Invasive plants-Galapagos

Here we present a short summary of the most invasive plant species in Galapagos. These summaries were prepared by the students of the class: “Ecology and management of native and introduced plants of the Galapagos”, held in April 2015.

34 thoughts on “Invasive plants-Galapagos

  1. ‘Non-native’ is a term commonly used to describe species that are not naturally found in an area but have been introduced directly or indirectly by human influences – the term is often synonymous with ‘introduced’ or ‘exotic’. Non-native plants that have the ability to reproduce in the area where they were introduced are considered ‘naturalized’. Naturalized species that produce offspring that spread to areas far from the parent population are considered ‘invasive’, and those invasive species that fundamentally change the structure of an ecosystem are considered ‘transformers’ (Richardson 2000). In the Galápagos non-native plants have reached the islands through a variety of means. Animal and water dispersion contributed to the original succession on the islands and continue to transfer species – though relative to human impact species these natural numbers are very low. Humans intentionally brought crop plants for consumption, timber species, and ornamental plants to the islands – as well as unintentional impacts of imported goods, ship ballast water, and other forms of accidental transfer (Mcmullen 1999)

    As students living in the Galápagos, many of us have witnessed the overtaking of large portions of the highlands around the lake, El Junco, in San cristobal by invasive guava (Psidium guajava) and mora bush (Blackberry: Rubus niveus) that are pushing out the native Miconia robinsoniana (Jorgé, Nature Guide). These species are large management problems because both bear fruits that are consumed and dispersed by native animals. Blackberry seeds can also potentially live in soil up to 40 years before germinating, making even removal of the entire plant a root system an uncertain solution for decades (Jager 2015). These berries in particular are quick to fill forest gaps and are a hardy species that can survive in a variety of mountainous and highland ecosystems. Daniela Cox, a guide for the National Park, noted that the park managers have resorted to the routine application of herbicides (same active ingredient as roundup – Glyphosate) on blackberry plants around los Gemelos in Santa Cruz. These chemicals are known to damage more than just the target plant and do not prevent future regrowth after the chemicals disperse, but they have not found successful, efficient long-term removal options yet (Cox, 2015). Invasive tree species also pose large risks because they can produce large volumes of wind-dispersed seeds, and trees that form dense stands make physical removal hard if it is necessary (Tye 2001). Cedrela odorata is one of these problem species in mountainous ecosystems in the Galapagos. The tree, valued for timber, creates a dense canopy and monospecific stand that stops natural successional processes in the ecosystem and requires full tree uprooting to remove (Richardson 1998). In the Galapagos attempts to cut bark rings and apply herbicide have been individually successful but also heavily impact surrounding plant life, and there is no guarantee that succession will allow native species to refill gaps from dead trees (Jager 2015).

    Listed above are just three of the commonly battled high-impact invasive species in the Galápagos. Others of high interest include the Quinine tree (Cinchona succirubra), an epiphytic air plant (Kalanchoe pinnata), Multicolored Lanana (Lantana camara), and Elephant Grass (Pennisetum purpureum) (McMullen 1999). Elephant grass is considered a high-risk invasive species because of its ability to overtake during early succession and completely transform an ecosystem. Grasses are hard to manage without complete ecosystem disruption. The major problem with management of invasive species in general is the almost certainty that maintenance will need to be sustained long-term – there does not yet exist a permanent solution that is economically sustainable.

  2. Home to many endemic species and with a lack of migrating plant species, the Galapagos is left extremely vulnerable to invasion of introduced species. Many plants have the ability to thrive in ecosystems home to the Galapagos, but if introduced the rapid spread of these plants can have drastic effects on the surrounding, native plants.
    The Cinchona pubescens (quinine) tree were introduced to Santa Cruz for agricultural purposes in 1946, but quickly spread into the highland vegetation zones of the miconia and ferns. The quinine trees are especially bad for these areas because not only is it invasive, it is a transformer as well, changing the ecosystem in negative ways for the ferns and miconia. The ferns are more impacted than the miconia at a decline of 57-88% to 41% respectively (Jager, 2007). The Quinine has spread to >11,000 ha, taking over much of the farm land of Santa Cruz.

  3. The arrival of humans to the Galapagos Islands has threatened many of the endemic species found on the islands. One such species is the red quinine tree, Cinchona pubescens. This species of tree has been found to be invasive in other oceanic islands and also significantly decreased species diversity. Additionally, it is a transformer, meaning that it changes the habitat around it, making it more difficult for other species to flourish (Jager et al. 2009). Another invasive species that was introduced by humans is the guava, Psidium guajava, a fruit-bearing plant. Unfortunately, the spread of this plant has also been faciliated by the animals of the Galapagos. One of the most notorious invasive plants of the Galapagos is the blackberry, or Rubus niveus. This species of plant began to spread uncontrollably with the eradication of invasive animals such as goats (Tye et al. 2007).
    All of these invasive species are so widespread that their eradication has been deemed impossible.} The Galapagos National Park and Charles Darwin Foundation have instead been focusing their efforts on controlling them (Tye et al. 2007).

  4. Some of the most invasive plant species in the Galápagos Archipelago are: blackberry (Rubus niveus), guava (Psidium guajava), quinine (Cinchona pubescens), cedrela (Cedrela odorata), and lantana (Lantana camara). The common blackberry (Rubus niveus) has invaded shrubland, forest and open vegetation, rapidly altering the landscape in areas of Santa Cruz, San Cristóbal, Floreana, Isabela and Santiago (Rentería et al. 2012). Its transformative effect makes invaded areas impossible to farm. In addition, higher cover of R. niveus is correlated with significantly lower species richness and cover of native species (Rentería et al. 2012). Guava (Psidium guajava) is also a transformer species. It generally inhabits disturbed areas, preventing regrowth of native fauna (Walsh et al. 2008); it has also invaded native forests (Binggeli et al. 1998). Both blackberry and guava produce fruits that are eaten by native birds, which facilitates the distribution of these species (Rentería et al. 2012; Walsh et al. 2008). The quinine tree (Cinchona pubescens) is most present in the Mountain Zone of the islands (Jäger et al. 2009), and now dominates the Miconia zone of Santa Cruz (Buddenhagen and Yánez 2005). Its light, winged seeds are carried easily by wind (Jäger et al. 2009). Cedrela (Cedrela odorata) is a fast-growing tree that shades the area it occupies, creating monocultures and preventing native species from growing (Weber 2003). It has spread in regions of Floreana, Isabela, San Cristóbal, and Santa Cruz (Charles Darwin Foundation 2008). Lantana bush (Lantana camara) thrives in open spaces, such as degraded or disturbed areas (abandoned farms, for example), and crowds out other species with rapid, dense growth (Sharma et al. 2005). Its seeds are mostly dispersed by birds (Sharma at al. 2005).

  5. The Galapagos Islands have been greatly affected by the high increase of invasive species that have arrived since the 1980s. The introduction of these invasive plants has been accelerated by the increase in human presence over the last few decades. The most harmful invasive species present is Rubus niveus, also known as the mountain blackberry. Blackberries are present on three islands and have taken over more than 10,000 ha (Veitch & Clout, 2002).

    Another large invader is the quinine (Cinchona pubescens) tree. Quinine has invaded over 11,000 ha of Santa Cruz Island. With the presence of quinine, native herb and grass species significantly declined by 57-88% and the dominant endemic Miconia robinsoniana decreased by 41% (Jäger et. al., 2007). Equally invasive is the guava (Psidium guajava) plant (Reaser et. al., 2007). Together, blackberries, quinine trees, and guavas pose some of the largest threat to native flora in the Galapagos.

    -Bryce Hostetler

  6. The Galápagos Islands have a unique climate and landscape, allowing them to develop endemic species of plants. However, increasing tourism and imports have led to introduced species becoming a problem to the local ecosystems. Three of these invasive plants are discussed here. Located within the Galápagos National Park and on farmland on various islands, the guava tree, psidium guajava, is found frequently. It lives best in pastures and grasslands, which allows it to thrive in the open environments of the Galápagos (Walsh et al., 2008).

    The red quinine tree, Cinchona pubescens, has caused great concern in the highlands of Santa Cruz. Since it’s introduction to the island in 1946, it has spread over 11,000 ha and is present in both the Miconia- and Fern-Sedge Zones. Since both these areas contain endemic species, the threat to both zones is severe (Jager, Tye, and Kowarik, 2007; Macdonald et al., 1988). The blackberry bush, or Rubus niveus, is another plant to cause major concern on the Galápagos islands. On Santa Cruz, it covers over 30,000 ha and reduces biodiversity by 50% when present in an ecosystem (Vince, 2011). These invasive plants outcompete the surrounding species and alter the conditions of an ecosystem, terming them as transformer species.

  7. A few words on Galapagos invasive plant species
    Taylor Nelsen

    The Galapagos Islands are considered to be relatively pristine compared to other colonized islands. 95% of the original biodiversity is said to still be intact (Bensted-Smith 2002). Nevertheless, with increasing connectivity between islands and the mainland invasive species are starting to pose a threat to maintaining the historic ecosystems and their biodiversity. Many species, initially introduced for practical purposes such as cultivation or ornamentation (Foxcroft et al 2013) have now become invasive.

    The most problematic species cited across the literature include (McMullen 1999) (Renteria and Buddenhagen 2006):

    Cinchona succirubra (quinine tree)
    Pennisetum purpureum (elephant grass)
    Psidium guajava (common guava)
    Rubus niveus (hill raspberry)

    Of these Rubus niveus is considered especially invasive due to its quick maturation, tenacious seed bank and remarkable dispersal ability (Gardener et al 2010). Fortunately, invasive plant species have not been shown to cause extinctions (Gurevitch and Padilla 2004). Yet they can drastically change ecosystem and function if not addressed (Foxcroft et al 2013).

  8. The Galápagos Islands are a popular example for nature at it’s finest in terms of the lack in human involvement that tarnishes the viewable succession of natural selection. However, often omitted in common texts is the actual damage done by humans in the islands. There has been great success in establishing protected areas, however even though most humans do not step foot in these areas, they still affect it since colonization of the islands. The introduction of invasive species has caused major problems and has potential to do more. Higher cover of Rubus niveas has been directly associated with lower species diversity and density of native species (Rentería et al. 2012).

    Another major invader is the quinine tree species. Cinchona pubescens has invaded >11,000 ha of land on Santa Cruz island alone (Jager et al. 2007). The difficulty is that the dispersal syndromes of these plants take fertilized seeds into protected areas. These hyper successful introduced species can then outcompete the native species transforming the ecology. Proper management techniques must be outlined and acted on in order to control the species from causing homogenous biodiversity.

  9. The Galapagos archipelago is a unique and vital location for the study evolution and ecology, and thus the conservation of the islands native biodiversity is of upmost importance. One of the greatest threats to the native flora of the Galapagos is the introduction and expansion of invasive plant species. Among the most damaging and widespread of these invasive species is Rubus niveus (Watson 2010). Originally from Asia and introduced for agriculture in the 1960’s, Rubus niveus has been found to be detrimental to a range of environments including the native Scalesia forests of Santa Cruz (Renteria 2012). The aggressive growth strategy of Rubus niveus has resulted in the displacement of native plant species, and a rapid expansion of range which now includes the islands of Santa Cruz, San Cristobal, Floreana, Santiago, and Isabela (Renteria 2012).

    Two invasive tree species have also transformed the landscape and displaced native plant species within the Galapagos archipelago. Psidium guajava and Cinchona pubescens, commonly known as guava and quinine respectively have both turned normally treeless shrublands into highland forests (Jager et al. 2007; Watson 2010). As a result there was a marked 57-88% decline in endemic herb species and grass species (Jager et al. 2007). In combination all three of these invasive species have caused a substantial amount of harm to the native floral composition of the Galapagos archipelago, and therefore are a critical target of conservation efforts (Watson 2010).

  10. Introduced species are one of the biggest threats to Galapagos ecosystems, and unfortunately humans are the biggest contributors to this problem. Many invasive plant species now thrive on Galapagos soil after being introduced by humans from other areas, squandering the lives of native species and displacing them from their natural environments.

    Invasive species can be categorized based on their level of effect, and those called “transformers,” which thoroughly transform the environment in which they invade, are considered the most destructive. One example of a transformer is Cinchona pubesencs (quinine), a large tree that displaces smaller Miconia shrubs (Jager 2007), completely changing the environment from a small shrub land into a large forest. Other examples of main invasive plant species in the archipelago are Rubus niveus (blackberry), which can rapidly overtake shrubs and forest alike, and poses a large threat to the endemic Scalesia pedunculata (Renteria and Buddenhagen 2006). Psidium guajava (guava) has become a large problem on Isabela because of its high reproduction rates, and is also displacing many native and endemic species (Galapagos Park Website). The Galapagos National Park names over 15 more major invasive plant species, including Pennesitum purpureum (elephant grass) and Cedrela odorata (Cedrela/Spanish cedar). Since plant invasions change the species composition at the primary level, effects scale upwards, affecting everything from consumers to complete ecosystem structure. For example, the Galapagos tortoises feed on various forms of vegetation in the highlands of several islands, and when their food source is overtaken by an invasive species, they too are displaced. It is clear that this issue of invasion is a large problem in the archipelago, which is why many projects and funds are working to eliminate invasive species and restore the ecosystem.

  11. One of the major threats to the islands and its biodiversity are the impact that invasive species have on the endemic and native species. This is particularly important for the Galapagos as their endemic species cannot be found in any other area of the world and are constantly at risk. According the the Charles Darwin Foundation as reported on their website the blackberry bush (Rubus niveus) is considered the greatest threat as it invades all vegetation types and is extremely aggressive. Seventy nine species of Rubus are a invasive problem in at least one country in the world, so it is no wonder it is one of the worst on the Islands (Rentería et el. 2012).Other plant species that are considered a close runner up are Psidium guajava (guava), Rennistetum purpureum (elephant grass), and quinine Cinchona pubescens (quinine).

    What constitutes a plant/animal to become invasive is its ability to threaten the native flora/fauna. Take for example the Cinchona pubescens (quinine) it is suited for a variety of vegetation zones whereas some of the native plants are limited so when invasive plants enter they spread and plants such as the Miconia robinsoniana decrease by 41% population size and become endangered (Jager et al. 2007). Another example of an almost as invasive plant is the Rennistetum purpureum (elephant grass). Either something is done about these species now or they will continue to rage through the Galápagos until nothing is left but introduced species.

  12. Non-native species are defined as any species that does not naturally occur in a given region. With an increase of human activity on the Galapagos Islands over the years, many species have been introduced. Many of the plant species that have been introduced have proven to be invasive and thus harmful to the ecosystems in which they thrive. One such species is the Red Quinine Tree, Cinchona pubescens. This tree was introduced in the 1940s to the highlands of Santa Cruz. Today the tree inhabits a minimum of 11,000 ha (Jager 2007). The introduction of the Red Quinine Tree has resulted in a significant decrease in native species and has given the invasive Stachys agraria bare ground to grow on.

    Another invasive species on the Galapagos Island’s is Rubus niveus. This is a species of hill raspberry that has spread throughout the Scalesia forests of the Galapagos since its introduction in 1983 (Wilkinson 2005). The species spreads about 175 ha every year (Renteria et al 2012). This hill raspberry must be destroyed at the root, otherwise, mechanically removing the plant is counterproductive because seeds will spread and the original root will continue to grow. This species grows rapidly in its environment and thus is more successful than the native Scalesia. These are just two of the many invasive species of the Galapagos. An extended list of species was made and can be found in this study (Mauchamp 1997).

    -TJ Haltigan

  13. When examining the non-native plants of the Galapagos and the disruption these introduced species have created, it is first important to note the varying levels of seriousness in regards to native plant displacement or ecosystem disruption. Non-native species are those that would not otherwise naturally occur in that location were it not due to an unnatural method of transport, most often by humans. Introduction can be either accidental or purposeful, such as with the introduction of species intended for human consumption. Non-native species can be either naturalized, meaning that they are able to survive, spread, and stabilize in the environment without assistance, or invasive, meaning that their presence in the environment is out competing and replacing the native species. For this we will focus on the most invasive plant species of the Galapagos, which are currently posing the greatest threat to native flora.

    One of the most well known species as well as the worst is Blackberry- Rubus niveus, which has had the greatest impact on the islands of Santa Cruz and San Cristobal (Charles Darwin Foundation). Another is Quinine- Cinchona pubescens, which was introduced in the 1940’s and has significantly reduced biodiversity and species cover, giving it strong consideration as a transformer species. (Heinke Jager et. all, 2009) For clarification, a transformer species is considered to be the highest threat level of invasive due to its ability to alter environmental structure and conditions. Some more examples of plants likely introduced for human consumption include Guava- Psidium guajava, and Maracuya- Passiflo edulis. Another invasive species threatening local flora is Lantana- Lantana camera, which is thought to have been introduced for ornamental decoration. Additional invasive species that are of the highest concern and are considered to require immediate attention include Spanish Cedar- Cedrela odorata, Elephant Grass- Pennisetum purpureum, Cabuya- Furcraea hexapetala, Higuerilla- Ricinus communis, and Sauco- Cestrum auriculatum. (Leonardo Garcia, 2009) Currently the national park is undergoing various methods of biocontrol, such as SICGAL, the Galapagos Inspection and Quarantine program in order to reduce new introduced species, and bioremediation or physical removal for existing invasive plants. (IGTOA)

  14. The Galapagos archipelago, located about 1000 km off the coast of Ecuador, is thought by most people to be a pristine paradise. To the contrary, the Galapagos Islands have many introduced and invasive species. The most prominent invasive species in the Galapagos are Cedrela odorata (Cuban Cedar), Psidium guajava (Guava), Cinchona pubescens (Quinine), and Rubus niveus (Hill Raspberry). All of these species are well established invasive that are negatively impacting native plants and transforming the ecosystems of the Galapagos. Despite several control and eradication programs, these species continue to spread due to their fast growth, large seed banks, and large distribution within the archipelago (Gardner et al. 2010).
    Rubus niveus is considered by many to be the worst invasive species in the Galapagos. It has spread to most of the islands and forms dense thickets up to four meters high. High cover of R. niveus is correlated with lower native species richness and changes in the forest structure (Rentería et al. 2012). Areas with Scalesia forests are especially threatened, as Scalesia experiences synchronous stand-level dieback, producing large openings that fast colonizing species like R. niveus can take advantage of (Itow 1995). Rubus niveus seeds can also survive for up to 10 years in the soil, making eradication virtually impossible and control difficult (Gardner et al. 2010). In addition to R. niveus, C. odorata, P. guajava, and C. pubescens are all highly invasive species that have been spreading throughout the archipelago in recent years. These three species are all trees and have been colonizing shrublands and turning them into forest ecosystems. Cinchona pubescens, like R. niveus, has been shown to reduce species diversity and cover by at least 50% in areas where it has invaded (Jager et al. 2009).
    Overall, invasive species in areas of high endemism, like the Galapagos, are serious threats to biodiversity. These invasive species should be high priority for eradication (if possible) or control if conservation initiatives seek to restore ecosystems and preserve endemic species. Due to the extreme difficultly of controlling highly invasive, transformer species like R. niveus or C. pubescens, new control methods should be actively sought, and perhaps money currently being spent on inefficient control methods would be better allocated to research looking for new control methods such as biological control.

  15. Among the main invasive plant species on the Galápagos Islands is Rubus Niveus, also called blackberry or black raspberry. It was first recorded in 1983 (Mauchamp 1997). It was introduced from Asia in the 1970´s and has become out of control on San Cristóbal and Santa Cruz islands. It is used commercially for the black raspberry fruits. Rubus grows very densely, preventing other herbaceous or woody growth (Tye 1999). Within two years of being introduced to Santa Cruz, it had already formed dense, thorny thickets (Tye 1999). Another common invasive fruit tree is the Guayaba. Psidium guajava, commonly called the guava or guayaba, is a tree widely dispersed on the populated islands (Soria et al 2002). It was introduced in 1869 to plantations and small farms, and had spread since 1950 to larger forest areas (Lawesson and Ortiz 1990). It is estimated to have dominated about 4000 hectares, especially the highlands of San Cristóbal and the southern volcanoes of Isabela (Lawesson and Ortiz 1990). The guava tree spreads rapidly by wind- or animal-dispersed seeds (Tye 1999).
    Several other tree species, introduced initially for a certain product, are invasive on the islands. For example, Cinchona pubescens is also known as red cinchona and is used in the production of quinine. It was introduced in 1925 and began to invade Miconia zones by 1966 (Tye 1999). It has dominated the Miconia ecosytems on Santa Cruz Island (Buddenhagen and Yánez 2005). In 1990 it was estimated to have invaded about 8500 hectares (Moll 1990). In El Niño years, species like Cinchona pubescens and Psidium guajava, which are not harmed by the cycles of precipitation, can invade the habitats of native species while the adults of those species die in drought (Tye 1999). Cedrela odorata , known as Spanish Cedar is very fast growing and is often still planted consciously for its light wood (Mauchamp 1997). It was first introduced in 1950 for cultivation, as were most of the other invasive Galápagos species (Mauchamp 1997). Like Psidium, the seeds are dispersed by wind or by animals (Tye 1999). Thus, it did not become invasive until the first trees produced seeds about 25 years after being planted (Tye 1999).

    Laura Kelly
    1 April, 2015

  16. As an archipelago with human settlements and large volumes of annual tourists, the Galápagos Islands face threats from numerous introduced species, some of which have had a substantial enough negative impact on the ecosystem to be considered invasive. Of these invasive species, some of the most infamous include hill raspberry (Rubus niveus), red quinine (Cinchona pubescens), Cuban cedar (Cedrela odorata), and guava (Psidium guajava), all of which occur in the highlands (Rentería & Buddenhagen 2006).

    At least two of these species, R. niveus and C. pubescens, can be considered transformer species (Gardener et al. 2013), which substantially change the characteristics of the ecosystems they inhabit (Richardson et al. 2000). Rubus niveus can grow in dense stands and decreases species richness in patches in which it dominates (Rentería et al. 2012). As the fast-growing R. niveus covers 30,000 ha of the Galápagos and is very difficult to control (Gardener et al. 2013), this species is likely to have a drastic impact on native flora over a large geographic area. Cinchona pubescens, which covers at least 11,000 ha of the humid highlands of Santa Cruz (Jäger 1999), substantially changes this habitat, which formerly was treeless. This species decreases the amount of light available for photosynthesis under the canopy by 87%, increases rainfall by intercepting more clouds, and decreases overall species diversity (Jäger et al. 2009). Without effective control, these two species are likely to alter ecosystem function and community composition in much of the inhabited areas of the Galápagos.

    The remaining species, C. odorata and P. guajava, also occur in the highlands of inhabited islands. Cedrela odorata is planted intentionally, mainly for timber (Mauchamp 1997), and now has been spreading through native Scalesia forest (Rentería & Buddenhagen 2006). The control of species of such importance to local people is difficult due to conflicts of interest (Gardener et al. 2010). Psidium guajava has overtaken at least 40,000 ha since its beginnings on small farms. This species now forms a near-monoculture in some areas (Lawesson & Ortiz 1990), at the expense of native species. All four of these invasive plants are continuing to threaten native flora, especially the endemic Scalesia genus, which originally covered nearly the entire evergreen zone on the inhabited islands of the Galápagos (Itow 1995). One of the last strongholds of Scalesia forest, the area surrounding Los Gemelos on Santa Cruz, is being threatened by the continual spread of invasive species (Rentería & Buddenhagen 2006). If control or eradication efforts by conservation entities are not effective soon enough, the consequences might include nearly irreversible changes to these unique highland ecosystems of the Galápagos.

  17. Rubus niveus (black raspberry) is considered the most invasive plants in the Galapagos Islands, having invaded various zones, including shrubland, forests, and open vegetation zones. Rubus niveus forms dense bushes that grow to up to 4m high. The species spreads rapidly and aggressively and appears to displace many native plant species, such as Scalesia pedunculata forest, making rubus niveus a transformer species. An invasion by rubus niveus makes land useless for agriculture which negatively impact farmers. It appears that a higher concentration of rubus niveus that is present in a given area causes significantly lower native species richness and cover and a different forest structure. (Rentería et al, 2012)
    Cinchona pubescens (quinine) is considered one of the most invasive plant species in the Galapagos, appearing to significantly change several different vegetation zones, such as the Miconia Zone and the Fern-Sedge Zone. Cinchona pubescens is a tree species that spreads rapidly and aggressively, appearing to reduce native plants species numbers significantly more in zones that are absent of tree species for various reasons, including the fact that certain vegetation zones are adapted to the shade that tree species like cinchona pubescens create while some vegetation zones are not, resulting in varying impacts of cinchona pubescens invasions in different vegetation zones. (Jager et al, 2007)
    Psidium guajava (guava) is also one of the most invasive plant species in the Galapagos. Guava was introduced for its fruit and has grown to dominate extensive areas of farmland and National Park. Guava is a cultivated small tree or shrub that stands 3-10m tall. Guava is considered a transformer species, thriving in grasslands, roadsides, cropland, pasture, natural forests, and other areas that are considered disturbed. Guava forms dese thickets that prevent native plants from regenerating, which results in the reduction of native plant species richness. Animals in the Galapagos aid in dispersing the seeds because the animals enjoy the fruit, and guava can survive in a variety of harsh environmental conditions, resulting in guava’s successful invasion. (Walsh et al, 2007)
    Cedrela odorata (cedrela) is also one of the most invasive plant species in the Galapagos. It is a fast-growing tree that is used for its wood, which drives native people to value the plant despite its negative consequences for native species of the Galapagos. It displaces native plant species by blocking out sunlight with its large leaves and it spreads rapidly. It invades disturbed areas, like pastures, the most quickly. The presence of Cedrela odorata appears to increase the frequency of fires, which further disturbs native plant species. (Mauchamp, 1997)

    Megan Dussault

  18. While the Galapagos Islands are considered to be one of the most pristine places in the world, remaining roughly 95% intact, they also are rapidly falling under threat due to introduced invasive species. Invasive species are those that are non-native, or in other words would not have been found in that location were it not for outside activities, such as direct or indirect introduction from humans. Differing from naturalized non-native plants, which are characterized by those able to survive, spread, and stabilize without human assistance, invasive plants pose a higher threat to native flora and diversity as they are able to outcompete and displace the native species. For this reason I will focus on the main invasive species of the Galapagos that currently pose the greatest threat.

    One of the most well known as well as most difficult to control is Blackberry- Rubus niveus, which today affects San Cristobal and Santa Cruz the strongest, although other islands contain this plant as well. This plant is particularly problematic due to its quick growth and thorny branches which tend to form a thick barrier, enabling the plant to quickly over take an area and effectively ruining it for farming and preventing usage or passage by animals. (Renteria et. all, 2012) Another example is Quinine- Cinchona pubescens, which has drastically affected Santa Cruz and has had the effect of reduced biodiversity and decreased native plant cover by 50%. For this reason this plant is considered to be a transformer species, or an invasive requiring the highest attention due to its ability to impact and restructure an environment. (Jager et. all, 2009) Examples of invasive plants likely introduced for the purpose of consumption include Guava- Psidium guajava and Maracuya- Passiflora edulis. Other examples of invasive species considered to require the most immediate action include Spanish Cedar- Cedrela odorata, Elephant Grass- Pennisetum purpureum, Cabuya- Furcraea hexapetala, and Sauco- Cestrum auriculatum. Today the national park is undertaking methods to control and prevent future and existing spread of invasive species, such as the Galapagos security and quarantine procedure upon entering any of the islands, as well as bio-control through methods such as physical control or bioremediation.

  19. While the Galapagos Islands are considered to be one of the most pristine places in the world, remaining roughly 95% intact, they also are rapidly falling under threat due to introduced invasive species. Invasive species are those that are non-native, or in other words would not have been found in that location were it not for outside activities, such as direct or indirect introduction from humans. Differing from naturalized non-native plants, which are characterized by those able to survive, spread, and stabilize without human assistance, invasive plants pose a higher threat to native flora and diversity as they are able to outcompete and displace the native species. For this reason I will focus on the main invasive species of the Galapagos that currently pose the greatest threat.
    One of the most well known as well as most difficult to control is Blackberry- Rubus niveus, which today affects San Cristobal and Santa Cruz the strongest, although other islands contain this plant as well. This plant is particularly problematic due to its quick growth and thorny branches which tend to form a thick barrier, enabling the plant to quickly over take an area and effectively ruining it for farming and preventing usage or passage by animals. (Renteria et. all, 2012) Another example is Quinine- Cinchona pubescens, which has drastically affected Santa Cruz and has had the effect of reduced biodiversity and decreased native plant cover by 50%. For this reason this plant is considered to be a transformer species, or an invasive requiring the highest attention due to its ability to impact and restructure an environment. (Jager et. all, 2009) Examples of invasive plants likely introduced for the purpose of consumption include Guava- Psidium guajava and Maracuya- Passiflora edulis. Other examples of invasive species considered to require the most immediate action include Spanish Cedar- Cedrela odorata, Elephant Grass- Pennisetum purpureum, Cabuya- Furcraea hexapetala, and Sauco- Cestrum auriculatum. Today the national park is undertaking methods to control and prevent future and existing spread of invasive species, such as the Galapagos security and quarantine procedure upon entering any of the islands, as well as bio-control through methods such as physical control or bioremediation.

  20. Perhaps the most well known invasive species of the Galapagos is the Hill’s raspberry, Rubus niveus, often referred to within the Galapagos as blackberry or mora. This plant poses a serious threat to not only the native flora, but also those who rely on it, including the giant tortoises. They are widely present on all four inhabited islands and is considered the worst of invasive species (Rentería et al. 2012).
    Guava, Psidium guajava, follows the raspberry in terms of notoriety, having taken over 40,000 ha (Lawesson and Ortiz 1990). Like the raspberry it is a transformer species and as such it threatens many native species. However, unlike the raspberry, the guava is less of a threat to the fauna of the islands, as both birds and tortoises are fond of, and thereby large seed dispersers of, the guava fruit (Rentería et al. 2012; Walsh et al. 2008).
    In dispersing the seeds of plants like the raspberry and the guava, animals inhibit the growth of other food sources and potentially negatively affect their nutrient intake.
    Another invasive species is the quinine tree, Cinchona pubescens. Best known for its malaria preventing compounds, this tree is a menace rather than help in the Galapagos. Its wind-dispersed seeds have allowed for its spread throughout the mountain zone of the populated islands ((Jäger et al. 2009; Weber 2003).
    Raspberry, guava and quinine provide an interesting example of how vulnerable smaller ecosystems are to transformer species. However, these are only a few of the invasive species that threaten the habit found on the Galapagos archipelago.

  21. Among the 31 invasive plant species recorded in Galapagos, Rubus niveus, Cinchona pubescens, Psidium guajava, Cedrela odorata, and Latana camara are considered to be some of the most harmful in terms of environmental impact.
    Rubus niveus (blackberry) has been labeled by some as “the worst weed in Galapagos” and continues to spread at a high rate as a result of consumption and dispersal by native fauna. It currently covers over 30,000 ha (Gardener et al. 2013). The woody shrubs mature quickly, and seeds can last in soil for at least 10 years, making eradication difficult. R. niveus also tends to quickly colonize open areas created by efforts to eradicate other invasive species (Gardener et al. 2010).
    Cinchona pubescens (quinine) is a tall tree with a dense canopy that reduces light availability in highland ecosystems, killing native vegetation. The canopy may also trap moisture, creating a damper understory and facilitating the growth of non-native species better adapted to wet conditions (Jager et al. 2009). It covers over 11,000 ha of land. Potential eradication of C. pubescens is further complicated by its use as a local source of timber (Gardener et al. 2010).
    Psidium guajava (guava) is an invasive tree that can survive both dry and wet conditions and grows well in a number of different soils. In many areas of Galapagos, it has nearly replaced Scalesia forests. Both native and introduced animals feed on the fruits, facilitating seed dispersal (Walsh et al. 2008).
    Cedrela odorata (Cuban cedar) is another fast-growing tree that has taken over Scalesia forests and other areas of the highlands. Its growth is facilitated by Scalesia’s periodic diebacks, and individual trees live for a long time. Formation of a high, dense canopy limits light availability for native species and facilitates colonization of the understory by other invasives, such as R. niveus (Renteria and Buddenhagen 2006).

  22. The introduction of alien plant species to an island can have detrimental effects for the native flora. Depending on the plants characteristics (i.e reproduction and growth rates, ability to disperse), they can quickly spread and displace the native vegetation. Rubus niveus (Blackberry), is a highly, and one of the worst, invasive plant species in the Galapagos archipelago, introduced in the 1960’s, and currently found on 5 of the islands (Santa Cruz, San Cristobal, Floreana, Isabela and Santiago). R. niveus is considered to be a transformer species, and therefore especially threatening to Galapagos’ ecosystems as it actually changes the nature and condition of the ecosystem, causing long-term cascade effects for all native flora and fauna in that area. Particularly discerning is the threat R. niveus has on the Scalesia pedunculata forest, which an important and unique ecosystem to the Galapagos (Renteria et.al, 2012).
    Another highly invasive species of the Galapagos is Cinchona pubescens, commonly known as Quinine, with a spread of over 10,000 ha on Isla Santa Cruz. This tree species has invaded and dominated the Miconia evergreen zones, which use to consist mainly of the endemic Miconia shrub, and were therefore naturally tree-less ecosystems. The Miconia is now one of the most endangered plants on the islands (due to both invasive species and cattle grazing) (Jager, Tye & Kowarik, 2007).

  23. Considered the worst plant invader on the Galapagos is blackberry (Rubus), which is “beyond the possibility of eradication on Santa Cruz and San Cristobal” (Charles Darwin Foundation 2004). Several species of blackberry inhabit the islands, but R. niveus is the worst of the worst, with 80-90% seed viability and ability to survive in soil for at least 28 months (CDF 2004).

    Quinine (Cinchona pubescens) and guava, (Psidium guajava), are two other highly transformative invasive species. Both “significantly reduce native vegetation” (CDF 2004). Guava specifically displaces native fern-sedge species and impacts Scalesia areas, which are ecologically important and already highly threatened by agriculture and invasive animal species.

    As a group, grasses are also some of the most severe invaders on the Galapagos. According to the Charles Darwin Foundation, in 2003, grass taxonomist Simon Lægaard found more than 10 previously overlooked species of introduced grasses. Elephant grass (Pennisetum purpureum) is particularly bad.

  24. The Galapagos have been a haven for introduced and invasive species since human arrival and settlement. Halfway through the 20th century there was a spike in the number of naturalized species on the archipelago that was inevitable with the rise of agriculture on the islands, particularly in the humid highlands. An especially affected area is the Scalesia forests which have been invaded by several species including Cinchona pubescens, Cedrela odorata, Psidium guajava, and Rubus niveus (Buddenhagen et al 2006).
    Several of these species (C.odorata, P. guajava, and R. niveus) spurted after the 1983 El Niño event (Gardener et al. 2013). Their ability to grow rapidly this period was likely emphasized by the Scalesia dieback phenomenon which occurred during the El Niño event (Buddenhagen et al. 2006). C. pubescens, however, was introduced to the highlands of Santa Cruz in the 40’s and began flourishing in the 70’s (Gardener et al. 2013). In 2010 it had an approximate distribution of 11,000ha (Gardener et al. 2010) and has created new forest land (Gardener et al. 2013). It’s success in the Scalesia forest is likely due to it’s ability to disperse seeds with wind (Gardener et al. 2010) and greater leaf area than its competetitor species, Miconia. Its leaves have a high leaf turnover rate, resulting in more nutrient rich soil than Miconia can provide. Attempts to control it have been somewhat successful, but hardened by several factors, including locas’ use of the tree for timber (Gardener et al. 2013).
    Another invasive species used for timber is the C. odorata, which reaches above the canopy of Scalesia pedunculata (Buddenhagen et al. 2006). Attempts to control the cedar were also somewhat successful (Gardener et al. 2013). Of the species listed to be controlled in the “Control of Invasive Species in the Galapagos Archipelago” project, one of the most unsuccessful eradications was that of R. niveus, which grows in “dense impenetrable thickets”. It was introduced to the highlands of Santa Cruz in the 60’s (Gardener et al. 2013). The shrub grows up to 4 m tall (Buddenhagen et al. 2006) and blocks all sunlight to the understory, while growing rapidly compared to native species, producing significantly larger seed banks (Gardener et al. 2013).

  25. The native ecosystems of the Galapagos Islands evolved in isolation due to its large distance to the continent, rough climate conditions shaped unique processes like the die-off of the endemic daisy-trees, Scalecia, during El Niño events. Consequently, these systems are likely to be fragile to disturbance. Many plants used by us humans for agriculture or as timber are selected for their fast and strong growth, resistance, and quick reproduction (many fruits/seeds/berries for us to feed). As humans arrived to the Galapagos Islands, they introduced those plants (and animals) to to provide themselves food during they stays. But not all species were and are brought intentionally, lots of species arrive as unnoticed as propagules sticking to boots or cloth or between other seeds. Today, aware of the problems of conservation caused by introduced and invasive species, we try to control first their introduction and second either control their reproduction and outspread on the islands, or even eradicate them.

  26. There have always been a decent number of invasives in the Galapagos since the first whalers and pirates came to the islands. However since the 1980s they have become a much larger problem. Some of the most destructive invasive species are blackberry (Rubus niveus), guava (Psidium guajava), quinine tree (Cinchona pubescens), and Lantana shrub (Lantana camara) (Mauchamp 2002). Blackberry and quinine have been known to cause the most problems in the Galapagos. The blackberry is an invasive shrub that was brought here in sometime in the 70’s. It has taken over a lot of habitat in many of the islands in the Galapagos archipelago including San Cristobal, Santa Cruz, and Isabela. Blackberry as well as many other invasive will take over disturbed areas like farmsteads roadsides and other disturbed areas. Blackberry is a pioneer species and so will move in and settle quickly to disturbed areas sometimes choking out other endemic and native plant species. The quinine tree will do this as well. The conservation agencies are trying to control these populations but animals and people spread them very quickly. For example the tortoises prefer guava to a lot of their normal diet and will eat it and spread the seed very quickly as well as cattle and other livestock (De Vries, Black 1983) .

  27. For over 30 years, there has been an ongoing battle against invasive introduced plant species in the Galapagos Islands. Rubus niveus (blackberry), along with Psidium guajava (guava) and Cinchona succirubra (quinine) are detrimental to the Galapagos ecosystems in that they reproduce rapidly, monopolize sunlight and other resources, and essentially suffocate the other [native] plants around them (Weisenmiller 2008). Efforts have been made to control and eradicate these species using methods ranging from pesticide use to manually pulling the plants out by their roots.

    One of the main reasons for the detrimental effects of these species is the initial vulnerability of the islands themselves (Mauchamp 2002). Due to their geographic isolation, unique environmental conditions and relative lack of species richness, the island ecosystems are easily affected by invasive species, and the native flora and fauna suffer the consequences.

  28. The paper by Castro et al. (2010) is an example of homogenization on a large temporal and spatial scale on archipelagos. They found that more homogenization had occurred in the Atlantic archipelagos than Pacific, likely because of a longer history of population and trade. This paper also concluded that invasions more than extirpations created homogenization. This is a teleconnected process because the same homogenization pattern is seen over a wide geographic area. Overall, all 12 archipelagos over 2 oceanic systems showed an increase in compositional similarity, consistent with the theme of biological homogenization.

    McKinney’s (2008) paper is a review of biological homogenization, largely taxonomic, in relation to ungulate populations. He states that it would be important to study abundance of shared and unshared species between areas. The results of a study on homogenization should depend on the spatial scale, in that closer ecosystems may be more similar than more separated ecosystems. He emphasizes that homogenization is based more on introductions than on extirpations or extinctions. It is also important that past studies on homogenization do not include enough information on changes in community composition on a large enough time scale.

  29. The galapagos archipelago is home to a delicate and unique set of ecosystems, made up of native and endemic species who have evolved to be part of a delicate balance, preserved through thousands of years of geographic isolation. In part due to the isolation of the islands, most native plant species are not longer equipped to compete with particularly fit strains from other areas of the globe. The moist upland forests of many of the Galapagos islands, including Scalesia and Miconia forests, are particularly susceptible to invasions from non-native species.

    Spanish cedar (Cedrela odorata) is one such species introduced from mainland South America. It is causing problems in native scalesia forests in the Galapagos and some expect it to replace other large trees as the dominant species in forests (Rentería 2006, Hamann 2001).

    Also widely considered to be one of the most widespread and harmful invasive plant species in the Galapagos, Hill Raspberry (Rubus niveus) is a powerful competitor with native flora for water, nutrients, and light (Rentería et al. 2012). In part due to the production of asexual clones, as well as large amounts of seeds-containing fruits, Rubus niveus has the ability to spread very quickly over a geographic area. The fruits of Rubus niveus are also a favorite among native frugivorous birds, who are a major vector for seed dispersal (Guerrero and Tye 2009). Invasions of this particular species are associated with a reduction in native species diversity and has contributed to the decline of much of the native Scalesia forests (Rentería et al. 2012).

  30. While the Galapagos Islands are considered to be one of the most pristine places in the world, remaining roughly 95% intact, they also are rapidly falling under threat due to introduced invasive species. Invasive species are those that are non-native, or in other words would not have been found in that location were it not for outside activities, such as direct or indirect introduction from humans. Differing from naturalized non-native plants, which are characterized by those able to survive, spread, and stabilize without human assistance, invasive plants pose a higher threat to native flora and diversity as they are able to outcompete and displace the native species. For this reason I will focus on the main invasive species of the Galapagos that currently pose the greatest threat.
    One of the most well-known as well as most difficult to control is Blackberry- Rubus niveus, which today affects San Cristobal and Santa Cruz the strongest, although other islands contain this plant as well. This plant is particularly problematic due to its quick growth and thorny branches which tend to form a thick barrier, enabling the plant to quickly over take an area and effectively ruining it for farming and preventing usage or passage by animals. (Renteria et. all, 2012) Another example is Quinine- Cinchona pubescens, which has drastically affected Santa Cruz and has had the effect of reduced biodiversity and decreased native plant cover by 50%. For this reason this plant is considered to be a transformer species, or an invasive requiring the highest attention due to its ability to impact and restructure an environment. (Jager et. all, 2009) Examples of invasive plants likely introduced for the purpose of consumption include Guava- Psidium guajava and Maracuya- Passiflora edulis. Other examples of invasive species considered to require the most immediate action include Spanish Cedar- Cedrela odorata, Elephant Grass- Pennisetum purpureum, Cabuya- Furcraea hexapetala, and Sauco- Cestrum auriculatum. Today the national park is undertaking methods to control and prevent future and existing spread of invasive species, such as the Galapagos security and quarantine procedure upon entering any of the islands, as well as bio-control through methods such as physical control or bioremediation.

    Torrie Brandon

  31. Species introduced to the Galapagos have been a concern since the establishment of the Galapagos National Park (and the founding of the Charles Darwin Foundation) in 1959. At this moment, introduced species include 36 vertebrate species, over 750 plant species, and over 540 insect species (Galapagos.org 2015). Of these species several are highly invasive.
    Highly invasive plant species such as the blackberry, quinine, and guava have been ravaging the ecosystems on various islands in the archipelago because they have been not only proliferating rapidly, but also eradicating various native plant species from the ecosystem in the process (The Nature Conservatory). The blackberry is actually the most invasive plant species, especially on the islands of Santa Cruz and San Cristobal where the majority of the plant species (such as Scalesia pedunculata) in the wetter highlands have been displaced with the blackberry’s dense thickets, transforming the entire ecosystem (Charles Darwin Foundation). Guava has been shown to be an increasing problem on Isabela where the natural ecosystem in some places has been completely replaced by this single species (Walsh et al 2008). Quinine is a huge problem on Santa Cruz where it negatively affects the abundance of Miconia and actually alters the phosphorus concentrations in the soil—disallowing for other native species to grow (Charles Darwin Foundation). Quinine has also had an effect on the Galapagos petrel as well because in the areas where quinine is dominant with its strong roots, the petrel cannot make its nest in the soil (The Nature Conservatory).
    In terms of invertebrates, probably the worst invasive invertebrate species is the ectoparasitic fly, Philornis downsi. These Muscid flies lay their eggs in the nests of birds, and the newly hatched maggots burrow into the chicks during their development and feed on their blood (internally and externally). Even if the chicks survive this ordeal to adulthood, they are deformed. The population of various Darwin’s finch species (the Mangrove finch and the Medium Tree Finch especially) has been declining over the entire span of the ectoparasite’s range due to the chicks not being able to live to adulthood (O’Connor et al 2010).
    Efforts to stop these invasive species have been widespread, including trying to contain the species and eradicate them, priority site control, or in some cases biological control has been necessary. Although many of these efforts have barely begun to put a dent in the invasive species populations, it is important to keep trying to eradicate these aliens to save as many native species as we (Charles Darwin Foundation).

  32. The Galapagos Islands have great potential for plants to thrive, but it has a great barrier, 600 miles of ocean, separating them from the main land. This barrier has served as a selection process for plants to be introduced to the islands. However, with increased traffic to the islands the threat of introduced species increases. Many plants have been introduced by humans for agricultural, and ornamental purposes, but with these introductions comes invasion. The introduced plants thrive in their new environment and become spread throughout the islands by various means of dispersal.

    A great example of how rampant this spread of introduced plants can be is the Rubus niveus, blackberry, that was introduced in the 1970’s has has spread throughout San Cristobal, Santa Cruz, and parts of Isabela. The blackberry is quick to disperse because of its small seeds that are popular among the diet of many of the birds. They are a pioneering plant, meaning they are need little time to grow and reproduce, making their dispersal rapid. They are a threat to many of the native and endemic plants they live amongst, by choking the native species out by competing for resources and growth. This species is debatably the most destructive introduced plants to the San Cristobal and Santa Cruz islands (Mauchamp 2002).

    Darcy Camp

  33. Biological homogenization can occur in two major ways: through the introduction of invasive species or through increased extinction of endemic species. Homogenization can be measured in many ways. There is genetic homogenization (mixing exotic genes into the native gene pool), functional homogenization (increase in similarity of ecological roles between communities), and–most commonly used–taxonomic homogenization (relative gain of number of shared species between two areas).

    There are many complexities involved when assessing human impact on biological homogenization. Firstly, it is difficult to compare homogenization between existing communities with little knowledge of the past community composition. Second, it is difficult to compare communities distant from each other since their initial compositions share few (if any) native species. Since their initial compositions are so different and they have few or no shared native species, introduced species would have a drastic homogenizing effect. However, neighboring communities where species have been introduced tend to have fewer shared species than shared native species.

    General trends synthesized by McKinney (2008) are that homogenization increases over time and that this is driven primarily by the introduction of invasive species instead of native species extinctions. Future study will need to be done as human urbanization grows; conservation from homogenization is extremely important because we’ll lose so much biodiversity and genetic information.

    Castro et al (2010) studied “floristic homogenization,” the increased similarity of the flora of a particularly region/ecosystem, in oceanic archipelagos including the Galapagos Islands. Islands are sensitive indicators of biological change, making it a great study site to observe plant homogenization. He conducted pairwise comparisons between “original” flora (pre-European colonization) and current flora of each region. It is a “teleconnected process” (linked pattern that spans large geographical areas); so as more non-native species are introduced by humans, they invade and change the environment so that it’s more homogenized. They found that archipelagos became much more similar in composition over time, indicating that biotic homogenization is a teleconnected process driven by human translocation. However, trends were not uniform across regions or species. They also concluded that invasions have a larger impact than extirpations as drivers of biotic change.

  34. On Friday’s field trip, we had the opportunity to observe two new ecosystems: transition forest and evergreen forest. We also saw some indicators of the humid highlands but were not at a high enough altitude to see a true example of this habitat. During the drive up to the highlands, we first passed through Puerto Baquerizo Moreno, where ornamental species but also some native dry forest species such as prickly pear cactus (Opuntia megasperma) and matazarno (Piscidia carthagenensis) were common. We quickly moved from the dry forest to the much greener, denser, and taller transition forest. This ecosystem experiences more rainfall and hosts species from both higher and lower areas. Although there was some cat’s claw (Zanthoxylum fagara), a native species, the transition forest along the road was composed mostly of introduced species, mainly Syzygium jambos then guava (Psidium guajava) as we drove higher up the mountain. Multicolored lantana (Lantana camara) and hill raspberry (Rubus niveus) also were present.

    The border between the transition forest and evergreen forest was unclear, possibly because both ecosystems are dominated by invasive species such as P. guajava and R. niveus. However, the Miconia robinsoniana we observed above a certain elevation was a clear indication that we were in the evergreen forest. Both the area by the wind turbines and El Junco were in this ecosystem, which has more precipitation and more epiphytes than the transition zone and contained mostly P. guajava and some M. robinsoniana. We found many ferns, some of which probably were a native species, Pteridium aquilinum, but they did not dominate the ecosystem as they would in the true humid highland zone that is found at higher elevations, mostly on other islands. Instead, the ferns were around and underneath the Miconia forest, such as at El Junco, and in the grazed areas near the wind turbines (ca. 640 m). Additionally, several introduced grasses were in both locations.

    Based on our observations during the field trip, the main invasive species in the transition and evergreen zones on San Cristóbal appear to be P. guajava (which dominates in a near-monoculture in many areas), R. niveus, S. jambos, and L. camara. Unfortunately, the Scalesia pedunculata that is supposed to define large patches of the evergreen forest is nearly absent from this island; we saw only three individuals intentionally planted near a greenhouse we visited. Miconia robinsoniana still survives but is likely to be suffering from intense competition with invasive species. Hopefully this endemic species will be able to persist despite this pressure.

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