Effects of soil surface disturbances after logging on plant functional types
Ann. For. Sci.
Effects of soil surface disturbances after logging on plant functional types
0 Institut National de la Recherche Agronomique , BP 27, 31326 Castanet-Tolosan , France
1 Centre National de la Recherche Scientifique, Centre d'Écologie Fonctionnelle et Évolutive , UMR 5175, 1919 route de Mende, 34293 Montpellier Cedex 5 , France
- Soil surface disturbances after logging influence plant species diversity. To estimate these effects, the objective of the present study was to test three hypotheses: (1) each soil surface disturbance type is characterized by a group of plant species that emerges following the disturbance, (2) each emergent group of plant species has distinct, recognizable biological traits, (3) in two different bio-geographic plant communities, each soil surface disturbance type is characterized by the same set of biological traits. We present results from Atlantic oak (Quercus pubescens Willd., Q. robur L. and Q. petraea (Mattuschka) Liebl.) coppices and natural Mediterranean Aleppo pine (Pinus halepensis Miller) forests of southern France. Both studies use the same methodology based on a typology of soil surface perturbation 1-3 years after logging combined with a vegetation inventory. Plant functional traits (morphological, life history and regeneration), not necessarily linked with taxonomic attribution, were used to constitute putative functional groups to allow comparison between the two studies. Results were similar in the two studies and confirmed the working hypotheses.
In recent years, there has been much concern about the
impact of forest management practices on biodiversity [
]. Society increasingly demands that forest managers reduce
the negative influences of their exploitation practices on
biodiversity, especially during logging operations that are the
most obvious human perturbations on forests. Consequently,
considerable research has been carried out on this topic,
especially concerning plant species diversity which is a component
of prime importance in terrestrial ecosystem functioning [
Plant species diversity in managed temperate forests is
generally strongly modified just after logging perturbations, with
an increase of species richness [
]. When the canopy
closes, species richness decreases and can return to its former
level . However, even if species richness decreases, rare
species can develop in old forests and thus yield enhanced
conservation value [
]. Logging changes canopy
structure and induces large understorey modifications with regards
to light [
], rainfall distribution on soil [
temperature and humidity , as well as chemical and microbiological
soil properties [
18, 37, 44, 51
]. All these factors have effects
on species diversity and thus on resistance , resilience [
and overall functioning of ecosystems. The modifications of
the ground surface, such as slash deposition and litter removal,
created by logging operations, are suspected to be possible
driving factors of plant species diversity. These perturbations
of the ground surface create a heterogeneity that could have
consequences on plant species diversity [
15, 27, 56
To analyze ecosystem responses to disturbances, life traits
appear to be an excellent tool [
]. Indeed, plant functional
types can be defined as comprising species that respond in a
similar fashion to specific environmental factors, as a result of
their shared biological traits . Functional classifications,
based on life traits, give biological robustness and cross-regional
comparability to models and field studies [
]. Life traits are
morphological, physiological or ecological traits, not
necessarily linked with taxonomic attribution [
]. Thus, plant
functional classification has recently received much attention from
ecologists even though functional classifications of species are
known and used since quite some time [
]. The use of life traits
for the comprehension and analysis of plant species dynamics
in relation with perturbation is clearly demonstrated by many
16, 17, 41, 45, 47
]. These authors generally concur
with a general hypothesis that there exists a pattern of response
to perturbation, linked to species biology, which is more or less
identical for plant communities belonging to vastly different
milieux and contexts [
The objective of the present paper is to use functional
groups based on plant life traits in order to analyze effects of
soil surface disturbances after commercial logging on plant
species diversity. For that purpose, we test three hypotheses:
(1) each soil surface disturbance type is characterized by a
group of plant species, (2) each emergent group of plant
species has distinct, recognizable biological traits, (3) in two
different bio-geographic plant communities, each soil surface
disturbance type is characterized by the same set of biological
traits. These hypotheses have been tested by combining two
separate studies employing similar methodologies in two
types of forests.
2. MATERIALS AND METHODS
The two types of forests studied are located in southern France.
The first one, hereafter called Atlantic (ATL), is near Toulouse in a
region with Atlantic climatic influence (800 mm mean annual
precipitation; 11 °C mean annual temperature; 200–400 meters above sea
level; molasses substratum). Broad-leaved trees including oaks
(Quercus pubescens Willd., Q. robur L. and Q. petraea (Mattuschka)
Liebl.), chestnut (Castanea sativa Miller) and cherry (Prunus
avium L.) are the main canopy species of the highly fragmented
forests which are generally managed in coppice, and coppice with
standards, since several centuries. There are few recent afforestations in
the area and most of the woodlots were already present before the
beginning of the twentieth century judging by old maps. This area has
been studied in 1998 [
The second area studied in 1999 [
], hereafter called
Mediterranean (MED), is near Draguignan, in southeastern France, in a region
with Mediterranean climatic conditions (800 mm mean annual
precipitation; 14 °C mean annual temperature; 200–300 m a.s.l;
limestone substrate) [
]. The studied forests are composed of Aleppo
pine (Pinus halpensis Miller) stands, with evergreen holm oak
(Quercus ilex L.) and downy oak (Quercus pubescens Willd.) in the
under canopy. Since the nineteenth century, abandonment of olive
trees and vineyards culture, the decline of grazing, and the spread of
plant diseases have favoured the expansion of Aleppo pine to the
detriment of holm oak [
]. This pine is a transient species which,
being unable to reproduce in its own understorey, is replaced by holm
oak or downy oak in the absence of fire. Logs of these Aleppo
pine-dominated forests are mainly harvested for transformation in
regional paper pulp factories.
In these forests, the description of the ground surface, in stands
logged since less than three years, was inspired from the method
developed by McMahon [
]. This method is based on visual
recognition of the ground surface at selected points or spots (30 cm radius
circle) with regard to a reference list of 23 possibilities. As many
ground surface classes had low frequencies in our studies, we
simplified the classes of the original reference list into three broad groups:
N = not perturbed, P = perturbed (litter removed but topsoil intact,
litter and topsoil mixed, rut etc.), R = remnant depot (slash cover deep)
]. Data collection on plant species composition was carried out on
the same spots as the ground surface description in the MED area and
on a 1 square meter in ATL.
In ATL, the sample was based on two sites with 3 and 4 plots,
respectively, and for each one a transect of 20 spots (n = 140) was set
up. The transects were perpendicular to the main axis of wood
transportation on the stand. In MED, the sample was based on 3 sites with
five 400 m2 circular plots in each, made up by 100 spots along 3
regularly spaced diameters (n = 1500). These data were synthesized in
order to obtain a measure of the affinity of the observed plant species
for each type of ground surface. Assuming Ni, Ri, Pi were the number
of presence of the species i in each respective ground surface type and
N, R, P the total number of samples of each type, the affinity for type
N was calculated as: FNi = (Ni/N)/(Ni/N + Ri/R + Pi/P), and similarly
for R and P. When a species was observed only in the N type, FNi = 1.
When it was never observed, FNi = 0. For a given species i, FNi, FRi
and FPi defined coordinates in a triangular system where each species
was plotted for each studied area. We defined 7 groups of species
called N, R, P, NP, NR, PR, NRP. The species of the group N had a
specificity FNi ≥ 0.75, idem for R and P, a species of the group NP
had a specificity FRi ≤ 0.25 and FPi ≥ 0.25 and FNi ≥ 0.25, idem for
NR and PR, the remaining species are in the group NRP.
To analyze the influence of ground surface modification on plant
species diversity after logging, species were characterized by life
traits that refer to structure and functioning [
]. We selected here the
life forms, defined by Raunkiaer [
], which are based on the position
on the plant of renewal buds from which new organs and foliage
develop after an unfavorable season, such as a cold winter. Life forms
(or growth forms) give relevant and revealing information of
functional ecological shifts taking place at the community or ecosystem
]. Moreover, life forms effectively synthesize various
life history traits, as they integrate both morphological and
physiological attributes [
]. The life forms selected in our study are:
therophytes (annual plants), geophytes (bulbous plants), hemicryptophytes
(herbaceous perennials), chamaephytes (shrubs) and phanerophytes
Dynamic ecosystem patterns and processes can also be studied by
dispersal modes that are important for plant species survey and
community structure [
]. Among the different classifications of species
based on seed dispersal vectors [
], we selected, after examining the
available data, four main dispersal modes: anemochory (seeds
dispersed by wind), endozoochory (dispersal associated with ingestion
of seeds by animals), epizoochory (seeds dispersed by animals
without being ingested) and other dispersal vectors (seeds dispersed by
water, gravity and unknown dispersal modes). We also analyzed
plant species distribution as a function of their capacity to grow in a
restricted area, like a logging area, by using Grime’s classification
] which allows classifying plant species in relation to their
sensitivity to stress tolerance (S), competitiveness (C) and ruderality
(R). Competitive strategy “involves selection for highly competitive
ability, which depends upon plant characteristics that maximize
vegetative growth in productive, relatively undisturbed conditions” [
By contrast, stress tolerant strategy is associated with “reductions in
both vegetative and reproductive vigor, adaptations which allow
endurance of continuously unproductive conditions arising from
environmental stress, severe resource depletion by the vegetation, or
the combined effect of the two” [
]. Ruderal strategy “is associated
with a short life span and with high seed production and has evolved
in severely disturbed but potentially productive environments” [
The mean positions of the species groups in the triangle defined by
Grime between R, S and C components defined the overall strategies
of the groups.
Information about these various traits was obtained for the ATL
site from Rameau et al. [
] for life forms and dispersal modes, and
from Grime et al. [
] for Grime strategies. In the MED site, we used
the data base BASECO (IMEP, Marseille, France) for all life traits
]. This data base gives information about life traits of
Mediterranean plant species from literature [
6, 12, 36, 49, 57, 62, 65
For each group of species defined by affinity for ground surface
types, we computed the proportion of species belonging to the classes
defined by a given life trait. These proportions were tested against a
random distribution of the species by the Pearson Chi2 test with
Systat 9 when the number of species was higher than the required number
of five; otherwise groups were merged [
In both study areas; plant species composition differed
according to ground surface condition (Fig. 1). In both areas,
of the 79 species observed in ALT and the 71 species observed
in MED, only 3 species and 5 species, respectively, were
exclusively associated with intact spots (i.e., not logged).
Conversely, most of the species were observed in intact spots; 43
(9 NP and 34 NRP) in ATL, and 42 (7 NR, 3 NP and 32 NRP)
in MED. Perturbation of the ground surface seems necessary
for many species that were observed only in such situations
– 29 (37% of total species richness) in ATL, and 13 (18% of
total species richness) in MED. The species associated with
slash decomposition were less numerous; 0 in ATL and 4 in
MED. It seems that more species have a high frequency in
slash depots in MED than in ATL. Only 14 species are
common between both samples (Fig. 1), but they did not have
similar trends with ground surface types, except for Cytisus
scoparius, Hedera helix, Ligustrum vulgare and Rubia peregrina
associated with NRP, while Lolium perenne and Teucrium
chamaedrys associated with P in the both areas.
3.1. Raunkiaer’s life forms
Geophytes, therophytes and chamaephytes were the life
forms least often observed in the two areas (Fig. 2). Only one
geophyte, Tamus communis, was observed in ATL - NR, and
no geophyte at all was recorded in MED. We found only
8 therophytes in ATL of which 1 in N, 5 in P and 2 in NP, and
only 4 therophytes in MED of which 1 in R, 2 in P, 1 in NP;
most of the therophytes appeared in perturbed places.
Chamaephytes represented only 7.1% of the total species
richness in ATL and 11.3% in MED; they were observed in
several ground surface types but with few species.
Hemicryptophytes and phanerophytes were the most observed life forms
in the two regions. Hemicryptophytes represented 52.5% of
total species richness in ATL and 31.3% in MED, while
phanerophytes represented 31.3% of total species richness in ATL
and 52.1% in MED. Thus, the statistical analyses were carried
out only with these life forms. In ATL, we recorded
significantly more hemicryptophytes than phanerophytes in
perturbed places (P, PR, NP, NPR; χ2(2) = 22.87; p < 0.001),
whereas no significant difference were found in MED
(χ2(2) = 1.35; p > 0.05). Conversely, in MED, there were more
phanerophytes than hemicryptophytes in unperturbed places
(N, NR, R; χ2(2) = 8.32; p < 0.01), whereas no significant
difference was found in ATL (χ2(2) = 1.23; p > 0.05).
3.2. Dispersal mode
Epizoochory, was the least observed mode of dispersal in
all ground surface types (Fig. 3), with only 6 species in ATL
(Brachypodium sylvaticum, Holcus mollis, Juncus
conglomerates, Phleum pratense, Ranunculus nemorosus and Vulpia
myuros), and 2 species in MED (Digitalis lutea and Galium
timeroyi). The category “other dispersal modes” (seeds
dispersed by water, gravity and unknown dispersal modes)
represented 21.1% of total species richness in ATL and 16.9% in
MED. It appeared with more than 2 species in P, NP and RP
in ATL, and in P and NP in MED; it was associated with
perturbed places. Anemochory and endozoochory were the most
observed dispersal modes in both studied areas; anemochory
represented 49.5% of the total species richness in ATL and
38.0% in MED, while endozoochory represented 23.1% of the
total species richness in ATL and 42.3% in MED. There were
significantly more species characterized by anemochory in
ATL than in MED (χ2(2) = 4.05; p < 0.05), and significantly
more with endozoochory in MED than in ATL (χ2(2) = 5.70;
p < 0.05). In ATL, anemochory was observed in N, P, NR, NP,
and only one species in NRP, thus essentially in unperturbed
and perturbed places. In MED, anemochory was observed in
all ground surface types but it was more present in NP and RP.
In ATL, endozoochory was higher in NP and P than in the
other ground surface types. In MED, endozoochory was
higher in P, NP and NRP.
3.3. Grime’s strategies S, C and R
All the groups of species were characterized by competitive
and stress tolerant (CS) strategies than ruderal (R ≤ 0.3)
(Fig. 4). In ATL, group species related to P (P, PR, NP) have
high values for the sensibility to perturbation (R), group
species related to R (R, NR, PR) have high values for the
sensibility to competition (C) and group species related to N (N, NP,
NR) had high values for sensibility to stress (S). In MED,
group species related to P, PR and NR showed high value for
perturbation (R), groups species related to PR, NR and NP
showed high value for competition (C), and groups species
related to N, R and NP showed high value for stress (S). Thus,
in MED there was not one strategy (S, C or R) more associated
with one ground surface type (P, R, N) than the others.
Analyzes carried out concerning effects of soil surface
disturbances after logging on plant species diversity allowed us to
confirm or partially confirm our three hypotheses. Hypothesis (1),
that each soil surface disturbance type is characterized by a
group of plant species, was verified. In the two areas, Atlantic
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and Mediterranean, few species were observed when remnant
depots were high, while many species were present in perturbed
places and numerous species were associated with not
perturbed places or were indifferent to perturbation. These results
agree with many other studies showing that logging increases
plant species diversity [
]. However, plant species in the
Mediterranean site had a lower affinity to ground surface types
than in the Atlantic site. The low number of species associated
with remnant depots can be explained by the fact that remnants
compensate for canopy suppression due to logging by
maintaining low light availability, high humidity and ample leaf
litter . Concerning the 14 species occurring in both the
Atlantic and Mediterranean areas, only 6 species have similar trends
with ground surface type. This variability in species response
to perturbation could be explained by low plant species
frequency. Moreover, all species which have been recorded in
stands studied, which have been logged since than less than
3 years, are common species. Analyses of vegetation
composition in similar stands, logged since 30 years, also indicated
that no rare species were observed in both area [
when canopy closes and species richness decrease, there are no
rare species that enhanced conservation value.
Hypothesis (2), i.e., that groups of plant species have
distinct biological traits, was partially verified. Indeed, the
analyses showed that perturbed areas (P) were associated more
particularly with hemicryptophytes, anemochorous and
ruderal species; remnant depot (R) areas with seeds dispersed by
animals and competitive species; and not perturbed (N) areas
with seeds dispersed by wind or animals and stress tolerant
species. There was no life form which characterized in
particular R or N. As in previous studies [
4, 20, 26, 28
], we found
that hemicryptophytes increased after logging and we
specified here that they increased more particularly in perturbed
places. These plant species were essentially dispersed by wind
and required perturbed areas, without litter, to germinate.
Moreover, hemicryptophytes have a short life span and were
probably not present in litter before logging. These forest and
farm species probably arrived from the surrounding mosaic of
forests and agricultural lands (essentially olive trees and
vineyards in the Mediterranean area, and pastures and crops in the
Atlantic area) . Moreover, modalities of implantation of
plant species depend on colonization pressure which is in turn
heavily influenced by proximity to the logged forest. The
temporal variation in plant diversity could also be analyzed.
Indeed, plant diversity has been generally studied in relation to
succession, few studies have addressed seasonal variation in
plant diversity [but see 33, 67]. Concerning Grime strategies,
plant species were globally speaking more competitive and
stress tolerant than ruderal. This supposes that ground surface
perturbations were so frequent and moderate that they were
considered like a stress and not a perturbation by plant species.
The life traits selected in our study are relatively general,
they synthesize other life traits as for example life forms that
integrate both morphological and physiological criteria. But,
all the possible life traits (leaf type, leaf consistency, nutrition
type, vegetative multiplication etc.) were not available for the
analysis because of lack of data on numerous species and also
because of a discrepancy between the databases of life traits
created separately in the two studies here compared. However,
we found the same pattern in both areas, Atlantic and
Mediterranean, for life forms and the dispersal modes; for Grime
strategies, the species repartition in function of ground surface
types was more stronger in Atlantic than in the Mediterranean
area. Thus, hypothesis (3), that two different bio-geographic
plant communities should have the same biological traits for a
given soil surface disturbance, was not clearly verified. We
conclude that life traits are a good tool to analyze ecosystem
responses to disturbances such as logging. Expressing and
grouping plant species primarily with regards their biological
characteristics allows avoiding taxonomic attribution and
thus, allows comparing result between two bio-geographic
The consequences of these sets of observations are that
ground surface status influence plant species diversity. Thus,
light availability and the related factors of moisture decrease,
temperature modification, etc., cannot be considered as the
only factor driving plant species diversity increase after
logging. Moreover, the consequences of logging by different
types of engines with increasing weight on the ground surface
should be more carefully studied in order to be able to predict
their influences on the vegetation.
Acknowledgements: We would like to thank the French Research
Ministry , the Institut National de la Recherche Agronomique and the
Société pour l’Exploitation des Bois du Sud Ouest for financial and
technical support of the study in the Atlantic area. We also thank the
European Union (DG XII), the Direction de l’Espace Rural et de la
Forêt of the French Ministry of the Agriculture, the Centre National
de la Recherche Scientifique, the Office National des Forêts, the
Centre Régional de la Propriété Forestière, the Association Forêt
Cellulose and the Société pour l’Exploitation des Forêts de l’Est for
financial and technical support of the study in Mediterranean area. We
also thank James Aronson for helpful comments on the manuscript.
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