Global impacts of exotic eucalypt plantations on wildlife

ABSTRACT

The establishment of exotic tree plantations poses a pervasive threat to wildlife across the globe. Among the most important tree species used for forestry purposes worldwide are members of the genus Eucalyptus, which have now been established in at least 107 countries outside of their native range. When introduced into non‐native areas, eucalypt plantations are associated with myriad novel challenges for native fauna, and have often been associated with reductions in the biodiversity of local communities. However, similar to other anthropogenic habitats, eucalypt plantations can also create novel opportunities for species that can allow them to survive and thrive in these novel environments. In this review, we use eucalypt plantations as a case study for understanding the ecological and evolutionary responses of wildlife to anthropogenic habitat loss and change. We begin by summarising the main avenues of research addressing the study of wildlife responses at the individual, community, and ecosystem levels, and highlight critical research gaps. We also consider the characteristics of different types of eucalypt plantations and how such attributes are linked with the ability of animals to respond appropriately to the establishment of plantations, and summarise important considerations for the conservation of animal communities in these human‐altered habitats.

I. INTRODUCTION

Intensive forestry is among the most widespread forms of human land‐use change, and poses a major threat to biodiversity globally due to the rapid and large‐scale demands of an ever‐growing human population (Fitzherbert et al., ²⁰⁰⁸; Acevedo‐Whitehouse & Duffus, ²⁰⁰⁹; Pyšek et al., ²⁰¹²; Iglesias‐Carrasco, Wong & Jennions, ^2022c). A prime example of this global environmental change is the planting of alien tree species (Pyšek et al., ²⁰¹²; Van Kleunen et al., ²⁰¹⁵), which began in the early 19th century and has accelerated rapidly during the 20th century. The genus Eucalyptus, which comprises more than 800 species, is the most extensively grown and globally expanded broadleaf tree taxon used in forestry (Coppen, 2002; Wingfield et al., ²⁰¹⁵). They are native predominantly to Australia (28 M ha), with a small number of species also occurring naturally in Indonesia, the Philippines, and Papua New Guinea (Chippendale, 1988). As a genus, eucalypts have been introduced and established across tropical, subtropical and temperate regions around the world (see regions marked in yellow in Fig. 1). In some areas the establishment of eucalypt plantations has taken place at the expense of native vegetation, including forests and open areas such as grasslands, while in others, eucalypts have been introduced to new areas with the aim of afforesting already degraded areas (Fig. 2). Regardless, the area covered by some of the most widely used eucalypt species has increased rapidly, from <1 million ha in 1950 to <20 million ha in 2015 (Wingfield et al., ²⁰¹⁵).

Fig. 1.

Countries marked in yellow represent those in which exotic eucalypt plantations have been established. The regions in which eucalypts are native are marked in orange. Information on the presence of these plantations was collected from Coppen (2002) and complemented by a systematic country‐by‐country search (e.g. “Namibia eucalypt plantation”) in Google Scholar. The map represents a reliable estimate of the magnitude of the global presence of these exotic plantations, with 107 countries recorded to date, rather than the current extent of the plantations within each country (Alaska state of USA is not highlighted in yellow to avoid increasing the overrepresentation of eucalypt plantations in the map), which shows different extensions that were not evaluated in this work. Green circles show the geographic distribution of the studies (N = 110) used for the exploration of the effects of eucalypt plantations at the species and community level. The size of the circle represent the relative abundance of studies (out of the 110) carried out in each country. Animal silhouettes represent the taxonomic groups most explored in each country. Note the strong geographical bias towards studies carried out in Brazil, which comprises 63 out of the 110 studies used in this review.

Fig. 2.

Summary of the main habitat characteristics that are affected during the transformation of native vegetation or degraded land into eucalypt plantations. The potential consequences of these changes for wildlife include: (i) altered habitat structure can lead to individual‐ and community‐level changes due to disturbed communication and changes in niche availability; (ii) altered resources result in changes in foraging, nesting and habitat use; (iii) release of secondary compounds can lead to shifts in behaviour and physiology; (iv) high toxicity leads to changes in feeding behaviour, increased stress and impaired physiology; (v) changes to microbial communities can result in altered pathogen dynamics and species interactions; (vi) hydrological shifts can lead to aquatic ecosystem‐level effects and a reduction in suitable habitat for species with low tolerance to desiccation; (vii) different leaf litter can change feeding behaviour and organic matter decomposition dynamics; (viii) increased risk of bushfires can potentially interact with other stressors and in so doing, affect wildlife at the individual, community and ecosystem levels. Illustrations for each habitat type were created with ChatGPT.

The rapid global expansion of eucalypt plantations is due to their fast growth and profitability, with eucalypt products being used in the paper industry, for timber and firewood, as well as in medical and cosmetic products (Coppen, 2002). Eucalypt plantations can include highly managed monocultures as well as naturalised eucalypt stands that result from the abandonment of plantations or the afforestation of degraded areas. In this review, we use the term plantation to encompass areas planted with these trees outside their native region, regardless of their structure and management. Hence, we not only consider plantation stands that are managed as monocultures, but also abandoned plantations, as well as plantations of different ages and sizes, and areas planted for forestry or as part of re/afforestation practices. However, although in some specific cases we mention examples of the effect of sparsely planted trees, in general we focus on relatively large areas covered with eucalypt trees, rather than, for example, trees planted in small lines as windbreaks.

Eucalypt plantations are associated with changes in biotic and abiotic conditions when compared with the vegetation they replace (Calviño‐Cancela, Rubido‐Bará, & van Etten, 2012; Juan‐Ovejero et al., ²⁰²⁵; Cordero‐Rivera, Martínez‐Álvarez & Álvarez, ²⁰¹⁷; Ferreira et al., ²⁰¹⁶; Da Silva et al., ²⁰¹⁹) (summarised in Fig. 2). When replacing native vegetation, for example, such differences are driven largely by the simplified and homogeneous environments that these plantations create, leading to environmental conditions that are often very different from the natural settings in which native species have evolved. The problem is exacerbated in managed eucalypt plantations (e.g. monocultures) where continuous cycles of logging result in highly disturbed environments that can alter physicochemical properties (Cook, Binkley & Stape, 2016; Zhou et al., ²⁰⁰²) and, consequently, threaten biodiversity in multiple ways (Fig. 2). Eucalypt plantations also represent novel environments for wildlife, the ecological and evolutionary consequences of which have often been overlooked or under‐appreciated. Thus, eucalypt plantations provide a valuable case study for understanding and predicting the impacts of anthropogenic pressures on natural systems, as well as the rapid evolutionary and ecological responses of wildlife to environmental change resulting from human activity.

Accordingly, our review aims to present the current state of knowledge about the impacts of eucalypt plantations at the individual, community, and ecosystem levels, as well as to uncover urgent research gaps for ecological and evolutionary research and conservation. To this end, we gathered and analysed information from studies that have investigated the effect of exotic eucalypts on wildlife, excluding native areas in Australia and South‐east Asia (see online Supporting Information, Appendix S1 and Fig. S1, for methodology). We excluded studies that focused on the interaction between eucalypts and pest species or pest species dynamics, since, due to the economic impact of pests in these plantations, the large number of studies on pest species warrants a separate review (see e.g. Paine, Steinbauer & Lawson, ²⁰¹¹). Our study, therefore, represents a comprehensive global overview of the effects of intensive forestry by eucalypts on wildlife.

II. INDIVIDUAL‐LEVEL RESPONSES

Environmental changes caused by the establishment of exotic eucalypt plantations – including altered habitat structure and changes in the availability of resources, such as food, nesting places, or refuges (Fig. 2, see references in Table S1) – can pose selection pressures on native wildlife that are often profoundly different from those encountered and adapted to in their evolutionary past. Since such novel pressures can affect reproduction and survival (Ibáñez‐Álamo & Soler, 2010), individuals can be expected to adjust behaviourally or physiologically to the presence of eucalypts. Although several studies have identified behavioural and physiological modifications in eucalypt plantations, it is unknown whether such responses are a product of phenotypic plasticity or the result of novel adaptations (or exadaptations) to selective pressures exerted by these novel environments. For instance, divergent selection, mediated by adaptation to particular factors (e.g. presence of toxic oils or hydrological alterations), could affect behaviour, reproduction, morphology and other life‐history traits, but non‐adaptive processes (e.g. genetic drift) can also contribute to the divergent patterns observed in wildlife populations living in eucalypt plantations. Indeed, evidence of genetic adaptation to such plantations is currently lacking, and the short evolutionary timespan (years or dozens of years of evolution) offered by the presence of exotic eucalypts implies that plastic responses, rather than selective processes, are likely to explain any changes observed in vertebrate and invertebrate populations inhabiting these plantations. Yet, real‐time evolution has been manifested in species when natural selection is strong (e.g. Stuart et al., ²⁰¹⁴) and, thus, the rapidly altered biotic and abiotic conditions caused by eucalypt plantations offer an exciting opportunity also to understand the impact of these plantations on important evolutionary processes. In this section, we explore the main behavioural adjustments that have been investigated in the literature, including changes in habitat use, foraging and nesting, as well as how alterations to the sensory environment might impact signals and signalling behaviours and, hence, communication, and the consequences of eucalypt plantations for the physiology of individuals.

(1). Habitat use, foraging and nesting

Many of the individual‐level adjustments described in eucalypt plantations are behavioural changes associated with the incorporation of novel/altered food resources into the diet of plantation‐dwelling wildlife, and the use of plantations for activities such as reproduction. While some species generally avoid plantations [mammals (Umetsu & Pardini, 2007; Rodrigues & Chiarello, ²⁰¹⁸; Cortés‐Alfonso, Valenzuela & Sánchez Barrera, ²⁰²¹); see also mammalian carnivores example in Table S1] others have been observed to use plantations for certain activities while avoiding them for others (de Azevedo et al., ²⁰¹⁰; Salazar & Fontúrbel, ²⁰¹⁶). Such context‐dependent use of eucalypt plantations suggests that there might be trade‐offs associated with their use (see elephant example in Table S1), thus causing animals to avoid eucalypts for activities where the costs might be high. For instance, simplified structural complexity and, hence, increased predation risk and/or perceived vulnerability can limit the use of eucalypt plantations as roosts, shelter and resting habitats, while individuals may still use these environments for other, less time‐consuming, more active and potentially less‐risky activities, such as feeding (Salazar & Fontúrbel, 2016; Spehar & Rayadin, ²⁰¹⁷). However, the avoidance of plantations for some activities could simply be due to a lack of specific resources resulting from altered environmental conditions (e.g. lack of suitable nesting places or food; Fernandes et al., ²⁰¹⁸), rather than a consequence of trade‐offs in habitat use per se.

Whether the use of eucalypts by wildlife has a fitness benefit or is the result of maladaptive adjustments to the novel habitat is largely unknown. Some animals seem able to match their activity to the space–time distribution of resources and exploit eucalypt plantations when the net benefits are high, for instance, through expansion of their trophic niches by seasonal feeding in eucalypt plantations (Bonilla‐Sánchez et al., ²⁰¹²; Luĉan et al., ²⁰¹⁶; Seiler & Robbins, ²⁰¹⁶; Gazagne et al., ²⁰²⁰). The ability to incorporate seasonally eucalypt products into the diet might be crucial for some species, buffering against fluctuations in food availability in their native habitat and thus enabling them to meet their nutritional demands. This might be especially important in highly fragmented areas where the landscape is composed of a mosaic of small patches of native and anthropogenic habitats, and where natural food sources are scarce due to the paucity of remnant habitat. An interesting focus for future research is therefore if and under what circumstances, the incorporation of eucalypt products confers a long‐term benefit for wildlife. For instance, for some nectar‐feeding birds, eucalypts can represent the most important flower resources in areas where these trees have been planted (Calviño‐Cancela & Neumann, 2015), while for other animals we simply do not know whether the incorporation of eucalypts into the diet confers a nutritional benefit, or if it is a maladaptive response to the presence of a potentially lower quality novel resource that could lead to malnourishment (see example of stream invertebrates in Table S1). Eucalypt plantations can also act as suboptimal habitats for many species due not only to the quality but also the quantity of resources present in those environments. For example, the lower diversity and abundance in eucalypt plantations of invertebrates may negatively impact predators such as birds (De la Hera, Arizaga & Galarza, 2013) and fish (Fierro et al., ²⁰¹⁶), for which they are the main food source.

Beneficial or detrimental effects might be associated with animals reproducing in plantations. The presence of eucalypt plantations has been suggested to increase the availability of suitable breeding habitat for some species (see raptor example in Table S1), while a handful of studies have shown that, for some species, individuals breeding in eucalypts have similar reproductive success to those in natural habitats. For instance, for the great tit Parus major in Spain and Portugal, individuals from eucalypt plantations and native forests did not differ in egg‐laying date, clutch size, chick body mass, or hatching and fledging success (Da Silva et al., ²⁰¹²; De la Hera et al., ²⁰¹³). This suggests that, at least for this generalist species with high plasticity, adults can potentially capitalise successfully on resources in eucalypt plantations. By contrast, for other species, eucalypt plantations might potentially result in reduced availability of breeding habitat and even act as ‘ecological traps’ (Schlaepfer, Runge & Sherman, 2002) if novel nesting‐site preferences lead to fitness costs. For example, a study exploring the effects of eucalypts on the avian breeding community in the Amani Plateau, in East Usambara, Tanzania, found low numbers of breeding nests of forest species, suggesting suboptimal or maladaptive reproductive responses in the novel habitat (John & Kabigumila, 2007).

Species mobility and landscape composition (see Section V.2) seem to be key characteristics shaping the ability of wildlife to respond behaviourally to altered resource availability in eucalypt plantations. On the one hand, dietary shifts and expansion of trophic niches have been mainly described for species that exhibit a high level of mobility – mostly birds and mammals – and, thus, have the ability to move between plantations and native habitats. On the other hand, whether an animal can partition their space use for different activities based on the net benefits of exploiting a particular habitat can also be influenced by connectivity between different vegetation stands, and their proximity to natural habitat patches. For instance, when suitable habitats are available in the landscape, some species with high mobility have been shown to prefer patches of native vegetation and avoid eucalypt plantations altogether as potential feeding habitat (Di Salvo, Russo & Sarà, 2009; de Azevedo et al., ²⁰¹⁰; Cruz, Sarmento & White, ²⁰¹⁵; Cortés‐Alfonso et al., ²⁰²¹). However, even species with high mobility might be forced to exploit resources in eucalypt‐dominated areas in regions with suboptimal landscape conditions, such as areas with few native forests (Aihartza et al., ²⁰⁰³).

(2). Communication

Eucalypt plantations can disrupt communication between individuals by altering the visual, acoustic and chemical sensory environment. However, the few studies that have explored the effects of sensory disturbance in eucalypt plantations have focused almost exclusively on alteration of the chemosensory environment linked to the release of oils and toxic substances into the soil and water.

Signal transmission and reception are locally adapted to the environment in which they have evolved, so the novel oils and secondary compounds leached to the surroundings by eucalypts can impact chemical cues and signals, with consequences for the behaviour of animals that rely on olfaction. In this regard, a few studies have reported changes in predator–prey interactions due to the presence of novel chemicals associated with eucalypt trees. A study exploring an anuran species, the common frog Rana temporaria, showed that tadpoles housed in tanks with eucalypt leaf litter hid less and were more active in the presence of predators than those housed with oak leaf litter (Burraco et al., ²⁰¹⁸). By contrast, tadpoles of R. temporaria and two other anuran species (common midwife toad Alytes obstetricans and Perez's frog Pelophylax perezi), regardless of whether they were reared in water with eucalypt or native oak leaf litter, reduced their activity level in response to the addition of predator odour to their tank (Iglesias‐Carrasco, Cabido & Ord, ^2022a). An additional study on male palmate newts, Lissotriton helveticus, showed that exposure to eucalypts can affect both cue detection and the ability to respond to predator cues, potentially due to physiological constraints (Iglesias‐Carrasco et al., ^2017b). If adaptations to signals or behavioural adjustments, e.g. avoiding ponds with predators, do not take place over the same timescale as the transformation of natural habitats into eucalypt plantations, then plantations could potentially lead to population declines of prey species due to increased predation. However, myriad other altered conditions in plantations (e.g. predators that use chemical cues to hunt might also be impacted by leachates), may influence the impact of the observed reduced antipredator responses.

Social and sexual dynamics can also be affected by disturbances to the chemosensory environment. For example, male palmate newts tested in eucalypt‐infused water were less likely to choose a pond with the presence of potential mates than were those tested in native oak water (Iglesias‐Carrasco et al., ^2017b). Long‐term exposure to eucalypt‐infused water altered female mating preferences in the same species, such that females no longer associated with high‐quality males (Iglesias‐Carrasco et al., ^2017a).

Compared to the replaced habitat, structural differences associated with eucalypt plantations can also be expected dramatically to impact acoustic and visual conditions. For example, light penetration differs between native, non‐altered forests, plantations and secondary/logged areas, which can affect the efficacy of colouration patterns and signals (Smith et al., ²⁰⁰⁸; Barnett et al., ²⁰²¹). Similarly, sound transmission differs between open and closed rainforests in Australia, with birds adjusting advertising calls to the prevailing conditions of different habitat types (Nicholls & Goldizen, 2006). However, to our knowledge, no studies have explored how changes in light and sound transmission affect communication in exotic eucalypt plantations. In this regard, studies of light and noise pollution in other human‐modified environments, such as urban areas, could provide useful insights, with evidence showing that such changes can dramatically affect organismal behaviour.

(3). Physiology, immune response, and development

Altered resources, such as the amount and quality of food or the presence of toxic leachates, have been shown to induce physiological and life‐history responses that could affect fitness and, hence, population survival in eucalypt plantations. Leachates can have detrimental effects (e.g. reductions in growth, survival, or reproduction) even for Australian wildlife that naturally co‐exist with eucalypts (Morrongiello et al., ^{2011, 2013}). Outside the eucalypt native range, exposure to water infused with eucalypt leaves, as well as low‐quality eucalypt leaf litter, has been shown to reduce growth and development, and to promote morphological changes, in a range of aquatic invertebrates and amphibians (Larrañaga et al., ²⁰⁰⁹; Iglesias‐Carrasco et al., ^{2016, 2022a}; Burraco et al., ²⁰¹⁸; Beleza et al., ²⁰¹⁹). Impaired growth could have important consequences for population dynamics in eucalypt plantations. For instance, reduced growth could result in lower recruitment and higher mortality rates because, in many species, individual size, especially during juvenile stages, determines survival and performance in later life stages (for example, in amphibians; Cabrera‐Guzmán et al., ²⁰¹³). Moreover, body size is often positively associated with female fecundity. Hence, if females living in eucalypt plantations are smaller and less fecund, this could lead to reductions in population size, or allocation trade‐offs between reproduction and other important fitness‐related traits.

Evidence of potential trade‐offs in resource allocation comes from studies exploring the effects of eucalypt plantations on immunity, pathogen infection, and body condition. In a range of taxa, individuals in eucalypt plantations show similar body condition to those in the native habitat (Rosalino et al., ²⁰¹³; Iglesias‐Carrasco et al., ²⁰¹⁶; Teixeira et al., ²⁰¹⁹; Afonso et al., ²⁰²³; but see Crocidura russula in the latter study), but in some species, research has identified a reduced investment in immune response (Iglesias‐Carrasco et al., ²⁰¹⁶), with animals from eucalypt plantations having higher ectoparasite loads (Teixeira et al., ²⁰¹⁹), possibly due to a life‐history trade‐off between somatic maintenance and investment in immunity. This response could also be adaptive if, for instance, eucalypts are associated with reduced pathogen diversity, abundance, or transmission, so that investing in strong immune responses is no longer necessary. However, a study on honeybees Apis mellifera suggests this might not be the case, since nutritional stress in colonies fed with pollen of Eucalyptus grandis led to higher infection levels, and reduced brood sizes and adult populations, both in the short and long term (Branchiccela et al., ²⁰¹⁹). Although we now have a strong theoretical and empirical understanding of disease dynamics in urbanised areas (Bradley & Altizer, 2007), we still do not know whether shifts in habitat use, activity, food provisioning and stress levels increase the susceptibility of wildlife to infectious diseases in eucalypts, or in plantations more generally, leading to fitness costs and population declines.

III. SPECIES‐ AND COMMUNITY‐LEVEL RESPONSES

Perhaps the best‐explored responses of wildlife to anthropogenic habitats involve studies at the community and species level, including changes in species richness, diversity, abundance, and community composition. Changes in structural complexity, and their consequences on food, competition and microhabitats (among others), are expected to lead to the exclusion of some species from plantations and, hence, a shift in community composition. Species‐ and community‐level responses of this kind, which are typically linked to the structural complexity of the habitat, have even been reported in plantations where eucalypts are native (e.g. Law et al., ²⁰¹⁷). The release of novel secondary compounds by eucalypts in regions where these trees have recently been planted can also create challenges for the establishment and viability of local wildlife communities. As a consequence, eucalypt plantations can create ‘winners’ and ‘losers’ as has been observed for other anthropogenic habitats (Newbold et al., ²⁰¹⁸): while some species are able to survive and even thrive in plantations, others decline rapidly or may be driven to extinction.

(1). Species richness, diversity, abundance, and community composition: comparing eucalypts with native vegetation

Many studies have reported negative effects of eucalypt plantations on diversity parameters compared to native vegetation. To investigate the impacts of these plantations across the world, we collected data from the published literature (see Appendix S1, Table S2 and Figs 1 and 3). We focused on comparisons with native vegetation since these were explored most often in the literature (but see Section III.2 for comparisons with other habitats). Comparisons with native vegetation are likely to be important regarding wildlife conservation since eucalypt plantations can either replace native vegetation or be used for afforestation of degraded areas rather than afforesting with native species.

Fig. 3.

Taxonomic distribution of studies (N = 110) used to explore the effects of eucalypt plantations compared to native vegetation on wildlife communities. (A) Taxonomic coverage of the studies used. Note that the total numbers sum to more than 110 since many of the studies explored several taxonomic groups. Numbers above the plot for insects, arthropods and invertebrates refer to studies that focused only on more general categories (e.g. soil invertebrates) rather than on specific taxonomic groups. Note the greater efforts investigating the effects of eucalypt plantations on vertebrates compared with invertebrate communities, especially for mammals and birds. (B) Effect of eucalypt plantations on community variables (abundance, diversity, species richness and community composition) compared to the original native habitat for vertebrates and invertebrates. We collected a total of 322 effects from 110 studies. The smaller circles represent the effects of eucalypt plantations on two vertebrate (birds and mammals) and three invertebrate (beetles, ants, arachnids) groups for which the most data are available.

For each study, we collected information on the effects of eucalypt plantations on species richness and abundance when compared to the native vegetation (see Appendix S1). We categorised the reported pattern as: ‘low’ if species richness, diversity and/or abundance were lower in the eucalypt plantation than in the equivalent native habitat; ‘high’ if the variable was higher in eucalypts; and ‘similar’ when no effect of the plantation was detected. Community composition was scored as either ‘similar’, when composition did not differ between habitats, or ‘different’, when composition differed between plantations and native vegetation. In total, we identified 322 summary effects from 110 studies (Table S2, Figs 1 and 3).

In a large proportion of studies, eucalypt plantations hosted poorer and less abundant wildlife communities compared to those observed in the equivalent native vegetation stands (Fig. 3B). Vertebrate and invertebrate communities revealed similar trends, however, the extent of the effect seemed to be dependent on taxonomic group (see small graphs in Fig. 3B for different clades). Such reductions in species richness, diversity and abundance have been linked to habitat transformation and the associated simplification of the horizontal and vertical structure of the vegetation, a reduced number of ecological niches, changes in microhabitat, as well as limited shelter, food and suitable reproductive habitat (e.g. water bodies for aquatic‐dependent species) in eucalypt plantations (Gardner et al., ²⁰⁰⁷; Neves et al., ²⁰¹²; De la Hera et al., ²⁰¹³; Gainsbury & Colli, ²⁰¹⁴; Jacoboski, Mendonça‐Lima & Hartz, ^2016b). Interestingly, 76% and 80% of studies in vertebrates and invertebrates, respectively, reported differences in community composition between eucalypt plantations and native vegetation (Fig. 3B). Many of these studies show that eucalypt plantations are often associated with limited numbers of unique species (Vallan, 2002; Fork et al., ²⁰¹⁵; Fontúrbel, Candia & Castaño‐Villa, ²⁰¹⁶; da Silva et al., ²⁰¹⁹), and in some cases, although not always (Beiroz et al., ²⁰¹⁴; Lopes et al., ²⁰¹⁵; Tymochko, Cuaranhua & Gumovsky, ²⁰²¹) with a reduction in species evenness (i.e. a change in the relative abundances of different species) (e.g. Corcuera et al., ²⁰¹⁰; Lopes Rodrigues et al., ²⁰¹⁰; Beiroz et al., ²⁰¹⁸; Ortiz et al., ²⁰¹⁹).

Evolutionary history is expected to influence species' responses to anthropogenic habitats. Phylogenetic relatedness can inform the evolutionary and ecological processes driving community establishment in novel habitats (Iglesias‐Carrasco, Medina & Ord, ^2022b). For instance, low phylogenetic diversity can be associated with niche conservatism, or the tendency for closely related species to occupy similar and more specific habitats due to the use of similar resources (Wiens & Graham, 2005). Similarly, phylogenetic overdispersion, such as that found in Brazilian lizard communities in eucalypt plantations, is likely to reflect competitive exclusion of closely related species associated with homogenisation of their environment and the consequent reduction in resources available (Gainsbury & Colli, 2019).

Phylogenetic relatedness can also be used as a proxy for phylogenetically conserved traits that shape wildlife responses to habitat transformation. Shared evolutionary history of species can determine their ability to colonise anthropogenic habitats, with communities in these habitats showing high phylogenetic signal and clustering (Sol et al., ²⁰¹⁷; Nowakowski et al., ²⁰¹⁸). Therefore, for conservation purposes, the study of phylogenetic diversity can potentially help us to identify clades with traits that are most sensitive to habitat transformation. However, direct measurements exploring the effect of eucalypt plantations on phylogenetic diversity are scarce. Among the few notable exceptions, eucalypt plantations did not appear to affect the phylogenetic diversity of either large mammals or birds (Campos, Charters & Verdade, 2018; Jacoboski et al., ²⁰¹⁹), however, bird communities in plantations exhibited reduced evolutionary distinctiveness (Jacoboski et al., ²⁰¹⁹). Additional studies have indirectly shown that eucalypt plantations might be leading to a loss of phylogenetically unique species. For instance, these novel habitats are associated with fewer grassland specialists and endemic species compared to native habitats (Garcia, Finch & Chávez León, 1998; Gainsbury & Colli, ²⁰¹⁴; Jacoboski et al., ²⁰¹⁹; Cravino & Brazeiro, ²⁰²¹). The loss of distinct clades seems to be especially acute in areas where grasslands and savannahs (e.g. Brazilian Cerrado) have been replaced by eucalypt plantations, suggesting that afforestation with eucalypts might pose an important threat to species adapted to such habitats.

Since the ability of species to respond to the transformation of their habitat is, at least in part, associated with specific organismal traits, novel ecological conditions in eucalypt plantations are expected to impact some traits more than others (see entry for wildlife communities in Table S1). In particular, resilience to habitat modification, as well as the ability of species to colonise and exploit eucalypt plantations, seem to be associated with habitat generalism, with plantations often adopted by a reduced number of specialist species (Umetsu & Pardini, 2007; Dias et al., ²⁰¹³; Costa‐Milanez et al., ²⁰¹⁴; Jacoboski et al., ^2016b). In addition, the communities found in plantations are often comprised of species that are preadapted to plantation life, and represent only a subset of the species present in the native environment [i.e. nestedness (Louzada et al., ²⁰¹⁰; Jacoboski et al., ^2016a,b)]. As a result, eucalypt plantations are typically associated with reduced functional diversity in several taxonomic groups (Trimble & van Aarde, 2014; Jacoboski et al., ^2016a; Martello et al., ²⁰¹⁸; Soares et al., ^2021b; but see Pinto et al., ²⁰²¹; Rabello et al., ²⁰²¹). However, the loss of functional diversity is not always inevitable if functionally redundant species end up being excluded, or if species are replaced by others that possess similar functional traits. Nevertheless, some studies have found a reduction in functional redundancy in eucalypts compared to the native vegetation (Winck et al., ²⁰¹⁷; Martello et al., ²⁰¹⁸), which could lead to lower community resistance and unstable ecosystems within plantations (see Section IV).

(2). Community responses: comparing eucalypts with other anthropogenic habitats

Although much research has focused on comparing communities between eucalypt plantations and native vegetation, planting of eucalypts does not necessarily involve the destruction and replacement of pristine habitats, and, in many cases, eucalypt plantations are established in previously degraded areas, such as farms, grazed grasslands, or croplands (as is also the case for other exotic plantations; e.g. Marshall et al., ²⁰²³). Such differences in the replaced habitat add an additional layer of complexity to the study of the impacts of plantations on local wildlife communities. For example, when eucalypts are established in previously degraded land, in which biodiversity has already become impoverished, then the probability of such plantations hosting a high diversity of species will already be low due to the limited pool of species inhabiting their surroundings (see also Brockerhoff et al., ²⁰⁰⁸). The colonisation of newly established eucalypt stands can be expected to be slower with increasing distance from species‐rich habitats, such as native vegetation patches. In this situation, comparisons of communities between plantations and native vegetation will almost inevitably find the former depauperate. Therefore, such studies must consider the habitat type that the eucalypt plantations are replacing.

In fact, in some cases, eucalypt plantations can provide a more beneficial habitat than other anthropogenic habitats. For example, diversity and species richness has been shown to be higher in eucalypt plantations than in some human‐made habitats, such as grazed pastures or croplands (Bartz et al., ^2014a; Siegloch et al., ²⁰¹⁴; Cuautle, Vergara & Badano, ²⁰¹⁶; Apolinário et al., ²⁰¹⁹). Although this might not necessarily always be the case (e.g. Baldissera et al., ²⁰⁰⁸; Gheler‐Costa et al., ²⁰¹²; Calviño‐Cancela, ²⁰¹³), we urge studies to compare directly, when possible, eucalypt plantations with the habitats they are replacing as well as with other anthropogenic habitats. Only in this way can we expect to obtain a more comprehensive picture of the impacts of eucalypt plantations on wildlife communities, and whether such plantations offer a more suitable habitat for animals compared to other degraded or modified areas.

(3). Consumer–resource interactions

The presence or absence of different animal and plant species, and the altered community and functional structure in eucalypt plantations, can have cascading effects in how different species interact with each other which can, in turn, affect their relative performance and abundance. For example, a large abundance of predatory wasps in eucalypt plantations in Brazil was sustained, in part, by the presence of high numbers of defoliating insect prey (Silva‐Filho et al., ²⁰²⁰). By contrast, reproduction and survival in a parasitoid bug Podisus nigrispinus, was lower in larvae fed on eucalypts than in those fed on native guava (Psidium guajava) plants, probably due to the toxicity of secondary compounds appropriated by the caterpillars (Holtz et al., ²⁰¹⁹). This suggests that the presence of novel leachates released by eucalypts as a defence against herbivores can also affect the natural predators of these herbivores, which could, in part, explain the often‐reported limited richness of this insect trophic guild (see also example of species interactions in predator communities in Table S1).

Eucalypt plantations can also affect animal–plant mutualistic interactions. While some studies found no effect of eucalypts on animal–plant interactions, thus suggesting that some ecological processes can be conserved in these monocultures (Kersch‐Becker, Buss & Fonseca, 2013), other interactions were found to have been disrupted in plantations. For example, invertebrate communities associated with specific plants in eucalypt plantations have been shown to be less diverse, and have more unstable populations, compared to those in native vegetation patches (Callisto, Barbosa & Moreno, 2002; Diniz, Lewinsohn & Prado, ²⁰¹²). In Chile, eucalypts attracted pollinating hummingbirds, with more individuals visiting the plantations than native forests (Cuadra‐Valdés, Vizentin‐Bugoni & Fontúrbel, 2021). In this case, the native plants will be sharing pollinators with the exotic trees, with potential consequences for patterns of pollination success in the native habitat. Changes to animal–plant interactions can have important cascading effects for ecosystem functioning (see Section IV), so future research might benefit from exploring, for example, the long‐term impacts of altered pollinator communities and pollination rates on plant establishment.

Lastly, recent studies on amphibians have shown a potential disrupting effect of eucalypt plantations on host–microbiota interactions. In a study on the salamander Batrachoseps attenuates, individuals in native oak forests showed greater skin microbiota diversity than those in eucalypt plantations, probably due to microbial species filtering and altered communities in the latter (Hernández‐Gómez et al., ²⁰²⁰). In an experimental study on the salamander Salamandra salamandra, ash from eucalypt wildfires altered the growth of skin bacterial communities (Afonso et al., ²⁰²³), which, in turn, weakened the immune system of the animals. Based on this evidence, one possibility is that changes in microbiota–host dynamics might impact amphibian populations due to the importance of the skin microbiota in amphibian health. Alternatively, if pathogen loads are lower in eucalypt plantations, changes in microbiota diversity might reflect a neutral or even adaptive response to the novel conditions in the plantations, whereby rich bacteria communities are no longer needed. Therefore, a potential future research avenue with important conservation consequences is to explore whether eucalypt plantations alter the ability of amphibians to overcome pathogens, such as chytrid fungus, effectively.

IV. ECOSYSTEM‐LEVEL RESPONSES

Changes in resources, such as the type of leaf litter, and biotic factors, such as temperature, can result in alterations to ecosystem dynamics. High phenolic, tannin and toxic oil content, in addition to changes in litter fall quantity, diversity and phenology, are expected to impact animal species involved in leaf litter processing dynamics. Such changes in litter decomposition could disrupt the nutrient cycle, with potential consequences for the ecosystem as a whole, both in terrestrial and aquatic environments. In addition, reduced wildlife functional diversity can also affect ecosystem services by modifying important ecological processes, such as seed dispersal and pollination. In this section, we summarise current evidence of the effects of eucalypt plantations on aquatic and terrestrial ecosystem services, including the decomposition of organic matter, pollination, and seed dispersal.

Most studies of ecosystem‐level responses to eucalypt plantations have come from research on neighbouring streams and rivers (reviewed in Graça et al., ²⁰⁰²). In these aquatic systems, changes in the surrounding vegetation can affect resource quality, the input of organic material, abiotic factors, such as light incidence, and other physio‐chemical characteristics of the water (Canhoto & Laranjeira, 2007). These changes, in addition to the low palatability, toughness, and poor nutritional value of eucalypt plant material, can affect detritivore macroinvertebrate ecology and communities, with potentially cascading ecosystem‐level effects, including impacts on ecosystem functioning, due to altered organic‐matter processing and decomposition (García, Richardson & Pardo, 2012; Casotti, Kiffer & Moretti, ²⁰¹⁴; Ferreira et al., ^{2015, 2016}). It has been suggested that the maintenance of a buffer in the native riparian corridor could be key to mitigating the negative effects of eucalypt plantations on these aquatic processes (Ferreira et al., ²⁰¹⁶). Most insights on this topic come from studies in temperate regions, highlighting the need to study decomposition rates also in tropical areas (Ferreira et al., ²⁰¹⁶). Similar effects on decomposition processes in response to altered resource quantity and quality might also be expected in terrestrial habitats. However, to date, studies on terrestrial leaf decomposition by soil invertebrates in eucalypt plantations are scarce.

In contrast to research on aquatic systems, evidence for the potential of eucalypt plantations to shape ecosystem‐level responses in the terrestrial realm is sparse. Ecosystem‐level impacts might occur due to reduced wildlife richness and the loss of organisms with specific functional traits and roles. For example, changes in predator communities, mostly through the loss of specialist species, can affect prey population dynamics, including populations of herbivorous pest species, with implications for vegetation structure (discussed in Teixeira et al., ²⁰²⁰). Pollination and seed dispersal services by specialist species could also be lost in plantations (Morante‐Filho et al., ²⁰¹⁸). However, the presence of some generalists, and the high abundances at which they can occur, could provide and maintain relatively important pollination and seed dispersal services (Barros et al., ²⁰¹⁹; Neuschulz, Botzat & Farwig, ²⁰¹¹). Exploring these ecosystem‐level effects is complex, and might depend on the heterogeneity of the landscape, since changes in ecosystem services in one specific stand of vegetation can negatively impact or buffer potential effects in nearby stands (Habel & Ulrich, 2020).

V. PLANTATION CHARACTERISTICS

Making strong predictions about the effects of eucalypt plantations on wildlife behaviour and communities is not easy (e.g. Table S2). The direction and magnitude of responses will depend not only on species ecology, life‐history traits, and climatic conditions, but also on myriad characteristics of the eucalypt stand itself. This review summarises research exploring very different types of eucalypt stands, ranging from young, simplified and managed stands to old, abandoned plantations. We also include plantations that replaced a wide range of habitats, from forests to grasslands or degraded areas, in different regions of the world, and from isolated plantations to those forming part of a matrix with other vegetation types. All these factors are likely to shape the extent of individual‐level adjustments or species diversity, and need to be considered when designing studies to explore the impacts of eucalypt plantations. In this section, we outline the main characteristics of eucalypt plantations that we have identified as potential drivers of the different responses, and the potential consequences from a conservation perspective.

(1). The local environment

Many studies cite characteristics of the local environment, and especially the structural simplicity of eucalypt plantations, as a main habitat feature that can impact wildlife. Several studies have shown that wildlife respond positively to increased spatial and taxonomic complexity in vegetation, which probably results in increased food and refuge resources (Barlow et al., ²⁰⁰⁸; Ribeiro‐Troian, Baldissera & Hartz, ²⁰⁰⁹; Fontúrbel et al., ²⁰¹⁶; Carrilho et al., ²⁰¹⁷; Teixeira et al., ²⁰¹⁷; Gao et al., ²⁰²¹; Zhao et al., ²⁰²¹). When the replaced habitat is a forest, eucalypt stands with a more forest‐like structure, a well‐developed understory and an abundance of tall trees (e.g. such as abandoned and older plantations, and polycultures) are associated with richer, more abundant and more stable wildlife communities than younger plantations (Steinbauer, Short & Schmidt, 2006; Suguituru et al., ²⁰¹¹; Millan, Develey & Verdade, ²⁰¹⁵; Sabatté et al., ²⁰²¹). Such eucalypt stands are also linked to high levels of activity in some animal species (Fontúrbel, Candia & Botto‐Mahan, 2014; Cruz et al., ²⁰¹⁶; but see Ramírez‐Mejiá, Echeverry‐Galvis & Sánchez, ²⁰²⁰) and may be more readily exploited as breeding habitats (see entry for raptors in Table S1). However, management activities, the use of pesticides, and the short harvesting rotation periods often used in these plantations can limit development of the understory and affect the age of the trees that are present, thereby impacting wildlife communities (e.g. Aslam et al., ²⁰¹⁵; Garlet et al., ²⁰¹⁵; da Silva et al., ²⁰¹⁹). In addition, reductions in animal occurrence have been observed in plantations at the end of the commercial cycle when stands are being prepared for harvesting (e.g. due to the use of pesticides for weed control; Timo et al., ²⁰¹⁴).

When plantations replace more open areas, such as grasslands, shrublands and savannahs, young (rather than old) stands often show richer and more similar communities to the original habitat due to their open structure (Phifer et al., ²⁰¹⁷; Ribero et al., ²⁰²¹). However, there is an inevitable increase in the complexity and growth of trees within plantations and, hence, a change in wildlife species assemblages and guild composition with time (e.g. Calviño‐Cancela, ²⁰¹³). This might explain why wildlife from open habitats, such as grasslands, seem to be more negatively impacted by the afforestation and edge effects created by eucalypt plantations (Reino et al., ²⁰⁰⁹). It has been suggested that eucalypt plantations are a ‘hybrid’ habitat, with a combination of abiotic conditions of both forests and open areas (Tavares et al., ²⁰¹⁹) that could contribute to the conservation of native grassland species when such habitat is scarce. However, whether eucalypts provide conditions suitable for forest or open‐area species is likely to depend on the type of management and development stage of the trees (old versus young plantations, e.g. Martín Avila et al., ²⁰²⁵). In addition, fast‐growing trees, like eucalypts, have very different ecological demands to plants in more open habitats, such as grasslands. These are likely to lead to high economic and environmental costs, such as the requirement for large amounts of water and the potential exhaustion of water sources to maintain tree growth (Le Maitre et al., ²⁰⁰²; Dzikiti et al., ²⁰¹⁶).

When eucalypt plantations replace previously degraded areas, such as farms or croplands, wildlife responses are likely to be similar to those observed when replacing grasslands, since there is also a switch from an open/low vegetation environment to a more forest‐like habitat. However, when degraded habitats cover large areas of land, it is expected that the number of species available in nearby surroundings will be lower than in natural grasslands, since croplands and grazed pastures are often species depauperate environments (e.g. Mancini et al., ²⁰²³). This is likely to affect the assemblage of communities in these plantations and, hence, shape species interactions and behaviours, but more research comparing wildlife responses between such degraded areas and plantations is needed. The establishment of eucalypt plantations in previously degraded areas can be beneficial for some forest species (Brockerhoff et al., ²⁰¹³), although it is important to consider that afforestation of patches within degraded areas can still have potential effects on local species by leading to species dynamics that differ from the original habitat (e.g. Reino et al., ²⁰¹⁰). However, the afforestation of degraded land with eucalypt plantations often brings more economic benefits to both large industrial and small non‐industrial land‐owners than afforesting with native vegetation (e.g. Tomé et al., ²⁰²¹). Under such circumstances, eucalypt plantations could be a profitable way of making use of land while promoting conservation, at least compared to other anthropogenic uses.

(2). Landscape composition

Landscape‐level effects, such as the size of the plantation and its connectivity to remnants of original vegetation and other anthropogenic habitats, can also shape wildlife responses at different levels. It has been suggested that eucalypt monocultures – and other tree plantations – interspersed in a mixed landscape with native vegetation patches can support healthier communities, higher diversity, and species with higher resource demands because of the large amounts of resources available among all of the different vegetation types (e.g. Piña et al., ²⁰¹⁹). However, for many species, the ability to exploit these mixed landscapes fully will only be possible if the different vegetation types are in sufficiently close proximity. In addition, compared with other anthropogenic habitats, eucalypt plantations have been suggested to increase connectivity by acting as potential corridors between different patches of vegetation for some tolerant animal species (Barlow et al., ²⁰⁰⁷; Hawes et al., ²⁰⁰⁹; da Rocha et al., ²⁰¹³; Biz, Cornelius & Metzger, ²⁰¹⁷). Therefore, these plantations could become a crucial link when used to afforest patches in areas where the majority of the land is covered by degraded habitats. High landscape complexity has also been associated with more functionally diverse communities, with the presence of species of different guilds helping to keep prey populations (including those of pest species) in check (reviewed in Brockerhoff et al., ²⁰¹³). Finally, it is important to note that most eucalypt stands are planted for forestry and economic purposes that are characterised by short rotation periods. Landscape heterogeneity and availability of other nearby vegetation patches can potentially facilitate the migration of wildlife (at least for some taxonomic groups) from the patch being cleared to fragments nearby.

The large‐scale planting of vast tracts of eucalypts is likely to be detrimental for wildlife, by creating more homogenous environments. Increased distance to the nearest stands of native vegetation can increase isolation for species unable to use eucalypt stands as corridors to traverse between native vegetation patches. Population isolation due to fragmentation can detrimentally impact wildlife in several ways, either via inbreeding due to bottleneck effects (Keller & Waller, 2002), or by forcing individuals to make energetically costly forays through altered habitats, limiting immigration rates and rescue effects that ultimately could lead to local extinctions, and alter interspecific interactions (Kupfer, Malanson & Franklin, 2006). Although, this is more likely to affect terrestrial species and those with limited mobility compared to those that are able to move across the landscape (e.g. Umetsu & Pardini, ²⁰⁰⁷), even in more mobile species, such as birds, large‐scale plantations have been shown to have a more detrimental effect on diversity than small plantations (Castaño‐Villa et al., ²⁰¹⁹). However, the benefits of landscape heterogeneity can be compromised if the remnants of native vegetation are too small, and if the specific shape of the stands increases forest edge effects – with consequential changes to microclimate, species interactions and diversity (Kupfer et al., ²⁰⁰⁶; Marsh et al., ²⁰¹⁸). In areas with small fragments and low native vegetation cover, or areas with stands of strip‐like shape, even native forest remnants may only be able to support sub‐optimal communities of species (Gheler‐Costa et al., ²⁰¹²).

Another consideration when establishing eucalypt plantations is the different vegetation stands that will form the matrix, since not all matrix compositions will have the same impacts on wildlife. For instance, in agricultural landscapes with low biodiversity eucalypts have in some cases been shown to have positive effects on wildlife activity, at least for those animal species that benefit from high levels of tree cover (Pita et al., ^{2009, 2020}; Martínez‐Sastre, Miñarro & García, ²⁰²⁰; but see Moreira et al., ²⁰⁰³). As a consequence, eucalypt plantations can have a positive effect on wildlife when those plantations are used for restoring previously degraded land (Brancalion et al., ²⁰²⁰, but see Wu et al., ²⁰²¹). Importantly, the type of original habitat remaining as part of the matrix is likely to play a key role in shaping animal responses. For instance, in originally forested areas, matrices formed by eucalypt plantations can be less detrimental for wildlife than those formed by other agroecosystems, such as pastures and croplands. Such plantation matrices have been associated with a reduced edge effect when eucalypt plantations are adjacent to forests and there is potential for plantations to act as corridors (Teixeira & De Azevedo, 2019; Hatfield et al., ²⁰²⁰). Critically, in this situation, local environmental and landscape‐level effects can interact, with the potential positive effect of the forest–eucalypt matrix being dependent on the quality of the local environment within the plantation.

(3). Considerations for conservation

Current management and planting strategies in eucalypt plantations are often linked to detrimental effects for wildlife conservation, leading to the loss of unique and endangered species, reducing biodiversity, disrupting ecosystem services, and inducing potentially maladaptive behavioural responses. Appropriate management strategies (e.g. longer rotation periods, low intensity of exploitation, or avoidance of pesticides) that enhance habitat complexity and improve microclimatic conditions might help promote conservation of wildlife in these plantations, at least when replacing forests (for a recent review on the positive effects of plantation age, see Tudge et al., ²⁰²³). However, the establishment of eucalypt plantations, or those of any rapid‐growth trees, in areas occupied by native open vegetation should be approached with caution. Such plantations pose an unavoidable threat for the conservation of species adapted to these fragile habitats. Eucalypt plantations should be established only in previously degraded areas as an afforestation mechanism, when afforesting with native trees is difficult, and never at the expense of native vegetation.

To balance economic and conservation outputs, consideration should be given to planting eucalypts intercropped with native trees in polycultures rather than monocultures (Wang et al., ²⁰²³). Polycultures help maintain more complex communities of animals, improving ecosystem stability by enhancing pollination, seed dispersal and/or pest control (e.g. Steinbauer et al., ²⁰⁰⁶), as well as potential economic benefits (e.g. reduced use of pesticides). Potentially, polycultures can also be more resilient to the effects of climate change because of a greater probability that some tree species will persist in the future environmental conditions (Seppälä, Buck & Katila, 2009).

Both the local environment‐ and landscape‐level effects need to be integrated when designing plantations. Designing plantations that benefit all taxonomic groups is likely to be difficult, since the relative importance of local environment versus landscape effects in the establishment of communities might vary among species (Millan et al., ²⁰¹⁵; Audino et al., ²⁰¹⁷), and can even have opposite effects depending on the community‐ or individual‐level response measured (Cardoso, Bueno & Morante‐Filho, 2023). As a general rule, it seems that reducing plantation size and increasing connectivity between plantations and native vegetation will contribute most to the conservation of a variety of wildlife taxonomic groups. The maintenance of large and healthy native vegetation patches will also be necessary. On a case‐by‐case basis, landscape and management planning could focus on more sensitive wildlife species, such as those with reduced mobility, lower adaptability, or key functional roles, that could serve as indicators of the adequacy of the measures taken.

VI. FUTURE DIRECTIONS

More research is needed to understand the impacts of eucalypt plantations on wildlife behaviour, resource use, reproductive output, and, hence on their net fitness costs or benefits for wildlife (Fig. 4). In addition, further research is required on whether species are able to adapt to plantations, with the available evidence suggesting that the behavioural and physiological responses observed are most likely the result of phenotypic plasticity. We need to gain better insights into the potential for eucalypt plantations to act as agents of selection, including studies using cross‐fostering of wildlife from native forests versus eucalypt plantations, high‐throughput genomic sequencing, tests for trait divergence between populations inhabiting eucalypts and native vegetation stands, and studying processes that can lead to reproductive isolation, such as assortative mating. Exploring whether and how eucalypt plantations lead to phenological responses, such as the onset and duration of breeding periods or daily activity patterns in wildlife (e.g., Ramírez‐Mejiá et al., ²⁰²⁰; Cravino & Brazeiro, ²⁰²³), could provide useful insights into genetic differentiation. Behavioural responses have been mainly described for highly mobile species, such as mammals and birds. By contrast, genetic adaptation and potential reproductive isolation in wildlife populations inhabiting plantations are more likely to occur in taxonomic groups with low mobility and high population isolation, so more studies in those animal groups are necessary.

Fig. 4.

Summary of current research gaps for individual‐, community‐ and ecosystem‐level responses to eucalypt plantations. Within each of these three categories, the text inside the darker square represents the variable being explored, and the text outside the dark square represents the research gap associated with that variable. Arrows show connections between different types of wildlife response, and arrow thickness shows the extent of the effect. Arrows from the central image represent the need to study how different types of eucalypt plantations affect animal responses. Animal silhouettes were obtained from phylopic.org.

There is evidence suggesting that the altered chemical sensory environment might affect the communication of animals living in eucalypt plantations, but we currently know little about how eucalypt plantation structure might affect acoustic and visual communication. In addition, research is needed to understand whether changes in signalling behaviours are the result of trade‐offs between signal expression, detection and reliability, and what fitness costs these may engender. Whether altered signals and signalling behaviours in plantations might result in a reduction in fitness, or whether eucalypt plantations are, instead, driving novel evolutionary solutions remains to be explored.

Future research could also be targeted towards a better understanding of whether eucalypt plantations are leading to global homogenisation of diversity and functional traits through the loss of specialist organisms, as has been observed for other human‐made habitats (e.g. Devictor et al., ²⁰⁰⁷; Clavel, Julliard & Devictor, ²⁰¹¹). Application of novel community ecology methods to the study of eucalypt plantations will help shed light on the ecological/evolutionary processes, as well as the species traits, shaping the establishment of wildlife communities in these novel habitats, and whether plantations are leading to functional homogenisation and the loss of specific clades. In addition, global‐scale phylogenetic comparative analyses could help identify whether sensitivity to this environment differs among taxonomic groups or geographical regions. Another rewarding avenue of research will be to explore not only whether plantations lead to homogenisation of functional diversity by filtering species with unsuitable traits, but also whether they drive selection towards more generalist habits (e.g. Becker, Joner & Fonseca, ²⁰⁰⁷).

Understanding the ecosystem‐level impacts of eucalypts in the terrestrial environment will require a deep exploration of the cascading effects of altered wildlife communities and plant–animal interactions such as pollination in plantations on the nearby native vegetation fragments. This might be especially important in highly fragmented areas with small patches of remnant native vegetation that are likely already to host sub‐optimal wildlife communities composed mainly by generalist species. The loss of some species might then have strong impacts on ecosystem services in the nearby native vegetation, and not just within the eucalypt stand.

As human activities continue to change our environment, eucalypt plantations are likely to interact with other stressors to impact wildlife responses. When multiple stressors act simultaneously, there is a risk that the combined effect will be greater than the sum of their individual effects (i.e. then act synergistically). A few studies have begun to explore the potential interactive effects for plantations, including effects of temperature (Correa‐Araneda et al., ^{2015, 2017}; Burraco et al., ²⁰¹⁸) and bushfires (Nadel, Scholes & Byrne, 2007; Pradhan et al., ²⁰²⁰). However, more research is needed to understand whether the interaction between novel ecological challenges in eucalypt plantations and other stressors (e.g. desiccation or pesticides) will impact wildlife communities in similar ways in different regions of the world, and also when plantations replace different types of native habitats.

There are many characteristics of plantations and species that should be considered when assessing the features of plantations that drive species responses. For instance, when they replace native forests, we predict that the effect of altered structure will be especially important for terrestrial wildlife in tropical areas, where highly complex native forests are transformed into simplified monocultures. We also predict larger effects where eucalypts are used to transform non‐forested habitats, such as grasslands, savannahs, or drylands (Reisman‐Berman, Keasar & Tel‐Zur, 2019). By contrast, for many aquatic species and ecologically important soil invertebrates, other stressors, such as the presence of toxic leachates, might pose a stronger challenge. In this regard, we predict that the negative impact of leachates on survival and reproduction will be stronger for species that have not previously encountered eucalypt trees than for those that have co‐evolved with eucalypts in their native environments. In addition, wildlife community composition and activity levels in plantations can be seasonal, with some studies reporting more abundant and richer species communities during periods of the year when eucalypts provide more resources (e.g. rainy season in the tropics or summer in temperate zones) (da Silva et al., ²⁰¹⁹; Lopes et al., ²⁰²⁰; Soares et al., ^2021b). The harshest periods of the year are associated with lower litter moisture, lack of water sources and lower availability of food, refuge and breeding resources for many species (e.g. Winck et al., ²⁰¹⁷). We predict that eucalypt plantations will have a stronger negative effect in drier areas and for animals dependent on water sources (e.g. some amphibians Russell & Downs, ²⁰¹²).

VII. CONCLUSIONS

• (1)Although eucalypt plantations often host wildlife communities depauperate in richness and with altered composition, they cannot be considered ‘green deserts’ since many species have thriving populations in these anthropogenic habitats. The abandonment of eucalypt plantation management is often followed by the recolonisation of native vegetation and wildlife in a process that results in complex and heterogeneous landscapes in which greater diversity is expected compared to eucalypt monocultures.
• (2)Nonetheless, eucalypt plantations will never be a complete substitute for native vegetation, so the maintenance of large stands of native remnants is vital for the conservation and health of wildlife communities.
• (3)When compared to native vegetation, eucalypt plantations are likely to be driving the functional homogenisation of communities and are contributing to the loss of endangered and endemic species. However, future comparisons of these plantations with other degraded habitats will be critical to an accurate understanding of the worldwide impacts of eucalypt plantations on wildlife communities.
• (4)For more sensitive species, their presence in plantations does not ensure their success in these habitats, but instead might represent suboptimal performance of individuals in novel and harsh environments, likely leading to rapid population declines over a short evolutionary timespan.
• (5)Eucalypt plantations share many characteristics with other types of tree plantations. These similarities could yield important insights for our understanding of tree plantations more generally. Do plantations of different tree species lead to similar effects in wildlife globally, or do different types of plantations result in different responses in animals?
• (6)Many of the knowledge gaps associated with the effects of eucalypt plantations on wildlife are also relevant to other types of tree plantations.
• (7)Studying and comparing eucalypt plantations with other types of monocultures could provide important insights into the potential evolutionary and conservation consequences of these human‐made habitats for wildlife.

Supporting information

Appendix S1. Literature search and methods.

Fig. S1. Summary of the literature search.

Table S1. Case study examples of some of the effects of eucalypt plantations on wildlife and the potential consequences for individuals and communities.

Table S2. Summary of the 110 studies exploring wildlife community responses (abundance, species richness, diversity and community composition) to eucalypt plantations.