… reached a steady-state equilibrium"

Others attributed temporal increases in mortality to stand development

Thorpe & Daniels. 2012. Can. J. For. Res. 42:1687-1696.

Luo & Chen. 2011. J. Ecol. 99:1470-1480.

Lutz & Halpern. 2006. Ecol. Monogr. 76:257-275.

CompetitionNegative 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. 2011. GCB: 17: 3697)

887 plots Measured: 1958-2007Stand age: 17 to 243 yr

Use Bayesian logistic modelsEndogenous mechanisms

Asymmetric competitionStand crowdingInterspecific interactionTree ageing

Exogenous mechanisms Year or Annual temperature anomaly or Drought

index (PDSI or CMI)

What is Bayesian statistics? --vs. frequentist statistics Frequentist

Parameters are fixed quantities

BayesianThe true value of a

parameter is thought of as being a random variable to which we assign a probability distribution, known specifically as prior information

Analyzed by young forests (≤ 80 years) and old (>80 years)

Picea glauca Picea mariana Populus tremuloides

Yea

r ef

fect

on

logi

t (p)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Without endogenous factorsWith endogenous factors

a Populus balsamifera Pinus banksiana

NS

b

Sen

sitiv

ity s

core

0.00

0.01

0.02

0.03

0.04

0.05

0.06Endogenous factorsExogenous factorsInteraction terms

All Young Old All Young Old All Young Old All Young Old All Young Old

Luo and Chen. 2013. Nature Comm. 4:1655

Tree mortality in young and old forests

Picea mariana

Year

1960 1970 1980 1990 2000

Populus tremuloides

Annual m

ort

alit

y pro

babili

ty

0.00

0.01

0.02

0.03

0.04

0.05

0.06 Populus balsamifera

Young forestsOld forests

Pinus banksiana

1960 1970 1980 1990 2000

0.00

0.01

0.02

0.03

0.04

0.05

0.06 Picea glauca

1960 1970 1980 1990 2000

Luo and Chen. 2013. Nature Comm. 4:1655

Multiple climate change drivers

Higher growth rates

Higher NPP

Higher turnover rates = high mortality?

Alternatively, more food (CO2) improves tree health, thus low mortality?

Surface temperature anomalies relative to 1951–1980 from surface air measurements at meteorological stations and ship and satellite SST measurements.

Hansen J et al. PNAS 2006;103:14288-14293

©2006 by National Academy of Sciences

Spatially heterogeneous N deposition

Recay et al. 2008. Nat Geosci 7:430

Global drought trends for past 60 years

Sheffied et al. 2012. Nature 491: 435

c

Year1960 1970 1980 1990 2000

AC

MIA

(cm)

-15

-10

-5

0

5

10

b

GP

A (m

m)

-100

-50

0

50

100

a

AT

A (ºC

)

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Increased mortality is positively associated with temperature anomaly

Negatively associated with drought index (ACMIA)

Climate change effects on tree mortality

The increased mortality is also higher in Pure than mixed forestsMore crowded forests

Among species Higher for Populus balsamifera among pioneersHigher Picea spp. than Populus tremuloides and Pinus

banksiana

Undergoing forest compositional shift that is independent of endogenous forest succession—an important conservation challenge!

Current and future research in Chen’s lab

FunctionProductivity & stability

Dynamics

Diversity

Disturbance

Species interaction

Climate change

Why/how species co-exist?

Biogeography of diversity and function of Canada’s forest

• Long-(>8,000 years) and short-term fire regime and forest dynamics

AcknowledgementsFunding

NSERC Discovery GrantNSERC Strategic ProjectNational Centre of Excellence Network of Sustainable Forest

ManagementOntario Early Research Award programNorthern Ontario Heritage Fund Cooperation

Partners and collaborators Resolute Inc.Tembec Inc.Louisiana-Pacific Canada Ltd.Ontario Forest Ecosystem Science Co-operative Inc.Provincial Governments Canadian Forest Service