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\begin{document}

\title{The benefits of land sparing are limited by invasions of alien species}



\author[1]{Magdalena Lenda}%
\author[2]{Piotr Skórka}%
\author[3]{Johannes Knops}%
\author[4]{Dorota Kotowska}%
\author[5]{Dawid Moroń}%
\author[6]{Hugh Possingham}%
\affil[1]{The University of Queensland - Saint Lucia Campus}%
\affil[2]{Affiliation not available}%
\affil[3]{Xi'an Jiaotong-Liverpool University}%
\affil[4]{Institute of Nature Conservation Polish Academy of Sciences}%
\affil[5]{Polish Academy of Sciences}%
\affil[6]{University of Queensland}%


\vspace{-1em}



  
  \date{May 22, 2024}


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\selectlanguage{english}
\begin{abstract}
Globally, agriculture intensification is a dominant driver of
biodiversity loss. The concepts of land sparing and land sharing are
alternatives to seek a balance between maintaining and restoring
biodiversity while producing adequate food. To date, land sparing has
been suggested as the best strategy to maintain biodiversity, but very
few intact lands remain on Earth for sparing. Recently, international
policies for nature conservation have proposed removing land from
agricultural management to meet the need for more land sparing. However,
the idea of land sparing has not considered the risk of biological
invasions in abandoned land. Many abandoned agricultural lands are
colonized by invasive species, creating monospecific patches with low
biodiversity. Such invasions have cascading effects on other trophic
levels and decrease ecosystem services in nearby agricultural fields,
which negatively impacts yield. Moreover, invaded abandoned fields have
lower biodiversity than extensively managed agricultural land. Thus, the
risk of inducing plant invasions and triggering detrimental impacts on
biodiversity, ecosystem services, and agricultural yields limits land
sparing from abandonment as a conservation strategy. Our simulations
also suggest that land sharing may be the best solution for sustaining
biodiversity when the risk of invasion is high.%
\end{abstract}%



\sloppy


\textbf{The benefits of land sparing are limited by invasions of alien
species}

Magdalena Lenda\textsuperscript{1,2*}, Piotr Sk\selectlanguage{ngerman}órka\textsuperscript{2},
Dorota Kotowska\textsuperscript{2}, Dawid Moro\selectlanguage{polish}ń\selectlanguage{english}\textsuperscript{3}, Hugh
P. Possingham\textsuperscript{1}, Johannes M.H. Knops\textsuperscript{4}

\textsuperscript{1} School of Biological Sciences, The University of
Queensland, Brisbane, Queensland, Australia, email:
Magdalena.lenda1@gmail.com, h.possingham@uq.edu.au

\textsuperscript{2} Institute of Nature Conservation, Polish Academy of
Sciences, Mickiewicza 33, 31-120 Krak\selectlanguage{ngerman}ów, Poland, Skorasp@gmail.com,
kotowska@iop.krakow.pl

\textsuperscript{3} Institute of Systematics and Evolution of Animals,
Polish Academy of Sciences

S\selectlanguage{polish}ł\selectlanguage{english}awkowska 17, 31-016 Krak\selectlanguage{ngerman}ów, Poland, dawidmoron1@gmail.com

\textsuperscript{4} Department of Health and Environmental Sciences at
Xi'an Jiaotong Liverpool University in Suzhou, Jiangsu, China,
Johannes.Knops@xjtlu.edu.cn

\textbf{Short running title:} Land sparing limited by biological
invasions

\textbf{Keywords:} biodiversity, cultural landscapes, ecosystem
services, invasion risk, invasive species, land sharing, land sparing

\textbf{The type of article:} Viewpoints

\textbf{Number of words in abstract:} 149

\textbf{Number of words in the main text:} 1755

\textbf{Number of references} : 34\textbf{Number of figures:} 2

\textbf{Number of tables:} 0\textbf{Number of text boxes:} 0

\textbf{*corresponding author:} Magdalena.lenda1@gmail.com, tel.
+48~530~344~595, fax: -

\textbf{Authorship statement:} M.L., PS, J.M.H.K, H.P., D.M, and D.K.
conceptualized the study and wrote the original draft; D.K., P.S., and
M.L. conducted formal analysis and visualization; M.L., P.S., and H.P.
provided resources, acquired funding, and administered the project;
M.L., J.M.H.K., P.S., H.P, D.K., and D.M. reviewed and edited the
manuscript.

\textbf{Data availability statemen} t\textbf{:} All data are attached to
the manuscript and will be made publicly available in Dryad after the
manuscript is accepted for publication.

\textbf{Abstract}

Agriculture intensification is a dominant driver of biodiversity loss.
Land sparing has been suggested as the best strategy to maintain
biodiversity, but very few intact lands remain on Earth for sparing.
Recently, international policies for nature conservation have proposed
removing land from agricultural management to meet the need for more
land sparing. However, the idea of land sparing has not considered the
risk of biological invasions in abandoned land. Many abandoned
agricultural lands are colonized by invasive species, creating
monospecific patches. Such invasions decrease biodiversity and have
cascading effects on other trophic levels and decrease ecosystem
services in nearby agricultural fields, which may negatively impacts
yield. Thus, the risk of inducing plant invasions and triggering
detrimental impacts on biodiversity, ecosystem services, and
agricultural yields limits land sparing from abandonment as a
conservation strategy. Our simulations suggest that land sharing may be
the best nature conservation strategy in invaded landscapes.

\textbf{Main text}

Agricultural intensification and further conversion of natural
ecosystems into agricultural lands are global threats to biodiversity,
causing extinctions of native fauna and flora. By 2050, the human
population may reach 9.6 billion (Gerland et al. 2014)---feeding more
and more people will increasingly demand more agricultural production
and land---leading to continuous agricultural intensification. This is
expected to add to further land clearing, pesticide and herbicide use,
soil pollution, water shortages, and greenhouse gas emissions
contributing to climate change.

Two concepts from classic landscape ecology have been proposed to
address this looming biodiversity crisis\textbf{:} 1) \emph{land
sparing} and 2) \emph{land sharing} (Green et al. 2005). Land sparing
refers to `sparing' of nature; coupling the intensive use of
agricultural land on one hand and saving intact areas where wildlife and
biodiversity thrive. Land sparing assumes that primary habitats are the
most biodiverse; that agricultural lands have very little biodiversity
value and that preserving natural lands, while intensifying management
of agricultural areas can maintain biodiversity while achieving
sufficient yields to feed humans (Gibson et al. 2011, Laurance et al.
2014). In contrast, land sharing is an integrative approach, defined as
accepting lower yields in agricultural lands combined with biodiversity
conservation and extensive land management (Lindenmayer and Cunningham
2013). Land sharing/sparing concepts have been developed and tested
mostly in pristine areas, such as intact tropical forests, where
agricultural land clearing creates a drastic land change into row crop
agriculture or rangelands. Studies conducted in tropical forests suggest
that land sparing is a better strategy for maintaining regional species
diversity while achieving agricultural yield goals (Phalan et al. 2011,
Kamp et al. 2015). However, this situation is not relevant to regions
invaded by alien species, which may complicate land sharing and land
sparing models.

Most of the world is not pristine and has been in human use for
hundreds, if not thousands of years, which includes virtually all of
Europe. In the European Plain, the only temperate, terrestrial pristine
nature remaining is the Bia\selectlanguage{polish}ł\selectlanguage{english}owie\selectlanguage{polish}ż\selectlanguage{english}a Forest in Central Europe. Outside of
Antarctica, thousands of years of agricultural management have shaped
cultural landscapes often with unique flora and fauna, which has adapted
and coevolved with land management. Over 8000 years ago, prior to
Neolithic agriculture, Europe was mostly a wooded continent. Starting
6000 years ago, forests have been progressively cleared for agriculture
and transformed into managed grasslands and tilled crop fields (Roberts
et al. 2018). The management of these agricultural landscapes created by
humans has shaped complex ecosystems and regions with high biodiversity
values, that depend on continuous agriculture (Rosin et al. 2016).
Nature conservation programs such as ``Natura 2000'', which is the
oldest and largest in the European Union, promote extensive land
management to maintain local biodiversity. For example, in Central
Europe, many protected insects, birds, and plant species depend on
extensive land management, such as mowing or cattle grazing.
Low-intensity management of grasslands, heathlands, and peatlands
supports threatened and declining species, such as large blue
butterflies, \emph{Phengaris teleius} and \emph{P} . \emph{nausithous} ,
both flagship species in European biodiversity conservation. Many
protected bird species occur only in managed landscapes, such as ortolan
bunting (\emph{Emberiza hortulana} ) or corncrake (\emph{Crex crex} ), a
grassland-specialized bird vulnerable to extinction (IUCN). Mown or
grazed meadows are also important for plants such as threatened orchids,
Siberian iris (\emph{Iris sibirica} ), globeflower (\emph{Trollius
europaeus),} chess flower (\emph{Fritillaria meleagris} ), and crocus
(\emph{Crocus scepusiensis} ). However, currently, these
agriculture-associated habitats have the worst conservation status among
all ecosystems (Pe'er et al. 2014). The increasing demand for food
continues to drive agricultural intensification in Europe. Aided by
subsidies, the scale and intensity of agricultural operations is
increasing throughout the EU with an increase in agrochemical inputs,
such as fertilizers. These processes have led to a continuing decline in
farmland biodiversity (Tryjanowski et al. 2011).

Although managed agricultural landscapes can harbor high levels of
biodiversity, in theoretical nature conservation, one may suggest
abandoning this land to create new spared areas designated for nature
conservation. Such theoretical considerations and the establishment of
new spared areas from already managed land due to agricultural
management cessation have already been applied in Europe. An
international nature conservation idea, ``Rewilding'', described
recently in the journal Science proposed to abandon agricultural land or
repurpose previously abandoned post-agricultural land into new nature
conservation areas (Navarro and Pereira 2012, Sylv\selectlanguage{ngerman}én and Windstrand
2015, Perino et al. 2019). Similarly, since 2013, the European Union
(EU) ``Greening policy'' has advocated abandoning at least 5\% of arable
land to create permanent set-aside land (i.e., ecological focus areas)
such as fallow lands, afforested areas, field margins, hedges, buffer
strips, etc. (Van Zeijts et al. 2011, Hauck et al. 2014). Both the
``Rewilding'' and ``Greening policy'' resemble the land sparing concept,
as both rely on reestablishing natural lands within landscapes that are
currently entirely, actively managed. In these policies, agricultural
land abandonment and natural secondary succession are usually combined
with further agricultural intensification (Van Zeijts et al. 2011, Hauck
et al. 2014, Sylvén and Windstrand 2015, Perino et al. 2019). The
Rewilding idea emphasized the positive effect of land abandonment on
nature conservation, as has happened in Chernobyl after the nuclear
catastrophe (Perino et al. 2019). However, none of these sparing
concepts propose a specific strategy for landscapes threatened by alien
species invasions. When invaded, such areas also become propagule
sources that further threaten other areas designated for nature
conservation. In a parallel to the Chernobyl vegetation succession,
abandoned paddy fields at Fukushima have become dominated by alien
invasive goldenrod \emph{Solidago altissima} within one year after the
nuclear catastrophe, which resulted in agricultural land abandonment in
the area (Fig. S1, Yamashita et al. 2014).

The theoretical concept of land sparing and land sharing together with
the applied nature conservation policies as ``Rewilding'' and
``Greening'' omit scientific, published data which show that abandoned
agricultural land is frequently threatened by invasive, alien plant
species (Figs. 1 \& 2, Cramer et al. 2008, Lenda et al. 2021). This
plant invasion risk has not been addressed in the land sharing/land
sparing conceptual framework and in practical solutions. Invasive
species need to be considered because they can disturb natural
succession (Gusev 2015), affect fire regimes (Otero et al. 2015),
decrease native biodiversity of plants, pollinators, ants, and birds
(Fig. 2, Moro\selectlanguage{polish}ń \selectlanguage{english}et al. 2009, Sk\selectlanguage{ngerman}órka et al. 2010, Lenda et al. 2013), and
homogenize ecosystems (Lenda et al. 2019). For example, in Central
Europe, up to 90\% of abandoned agricultural land is dominated by alien
goldenrods \emph{Solidago} sp. (\emph{S. canadensis} and \emph{S.
gigantea} ) (Szymura et al. 2016, Lenda et al. 2019, 2021). Goldenrods
create homogenous habitat patches with up to 100\% dominance within just
a few years, (Fig. 1, Moro\selectlanguage{polish}ń \selectlanguage{english}et al. 2009, Lenda et al. 2019) that
negatively affect ecosystem service providers (Fig. 2) and decrease
their functional diversity (Patchey and Gaston 2006). Invasive species
can cause up to 70\% decline in wild pollinator abundance (Fig. 2, Moro\selectlanguage{polish}ń
\selectlanguage{english}et al. 2009, 2019), and a 50\% decline in farmland bird abundance and
ant diversity (Fig. 2, Sk\selectlanguage{ngerman}órka et al. 2010, Lenda et al. 2013). Thus, if
invasive species establish dominance in spared ``natural'' land, the
biodiversity of such areas would be much lower than that of extensively
managed agricultural habitats (Fig. 1; Moro\selectlanguage{polish}ń \selectlanguage{english}et al. 2009, Sk\selectlanguage{ngerman}órka et al.
2010). In addition, creating such ``natural areas'' using agricultural
land abandonment and land sparing in the presence of invasive plant
species will lower native species richness and abundance by increasing
invasion on new, post-agricultural land. We also demonstrated this
effect on birds recorded from managed fields, non-invaded abandoned
fields, and invaded abandoned fields (Fig. 2). Using simulations, we
created virtual landscapes varying in cover of abandoned fields in two
scenarios: with and without invasions (see description of Methods in
Supplementary material). It was clear that non-invaded land sparing
(land abandonment) increases bird species richness (up to about 40\%
cover in a landscape) and abundance in an agricultural landscape,
however, there was no gain in bird diversity if the abandoned land was
invaded (Fig. 2, details in Supplementary material).

The problem of alien plant species invading abandoned lands is a global
problem. For example, dense stands of the invasive grass \emph{Saccharum
spontaneum} prevent forest regeneration in abandoned pastures in Panama
(Joo Kim et al. 2006). The grass invasion of \emph{Ampelodesmos
mauritanica} on abandoned farmland in Catalan, Spain increases fire
frequency and intensity (Grigulis et al. 2005), which increases soil
erosion (Otero et al. 2015).

In this study, based on our new and earlier results, we suggest that
land sharing may be the best solution for sustaining biodiversity when
the risk of invasion is high. This is because land management practices
such as plowing, cutting, and grazing, even if they are undertaken
extensively, usually prevent the successful establishment and spread of
invasive alien species (Fig. 1). A clear example of this are the recent
Persian Walnut and goldenrod invasions in Central Europe. Seed catching
birds each year carry Persian walnut seeds over distances up to 1 km
from a seed source, and bury them in arable fields, creating a seedbank.
These walnut seeds germinate and grow; however, each year's land
management, such as plowing and cutting, prevents establishment and
thereby invasion (Fig. 1, Lenda et al. 2012, 2018). The mechanism of
goldenrod invasion is similar, with the difference being that goldenrod
seeds are wind-dispersed (Fig. 1). In this case, with land abandonment
and management cessation, goldenrod seedlings can establish and become
dominant in agricultural lands.

Vast land abandonment and/or management cessation allows the
establishment of invasive plants in agricultural lands. Seeds of many
invasive species are already present in the soil; hence, after
germination, fast-growing, highly competitive, and often allelopathic
seedlings can achieve dominance. Furthermore, these invaded abandoned
agricultural lands can become hotspots of invasive species dominance
that can spread further into other natural landscape elements. Thus, a
land sparing strategy in such an environment promotes further
progression of plant invasions.

If the land sparing concept is intended to improve food production and
biodiversity conservation, intensively managed cropland alongside
invaded spared land could be a catastrophe for both agriculture and
biodiversity. This is because biodiversity in agricultural ecosystems
provides biodiversity and ecosystem services. We believe that land
sharing mitigates many of the dangerous consequences of large-scale
invasions.

\textbf{ACKNOWLEDGEMENTS}

We are grateful to Kerrie A. Wilson and Adrian Ward for discussions and
advice. This work was supported by the Australian Research Council
Centre of Excellence for Environmental Decisions CE11001000104, Iuventus
Plus, Polish Ministry of Science and Higher Education grant number:
IP2012 029472, Mobilnosc Plus, Polish Ministry of Science and Higher
Education 1324/1/MOB/IV/15/2016/0, and the Australian Government.

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\textbf{Figures}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Fig. 1. Conceptual framework of invasive plant species spread into
abandoned agricultural lands, showing the ecological mechanism driving
the invasion. This model is applicable when invasive plant species are
present in the landscape and agricultural land is abandoned for nature
conservation. The model is based on walnut \emph{Juglans regia} and
goldenrod \emph{Solidago sp.} invasions but can also be applied to other
taxa. A) Landscape elements, such as backyards and already abandoned
fields contain walnut and goldenrod plants that are seed sources. B)
Birds collect and disperse seeds (walnut) or seeds are dispersed by wind
(goldenrod). C) Birds cache seeds into managed arable fields, pastures,
and meadows (Lenda et al. 2012); here rooks (\emph{Corvus frugilegus} )
cache walnut seeds. Wind dispersed seeds are carried and deposited
randomly, including in sites such as managed agricultural land
(goldenrod). In both cases, dispersed seeds form a soil seedbank. D)
Seeds germinate and grow. E) Invasive plant seedlings are eliminated by
agricultural management in a land sharing strategy. F) Although the
plant invasion risk is high because seed sources and dispersers are
present, the invasion does not progress. The invasion is stopped by
agricultural land use (here plowing), which damages seeds and seedlings,
thus the native biodiversity remains. G) In a land sparing strategy,
seedlings are no longer damaged by agricultural management after land
abandonment. H) Land use change and land abandonment including
management cessation allow seeds of invasive species to germinate, grow
into mature plants, and create monocultures. Here, goldenrod invasion
can be seen after 2 years of agricultural field abandonment. The
monospecific goldenrod patches drastically reduce biodiversity of native
plants, pollinators, ants and birds, while increasing soil N (see Fig.
2). Scenario for the walnut invasion is similar. This mechanism clearly
shows that land sparing is an unfavorable strategy in the presence of
invasive species. In such sites, land sharing is the best strategy,
because it prevents local biodiversity from extinctions caused by
invasive species.\selectlanguage{english}
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Fig. 2. Species richness (A) and abundance (B) of the ecosystem service
providers in invaded (orange) and not invaded (blue) agricultural land.
Means with 95\% confidence intervals are shown. Abundance of plants
represents the mean cover of native plants per plot, for insect
pollinators it is the mean number of individuals per 200 m transect, for
ants it is the number of their nests in a 100 m\textsuperscript{2} plot
and for birds it is the number of breeding pairs in a habitat patch.
Data for vascular plants, bees, butterflies, and hoverflies recalculated
from Moro\selectlanguage{polish}ń \selectlanguage{english}et al. (2009), data for ants taken from Lenda et al. (2013)
and data on birds are from Sk\selectlanguage{ngerman}órka et al. (2010). Unpublished data from
bird mapping in abandoned fields (both invaded and not invaded by
goldenrods) and managed fields were used to demonstrate how different
proportions of spared land may affect bird species richness (C) and
number of breeding pairs (D) in landscapes with no invasion of
goldenrods (blue) and under the invasion (orange). Virtual landscapes of
about 1 km\textsuperscript{2} were created from managed fields and
abandoned fields (spared land) by a random selection of the real data.
The proportion of spared land varied from 0 (only managed fields) to
100\% (only abandoned fields) for two scenarios (i.e., invaded and not
invaded landscape). For each cover of spared land, 100 landscapes were
simulated. Curves are general additive models fitted to the data
(details in Supplementary material 1).

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