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Invasion of the Portuguese dune ecosystems by the exotic species Acacia longifolia (Andrews) Willd.: Effects at the community level


Abstract and Figures

Pristine ecosystems are becoming rare along the Portuguese coastline because the sand dunes have been invaded by several exotic plant species, particularly Acacia species from Australia. At the beginning of the 20 th century, a few Acacia species, e.g. Acacia longifolia (Andrews)Willd., were deliberately introduced into Portugal for dune stabilization. The invasion process is strongly correlated with the occurrence of fires, so there are long periods of stability interspersed with rapid increases in abundance of the exotic Acacia species. In this study, three sites, S.Jacinto, Palheirão and Quiaios, were monitored along the Portuguese coast to determine the impact of the invasions by A.longifolia. At each site, 12 permanent plots were established, six with and six without A. longifolia. The plots were monitored from winter 1998 to autumn 1999, and species numbers and plant cover were recorded. Shannon diversity indices and dominance-diversity curves confirmed that A. longifolia is changing the community composition and structure of the dune ecosystems promoting monospecific communities, decreasing species richness and increasing plant total cover.
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Invasion of the Portuguese dune ecosystems by the
exotic species Acacia longifolia (Andrews) Willd.:
effects at the community level.
Hélia Marchante1*; Elizabete Marchante2 and Helena Freitas2
1. Escola Superior Agrária de Coimbra, Bencanta, 3040-316 Coimbra, Portugal 2.
Departamento de Botânica, Faculdade de Ciências e Tecnologia, Universidade
de Coimbra, 3000 Coimbra, Portugal; e-mail: *
Pristine ecosystems are becoming rare along the Portuguese coastline because the sand dunes have
been invaded by several exotic plant species, particularly Acacia species from Australia. At the
beginning of the 20th century, a few Acacia species, e.g. Acacia longifolia (Andrews)Willd., were
deliberately introduced into Portugal for dune stabilization. The invasion process is strongly correlated
with the occurrence of fires, so there are long periods of stability interspersed with rapid increases in
abundance of the exotic Acacia species.
In this study, three sites, S.Jacinto, Palheirão and Quiaios, were monitored along the Portuguese
coast to determine the impact of the invasions by A.longifolia. At each site, 12 permanent plots were
established, six with and six without A. longifolia. The plots were monitored from winter 1998 to
autumn 1999, and species numbers and plant cover were recorded. Shannon diversity indices and
dominance-diversity curves confirmed that A. longifolia is changing the community composition and
structure of the dune ecosystems promoting monospecific communities, decreasing species richness
and increasing plant total cover.
Ecosystem structure and functioning is seriously affected by invasive species, which
pose one of the most substantial threats to the Earth’s biodiversity (Cronk and Fuller
1995, Chapin et al. 2000). Biological invasions lead to “ecological homo-
genisation” of the world and contribute considerably to global change (D’Antonio
and Vitousek 1992, Lodge 1993, Arroyo et al. 2000, Mooney and Hobbs 2000).1
Coastal ecosystems are important barriers against the advance of the ocean. Sand
dunes in particular are vulnerable to disturbance through natural and human
pressure (Hanson and Lindh 1993, Carter 1995). The stability of dune ecosystems
relies on their natural high diversity of native plant species, which bind the sand and
minimize the effects of erosion (van der Putten and Peters 1995). Along the
Portuguese coast, pristine dune systems are becoming increasingly rare, with native
plant species being replaced by several invasive exotic species, mainly Acacia
Miller species from Australia (Alves et al. 1998).
Plant Invasions: Ecological Threats and Management Solutions, pp. 75-85
Edited by L.E.Child, J.H. Brock, G.Brundu, K. Prach, P.Pysek, P.M. Wade, M. Williamson
© Backhuys Publishers, Leiden, The Netherlands
76 Hélia Marchante et al.
The genus Acacia includes about 1200 species, the majority native to Australia and
Southern Africa (Whibley 1980). It belongs to the subfamily Mimosoidea, which
comprises several of the worst invasive plant species in the world (Cronk and Fuller
1995). The genus Acacia is absent from the Portuguese native flora (Franco 1971,
Castroviejo et al. 1999).
The invasive success of Acacia species is attributable mainly to high growth
rates of the plants, prolific seed production, with high longevity in the soil and high
dispersal efficiency (Cronk and Fuller 1995), stimulation of seed germination by
fire (Ross 1975, Taylor et al. 1985, Crawley 1997), and the absence of natural
enemies in areas where the plants have been introduced (Callaway and Aschehoug
2000). The ability to fix nitrogen (Leguminosae) has enabled the acacias to invade
nutrient-poor environments.
Since the beginning of the 20th century, 13 Acacia species have been introduced
to Portugal (Castroviejo et al. 1999). Of these A.melanoxylon R.Br. in W.T.Aiton,
A.longifolia (Andrews) Willd. and A.saligna (Labill) H.L.Wendl. were utilized for
dune stabilization in coastal ecosystems (Rei 1924, Neto 1993). At present,
A.dealbata Link, A.melanoxylon and A.longifolia are the most prolific invaders in
Portugal, especially in conservation areas where the climate is comparable with the
native range of the plants. Invasions by Acacia species are strongly correlated with
fire events when the accumulated Acacia seeds in the soil are stimulated to
germinate and the rapidly-growing young acacia plants smother seedlings of native
The aim of this work was to assess the ecological impact of the invasions of
Acacia species in some Portuguese dune ecosystems.
Study sites
Three study sites were selected and monitored along the Portuguese coast, all
located in the central-northern regions-S.Jacinto Natural Reserve (SJ), Beach of
Palheirão (BP) and Beach of Quiaios (BQ) (Figure 1). At present, SJ is classified as
a Natural Reserve, and BP and BQ are Natura 2000 sites. All three sites have high
conservation potential (Neto 1993, Martins 1999). Despite its classification, the BQ
site is extremely disturbed by tourist pressure.
The experimental study was performed landward of the first dune, where the
characteristic dune vegetation consists of a low cover, open structure and just a few
nano/microphanerophytes with a role similar to A.longifolia, (Corema album
(L.)D.Don, common in all studied places, Cistus salvifolius L., present in just 3
plots BQ and 2 plots BP and Pinus pinaster Aiton, present in only 2 plots in both
BP and BQ), whose frequency increases with the distance from the sea. At the time
of the study, the three sites had patches of vegetation that was uninvaded and
patches that had been invaded to a greater or lesser extent by A.longifolia . All three
sites had patches that supported a dense over-story of A.longifolia (Marchante
2001), but patches with 100% A.longifolia cover were not included in the surveys.
Invasion of the Portuguese dune ecosystem by the exotic species Acacia longifolia 77
Fig. 1. Position of the study sites on the Portuguese central-northern coast: S.Jacinto Natural
Reserve (SJ), Beach of Palheirão (BP) and Beach of Quiaios (BQ).
Nevertheless, monospecific A.longifolia stands are very frequent, becoming more
and more common as far as the distances to the sea increases. Cartographic
information confirms the increase of monospecific Acacia patches over time.
Although geographically isolated, all three study sites had similar fire histories
(the most recent fires happened seven years before the surveys in SJ and nine years
before the surveys in BQ and BP) and species composition and vegetation struc-
tures were relatively similar. The introduction of Acacia species in the early parts of
the 20th century used different methodologies but always aimed at dune stabiliza-
78 Hélia Marchante et al.
tion. In fact, A.longifolia promotes dune fixation but spreads after fire events and it
does not respond to sand mobility as, for example, the marram grass (Ammophila
arenaria (L.) Link subsp. arundinacea H.Lindb.fil.). In SJ, only A.longifolia was
introduced while in BP and BQ others species (namely A.melanoxylon) were
planted along with A.longifolia (Rei 1924). However, nowadays A.longifolia is the
dominant species and the only one present in the experimental plots. Despite its
introduction about 100 years ago, it was only after the fire in the beginning of 1990
that A.longifolia started to show invasive behaviour in the studied places, with
remarkable increases in the biomass in a short period of time.
Experimental design and data analysis
In December 1998, twelve permanent plots of 25m2 were demarcated in an area of
approximately 3000m2, six with A.longifolia and six without A.longifolia . Quadrat
selection was made in a semi-randomised stratified pattern (Goldsmith 1996), to
include areas with and without A.longifolia. The plots were monitored seasonally
from winter 1998 to autumn 1999. For each quadrat sampled, species number and
percentage canopy cover of each species were recorded. For each community,
Shannon diversity indices and Pielou evenness indices (Magurran 1988) were
calculated and dominance-diversity curves (Whittaker 1972, Kent and Coker 1992)
were computed. Parameters were used to compare invaded and uninvaded quadrats.
The data were analysed using a 2-way ANOVA to test if the species richness and
cover remained constant after invasion, with season considered as the second factor
(Zar 1996). Significant effects (P<0.05) were then tested using the Newman-Keuls
multiple comparison test. All six replicates were gathered in a composite plot, and a
t test proposed by Hutcheson in 1970 (see Magurran 1988, Zar 1996) was used to
compare the Shannon diversity indices in invaded and uninvaded quadrats.
A.longifolia was always treated as just one more species.
Species richness
In general, species richness was higher in uninvaded plots (Figure 2), and in two
sites was significantly dependent on the presence of A.longifolia, SJ (F(1,40)= 12.998;
P = 0.0009) and BP (F(1,40)= 15.36; P= 0.0003). However, significant differences
were only detected in spring (Figure 2).
A.longifolia presence accounted for highly significant increases in total plant cover
at all three sites during all seasons (SJ F(1,40)=147.86; P<0.0001; BP F(1,40)=200.51;
P<0.0001 and BQ F(1,40)=206.83; P<0.0001) (Figure 3).
Invasion of the Portuguese dune ecosystem by the exotic species Acacia longifolia 79
1 2 3 4
SJ 1 2 3 4
BP 1 2 3 4
species richness
g. 2. Species richness (mean+SE; n=6) of invaded and uninvaded plots, at all sites SJ=
S.Jacinto, BP = Palheirão, BQ = Quiaios, along four seasons 1 = winter, 2 = spring, 3 =
summer, 4 = autumn. Columns with different letters are significantly different from each
other at P<0,05 (Newmans-keuls Test).
1 2 3 4
SJ 1 2 3 4
BP 1 2 3 4
species cover (%)
Fig. 3. Species total cover (mean+SE; n=6) of invaded and uninvaded plots, at all sites SJ =
S.Jacinto, BP = Palheirão, BQ = Quiaios, along four seasons 1 = winter, 2 = spring, 3 =
summer, 4 = autumn. Columns with different letters are significantly different from each
other at P<0,05 (Newmans-keuls Test).
Shannon Diversity Index and Pielou Evenness Index
Diversity measures for invaded and uninvaded plots produced different Shannon
indices and evenness at all three sites, for all seasons (Table 1). In each situation,
uninvaded plots had significantly higher diversity than A.longifolia invaded plots
(Hutcheson, P < 0,001 for all situations but two seasons in BQ and one in SJ).
In all invaded plots evenness showed lower values (0,471, Autumn SJ, to 0,602,
Summer BQ) when compared with uninvaded plots (0,639, Summer SJ, to 0,834,
Autumn BQ), as a result of higher dominance of A.longifolia.
80 Hélia Marchante et al.
Table 1. Diversity (H’) and evenness (E) indexes in A.longifolia invaded and uninvaded plots at all
sites and all seasons. Data are calculated for composite plots. Hutcheson t test was used to test for
Shannon index differences among invaded and uninvaded plots in each site (* = P < 0,005; ** = P <
Winter Spring Summer Autumn
Shannon index H’ Invaded plots 1.365 1.321 1.283 1.207
2.149 2.210 1.882 1.936
Hutcheson t value 4.198** 4.759** 3.328* 4.041**
Pielou i ndex E Invaded plots 0.517 0.488 0.486 0.471
0.717 0.695 0.639 0.658
Shannon index H’ Invaded plots 1.550 1.670 1.553 1.589
2.117 2.337 2.134 2.258
Hutcheson t value 3.356** 3.985** 3.556** 4.115**
Pielou index E Invaded plots 0.547 0.567 0.548 0.540
0.782 0.780 0.788 0.814
Shannon index H’ Invaded plots 1.782 1.900 1.834 1.840
2.208 2.501 2.323 2.455
Hutcheson t value 2.473* 3.663** 3.199* 4.092**
Pielou index E Invaded plots 0.569 0.590 0.602 0.587
0.737 0.759 0.789 0.834
Dominance-diversity curves
Only spring curves are shown because that was the season when the plant
communities had most annual and biennial species. All the species computed in
dominance-diversity curves can be accessed in Appendix 1.
The dominance-diversity curves clearly showed that:
1) In SJ (Figure 4), BP (Figure 5) and BQ (Figure 6) invaded quadrats were
dominated by a single species, A.longifolia (about 60% cover in BP and SJ
and 45% in BQ). In these invaded communities, species with lower cover
never reach more than 10% (in SJ) 15% (in BP and BQ).
2) In SJ, in uninvaded quadrats, one species is partially dominant (Ammophila
arenaria subsp. arundinacea, with about 35% cover) and Helichrysum
italicum (Roth) G.Don fil. subsp. picardi (Boiss.&Reuter) Franco and
Crucianella maritima L. species have similar covering areas, 15-25%. In
BP and BQ in uninvaded quadrats 3-4 species co-dominate (Ammophila
arenaria subsp. arundinacea, Corema album, Helichrysum italicum and
Crucianella maritima), each one responsible for 10 -15% cover area.
3) All three sites showed higher evenness in uninvaded communities.
4) Especially in BP and BQ, a higher number of species with extremely low
cover was observed in invaded plots.
5) Species richness is higher in uninvaded plots, particularly in SJ.
Invasion of the Portuguese dune ecosystem by the exotic species Acacia longifolia 81
11357911 13 15 17 19 21 23 25
species sequence
abundance (log)
com Acacia
sem Acacia
Fig. 4. Dominance-diversity curves showing the diversity of uninvaded and Acacia invaded
communities in SJ, in spring. Abundances (logarithmic scale), on the ordinate, are plotted against
species number in the sequence from most to least abundant, on the abscissa.
1357911 13 15 17 19 21 23
species sequence
abundance (log)
com Acacia
sem Acacia
Fig. 5. Dominance-diversity curves showing the diversity of uninvaded and Acacia invaded
communities in BP, in spring. Abundances (logarithmic scale), on the ordinate, are plotted against
species number in the sequence from most to least abundant, on the abscissa.
1357911 13 15 17 19 21 23 25 27 29
species sequence
abundance (log)
com Acacia
sem Acacia
Fig. 6. Dominance-diversity curves showing the diversity of uninvaded and Acacia invaded
communities in BQ, in spring. Abundances (logarithmic scale), on the ordinate, are plotted against
species number in the sequence from most to least abundant, on the abscissa.
82 Hélia Marchante et al.
Monitoring the three communities invaded by A.longifolia was necessary to assess
the species impact at several levels. In SJ, BP and BQ, A.longifolia has apparently
caused a decline of other species in all seasons (Figure 2), but differences are not
always significant. In BP and BQ, a significant difference among invaded and
uninvaded plots was observed in spring, due to the sprouting of annual and biennial
species only in uninvaded plots. A.longifolia is thus preventing the germination of
therophytes and hemicryptophytes in spring. Plant species present in the three sites
are quite different (Appendix 1) which can be partially responsible for the between-
site observed differences.
In BP and BQ, the dominance-diversity curves describing communities invaded
by A.longifolia revealed high diversity then SJ but some species with extremely low
abundances; the presence of one single specimen was quantified in species richness
but its very low representativity can be an evidence of being threatened. The
presence of A.longifolia is thus depressing the abundance of some species, as has
been shown for other invasive Acacia species in the South African fynbos
(Richardson et al. 1992, Holmes and Cowling 1997a).
Increasing A.longifolia cover (Figure 3) can promote shade, thus affecting
native species. A.longifolia has a high growth rate when compared with native
species, and this fact together with its abundant seed bank and strong regeneration
response after fire (Taylor et al.1985, Jeffery et al. 1988), may explain its increase
in cover. In fact, by increasing its cover Acacia takes advantage of light, controls
shade to other species and get space otherwise available to other species. This is
particularly important when the invasive species establish hes dense
populations (Weber 2000), as was observed in many areas of the systems studied.
Dune species have small leaf area and low growth habits. This normally allows
relatively high light levels at soil level. Species naturally adapted to these conditions
do not easily tolerate low light (Smith and Huston 1989), and A.longifolia, by
causing shade, threatens their survival. Plant species in dunes develop strategies that
focus on survival rather than domination (Carter 1995). With the presence of
A.longifolia, these systems are being replaced and the dominance of one single
species is prevailing.
A.longifolia decreased plant diversity in all sites studied. Reducing biodiversity
is one of the main effects of invasive species (Binggeli 1996, Williamson 1999,
Chapin et al. 2000), as was already found with other species of Acacia invading the
South African fynbos (Holmes and Cowling 1997a, b).
The presence of A.longifolia is accompanied by a substantial accumulation of
dormant seeds in the soil. With the high frequency of fires in Portugal, these seeds
will be stimulated to germinate, resulting in the expansion of A.longifolia
populations and the further loss of native species.
Invasion of the Portuguese dune ecosystem by the exotic species Acacia longifolia 83
A.longifolia is invading the studied Portuguese dune ecosystems, decreasing
biological diversity and promoting monospecific communities. As a microphanero-
phyte, a different life form compared to the majority of the native species present in
the studied communities, A. longifolia is causing structural changes in these com-
munities. Plant communities in dunes, naturally characterized by an open structure
and low cover, are gradually being transformed into Acacia woodlands, with arbo-
real structure, higher cover and low species number. The presence of this invasive is
decreasing species richness.
The results of this work emphasize the need to prioritise areas for management
and control measures in the invaded Portuguese dune systems, as well as the
identification of specific effects that should be mitigated in future programs for the
rehabilitation of invaded systems.
We are grateful to John Hoffman and Ilídio Moreira for valuable comments on the
manuscript, and to Filipe Campelo for valuable help in fieldwork.
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Invasion of the Portuguese dune ecosystem by the exotic species Acacia longifolia 85
Appendix 1.
The species present in each studied system which were represented in dominance
diversity curves are sequenced from the dominant to the rarest (left to right end of
the curves). Nomenclature follows Franco (1971-1984), Franco and Afonso (1994-
1998) and Coutinho (1939).
Figure 4: SJ invaded plots - Acacia longifolia, Helichrysum italicum subsp. picardi, Carpobrotus
edulis (L.) N.E.Br. in Phillips, Ammophila arenaria subsp. arundinacea, Corema album, Crucianella
maritima, Iberis procumbens Lange subsp. procumbens, Antirrhinum majus L. subsp. cirrhigerum
(Ficalho) Franco, Calystegia soldanella (L.)R.Br., Conyza canadensis (L.)Cronq., Otanthus maritimus
(L.) Hoffmanns.& link., Euphorbia paralias L., Poaceae (seedlings), Leontodon taraxacoides
(Vill.)Mérat subsp. taraxacoides, Pancratium maritimum L.; SJ uninvaded plots: Ammophila
arenaria subsp. arundinacea, Helichrysum italicum subsp. picardi, Crucianella maritima, Corema
album, Carpobrotus edulis, Silene littorea Brot., Iberis procumbens subsp. procumbens, Sedum
sediforme (Jacq.)Pau, Otanthus maritimus, Leontodon taraxacoides subsp. taraxacoides, Calystegia
soldanella, Pancratium maritimum, Euphorbia paralias, Corynephorus canescens (L.)Beauv.,
Herniaria ciliolata Melderis subsp. ciliolata, Conyza canadensis, Senecio gallicus Vill., Acacia
longifolia, Linaria caesia (Pers.)Chav. subsp. decumbens (Lange)Laínz, Polycarpon tetraphyllum (L.)
L., Poaceae (seedlings), Eryngium maritimum L., Antirrhinum majus subsp. cirrhigerum, Medicago
marina L.
Figure 5: BP invaded plots - Acacia longifolia, Carpobrotus edulis, Corema album, Crucianella
maritima, Ammophila arenaria subsp. arundinacea, Helichrysum italicum subsp. picardi, Pinus
pinaster, Sedum sediforme, Cistus salvifolius, Antirrhinum majus subsp. cirrhigenum, Corynephorus
canescens, Medicago marina, Pancratium maritimum, Calystegia soldanella, Tuberaria guttata (L.)
Raf. Fourr, Polycarpon tetraphyllum, Reichardia gaditana (Willk.)Coutinho, Vulpia membranacea
(L.)Dumont, Cyperus capittatus Vandelli; BP uninvaded plots: Crucianella maritima, Ammophila
arenaria subsp. arundinacea, Helichrysum italicum subsp. picardi, Corema album, Corynephorus
canescens, Carpobrotus edulis, Sedum sediforme, Antirrhinum majus subsp. cirrhigenum, Policarpon
tetraphyllum, Tuberaria guttata, Calystegia soldanella, Cyperus capittatus, Vulpia membranacea,
Herniaria ciliolata subsp. ciliolata, Erodium cicutarium (L.)L'Hér., Medicago marina, Pancratium
maritimum, Reichardia gaditana, Leontodon taraxacoides subsp. taraxacoides, Lagurus ovatus L.
Figure 6: BQ invaded plots - Acacia longifolia, Corema album, Pinus pinaster, Carpobrotus edulis,
Artemisia campestris subsp. maritima, Cistus salvifolius, Sedum sediforme, Helichrysum italicum
subsp. picardi, Rubia peregrina L., Seseli tortuosum L., Tuberaria guttata, Antirrhinum majus subsp.
cirrhigenum, Crucianella maritima, Medicago marina, Pancratium maritimum, Sedum album L.,
Ammophila arenaria subsp. arundinacea, Compositae (seedlings), Calystegia soldanella,
Corynephorus canescens, Poaceae (seedlings), Briza maxima L., Silene littorea, Verbascum litigiosum
Samp., Euphorbia portlandica L.; BQ uninvaded plots: Corema album, Carpobrotus edulis, Sedum
sediforme, Crucianella maritima, Seseli tortuosum, Corynephorus canescens, Helichrysum italicum
subsp. picardi, Artemisia campestris subsp. maritima, Sedum album, Ammophila arenaria subsp.
arundinacea, Medicago marina, Pancratium maritimum, Cistus salvifolius, Tuberaria guttata, Silene
littorea, Cyperus capittatus, Lagurus ovatus, Cerastium glomeratum Thuill., Compositae (seedlings),
Antirrhinum majus subsp. cirrhigenum, Calystegia soldanella, Verbascum litigiosum, Euphorbia
portlandica, Rumex bucephalophorus subsp. hispanicus (Steinh.)Rech. Fil, Medicago littoralis Loisel,
Senecio gallicus Vill., Plantago coronopus L.
... Coastal ecosystems are highly vulnerable to global environmental change and listed among the most intensely converted ecosystems on the planet as a result of occupation and transformation by humans for centuries (Marchante et al. 2003;Martínez et al. 2007;Carboni et al. 2010). These ecosystems provide numerous benefits to human societies, such as protection against storms and strong winds, stabilization of the shoreline and erosion control, as well as climate regulation at local and global scales (Barbier 2017;Drius et al. 2019). ...
... Invasion by non-native trees is a recurring problem especially in coastal scrub on sand dunes that do not naturally develop forest cover (Marchante et al. 2003;Steers et al. 2013). For example, species in the genera Pinus and Acacia are among the most widely distributed invasive plants, and adversely impact dune systems as they represent a previously non-existent life form in these plant communities (Marchante et al. 2003;Simberloff et al. 2010;Richardson and Rejmánek 2011). ...
... Invasion by non-native trees is a recurring problem especially in coastal scrub on sand dunes that do not naturally develop forest cover (Marchante et al. 2003;Steers et al. 2013). For example, species in the genera Pinus and Acacia are among the most widely distributed invasive plants, and adversely impact dune systems as they represent a previously non-existent life form in these plant communities (Marchante et al. 2003;Simberloff et al. 2010;Richardson and Rejmánek 2011). Such invasions often transform open ecosystems into ecosystems with a continuous tree canopy, reducing native plant cover as well as local richness and diversity (Richardson et al. 1994;Simberloff et al. 2010;Steers et al. 2013). ...
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Biological invasions are part of the global environmental changes that characterize the Anthropocene. Invasive trees can reduce native species cover and richness in plant communities. The mechanisms that cause such changes may be related to the presence (direct factors) or functional traits of introduced species (indirect factors), in addition to changes in abiotic factors. In this study, joint species distribution models were built based on a Bayesian framework to assess direct and indirect effects of the presence of the invasive tree Terminalia catappa on different structural levels of plant communities, including species diversity and composition, along with functional traits and co-occurrence patterns of native species. Plants were sampled in areas underneath the crown of T. catappa trees (n = 30), paired with areas without the invasive tree (n = 30). Height and crown area of each T. catappa tree as well as litter thickness and percentage of bare soil were measured/estimated in all plots. The presence of T. catappa changed the composition of plant communities, facilitated the development of shade-tolerant species, and led to the loss of positive and negative associations between native species. The coastal ecosystem assessed in our study tends to be converted from a herb-shrub heliophyte assembly to vegetation dominated by trees and vines that develop better in shady or diffused light habitats. We highlight the relevance of collecting data on structural and functional characteristics of the plant community to allow for a detailed understanding of the direct and indirect effects of plant invasions on coastal ecosystems.
... Since the nineteenth century, afforestation has been carried out to increase the touristic appeal (Dadon 2002), and some of the most commonly used species for these purposes include Acacia, Pinus, Populus and Tamarix (Zalba and Villamil 2002). Their dispersion represents one of the main threats to coastal dunes conservation, since they are species capable of decreasing biological diversity and promoting monospecific communities (Marchante et al. 2003;Pauchard et al. 2016). In this context, the capacity of these relicts of grassland to sustain biodiversity and ecosystem services will depend on the quantity and quality of habitat in remnants, their degree of connectivity, and how they are affected by other human-induced perturbations (Haddad et al. 2015). ...
... Acacia longifolia (Andrews) Willd. is a tree native to southeastern Australia (Dimitri 1999). Acacias are used to stabilize coastal dunes in different countries, subsequently spreading and invading considerable areas (Marchante et al. 2003;Alberio and Comparatore 2014). Acacia longifolia has been recorded as a highly aggressive invasive species in coastal areas of South Africa and Portugal ( ...
Habitat fragmentation and biological invasions have long been considered the primary cause for biodiversity loss and the most threats to the conservation of ecosystems and their environmental services. Research on these two drivers of species decline is often approached separately, rather than as interactive factors, in spite of their synergic effects. Pampa biome has undergone a process of transformation and fragmentation due to the advancement of various forms of anthropic intervention. The substitution of natural grasslands for forest plantations stands out among them. The presence of woody plants in grasslands represents not only the addition of species, but also the introduction of a completely new way of life in environments where native trees are rare or absent. Among the consequences of the introduction of woody species in grassland environments, stand out the fragmentation of the ecosystem and the modification of the frequency and intensity of fires. We analyze the synergy that occurs between fire and invasion of woody plants adapted to fire, once grassland environments have been fragmented, a little evaluated aspect. This study focuses on relicts of coastal grasslands of different area, fragmented by a plantation of Pinus pinaster and Acacia longifolia. This area was completely burnt by a fire. Our results show that in the studied fragmentation scenario, the number of smaller (< 0.05 and 0.05-0.1 ha) and larger (> 2 ha) fragments decreased after fire, while the number of medium sized fragments (0.1-0.5 and 0.5-2 ha) augmented. This was a consequence of the disappearance of the smallest remnants, the decrease in the area of largest remnants, and the subdivision of the medium fragments, as a consequence of the expansion of exotic woody species over originally covered by grasslands. Taken together, these changes in the landscape limit native vegetation to increasingly smaller and more isolated areas, thereby increasing the edge effect, and leads to the replacement of natural grasslands by invasive trees, with the consequent loss of the original habitat. The situation described show that fire favored the expansion of pines and acacias in coastal grasslands, intensifying the loss and fragmentation of one of the most threatened ecosystems in the southern cone of America. The effective protection of the biodiversity that these particularly valuable areas of the Pampas grassland still contain will depend on the identification and effective protection of the remnants in a better state of conservation and, in particular, on the containment of invasive woody species.
... Conversely, these reforestations provide multiple ecosystem services: protection of agricultural crops from sea wind, tourism development (Tomao et al. 2016(Tomao et al. , 2018 and they curb urban sprawl (Gasparella et al. 2017, Grotti et al. 2019. Moreover, forest stands have often proved to maintain varied coastal vegetation, although in the past they have been criticized due to the negative effect they can have on biodiversity (Van der Meulen & Salman 1996, Marchante et al. 2003, Bonari et al. 2017. ...
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Mediterranean stone pine reforestations are common characteristics of the Italian Tyrrhenian coast, which mostly maintain uniform and monolayered stand structures. However, improving structural diversity is an effective climate change adaptation strategy in forest management. The aim of this study was to implement a methodology which allows distinct reforested areas such as a single green infrastructure to be managed according to the surrounding land use and the characteristics of the forest stands. 240 hectares of Mediterranean stone pine forests located along a 16 km strip of the Lazio coast (Central Italy) were mapped. Twelve attributes describing the pine stands and showing possible constraints for future management decisions were associated to each forest patch. A hierarchical cluster analysis was performed to group the pinewood patches according to their similarity level and five different groups were identified. For each group, different silvicultural methods were proposed to guide the compositional and structural evolution of the stands, in order to make them suitable for providing services required locally and increasing overall diversity at landscape scale. The results of the study highlight how coastal land uses can offer effective inputs to differentiate the management of forest systems and therefore achieve greater variety and resilience in the landscape over time. This approach is particularly useful in the case of very homogeneous stands such as the stone pine reforestations under study.
... Accordingly, we found higher concentrations of soil nutrients and phosphatase activity under V. nilotica canopies than under S. africana canopies. This can be explained by the fact that acacias have rapid growth rates and the capacity to fix atmospheric nitrogen via rhizobium symbioses, and legumes in general have been repeatedly shown to induce changes in soil nutrient levels and cycles [40][41][42][43][44] . Moreover, V. nilotica has previously been found to increase soil nutrient concentrations due to high above-and belowground organic matter input 45 . ...
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The patchy distribution of trees typical of savannas often results in a discontinuous distribution of water, nutrient resources, and microbial communities in soil, commonly referred to as “islands of fertility”. We assessed how this phenomenon may affect the establishment and impact of invasive plants, using the invasion of Opuntia stricta in South Africa’s Kruger National Park as case study. We established uninvaded and O. stricta -invaded plots under the most common woody tree species in the study area ( Vachellia nilotica subsp. kraussiana and Spirostachys africana ) and in open patches with no tree cover. We then compared soil characteristics, diversity and composition of the soil bacterial communities, and germination performance of O. stricta and native trees between soils collected in each of the established plots. We found that the presence of native trees and invasive O. stricta increases soil water content and nutrients, and the abundance and diversity of bacterial communities, and alters soil bacterial composition. Moreover, the percentage and speed of germination of O. stricta were higher in soils conditioned by native trees compared to soils collected from open patches. Finally, while S. africana and V. nilotica trees appear to germinate equally well in invaded and uninvaded soils, O. stricta had lower and slower germination in invaded soils, suggesting the potential release of phytochemicals by O. stricta to avoid intraspecific competition. These results suggest that the presence of any tree or shrub in savanna ecosystems, regardless of origin (i.e. native or alien), can create favourable conditions for the establishment and growth of other plants.
... Their degradation is commonly the result of traditional human activities such as cultivation, grazing or the use of vegetation as fuel (Tsoar and Blumberg, 2002;Kutiel et al., 2004;Levin and Ben-Dor, 2004;Provoost et al., 2011), as well as modern activities such as recreational uses, urbanization or the extraction of aggregates (Nordstrom, 1994(Nordstrom, , 2004García-Romero et al., 2019;Marrero-Rodríguez et al., 2020b). In consequence, dune surface areas and sediment budgets have been reduced (Hernández-Cordero et al., 2018), changes in vegetation (Hernandez-Cordero et al., 2017;Delgado-Fernández et al., 2019a) and landforms (Tsoar and Blumberg, 2002) have taken place, and invasive species (used for grazing, as fuel, or for ornamental purposes) have successfully occupied large areas (Marchante et al., 2003;Esquivias et al., 2015;Parra-Tabla et al., 2018). Along with climate change (Clarke and Rendell, 1998;Tsoar et al., 2009), such degradation has compromised the capacity of ecosystems to provide services all over the world (Vilà et al., 2010;Van Oudenhoven et al., 2012;Walsh et al., 2016;Mehvar et al., 2019;Asmus et al., 2019;Weiskopf et al., 2020). ...
The loss of ecosystem services (ESs) is one of the main consequences of the inadequate management of natural environments. However, the drivers that shape the provision of ESs continue to be poorly characterized at local and regional scales, and their protection, generally, has not been a priority. This study analyzes the anthropic alteration process of an arid aeolian sedimentary system, the associated environmental consequences and changes in the social relevance of ESs for the local population. The social relevance of an ES was analyzed using historical sources (analysis of testimonies of travelers, press, government minutes, aerial photographs, field photographs and oral interviews, among others) for five land uses: urbanization, aggregate extraction, grazing, cultivation and logging. Using the available information, three criteria were selected to define their social relevance: social sensitivity, economic and political. Considering El Jable (Lanzarote, Canary Islands, Spain) as study area, the main results show that different historical land uses have generated different social reactions in relation to changes in the capacity of the ecosystem to provide its ESs. The ESs that directly benefitted the population (provision of food, fuel and raw materials, and the regulation of natural hazards) were found to have the greatest social relevance before 1960. However, since then, the change to the island's economic model has resulted in high levels of social relevance for ESs related to the promotion of tourism (cultural heritage, recreation and leisure, and aesthetic values), citizen security (regulation of natural hazards), wildlife (habitat preservation) and culture (cultural heritage). This type of analysis can provide information on the perception of society to changes in the local environment, the effects of such changes on people's lives, and the management response of the society in question.
... Trichilogaster acaciaelongifoliae galls are sensitive to desiccation since they lack the ability to regulate evapotranspiration, negatively influencing the development of immature stages within the galls (Dennill and Gordon, 1990). Coastal dunes, the most impacted habitat by A. longifolia invasion (Marchante et al., 2003) and where T. acaciaelongifoliae releases were performed, are typically dry, with little protection from the sun, which can limit or damage A. longifolia buds or even impair the viability of T. acaciaelongifoliae eggs or larvae (Dennill and Gordon, 1990). Although the impacts of T. acacielongifoliae were only measured in 2019 and 2020, a decrease in the number of pods and seeds was evident, showing that the wasp is reducing pod production (84.1%) and consequently seeds (95.2%). ...
Classical biocontrol is key for the successful management of invasive alien plants; yet, it is still relatively new in Europe. Although post-release monitoring is essential to evaluate the effectiveness of a biocontrol agent, it is often neglected. This study reports the detailed post-release monitoring of the first biocontrol agent intentionally introduced against an invasive plant in continental Europe. The Australian bud-galling wasp Trichilogaster acaciaelongifoliae (Frogatt) is used to control the invasive Acacia longifolia (Andr.) Willd., with a long history of success in South Africa. This biocontrol agent was first released in Europe in 2015 at several sites along the Portuguese coast. We monitored the establishment, spread and early impacts of T. acaciaelongifoliae on target-plants in Portugal, across 61 sites, from 2015 to 2020. Initial release of adults emerging from galls imported from South Africa and the subsequent releases from galls established in Portugal (2018 onwards) was compared, assessing the implications of the hemisphere shift. The impacts on the reproductive output and vegetative growth of A. longifolia were evaluated in more detail at three sites. From 2015 to 2019, 3567 T. acaciaelongifoliae were released at 61 sites, with establishment confirmed at 36 sites by 2020. The transfer of the wasp from the southern hemisphere limited its initial establishment, but increased rates of establishment followed with synchronization of its life cycle with northern hemisphere conditions. Therefore, after an initial moderate establishment, T. acaciaelongifoliae adapted to the northern hemisphere conditions and experienced an exponential growth (from 66 galls by 2016, to 24000 galls by 2018). Galled A. longifolia branches produced significantly fewer pods (−84.1%), seeds (−95.2%) and secondary branches (−33.3%) and had fewer phyllodes but increased growth of the main branch compared to ungalled branches. Trichilogaster acaciaelongifoliae successfully established in the northern hemisphere, despite the initial phenological mismatch and adverse weather conditions. To achieve this, it had to establish and synchronize its life cycle with the phenology of its host-plant, after which it developed exponentially and began to show significant impacts on the reproductive output of A. longifolia.
... Plant invasions are particularly problematic in Mediterranean-type ecosystems, which constitute global biodiversity hotspots. Effects have been studied in regions including Portugal (Marchante et al., 2003), California (D'Antonio et al., 2007) and Western Australia (Fisher et al., 2009), as well as South Africa (Van Wilgen et al. 1998) where the Working for Water Programme was initiated to deal with invasive species. ...
Invasive alien plants negatively impact ecosystems, but recovery of native vegetation may fail following standard methods of alien species removal alone. Alternative management actions may thus be required. Cape Flats Sand Fynbos is a critically endangered vegetation type in the Cape Floristic Region of South Africa which is threatened by Acacia saligna invasion, but standard clearing methods have failed to restore native vegetation structure. A restoration study was performed comparing passive treatments i.e. clearing without burning (stack-block) versus clearing and burning (burn-block), as well as active intervention by sowing seeds of native species, either initially after burning or a year later, in which seeds were either not pre-treated or pre-treated with smoke and heat exposure before sowing. After two years all treatments resulted in different recovery trajectories, although none resembled the reference condition. Clearing without burning facilitated recovery in less degraded areas with higher initial native shrub cover, but otherwise resulted in limited vegetation recovery. Limited recovery facilitated secondary invasion by herbaceous weeds. Active seed sowing resulted in the highest recovery of native shrub cover and diversity. These findings suggest that passive restoration is constrained by seed limitation, due to the lack of recovery of vegetation components under passive clearing treatment. Active sowing was able to partially overcome this constraint through improved recovery of total shrub cover. However, non-sprouting shrub cover was higher while resprouting shrubs and species of Restionaceae were lower compared to the reference condition. Pre-treatment of seeds before sowing improved establishment of some species. Active treatment involving sowing pre-treated seeds after clearing and burning therefore resulted in best fynbos recovery compared to either of the passive treatments tested. A decision tree has been developed based on these findings in order to guide best protocol for managers.
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Coastal dunes of the southern Buenos Aires province, in Argentina, are one of the last remnants of biodiversity in the southern Pampa unit, within the Rio de la Plata Grasslands. While the direct loss of grasslands due to the advance of cities and afforestation is conspicuous, the negative effects of the subdivision of the remaining environments on biodiversity and ecosystem dynamics are less considered. Our work aimed to analyze the combined effect of fires and subdivision of grasslands by invasive alien trees. Our results suggest that fragmentation affects the resilience of coastal grasslands after fire and affects the course of succession, promoting the establishment of invasive alien plants. We also suggest that fires favor the advance of pines and acacias towards the interior of grassland remnants, further reducing their area. The effective conservation of the components of Pampas biodiversity that still persist in these coastal ecosystems will depend on preventing, mitigating and compensating the insularization effects associated with forest plantations and the expansion of invasive trees, by means of adequate territorial planning that allows remnants to be maintained in a good state of conservation.
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One of the main causes of biodiversity loss in the world is the uncontrolled expansion of invasive plants. According to the edaphoclimatic conditions of each region, plants acquire different invasion behaviors. Thus, to better understand the expansion of invasive plants with radial growth, it is proposed to use two equations, the Annual Linear Increment (ALI) and the Annual Invasiveness Rate (AIR). These equations are applied using spatiotemporal data obtained from the analysis of orthophotomaps referring populations of Acacia dealbata Link. in areas located in Serra da Estrela, Portugal. As a result, the area occupied by this species in the parish of Cabeça was evaluated and a 20-year projection was carried out. The data produced by these equations contributed to improving the knowledge about the invasion behavior of exotic species in a rigorous and detailed way according to local ecological conditions. This study may serve as the basis for the application of other similar situations concerning invasive species in other territories, to improve the efficiency of future projections for these species. Local technical and scientific knowledge will contribute to improving spatial and management planning, enabling a better adequacy and effectiveness of the control measures to be adopted.
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Acacia spp. are widespread all over the Portuguese territory, representing a threat to local biodiversity and to the productivity of the forest sector. The measures adopted in some countries for their eradication or to control their propagation are expensive, have been considered unfeasible from practical and economical perspectives, and have generated large amounts of residue that must be valorized in a sustainable way. This review brings together information on the valorization of bark, wood, leaves, flowers, pods, seeds, roots, and exudates from Acacia spp., through the production of high-value bioactive extracts (e.g., antioxidant, antimicrobial, anti-inflammatory, antidiabetic, antiviral, anthelmintic, or pesticidal agents, suitable to be explored by pharmaceutical, nutraceutical, cosmetics, and food and feed industries), its incorporation in innovative materials (e.g., polymers and composites, nanomaterials, low-cost adsorbents), as well as through the application of advanced thermochemical processes (e.g., flash pyrolysis) and pre-treatments to decompose biomass in its structural components, regarding the production of biofuels along with valuable chemicals derived from cellulose, hemicellulose, and lignin. The knowledge of this research is important to encourage an efficient and sustainable valorization of Acacia spp. within a biorefinery concept, which can bring a significant economic return from the valorization of these residues, simultaneously contributing to forest cleaning and management, to reduce the risk of fires, and to improve the social-economic development of rural areas.
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The first species of Acacia from Australia are thought to have been brought to the Cape in 1845. Some of the factors which are believed to have contributed to the success of the exotic Acacia species are enumerated briefly. A key to the identification of the naturalized Acacia species is provided, together with descriptions of each species and an indication of their range of distribution in our area.
Ecologists frequently focus on vegetation for their monitoring studies. But why? The answer is probably due to its relative permanence, at least compared with many groups of animals and relative ease of recording. Also because its species composition reflects the nature of underlying soils, local climate, current and past management and is the medium in which animals live and feed. This wide range of controlling factors makes it difficult to interpret the requirements of the species that we record although the more we learn of the ecology of individual species the easier it becomes to interpret the vegetation of a particular area.
Coastal zones are particularly vulnerable to the impacts of nature and man and are physically very unstable as shown by erosion and associated loss of land. Negative shoreline trends cause secondary effects that affect society through threats to human settlements, harbors, coastal recreation areas, wetlands, marshes etc. These impacts are expected to increase as a consequence of climate change and sea-level rise. Thus, in the short- as well as in the long-term perspective coastal erosion must be regarded as an environmental problem that deserves much attention. Planners and decision makers need a greater awareness of the instability of sandy beaches and the possible impact of human activities. Efforts are needed to improve our knowledge about nearshore processes and to develop methods to quantitatively determine the behavior of beaches. -from Authors
The population changes of the 5 major invasive species between 1966 and 1976-1980 are described, with observations on 3 additional invaders of less importance. -from Authors
The increasing number of naturalized non-native plant species with a negative ecological impact on the communities where they grow (invasive species) is viewed as a major component of global change and is an important topic of current ecological research. In most regions of the world, the number of alien species is increasing as a result of trade, tourism, and disturbance, thus increasing the likelihood of plant invasions. Several international organizations have incorporated the invasive plant species issue in their main activities and have formulated guidelines for the management and eradication of invasive species. Switzerland as a central European country does not have as many invasive species as for example countries of other continents; however, some species are regarded as being invasive and are of special concern due to the highly fragmented and intensively used landscape. With the exceptions of the Alps, wildlife and areas of high conservation value are restricted to usually small areas, surrounded by heavily disturbed habitats or urban areas. In such places, invasive plant species may pose additional threats to the native diversity. Species of high concern are for example the north American Robinia pseudoacacia, Solidago altissima, S. gigantea, and the Asian species Impatiens glandulifera and Reynoutria japonica. In this article, the invasive species issue is highlighted with regard to the Swiss flora, and the needs for actions are discussed.
A quick dip into the literature on diversity reveals a bewildering range of indices. Each of these indices seeks to characterize the diversity of a sample or community by a single number. To add yet more confusion an index may be known by more than one name and written in a variety of notations using a range of log bases. This diversity of diversity indices has arisen because, for a number of years, it was standard practice for an author to review existing indices, denounce them as useless, and promptly invent a new index. Southwood (1978) notes an interesting parallel in the proliferation of new designs of light traps and new permutations of diversity measures.
1. The impact of dense stands of the alien invasive species Acacia saligna (Labill) Wendl. on the guild structure of indigenous fynbos vegetation was investigated at three sites on the Cape Peninsula, South Africa. Two Acacia stands of either recent (1-2 fire cycles) or longer (>2 fire cycles) origin were compared with neighbouring uninvaded vegetation. 2. At one site fynbos recruitment was monitored following complete removal of vegetation in the three different stands in order to assess the restoration potential of invaded vegetation. 3. Fynbos species richness, cover and frequency all declined through each invasion stage in the standing vegetation. Guild structure also changed: species with vertebrate-dispersed seeds were relatively more frequent in long-invaded stands and at two of the three sites long-invaded stands had relatively more tall shrubs and fewer shrubs with leptophyllous (ericoid) leaves compared to fynbos. Serotinous shrubs were virtually absent in long-invaded stands. 4. Richness per plot of species recruited by seedlings was highest in fynbos and declined both with stage of invasion and time after clearing. However, the total stand species richness was nearly as high in recently invaded as in uninvaded fynbos. 5. Ephemeral forbs constituted the majority of seedlings in all stands, but after two years they remained the most important growth form in terms of density and cover only in the long-invaded stand. 6. At 18 months after clearing, indigenous canopy cover was about 50% in all stands, but only in uninvaded fynbos did this continue to increase over the second summer. After two years, resprouters formed about half the canopy cover in fynbos and recently invaded stands, but were insignificant in the long-invaded stand. 7. After clearing, many species recruiting in the long-invaded stand were not present in the standing vegetation, indicating that persistent seed banks exist. 8. As representatives of all the major fynbos growth forms were recruited into the long-invaded stand after clearing, albeit at a low density, such stands could revert to vegetation resembling fynbos in structure. However, in order to speed up the restoration process and to improve the probability of a fully functioning ecosystem being established, guilds which have been eliminated, such as serotinous Proteaceae, should be reintroduced.