Conservation opportunities in commercial plantations: The case of mammals

Conservation opportunities in commercial plantations: The case of mammals

Journal for Nature Conservation 19 (2011) 351–355 Contents lists available at ScienceDirect Journal for Nature Conservation journal homepage: www.el...

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Journal for Nature Conservation 19 (2011) 351–355

Contents lists available at ScienceDirect

Journal for Nature Conservation journal homepage: www.elsevier.de/jnc

Conservation opportunities in commercial plantations: The case of mammals Patricia A. Ramírez, Javier A. Simonetti ∗ Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, PO Box 653, Santiago, Chile

a r t i c l e

i n f o

Article history: Received 4 September 2010 Received in revised form 27 May 2011 Accepted 9 June 2011 Keywords: Biodiversity Land sparing Meta-analysis Structural complexity Understory Wildlife-friendly farming

a b s t r a c t Enhancing the structural complexity of commercial plantations could enrich the presence of mammals within them. We tested this hypothesis through a meta-analysis in order to determine whether more complex plantations, with a dense understory, can sustain more mammal diversity and if mammals respond differently pending on its taxonomic affiliation, body size, and diet group. We recorded 71 cases of forest–plantation comparisons, and 10 cases of plantation–plantation comparisons. Both richness and abundance of native mammals were lower in plantations than in native forests, although there was no significant difference in body size, dietary group, and taxonomic affiliation between those two habitats. Complex plantations showed higher richness and abundance of native mammals, independently of the plantation type. Taxonomic affiliation, body size and diet did not significantly differ between complex and simple plantations. Structural complexity of commercial plantations may increase mammal diversity, hence, enriching the auxiliary value of forestry plantations for biological conservation. Therefore, forest plantation management ought to pursue the enhancement of structural complexity. © 2011 Elsevier GmbH. All rights reserved.

Introduction The establishment of protected areas is the most common strategy for biodiversity conservation worldwide (Naughton-Treves et al. 2005). Setting aside lands or “land sparing” for nature conservation assumes that wildlife survival is unlikely in lands intensively used for commodity production or will be severely diminished compared to the wildlife in protected environments (Fischer et al. 2008). However, these protected but isolated areas are not able to sustain all species from the original landscape (Pimentel et al. 1992; Simonetti 1998). Further, a significant number of species survive and populations thrive outside parks and reserves (Pimentel et al. 1992; Western 1989). Therefore, to conserve biodiversity in seminatural and productive landscapes is both an increasing need and an opportunity (Daily 2001). In fact, to promote the “wildlife-friendly farming” approach aims to increase the possibility of conserving biodiversity in areas devoted to commodity production while maintaining similar levels of production (Fischer et al. 2008). Both strategies, “land sparing” and “wildlife-friendly farming”, are complementary and can enhance biodiversity conservation, especially when the demand for land is increasing (Fischer et al. 2008) due to the growth of the human population and the subsequent need for more goods and services (Musters et al. 2000; Vitousek et al. 1997). The demand of wood products, for instance, has resulted in an increase of global plantations (Lindenmayer et al.

∗ Corresponding author. Tel.: +56 2 9787264; fax: +56 2 2727363. E-mail address: [email protected] (J.A. Simonetti). 1617-1381/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.jnc.2011.06.003

2003). By 2005, forest plantations covered 271 million hectares worldwide, or 2.1% of the total land area (FAO 2009). Although the primary goal of these plantations is the production of goods such as wood and fiber, they also provide habitat to many species, including at least some mammals, suggesting that there may be opportunities for biological conservation in commercial plantations (Lindenmayer & Hobbs 2004; Nájera & Simonetti 2010a). Species richness and abundance in forestry plantations is presumably associated with structural characteristics, particularly their structural complexity (MacArhtur 1972), such as the presence of understory vegetation, remnants of native vegetation or multiple vegetation strata (Hartley 2002; Lindenmayer & Hobbs 2004; Nájera & Simonetti 2010a). Structurally complex plantations might hold more native species than simple ones serving as temporary habitat for numerous species of fauna, including birds, small mammals and invertebrates (Grez et al. 2003; Hartley 2002; Lindenmayer & Hobbs 2004; Lindenmayer et al. 2003). In fact, Nájera and Simonetti (2010a) tested if structural complexity within agro-forestry systems could enhance avian diversity. They show that, independently of the plantation type, structurally complex plantations with multiple vegetation strata or a well-developed understory hold a greater species richness and abundance than structurally simple ones, resulting in environmentally “friendlier” plantations. Nonetheless, if this is a general phenomena occurring among other taxa is yet to be assessed. If biodiversity enrichment is related to plantations’ structural complexity, it would be expected that structurally complex plantations will hold greater richness and abundance of taxa other than birds, such as mammals. After Nájera and Simonetti (2010a), we

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tested the structural complexity hypothesis using a meta-analysis of the available information on the response of mammals to structural complexity of plantations. First, we tested whether structural simplification from native forests to plantations leads to a decrease in richness and abundance of native mammals, and whether species are differentially affected regarding their taxonomic affiliation. Second, we tested if structurally complex plantations can enhance native mammal’s richness and abundance, and if species are differentially affected regarding their taxonomic affiliation. Usually, large-bodied species and carnivores are more affected by habitat loss than small-bodied species or diet generalists (Andrén 1994; Beier 1993; Maehr & Cox 1995; Laidlaw 2000). Therefore, we also tested whether structural simplification and complexity affect mammal species differentially, regarding their body size and diet. Finally, we analysed the conservation impact of structural simplification and complexity, comparing species conservation status and endemism among the fauna inhabiting forests, and simple and complex plantations. To identify the variables that determine the presence and abundance of biodiversity within plantations will allow the design of appropriate management policies to increase conservation in productive lands promoting “wildlife-friendly farming”. This is urgent for 36% of the mammal species that are threatened due to habitat change and loss (IUCN 2008). This will be a win-win approach where wildlife and biodiversity in general will benefit (Norton 1998) and where producers will be able to get environmental certifications to compete in international markets which are increasingly interested in sustainable products (FAO 2009; Norton 1998).

Methods We reviewed the ISI Web of Knowledge database for articles published between 1988 and 2009, dealing with mammalian diversity and abundance in plantations, using the search terms “mammal*” and “plantation*”. These articles were then collated into those that compared mammal richness and/or abundance between natural habitats and plantations, and those that compared plantations with different structural complexity. We also included relevant publications cited in these works in case they were not captured in the ISI database, increasing our sample size. Each comparison was considered as an independent case; more than one case was obtained from publications that performed more than one comparison. Structural complexity of plantations was classified as simple or complex depending on the development of the vertical strata within the plantation (August 1983). Simple plantations are those with single vegetation strata, single or multiple species canopy cover with thinned or cleared undergrowth, scarce or no shrub cover. Structurally complex plantations are those with multiple vegetation strata, single or multiple species canopy cover with dense undergrowth or abundant shrub development (modified from Nájera & Simonetti 2010a). First, we determined the response of mammals to change from native forest to plantation, regardless of the plantation type, and then, the response of mammals to structural complexity within plantations of the same commodity, in terms of decrease or increase in total or mean abundance or richness. Significance of changes was tested using a Sign test, considering only the direction but not the magnitude of the differences between the samples (Zar 1996). An increase of abundance or richness in plantations was considered as a positive response; meanwhile, for plantation–plantation comparisons, an increase of abundance or richness in complex plantations was considered as a positive response. Finally, we analysed if structural simplification, from forests to plantations, and complexity within plantations affected mammals species differentially

Table 1 Number of publications and cases per plantation type used for comparisons between native forest and plantations, and between plantations with different structural complexity. Type of plantation

Publications

Cases

Publications used for comparisons forest–plantation Eucalypts 10 Timber (other species) 9 Pines 9 Coffee 5 Cacao 5 Rubber 2 Teak 2 Oil palm 2 8 Others 39 Total

14 13 9 8 6 4 4 3 10 71

Publications used for comparisons plantation–plantation 2 Coffee 1 Cryptomeria japonica Eucalypts 1 1 Pine 1 Populus sp. Total 6

4 3 1 1 1 10

regarding taxonomic affiliation (order), body size (kg), diet (carnivores, herbivores or omnivores), threat categories (IUCN 2008) and endemism (at country level) (Wund & Myers 2005). Results A total of 245 papers were retrieved for the 1988–2009 period. From these, only 43 (17.6%) gave quantitative data on mammal richness and/or abundance suitable for our analyses. Comparisons of forest–plantations comprised the bulk of the screened literature (39 articles), while plantation–plantation comparisons accounted only for six articles. Two studies had both forest–plantation and plantation–plantation comparisons. We recorded 71 cases involving forest–plantation comparisons in 19 countries, the most studied plantations being: Eucalyptus (19.7%); timber (18.3%); and pines (12.7%; Table 1). Studies were carried out in South America (11 studies), Africa (8), Asia (7), Australia (5), Central America (4), North America (3), and Oceania (1), and the main focus were tropical forest (18), and temperate forest (9). Concerning comparisons between different levels of structural complexity in a given plantation, we recorded 10 cases in five countries. Three articles were from Central America, two from South America, and one from Asia. The most studied plantation was coffee comprising 40% of the cases (Table 1). Only 24 out of 43 publications were suitable for taxonomic, body size, endemism, and dietary analyses. This resulted in 20 articles for forest–plantation comparisons, and four for plantation–plantation comparisons. Richness and abundance of native mammals were significantly higher in native forests than in plantations. Plantations held fewer species than forests in 81% of the cases (44 out of 54), and lower abundance in 75% (46 out of 61), regardless of plantation type (Sign test p < 0.001 for both cases). However, ten plantations exhibited an increase in species richness and 15 in abundance. Of these, 63% of plantations with higher richness and 82% of those with higher abundance than the original forests were structurally complex, with development of understory or several vegetation strata. Regarding the number of species, 66% (111 out of 169) experienced a decrease of abundance in plantations (Sign test p < 0.001). In 90% (9 out of 10) of the cases complex plantations held higher species richness than simple plantations, but no differences were found in native mammal abundance (5 out of 9 increased; Sign test p = 0.01 and p = 0.5, respectively). This absence of differences could be due to a lack of statistical power (0.70) given the reduced sample size (Cohen 1988; Zar 1996). However, when assessed species by

P.A. Ramírez, J.A. Simonetti / Journal for Nature Conservation 19 (2011) 351–355 Table 2 Percentages of the total of species present in forest and plantations, in regard to their taxonomic affiliation at ordinal level. Na Orders Rodentia Carnivora Marsupialb Primate Ungulatec Scandentia Soricomorpha Pilosa Lagomorpha Insectivora Cingulata Tubulidentata Proboscidea Diet Omnivores Herbivores Carnivores a b c

% In forests

Table 5 Changes in mammal’s abundance in response to the increment of structural complexity within plantations.

% In plantations

54 24 17 16 14 7 3 3 2 2 2 1 1

79.6 87.5 94.1 87.5 92.9 85.7 100.0 0.0 100.0 50.0 50.0 100.0 100.0

68.5 83.3 76.5 37.5 78.6 28.6 100.0 100.0 100.0 100.0 50.0 0.0 0.0

80 22 44

81.2 84.1 90.9

68.8 65.9 72.7

353

Orders Primate Rodentia Ungulatea Carnivora Soricomorpha Diet Omnivores Herbivores Carnivores a

Increasing (%)

Decreasing (%)

100.0 87.5 75.0 66.7 0.0

0.0 12.5 25.0 33.3 100.0

100.0 60.0 50.0

0.0 40.0 25.0

Superorder.

were found in plantations than in forest; on the contrary, introduced mammals were twice as often found in plantations than in forest. Still, the latter accounted for only 2% and 0.82% of the mammal species, respectively (Table 4). On the other hand, plantations supported only 0. 5 times the number of vulnerable and 0.2 times the endangered species (Table 4). All vulnerable and endangered species found in plantations (seven and one species, respectively) were also found in forest. There were no taxonomic changes in response to structural complexity within plantations (Wilcoxon p = 0.42; Table 5). The order Insectivora was present in both simple and complex plantations, but was left out from this analysis because there was no quantitative data on their abundance. Likewise, no statistical differences were found regarding species dietary groups (Wilcoxon p = 0.11; Table 5). Body size of mammals did not differ between simple and complex plantations (Rodentia U = 13.0, p = 0.50; Ungulates U = 220, p = 0.26; Carnivora U = 162.5, p = 0.50). Regarding body size of Insectivora and Soricomorpha, there were no changes as the same species were present in both kinds of plantations. Complex plantations hosted only one more endemic species than simple

Total of species reported by publications. Infraclass. Superorder

species rather than by number of cases, 75% (15 out of 20) of the species were more abundant in complex plantations than in simple ones (Sign test p = 0.02). There was no significant difference in the taxonomic representation between forests and plantations (2 = 9.02, df = 4, p = 0.60; Table 2), although Tubulidentata and Prosboscidea were absent from plantations while Pilosa was only found in plantations. The proportions of species in each dietary group did not differ significantly among habitats (2 = 4.07, df = 2, p = 0.13; Table 2). Mammal’s body size showed no significant difference between forest habitats and plantations (Table 3). Sixty-two percent fewer endemic species Table 3 Mean body size (kg) of mammals per orders present in forests and plantations. Orders

Mean weight (±SE) Na

Rodentia Carnivora Marsupialb Primate Ungulatec Scadentia Insectivora a b c

U Na

Forests 0.8 ± 0.4 12.9 ± 4.6 5.4 ± 3.7 8.4 ± 3.7 166.8 ± 65.3 0.1 ± 0.02 0.01

43 21 16 14 13 6 1

37 20 13 6 11 2 2

p-Value

Plantations 0.7 12.3 7.0 13.1 165.1 0.2 0.5

± ± ± ± ± ± ±

0.4 4.9 4.6 8.4 77.5 0.008 0.5

3137 615.5 389.5 139 138 24.5 4.5

0.45 0.32 0.49 0.41 0.35 0.48 0.40

Total of species reported by publications. Infraclass Superorder.

Table 4 Conservation status and endemism of mammals, in response to structural simplification from forests to plantations, and to structural complexity within plantations (shown in number of species).

Category Native Endemic Introduced Status Least concern Vulnerable Near threatened Endangered Data deficient

Response to structural simplification

Response to structural complexity

Forests

Simple plantations

Plantations

Complex plantations

114 8 1

95 3 2

16 4 0

19 5 1

93 13 9 5 3

83 7 6 1 3

12 3 3 0 2

15 3 5 0 2

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plantations and, unlike the latter, hosted one introduced rodent species, but it only accounted for the 4% of the mammal species (Table 4). Finally, no endangered species were found in either type of plantation; however, complex plantations hosted 40% more near threatened species than simple plantations (Table 4); all three near threatened species found in simple plantations were also found in complex plantations.

Discussion The rapid growth of human population has led to a major land transformation (Vitousek et al. 1997) changing native forests into other land uses, such as commercial plantations, in order to fulfill demand for goods and services (FAO 2009). As forests shelter a major part of all terrestrial species, the impacts of land transformation on biodiversity is a matter of concern (Carnus et al. 2003). In comparison to native forests, plantations held fewer species richness and abundance of native mammals, and a diminished proportion of species of conservation concern, which reflects changes in species composition. This is due mainly because mammal assemblages in plantations usually comprise habitat generalist, common, and widespread species that have a wide habitat elsewhere (Christian et al. 1996, 1998). However, it is noteworthy that in 10 and 15 cases plantations exhibited greater species richness and abundance, respectively, than native forest; these plantations are mainly structurally complex ones with well developed understory or a heterogeneous interior with remains of native forest or a multiple vegetation strata. Therefore, while plantations by no means are equivalent to the original forests in its mammalian diversity, structurally complex plantations can contribute to mitigate species loss and offer additional habitat for a suite of species (e.g. Brockerhoff et al. 2008; Fonseca et al. 2009). Conservation of biological diversity restricted to protected areas only will not suffice (Fonseca et al. 2009; Pimentel et al. 1992; Simonetti 1998). Therefore, plantations managed for holding a complex understory might contribute to conservation off-reserves (Daily 2001; Hartley 2002; Lindenmayer & Hobbs 2004; WilliamsGuillén et al. 2006). Structural complexity within plantations provides habitat heterogeneity, increasing the resource base allowing for more species to coexist (MacArhtur 1972). Further, it increases structural similarity to natural habitats, improving habitat quality (Prevedello & Vieira 2010). In general, there were few available studies regarding structural complexity within plantations. The support of any decision making for conservation must be based on the systematic appraisal of the evidence, so, this lack of studies highlights the need for more research in order to increase the evidence upon which conservation decisions should rely on (Pullin & Stewart 2006; Sutherland et al. 2004). Although it has been recognised that the maintenance of the understory vegetation can improve habitat quality within plantations by providing resources for mammals (Bellows et al. 2001; Hartley 2002; Lindenmayer & Hobbs 2004), no experimental studies have addressed this issue at this time. Nájera and Simonetti (2010b) have demonstrated that the removal of the understory vegetation reduces bird diversity and abundance in oil palm plantations, but this kind of research is absent in the case of mammals. Thus, more experimental studies should take place in plantations in order to study and monitor the variables that improve mammal occurrence in plantations. Human-managed ecosystems can play a key role for conservation purposes (Ceballos et al. 2005). To do so, plantations quality must be improved so they can shelter more species. In this sense, promoting structural complexity within plantations enhances not only mammal but also native bird and insect diversity (Grez et al. 2003; Nájera & Simonetti 2010a), and highlights the possibility of

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