37

Loss of Ecosystem Functions Caused by Severe Disturbances in
the Ogasawara Islands Can Limit Restoration : Implications fora New Framework of Practical Restoration of Disturbed Ecosystems
after Eradication of Feral Goats
Kenji HATA
Nihon University, College of Commerce
5-2-1 Kinuta, Setagaya-ku, Tokyo 157-8570, Japan
Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University
1-1 Minami-Osawa, Hachioji-shi, Tokyo 192-0397, Japan
E-mail: hata.kenji@nihon-u.ac.jp

Abstract
Feral goats (Capra hircus), an invasive non-native ungulate, have naturalized on many of the world’s
oceanic islands. Overgrazing and trampling by feral goats often cause vegetation degradation and soil erosion,
resulting in loss of biodiversity and ecosystem functions on oceanic islands. For restoration and managementof the disturbed ecosystems, eradication and control of feral goats have been conducted on many islands.
Recovery of vegetation after goat eradication has occurred at some sites but not others. To explain reasons forthe lack of vegetation recovery even after goat eradication, I describe processes of changes in ecosystem
functions before and after eradication of feral goats on an island, Nakoudo-Jima, in a subtropical archipelago
in the northwestern Pacific Ocean. I focus on the relationships between vegetation states and soil chemical
properties with vegetation degradation and soil erosion. Loss of vegetation cover caused by overgrazing andtrampling by feral goats causes loss of surface soil, which can expose deeper soil horizons. The exposed soils
often have lower amounts of nutrients and extremely low pH on the island. Soil with fewer nutrients andlower pH often limits plant growth, and can prevent recovery of vegetation even after goat eradication. In
addition, I explore the process of loss of ecosystem functions using a conceptual model based on therelationships between ecosystem states and functions. According to this model, loss of functions occurs in two
steps. The first step is vegetation degradation and the second is soil erosion. Finally, I propose a newframework for more flexible and practical restoration of island ecosystems disturbed by invasive mammals,
using the concept of a “novel ecosystem,” which should be one of the goals for disturbed ecosystems on
islands.
Key words :	invasive mammals, novel ecosystem, oceanic islands, soil chemical properties, soil erosion,vegetation degradation

1. Feral Goats on Oceanic Islands
Feral goats (Capra hircus), one of the most invasive
mammals, have damaged many ecosystems, especially on
islands (Coblentz, 1978; Loope et al., 1988). Goats havebeen introduced onto many islands, and have naturalized
in their new environments (Courchamp et al., 2003).
Native plant species on oceanic islands tend to bevulnerable to disturbances by non-native herbivorous
mammals (e.g. goats, sheep, pigs, horses and donkeys)
because of lack of defensive traits such as thorns or
chemical toxicity (Carlquist, 1974). Therefore, introduction
and naturalization of goats onto islands often have large
impacts on native vegetation, resulting in loss of
Global Environmental Research
23/2019: 037-044
printed in Japan

biodiversity and ecosystem functions (Coblentz, 1978;
Shimizu, 2003). On islands, the native vegetation is often
severely degraded by overgrazing and trampling by feral
goats, which can cause extinction of native plants andloss of habitats for native animals (Coblentz, 1978;
Leathwick et al., 1983; Loope et al., 1988; Hamann,
1993; Cox, 1999). In addition, vegetation degradation,i.e. loss of vegetation cover, often results in serious lossof ecosystem functions, such as through erosion of
surface soils (Loope et al., 1988; Hata et al., 2019).
“Ecosystem function” is a general term that includes
stocks of materials and fluxes of energy and matter
between organisms and the abiotic environments throughprimary production of organic matter, food webs and©2019 AIRES

38

K. HATA

recycling to inorganic matter, which make sustainable
states possible for humans and all other organisms.
Feral goats have therefore been eradicated toconserve endemic ecosystems and biodiversity on oceanicislands (Campbell & Donlan, 2005). Native vegetation onsome oceanic islands recovers after the eradication ofgoats (Hamann, 1975, 1979; Mueller-Dombois & Spatz,
1975; Loope & Scowcroft, 1985; Bullock et al., 2002;
Kessler, 2002; Shimizu, 2003), which would be related to
cessation of grazing and trampling by feral goats.
Recovery of native vegetation after goat eradication,
however, does not occur on other islands (e.g., Stone etal., 1992; Courchamp et al., 2003; Hata et al., 2010a;
Weller et al., 2011).
Why does vegetation recover after goat eradication
at some sites but not at other sites? To answer thatquestion, I describe processes of changes in ecosystem
functions before and after eradication of feral goats on an
island, Nakoudo-Jima, in a subtropical archipelago in thenorthwestern Pacific Ocean. In particular, I focus on therelationships between vegetation states and soil chemical
properties (amounts of nutrients and pH) with vegetation
degradation, soil erosion before goat eradication andvegetation recovery after eradication. In addition, I
explore the processes of loss of ecosystem functions due
to disturbances using a conceptual model based onrelationships between ecosystem states and functions.
Finally, I propose a new framework based on the “novel
ecosystem” concept for practical restoration of a native
ecosystem that has been disturbed by invasive species.

2. Location and History of Nakoudo-Jima
Nakoudo-Jima (27º37′–27º38′N, 142º10′–142º11′E,
1.37 km2 in area) is located in the Ogasawara (Bonin)
Islands (Fig. 1). It is likely that Nakoudo-Jima wascovered with forest dominated by native species prior to
the introduction of goats (Shimizu, 1993). Details of thespecies composition of the forests in Nakoudo-Jima prior
to introduction of goats are unclear, but the forests
remaining after goat eradication would be similar to theforests present before the introduction of goats (Shimizu,
1993). The native forests are dominated by Pisonia
umbellifera, Pandanus boninensis, Livistona chinensis,
Neisosperma nakaianum and Ardisia sieboldii (Shimizu,
1993).
Human settlement and the introduction, naturalizationand eradication of goats on Nakoudo-Jima have occurred
over approximately 100 years. It is assumed that people
introduced domestic goats for grazing from 1912
(Shimizu, 1993). All people left the island after 1945 but
the goats remained and became naturalized on NakoudoJima (Japan Wildlife Research Center, 1992). Feral goats
destroyed native vegetation, which led to about 90% of
the original forest transitioning into grassland and bareground (Japan Wildlife Research Center, 1992). The

Fig. 1 L ocation of Nakoudo-Jima in the Ogasawara (Bonin) Islands.

number of goats in 1991 was about 500 (317/km2) (Japan
Wildlife Research Center, 1992). All goats on the island
were eradicated between 1997 and 1999 (Japan Wildlife
Research Center, 2002).

3.	Vegetation Changes Before and After Goat
Eradication
Before the goats were eradicated, they had disturbed
the vegetation on Nakoudo-Jima, resulting in vegetation
degradation and soil erosion. Between 1978 and 1991,
areas of grassland and forest decreased and those of bareground increased (Fig. 2a, b). Shimizu (1993) suggested
that grazing on tree and shrub seedlings by the goats
prevented the regeneration of native forests after thedeath of the canopy trees, causing the forests to transition
to grasslands. Thereafter, some of these grasslands werelost due to continuous grazing and trampling, whichcaused exposure of surface soils. At sites with bareground, vegetation cover was lost and surface soil was
exposed, which would result in erosion of the soil
(Fig. 3a). The eroded soil flowed into the sea (Fig. 3b),which affected coastal communities such as coral andfishes (Japan Wildlife Research Center, 2002).
Overall, vegetation recovery, especially grasslandvegetation, occurred after goat eradication (Fig. 3c).

Changes in Ecosystem Function after Goat Eradication

Fig. 2 
Spatial distribution patterns of forests, grasslands, bareground and other terrain (e.g., cliffs or rock) on NakoudoJima in (a) 1978, (b) 1991 and (c) 2003 based on analyses
of aerial photographs in 1978 (1:10000, Geographical
Survey Institute), 1991 and 2003 (1:10000, Japanese
Ministry of the Environment). These figures were adaptedfrom Hata et al. (2010b).

39

Fig. 3 Ecosystem states on Nakoudo-Jima before and after goat
eradication. (a) Vegetation degradation and soil erosion(photo from 2001), (b) Inner bay with inflow of eroded soil
(photo from 2001), (c) Grasslands that recovered after goat
eradication (photo from 2015), (d) Loss of surface soils
without vegetation cover after goat eradication (photo from2016).

40

K. HATA

Between 1991 and 2003, areas of grassland increased andthose of bare ground decreased (Fig. 2b, c), which would
be related to releases from disturbance by feral goats with
their eradication. Similar changes in vegetation weredetected between 2003 and 2012 (Osawa et al., 2016).
There are two types of grasslands there according to thedominant grass species: non-native perennial grasses,
Paspalum scrobiculatum and P. dilatatum and a native
perennial grass, Zoysia tenuifolia (Hata et al., 2003; Hata
& Kachi, 2012).
There was substantial variation in the extent ofvegetation recovery after goat eradication within theisland, which was spatially heterogeneous (Fig. 2c). The
heterogeneity in vegetation states after the eradication
indicates that vegetation degraded by goat disturbances
does not always recover, even after goat eradication. At
the sites without vegetation recovery, the loss of surface
soil with erosion has continued for more than 15 years
after the eradication (Fig. 3d).

4.	Impacts of Vegetation Degradation and Soil
Erosion on Soil Chemical Properties andPrimary Production
Vegetation degradation and soil erosion with
disturbances by feral goats alters soil environments,
especially soil chemical properties (e.g., amounts oforganic matter, inorganic nutrients and pH), and thealtered soil chemical properties continue even after
eradication of the prevailing disturbance. Indeed, soil
chemical properties and primary production of herbaceous
vegetation on the island after goat eradication would be
related to the occurrence of vegetation degradation andsoil erosion before goat eradication (Hata et al., 2014a).
Significantly lower amounts of nutrients and higher
acidity in the surface soil were detected in 2010 at sites
with vegetation cover in 1991 (Hata et al., 2014b). Thismeans that soils with vegetation degradation and soil
erosion are highly acidic with low nutrient levels, evenafter eradication.
The alteration of soil chemical properties would
result from the loss of surface soil due to erosion, whichis indirectly related to disturbance by feral goats throughvegetation degradation. Amounts of surface soil loss after
goat eradication were higher at sites with large areas ofbare ground in Nakoudo-Jima (i.e., small vegetation
cover) (Hata et al., 2019). This may result from a lack ofsoil accumulation by overlying vegetation (Palacio et al.,2014) and increased soil runoff from exposed ground due
to wind and rainfall (Ludwig et al., 2005). The loss of
surface soil can expose deeper soil horizons, which often
have extremely low nutrient levels and pH on the island(Hiradate et al., 2015).
The alteration of soil chemical properties with soil
erosion can prevent establishment of herbaceous species.
This may contribute to lack of vegetation recovery evenafter goat eradication. Along with nutrient deficiencies inthe subsoil at deeper soil horizons, lower pH in soil canlimit plant growth. For example, aluminum ion dissolves
from soil under lower pH conditions, and can limit plant
growth through aluminum toxicity (Hiradate et al., 2007).
Also, the dissolution of aluminum (Al3+) under lower pH
conditions typically immobilizes labile and inorganic
phosphorus in soils, rendering them unavailable for plants(Bardgett, 2005). Such reductions in amounts of available
nutrients can limit plant growth after goat eradication.
Indeed, most herbaceous species on Nakoudo-Jima 15
years after goat eradication were absent at sites where
soil pH was low (Hata et al., 2019).

5.	Processes of Ecosystem Function Loss due toDisturbance by Feral Goats
The lack of vegetation recovery even after goat
eradication detected on Nakoudo-Jima can be explainedby processes of ecosystem function loss related to
disturbance by feral goats and alteration of soil chemical
properties. According to a conceptual model by
Whisenant (1999), when an intact ecosystem transitions
to more degraded states with disturbance or stress andcrosses a barrier (threshold) between states, ecosystem
functions are reduced and lost (shifting to the left in
Fig. 4). The barrier may be crossed due to biotic or
abiotic factors, preventing the system from returning to a

Fig. 4 Conceptual model representing processes of ecosystem
function loss (e.g., fluxes of matter and energy throughprimary production and decomposition of organic matter)with degradation of ecosystem state adapted from
Whisenant (1999). In the model, each hollow represents analternative ecosystem state, which is a resultant transition
towards a degraded state (moving to the left) due to the
disturbances. There are several barriers (or thresholds, twoin this case) to prevent degradation of the ecosystem state.
In the case of Nakoudo-Jima, both vegetation and soil
structure are intact in Stage 1, vegetation is absent but thesoil structure is intact in Stage 2, and both vegetation andsoil structure are absent. When vegetation becomes so
degraded it has difficulty recovering, the “ball” in the figure
crosses over “biotic barrier.” When soil erosion continues
and the soil functions in the ecosystem (e.g., support ofplant roots and supply of water and nutrients) is lost, the“ball” crosses over “abiotic barrier.”Changes in Ecosystem Function after Goat Eradication
less degraded state. Once the ecosystem state crosses athreshold and transits to a degraded state, it is difficult toreturn to it a less degraded state (shifting to the right in
Fig. 4) without management effort input (e.g., Hobbs &Norton, 1996; Hobbs & Harris, 2001).
According to the conceptual model, processes of
ecosystem function loss on Nakoudo-Jima consist of two
steps. The first step is vegetation degradation and thesecond is soil erosion. On the island, the biotic factorsthat broke the biotic barrier were overgrazing andtrampling by feral goats, resulting in vegetation
degradation. This was an initial loss process affecting
ecosystem functions (from stage 1 to 2 in Fig. 4).
Thereafter, exposure of the surface soil due to vegetation
cover loss resulted in soil erosion, the abiotic factor thatbroke the abiotic barrier. This was a secondary loss
process (from stage 2 to 3 in Fig. 4).
Restoration efforts and strategies for the degradedecosystems on the island would depend on the state of theecosystem. In the first step, vegetation degradation iscaused directly by disturbances by feral goats. In that
ecosystem state, there is loss of vegetation cover but notsoil erosion, suggesting that the soil environment as an
ecosystem function has been not degraded yet. Therefore,
it is likely that the ecosystem state can recover after goat
eradication if plant propagule pressure, e.g., amount ofseed dispersal, is sufficient. Conversely, soil erosion in
the second step is caused by exposure of surface soil andsoil runoff due to wind and rainfall. This process is notdirectly related to disturbances by feral goats but
indirectly. Thus, restoration of ecosystems damaged bysoil erosion after goat eradication becomes difficult
because the soil environment has been lost. These
processes may occur in other island ecosystems. For
example, on Mediterranean islands, grazing by feral goatshas decreased the average plant height, above-groundplant biomass and soil depth, while increasing the amountof exposed bedrock, exerting a partial effect after goat
eradication (Gizicki et al., 2018). For ecosystem
restoration, it is necessary first to prevent further erosionof the surface soil through anthropogenic efforts suchsandbag dams, which can keep ecosystems from crossing
the degradation threshold and winding up in a lower state(Hata et al., 2019). In addition to preventing soil erosion,
it is necessary to facilitate plant establishment on erodedsoil via fertilizer application, seeding and transplanting.

41

nesting results in inputs of nutrients into the soils throughthe supply of deposited feces, egg shells and dead chicks
or adults, which can affect soil chemical properties (e.g.,Anderson & Polis, 1999; Fukami et al., 2006; Morita etal., 2010). Also, physical disturbances such as trampling,
scraping and burrowing for nesting can alter the soil andvegetation structure (Roverts et al., 2007; Grant-Hoffman
et al., 2010; Aoyama, 2013).
Seabird nesting on many islands is prevented byinvasive mammals. In addition to predation of seabird
adults and eggs by invasive rats, foxes and cats (Drake etal., 2011), physical disturbance by invasive ungulates
through overgrazing and trampling can prevent seabirds
from nesting (Coblentz, 1978; Gizicki et al., 2018).
Therefore, eradication of these mammals can restore theecosystem state, allowing nesting to recover (Fig. 5). In
fact, the numbers of seabird nests have increased since
the goat eradication (Japan Wildlife Research Center,2012). This could have both positive and negative effects:
nesting can reduce the herbaceous vegetation biomass but
not affect vegetation cover. It can also increase theamounts of soil nutrients, while reducing soil pH(Aoyama, 2013).
The above-mentioned processes of ecosystem

6.	Interrelationships among Multiple Events
Before and After Goat Eradication
In addition to vegetation degradation and soil
erosion, ecosystem functions on islands before and after
goat eradication could be affected by seabird nesting as
an “ecosystem engineer” through alteration of soil
environments and vegetation states (Smith et al., 2011).
Seabirds usually feed at sea and nest on land. Their

Fig. 5 Seabird nesting on Nakoudo-Jima after goat eradication. (a)Brown booby, Sula leucogaster, nests on grasslandvegetation dominated by a native perennial, Zoysia
tenuifolia, (b) Wedge-tailed shearwater, Puffinus pacificus,
nests under soil (invisible in the photo), which disturb
above-ground vegetation.

42

K. HATAchanges represented in this paper interact with each otherdirectly and indirectly, and these complex interactions
influence changes in ecosystem states (e.g., primary
production, soil chemical properties and species
composition) before and after goat eradication. Hata et al.
(2014b) comprehensively quantified the direct andindirect interactions among multiple factors in NakoudoJima using their Structure Equation Model, a statisticalmodel. According to this statistical model (Fig. 6), there
have been multiple interrelationships among vegetation
states, soil environments and events before and after goat
eradication on this island (Hata et al., 2014b). The model
suggests that individual factors interact with each othernot only directly but also indirectly. For example,
vegetation degradation and consequent erosion of surface
soil before goat eradication can increase soil acidity (redarrow 1 in Fig. 6), which can result in limitation ofprimary production of herbaceous vegetation even after
goat eradication (red arrow 2 in Fig. 6). This means thatsoil erosion can not only increase soil acidity but also
limit primary production indirectly via increased soil
acidity (blue arrow 3 in Fig. 6). Also, Sula leucogaster, adominant seabird species on the island, is more frequently
present on ridges than on slopes and is completely absent
from valleys (red arrow 4 in Fig. 6), and the presence ofseabird nesting is positively related to amounts of soil
nutrients, especially available phosphorus (red arrow 5 inFig. 6). This suggests that topography can indirectly

affect soil chemical properties through seabirds’ choice ofnesting sites (blue arrow 6 in Fig. 6).
This model suggests that vegetation degradation andsoil erosion before goat eradication strongly affectmultiple factors and their interrelationships and therefore
can shift the island ecosystem to alternative states that are
irreversible to the intact state before the goat disturbance.
The model also suggests that seabird nesting can affectsoil environments, which may help recovery from theirreversible ecosystem states.

7.	Future Perspectives
Finally, I discuss restoration and management goals
for island ecosystems that have been disturbed by invasive
species and lost their functions. The ideal goal is an intact
ecosystem undisturbed by invasive species, which ismainly composed of native species. This goal, however,is not always practicable. For example, if extremely
severe disturbances result in decline or extinction of a
population of native species, the population will notrecover even after release from the disturbances. Also,
loss of ecosystem functions caused by disturbances suchas soil erosion on Nakoudo-Jima make it unfavorable forsurvival and growth of plants. Therefore, the more priorand practical goal of restoration and management onhighly disturbed islands such as Nakoudo-Jima should be
attaining sustainable ecosystem functions rather than theFig. 6 Direct and indirect relationships among vegetation states, soil chemical properties and events before and after goat eradication on
Nakoudo-Jima. The figures have been revised by results based on Structural Equation Modeling in Hata et al. (2014b).

Changes in Ecosystem Function after Goat Eradicationconservation of a certain native species or native
diversity.
Recently, quite a number of researchers studying
restoration and management of ecosystems have focusedon the concept of “novel ecosystems” as a goal. Hobbs etal. (2013) defined a novel ecosystem as a system of
abiotic, biotic and social components (and theirinteractions) that, by virtue of human influence, differ
from systems that prevailed historically, having atendency to self-organize and manifest novel qualities
without intensive human management. For restoration toa novel ecosystem, it is more important to achieve an
intact ecosystem similar to the original in terms of
ecosystem functions rather than in terms of species
composition (Hallett et al., 2013). In other words, it is notalways necessary for a restored and managed target
ecosystem to be composed of native species if theirfunctions are similar to the native ones and sustainable.
This concept makes it possible to set more flexible andpractical goals for restoration and management of island
ecosystems.

Acknowledgments
We thank the Ministry of the Environment and theDepartment of National Forests in the Ogasawara Islands
for allowing the author to conduct this study. This work
was partly supported by JSPS KAKENHI Grant Number
25241025, 16H01794, 17K00648 and 19H02978. Twoanonymous reviewers
made numerous valuablecomments that improved this manuscript.
References
Anderson, W.B. and Polis, G.A. (1999) Nutrient fluxes from waterto land: seabirds affect plant nutrient status on Gulf of California
islands. Oecologia, 118, 324–332. Retrieved from https://doi.
org/10.1007/s004420050733
Aoyama, Y. (2013) Alien mammal impacts on seabird populations
and seabird impacts on flora in the Ogasawara Islands. Ph.D.
Thesis, Tohoku University, Miyagi, Japan.
Bardgett, R. (2005) The Biology of Soil: a Community andEcosystem Approach. Oxford University Press, Oxford, UK.
Bullock, D.J., North, S.G., Dulloo, M.E. and Thorsen, M. (2002)
The impact of rabbit and goat eradication on the ecology ofRound Island, Mauritius. In: Veitch, C.R. and Clout, M.N. (eds.),
Turning the Tide: the Eradication of Invasive Species, IUCN SSC
Invasive Species Specialist Group, 53–63. IUCN, Gland,
Switzerland and Cambridge, UK.
Campbell, K.J. and Donlan, C.J. (2005) Feral goat eradication on
islands. Conservation Biology, 19, 1362–1374. Retrieved from
10.1111/j.1523-1739.2005.00228.x (Accessed 8 October 2019)
Carlquist, S. (1974) Island Biology, Columbia University Press,
New York.
Coblentz, B.E. (1978) The effects of feral goats (Capra hircus) on
island ecosystems. Biological Conservation, 13, 279–286.
Retrieved from https://doi.org/10.1016/0006-3207(78)90038-1
Courchamp, F., Chapuis, J.-L. and Pascal, M. (2003) Mammal
invaders on islands: impact, control and control impact.
Biological Reviews, 78, 347–383. Retrieved from 10.1017/

43

S1464793102006061 (Accessed 8 October 2019)
Cox, G.W. (1999) Alien Species in North America and Hawaii:
Impacts on Natural Ecosystems, Island Press, Washington, DC.
Retrieved from https://doi.org/10.1642/0004-8038(2001)118[0278:]
2.0.CO;2
Drake, D.R., Bodey, T.W., Russell, J.C., Towns, D.R., Nogales, M.
and Ruffino, L. (2011) Direct impacts of seabird predators on
island biota other than seabirds. In: Mulder, P.H., Anderson,
W.B., Towns, D.R. and Bellingham, P.J. (eds.) Seabird Islands:
Ecology, Invasion, and Restoration, 91–132. Oxford University
Press, New York. Retrieved from 10.1093/acprof:osobl/9780199735693.003.0004 (Accessed 8 October 2019)
Fukami, T., Wardle, D.A., Bellingham, P.J., Mulder, C.P.H., Towns.
D.R., Yeates, G. W., Bonner, K.I., Durrett, M.S., Grant-Hoffman,
M.N. and Williamson, W.M. (2006) Above- and below-ground
impacts of introduced predators in seabird-dominated island
ecosystems. Ecology Letters, 9, 1299–1307. Retrieved from
10.1111/j.1461-0248.2006.00983.x (Accessed 8 October 2019)
Gizicki, Z.S., Tamez, V., Galanopoulou, A.P., Avramidis, P. andFoufopoulos, J. (2018) Long-term effects of feral goats (Capra
hircus) on Mediterranean island communities: results fromwhole island manipulations. Biological Invasions, 20, 1537–
1552. Retrieved from https://doi.org/10.1007/s10530-017-1645-4
Grant-Hoffman, M.N., Mulder, C.P.H. and Bellingham, P.J. (2010)
Effects of invasive rats and burrowing seabirds on seeds andseedlings on New Zealand islands. Oecologia, 162, 1005–1016.
Retrieved from 10.1007/s00442-009-1500-0 (Accessed 8 October
2019)
Hallett, L.M., Standish, R.J., Hulvey, K.B., Gardener, M.R.,
Suding, K.N., Starzomski, B.M., Murphy, S.D. and Harris, J.A.
(2013) Towards a conceptual framework for novel ecosystems.
In: Hobbs, R.J., Higgs, E.S. and Hall, C.M. (eds.) Novel
Ecosystems: Intervening in the New Ecological World Order,
16–28. Wiley-Blackwell, UK. Retrieved from https://doi.org/
10.1002/9781118354186.ch3
Hamann, O. (1975) Vegetational changes in the Galápagos Islands
during the period 1966-73. Biological Conservation, 7, 37–59.
Retrieved from https://doi.org/10.1016/0006-3207(75)90029-4.
Hamann, O. (1979) Regeneration of vegetation on Santa Fé and
Pinta Islands, Galápagos, after the eradication of goats.
Biological Conservation, 15, 215–236. Retrieved from https://doi.org/10.1016/0006-3207(79)90042-9.
Hamann, O. (1993) On vegetation recovery, goats and giant
tortoises on Pinta Island, Galápagos Ecuador. BiologicalConservation, 2, 138–151. Retrieved from https://doi.org/10.
1007/BF00056130
Hata, K., Kachi, N. and Ichikawa, S. (2003) Vegetation changes in
the Nakoudojima Island after goat eradication. Annual Report ofOgasawara Research, 26, 39–46. (in Japanese)
Hata, K., Suzuki, J.-I. and Kachi, N. (2010a) Fine-scale spatial
distribution of seedling establishment of the invasive plant,
Leucaena leucocephala, on an oceanic island after feral goat
extermination. Weed Research, 50, 472–480. Retrieved from
10.1111/j.1365-3180.2010.00795.x (Accessed 8 October 2019)
Hata, K., Suzuki, J-I. and Kachi, N. (2010b) Vegetation changes
between 1978, 1991 and 2003 in the Nakoudojima island that
had been disturbed by feral goats. In: Kawakami, K. and Okochi,
I. (eds.), Restoring the Oceanic Island Ecosystem, 85–91.
Springer, Tokyo. Retrieved from https://doi.org/10.1007/978-4431-53859-2_14 (Accessed 8 October 2019)
Hata, K. and Kachi, N. (2012) Nine yeas changes in herbaceous
vegetation on the Nakoudojima island after goat eradication.
Annual Report of Ogasawara Research, 35, 23–28. (in Japanese)
Hata, K., Kohri, M., Morita, S., Hiradate, S. and Kachi, N. (2014a)
Fine-scale distribution of aboveground biomass of herbaceous
vegetation and soil nutrients on an oceanic island after goat

44

K. HATA

eradication are correlated with grazing damage and seabird
nesting. Pacific Conservation Biology, 20, 344–353. Retrieved
from 10.1071/PC140344 (Accessed 8 October 2019)
Hata, K., Kohri, M., Morita, S., Hiradate, S. and Kachi, N. (2014b)
Complex interrelationships among aboveground biomass, soil
chemical properties, and events caused by feral goats and their
eradication in a grassland ecosystem of an island. Ecosystems,
17, 1082–1094. Retrieved from https://doi.org/10.1007/s10021014-9780-6
Hata, K., Osawa, T., Hiradate, S. and Kachi, N. (2019) Soil erosion
alters soil chemical properties and limits grassland plantestablishment on an oceanic island even after goat eradication.
Restoration Ecology, 27, 333–342. Retrieved from https://doi.
org/10.1111/rec.12854
Hiradate, S., Ma, J.F. and Matsumoto, H. (2007) Strategies ofplants to adapt to mineral stresses in problem soils. Advances inAgronomy, 96, 65–132. Retrieved from https://doi.org/10.1016/
S0065-2113(07)96004-6
Hiradate, S., Morita, S., Hata, K., Osawa, T., Sugai, K. and Kachi,
N. (2015) Effects of soil erosion and seabird activities on
chemical properties of surface soils on an oceanic island in
Ogasawara Islands, Japan. Catena, 133, 495–502. Retrieved
from https://doi.org/10.1016/j.catena.2015.04.013
Hobbs, R.J. and Norton, D.A. (1996) Towards a conceptual
framework for restoration ecology. Restoration Ecology, 4, 93–110. Retrieved from https://doi.org/10.1111/j.1526-100X.1996.
tb00112.x
Hobbs, R.J. and Harris, J.A. (2001) Restoration ecology: repairing
the earth’s ecosystems in the new millennium. Restoration
Ecology, 9, 239–246. Retrieved from https://doi.org/10.1046/
j.1526-100x.2001.009002239.x.
Hobbs, R.J., Higgs, E.S. and Hall, C.M. (2013) Defining novel
ecosystems. In: Hobbs, R.J., Higgs, E.S. and Hall, C.M. (eds.)
Novel Ecosystems: Intervening in the New Ecological World
Order, 58–60. Wiley-Blackwell, UK. Retrieved from https://doi.
org/10.1002/9781118354186.ch6
Japan Wildlife Research Center (1992) Report on the Urgent
Research about Damage of Feral Goats on Plants and Animals
in the Ogasawara Islands, Japan Wildlife Research Center,
Tokyo, Japan. (In Japanese)
Japan Wildlife Research Center (2002) Report on the Research of
Vegetation Recovery in the Ogasawara National Park,
Ogasawara branch of Tokyo Metropolitan Government, Tokyo,
Japan. (in Japanese)
Japan Wildlife Research Center (2012) Report on the Research of
Vegetation Recovery in the Ogasawara National Park,
Ogasawara branch of Tokyo Metropolitan Government, Tokyo,
Japan. (in Japanese)
Kessler, C.C. (2002) Eradication of feral goats and pigs andconsequences for other biota on Sarigan Island, Commonwealthof the Northern Mariana Islands. In: Veitch, C.R. and Clout,
M.N. (eds.) Turning the Tide: the Eradication of Invasive
Species, IUCN SSC Invasive Species Specialist Group, 132–140.
IUCN, Gland, Switzerland and Cambridge, UK.
Leathwick, J.R., Hay, J.R. and Fitzgerald, A.E. (1983) The
influence of browsing by introduced mammals on the decline ofNorth Island kokako. New Zealand Journal of Ecology, 6, 55–70.
Loope, L.L. and Scowcroft, P.G. (1985) Vegetation response within
exclosures in Hawaii: A review. In: Stone, C.P. and Scott, J.M.
(eds.), Hawaii’s Terrestrial Ecosystems: Preservation andManagement, 377–400. University of Hawaii, Honolulu, USA.
Loope, L.L., Hamman, O. and Stone, C.P. (1988) Comparative
conservation biology of oceanic archipelagoes. Bioscience, 38,
272–282. Retrieved from 10.2307/1310851 (Accessed 8 October
2019)
Ludwig, J.A., Wilcox, B.P., Breshears, D.D., Tongway, D. J. andImeson, A.C. (2005) Vegetation patches and runoff-erosion asinteracting ecohydrological processes in semiarid landscapes.
Ecology, 86, 288–297. Retrieved from https://doi.org/10.1890/
03-0569
Morita, S., Kato, H., Iwasaki, N., Kusumoto, Y., Yoshida, K. andHiradate, S. (2010) Unusually high levels of bio-available
phosphate in the soils of Ogasawara Islands, Japan: putative
influence of seabirds. Geoderma, 160, 155–164. Retrieved fromhttps://doi.org/10.1016/j.geoderma.2010.09.008
Mueller-Dombois, D. and Spatz, G. (1975) The influence of feral
goats on the lowland vegetation in Hawaii Volcanoes National
Park. Phytocoenologia, 3, 1–29.
Osawa, T., Hata, K. and Kachi, N. (2016) Eradication of feral goatsenhances expansion of the invasive shrub Leucaena
leucocephala on Nakoudo-jima, an oceanic island. Weed
Research, 56, 168–178. Retrieved from https://doi.org/10.1111/
wre.12198
Palacio, R.G., Bisigato, A.J. and Bouza, P.J. (2014) Soil erosion inthree grazed plant communities in northeastern Patagonia. Land
Degradation & Development, 25, 594–603. Retrieved fromhttps://doi.org/10.1002/ldr.2289
Roberts, C.M., Duncan, R.P. and Wilson, K.J. (2007) Burrowing
seabirds affect forest regeneration, Rangatira Island, Chatham
Islands, New Zealand. New Zealand Journal of Ecology, 31,
208–222.
Shimizu, Y. (1993) Vegetation of Mukojima Island Group in the
Bonin Ogasawara Islands with reference to the ecology of
Ardisia dominant forest and the influence of feral goats.
Komazawa Geography, 29, 9–58. (In Japanese)
Shimizu, Y. (2003) The nature of Ogasawara and its conservation.
Chikyu Kankyo, 7, 3–14. (In Japanese)
Smith, J.L., Mulder, C.P.H. and Ellis, J.C. (2011) Seabirds as
ecosystem engineers: nutrient inputs and physical disturbance.
In: Mulder, P.H., Anderson, W.B., Towns, D.R. and Bellingham,
P.J. (eds.) Seabird Islands: Ecology, Invasion, and Restoration,
27–55. Oxford University Press, New York. Retrieved from
10.1093/acprof:osobl/9780199735693.003.0002 (Accessed 8
October 2019)
Stone, C.P, Cuddihy, L.W. and Tunison T. (1992) Response of
Hawaiian ecosystems to removal of pigs and goats. In: Stone,
C.P, Cuddihy, L.W. and Tunison T. (eds.), Alien Plant Invasions
on Native Ecosystems in Hawaii: Management and Research,
666–702. Honolulu, University of Hawaii Cooperative National
Park Studies Unit.
Whisenant, S. (1999) Repairing Damaged Wildlands: a ProcessOrientated, Landscape-scale Approach, 1, Cambridge University
Press.
Weller, S.G., Cabin, R.J., Lorence, D.H., Perlman, S., Wood, K.,
Flynn, T. and Sakai, A.K. (2011) Alien plant invasions,introduced ungulates, and alternative states in a mesic forest in
Hawaii. Restoration Ecology, 19, 671–680. Retrieved from
10.1111/j.1526-100X.2009.00635.x (Accessed 8 October 2019)

Kenji HATA
Kenji Hata, Ph.D, is an associate professor at the
Nihon University, College of Commerce. He
received his PhD from the Graduate School of
Science, Tokyo Metropolitan University. His
research field is plant ecology, especially invasion
ecology in island ecosystems. He has focused on
impacts of disturbances caused by invasive
animals and plants and their eradication on dynamics of plant populations,community structure and ecosystem function.
(Received 8 October 2019, Accepted 25 November 2019)