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Forest Ecology and Management 262 (2011) 178–187
Contents lists available at ScienceDirect
Forest Ecology and Management
journal homepage: www.elsevier.com/locate/foreco
Distribution, habitat and biomass of Pittosporum undulatum, the most important
woody plant invader in the Azores Archipelago
Patrícia Lourenc¸oa,∗, Vasco Medeirosb, Artur Gil a, Luís Silvaa
aCIBIO & CCPA, Departamento de Biologia, Universidade dos Ac¸ ores, Apartado 1422, 9501-801 Ponta Delgada, Portugal
bDirecc¸ ão Regional dos Recursos Florestais dos Ac¸ores, Rua do Contador, 23, 9500-050 Ponta Delgada, Portugal
article info
Article history:
Received 27 October 2010
Received in revised form 20 February 2011
Accepted 17 March 2011
Available online 6 April 2011
Keywords:
Azores
Biomass
Forestry
Invasive plants
Pittosporum undulatum
abstract
Pittosporum undulatum Ventenat (Pittosporaceae) is a tree or shrub native to Australia introduced in the
Azores Islands in the 19th century, presently naturalized in the nine islands. According to a random survey
of vascular plants in the Azores, the invader is present throughout the archipelago, in 62% of 547 1-km2
samples. It was found in pure or mixed stands, forming groups and also as isolated trees. P. undulatum was
frequently found in native scrubland (62%), mixed woodland (39%) and hedgerows (25%). The altitudinal
range extended from sea level up to about 800 m a.s.l., with the highest frequency between 100 and
400 m. The woody species more strongly associated with P. undulatum included characteristic native
and endemic species as well as non-indigenous and invasive taxa. Based on a forest inventory, 49% of the
forested area in the Azores, about 24,000 ha, is occupied by P. undulatum. Considerable areas inside Island
Natural Parks are covered by this species. The estimated annual P. undulatum biomass production in the
Azores might range from only about 150 Mg in the small island of Corvo up to more than 60,000 Mg in
Pico Island. The heating value of its wood and its chemical composition make it a good candidate for use
in combustion or gasification processes. Since there are no resources available to control this large-scale
invasion, using P. undulatum biomass for energy production might be an important factor to stimulate
the progressive and sustainable cutting of its stands and its replacement by Macaronesian species.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Non-indigenous plants are a major component of plant com-
munities around the world and are considered as a serious threat
to global biodiversity (Banshkin et al., 2003; Denslow et al., 2009;
Fornwalt et al., 2003; Keane and Crawley, 2002; Lake and Leishman,
2004; Lindenmayer and McCarthy, 2001; Pyˇ
sek et al., 2002; Rouget
et al., 2003; Schumaker et al., 2009; Shiferaw et al., 2004; Weis and
Weis, 2003). Plant invaders can exclude native plant species from
their original habitats through direct resource competition (Kueffer
et al., 2010). Such replacement produces dramatic changes in the
functioning of island systems, causing serious problems not only
for conservation but also in forestry, farming, hydrologic cycles and
even in human health (Caujapé et al., 2010; Silva et al., 2008).
Abbreviations: DRRF, Regional Direction For Forest Resources (Forest Services);
EDA, Azores electricity; GIS, Geographic Information System; GPS, Global Position-
ing System; INP, Island Natural Parks; IUCN, International Union for Conservation of
Nature; SPSS, statistical package for the social sciences; UTM, Universal Transverse
Mercator.
∗Corresponding author. Tel.: +351 296 650 803; fax: +351 296 650 100.
E-mail addresses: pmrlourenco@gmail.com,pmrlourenco@gmail.pt
(P. Lourenc¸ o), Vasco.AM.Medeiros@azores.gov.pt (V. Medeiros),
arturgil@gmail.com (A. Gil), lsilva@uac.pt (L. Silva).
Meanwhile, the costs associated with the control and removal
of invasive plants with ample distribution areas in one region will
probably limit the implementations of an effective management
strategy (Pimentel et al., 2000; Van Driesche et al., 2010). Finding
alternatives which generate an economic return for the resulting
biomass would greatly reduce related management and control
costs, thus ensuring the continuity of such effort going forward
(Penniall and Williamson, 2009). Furthermore, the energetic val-
orization also ensures that any agricultural and forestry biomass
residues are managed in an environmentally sound way, which
would otherwise generate additional costs given high landfill fees
and limited availability of space (Evans et al., 2010; Mamphweli and
Meyer, 2009). The use of wood-based energy lowers greenhouse
gas emissions over fossil fuels because the carbon dioxide released
when woody biomass is burned is balanced out by new, carbon-
sequestering biomass growing in its place (Demirbas, 2001). For
this reason, developing renewable systems such as growing trees
as energy crops on private land has gained considerable attention
and support and is an important tool in influencing forest processes
that contribute to social, economic, and ecological sustainability
(Evans et al., 2010; USDA, 2008).
In the Azores islands, and in other island systems, non-
indigenous species are an important threat to biodiversity
conservation, particularly invasive plants (Castro et al., 2010;
0378-1127/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2011.03.021
P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187 179
Fig. 1. Frequency distribution of Pittosporum undulatum abundance in 547 samples of 1-km2in the Azores Islands. Ordinal scale: 0, absence; 1, isolated plant; 2, scattered
plants; 3, plants in groups; 4, plants forming mixed stands; and 5, plants forming pure stands. (A) Results for the whole archipelago; (B) results by island.
Kueffer et al., 2010; Silva et al., 2008; Silva and Smith, 2004, 2006).
Woody plant biomass resources in the Azores have been used for
fuel in a wide scale from the first centuries of human settlement
up to the late 20th century, when biomass was still being used as a
primary source of fuel for certain industries, however, throughout
the history of the Azores there were frequent episodes of wood
deficiency (Costa, 1953, 1962; Dias, 1996; Moreira, 1987; Silva,
2001, 2009). In the 20th century many areas were cleared for pas-
tureland and many others were abandoned due to lack of human
resources, leading to a reduction of the forested areas and also
to the expansion of invasive species (Cordeiro and Silva, 2003;
Moniz and Silva, 2003; Silva et al., 2008; Silva and Smith, 2004,
2006).
This paper aims to evaluate the importance of the invasion
by Pittosporum undulatum Vent. (Pittosporaceae) in the Azorean
islands, based on its present distribution; type of habitat invaded;
and associated species. On the other hand, we aim to evaluate
the importance of P. undulatum as a potential biomass resource
as compared to other important forestry species. For this we used
data from two sources (1) an archipelago wide survey for plant
invaders, and (2) data from the Azorean Forest Inventory. We also
present first estimates regarding P. undulatum annual biomass pro-
duction, and the heating value and chemical composition of its
wood.
2. Materials and methods
2.1. Study area
The Azores archipelago comprises nine islands of volcanic ori-
gin located in the North Atlantic Ocean and with a total surface
area of 2322 km2. The distance between the archipelago and the
nearest continent (Europe) is about 1500 km and the islands span
615 km. The climate is temperate oceanic with a mean annual tem-
perature of 17 ◦C at sea level. Relative humidity is high and rainfall
ranges from 1500 to more than 3000 mmm−2per year, increas-
ing with altitude and from east to west. The natural vegetation
includes diverse communities, namely coastal vegetation, coastal
and inland wetlands, meadows, peat bogs and several types of
native forest and scrub. Human settlement in the archipelago began
in the 15th century. Since then, several activities have altered native
plant communities, namely, replacement of the original vegetation
cover with cereal crops, pasture and forestry and the introduction
of numerous crop, fodder, forest, ornamental and hedgerow plant
species (Silva et al., 2008; Silva and Smith, 2006).
180 P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187
2.2. P. undulatum
P. undulatum is a scrub or tree up to 15 m tall native from
Australia, where it is found in different types of Eucalyptus forest,
being one of the most abundant understorey species (Gleadow and
Ashton, 1981). Introduced in the Azores in the 19th century as a
hedgerow species for the protection of orange tree plantations, P.
undulatum later dispersed to a wide range of habitats throughout
the Azores islands (Sjögren, 1973; Trelease, 1897). P. undulatum
is an invader in tropical and subtropical mountain forest and in
warm temperate regions of Northern Hemisphere, in many islands
of the Atlantic and Pacific oceans and in South Africa (Goodland
and Healey, 1996; Manders and Richardson, 1992). P. undulatum
has also invaded plant communities in its native country, where it
is spreading outside its natural range (Gleadow and Ashton, 1981;
Rose, 1997a; Rose and Fairweather, 1997). According to a recent
evaluation of the top 100 invasive species in Macaronesia, P. undula-
tum was considered invasive in the Azores, Madeira and the Canary
islands, and ranked 8th in a total of 195 evaluated species, occu-
pying different types of protected areas, from nature reserves to
protected landscapes, and affecting several native and endemic
plant taxa (Silva et al., 2008). It was thus considered as one of the
priority species for the implementation of control actions in the
Azores.
2.3. Archipelago wide survey for plant invaders
The methods used in this section followed Silva and Smith
(2006), and are described below.
Sampling stations were selected randomly, from the Universal
Transverse Mercator (UTM) 1-km grid, using a computer random
numbers function. For each island, the number of selected stations
was about 20% of the total number of 1-km2plots, with a total
of 547 samples, corresponding to 23.6% of the total surface of the
archipelago. Selection of stations was made separately for each of
the 36 sheets of the map covering the Azores archipelago (Carta Mil-
itar de Portugal, scale 1:25,000 – Servic¸ os Cartográficos do Exército,
2001). Each island was sampled on two different occasions, with the
exception of São Miguel, which was sampled on three occasions,
due to its larger land surface, from 1999 to 2003.
Sampling stations were located using the respective map sheet
and a GPS (Magellan Colour Track). Vascular plant taxa were
recorded by driving and walking throughout the different habitats
present in each 1-km2sampling plot. The definition of the habitat
was based on the type of vegetation (species composition) where
the species was present and on the physical characteristics of the
ground (type of substrate; slope). At each station a rank was given to
each taxon, following an ordinal scale (Kershaw and Looney, 1985):
0, not present; 1, isolated plant (only one plant within the sta-
tion); 2, scattered plants (isolated plants spread within the station);
3, plants in groups (clusters of plants spread within the station);
4, plants forming mixed stands with other species; and 5, plants
forming pure stands. This scale was used as a standard procedure
in several sampling programs for which the resulting data were
included in Atlantis Tierra database, publicly available at the Azores
Biodiversity Portal (http://www.azoresbioportal.angra.uac.pt/).
For each island, the frequency of P. undulatum was calculated
and the frequency distribution of abundance scores (0–5) was
determined. The frequency of occurrence of P. undulatum in each
habitat and its frequency distribution with altitude was calculated
for altitude classes of 50 m. For altitude classes, possible differ-
ences in P. undulatum frequency were evaluated using contingency
table analysis with 2test, followed by a multicomparison test
for proportions (Zar, 1998). To determine if the occurrence of P.
undulatum in each habitat was proportional to the occurrence of
that habitat, those frequencies were compared using Yates’ 2test.
For each island, a correlation (Spearman) matrix based on taxa
abundance was calculated for woody species using SPSS v. 15 and
taxa were ranked according to their correlation with P. undula-
tum. The relationship between P. undulatum abundance scores and
environmental variables was determined with a canonical corre-
spondence analysis, using SPSS v. 15. The variables were as follows:
mean elevation (ELE), slope (SLP), presence of bogs (BOG), lakes
(LAK), ponds (PON), anthropogenic vegetation, including small gar-
dens and ornamental plants located along roads (ANT), main water
streams (MWS), seasonal water streams (SWS), coast (COS), build-
ings (BUI), agricultural crops (AGR), pasture (PAS), planted forest
(WOD), native scrub (SCB), roads (RDS), trails (TRL), hedgerows
(HGW), number of habitats (HAB), percentage of endemic (END),
native (NAT) and introduced species (INT), total number of species
(S).
2.4. Forest inventory
Forest stands were delimitated through photo interpretation
from orthophotomaps (2004) and the map covering the Azores
archipelago (Carta Militar de Portugal, scale 1:25,000 – Servic¸os
Cartográficos do Exército, 2001). A first separation was made
between forested areas and other types of land use, including, agri-
cultural fields and pastures, urban households, social areas, natural
or semi-natural areas, hydric resources, abandoned or unproduc-
tive land, highways, and watercourses. Field work was performed
between 2003 and 2007 to identify the different types of for-
est stands. According to percentage of canopy cover, stands were
defined as pure, more than 75% of cover by P. undulatum;dominant,
between 50 and 75% of cover by P. undulatum; and secondary, less
than 50% of cover by P. undulatum. Similar classifications were used
for stands dominated by other species. A Geographic Information
System (ArcGis 9.3; ESRI, 2008) was used to map the identified for-
est stands and the areas occupied by the Island Natural Parks (INP).
For each island, this was used to calculate the total forested area
and the areas occupied by the main forest species (those with a
land cover >1%). To evaluate the impact of P.undulatum in the INP,
we also calculated the total forested area and the areas occupied
by P. undulatum, inside the INP, divided according to the classifi-
cation proposed by International Union for Conservation of Nature
(IUCN, 2008). The categories present in the Azores are I – nature
reserve (strict protection); III – natural monument/national land-
mark (conservation of natural features); IV – nature conservation
reserve (conservation through active management); V – protected
landscape/seascape (conservation and recreation); VI – resource
reserve (sustainable use of natural resources).
2.5. Biomass availability and quality
Based on forest inventory data, the areas occupied by P. undula-
tum were estimated per island. The maximum exploitable area was
set at 65% of the total area, assuming the principles of sustainable
forest management (Secretariat of the Convention on Biological
Diversity, 2009). It should be noted that the areas used for these
calculations only included those stands classified as dominant or
pure in Section 2.4. The revolution period was 10 years, based on
field data from the Forest Services (DRRF, 2007). Thus, the annually
exploitable area was obtained by dividing the total exploitable area
by the revolution period. The calculations of the amount of biomass
per hectare at the end of the revolution period, assumed an aver-
age of 130 m3of wood per hectare and a conversion factor for dry
biomass per hectare of 0.56 Mg m−3(dry weight) according to data
obtained at P. undulatum stands, using ten 200 m2plots where trees
were cut, measured and weighted (DRRF, 2007). Annual biomass
production was obtained as the product of annually exploitable
area by biomass per hectare at the end of the revolution period.
P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187 181
Fig. 2. Frequency of Pittosporum undulatum at each altitude class, in 547 1-km2
samples in the Azores Islands. The xaxis refers to medium values for each altitude
class. Different letters indicate significant differences (˛= 0.05) in the frequency of
P. undulatum occurrence between altitudes (results of a multiple comparison test
applied after contingency table analysis).
It was also assumed that about 20% of the biomass corresponded to
operational waste, as expected in a typical area of forest exploita-
tion in the Azores (DRRF, 2007).
Three wood samples of trunk (>8 cm diameter) and branches
(<8 cm diameter) were collected at Pinhal da Paz (São Miguel,
Azores) in spring and analysed in Laboratório de Análise (Instituto
Superior Técnico, Lisbon, Portugal). The following parameters were
analysed: moisture content, ash content (CEN/TS 15,403), heating
value (CEN/TS 15,400), N, C, H, S (M.M. 8.6 E.A.), trace element anal-
ysis – As, M.M. 5.2 (EAA-GH); Hg, M.M. 5.3 (EAA-VF); Cd, Cr, Cu, Ni,
PB, V, and Zn, SMEWW 3120 (ICP) – and Cl (combustion/C.I.).
The estimated energy production from biomass assumed, based
on the amount produced per year, per island, was obtained by
converting the heating value per Mg into potential electricity pro-
duction in GWh per year (Paiva, 2007) and assuming an average
efficiency of energy conversion from woody biomass into electric-
ity of 27% (Evans et al., 2010). This was compared with annual
electricity consumption per island (EDA, 2009).
3. Results
3.1. Archipelago wide survey for plant invaders
P. undulatum was present throughout the Archipelago, in
almost 62% of the 547 total samples. It was commonly found
as isolated trees, but also forming groups and mixed stands
(Fig. 1A). Its frequency in different islands ranged from about
35% up to about 70% of the 1-km2samples, and there was some
Fig. 4. Frequency of Pittosporum undulatum in different habitats and frequency of
each habitat in 547 1-km2samples in the Azores Islands. *Significant difference
(˛= 0.05) between habitat occurrence in the samples and P. undulatum occurrence
in the habitat (results of Yates 2test).
variation among the abundance scores for the different islands
(Fig. 1B).
P. undulatum was found from sea level up to 700 m a.s.l.,
although it was less frequent from sea level up to 50 m and at ele-
vations above 500 m (Fig. 2). In general, P. undulatum was widely
scattered across the surface of the islands but it was less abundant in
the central areas, which correspond to the higher elevations (Fig. 3).
Furthermore, P. undulatum was found in a wide range of habitats,
including coastal areas (lava flows and cliffs), anthropic habitats
(hedgerows, vineyards), mixed woodland with other introduced
taxa, and was more frequent in native scrubland (Fig. 4).
P. undulatum was associated with a wide variety of woody
species (Table 1). It showed a relatively strong correlation with
the native Morella faya, but also with the introduced taxa Acacia
melanoxylon,Eucalyptus globulus and Pinus pinaster, and more rarely
with Persea indica. In this case, it was often found as an under-
storey species. Regarding endemic taxa, the strongest correlations
were found with Erica azorica,Picconia azorica and Laurus azor-
ica (Table 1). However, there was considerable variation among
islands. On the other hand, several indigenous woody species
Fig. 3. Distribution of forested areas and of the invasive species Pittosporum undulatum in the Azores Islands. Data from the Forest Inventory, gathered from 2003 to 2007 by
DRRF.
182 P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187
Table 1
List of the woody species (indigenous and non-indigenous) present in a survey of invasive plants (547 1-km2samples) performed in the Azores Islands. For each island, the species are ordered according to decreasing values of
their correlation with Pittosporum undulatum. Spearman correlation coefficient, based on abundance values (0–5, as defined in the text).
Rank S. Maria S. Miguel Terceira Graciosa S. Jorge Faial Pico Flores Corvo
1 0.74 Mor fay 0.57 Aca mel 0.56 Euc glob 0.80 Mor fay 0.75 Mor fay 0.53 Rub ine 0.62 Mor fay 0.57 Mor fay 1.00
2 0.56 Eri azo 0.34 Mor fay 0.56 Mor fay 0.50 Rub ine 0.49 Aca mel 0.39 Mor fay 0.45 Pin pin 0.54 Aru don 0.57
3 0.49 Pic azo 0.29 Euc glob 0.47 Aca mel 0.25 Euc glob 0.33 Aru don 0.34 Cry jap 0.41 Aca mel 0.35 Fic car 0.50
4 0.42 Euc glob 0.21 Sol mau 0.41 Sol mau 0.24 Fic pum 0.32 Rub ine 0.29 Sol mau 0.27 Aru don 0.35 Aca mel 0.36
5 0.38 Rub ine 0.20 Rub ine 0.39 Pin pin 0.22 Lau azo 0.32 Euc glob 0.21 Aca mel 0.25 Euc glob 0.35 Sol mau −0.11
6 0.38 Cry jap 0.17 Eri azo 0.33 Rub ine 0.22 Per ind 0.31 Fic car 0.16 Lau azo 0.21 Rub ine 0.26 Euc glob −0.11
7 0.31 Pin pin 0.17 Pic azo 0.19 Lau azo 0.22 Fic car 0.31 Eri azo 0.13 Vac cyl 0.21 Pic azo 0.26 Pin pin −0.11
8 0.25 Per ind 0.17 Per ind 0.13 Eri azo 0.11 Eri azo 0.25 Pin pin 0.10 Eri azo 0.17 Cry jap 0.25 Myr afr −0.11
9 0.24 Vac cyl 0.15 Ban int 0.12 Cry jap 0.05 Aca mel 0.24 Vib tin 0.09 Fic car 0.15 Fic car 0.25 Pit tob −0.11
10 0.20 Aru don 0.11 Lau nob 0.08 Vib tre −0.12 Pin pin 0.23 Pic azo 0.08 Euc glob 0.15 Lau azo 0.24 Eri azo −0.22
11 0.18 Aca mel 0.10 Cry jap 0.06 Myr afr −0.22 Cry jap 0.22 Sol mau 0.08 Ile per 0.13 Tam afr 0.23 Pic azo
12 0.17 Lau azo 0.09 Pit tob 0.06 Ile per −0.28 Aru don 0.20 Ile per 0.07 Pic azo 0.12 Fic pum 0.22 Tam afr
13 0.17 Vib tre 0.08 Aru don 0.05 Vac cyl −0.31 Jun bre 0.18 Fic pum 0.00 Hyd mac 0.11 Ban int 0.18 Vib tre
14 0.13 Tam afr 0.06 Pin pin 0.03 Jun bre −0.36 Tam afr 0.16 Tam afr 0.00 Lau nob 0.11 Myr afr 0.02 Lau azo
15 0.12 Ile per −0.04 Fic car −0.05 Fic pum 0.13 Myr afr −0.08 Met tom 0.10 Met tom −0.03 Hyd mac
16 0.12 Fic car −0.08 Hyd mac −0.10 Fic car 0.10 Pit tob −0.12 Pin pin 0.10 Per ind −0.09 Ile per
17 0.12 Hyd mac −0.09 Fic pum −0.20 Aru don −0.03 Cry jap −0.19 Aru don 0.04 Vib tre −0.10 Cry jap
18 0.08 Myr afr −0.10 Cle arb −0.31 Tam afr −0.08 Hyd mac −0.31 Jun bre −0.10 Eri azo −0.13 Rub ine
19 −0.06 Jun bre −0.12 Lau azo −0.10 Vac cyl −0.42 Tam afr −0.27 Ile per −0.17 Jun bre
20 −0.06 Met tom −0.13 Tam afr −0.21 Jun bre −0.35 Jun bre −0.38 Vac cyl
21 −0.14 Met tom −0.44 Vac cyl
22 −0.16 Vib tin
23 −0.17 Myr afr
24 −0.19 Ile per
25 −0.20 Jun bre
26 −0.23 Vac cyl
Indigenous:Erica azorica (Eri azo); Ilex perado spp. azorica;Juniperus brevifolia (Jun bre); Laurus azorica (Lau azo); Morella faya (Myr afr); Myrsine africana (Myr afr); Picconia azorica (Pic azo); Vaccinium cylindraceum (Vac cyl);
Viburnum treleasei (Vib tre).
Non-indigenous:Acacia melanoxylon (Aca mel); Arundo donax (Aru don); Banksia integrifolia (Ban int); Clethra arborea (Cle arb); Cryptomeria japonica (Cry jap); Eucalyptus globulus (Euc glob); Ficus carica (Fic car); Ficus pumila (Fic
pum); Hydrangea macrophylla (Hyd mac); Laurus nobilis (Lau nob); Metrosideros tomentosa (Met tom); Persea indica (Per ind); Pinus pinaster (Pin pin); Pittosporum tobira (Pit tob); Rubus inermis (Rub ine); Solanum mauritianum
(Sol mau); Tamarix africana (Tam afr).
P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187 183
Table 2
Results of a canonical correspondence analysis applied to the Pittosporum undulatum survey data performed in the Azores Islands, including 547 1-km2samples with different
abundance levels (0–5, as defined in the text) and characterized by 23 variables (see text). Statistics relative to the five extracted canonical functions: eigen value, percentage
of explained variance, cumulative explained variance, and results of Wilks’ test (testing the null hypothesis that there are no differences between the abundance groups).
Function Eigen-value Variance (%) Cumulative (%) Test of function(s) Wilks’ 2dfp
1 0.662 65.0 65.0 1–5 0.430 446.9 110 <0.001
2 0.195 19.2 84.1 2–5 0.715 177.7 84 <0.001
3 0.083 8.1 92.2 3–5 0.855 83.2 60 0.025
4 0.047 4.6 96.8 4–5 0.925 41.1 38 0.338
5 0.032 3.2 100.0 5 0.969 16.9 18 0.528
showed very low correlation values with P. undulatum (Table 1).
This agrees with the distribution of the invader with altitude,
since those indigenous species are more commonly found at higher
elevations, where the invader was less common. A canonical cor-
respondence analysis, where the first two extracted functions
explained more than 80% of the variance of the data, indicated a
clear separation between samples with abundance levels of 0 and
1 from samples with higher scores (Table 2 and Fig. 5). The vari-
ables more correlated with Function 1 were the number of habitats
(HAB, −0.41), the presence of peat bogs (BOG, 0.26) and lakes (LAK,
0.18) whereas those more correlated with Function 2 were the
number of species (SPP, −0.49) the presence of hedgerows (HGW,
0.36) and the presence of main water streams (MWS, 0.33). The
presence of native scrubland (SCB) was the variable most closely
associated with high abundance scores whereas the absence of
P. undulatum was associated with high elevation (ELE) and with
coastal areas (COS, Fig. 5). P. undulatum was more often found as
isolated plants (abundance score 1) in areas with high percentage
of introduced species, high numbers of habitats and the presence
of anthropogenic vegetation, that is in human disturbed locations
(Fig. 5).
3.2. Forest inventory
Data gathered in the forest inventory showed that P. undula-
tum presently invades a total of 23,891 ha, where it forms pure
Fig. 5. Canonical correspondence analysis showing the relationship between envi-
ronmental descriptors and the abundance scores for P. undulatum. Explained
variance: factor 1, 65.0%; factor 2, 19.2%; total, 84.1%. Elevation (ELE); slope (SLP);
presence of bogs (BOG), lakes (LAK), ponds (PON), anthropogenic vegetation, includ-
ing garden plants (ANT), main water streams (MWS), seasonal water streams (SWS),
buildings (BUI), agricultural crops (AGR), pasture (PAS), exotic woodland (WOD),
native scrubland (SCB), roads (RDS), trails (TRL), hedgerows (HGW); number of habi-
tats (HAB); percentage of endemic (END), native (NAT) and introduced species (INT);
total number of species (S).
stands or is the dominant species, which corresponds to 49% of
the forested area in the Azores Archipelago (Table 3 and Fig. 3).
Furthermore, P. undulatum occupied more than 50% of the forested
area except in São Miguel and Terceira islands (Fig. 6). It is thus
more important in terms of occupied area than Cryptomeria japon-
ica (26%), Eucalytus globulus (8%) and Pinus pinaster (2%), the most
important forestry species in the Azores. Of the total forested areas
found inside INP (14,428 ha), 37% were occupied by P. undulatum
while 41% corresponded to C. japonica, but this varied widely among
islands from 1 to 88% (Table 3). P. undulatum pure or dominated
stands inside INP tended to occur mainly on IUCN categories IV and
V (habitats/species management areas, and protected landscapes,
respectively).
3.3. Biomass availability and quality
The total annual biomass production estimates ranged from
only abut 150 Mg in the small island of Corvo up to more than
60,000 Mg in Pico Island (Table 4), depending on the surface area
occupied by P. undulatum. Laboratory analysis showed a mois-
ture content of 46–47%, a heating value ranging from 19.6 to
20.4 MJ kg−1(dry matter), corresponding to 5.6 MWh Mg−1, and
an ash content ranging from 0.9 to 1.1% (dry matter). Chemi-
cal analysis revealed an elemental composition (dry matter) of
0.9% N, 49–68% C, 2% H and 4% S, low quantities of trace ele-
ments (As < 1 gg
−1, Cd<1gg
−1, Hg < 0.1 gg
−1, Pb<5gg
−1,
Cu<5gg
−1,Cr<3gg
−1,Ni<5gg
−1,V<2gg
−1,Zn12gg
−1,
dry matter), and levels of Cl below 0.10% (0.05–0.08%, dry matter).
When comparing electricity consumption with potential energy
production from biomass, the later could potentially cover from
6 up to more than 200% of the electricity demands, depending on
the island (Table 4).
Fig. 6. Percentage of area occupied by the main forestry species and by the invasive
tree Pittosporum undulatum for each Azorean island. Data from the Forest Inventory,
gathered from 2003 to 2007 by DRRF.
184 P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187
Table 3
Surface area occupied by Pittosporum undulatum in the Azores Islands, globally and inside Island Natural Parks (INP). Based on the Forest Inventory data gathered by DRRF from 2003 to 2007. Total island surface, area dedicated to
forest and forested area invaded by P. undulatum; INP surface, area dedicated to forest, and forested area invaded by P. undulatum inside INP, globally or according to the type of area (IUCN, 2008). Only areas where P. undulatum
was found in pure stands or as the dominant tree were included in the table.
Island Island (area) Island Natural Parks (area)
Surface Forestry P. undulatum Surface Forestry P. undulatum Pure Dominant
(ha) (ha) (%) (ha) (%) (ha) (%) (ha) (%) (ha) (%) I III IV V VI I III IV V VI
S. Maria 9740 1957 20 1173 60 1709 18 230 13 142 62 0 0 1 1 0 0 3 72 65 0
S. Miguel 74,457 16,274 22 3701 23 14,321 19 6561 46 1344 20 30 0 354 132 0 0 10 280 537 1
Terceira 40,041 5914 15 1348 23 8029 20 1638 20 227 14 0 0 5 51 3 14 0 27 124 3
Graciosa 6066 727 12 342 47 331 5 99 30 1 1 0 0 0 0 0 0 1 0 0 0
S. Jorge 24,372 3694 15 2021 55 5184 21 959 18 327 34 0 0 0 0 0 0 0 60 267 0
Faial 17,324 3034 18 1760 58 3036 18 934 31 503 54 0 0 3 48 0 0 0 64 388 0
Pico 44,524 14,941 34 11,705 78 15,702 35 3448 22 2385 69 34 8 1 224 0 0 42 83 1993 0
Flores 14,096 2493 18 1812 73 4822 34 552 11 369 67 0 0 66 4 0 36 4 118 141 0
Corvo 1711 36 2 29 80 774 45 7 1 6 88 0 0 0 0 0 0 0 6 0 0
Azores 232,332 49,070 21 23,891 49 53,908 23 14,428 27 5306 37 64 8 430 460 3 50 60 711 3515 4
4. Discussion
According to the results from the invasive plant survey and the
forest inventory, P. undulatum is a widespread invader in the Azores
and revealed to be a dominant forest species, even when compared
with the main species used in forestry.
Several factors might explain the success of P. undulatum in the
Azores, including: (i) favorable climatic conditions – the mild and
humid climate of the Azores is favorable to P. undulatum since
it grows in mild, humid and sub-humid climatic zones, although
with some limitation to grow at higher elevations (more cold an
humid) (Gleadow and Ashton, 1981; Goodland and Healey, 1996;
Hortal et al., 2010; Rose and Fairweather, 1997; Sanford et al., 2003;
Sjögren, 1973); (ii) existence of available habitats – areas cleared of
native forest, abandoned land (orchards, vineyards), exotic wood-
land (Eucalyptus and Acacia) where it ranges from understory to
dominant species and reflecting its association with similar species
in its native range, natural habitats similar to its native habitat
(very shallow soils in coastal scrub and on lava flows, forest types
dominated by sclerophyllous and microphyllous species) (Cronk
and Fuller, 1995; Dias, 1996; Gleadow and Ashton, 1981; Goodland
and Healey, 1996; Lake and Leishman, 2004; Rouget et al., 2003;
Shiferaw et al., 2004; Silva and Smith, 2006); (iii) the existence of
dispersal agents and pollinators – there were limited obstacles to
dispersal and pollination, since it was widely planted as hedgerows,
its seeds are dispersed by birds and insect pollinators are available
(it is one of the main species for honey production in the Azores)
(Gleadow, 1982; Gleadow et al., 1983; Goodland and Healey, 1996;
Rose, 1997a); and (iv) release from its natural enemies, since only
a reduced number of phytophagous insects are found associated
with P. undulatum in the Azores (Keane and Crawley, 2002; Silva
and Tavares, 1995).
P. undulatum has invaded many of the protected areas presently
included in the recently approved Island Natural Parks and has
potential to still expand its range (Hortal et al., 2010). The correla-
tion values between P. undulatum and several Azorean indigenous
species (Morella faya,P. azorica,E. azorica,L. azorica) gives rise to
some conservation concerns. Although the 1-km2plots used for
sampling are relatively large, and might in theory allow the sep-
arated presence of P. undulatum and native species, only woody
species were considered. As seen in the analysis of P. undula-
tum habitat, it will most probably share the same habitat as
native species, as confirmed in numerous field samples. If there
is not an interaction at the moment, it will most likely happen in
the future, since the natural tendency of P. undulatum has been
to progressively dominate invaded stands when associated with
native vegetation remnants, by overgrowing the native vegeta-
tion (Gleadow, 1982; Goodland and Healey, 1996; Machado, 1946;
Palhinha et al., 1942; Ricardo et al., 1977; Rose and Fairweather,
1997; Sjögren, 1973). P. undulatum has a dense canopy, with 8–24%
penetration of full sunlight (winter and summer), and as inva-
sions progresses the canopies coalescence forming a continuous
stratum with light intensities less than 1% full sunlight at ground
level (Gleadow et al., 1983). Therefore, heavy shade is the pri-
marily responsible for species richness reduction in invaded areas
(Bradstock et al., 1997; Gleadow and Ashton, 1981).
Control measures have been essayed and used (Gleadow and
Narayan, 2007; Rose, 1997b; Silva et al., 1999) and might be use-
ful in the conception of a management plan. However, due to the
large extent of the invaded areas, it is not possible to control P.
undulatum in the whole archipelago, since no resources are avail-
able for such a task. Gleadow and Narayan (2007) concluded that
high temperatures associated with wild fires are sufficient to act
as a circuit breaker on the invasion cycle. However, wild fires are
an extremely rare event in the Azores, and the native vegetation
is not adapted to this type of disturbance. On the contrary, native
P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187 185
Table 4
Estimated available Pittosporum undulatum biomass in the Azores Islands, and potential electricity production. Total area estimated using GIS, annually exploitable area
(considering only 65% of the total area and for a rotation period of ten years), wood annual production (considering an average of 130 m3of wood per hectare and a
conversion factor for dry biomass per hectare of 0.56 Mg m−3), operational waste (about 20% of the biomass), total annual biomass, total annual energy available (assuming
5.555 MWh Mg−1, and a plant efficiency of 27%) (Evans et al., 2010), annual electricity consumption (EDA, 2009), and percentage of electricity consumption potentially
covered by biomass. Only areas where P. undulatum was found in pure stands or as the dominant tree were included in the table.
Island Total area
(ha)
Annually
exploitable
area (ha)
Annual wood
production
(Mg year−1dry
weight)
Operational waste
(Mg year−1dry
weight)
Total annual
biomass (Mg year−1
dry weight)
Total annual
energy available
(GWh)
Annual electricity
consumption
(GWh)
Electricity
consumption
covered by
biomass (%)
Santa Maria 1173 76 5551 832 6383 9.6 19.0 50
São Miguel 3701 241 17,513 2627 20,140 30.2 407.0 7
Terceira 1347 88 6374 956 7330 11.0 192.2 6
Graciosa 342 22 1618 243 1861 2.8 12.7 22
São Jorge 2021 131 9563 1434 10,998 16.5 26.4 62
Faial 1757 114 8314 1247 9561 14.3 47.0 31
Pico 11,705 761 55,388 8308 63,696 95.5 39.8 240
Flores 1812 118 8574 1286 9861 14.8 11.3 131
Corvo 29 2 137 21 158 0.2 1.2 20
plants are adapted to high levels of humidity and rainfall (Dias,
1996). The use of this type of management approach in the Azores
could contribute to further expand invasive species, if not P. undu-
latum, many others present in the islands (e.g., Arundo donax,Ulex
europaeus,Solanum mauritianum). Thus, management of P. undu-
latum will demand coordination at regional level, with selective
control, removal at priority sites for conservation and restoration of
the invaded communities, replacement of hedgerows, progressive
substitution in mixed forest, and economic utilization where advis-
able (Goodland and Healey, 1996; Hortal et al., 2010). P. undulatum
is not being used for any important private or public economic
activities, besides as a source of compost for pineapple planta-
tions in greenhouses, in São Miguel Island, and the production of
honey. The later is still a small scale activity and other plants are
also important for honey production, namely Trifolium spp. since
large areas in the Azores are occupied by pastures. Finding alterna-
tives to generate economic return for the resulting biomass would
greatly reduce management and control costs, thus ensuring the
continuity of such effort. Forest energy involves the use of forest
biomass which is currently not being used in the traditional forest
product industry. Woody biomass is suitable for combustion, gasi-
fication, pyrolysis and fermentation (Evans et al., 2010; McKendry,
2002). The values obtained for heating value, ash content and the
chemical composition (including chlorine) of P. undulatum wood
are within the known range for woody materials, and seem to be
acceptable in terms of avoiding high ash formation, fouling and
slagging (Broek and Faaij, 1996; Jenkins et al., 1998; McKendry,
2002; Ragland et al., 1991; Yorulmaz and Atimtay, 2009). In São
Miguel Island, an incinerator for municipal solid waste which is
presently in the process of environmental impact assessment will
use about 30,000 Mg of woody plant residues per year, leading to
a dramatic increase in the demand for this type of material. More-
over, the considerable amounts of biomass produced in Pico and
Flores islands are potentially enough to cover annual electricity
consumption on those islands (EDA, 2009).
Biomass provides a clean, renewable energy source that could
improve environmental quality, stimulate local economy and
increase energy security; it generates far less air emissions than fos-
sil fuels, reduces the amount of waste sent to landfills and decreases
the reliance on fossil fuels; it could also create job opportunities
and help revitalized rural communities (Demirbas, 2004; Demirbas
et al., 2009; Evans et al., 2010). In the Azores, that could be coupled
to the containment of a widespread invasive species by stimulat-
ing P. undulatum harvesting and its progressive and sustainable
replacement by Macaronesian species, with positive economic and
environmental impacts. At a first stage, P. undulatum harvest could
be maintained to allow the establishment of the necessary opera-
tional mechanisms (cutting, transportation, preparation, end use).
Resprouting of cut stumps could be useful at this stage of the pro-
cess to assure the continuous production of biomass. However, at
medium and long term, to start P. undulatum gradual replacement
by Macaronesian species, cut stump treatments or injection of cut
stumps would have to be used to avoid resprouting (Silva et al.,
1999). As shown by our data, large areas are occupied by the invader
with reduced economic return whereas no resources are available
to control such a widespread invasion. Biomass resources are com-
pletely neglected while they might work as a driver for an effective
management of P. undulatum. Moreover, the total eradication of P.
undulatum is neither feasible nor advisable and in the calculations
for biomass production, only 65% of the area was included. Like-
wise, a considerable area were P. undulatum is not the dominant
species was also excluded from the calculations. That is, P. undula-
tum could still be used in the small scale activities mentioned above
as well as in other possible alternatives like essential oil production
(Ferreira et al., 2007; Lago et al., 2006).
It should be clearly noted that the transformation of the Azores
Islands into a P. undulatum monoculture for biomass production
or other purposes would not be environmentally sound and would
have unacceptable consequences for biodiversity conservation, as
seen in the past with other monocultures (e.g., cereals, orange tree
plantations, pastures). In fact, the aim of this research is precisely
the opposite, to discuss alternative management strategies that
might lead to an effective reduction of the area presently occupied
by P. undulatum in the Azores.
After the recent work by Hortal et al., 2010 about the poten-
tial distribution of P. undulatum in São Miguel Island, new research
done in remote sensing (Gil et al., 2011) and the present work,
particular attention has been given to the distribution, and the
large area occupied by this exotic tree in the Azores. In the future,
more field work will allow describing biomass production in more
detail, while modeling the distribution of P. undulatum and of sev-
eral native woody species will help to define the areas where the
invader could be effectively replaced. A multi-criteria evaluation or
other decision support methodology might then be used to evaluate
future management scenarios, allocating portions of P. undulatum
distribution area to different purposes (i) areas where it should
be controlled (e.g., nature reserves) and replaced by native and
endemic species (e.g., Morella faya,P. azorica,E. azorica); (ii) areas
devoted to biomass (trunks and larger branches), compost (low cal-
iber stems and leaves), honey and/or essential oil production; (iii)
areas where it could be gradually replaced by Macaronesian species
(Morella faya,Persea indica) for biomass and/or wood production;
(iv) areas where any intervention is most likely not possible (very
steep or inaccessible locations). This approach could also be seen as
186 P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187
a contribution for a diversification of the Azorean production for-
est, presently relying almost entirely on C. japonica, with a relatively
long production cycle (30 years).
This study could serve as a model to other regions or islands
systems where a significant invasion by woody plants occurs but
where no resources are available for an effective management.
Acknowledgments
This research was funded by project Woody Biomass, included
in the program Green Islands (MIT Portugal) supported by the
Azorean Government. We are grateful to Professors Jorge Medeiros,
Mário Alves and Suzana Cladeira (University of the Azores) and to
Nuno Domingues (ARENA) for coordination of Green Islands.Weare
grateful to José Maria Oliveira (ARENA) for insightful suggestions
regarding electricity production from biomass and electricity con-
sumption in the Azores. We thank Stephen Connors and Edward
Spang (Massachusetts Institute of Technology, Boston) for revising
the manuscript. The manuscript was improved with the sugges-
tions from two anonymous reviewers.
References
Banshkin, M., Stohlgren, T.J., Otsuki, Y., Lee, M., Evangelista, P., Belnap, J., 2003.
Soil characteristics and plant exotic species invasions in the Grand Staircase-
Escalante. National Monument, Utah, USA. Applied Soil Ecology 22, 67–77.
Bradstock, R.A., Tozer, M.G., Keith, D.A., 1997. Effects of high frequency fire on floristic
composition and abundance in a fire-prone heathland near Sydney. Australian
Journal of Botany 45, 641–655.
Broek, R., Faaij, A., 1996. Biomass combustion power generation technologies.
Biomass Bioenergy 11, 271–281.
Castro, S.A., Daehler, C.C., Silva, L., Torres-Santana, C.W., Reyes-Betancort, J.A.,
Atkinson, R., Jaramillo, P., Guezou, A., Jaksic, F.M., 2010. Floristic homogeniza-
tion as a teleconnected trend in oceanic islands. Diversity and Distributions,
doi:10.1111/j.1472-4642.2010.00695.x.
Caujapé, J., Tye, A.T., Crawford, D.J., Santos-Guerra, A., Sakai, A., Beaver, K., Lobin, W.,
Florens, F.B.V., Moura, M., Jardim, R., Gomes, I., Kueffer, C., 2010. Conservation of
oceanic island floras: present and future global challenges. Perspectives in Plant
Ecology, Evolution and Systematics 12, 107–129.
Cordeiro, N., Silva, L., 2003. Seed Production and vegetative growth of Hedy-
chium gardnerianum Ker-Gawler (Zingiberaceae) in São Miguel Island (Azores),
Arquipélago. Life and Marine Sciences 20A, 31–36.
Costa, C., 1953. Arvoredos dos Ac¸ ores. Algumas Achegas Para a Sua História, vol. 17.
Boletim da Comissão Reguladora dos Cereais, Ac¸ ores, pp. 1–24.
Costa, C., 1962. Arvoredos dos Ac¸ ores. Algumas Achegas Para a Sua História, vol.
33/36. Boletim da Comissão Reguladora dos Cereais, Ac¸ ores, pp. 69–110.
Cronk, C.B., Fuller, J.L., 1995. Plant Invaders. Chapman & Hall, London, p. 241.
Demirbas, A., 2001. Biomass resource facilities and biomass conversion processing
for fuels and chemicals. Energy Conservation and Management 42, 1357–1378.
Demirbas, A., 2004. Combustion characteristics of different biomass fuels. Progress
in Energy and Combustion Science 30, 219–230.
Demirbas, M.F., Balat, M., Balat, H., 2009. Potential contribution of biomass to the
sustainable energy development. Energy Conservation and Management 50,
1746–1760.
Denslow, J.S., Space, J.C., Thomas, P.A., 2009. Invasive exotic plants in the tropical
pacific islands: patterns of diversity. Biotropica 41 (2), 162–170.
Dias, E., 1996. Vegetac¸ ão Natural dos Ac¸ ores. Universidade dos Ac¸ ores, Angra do
Heroísmo, p. 302.
DRRF, 2007. Avaliac¸ ão da Biomassa Disponível em Povoamentos Florestais na Região
Autónoma dos Ac¸ ores (Evaluation of Available Biomass in Forestry Stands in the
Azores Autonomic Region). Inventário Florestal da Região Autónoma dos Ac¸ ores.
Direcc¸ ão Regional dos Recursos Florestais, Secretaria Regional da Agricultura e
Florestas da Região Autónoma dos Ac¸ ores, p. 8.
EDA, 2009. Informac¸ ão Estatística – Dezembro 2009, Electricidade dos Ac¸ ores www.
eda. pt, Ponta Delgada. p. 34.
Evans, A., Strezov, V., Evans, T.J., 2010. Sustainability considerations for electric-
ity generation from biomass. Renewable and Sustainable Energy Reviews 14,
1419–1427.
Ferreira, N.J., Sousa, I.G.M., Luís, T.C., Currais, A.J.M., Figueiredo, A.C., Costa, M.M.,
Lima, A.S.B., Santos, P.A.G., Barroso, J.G., Pedro, L.G., Scheffer, J.J.C., 2007. Pittospo-
rum undulatum Vent. grown in Portugal: secretory structures, seasonal variation
and enantiomeric composition of its essential oil. Flavour and Fragrance Journal
22, 1–9.
Fornwalt, P.J., Kaufmann, M.R., Huckaby, L.S., Stoker, J.M., Stohlgren, T.J., 2003. Non-
native plant invasions in managed and protected ponderosa pine/Douglas-fir
forests of the Colorado Front Range. Forest Ecology and Management 177,
515–527.
Gil, A., Yu, Q., Lobo, A., Lourenc¸ o, P., Silva, L., Calado, H., 2011. Assessing the effec-
tiveness of high resolution satellite imagery for vegetation mapping in small
islands protected areas. Journal of Coastal Research, SI 64. Szczecin, Poland, ISSN
0749-0208.
Gleadow, R.M., 1982. Invasion by Pittosporum undulatum of the forests of Central Vic-
toria. II. Dispersal, germination and establishment. Australian Journal of Botany
30, 185–198.
Gleadow, R.M., Ashton, D.H., 1981. Invasion by Pittosporum undulatum of the forests
of Central Victoria. I. Invasion patterns and plant morphology. Australian Journal
of Botany 29, 705–720.
Gleadow, R.M., Narayan, I., 2007. Temperature thresholds for germination and sur-
vival of Pittosporum undulatum: implications for management by fire. Acta
Oecologica 31, 151–157.
Gleadow, R.M., Rowan, K.S., Ashton, D.H., 1983. Invasion by Pittosporum undulatum
of the forests of Central Victoria. IV. Shade tolerance. Australian Journal of Botany
31, 151–160.
Goodland, T., Healey, J.R., 1996. The invasion of Jamaican montane Rainforests by
the Australian Tree Pittosporum undulatum. School of Agricultural and Forest
Sciences, University of Wales, Bangor, p. 54.
Hortal, J., Borges, P.A.V., Jiménez-Valverde, A., Azevedo, E.B., Silva, L., 2010. Assessing
the areas under risk of invasion within islands through potential distribution
modelling: the case of Pittosporum undulatum in São Miguel, Azores. Journal for
Nature Conservation 18 (4), 247–257.
IUCN, 2008. Guidelines for Applying Protected Area Management Categories. Inter-
national Union for the Conservation of Nature, World Headquarters, p. 106.
Jenkins, B.M., Baxter, L.L., Miles Jr., T.R., Miles, T.R., 1998. Combustion properties of
biomass. Fuel Processing Technology 54, 17–46.
Keane, R.M., Crawley, M.J., 2002. Exotic plant invasions and the enemy release
hypothesis. Trends in Ecology & Evolution 17 (4), 164–170.
Kershaw, K.A., Looney, J.H., 1985. Quantitative And Dynamic Plant Ecology, third ed.
Edward Arnold, Victoria, p. 282.
Kueffer, C., Daehler, C.C., Torres-Santana, C.W., Lavergne, C., Meyer, J.-Y., Rüdiger, O.,
Silva, L., 2010. Magnitude and form of invasive plant impacts on oceanic islands:
a global comparison. Perspectives in Plant Ecology, Evolution and Systematics
12, 145–161.
Lago, J.H.G., Fávero, O.A., Romoff, P., 2006. Microclimatic factors and phenology
influences in the chemical composition of the essential oils from Pittospo-
rum undulatum Vent. leaves. Journal of the Brazilian Chemical Society 17 (7),
1334–1338.
Lake, J.C., Leishman, M.R., 2004. Invasion success of exotic plants in natural ecosys-
tems: the role of disturbance, plant attributes and freedom from herbivores.
Biological Conservation 117, 215–226.
Lindenmayer, D.B., McCarthy, M.A., 2001. The spatial distribution of non-native
plant invaders in a pine–eucalypt landscape mosaic in south-eastern Australia.
Biological Conservation 102, 77–87.
Machado, F., 1946. Génese de alguns solos dos Ac¸ ores. Comissão Reguladora dos
Cereais do Arquipélago dos Ac¸ ores. Boletim 3, 1–8.
Mamphweli, N.S., Meyer, E.L., 2009. Implementation of the biomass gasification
project for community empowerment at Melani village, Eastern Cape, South
Africa. Renewable Energy 34, 2923–2927.
Manders, P.T., Richardson, D.M., 1992. Colonization of Cape fynbos communities by
forest species. Forest Ecology and Management 48, 277–293.
McKendry, P., 2002. Energy production from biomass. Part 3. Gasification technolo-
gies. Bioresource Technology 83, 55–63.
Moniz, J., Silva, L., 2003. Impact of Clethra arborea Aiton (Clethraceae) in a special pro-
tection area of São Miguel island, Azores. Arquipélago. Life and Marine Sciences
20A, 37–46.
Moreira, J.M., 1987. Alguns Aspectos da Intervenc¸ ão Humana na Evoluc¸ ão da Pais-
agem da Ilha de S. Miguel (Ac¸ ores). Servic¸ o Nacional de Parques, Reservas e
Conservac¸ ão da Natureza, Lisboa, p. 83.
Paiva, J.P.S., 2007. Redes de Energia Eléctrica – Uma Análise Sistémica, second ed.
Instituto Superior Técnico Press, Lisboa.
Palhinha, R.T., Cunha, A.G., Sobrinho, L.G., 1942. Algumas observac¸ ões ecológicas
sobre o Arquipélago Ac¸ oriano. I Congresso Nacional de Ciências Naturais, pp.
197–205.
Penniall, C.L., Williamson, C.J., 2009. Feasibility study into the potential for gasifi-
cation plant in the New Zealand wood processing industry. Energy Policy 37,
3377–3386.
Pimentel, D., Lach, L., Zuniga, R., Morrison, D., 2000. Environmental and economic
costs of nonindigenous species in the United States. BioScience 50 (1), 53–65.
Pyˇ
sek, P., Jaroˇ
sik, V., Kuˇ
cera, T., 2002. Patterns of invasion in temperate nature
reserves. Biological Conservation 104, 13–24.
Ragland, K.W., Aerts, D.J., Baker, A.J., 1991. Properties of wood for combustion anal-
ysis. Bioresource Technology 37, 161–168.
Ricardo, R.P., Madeira, M.A.V., Medina, J.M.B., Marques, M.M., Furtado, A.F.A.S., 1977.
Esboc¸ o Pedológico da Ilha de São Miguel, Ac¸ores. Anais do Instituto Superior de
Agronomia 37, 275–385.
Rose, S., 1997a. Integrating management of Pittosporum undulatum with other envi-
ronmental weeds in Sidney’s urban bushland. Pacific Conservation Biology 3,
350–365.
Rose, S., 1997b. Influence of suburban edges on invasion of Pittosporum undulatum
into the bushland of northern Sydney, Australia. Australian Journal of Ecology
22, 89–99.
Rose, S., Fairweather, P.G., 1997. Changes in floristic composition of urban bushland
invaded by Pittosporum undulatum in Northern Sydney, Australia. Australian
Journal of Botany 45, 123–149.
Rouget, M., Richardson, D.M., Cowling, R.M., Lloyd, J.W., Lombard, A.T., 2003. Cur-
rent patterns of habitat transformation and future threats to biodiversity in
P. Lourenc¸ o et al. / Forest Ecology and Management 262 (2011) 178–187 187
terrestrial ecosystems of the Cape Floristic Region, South Africa. Biological Con-
servation 112, 63–85.
Sanford, N.L., Harrington, R.A., Fownes, J.H., 2003. Survival and growth of native and
alien woody seedlings in open and understory environments. Forest Ecology and
Management 183, 377–385.
Schumaker, E., Kueffer, C., Edwards, P.J., Dietz, H., 2009. Influence of light and nutri-
ent conditions on seedling growth of native and invasive trees in the Seychelles.
Biological Invasions 11, 1941–1954.
Secretariat of the Convention on Biological Diversity, 2009. Sustainable Forest Man-
agement, Biodiversity and Livelihoods: A Good Practice Guide. Secretariat of the
Convention on Biological Diversity, Montreal, pp. 47+iii.
Shiferaw, H., Teketay, D., Nemomissa, S., Assefa, F., 2004. Some biological character-
istics that foster the invasion of Prosopis juliflora, Sw., DC. At Middle Awash Rift
Valley Area, north-eastern Ethiopia. Journal of Arid Environments 58, 135–154.
Silva, L., 2001. Plantas Vasculares Invasoras no Arquipélago dos Ac¸ ores.
Caracterizac¸ ão Geral e Estudo de um Caso: Clethra arborea Aiton, Clether-
aceae. Tese de Doutoramento, Universidade dos Ac¸ ores, Ponta Delgada,
p. 541.
Silva, L., 2009. Exotic Woodland. In: Cardoso, P., Gaspar, C., Borges, P.A.V., Gabriel,
R., Amorim, I.R., Martins, A.F., Maduro-Dias, F., Porteiro, J.M., Silva, L., Pereira, F.
(Eds.), Azores – A Natural Portrait/Ac¸ ores–um Retrato Natural. Verac¸ or, Ponta
Delgada, pp. 146–151.
Silva, L., Smith, C., 2004. A characterization of the non-indigenous flora of the Azores
Archipelago. Biological Invasions 6, 193–204.
Silva, L., Smith, C., 2006. A quantitative approach to the study of non-indigenous
plants: an example from the Azores Archipelago. Biodiversity and Conservation
15, 1661–1679.
Silva, L., Tavares, J., 1995. Phytophagous insects associated with endemic, Mac-
aronesian and exotic plants in the Azores. In: (Comité Editorial) Avances en
Entomología Ibérica. Museo Nacional de Ciencias Naturales (CSIC) y Universidad
Autónoma de Madrid, pp. 179–188.
Silva, L., Ojeda-Land, E., Rodríguez-Luengo, J.L., 2008. Invasive terrestrial flora and
fauna of Macaronesia. Top 100 in Azores, Madeira and Canaries. ARENA, Ponta
Delgada, p. 546.
Silva, L., Smith, C., Tavares, J., 1999. Essays for the control of Clethra arborea and
Pittosporum undulatum. In: Actas do I Encontro Invasoras Lenhosas, 16–18 de
Novembro de 1999, Gerês. Sociedade Portuguesa de Ciências Florestais, ADERE,
pp. 143–148.
Sjögren, E., 1973. Vascular plants new to the Azores and to individual islands in the
Archipelago. Boletim do Museu Municipal do Funchal 124, 94–120.
Trelease, W., 1897. Botanical observations on the Azores. Annual Report Missouri
Botanical Garden 8, 77–220.
USDA, 2008. ARS National Genetic Resources Program. Germplasm Resources Infor-
mation Network (GRIN). National Germplasm Resources Laboratory, Beltsville,
MD, http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?311586.
Van Driesche, R.G., Carruthers, R.I., Center, T., Hoddle, M.S., Hough-Goldstein, J.,
Morin, L., Smith, L., Wagner, D.L., Blossey, B., Brancatini, V., Casagrande, R.,
Causton, C.E., Coetzee, J.A., Cuda, J., Ding, J., Fowler, S.V., Frank, J.H., Fuester, R.,
Goolsby, J., Grodowitz, M., Heard, T.A., Hill, M.P., Hoffman, J.H., Huber, J., Julien,
M., Kairo, M.T.K., Kenis, M., Mason, P., Medal, J., Messing, R., Miller, R., Moore,
A., Neuenschwander, P., Newman, R., Norambuena, H., Palmer, W.A., Pember-
ton, R., Panduro, A.P., Pratt, P.D., Rayamajhi, M., Salom, S., Sands, D., Schooler, S.,
Schwarzländer, M., Sheppard, A., Shaw, R., Tipping, P.W., van Klinken, R.D., 2010.
Classical biological control for the protection of natural ecosystems. Biological
Control 54, S2–S33.
Weis, J.S., Weis, P., 2003. Is the invasion of the common reed, Phragmites australis,
into tidal marshes of the eastern US an ecological disaster? Marine Pollution
Bulletin 46, 816–820.
Yorulmaz, S.Y., Atimtay, A.T., 2009. Investigation of combustion kinetics of treated
and untreated waste wood samples with thermogravimetric analysis. Fuel Pro-
cessing Technology 90, 939–946.
Zar, J.H., 1998. Biostatistical Analysis. Prentice Hall, New Jersey.
