Does biodiversity play a significant role in ecosystem function? ASB Sustainable Land Use Mosaic...

Does biodiversity play a significant role in ecosystem

function?

ASB Sustainable Land Use Mosaic (SLUM) Working Group

Symposium

12-15 November 2001

Chiang Mai, Thailand

CBM

DefinitionsBiodiversityConceptual: The variety of life on earth expressed in terms of gene, species and ecosystem. (cf. Heywood & Baste, 1996)

Operational: The quantity and composition of species and functional types recordable in any area. (Gillison, 2001).

Functional types: (FTs) are sets of organisms showing similar responses to environmental conditions and having similar effects on the dominant ecosystem processes.(Diaz, 1998).

ASB SLUM Mtg Chiang Mai 11 Nov 01

Diversity

…The number of different items and their relative frequency. For biological diversity these items are organized at many levels …. Thus the term biodiversity encompasses different ecosystems, species, genes and their relative abundance. (US Congress, Office of Technology Assessment, 1987).


Indicators and surrogates

The vast number of biota that influence ecosystem function are mainly small organisms that are very difficult to measure. For most practical purposes their diversity and that of other larger, difficult-to-measure organisms, is assumed to be indicated by more readily observable units such as plant species and functional types.

(This tends to be an act of faith commonly applied in private and denied in public).


Ecosystem

1. A community of interdependent organisms together with the environment which they inhabit and with which they interact. (Allaby, 1977).

2. A functional system which includes the organisms of a natural community together with their environment. (Lapedes, 1976)

3. … the sum total of vegetation, animal, and physical environment in whatever size segment of the world is chosen for study. (Fosberg, 1967)


The ecosystem concept is used widely but ambiguously. It can:

a) contain only a functional meaning,

b) have a spatial connotation which includes any level of scale or

c) the spatial aspect can be included, but additionally, relative homogeneity must characterize the system

(Johnson and French, 1981, quoted by Godron & Forman, 1983)


Differences between ecosystem and landscape:

Ecosystems: are relatively homogeneous

Landscapes: are relatively heterogeneous.

A landscape is “…a kilometers wide area where a cluster of interacting stands or ecosystems is repeated in similar form” (Godron & Forman, 1983)


‘Ecosystem’ conversion to ‘landscape’


Landscape assemblagesIn NW Mato

Grosso,Western Amazon

basin

Brazil


Species Elevation (m) 500 700 900 1100 1300 1500 1700 1900 2100 2300 2500

Plants Dipterocarpus tuberculatus Shorea obtusa Castanopsis sp. Chromolaena odorata Imperata cylindrica Smilax sp. Melastoma malabathrica Arisaema sp.

Birds Collared Falconet Sooty-headed Bulbul Red Jungle Fowl Scarlet Minivet Striped Tit-babbler Grey-throated Babbler Arctic Warbler

Range (elevational) distributions of some key taxa across different landscapes – Mae Chaem,

Northern Thailand


Differing views of species role in ecosystems

1. Systematists and population biologists:1. Systematists and population biologists:– No two species can exist in exactly the same

habitat– Every species has a unique resource

requirement and hence use pattern


2. Ecologists2. Ecologists:– More than one species can occupy a functional

type or resource niche (e.g. mesophyte, xerophyte, producer, consumer, life form, C3, C4 path, nitrogen fixer, PFT…)

– More than one functional type can occur within a species.

Approaches to species, biodiversity and ecosystem function:

Traditional: Community ecology: Species diversity is a dependent variable controlled by abiotic conditions and ecosystem constraints. Ecosystem ecology: Dominant species control ecosystem properties.

Recent: Now consider role of biodiversity as a potential modulator of ecosystem processes.


Some general assertions

• Ecosystem stability and primary productivity vary directly with diversity in species and functional type

• Species properties expressed as functional types exert a greater degree of control on ecosystem function than species diversity (richness)


(After Springett, 1976)


See also Swift & Anderson (1993)

Biodiversity and ecosystem function: Recent consensus*

• Some minimum number of species is essential for maintaining ecosystem function under constant conditions

• A larger number of species is probably required for maintaining ecosystems in changing environments

• Determining which species have significant impact on which processes in which ecosystem remains an open emiprical question

*Loreau et al. (2001)


Cont..• Increased primary production via higher plant diversity

can be expected to stimulate secondary productivity.• Changes in one trophic level may lead to a variety of

potential responses for processes at higher trophic levels.

• Mechanisms for generating primary productivity may range from systems with a few dominant species or functional types (low diversity) to systems with high diversity, low level dominance and high complementarity (synergy).


Hypothetical mechanisms involved in biodiversity experiments using synthetic communities

Loreau et al.

(26 October, 2001)

Science: 294:804-808

Primaryproductivity

Diversity of Spp and FTs

Low

High

High(few groups)

Low (many ‘ rare’ )

Complementarity

low

High

Local, regional, random processes. Within and between landscape heterogeneity high

Local, deterministic processes. Niche diff’n high . Within landscape heterogeneity low

?

Dominance

Dual hypothetical mechanisms for species, FT diversity and ecosystem productivity


Function/ Process ActionNutrient capture

Decomposition and soil formation

Mycorrhizal activity

Photosynthesis

Herbivory

Pollination

Species interactions (mutualisms, symbiosis, predation, parasitism, competition)

Water uptake and lossSource: Hobbs (1992)

See also Giller et al. ( 1997 ) for below-ground

Nutrient cycling

Nutrient cycling

Enhanced nutrient uptake

Energy capture and productivity

Energy and nutrient capture

Genetic information transfer

Energy, water and nutrient transfer

Water transfer

Ecosystem functions and processes related to the transfer of energy, nutrients, water and genetic information


Plants as basal ecosystem units

• Most terrestrial (mobile, heterotrophic) biota ultimately depend on plants for survival

• Plants as mostly sessile, autotrophic units are readily observable in nature

• Variation in plant form and function is measureable along key environmental gradients


Water

High Medium LowL

igh

t (e

ner

gy)

L

ow

M

ediu

m

Hig

h


Plant Functional Types*

• Photosynthetic envelope (leaf size, inclination, chlorotype, morphotype)

• Physical support system or life form based on position of perennating buds

• Above-ground rooting system• Minimum set of attributes• ‘Coherent’ functional model

* after Gillison (1981)


VegClass, Windows-based, user-friendly software for data entry and meta-analysis; integrated with field proforma to support

rapid vegetation survey

Plant Functional Types: leaf + stem photosynthesis, incl. parasites, carnivores


Function/ Process ActionNutrient capture

Decomposition and soil formation

Mycorrhizal activity

Photosynthesis

Herbivory

Pollination

Species interactions (mutualisms, symbiosis, predation, parasitism, competition)

Water uptake and loss* PFT relevance highlighted in red

Nutrient cycling

Nutrient cycling

Enhanced nutrient uptake

Energy capture and productivity

Energy and nutrient capture

Genetic information transfer

Energy, water and nutrient transfer

Water transfer

Ecosystem functions and processes related to the transfer of energy, nutrients, water and genetic information*


0 10 20 30 40 50 60

Modi

0

20

40

60

80

100

120

140

160

Spe

cies

Patterns of richness in plant species and functional types under different land use types

Indonesia : Jambi - Lampung

Legend CassavaImperataMono. Plantation

AgroforestryLogged ForestNatural Forest

Plant FunctionalTypes (modi)


0 2 4 6 8 10 12 14 16 18 20 22 24

Basal Area m2 ha-1

0

10

20

30

40

50

60

70

80

90

100

Ter

mit

e A

bu

nd

ance

Regression plot of termite abundance & basal area of woody plants [r2=0.985]

over 7 land use systems: Jambi BS Nov. 97

Primary Forest

SecondaryForest

Imperata

Cassava

Rubber Plantation

Jungle Rubber

ParaserianthesPlantation


1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

0

10

20

30

40T

erm

ite

sp

ecie

s r

ich

nes

s

Primary Forest

SecondaryForest

Imperata

Cassava

Rubber Plantation

Jungle Rubber

ParaserianthesPlantation

Ratio of plant species richness to plant functional types as an indicator of Termites species richness [R-Sq = 0.97]

over 7 land use systems : Jambi BS Nov. 97

Ratio of plant species to plant functional types (modi)


Correlations between key plant variables, fauna and above-ground Carbon

Jambi Baseline survey

Attribute Species Modi Spp/Modi

Ground-dwelling Termite abundance 0.872 0.766 0.946 Termite species 0.849 0.698 0.976 Lep/ground 0.834 0.790 0.920 Canopy: Unident. insects 0.771 0.418 0.839 Collembola 0.643 0.089 0.882 Ant-total 0.633 0.729 0.393 Total insects 0.593 0.487 0.526 Orthoptera 0.545 0.378 0.528 Thysanoptera 0.470 0.756 0.138 Isoptera (canopy) 0.417 0.140 0.496 Psocoptera 0.398 0.148 0.457 Coleoptera 0.312 0.458 0.127 Hymenoptera 0.302 0.446 0.129 Formicidae 0.274 0.370 0.142 Acari 0.190 -0.232 0.443 Spiders 0.186 0.307 0.050 Blattodea 0.124 -0.014 0.204 Hemiptera 0.098 0.229 -0.026 Diptera 0.038 0.404 -0.197 Bird total spp. 0.599 0.347 0.704 Above-ground carbon

0.796 0.558 0.909

# Shaded areas with r = >0.500. Bold type = high indicator value.


Above-ground carbon and species: PFTs along

a gradient of Land Use Types, Jambi [r2 = 0.814]

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

0

10

20

30

40

50

60

1

2 5

4

101139

86

7

151316

1412

AG

-car

bo

n

Species : PFTs

(Y=13.56 23.52X + 11.30 X**2)


0.50

1.00

1.50

2.00

2.50

3.00

0 50 100 150 200 250 300 350 400

Aboveground Carbon and Species:PFTsAll ASB benchmark sites

Pla

nt

Sp

p:P

FT

ra

tio

Aboveground - C t/ha

Primary Forest

Managed Forest

Tree-based

Fallow

CropPasture

Correlations between soil and vegetation variables* Variable pH-H2O pH-KCl C% N% C/N% Na Al3 H+

PFT -0.448 -0.459 0.586 0.592 0.497 0.568 0.465 0.503 0.028 0.024 0.003 0.002 0.013 0.004 0.022 0.012

Species -0.424 -0.427 0.529 0.585 0.435 0.503 0.458 0.441 0.039 0.037 0.008 0.003 0.033 0.012 0.024 0.031

Mean Height -0.358 -0.331 0.559 0.530 0.477 0.457 0.379 0.480

0.086 0.114 0.005 0.008 0.019 0.025 0.068 0.018

Basal Area -0.331 -0.260 0.482 0.572 0.383 0.375 0.400 0.402 0.114 0.219 0.017 0.003 0.064 0.071 0.053 0.052

V-Index -0.433 -0.432 0.550 0.622 0.448 0.495 0.486 0.457 0.034 0.035 0.005 0.001 0.028 0.014 0.016 0.025

Tree wt1 -0.588 -0.586 0.777 0.566 0.722 0.700 0.570 0.755 0.002 0.003 0.000 0.004 0.000 0.000 0.004 0.000

Tree wt2 -0.576 -0.568 0.753 0.557 0.697 0.668 0.558 0.735 0.003 0.004 0.000 0.005 0.000 0.000 0.005 0.000

Plot Age -0.421 -0.410 0.613 0.566 0.528 0.569 0.390 0.546 0.041 0.046 0.001 0.004 0.008 0.004 0.060 0.006

* Upper line = ‘r’ value; lower line = ‘P’ value; shaded areas with P <0.020 Tree wt1 = Quirine data; Tree wt2 = Brown data; only variables with highest correlations listed.(Source: Gillison, 2001; Hairiah and van Noordwijk, 2001)

Conclusions• Specific knowledge of functional types may be essential to

predict ecosystem responses under different global scenarios or where management seeks to manipulate species composition directly as in complex agroecosystems.

• Hypotheses and models must be tested in a wider array of ecosystem types e.g. tropical forests.

• To predict and understand changes in biodiversity and ecosystem function we need to move beyond simple causality and address multiple feedbacks.

• Relationships between local, landscape and regional scales require critical attention.


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