1. Euphorbia Encroachment
An investigation of the vegetation dynamics on
Aride Island since 1976, with special
consideration to the prevalence of Pisonia
grandis
Introduction
Aride is a small 72ha granitic Island situatedinthe
northern groupof the Seychelles, 4° southof the
Equator. It is consideredto be the most diverse and
harbours the greatest abundance of native plants of all
the granitic group(Fursinger andPutallaz, 2008). Due
greatlyto the management techniques of the Island’s
wardens large areas of the hills are still absent of
introduced species, thus maintainingthe Bwa Mapu
forests (Pisonia grandis) that are both prevalent and
unique to this granitic archipelago.
Nevertheless, its colonial past saw considerable
alterations to vegetation composition, which mayhave
causedlasting effects for the repopulation ofcertain
slower colonisingspecies. The plateauwas cleared to
cater for coconut (Cocos nucifera) plantations, whilst
extensive coppicing occurred onthe Island’s hill
vegetationto artificiallyincrease the number of Sooty
Terns, (Sterna fuscata) nesting, withtheir eggs being
soldas a cultural delicacyon the neighbouringisland of
Praslin (Fursinger and Putallaz, 2008). Aride was
declareda nature reserve in1973, following its
ownershipbythe Cadburyfamily, initiallyto protect
breedingcoloniesof over a millionseabirds. However
given its unique ecosystem, extensive habitat
management andmonitoring hasbeen undertakenin an
attempt to returnAride’s vegetationbackto the native
coastalforest, which existedprevious to human
intervention.
In the first 20years of becoming a nature reserve the
amount of mature woodlandmore thandoubled in size,
with climatic speciesindicative of native woodland:
Euphorbia, Ficus reflexa, Ficus nauticum and specifically
Pisonia, recolonising the hillside environment. Yet this
increase inwoodlanddiversity, naturally[1] resultedin a
decrease of the more diverseglade habitat. As the
canopyspreadit reduced the abundance of light, to the
advantage of shade tolerant groundflora;namely
Nephrolepis which have spreadand become a dominant
under-canopylayer ofthe hillside habitat.
Of all the trees on Aride, Pisonia grandis has become the
most dominant, accounting for over 80% of the lead
trees[2], withclusters ofmonospecific stands scattered
across the hillside environment (Fursinger and Putallaz,
2008). It is a prevalent pioneer species and
consequentiallyhas traits whichenable it to dominate
the earlystages ofwoodland successionon a small
island: fast andefficient vegetative propagation,
tolerance to salt spray, shallowsoil and slope, and like
Ficus are typicallyfaster growing andtaller than
Rothmannia and Euphorbia. Despite these advantages,
as is the case withmost pioneer species, Pisonia has a
short life cycle of roughly30years. It canthus be
assumed that competing species witha distinct
longevitywill outcompete in time.
Figure 1: flow diagram manipulated from Ayrton (1994) illustrating
general vegetative succession on hill-slope glades.
[1] Natural succession dictates that with a transition to mature woodland
biodiversity declines as shade becomes a greater limiting factor in the growth of the
now understorey species.
[2] A lead tree is defined as that which contributes most to the woodland canopy
Asystasia Encroachment
Pisonia Encroachment
Euphorbia canopy develops at a
slower rate allowing light to
penetrate the understorey and
species diversity persists
Cyperacae/Graminae
DominatedGlade
Ficus sp. slowly encroach whilst
Pisonia canopy increases in
height and density. shade
tolerant species namely
Nephrolepis become dominant
ground flora, invading in swades.
Fallen Pisonia may propogate
reulting in low Pisonia scrub in
areas.
Asystasia Dominated Glade
Canopy cover increases and
ground flora diminish as light
becomes limited. Cyperacae and
Graminae sp. most notiably
decline whilst Asystasia is lost
under the denser canopies
Species diversity slowly declines
as canopy develops. In rocky
slopes Euphorbia often stay
dominant, whilst Pisonia will
invade where conditions are
more favourable and potentially
encroach further. Nephrolepis
may spread, although ground
cover will remain low as
conditions often not optimal

2. Project Description
The aim of the present investigationis to observe and
where possible quantify anychanges that have occurred
in herbaceous and structural diversity, tree
demographics andas a bi-product examine the
continued prevalence of Pisonia grandis. This will be
accomplishedbyre-visitingthe permanent vegetation
plots set up in 1976 byWarmanet, al. (1976), which
have not been statisticallyanalysed since the turnof the
century. Despite there being a detailedmethodologyof
how to sample the plots in the initial 1976 report that
will be usedas a core manual, a collectionof other
sampling techniqueswill be usedto tailor the data
collected, especiallyinrelationto tree demographics.
These additional methods are simplymade upof
subsequent collectionefforts on Aride that have seemed
successful, along with previous experience inquantifying
speciesdiversities withindices.
According to past reports (list) it wouldbe expectedthat
herbaceous diversityon the islands has continuedto
decrease as the vegetationprogressivelyshrinks glade
habitats inits successionto woodland. It wouldfurther
be expectedthat whilst the understory canopywillhave
a low structural diversitygiventhe dominance andoften
monospecific nature of shade tolerant species, the mid
and upper-storeycanopiesshouldin theoryprove more
complex. The woodland shouldhave naturallyincreased
in height whilst younger trees andsapling will have
colonised available gaps to create heterogenic stands in
relationto age;although likelynot species.
General objectives:
 To relocateprevious permanentquadrats and add several
new ones toincreasedata stock and representation.
 Carry out appropriatesampling as permethodology.
 Provide statistically sound comparisons withprevious
data wherepossible.
Provide some currentconclusionsabout Aride’svegetation to
contribute tofuture monitoring and management
programmes.
In-Field Methodology
The method for investigating the permanent quadrats
(Warman, et al 1976) canbe foundsummarised onthe
back of the laminatedmap ofthe original permanent
vegetationplots;made in2011.
In relationto this investigation some minor alterations
were made andwill be briefly summarised(see field
data sheet Appendix 1 for clarification):
1) The previous permanent plots, or the area which
best fits their location(inaccordance withthe map
generatedin2011) were relocatedanda 10mx10m
plot was either re-establishedor established
(depending onwhat remains of the previous plot).
2) The GPS was usedto note Altitude andthe
SoutherlyandEasterlycoordinates, whichwhen
accompaniedbythe gridreference from the map
should facilitate the re-locationprocess.
3) A quick sketch anddescription of the site was then
carriedout to highlight the significant site
characteristics i.e. large boulders, rare speciesor
the general vegetation layout.
4) All the trees withinthe plot were recordedina
specieslist and eachallocated 3 abundance classes:
for saplings, for adults andanaggregate (fieldsheet
shows abundance scale). Thisscale was usedas a
means to imbalance the weighting towards less
abundant species. Inaddition the 4 leadtreeswere
noted andmapped.
5) The canopyat three levels (<0.5m,0.5-2.5m,>2.5m)
was thenassessedproviding anestimated
percentage cover at eachlevel. The 3 species which
contribute greatest to these canopies were
recordedalong witha contributionpercentage.
6) Thirteen 1mx1m quadrats were placedin a “X”
pattern across the larger plot, with sub-plot A top-
left, D centre, G bottom-right, H top-right andM
bottom-left. A percentage cover of abiotic and any
identifiedspecies was estimated[1] and anaverage
calculated.
[1] The total cover of a subplot including both abiotic elements and species can be
over 100% (as species cover may overlap due to height variations) or under 100%
(due to obstacles i.e. tree trunks).

3. Data Methodology
In analysingthe data severalcalculations were applied
to achieve measures of diversityandtree prominence,
with observations made of the canopycovers to indicate
structural complexity. Basic statistics includingmeans,
standarddeviation and normalitytests were run to
gather a general viewof the collated dated, whilst
regression analysis wasusedto indicate significant
relationships, their strength and direction. ANOVA could
not be used to signifysignificant differencesacross the
time as the data was either unavailable to deferred in
nature. As suchcomparisons were made from previous
observations andstatistical conclusions rather than
parallel analyses.
1) Data was input intoExcel® usingseparate
spreadsheets for percentage cover, canopyand
tree prominence (see Appendices B, CandD).
2) A Simpson’s diversityindex was thancalculated for
the island (onlytakinginto account herbaceous
species) using the equation:
 
 1NN
1nn
D



 ii
Where ni = the total number of organisms ofeach
individualspecies.
N = the total number of organisms of all species
The value of D rangesfrom 0 to 1. With 0 representing
infinite diversityand1 no diversity. That is, the bigger
the value the lower the diversity. Purelyfor aesthetic
purposes the value wasinverted(‘1-D’)sothat a larger
value indicatedgreater species diversity.
3) Using the abundance scores relative frequencyand
abundance was calculatedfor tree saplings, adults
and anaggregate of the two so that PVs[1] couldbe
determinedusing the equation:
𝑃𝑉𝑖𝑗 =
𝑓𝑖𝑗
∑ 𝑖𝑓𝑖𝑗
× 100% +
∑ 𝑘𝑎𝑖𝑗𝑘
∑ 𝑖 ∑ 𝑘𝑎𝑖𝑗𝑘
× 100
Where aijk denotesthe abundance class value of
speciesi in sampling unit k of plot j
Sapling andadult PVs for different species were
plotted ona scatter graphto forecast potential
demographic changes.
4) The canopydata wasthen coloured to signify
different species (>0.5m:red-P.grandis, blue-
E.pyrifolia, yellow- Ficus. Sp, green- R. annae). This
helped to highlight species differencesobservedin
the canopydata.
5) Regressionanalysis was performedcanopies of vary
height, along withother variables that shared a
likelyrelationship(either from observations made
in the fieldor from the data (or commonsense))
and proved to have a normal distribution.
[1] A Prominence Value (PV) is the sum of the relative frequency and relative
abundance of a species. It reaches a maximum value of 200.

4. Results
Average Percentage Cover
Abiotic X3 New 5 G6 F6 New 1 N6 F4 New 2 X6 K5 New 4 F5 E6 New 3 M4 N4 M5 X7
Exposed Rock 39.85 20.46 41.92 13.00 23.38 37.38 11.69 60.92 23.85 26.62 9.46 12.61 38.00 14.46 9.46 46.31 4.15 25.54
Bare Soil 14.92 15.77 32.00 37.15 41.69 13.31 8.85 27.85 17.92 26.15 7.85 51.92 32.08 6.23 11.69 13.46 5.30 27.31
Dead Wood 11.77 7.00 10.85 6.77 7.92 17.23 16.31 5.31 8.77 4.00 23.31 15.08 8.23 35.00 13.77 9.85 1.77 2.77
Leaf Litter 33.46 21.08 8.38 28.77 18.54 30.00 24.69 3.23 20.62 21.46 26.23 16.15 19.23 14.46 30.77 25.77 8.31 5.31
Herbaceous
Nephrolepis biserrata 6.77 46.15 9.61 5.46 28.92 5.31 29.54 17.92
Panicumbrevifolium 2.46 0.15 1.23 1.31 4.85 7.23 4.69 4.54
PanicumMaximum 0.77 6.92
Asystasia gangetica 1.38 26.69 1.00 56.85 18.85 43.31 1.15
Dygitaria horizontalis 5.08
Sida cordifolia 5.54 1.23 4.54
Setaria barbata 7.62 1.46 2.31 1.38 0.69
Kyllinga polyphylla 0.31
Ipomoea pes-capra 1.85
Canavalia cathiratica 1.15
Ananas comosus 3.00 7.38
Mariscus ligularis 3.31 20.00
Achyranthes aspera 0.08
Pandanus balfourii 3.92
Trees
Pisonia grandis 35.3 78.1 78 77.3 68.4 69.4 61.4 58.9 10.2 3.8 22.6 43.2 19.7 3.2 1.2 20.9 4.65 8.9
Euphorbia pyrifolia 28.1 4.7 0 0 6.1 2.3 8 33.3 36.7 9.1 0 1.8 0 7.7 8.90 0.00 0.00 1.20
Ficus reflexa 8.64 10.2 0 8.28 1.52 1.6 19.6 2.9 4.1 0 0 46.4 62.3 19.2 42.80 0.00 0.00 5.00
Ficus nautarum 0 0 0 6.4 0 2.9 0 0 0 18.2 55.4 0 0 69.1 0.00 6.10 0.00 0.00
Table3.1: Abioticandherbaceous averagepercentagecovers calculated as a mean ofthe13 sub-plots withineachofthe18 permanent plots. Treepercentagecover is also givenfor the4 dominant hillside
species.

5. Species Total Aggregate Score Relative Aggregate Frequency Relative Aggregate Abundance Aggregate PV
Pisoniagrandis 66 100.00 36.87 136.87
Euphorbiapyrifolia 49 66.67 27.37 94.04
Ficusreflexa 35 77.78 19.55 97.33
Ficusnautarum 10 33.33 5.59 38.92
Rothmaniaannae 17 22.22 9.50 31.72
Phyllanthuscasticum 1 5.56 0.56 6.11
Cocusnucifera 1 5.56 0.56 6.11
Species Total Sapling Score Relative Sapling Frequency Relative Sapling Abundance Sapling PV
Pisoniagrandis 51 88.89 46.36 135.25
Euphorbiapyrifolia 32 61.11 29.09 90.20
Ficusreflexa 19 55.56 34.20 89.76
Ficusnautarum 2 11.11 18.00 29.11
Rothmaniaannae 6 16.67 36.00 52.67
Phyllanthuscasticum 0 0.00 0.00 0.00
Cocusnucifera 0 0.00 0.00 0.00
Species Total Adult Score Relative Adult Frequency Relative Adult Abundance Adult PV
Pisoniagrandis 53 100.00 39.85 139.85
Euphorbiapyrifolia 35 66.67 26.32 92.98
Ficusreflexa 24 72.22 18.05 90.27
Ficusnautarum 8 33.33 6.02 39.35
Rothmaniaannae 11 22.22 8.27 30.49
Phyllanthuscasticum 1 5.56 0.75 6.31
Cocusnucifera 1 5.56 0.75 6.31
Tables 3.2a, b, c: Calculated PVs for saplings, adults and an aggregateofthetwo for therecorded species of the18 sampled plots. Notethat both Cocus nucifera and Phyllanthus casticumwereonly encountered
once, both as adults.

6. Graph 3.1: Sapling and Adultprominencevalues plottedon a scatter graph witha standardised lineto indicatesampling-adult equilibrium. Notethebottom left data values areboth Cocus nucifera and
Phyllanthus casticum whichwereonly encountered onceand thus havea no corresponding saplingdata. It is evident that Ficus nautarum and Pisoniagrandis adults aremoreprominent than saplings whilefor
Rothmania annaesapling aremoreprominent. BothEuphorbia andFicus reflexa liecloser to thestandardised lineindicating that thesespecies nearer a demographic equilibrium.
Pisonia grandis
Euphorbia pyrifolia
Ficus reflexa
Ficus nautarum
Rothmaniaannae
0
20
40
60
80
100
120
140
160
0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00
AdultPV
SaplingPV

7. Canopy Layers
Plots <0.5m 0.5m - 2.5m >2.5m
X6 70 51 13
E6 2 9 82
F4 96 60 89
F5 6 2 92
F6 0 28 92
G6 0 13 78
K5 69 10 91
M4 70 10 69
M5 92 43 31
N4 62 6 87
N6 0 61 78
New 1 8 16 76
New 2 8 7 95
New 3 47 16 96
New 4 69 46 78
New 5 69 22 93
X3 81 32 72
X7 89 39 15
Table3.3: Estimated canopy values ofthethreelayers for each ofthe18 plots. Thecolours highlight thedominantspecies within that plot with: red-P.grandis, blue-E.pyrifolia, yellow-Ficus. Sp, green-R. annae.

8. Graphs 3.2a (top left), b (top right), c (bottomleft): scatter plots to demonstraterelationship between
thecanopy cover at thethreemeasuredlayers. Bothanalyses which including a canopy layer of>2.5m
could not besubjected to regressionanalysis dueto thelack ofnormality in thedata distribution,the
graphs arepresented as 3.2a andb. Nevertheless canopy layers 0.5m and 0.5m –2.5mprovedto have
a significant weak positiverelationship (Fs 29.3, DoF 1.6 and P<1%)withthelinear regressioncurve
provided in thegraph3.2b. Theresiduals weretested in a standardresidual plot anda normal quantile
plot as a means ofregression model diagnostic.
0
20
40
60
80
100
120
0 20 40 60 80 100 120
CanopyLayer<0.5m
Canopy Layer >2.5m
0
10
20
30
40
50
60
70
0 20 40 60 80 100 120
CanopyLayer0.5m-2.5m
Canopy Layer >2.5m
0
20
40
60
80
100
120
0 10 20 30 40 50 60 70
CanopyLayer<0.5m
Canopy Layer 0.5m - 2.5m

9. Discussion of Results
Diversity
The Simpson’s diversityindex calculatedsolelyfrom the
understoreyherbaceous species was0.285, whichwhen
invertedcomesto 0.715. This wouldindicate that
Aride’s hillslope habitat (as basedon the 18 surveyed
plots) is moderatelyhigh. In additionthe glade
environments offer the greatest diversitydue to the
higher frequencyof species present, while steeper
rockier regions where the soil is shallow;yieldedthe
lowest diversitylevels. Incomparisonwithprevious
reports regardingAride’s diversity, it would appear that
it has remains relativelyconstant inthe past 10 – 15
years. Thisis surprising consideringthe forecasted
shrinkingand loss ofglade environments predicted in
previous studies. Correspondinglythe presence of
Asystasia gangetica, anindicator of glade habitats,
matches the trends discussedinthe 1996, witha
continueddecrease inspecies frequency. A likely
explanationfor the stagnated diversitylevel couldbe
derivedfromthe alternate measure of species cover,
adoptinga percentage cover method rather thana
simple present-or-absence recording. The more likely
explanation, and one which makes comparingdata sets
over the years relativelyredundant, is the additionof
the four newplots andthe lossof some of the past sites
to increase the distributionandthus environmental
representation.
Structural diversity
Despite the failures of statisticallyproving anysignificant
relationships between most of the canopylayers (given
the lackof normalityof the data distribution for the
higher canopylayer), trends can be observed when
specific speciesand their abundances are considered.
FirstlyFicus spare able to dominate a plot’s woodland
canopywith few species. This was seeninthe fieldto be
greater withFicus naudicum, where a single specimen
could account for 50% of the overallcover. Conversely
Euphorbia provedto have a muchmore diminished
influence onthe general woodlandcanopy. It’s less
expansive coverage coupledwith its comparatively
stunted height, means it onlydominates the canopyif
nothing else is able to outcompete. This is true for plot
X6 where the rockyterrainplays to Euphorbia’s abilityto
grow in the shallowest of soils, withstatistical evidence
given inthe significant positive relationship(Fs 39.3, DoF
1.1 and P<1%) betweenexposedrock and percentage
cover of Euphorbia. There is further evidence to suggest
that while the dominance of Ficus sp. oftenrelated to a
lack of cover inthe lower two canopylayers (with
circular patches of bare earth often directlybelowFicus
trunks) the presence of Euphorbiainhighabundances
was oftencoupledwitha greater speciesrichness and
abundance at the understoreylayer. Nevertheless, it
cannot be statisticallyproven that this is due to the
presence of Euphorbia, but it wouldbe a
commonsensical notionto suggest that the small canopy
woulddiminishlight as a limiting factor, allowing shade
intolerant species (of which there are more present on
the island)to establishor prevailagainst shade tolerant
species(namelyNephrolepis).
Pisonia grandis effects onwoodland structure is the
most dramatic of allthe tree species, due to both its
indisputable prominence andits propagative traits.
Previous studiesof the permanent plots have focused
on the tree height of the four lead treeswith little
consideration of the middle canopy(0.5m – 2.5m), yet
this middle sectioninwhich Pisonia is soactive,
determines future tree dominance andalsoacts as a
crucial habitat niche for the manynesting birds. Its
abilityto grow from fallen adults allows it to
immediatelyoutcompete other trees for the newly
available space, but it also provides a platform, which is
raised above the understorey, whichagaineliminates
competitionfrom herbaceous plants. It is throughthis
abilitythat dense and structurallycomplex middle-
canopiesarise, whichare observablybeneficial for tree
nesting species (and are thus incremental to the high
populations of Aride’s lesser noddies and fairyterns).

10. In terms ofthe herbaceous understoreylayer (<0.5m),
Rothmaniaannae appears to have a recorded
relationship(see both table 3.1 and3.3) withglade
environments or more preciselyAsystasia;anindicator
speciesfor glade environments. Of the 7 sites that
Asystasia gangetica was present, Rothmaniadominated
the upper canopyin 4 sites:K5, N4, M5, X7 and was
present inall but plot NEW 3. In relationto canopy
structure Rothmania createsa wide apparentlydense
canopyof leaves, makingthe relationshipwith an
understoreyshade intolerant species unlikely.
Nevertheless, the relationship could, andthis is simply
hypothesising, be due to the shape, size and structure of
the leaves allowinglight to penetrate, especiallywhen
there is a breeze.
Tree Dynamics
The results for the tree dynamics reflect those of
Fursinger and Putallaz (2008) (see graph3.1), with
Pisonia having a muchgreater prominence value for
both adults and saplings thananyof the other species
recorded. The successof this species is not onlydue to
its efficient andfast propagation, but its abilityto
inhabit andremain competitive inenvironmentally
difficult conditions:salt spray, steepslopes, shallowsoils
and at times strong winds. The noticeablyhighPVs of
Rothmaniaannae saplings in comparison to adults
indicates that its population inthe recordedplots is able
to sustain itself, andlikelyincrease inthe future due to
its general longevity. The opposite canbe said for Ficus
nautarumwhichhasa greater PV for adults rather than
saplings. Its abilityto grow to a greater height then
surroundingspecies, create a dense canopyto inhibit
competition, extendan expansive stabilising root
system, anddistinct longevity does however indicate it
has the abilityto wait for future saplings to establish.
Both Euphorbia andFicus reflexa share similar PVs for
saplings andadults despite possessing different plant
traits inorder to establishin an area. As mentioned
previous Euphorbia hasthe abilityto colonise regions of
extensive bare rock without requiringa great depth of
soil inorder to root. Ficus reflexa however, like Ficus
nautarumis able to spreadits roots over the surface of
rocks in searchof pockets ofdeeper soil. Although
apposing methods of colonisationboth appear to be as
successful as the other withthe populations of the two
speciesable to sustainthemselves.
Report summary
Taking the 18 measuredplots to be a true
representation of Aride’s hillslope environment several
concluding remarks canbe made fromthis investigation:
 Despite a considerable change indiversity index,
the frequencyof Asystasiagangetica has continued
to decrease, andthus indicatesa shrinking of the
more diverse glade environments.
 Consequentiallyfurther measures should be made
to maintainandwhere possible establish newglade
areas, especiallywhere Pisonia is encroaching.
 Rothmaniaannae, despite being able to dominate a
canopy, has anobservedandproven relationship
with glade environments.
 Pisonia grandis remains the most prominent
speciesof tree onAride, occuring as either an adult
or saplinginall the surveyedplots withits high
populationcapable of sustainedgrowth. Pisonia’s
propagative abilityis alsoresponsible for the
creationof dense middlecanopies, whichoffer a
habitat niche for nestingbirds.
 Ficus nautarumhas an agingpopulation, but its
plant traits will likelyinhibit anymajor decreases in
populationinthe long-term.
It can be noted that tree diversityis a requirement
within the hillside environment given eachspeciesoffers
differingattributes that affect a habitat:Ficus sp provide
intricate root systems offeringcover for the ground
nesting white-tailedtropic birds and bothburrowing
shearwater species, Pisonia grandisfor the dense
middle-section canopyfor tree nesting species, with
glade regions benefitingfrom Euphorbia’s and
Rothmania’s specific canopycovers.

11. References
Aride Island, Annual Report (1979). ICS Internal Document
(unpublished).
Betts. Aride Island Annual Report (1997). ICS Internal Document
(unpublished).
Carty and Carty. Aride Island Annual Report (2005). ICS Internal
Document (unpublished).
G. E Castle and R.Mileto. (1994). Flora of Aride Island. Seychelles. Eco
Tech.
F. Freidmann. (1986). Flowers and Trees of Seychelles. Editions
Delroisse.
Fursinger, D and Putallaz, O. (2008). Vegetation Monitoring Aride Island
(Seychelles). Geobatanical Institute,Zurich.
S. A. Robertson. (1984).Flowering Plants of Seychelles.Royal Botanic
Gardens.
B. Sampson and Sampson E. Aride Island Annual Report (1997). ICS
Internal Document (unpublished)