Impact of livestock grazing on forest structure, plant species composition and biomass in Southwestern Madagascar

Abstract

Background and aims – To contribute towards a better understanding of habitat utilization by livestock and its impact on biodiversity components in the dry ecosystems of Madagascar.

Location – Southwestern Madagascar, in and around Tsimanampesotsa National Park.

Methods – We quantified species composition, life forms, structure, and plant biomass of different vegetation formations in areas of four different grazing intensities: (1) ungrazed for four years prior to the study, (2) grazed by zebu during the dry season, (3) grazed by zebu at the end of wet season and during the dry season, and (4) grazed by goats during the wet and the dry season and by zebu at the beginning of the dry season. The food biomass available was compared with the food biomass required.

Key results – Zebu feed on the east side of the National Park during the wet season as long as there is enough water in that area. When water becomes scarce, the zebus return to the western side of the park. Goats are restricted to the littoral zone year-round. As a result, goats and zebus occupy different proportions of the various vegetation types of our study area. Zebus also use the littoral forest, but only at the end of wet and during the dry season. Large parts of the spiny bush on the limestone massif and dry forest on ferruginous soil are not used regularly by zebu.
Plant species richness and diversity varied in relation to grazing pressure and soil conditions. In the littoral and on red sand, plant diversity decreased with grazing pressure. This change was most pronounced in the littoral zone. Since grazing pressure increases during the dry season, grazing affects mostly woody species, since herbs are no longer available during the dry season. In contrast to the bush encroachment due to grazing in Africa, grazed areas in southwestern Madagascar contain fewer woody plant species than areas not used by livestock.

Full text

Scripta Botanica Belgica 50: 82–92, 2013
African Plant Diversity, Systematics and Sustainable Development –
Proceedings of the XIXth AETFAT Congress, held at Antananarivo, Madagascar, 26–30 April 2010.
Natacha Beau, Steven Dessein and Elmar Robbrecht (eds)
Impact of livestock grazing on forest structure, plant species
composition and biomass in southwestern Madagascar
Rakotomalala Yedidya Ratovonamana1,2,*, Charlotte Rajeriarison1,
Edmond Roger1, Iris Kiefer3 & Jörg U. Ganzhorn2
1University of Antananarivo, Department of Plant Biology and Ecology, BP 906, Antananarivo, Madagascar
2University of Hamburg, Biocenter Grindel, Martin-Luther-King Platz 3, 20146 Hamburg, Germany
3University of Bonn, Nees Institute for Biodiversity of Plants, Meckenheimer Allee 170, 53115 Bonn, Germany
*Author for correspondence: ryrorch@yahoo.fr
INTRODUCTION
In most dry regions of the world, livestock represents a very
important source of income and insurance against variation
in agricultural production due to climatic unpredictability
and erratic rainfall (Riginos & Hoffman 2003, Dickhoefer et
al. 2010). The dry regions of Madagascar are no exception.
In many parts of Madagascar grazing leads to the degrada-
tion of the natural ecosystems. While the degradation of for-
est and non-forest ecosystems due to grazing seems obvious
in many parts of south and southwestern Madagascar, quan-
titative data on livestock carrying capacity and indicators for
degradation or overgrazing are not available (ANGAP et al.
1999, Mahazotahy 2006). This lack of information hinders
the establishment of a monitoring program for habitat quality
and the implementation of a management plan for sustain-
able land use that reconciles the need for livelihoods of the
human population and conservation of Madagascar’s unique
ecosystems.
Southwestern Madagascar is a prime example where
livestock is a most important cultural and economic com-
ponent (Sourdat 1970, Pannoux 1991, Razanaka et al. 2001,
Rakotoarison 2005, SuLaMa 2011) embedded in biologi-
cally unique ecosystems that are under high pressure from
human land use (Fenn 2003). Stockbreeders in southwestern
Madagascar face several problems. First, the region is char-
acterized by a long dry period with irregular rainfall includ-
ing years without rain. The insufcient water supply reduces
the range of cattle as the dry season progresses. Since cat-
All rights reserved. © 2013 National Botanic Garden of Belgium – ISSN 0799-2387
Background and aims – To contribute towards a better understanding of habitat utilization by livestock
and its impact on biodiversity components in the dry ecosystems of Madagascar.
Location – Southwestern Madagascar, in and around Tsimanampesotsa National Park.
Methods – We quantied species composition, life forms, structure, and plant biomass of different
vegetation formations in areas of four different grazing intensities: (1) ungrazed for four years prior to the
study, (2) grazed by zebu during the dry season, (3) grazed by zebu at the end of wet season and during the
dry season, and (4) grazed by goats during the wet and the dry season and by zebu at the beginning of the
dry season. The food biomass available was compared with the food biomass required.
Key results – Zebus feed on the east side of the National Park during the wet season as long as there is
enough water in that area. When water becomes scarce, the zebus return to the western side of the park.
Goats are restricted to the littoral zone in the west year-round. As a result, goats and zebus occupy different
proportions of the various vegetation types of our study area. Zebus also use the littoral forest, but only at
the end of wet and during the dry season. Large parts of the spiny bush on the limestone massif and dry
forest on ferruginous soil are not used regularly by zebus. Plant species richness and diversity varied in
relation to grazing pressure and soil conditions. In the littoral and on red sand, plant diversity decreased with
grazing pressure. This change was most pronounced in the littoral zone. Since grazing pressure increases
during the dry season, grazing affects mostly woody species, since herbs are no longer available during
the dry season. In contrast to the bush encroachment due to grazing in Africa, grazed areas in southwestern
Madagascar contain fewer woody plants and plant species than areas not used by livestock.
Key words – Forest-pasture, transhumance, grazing effect, fodder biomass, Tsimanampesotsa National
Park.
XIXth AETFAT CONGRESS
PROCEEDINGS
ECOLOGY & VEGETATION

83
Ratovonamana et al., Impact of livestock grazing on vegetation characteristics in Madagascar
tle have to stay close to water, more distant areas are grazed
only lightly with substantial amounts of plant biomass re-
maining at the end of the wet season (Bosser 1954). Second,
the pasture is dominated by herbaceous species of low forage
value, such as Cenchrus ciliaris, Panicum pseudovoeltzkowi,
Eragrostis cilianenensis and E. pilosa (Bosser 1954, Morat
1973). Third, parts of the pasture are transformed to agricul-
tural land (Sourdat 1970). Forth, Madagascar is extending
its protected area system, particulary forest ecosystems, thus
reducing the access to forest pasture during the dry season
(Borrini-Feyerabend & Dudley 2005a, 2005b).
Within this context, the goal of this study was to contrib-
ute towards a better understanding of the impact of livestock
on the vegetation in the driest ecosystem of Madagascar.
Within this framework, the specic objectives of this study
were to: (1) document grazing impact on structural vegeta-
tion characteristics, (2) determine the impact of grazing on
plant species composition, (3) identify plant species as indi-
cators for grazing pressure, and (4) measure the biomass of
fodder for livestock during different seasons.
METHODS
Site description
The study was carried out in the northern and western part of
the Tsimanampesotsa National Park and at adjacent sites west
of the national park. The national park is located in south-
western Madagascar (24°03’ – 24°12’S, 43°46’ – 43°50’E)
on the escarpment of the Mahafaly Plateau. The park was ex-
tended from 43,200 ha to 203,000 ha in 2007. This extension
reduces access to forest pasture during the dry season. Tra-
ditionally, cattle use the forests during the dry season where
they browse on woody plant species. This is considered one
of the major threats to the biotic diversity of Tsimanampesot-
sa National Park (ANGAP et al. 1999, Goodman et al. 2002,
Mahazotahy 2006). The Tsimanampesotsa NP represents
Madagascar’s peculiar dry and spiny forest ecosystems and
covers a substantial portion of the Mahafaly Plateau. It sepa-
rates extensive grassland towards the east from the littoral
zone in the west. During the wet season all zebu around the
Tsimanampesotsa NP are brought to the east of the Mahafaly
Plateau into the region of Itomboina where extensive grass-
Figure 1 – Study area and seasonal migration (transhumance) of livestock between the western and eastern parts of the Mahafaly Plateau at
the beginning of the wet season. The migration is reversed at the end of the wet season.

84
Scripta Bot. Belg. 50
lands provide food. However, water is limited in this region.
When water becomes scarce, zebus cross the limestone pla-
teau on a traditional track of transhumance north of the Lac
Tsimanampesotsa at the end of the wet season (March) even
though the areas in the east still provide plenty of food. Then,
cattle remain on the coastal plain where water is available
year round, but food availability is low. With the progressing
dry season, cattle move into the national park. They return
to the east (region of Itomboina) at the end of the dry season
in November (g. 1). Goats remain in the littoral zone year
round. Thus, the number of livestock west of and within the
national park is highest during the dry season when herba-
ceous forage is not available. At this time of the year, woody
plant species (liana, shrubs and trees) provide food for the
animals (Le Houérou 1980).
Field research on grazing was carried out between March
2008 and March 2009. Vegetation descriptions have been
performed during the wet seasons. The study is part of a
more comprehensive study on the vegetation of Tsimanamp-
esotsa NP (Ratovonamana et al. 2011).
Climate
Based on long-term averages, the region can be character-
ized as a semi-arid tropical climate with eight dry months
(April–November) and four wet months (December–March).
Months are considered ‘dry’ when rainfall (R) is less than
twice the mean monthly temperature (R < 2T). During the
dry season, the temperature varies from 17.8°C to 32.6°C
and from 24°C to 35.5°C during the wet season (g. 2). The
average annual rainfall is less than 500 mm (range at Tulear
between 1951 and 1990: 166 – 719 mm / year; CNRE 1992),
but can be irregular with ‘wet’ seasons without rain.
Vegetation
The Tsimanampesotsa forest is part of the southwestern
spiny forest of Madagascar (Moat & Smith 2007). It contains
some of the most unique plant communities on the island and
harbors the highest level of plant endemism with 48% of the
genera and 95% of the species being endemic (Elmqvist et
al. 2007). The forest is characterized by many xerophytic
and drought tolerant woody species of the Didiereaceae and
Figure 2 – Climate of the study area; (*) indicates dry months. Data
from 1950 to 2000 from DIVAGIS (http://www.diva-gis.org). Data
for the study area were recorded from 2006 to 2009 with i-buttons
(temperature loggers; from Ratovonamana et al. 2011).
Euphorbiaceae. The littoral zone with sandy soil is charac-
terized by dry forest, degraded forest and different herba-
ceous layers. The limestone is covered by xerophytic bush
with dry forest on ferruginous soil (g. 3). Depressions on
the limestone plateau are lled with red, ferruginous soil (red
sand) and covered by forest that is similar to the littoral zone.
Degradation is the result of direct and indirect anthropogenic
pressure, such as collection of re and construction wood,
slash and burn agriculture, re and grazing. The different
vegetation types and their phenology have been described by
Ratovonamana et al. (2011).
Process of site selection
We started with an analysis of images available in Google
Earth to include the full range of degradation of vegetation
types, and to identify zebu trails crossing the Mahafaly pla-
teau. True migration routes were identied on the ground.
True trails were distinguished from false routes based on the
presence of dung. The map and area assessment occupied by
livestock have been analyzed with ArcGIS. Based on these
pilot studies, we selected an area of 7591 ha for more de-
tailed studies, located between 23°58’ – 24°02’S and 43°42’
– 43°47’E. Within this area, eleven sites were selected which
are subject to different forms of utilization by livestock (table
1, g. 4). The eleven sites included: dry forest on the littoral,
degraded dry forest on the littoral, herbaceous formations on
the littoral, dry forest on ferruginous soil, xerophytic bush on
limestone, degraded xerophytic bush on limestone, bare soil
and water, and herbaceous wetland formations.
Categories of grazing pressure
Since stocking rates were not known at the beginning of the
study, we assigned sites to grazing intensities ranging from 1
(lowest) to 4 (highest):
(1) Not used by livestock since 2006
(2) Used by zebu during the dry season
(3) Used by zebu at the end of wet season and during the
dry season
(4) Used by goats during the wet and the dry season and
by zebu at the beginning of the dry season.
Floristic and structural vegetation description
We measured maximum height (in m) and trunk diameter at
breast height (for trees, in cm) of woody plants within 15
× 15 m2 plots. Crown diameter (Cd) was measured by pro-
jecting the edges of the crown onto the ground and meas-
uring the diameter along two axis (maximum: Cdmax and
minimum: Cdmin crown diameter axis in meters) through
the crown center (Brack 1999). Crown radius (Cr) was calcu-
lated as Cr = (Cdmax + Cdmin) / 4. Crown volume (Cv) was
calculated by using the formula for the volume of a cylinder
with: Cv = (pi) × (Ch) × (Cr)2/4; Ch is the vertical extension
of the crown from the rst branch to the maximum height of
the tree.
The herbaceous cover was estimated per species in ve 1
m2 subplots within each 15 × 15 m2 plot following the system

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Ratovonamana et al., Impact of livestock grazing on vegetation characteristics in Madagascar
Figure 3 – Vegetation types and location of study sites in areas of different grazing regimes. Categories of grazing and site numbers are listed
in table 1. Grazing pressure categories: category 1: site 1; category 2: sites 1, 2, 8, 9, 10; category 3: sites 7, 11; category 4: sites 3, 4, 5, 6.
of Braun-Blanquet. The percent coverage per species and
plot was averaged for the each of the ve 1 m2 subplots.
Plant specimens collected in the eld were identied
in the herbaria of the Département de Biologie et Ecologie
Végétales, FOFIFA (http://www.fofa.mg/) and the Parc
Biologique et Zoologique de Tsimbazaza. Since scientic
names are being updated continuously, we used the names
listed by Tropicos (http://www.tropicos.org/NameSearch.
aspx). For the time being, the specimens are kept in the of-
ce of the Arboretum d’Antsokay in Toliara.
Plant species richness and plant diversity were used to
characterize the effect of grazing on the different plant com-
munities. Species diversity was evaluated using species
richness (S) and specic richness (SR) (Shannon & Weaver
1949). Specic richness takes into account the number of
species and the number of individuals. The similarity of plant
composition for each zone under different grazing pressure
was evaluated with the Spearman correlation coefcient.
The relative importance of species was calculated to deter-
mine important species, considered as indicators for differ-
ent forms of grazing pressure. The importance index of each
species was calculated by adding relative frequency, relative
density and relative dominance (Evariste et al. 2008).
Vertical vegetation structure was used as a proxy for
degradation. For this, the vegetation was subdivided in ve
height classes (< 25 cm, 25–49.9 cm, 50–99.9 cm, 100–149.9
cm and ≥ 150 cm) and the percentage of individuals with
different life forms (tree, shrub, and liana) was measured.
Detailed analyses of the vertical structure were limited to
heights below 1.5 m as this is the height that can be reached
by livestock in the area.
Plant biomass available as food for livestock
Since we rst had to identify the most important food plant
species for zebu and goats, we could not establish a rigorous
sampling design to measure the productivity of the differ-
ent food plant species year-round. Rather, as a rst step, we
identied the most important food plants for a given season
and then measured their standing biomass which was avail-
able as roughage at the time the species was identied as an
important food species. For woody species, we measured
the crown volume of various individuals per species. Sub-

86
Scripta Bot. Belg. 50
Site name and site
number
Number of
15 × 15 m2
plots
Categories
of grazing
pressure
Latitude S Longitude E Soil type and
topography
Distance to
water source
(m)
Andranovao (1) 4, 4 1, 2 24°1’ 25.55” 43°44’ 9.21” Sand, Littoral 2500
Ambahatry (2) 4 2 24°2’ 7.61” 43°44’35.35” Sand, Littoral 4000
Saia (7) 4 2, 3 24°0’ 19.05” 43°44’ 45.02” Limestone 2220
De Gaule (8) 3 2 24°1’ 20.43” 43°44’ 48.99” Limestone 3110
Andolomitsanga (9) 2 2 24°1’ 59.65” 43°44’ 55.25” Limestone 4220
Ambolely (10) 10 2 24°1’ 31.80” 43°45’ 30.48” Read sand 4000
Maintilimy (3) 7 4 24°0’ 41.79” 43°43’ 10.10” Sand, Littoral 1600
Kilibory (4) 4 4 23°58’ 14.02” 43°43’ 3.28” Sand, Littoral 3600
Fijona (5) 10 4 24°0’ 7.69” 43°43’ 50.45” Sand, Littoral 600
Andemodemoky (6) 5 4 23°59’ 7.44” 43°43’ 43.07” Sand, Littoral 1900
Ankazomaneno (11) 9 3 23°59’ 0.62” 43°46’ 47.78” Read sand 5900
Table 1 – Study sites; vegetation formations in the littoral and on red sand are formed by dry forest.
Low spiny bush is growing on limestone (Ratovonamana et al. 2011). Classication of grazing pressure: (1) not used by livestock since 2006,
(2) used by zebu during the dry season, (3) used by zebu at the end of wet season and during the dry season, (4) used by goats during the wet
and the dry season and by zebu at the onset of the dry season.
Figure 4 – Study sites in areas of different grazing intensities as described in table 1.

87
Ratovonamana et al., Impact of livestock grazing on vegetation characteristics in Madagascar
sequently, all edible parts (leaves and twigs to a diameter of
3 mm) were collected from the individual plant, dried and
weighted. For each species, the dry biomass of edible parts
was regressed against the crown volume with a linear re-
gression that describes the allometric relationship between
crown volume and food for livestock (Gregoire et al. 1995;
electronic appendix 3). For the estimation of herbaceous
biomass, all herbaceous plants were cut within the 1 m2
subplots, dried and weighted. Available food biomass was
summed for the different woody and herbaceous species and
extrapolated to kg/ha.
Livestock stocking rates and ranging patterns
Assessment of the stocking rates and the habitat utilization
by livestock is difcult as the number of livestock owned by
a person is an economic (and thus tax) issue. The number of
cattle and goats has been obtained from the ofcial admin-
istration of the Commune of Beheloke. Analyses of habitat
utilization patterns are hindered by the fact that livestock are
not supposed to use the national park, while goats and cattle
actually do use it. Therefore, the spatio-temporal patterns of
grazing are based primarily on information provided by our
long-term assistants from local villages based on their own
experience and interviews.
Grazing pressure and carrying capacity
The determination of the carrying capacity requires knowl-
edge about plant biomass production, consumption rate per
unit livestock per day and the stocking rate per unit time.
One livestock unit (head of cattle under tropical condi-
tions) is dened as an animal of 250 kg body mass (Unité
de Bétail Tropical: UBT). Its consumption is dened as 6.25
kg of dry plant biomass per day (Consommation Journalière;
Boudet 1975). One UBT is equivalent to one zebu or twelve
goats. The grazing pressure was determined by comparison
of the biomass production of the most important plant spe-
cies and the food requirement of livestock.
Statistical analysis
Measurements of plant and vegetation characteristics were
averaged per 15 × 15 m2 plot. The individual plots served
as unit for subsequent analyses. Data were tested for devia-
tion from normality. Data deviating from normality were
analyzed with non-parametric tests. All other variables were
analyzed with parametric tests followed by Tukey’s Hon-
est Signicant Difference test for multiple comparisons. All
tests were performed with the statistical package SPSS Base
for Windows 13.0. Differences were considered signicant
at p ≤ 0.05.
RESULTS
Plant species and vegetation types within the study area
In the 66 plots of 15 × 15 m2, we recorded 189 plant spe-
cies from 56 different plant families with 126 plant species
in the dry forest on sandy soil (littoral zone), 127 species on
ferruginous soil (red sand), and 78 species in the xerophytic
Littoral Limestone Red sand
Number of 15 ×15 m2
plots 38 9 19
Families 46 33 44
Species
Life forms
T 24 15 26
S 54 43 60
L 17 8 18
H 30 12 23
P 1 0 0
Total 126 78 127
Table 2 – Number of 15 × 15 m2 plots, plant families, species and
life forms in the major habitat types.
T: tree; S: shrub; L: liana; H: herb; P: parasite.
bush on limestone (table 2). The different numbers of species
and families in the different formations cannot be compared
directly due to the different number of plots per formation.
The most important families are Fabaceae (29 species), Mal-
vaceae (thirteen species), Apocynaceae and Euphorbiaceae
(twelve species), Poaceae (ten species), Acanthaceae (nine
species), Burseraceae (eight species) and Brassicaceae (six
species). The different plant species, their growth forms,
mean abundance per plot and their index of relative impor-
tance in the different zones are shown in the electronic ap-
pendix 1.
Livestock distribution
Goats and zebus occupied different proportions of the dif-
ferent vegetation types (table 3). Goats use only the littoral
throughout the year. The animals leave the village every
morning to graze in the littoral forest, especially those that
are located around water points. Zebus also use the littoral
forest, but only at the end of wet and the beginning of the dry
season. Large parts of the spiny bush on the limestone massif
Vegetation types Study
area Goats Zebus
Dry forest in the littoral 601 472 596
Degraded dry forest
in the littoral 1356 1288 1356
Herbaceous formations
in the littoral 905 656 749
Dry forest on ferruginous soil 359 0 359
Xerophytic bush on limestone 434 0 55
Degraded xerophytic bush
on limestone 3726 0 835
Bare soil and water 162 0 0
Herbaceous wetland
formations 48 0 0
Total 7591 2416 3950
Table 3 – Surface (ha) of different vegetation types in the study
area and the area used by goats and zebu during the wet and the
dry season.

88
Scripta Bot. Belg. 50
and dry forest on ferruginous soil (16% of the study area) are
not used by zebus regularly (table 3, gs 1 & 4).
At the end of the dry season / beginning of the rainy sea-
son (November–December) the zebus west of Tsimanam-
pesotsa NP are brought to the eastern part of the limestone
massif to the region of Itomboina where extensive grasslands
provide good pasture. At the end of the wet season (March),
zebus cross the limestone plateau from east to west on a tra-
ditional track of transhumance in the northern part of Tsima-
nampesotsa NP. Initially, they remain on the coastal plain,
but start moving into the national park as food abundance de-
clines on the coastal plain during the dry season (gs 1 & 4).
Effects of grazing on the oristic composition and plant
life forms
Plant species diversity changes with different grazing pres-
sure and topographic position (table 4). In the littoral and on
red sand, the mean number of plant species decreases signi-
cantly with increasing grazing pressure. On limestone, the
species richness between sites with different grazing pres-
sure did not differ signicantly. The representation of differ-
ent life forms did not differ under different grazing pressure
in any of the habitats. An analysis of community similarity
based on Spearman correlations between the occurrences of
different plant species indicates that plant species composi-
tion is related more to the vegetation formation than to deg-
radation (g. 5).
In the littoral, the plots with low pressure (GP 1) are
dominated by higher plant individuals (height > 50 cm) than
the plots with medium (GP 2) and high (GP > 3) grazing
pressure (g. 6). In the limestone area, no signicant differ-
ences were observed. On red sand, the communities are char-
acterized by plants with heights below 25 cm, with a domi-
nance of herbaceous species and rarity of woody plant in the
100–150 cm height class.
Indicator species
Electronic appendix 2 shows the most important plant species
(dened by high values of relative importance) in relation to
grazing pressure in the different vegetation types. The littoral
plots with high grazing intensities (GP 3 and 4) were domi-
nated by Aerva javanica (Amaranthaceae), Setaria pumila
(Poa ceae) and Solanum hippophaeoïdes (Solanaceae). These
three species were absent in the plots not used by livestock.
Some shrubs were more abundant in grazed than in ungrazed
plots. These are Acacia rovumae, Alantsilodendron alluau-
dianum, Chadsia grevei, Mimosa delicatula (Fabaceae) and
Rhigozum madagascariense (Bignoniaceae). On limestone,
the plots not used by zebu during the dry season, were domi-
nated by Panicum mahafalense (Poaceae) and Xerophyta
tulearensis (Velloziaceae). These two species constitute the
main food source for cattle at the onset and during the dry
season. On red sand Aerva javanica (Amaranthaceae), Ja-
tropha mahafaliensis (Euphorbiaceae), Uncarina stelluli fera
(Pedaliaceae), Alantsilodendron alluaudianum (Fabaceae)
and Cucurbita sp. (Cucurbitaceae) were more abundant in
Figure 5 – Similarity of the oristic composition of plots in different
categories of grazing pressure in the different zones.
Zone N Total number of species Herb Liana Shrub Tree
Littoral
GP 1 4 47 ± 14a6 ± 2 3 ± 2 22 ± 7a15 ± 4a
GP 2 8 23 ± 5b7 ± 3 3 ± 2 7 ± 4b5 ± 2b
GP 4 26 20 ± 6b8 ± 2 2 ± 1 8 ± 3b3 ± 2b
Chi-Square 11.78** 3.52 4.26 10.77** 16.51***
Limestone
GP 1 5 33 ± 5 4 ± 1 4 ± 1 20 ± 3 6 ± 1
GP 2 2 23 ± 1 3 ± 1 2 ± 0 14 ± 1 5 ± 1
GP 3 2 28 ± 11 5 ± 1 3 ± 1 18 ± 7 3 ± 1
Chi-Square 2.96 1.54 2.82 2.90 5.83
Red sand
GP 1 6 45 ± 7a3 ± 1 7 ± 2a21 ± 4a15 ± 2a
GP 2 4 35 ± 4b3 ± 0 6 ± 1a15 ± 2b12 ± 2a
GP 3 9 19 ± 3c4 ± 4 2 ± 2b7 ± 3c4 ± 4b
Chi-Square 15.16*** 1.65 11.72** 15.48*** 14.51***
Table 4 – Effects of grazing on plant species numbers and different life forms in plots subject to different grazing pressure (GP, as
dened in table 1).
N: number of 15 × 15 m2 plots. Values are means ± standard deviations. Asterisks indicate signicance levels according to Kruskal-Wallis
analysis of variance: * p ≤ 0.05; ** p ≤ 0.01; *** p ≤ 0.001. Different letters indicate differences according to post-hoc tests.

89
Ratovonamana et al., Impact of livestock grazing on vegetation characteristics in Madagascar
plots with high grazing pressure (GP 3) than in plots with
low grazing pressure (GP 1) (electronic appendix 2).
Plant biomass
Table 5 shows the average biomass (dry plant material:
DPM) of the most important food species in the study area.
During the wet season (January–April) livestock used mainly
the littoral. At this time of the year the most important food
plants were: Aerva javanica (19.5–258.3 kg DPM/ha), Boer-
havia diffusa (4.8–206.4 kg DPM/ha), Dactyloctenium capi-
tatum (4.8–6.3 kg DPM/ha), Indigofera diversifolia (13.8 kg
DPM/ha), Panicum pseudovoeltzkowii (37.8–75.6 kg DPM/
Figure 6 – Vegetation structure under different grazing pressure.
Grazing pressure as described in table 1.
Littoral Littoral
and limestone
Limestone
and red sand
Wet season Onset of the
dry season Dry season
Month of roughage biomass estimates Jan. Feb. Mar. Apr. May–Jun. Jul.–Dec.
Species Family
Panicum pseudovoeltzkowii Poaceae 75.6 37.8 34.1 - - -
Aerva javanica Amaranthaceae 258 50.4 19.5 - - -
Dactyloctenium capitatum Poaceae - 6.3 4.8 - - -
Boerhavia diffusa Nyctiginaceae - 12.6 4.8 206.0 - -
Tribulus cistoïdes Zygophyllaceae - 31.5 230.0 176.0 - -
Indetermined (‘Tirinkitroky’) Nyctiginaceae - - 12.9 189.0 - -
Indigofera diversifolia Fabaceae - - 13.8 - - -
Panicum subalbidum Poaceae - - - 17.6 - -
Panicum maximum Poaceae - - - 28.1 - -
Panicum mahafaliense Poaceae - - - - 232.4 -
Indigofera peltieri Fabaceae - - - - 1.5 -
Commiphora lamii Burseraceae - - - - 6.8 4.1
Commiphora marchandii Burseraceae - - - - 263.6 5.2
Plumbago aphylla Plumbaginaceae - - - - 3.4 0.9
Xerophyta tulearensis Velloziaceae - - - - 28.4 55.5
Mollugo decandra Aizoaceae - - - - - 6.1
Gyrocarpus americanus Hernandiaceae - - - - - 15.4
Total Biomass 333.9 138.6 319.9 617.5 536.1 87.2
Table 5 – Average biomass of roughage per month of the most important food plant species during different times of the year.
Values are kg of dry plant material per ha. Biomass was measured for the areas used by livestock in the different months. Setaria pimula had
not been recorded in the standardized plots due to its patchy distribution, but represents an important fodder plant.
ha), Panicum subalbidum (176 kg DPM/ha), Panicum maxi-
mum (28.1 kg DPM/ha), Tribulus cistoïdes (50–365.2 kg
DPM/ha), ‘Tirinkitroky’ (20–300 kg DPM/ha). The highest
roughage biomass was recorded in April, at the end of the
wet season (607 kg DPM/ha). The minimum was measured
in February with 138.6 kg DPM/ha. The species Tribulus cis-
toïdes, Panicum pseudovoeltzkowii, and Aerva javanica were
the most important food species at this time of the year. The
average biomass available from these plant species per ha
and their monthly changes are listed in table 5.
At the beginning of the dry season zebu started moving
into the limestone area. During this time, roughage availabil-
ity was still high due to the shift from herbs to the annual
growth of trees and regenerating plants. Indigofera peltieri
(1.5 kg DPM/ha), Commiphora lamii (4.1–6.8 kg DPM/ha),
C. marchandii (263 kg DPM/ha), and Plumbago aphylla
(3.38 kg DPM/ha) were the most important species for the
littoral zone. Apart from these widely distributed species
there were some highly productive patches of Setaria pimula
(260 kg DPM/ha). Xerophyta tuleariensis (28.4 kg DPM/ha)
and Panicum mahafaliense (232 kg DPM/ha) were most im-
portant in the limestone area.
During the dry season most woody plants lose their
leaves and herbs disappear. In this season cattle were fre-
quently found in the Tsimanampesotsa NP. Their staple food
consisted almost exclusively of Xerophyta tuleariensis (55.5
kg DPM/ha), Mollugo decandra (6.1 kg DPM/ha), and Gyro-
carpus americanus (15.4 kg DPM/ha) (table 5).

90
Scripta Bot. Belg. 50
Plant biomass available and total food requirements of
livestock
The study area is stocked by the villages of Maromitilike,
Efoetse, Marojery and Ankilibory. According to ofcial
sources, their number of livestock was equivalent to 5009
UBT (4434 zebus + (6897 goats / 12) = 4434 + 574.75 UBT;
total of 5008.75 UBT). Table 6 summarizes a rough estimate
of the carrying capacity of the area where people of the vil-
lages listed above herd their livestock. The estimates are
based on the following assumptions:
1. Goats were limited to the littoral zone and range over
2416 ha (table 3).
2. Zebu used 2701 ha of the littoral zone at the end of the
wet season and included another 1249 ha on the limestone
and red sand after the onset of the dry season (table 3).
3. The number of animals was assumed to be constant
throughout the year, thus not taking into account
reproduction. This underestimates food requirements.
4. Since zebu moved into the limestone area at the end of the
dry season due to reduced food availability in the littoral
zone, we assumed that food availability in the littoral
zone is as low, or even lower than food availability in the
limestone area. For the estimate of the carrying capacities
we assumed that the same quantity of roughage would be
available in both areas during the dry season (87.2 kg/
ha). This overestimates food availability in the littoral
zone.
5. Food requirements per unit of livestock are set as 6.25 kg
roughage per day. This amounts to 187.5 kg of roughage
per month per unit of livestock.
During the wet season, livestock which does not partici-
pate in the seasonal migration uses mainly the littoral zone.
Here, the total biomass increased until the end of the wet sea-
son and decreased gradually during the dry season (table 6).
According to the comparison between plant biomass avail-
able and total food requirements of livestock, food availabil-
ity exceeded the needs of livestock during the six months be-
tween the wet and the onset of dry season. In contrast, food
requirements of the animals were higher than food availabil-
ity during the six dry months. At this time, livestock relied
heavily on the fodder produced within Tsimanampesotsa NP.
DISCUSSION
Grazing is a widespread form of land use in arid and semi-
arid region (Riginos & Hoffman 2003). It can modify the o-
ristic composition, spatial structure and representation of life
forms in plant communities either through direct impact or
to altered species interactions (Tielbörguer & Kadmon 2000,
Pykälä 2004, Cipriotti & Aguiar 2005, Jacobo et al. 2006,
Sankey 2007, Škornik et al. 2010). Our study showed that
species richness and diversity were affected differently by
different grazing intensities and in different vegetation for-
mations. In the littoral and on red sand, the plant diversity
decreased with grazing pressure. Plots that were not used
contained more woody plant species than area used by live-
stock at the end of wet season and during the dry season. The
change in woody plant species structure favors the growth
forms of herbaceous, desirable as well as unpalatable spe-
cies. This change was most pronounced in the littoral zone,
i.e. the area that is used by goats year-round and by zebu dur-
ing the dry season. In contrast, livestock grazing had no sta-
tistically signicant effect on species composition, diversity
or structure on limestone. It seems unlikely that grazing does
not have any effect on the plant communities on limestone.
But we simply could not measure any effect, either because
grazing intensity is actually very low or regeneration is so
slow that effects of unhindered regeneration are not measur-
able, not even after four years without grazing (our category
GP 1).
The effect of grazing on plant community structure and
plant diversity can be explained by the availability of herbs
and grass in the pasture area (Škornik et al. 2010). In our
study, the total fodder biomass increased until the end of
the wet season. It decreased gradually during the dry sea-
son. The comparison between plant biomass available and
total food requirements of livestock showed that the plant
biomass available exceeded the food requirements of the
animals which remain in the area until the onset of the dry
Wet season End of wet
season
Onset of dry
season Dry season
Livestock units: goats 574.75 574.75 574.75 574.75
Livestock units: zebu - 4434 4434 4434
Livestock units per ha of littoral: goats 0.238 0.238 0.238 0.238
Livestock units per ha of littoral: zebu - 1.642 - -
Livestock units per ha of littoral and limestone: zebu - - 1.122 1.122
Food requirements per unit livestock (goats)
per month occupying one ha 44.6 kg 44.6 kg 44.6 kg 44.6 kg
Food requirements per unit livestock (zebu)
per month occupying one ha - 307.9 kg 210.4 kg 210.4 kg
Total food requirements of livestock / ha 44.6 kg 352.5 kg 255 kg 255 kg
Available biomass of roughage
(kg of dry plant material / ha) 264 kg 617.5 kg 536.1 kg ≤ 87.2 kg
Table 6 – Available biomass of roughage and estimates of food requirements of goats and zebu in different zones used at different
times of the year.
Wet season: January-March; end of the wet season: April; onset of the dry season: May-June; dry season: July-December.

91
Ratovonamana et al., Impact of livestock grazing on vegetation characteristics in Madagascar
season. But during the dry season the food requirement of
the livestock exceeded the plant biomass available. By then,
cattle switch from grazing on herbs and grasses to brows-
ing on woody plants that still have leaves. The utilization of
woody forage depends on the animals that remain in the pas-
ture area. Goats eat a signicant proportion of leaves from
woody plants year-round, while zebu browse mainly during
the dry season when the herbaceous forage is not available
(Grouzis & Sicot 1980, Maiga 1995). Thus, the decline of
liana, shrub and tree species with increasing grazing pressure
indicate the dependence of livestock on woody species at the
end of the wet season and during the dry season when the
herbaceous plant species are not available. It should be kept
in mind that data on livestock and ranging pattern are prob-
ably underestimated because the numbers obtained from the
regional administration are unlikely to be complete. People
at the villages are afraid that the neighbouring villages will
know the number of their livestock. Furthermore, people use
the national park as pasture. Since people recognize this as
illegal, they are unwilling to reveal details about these activi-
ties and are hesitant to allow outside monitoring of their ac-
tivities. In addition, livestock reproduction and thus seasonal
changes in livestock numbers are not taken into account.
The increase of some species at high grazing intensities
could be used as indication for grazing pressure. The increas-
ing dominance of these plant species in grazed areas can be
explained by two processes. First, some of the species are
spread by livestock. These are Aerva javanica (Amaran-
thaceae), Setaria pimula (Poaceae), Solanum hippophae-
noïdes (Solanaceae), Alantsilodendron alluaudianum (Fa-
baceae), Erythrophysa aesculina (Sapindaceae), Poupartia
minor (Anacardiaceae), Uncarina stellulifera (Pedaliaceae)
and Cucurbita sp. (Cucurbitaceae). Second, others species
have a high regeneration capacity and are more resistant to
cattle trampling. These are Cedrelopsis grevei, Cedrelopsis
gracilis (Ptaeroxylaceae), Rhigozum madagascariense, Ste-
reospermum nematocarpon (Bignoniaceae), Chadsia grevei,
Acacia rovumae, Mimosa delicatula (Fabaceae) and Boscia
longifolia (Boraginaceae).
Apart from changes in species composition, we observed
a relatively large difference in the representation of growth
forms of plants across the different categories of grazing
pressure. In grazed plots the percentage of plants in the low-
est stratum increased in the littoral zone. This this is opposite
to the situation in many parts of Africa where grazing results
in bush encroachment (Skarpe 1990, Moleele & Perkins
1998). In southwestern Madagascar herbaceous vegetation
seems to increase with increasing grazing pressure. Yet, this
is not due to an actual increase of herbaceous vegetation, but
due to the reduction of trees and shrubs that are fed upon dur-
ing the dry season when herbaceous plants are absent. Thus,
the observed pattern is the outcome of the effect of grazing
during the dry season when animals feed on woody vegeta-
tion because herbs are absent.
In summary, vegetation characteristics (species rich-
ness, species composition, plant life forms and vegetation
structure) change with grazing pressure. The impact is most
pronounced in the littoral and the red sand where vegetation
cover is higher than on limestone. In the latter, grazing pres-
sure seemed too low to have a measurable effect on plant
diversity and structure. Contrary to expectation, grazing did
not result in bush encroachment as in many African coun-
tries, but favours herbs at the expense of woody vegetation,
because herb biomass exceeds livestock food requirement
during the wet season. During the dry season, herbs are no
longer present according to their annual cycle. At this time
of the year, livestock feeds extensively on woody vegetation
that does not match the food requirements of the livestock
at the present stocking rate and thus results in a decline of
woody vegetation.
SUPPLEMENTARY MATERIAL
Supplementary data are available in pdf at the Supplemen-
tary Data Site of publications from the National Botanic
Garden of Belgium (http://www.nbgpublisher.be > SBB50 >
folder 612) and consist of (1) mean abundance of different
plant species and their mean relative importance in the 15 ×
15 m2 plots of the different major habitat types in the study
area; (2) relative importance of species under different graz-
ing pressure; and (3) allometric calculation of edible plant
biomass for various woody species.
ACKNOWLEDGEMENTS
The study was carried out under the collaboration between
Madagascar National Parks (ex-ANGAP), the Departments
of Animal Biology and Conservation, Department of Plant
Biology and Ecology (Antananarivo University, Madagas-
car) and Department of Animal Ecology and Conservation
(Hamburg University, Germany). We thank Mark Fenn, Joce-
lyn Rakotomalala and Domoina Rakotomalala (MNP Toli-
ara, WWF Madagascar) Juliana Rasoma V. Rahantavololona,
Jacques Solofomalala Rakotondranary and Peggy Giertz for
their support. Special thanks go to our para-ecologists Mr.
Louis Fisy and Mr. Mahita for their help in the eld and for
their communication skills with the local communities. The
study was nanced by WWF Sweden / WWF Madagascar
with additional support from DFG/BMZ (Ga 342/15), VW
Foundation, DAAD, WWF Germany and SuLaMa/BMBF.
We highly appreciate the help and comments of Natacha
Beau and two reviewers. The participation of R.Y. Ratovona-
mana at the AEFTAT congress was supported by the Ham-
burger Universitätsvermögen.
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Communicating Editor: Laurent Gautier.

Electronic appendix 1 to:
Rakotomalala Yedidya Ratovonamana, Charlotte Rajeriarison, Edmond Roger, Iris Kiefer &
Jörg U. Ganzhorn (2013)
Impact of livestock grazing on forest structure, plant species composition and biomass in
southwestern Madagascar
Scripta Botanica Belgica 50
Appendix 1 – Mean abundance of different plant species (AB) and their mean relative
importance (IR) in the 15 × 15 m² plots of the different major habitat types in the study
area.
N = number of plots.
Littoral
(N=38)
Limestone
(N=9)
Red sand
(N=19)
Family
Scientific name
AB
IR(%)
AB
IR(%)
AB
IR(%)
Acanthaceae
Barleria humbertii
-
-
26
4.34
-
-
Acanthaceae
Blepharis calcitrapa
8
1.75
10
5.42
18
5.86
Acanthaceae
Blepharis sp
-
-
-
-
14
3.95
Acanthaceae
Hypoestes phyllostachya
3
3.40
-
-
3
0.86
Acanthaceae
Justicia spicata
120
13.37
-
-
19
21.66
Acanthaceae
Ruellia albopurpurea var. sulfureoviolacea
-
-
19
5.41
1
0.31
Aizoaceae
Mollugo decandra
13
3.05
23
4.71
22
1.94
Amaranthaceae
Aerva javanica
138
21.84
-
-
385
39.23
Amaranthaceae
Aerva madagassica
22
4.23
-
-
-
-
Amaranthaceae
Aerva sp
-
-
9
3.75
10
1.98
Amaranthaceae
Henonia scoparia
2
5.65
-
-
-
-
Anacardiaceae
Operculicarya hyphaenoïdes
-
-
3
3.92
3
0.46
Anacardiaceae
Poupartia minor
2
0.87
2
0.76
3
5.78
Apocynaceae
Stapelianthus insignis
1
0.93
-
-
-
-
Bignoniaceae
Rhigozum madagascariense
7
8.21
3
2.51
5
4.88
Bignoniaceae
Stereospermum nematocarpon
4
3.51
-
-
4
2.86
Brassicaceae
Boscia longifolia
6
3.59
-
-
1
4.31
Brassicaceae
Cadaba virgata
7
1.36
-
-
-
-
Buddlejaceae
Androya decaryi
6
3.34
-
-
-
-
Burseraceae
Commiphora humbertii
4
0.44
10
4.83
4
0.92
Burseraceae
Commiphora mahafaliensis
-
-
5
4.19
6
3.24
Burseraceae
Commiphora marchandii
16
3.00
1
0.50
5
3.32
Burseraceae
Commiphora orbicularis
-
-
2
5.56
3
5.30
Cactaceae
Opuntia monocantha
8
4.59
-
-
-
-
Combretaceae
Terminalia disjuncta
1
0.49
12
3.63
6
2.80
Combretaceae
Terminalia ulexoïdes
21
3.01
2
0.42
3
2.43
Cucurbitaceae
Cucurbitum sp
-
-
-
-
6
4.22
Didieraceae
Didierea madagascariensis
7
3.06
-
-
9
3.06
Dioscoreaceae
Dioscorea fandra
1
0.35
10
4.18
-
-
Ebenaceae
Diospyros manampetsae
3
0.56
11
4.57
9
3.39
Euphorbiaceae
Acalypha decaryana
-
-
3
2.48
2
2.85
Euphorbiaceae
Croton cotoneaster
-
-
16
3.29
-
-
Euphorbiaceae
Croton geayi
4
0.83
-
-
26
3.33
Euphorbiaceae
Croton salviformis
11
5.35
7
2.76
4
1.47
Euphorbiaceae
Euphorbia stenoclada
-
-
5
2.99
3
0.84
Euphorbiaceae
Euphorbia tirucalli
21
4.31
-
-
1
3.56

Littoral
(N=38)
Limestone
(N=9)
Red sand
(N=19)
Family
Scientific name
AB
IR(%)
AB
IR(%)
AB
IR(%)
Euphorbiaceae
Givotia madagascariensis
-
-
-
-
2
3.12
Euphorbiaceae
Jatropha mahafalensis
-
-
-
-
7
8.83
Euphorbiaceae
Securinega seyrigyi
-
-
12
2.38
4
3.22
Euphorbiceae
Croton sp8
-
-
-
-
9
7.13
Fabaceae
Acacia bellula
9
7.97
-
-
-
-
Fabaceae
Acacia rovumae
18
8.51
-
-
11
1.46
Fabaceae
Alantsilodendron alluaudianum
16
9.25
12
5.14
2
5.97
Fabaceae
Albizia mahalao
13
3.28
-
-
4
2.00
Fabaceae
Albizia tulearensis
13
2.77
1
4.96
8
5.92
Fabaceae
Chadsia grevei
58
26.37
-
-
13
2.29
Fabaceae
Crotalaria androyensis
21
9.95
-
-
-
-
Fabaceae
Crotalaria humbertiana
2
0.99
7
3.41
2
0.96
Fabaceae
Indigofera sp
64
14.58
-
-
5
3.25
Fabaceae
Mimosa delicatula
5
11.62
2
0.94
-
-
Fabaceae
Mundulea micrantha
13
3.00
3
1.84
2
10.49
Fabaceae
Mundulea sp2
11
2.39
-
-
1
11.13
Fabaceae
Senna meridionalis
-
-
8
3.04
-
-
Fabaceae
Tephrosia alba
1
0.23
9
3.75
-
-
Hernandiaceae
Gyrocarpus americanus
13
2.28
-
-
64
11.94
Lamiaceae
Karomia microphylla
4
1.69
5
5.75
5
1.22
Lythraceae
Capuronianthus mahafaliense
3
1.70
2
1.82
8
3.71
Malvaceae
Grewia grevei
20
6.69
-
-
1
0.73
Malvaceae
Grewia humblotii
10
3.48
-
-
1
0.36
Malvaceae
Indetermined (Kotaky)
-
-
8
3.28
-
-
Malvaceae
Megistostegium microphyllum
-
-
1
2.92
-
-
Malvaceae
Sida acuta
2
0.74
-
-
1
0.50
Meliaceae
Neobeguea mahafaliensis
-
-
-
-
6
3.23
Olacaceae
Ximenia perrieri
21
3.91
-
-
-
-
Pedaliaceae
Uncarina stellulifera
3
3.72
1
1.73
3
6.12
Plumbaginaceae
Plumbago aphylla
7
3.53
-
-
-
-
Poaceae
Panicum mahafalense
4
0.14
18
8.32
-
-
Poaceae
Setaria pumila
83
18.49
-
-
13
3.03
Polygalaceae
Polygala greveana
1
0.48
3
1.30
7
3.04
Ptaeroxylaceae
Cedrelopsis gracilis
-
-
65
11.11
-
-
Ptaeroxylaceae
Cedrelopsis grevei
74
2.66
-
-
10
4.77
Salvadoraceae
Azima tetracantha
4
6.06
-
-
3
20.63
Salvadoraceae
Salvadora angustifolia
7
4.52
1
0.46
-
-
Sapindaceae
Erythrophysa aesculina
-
-
2
0.76
3
6.75
Solanaceae
Lycium acutifolium
4
4.05
-
-
-
-
Solanaceae
Solanum hippophaenoïdes
4
14.59
-
-
2
16.34
Velloziaceae
Xerophyta tulearensis
-
-
126
12.07
304
11.92
Zygophyllaceae
Zygophyllum depauperatum
8
3.46
-
-
-
-

Electronic appendix 2 to:
Rakotomalala Yedidya Ratovonamana, Charlotte Rajeriarison, Edmond Roger, Iris Kiefer & Jörg U. Ganzhorn (2013)
Impact of livestock grazing on forest structure, plant species composition and biomass in southwestern Madagascar
Scripta Botanica Belgica 50
Appendix 2 – Relative importance of species under different grazing pressure: A, littoral; B, limestone; C, red sand.
A
B
C

Electronic appendix 3 to:
Rakotomalala Yedidya Ratovonamana, Charlotte Rajeriarison, Edmond Roger, Iris Kiefer & Jörg U. Ganzhorn (2013)
Impact of livestock grazing on forest structure, plant species composition and biomass in southwestern Madagascar
Scripta Botanica Belgica 50
Appendix 3 – Allometric calculation of edible plant biomass for various woody species. VPA: Crown volume in cm3; Wet biomass
in g.