Convergence in plant traits between species within grassland communities simplifies their monitoring

e c o l o g i c a l i n d i c a t o r s 9 ( 2 0 0 9 ) 1 0 2 0 – 1 0 2 9

Convergence in plant traits between species within grasslandcommunities simplifies their monitoring

Pauline Ansquer, Michel Duru *, Jean Pierre Theau, Pablo Cruz

INRA, UMR1248 Agir, F-31326 Castanet Tolosan, France

a r t i c l e i n f o

Article history:

Received 7 July 2008

Received in revised form

22 October 2008

Accepted 4 December 2008

Keywords:

Managed grasslands

Grazing

Cutting

Fertilization

Specific leaf area

Nitrogen

Leaf dry matter content

Flowering

Land use

Field indicator

a b s t r a c t

Plant trait measurement is a very powerful and promising method for assessing the effects

of land use change on ecosystem behavior in grasslands, but it is very time-consuming.

Hence we pose the following questions for simplifying diagnosis and monitoring: (i) are

plant traits (PTs) similar between plant life forms (PLF: grasses, rosettes, upright forbs,

legumes) within a plant community? (ii) is it possible to define the main plant community

characteristics by measuring traits on one PLF or a limited number of dominant species?

Six PTs known for their ability to characterize the capacity of species to exploit resource-

rich or -poor environments and for their competitive dominance in response to disturbance

(specific leaf area (SLA), leaf dry matter content (LDMC), plant height (H), C and N contents,

flowering time) were measured on the species of 18 plant communities located in Central

Pyrenees. The experiment combined 2 fertility levels and 3 defoliation regimes (cutting,

grazing). Comparisons were made between the weighted values at community, PLF and two

dominant species levels. Regression analysis shows that there were significant correlations

between grasses and rosettes for 4 PTs. For H, N and C:N ratio, data for both grass and rosette

PLFs were close to the bisecting line. The largest difference in the intercept was observed for

LDMC. On the basis of plant traits weighted for all the species, plant communities were

ranked in similar ways for SLA and H (Spearman r > 0.93; p < 0.001) and to a lesser extent for

LDMC (r = 0.72; p < 0.001). Convergence in weighted plant traits for different PLFs within a

plant community mean that in the studied grasslands, defoliation regime and nutrient

availability act as strong filters that impose, at least at PLF level, very similar PFTs. This

determines a specific local community structure and composition. An application of this

result in managed grasslands is the possibility of focusing on one PLF or a limited number of

species for vegetation diagnosis and monitoring.

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1. Introduction

Policy makers are interested to evaluate the effects of agri-

environmental measures on land use and the environment,

and advisory services want to assess the effect of farmers’

management practices on technical and economic perfor-

mance (Caballero, 2007). Plant trait measurement is a

promising method for assessing the effects of land-use change

* Corresponding author. Fax: +33 5 61 73 55 37.E-mail address: [email protected] (M. Duru).

1470-160X/$ – see front matter # 2008 Elsevier Ltd. All rights reservedoi:10.1016/j.ecolind.2008.12.002

or environmental factors on ecosystem functioning, including

productivity and nutrient cycling, in grasslands (Lavorel and

Garnier, 2002). Plant traits can be considered as field indicators

instead of species composition of the plant communities for

monitoring the impact of environmental or management

changes on their agricultural and environmental character-

istics. However measurements on all the plant species at field

level is very time-consuming. Thus we are studying how to

d.

mailto:[email protected]

http://dx.doi.org/10.1016/j.ecolind.2008.12.002

e c o l o g i c a l i n d i c a t o r s 9 ( 2 0 0 9 ) 1 0 2 0 – 1 0 2 9 1021

simplify them by making measurements on a limited number

of plant species.

It has long been recognized that predicting the response of

plant species to variation in resources requires a functional

classification of species (Grime et al., 1988; McIntyre, 1999)

based on functional parameters directly linked to growth and

developmental functions of plants, or strongly correlated to

other variables describing these functions (Weiher et al., 1999).

Most of this research is based on studying the proportion of

different plant life forms (PLFs: grasses, rosettes, uprights

forbs, legumes) in response to ecological factors. On the other

hand, a short list of key plant functional traits has been

established for grouping species independently of their

botanical family (Diaz and Cabido, 1997). The approach is

based on an analysis of the traits developed by plants growing

in communities (Garnier et al., 2004). However, applying this

approach based on the recognition of all the species within a

community, especially at a vegetative stage, is very time-

consuming and requires reliable botanical knowledge. Thus,

the approach can be regarded as a practical tool to reduce a

wide diversity of species to a small number of entities for

simplifying field diagnosis and/or monitoring.

We have considered key traits that drive the properties of

species-rich grasslands, studying those characterizing the

capacity of species to exploit resource-rich or -poor environ-

ments and the capacity for competitive dominance in

response to disturbance (Westoby, 1998; Wilson et al., 1999).

For the former, four plant traits can be considered: the specific

leaf area (SLA), the leaf dry matter content (LDMC), the leaf

nitrogen content and leaf C:N ratio. They allow species to be

located on a resource capture/use—availability axis Wilson

et al. (1999). Species adapted to poor resource availability (low-

growing species) have a low SLA and N content, and a high

LDMC and leaf C:N ratio (Louault et al., 2005). LDMC was much

less variable than the other leaf traits, being largely indepen-

dent of leaf thickness (Garnier et al., 2001), and consequently a

better predictor of location on the resource capture/use—

availability axis (Wilson et al., 1999). Plant height or specific

shoot height are considered to be the most relevant traits

indicating capacity for competitive dominance (Hodgson et al.,

1999), because they express an ability to capture light

(Hartvigsen and McNaughton, 1995; Vesk et al., 2004). They

respond to management intensity (Bello et al., 2005). Flowering

time is related to plant growth rates and the capture and use of

nutrients (Sosebee and Weibe, 1973), and these latter variables

are correlated with leaf traits (Cruz et al., 2002). It responds to

the frequency of defoliation (Louault et al., 2005), and is closely

related to herbage growth pattern (Duru et al., 2005).

In this paper we address two objectives. First we examine

the similarity in plant traits for species growing together

within a plant community. We sought evidence as to how

species gather together under contrasting management

practices, given the opportunity to evaluate the assembly

rule theory, stating that any filter imposed on a regional

species pool acts to determine local community structure and

composition (Weiher and Keddy, 1999). Environmental filter-

ing is thought to result in the formation of groups of species

with similar traits that tend to occur together more often than

expected by chance alone (Holdaway and Sparrow, 2006).

Secondly, in applied terms, we examine if focusing measure-

ments only on the grass PLF, or on the two dominant species or

two dominant grass species, provides similar results as

measurements made on the overall plant community through

comparison of rosettes and upright forbs.

For studying the similarity in plant traits between plant life

forms within grassland communities, we used a set of

grasslands having different fertility levels and defoliation

regimes. We first examined if there was an effect of manage-

ment practices considered as ecological factors upon plant

trait values for each PLF. Secondly, we compared plant traits of

grass species to those of other main PLFs (rosettes, upright

forbs). Then, for simplifying the characterization of vegeta-

tion, we compared weighted plant traits for all the species to

those of grass species or only the two dominant species or two

dominant grass species. Finally, we examined the value of

these results to highlight species assemblage rules in

temperate managed grasslands and to propose a simplified

method for vegetation diagnosis and/or monitoring at the field

level.

2. Materials and methods

2.1. Experimental design

The experiment consisted of a set of 18 grassland commu-

nities sampled on four livestock farms in the Pyrenees (lat

42851’ N, long 1817’ E, 600–1200 m a.s.l.). Soil parent material

varies from alluvium in the bottom of the valley to shale or

granite on the slopes. Mean annual temperature is 10 8C and

annual rainfall is 1080 mm (5 years’ data). Grassland commu-

nities were chosen to represent the field diversity in terms of

defoliation management (grazing and/or cutting), nutrient

availability (Ansquer et al., 2004) and the functional composi-

tion of the vegetation: the grass abundance (Fig. 1a) and the

weighted grass LDMC (Fig. 1b). There were3 defoliation regimes,

combined with 2 levels of fertility (assessed empirically through

fertilizer management and qualitative observations on botani-

cal composition in the previous year, and denoted + and�) with

3 replications: 3 meadows (M) cut twice a year then grazed in

autumn, 3 meadows (GM) grazed in spring then cut, and 3

pastures (P) which were only grazed (Appendix A). The

maximum distance between fields was 500 m.

2.2. Botanical composition

The floristic composition of each community was obtained

through the list of species and their relative specific

abundance expressed as their oven-dry mass divided by the

total sampled above-ground dry biomass. Ten samples were

cut from each community at the peak of biomass production

(at the end of spring) on subplots of 35 m2. All the biomass

samples of a given subplot were pooled and the different

species were separated and identified.

Five PLFs were distinguished. Rosettes and upright forbs

are defined respectively as dicotyledons having, at the

vegetative stage, simple leaves without stems and compound

leaves with stems and/or large petioles (Cruz et al., 2002).

Graminoids are Carex and Luzula species. Others PLFs are

grasses and legumes. In most of the plots (15/18), the most

Fig. 1 – Distribution of plots for leaf dry matter content (LDMC) and abundance of grasses: the 18 studied plots (black bars)

among 240 plots (white bars) covering the diversity of grasslands observed in the central Pyrenees.


dominant species was a grass (see Appendix A). Nine grasses

and seven forbs represented the pool of dominant species in

the set of studied grasslands (contributing between 40 and 90%

of the total standing biomass).

2.3. Plant sampling and measurements

Measurements of plant traits were made following a standar-

dized protocol (Cornelissen et al., 2003), in the same area as for

sampling for botanical composition. Traits and phenological

stages were determined on the species contributing at least

80% of the total standing biomass in each community. Ninety-

two species were found, of which 67 were measured for

vegetative plant traits (LDMC, SLA, plant height) and plant

composition (N, C), and 60 for flowering time. Mean commu-

nity values of leaf and phenological traits were calculated by

weighting each specific trait value by the corresponding

specific abundance (Garnier et al., 2004).

Table 1 – Mean values of species number, plant life form anddefoliation.

Treatments andeffects

Numberof species

Plant life form

Grasses Legumes Uprightforbs

Rose

M+ 17 64 4 29 3

M� 21 73 12 11 4

GM+ 19 73 4 14 9

GM� 32 55 3 9 3

P+ 19 82 1 8 9

P� 37 47 9 11 2

Fertility (F) + ns * ns n

Defoliation (D) ns ns ns n

F � D * ns + ns *

+p < 0.1; *p < 0.05; ***p < 0.001.

M: meadow; GM: meadow grazed in spring; P: pastures; + and � meansa % of standing herbage mass.

Vegetative plant traits (LDMC, SLA) and plant composi-

tion (N, C) were measured, removing 20 leaves for each of

the species. Leaf area was measured using a planimeter.

Plants were dried at 70 8C for 48 h. C (LCC) and N (LNC)

contents were determined after milling the leaves (mesh

<0.5 mm) using a CHN analyser (LECO Corporation, USA).

Plant heights were measured in the field with a meter

rule. For the flowering stage, the identified species were

monitored once a week. We selected the date at which

about 10% of each population reached the peak of these

stages (e.g. more than 50% of the flowers of an individual

open).

For characterizing defoliation regimes, herbage mass was

measured on a 0.25 m � 0.75 m quadrat, with three replicates

per field before and after each of the first two cuts or grazings

made by the farmer. Rate of herbage utilization was calculated

as: (herbage mass before defoliation � herbage mass after

defoliation)/herbage mass before defoliation.

fertility for each treatment and effects of fertility and

Fertility Herbageremoveda

ttes Carexand luzule

Plant nitrogenindex

Soil P content(ppm P2O5)

0 0.77 67 85

0 0.66 64 77

0 0.78 56 67

1 2 0.66 28 67

0 0.86 31 47

9 4 0.60 27 49

s ns *** + ns

s ns ns * ***

ns ns ns *

respectively high and low fertility level.


2.4. Data analysis

For examining the variation of the plant trait (direction of

variation, order of magnitude, etc.) along an ecological gradient,

several cases can be considered: (i) strong convergence in the

direction where a trait responded whatever the plant functional

group; (ii) part convergence, one of the two forms of growth

always having higher values than the other (this can result from

an intrinsic characteristic to the growth form considered); (iii)

part convergence when the different plant functional groups

did not have the same response to the ecological gradient.

Soil fertility and nutrient availability were assessed through

soil analysis (layer 0–5 cm) for phosphorus (Olsen method) and

plant analysis for nitrogen (Table 1). For the latter, plant

nitrogen index (Ni) is calculated from N concentration and

herbage mass. It is the ratio of the actual %N (%Na) to the critical

%N (%Nc) which corresponds to: %Nc = 4.8 (DM)�0.32 reported by

Lemaire and Gastal (1997). It provides a rigorous ranking of plots

for their nitrogen limitation for herbage production A valueof Ni

of 1 means that herbage growth is not limited by nitrogen.

ANOVA, correlations and correlations (Pearson and Spear-

man) were calculated using Statistix 7.0 software. Percentages

were loge-transformed to meet ANOVA conditions.

3. Results

3.1. Characterization of the treatments for plant life formsand management practices

There was a significant effect of treatments on the proportion of

the different PLFs and numbers of species (Table 1). The rosette

PLF was most abundant on the GM- and P-treatments and least

abundant on the M treatments. Rosette forms usually increased

the most when grasses decreased (r = �0.8; p < 0.001). The

defoliation treatments resulted mainly in a difference in the

proportion of herbage removed while the difference in field

fertility corresponded to differences in nitrogen availability

(plant nitrogen index) or soil phosphorus availability (Table 1).

3.2. Plant trait variations in different plant life forms

Significant differences were observed between PLFs for the 6

plant traits, and the highest significant levels were found for

Table 2 – Comparison of the means of the six plant traits for t

Traits Significance Grasses

20a

Flowering date (Julian days) ¤ 158ab

Plant height at vegetative stage (cm) * 22.2a

SLA (m2 kg�1) * 26.0a

LDMC (g kg�1) *** 257a

LNCmass (g kg�1) *** 27.9b

Lamina C:N ratio *** 18.9ab

CL: carex and luzule.¤p < 0.1; *p < 0.05; ***p < 0.01.

Data having a different letter in the same line were significantly differena Number of species considered.

LDMC, LNC and C:N ratio (Table 2). Grass and rosette PLFs were

the most distinct. There were significant differences for plant

height, SLA, LDMC. Grass life forms were characterized by

their late flowering dates, greatest plant heights and LDMCs

(together with Carex and Luzule) and SLA (together with

legumes). Small significant differences between PLFs were due

to large variation within groups. This was especially observed

for flowering date. For example, in comparison of grass

species, some rosette species can flower early in the season,

such as Carex and Luzule (around 100 Julian days for

Taraxacum officinale L., Bellis perennis L. and Plantago lanceolata

L.) or later (around 150 Julian days for Scabiosa columbaria L.,

Knautia arvensis L., Picris hieracioides L.).

3.3. Comparison of weighted plant traits betweenrosettes, upright forbs and grasses

Plant traits measured on grasses and dicotyledons were

significantly positively correlated, except for LDMC (not

shown). Correlations were usually higher when considering

only the rosette PLF, except for SLA. This suggests that not all

dicotyledons have the same behavior, depending on the plant

trait considered. Thus for further result analysis, we distin-

guished upright and rosette forbs.

For SLA there was a significant correlation only between the

grass and the upright forbs (Fig. 2a). Furthermore, dicotyledons

have only half the range of variation in SLA as the grasses. Grass

and rosette PLFs were significantly correlated for LDMC, but

there was a significant difference in the intercept (Fig. 2b). On

the other hand, there was no significant correlation between

grasses and the upright forb PLF.

The plant height, measured at the vegetative stage, is an

almost perfect example of convergence between grass PLF and

rosette as well upright forbs (Fig. 2c). Indeed, the linear

regressions were almost identical with the bisecting line.

The leaf N content (Fig. 2d) and C:N ratio (Fig. 2e), although a

little further away from the bisecting line, behave as they do

for plant height. The nitrogen content of grass PLF tended to be

slightly higher than those of rosette PLF and lower than those

of upright forb PLFs.

For the date of flowering (Fig. 2f), the correlations between

grass PLF and rosette as well as upright forbs PLFs were

significant but weaker (p < 0.1) than for the vegetative plant

traits. Rosettes and upright forbs flowered earlier than the

he five functional groups.

Rosettes Upright forbs Legumes CL

15 22 6 4

136a 139ab 147a 99b

13.5b 18.2ab 15.8ab 9.1b

21.2b 24.1ab 27.6a 18.3b

147c 201b 213ab 271a

25.0b 31.9ab 44.8a 21.9b

21.0a 16.9ab 11.9b 24.0a

t.

Fig. 2 – Relationships between the 6 weighted plant traits (SLA, LDMC, plant height, LNC, C:N lamina, flowering date) for

grasses (X-axis) and for forbs (Y-axis: open symbols for rosettes, full symbols for uprights); regressions were drawn for

significant Pearson correlations (ap < 0.1; *p < 0.05; **p < 0.01; ***p < 0.01).


grasses. These results suggest that, although some dicotyle-

dons can flower later than the majority of grasses on the

grassland in general (at the individual species scale, cf.

Table 1), within a given community the dicotyledons tend to

flower earlier than the grasses.

3.4. Comparison of weighted plant traits for differentgroups of species

We evaluated how weighted plant traits changed when

consideringdifferentgroupsofspecies:allthemeasuredspecies,

the grass species only or the two dominant grass species.

Comparisons were made for those for SLA, LDMC and plant

height which were the easiest to measure and the most strongly

linkedtoresourcescapturedandusedbytheplants.Comparison

of weighted plant traits between the overall measured species

and the grass PLF show very close relationships for plant height

and SLA (no significant differences in the slope and in the

intercept; r > 0.95),butdifferences inthe intercept forLDMCand

a poorer correlation (r = 0.72) (Fig. 3). Considering only the two

dominant grass species did not greatly alter the regression

coefficients, but the correlations were the lowest, although

significant (p < 0.001 for SLA and H, p < 0.01 for LDMC).

Plant community rankings were always significant when

comparing all the measured species to the grass species alone,

or the two dominant species or the two dominant grasses,

Spearman correlations being the highest for plant height and

SLA (Table 3). The least corroborating rankings were observed

for LDMC when comparing one component with grasses and

another one including dicotyledons.

4. Discussion

4.1. Convergence in plant traits between plant life forms

This research shows clearly that there is similarity in behavior

between grass and dicotyledonous (at least rosettes) PLFs

Fig. 3 – Relationships between three weighted plant traits

(SLA, LDMC, plant height) for the whole plant community

(X-axis) and the grass group (open symbols) or the two

dominant grasses (full symbols); regressions were drawn

for significant Pearson correlations (ap < 0.1; *p < 0.05;**p < 0.01; ***p < 0.01).


found within a given community for a set of weighted plant

traits characterizing species for the capture and use of

resources and competitiveness. These results were obtained

for a range of defoliation managements (grazing vs cutting)

Table 3 – Spearman correlation coefficients between plant traitwo dominant species; (iii) the two dominant grasses (n = 18).

Correlation between the weightedplant trait for the overall species and

Leaf dry matter

* All grass species 0.73**

* The two dominant species 0.71**

* The two dominant grass species 0.72**

** p < 0.01.*** p < 0.01.

and intensities of defoliation, as well as fertility gradients

(Table 1) which were typical of temperate managed grass-

lands. Indeed, such comparisons are usually made for more

contrasting treatments (used vs abandoned grasslands)

(Tremont, 1994) or larger spatial scales (Diaz et al., 2004). This

means that even at the spatial scale at which we worked,

defoliation regime and fertility act as strong filters that

impose, at least at PLF level, very similar plant traits

determining specific local community structure and composi-

tion (Holdaway and Sparrow, 2006). Consequently, for each

combination of environmental factors, there is a group of

species with similar traits that tend to occur together more

often than expected by chance alone. Our observations

confirm that there is a relative uniformity within the plant

community of productivity-related traits, whereas diversity is

often observed in regenerative traits (Grime, 2006).

Our results confirmed the well-known effect of manage-

ment practices, considered as ecological factors, on the

proportions of the different PLFs (see Section 2). The original

result of this study concerns the effect of management on

weighted plant traits for the different PFFs. When an

ecological factor increased (or decreased) a plant trait for

the grass PLF, it also did so for other PLFs, usually to a similar

extent. This similarity in response, especially for grass and

rosette PLFs, was observed clearly for 4 plant traits involved in

the plant strategy for resource acquisition and use (Craine

et al., 2001): LDMC, that reflects the ‘‘tissue density’’ strategy,

height, %N and C:N ratio.

Such similar behavior between grasses and dicotyledons

was also observed when comparing different PLFs within a

plant community, especially for SLA (Diaz et al., 2004). For %N,

a better correlation was found between grasses and rosettes

than between grasses and upright forbs. Litter C:N ratio, an

index of litter quality, was depended significantly of stocking

rate; it was lower at 4.0 sheep ha�1 year�1 compared with 1.3

and 5.3 sheep ha�1 year�1 (Barger et al., 2004). For the height,

Craine et al. (2001) show that along a fertility gradient, there

was a parallel pattern of growth form for both grasses and

forbs on low-fertility plots. We observed that the height of

some rosettes can equal that of grasses at medium fertility

level (Fig. 2c), because leaves that grow roughly parallel to the

ground become erect when there is competition for light. On

the other hand, there was a significant difference in the timing

of flowering between grasses and dicotyledons, as reported

previously (Negi et al., 1992), but to a lesser extent than for

other plant traits, probably because variations in flowering

time associated with nutrient availability are minor (Al Haj

ts for all species combined and (i) all grass species; (ii) the

Plant traits

content Specific leaf area Plant height

0.95*** 0.97***

0.96*** 0.96***

0.95*** 0.93***


Khaled et al., 2005). Indeed, this result strengthened the view

that phenological stages are related to these plant character-

istics, at least to LDMC (Sosebee and Weibe, 1973).

Differences and similarities between grasses and dicoty-

ledons (upright forbs, rosettes) were also observed for plants

growing in pure stands. In this way, LDMC values separated

the species into three PLFs (grass, rosette forbs and upright

forbs, p � 0.001) while this is not the case for SLA and height (Al

Haj Khaled et al., 2005). Thus, LDMC should not be measured at

plant community level without considering PLFs separately.

On the other hand, Craine et al. (2002) found that there was

more variation within C3 grasses and forbs than between the

two groups. Both were distinguished because of some

morphological and allocation traits, but not by traits asso-

ciated with growth and production. In the same experiment,

Tjoelker et al. (2005) show that the mean values of SLA

between grasses, forbs, legumes were similar (99–118 cm2 g�1)

but not significantly different. However, significant differ-

ences were found for %N and C:N ratio as regards the

proportion of grasses and legumes. Craine et al. (2001) show

that the separation of grasses and forbs in theory-based

classifications is obvious when the traits used for the

classification rely heavily on morphology. On the other hand,

they noted that there was little difference in functional traits

such as SLA, leaf longevity and growth in low-nutrient

conditions.

The similarity in traits between PLFs within a plant

community in response to ecological gradients is in agreement

with the similarity observed previously for agronomic char-

acteristics. The similarity found between grasses and dicoty-

ledons within a set of plant communities for leaf:stem ratio

(Calviere and Duru, 1999) and plant part digestibility (Duru,

1997) means that the studied plant traits are appropriate as

response and effect traits (Hooper et al., 2002).

4.2. Implications for field diagnosis and monitoring theeffect of land-use change on ecosystem behavior throughplant trait measurements

For the six plant traits known to be suitable for characterizing

the capacity of species to exploit resource-rich or -poor

environments or the capacity for competitive dominance in

response to disturbance on the one hand, and to assess

agronomic or environmental properties on the other, there is

good correlation between measurements made for the two

main species or the two main grasses and for all the species

combined. These results differ from those of Cousins and

Lindborg (2004) who found that differences in plant traits were

mainly related to a wetness gradient rather than management

intensity, but they are in agreement with Garnier’s findings

(Garnier et al., 2004). These authors show that the correlations

between leaf traits (LDMC and SLA) and environmental or

management factors (in their case, the period of abandonment

of the pasture) are more sound when one considers only the

two dominant species or the weighted plant traits at

community level rather than the actual values for each of

the species. This was due to the ‘‘mass ratio hypothesis’’

postulating that ecosystem properties should depend on

species traits and on species contribution to the whole

above-ground biomass of the community (Grime, 1998; Vile

et al., 2005). To summarize, the two dominant grasses or

species that constitute at least 18 and 29% respectively (up to

69 and 79%) of the herbage mass represent well the behavior of

the whole pasture as regards the studied plant traits. Thus,

they can be used as indicators for field diagnosis or monitoring

in order to evaluate if there are changes in land use or

management intensity and on their impacts upon environ-

ment and agriculture. However, for field diagnosis, care should

be taken to ensure that differences in plant traits are due to

differences in management intensity and not to environ-

mental gradients such as wetness (Cousins and Lindborg,

2004).

In order to use plant functional parameters for ranking

plant communities according to their response to ecological

gradients (Kleyer, 1999; Pakeman, 2004) or their effect on

agronomic characteristics (Duru et al., 2005), methods to

simplify their application in the field would be welcome. We

can distinguish methods based on trait measurements and

those based of the use of plant trait databases (Lavorel et al.,

2007). For the former, one must be able to identify species.

However, we show that it is possible to reduce dramatically the

number of species on which plant traits are measured without

toomuchchange in the plant community ranking. The choice of

the grass PLF is justified by its abundance in semi-natural

grasslands and their similar morphology (one botanical family)

which avoids having to adapt the procedure of trait measure-

ments. Furthermore, by measuring only the grass PLF, the loss

of information is small for the whole community. However, we

think that this simplified method performs better for ranking

grassland communities according to plant traits than for

providing absolute values. Another method is to list traits

chosen at random (Gaucherand et al., 2006). In this case, it is not

necessary to identify the species, but caution should be

exercised, especially for LDMC measurements, due to the big

differences which exist between PLFs.

5. Conclusion

Grasses and dicotyledonous (especially rosette) plant life

forms behaved very similarly within a set of grassland

communities differing in soil fertility and defoliation regimes

for several plant functional parameters that respond to

management (nutrient availability and defoliation regime).

The closest relationships were observed for plant height at the

vegetative stage, leaf nitrogen content and C:N ratio. On the

other hand, the dicotyledonous species have lower LDMC and

flowered on average earlier than grasses. Reducing the plant

community to the grass PLF or even to the two dominant

species did not greatly alter the ranking of the set of studied

grasslands, leading to the possibility of using a simple method

for assessing the effects of land-use change on ecosystem

behavior by monitoring the targeted plant traits.

Acknowledgment

The work was funded by the EU project VISTA (Vulnerability of

Ecosystem Services to Land Use Change in Traditional

Agricultural Landscapes) (Contract no. EVK2-2001-15 000356).

Appendix A. Characteristics of grasslands studied (altitude, aspect and management method) and their dominant species

Grassland name Altitude Aspect Fertilizationa Defoliation Grasses Dicotyledons

AGR ANT ARR DAC FESR HOL LOL MOL POA CEN CHA PIC PLA RAN RUMA

Angladure 600 BV Yes M 3 4 2 1

Moulaque 600 BV Yes M 3 4 5 1 2

Ville Ajas 1b 600 BV Yes M 2 4 1 3 5

Le Carre 600 BV Yes M 4 1 2 3

Campagne 600 BV Yes M 5 1 4 2 5

Ville Ajas 2 600 BV Yes M 2c 5 4 1 3

Camplong 1 900 S-W Yes GM 1 2 3 4 5

Rives 600 BV Yes GM 3 2 1 5 4

Coste Bas 1 800 S-W No GM 2 1 5 3 4

Camplong 2 900 S-W Yes GM 2 1 5 4 3

Routies 900 S-W Yes GM 5 4 3 2 1

Coste Bas 2 800 S-W No GM 4 3 1 5 2

Gironsas 1 1000 S-W No P 2 1 3 4

Peyche Petit 2 950 S-W No P 2 1 3 4

Lassus 1 900 S-W No P 1

Gironsas 2 1000 S-W No P 2 1 3

Peyche Petit 2 950 S-W No P 1 3 2 4

Lassus 2 900 S-W No P 3 1 2

Species frequencyd 21 21 18 75 18 78 64 4 29 25 18 11 36 07 11

M: meadow, GM: meadow grazed in spring, P: pasture.

AGR, Agrostosis capillaris L.; ANT, Anthoxanthum odoratum L.; ARR, Arrhenatherum elatius L.; DAC, Dactylis glomerata L.; FESR, Festuca rubra L.; HOL, Holcus lanatus L.; LOL, Lolium perenne L.; MOL, Molinia

coerulea L.; PIC, Picris hieracioides L.; PLA, Plantago lanceolata L.; POA, Poa trivialis L.; RAN, Ranunculus acris L.; RUMA, Rumex acetosa L.; TAR, Taraxacum officinalis L.a Fertilization consisted in application of around 20 t of manure per ha and per year.b 1 and 2 means 2 facies within the same grassland field.c Numbers indicate the rank of the species for its abundance; the two main grasses are indicated in bold.d Average in percent for the 18 plant communities.

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Convergence in plant traits between species within grassland communities simplifies their monitoring

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