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Journal ArticleDOI

Comparative footprint of alien, agricultural and restored vegetation on surface-active arthropods

01 Jan 2012-Biological Invasions (Springer Netherlands)-Vol. 14, Iss: 1, pp 165-177
TL;DR: The results suggest that vineyards retain a greater complement of indigenous species than alien trees, but that clearing of these aliens soon encourages establishment of indigenousspecies, an encouraging sign for restoration.
Abstract: Both invasive alien trees and agricultural conversion have major impacts on biodiversity. We studied here the comparative impact of these two types of land transformation on a wide range of surface-active arthropod species using pitfall traps, with evergreen sclerophyllous natural vegetation (fynbos) as the control. The study was in the Cape Floristic Region, a global biodiversity hotspot, where alien trees are of major concern and where vineyards replace natural fynbos vegetation. Surface-active arthropods were selected as they are species rich, relatively immobile, and occur in high abundance. We hypothesized that the impact of the two types of land cover transformation would produce similar qualitative and quantitative effects on the arthropods. We also compared the results in the transformed and natural areas with those in areas cleared of alien trees. Arthropod species richness in cleared areas was higher than in vineyards and more similar to that in natural fynbos, while alien trees had the lowest. Overall abundance scores were highest in cleared areas, closely followed by fynbos, then vineyards and lowest in alien trees. Several species were restricted to each vegetation type, including alien trees. In terms of assemblage composition, all vegetation types were significantly different, although fynbos and vineyards grouped, suggesting that vineyards have less impact on the arthropod community than do alien trees. When rare species were excluded, vineyards and cleared sites grouped, indicating some recovery but only involving those species that were common and habitat tolerant. Our results suggest that vineyards retain a greater complement of indigenous species than alien trees, but that clearing of these aliens soon encourages establishment of indigenous species. Although there were significant differences in soil moisture and litter depth within and between vegetation types, we did not record them as significantly affecting species richness or abundance, even in alien vegetation, an encouraging sign for restoration.

Summary (2 min read)

Introduction

  • Yet there is little knowledge on the comparative impact, or footprint, of these two types of human-induced land transformations on this biodiversity, so the authors investigate here the comparative impact of IATs and vineyards on soil-surface arthropod diversity, and compare it with patches where IATs had been removed.
  • The authors chose this group of arthropods as it is species-rich, occurs in high abundance, and most species are relatively immobile (therefore allowing spatially-explicit interpretation of the arthropod data).

Study area and methods

  • Study sites Sampling was in three nature reserves and seven wine estates within the CFR (Table 1).
  • This reserve was considered due to the presence of mountain fynbos adjacent to invasive alien trees (i.e. Pinus and Hakea spp.).
  • Arthropod samples from each trap set were combined, resulting in one sample per sampling station (i.e. 1000 pitfall traps gave 500 samples per sampling period, making 1 500 samples over the three sampling periods).
  • Multiple comparisons of the means were made using Bonferroni methodology (Legendre and Legendre 1998).
  • Multivariate analysis, using Primer Ver. 5 (Clarke and Gorley 2001), was used to detect trends and to explore the differences in arthropod assemblages between different vegetation types.

Results

  • In turn, IATs and vineyards were significantly different from each other in species richness, and both were not comparable to either fynbos or CIATs (Fig. 1).
  • Classification of different vegetation types in terms of arthropod abundance gave three different nodes (Fig. 2).
  • Cleared = vegetation cleared of invasive alien trees, natural = fynbos, IATs = invasive alien trees Fig. 2 Classification tree of vegetation in terms of mean arthropod abundance.
  • These arthropod species can be considered as typical of associated vegetation types, although L. humile is alien (Table 6).

Discussion

  • Species richness and abundance in the different vegetation types.
  • In terms of overall abundance, invaded areas were much poorer than vineyards, indicating greater impact of alien trees over that of vineyards.
  • Yet species richness of the cleared areas was close to that of fynbos, showing that clearing of alien trees increases species richness, an encouraging sign for restoration.
  • This is not surprising because alien trees can impoverish the local terrestrial fauna even over a few metres (Samways et al. 1996).

Conclusions

  • This suggests that conversion of vineyards to more biodiversity friendly farming methods, as outlined by Gaigher and Samways (2010), has a good base on which to work.
  • In turn, clearing of alien trees will continue to benefit biodiversity recovery, but it will take time for the original set of species to return, as it is only the common, and presumably more habitattolerant, species which readily recover.
  • Acknowledgments Financial support was from the Centre for Invasion Biology and the Andrew Mellon Foundation.
  • Rejoyce Gavhi, Rozwivhona Magoba, Mbula Tshikalange, Adam Johnson, Tshilidzi Muofhe and Sne Mchunu kindly assisted in the field.
  • The authors also appreciate the very constructive criticisms of two anonymous referees which greatly improved the manuscript.

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ORIGINAL PAPER
Comparative footprint of alien, agricultural and restored
vegetation on surface-active arthropods
Rembu N. Magoba
Michael J. Samways
Received: 21 October 2010 / Accepted: 4 April 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Both invasive alien trees and agricultural
conversion have major impacts on biodiversity. We
studied here the comparative impact of these two
types of land transformation on a wide range of
surface-active arthropod species using pitfall traps,
with evergreen sclerophyllous natural vegetation
(fynbos) as the control. The study was in the Cape
Floristic Region, a global biodiversity hotspot, where
alien trees are of major concern and where vineyards
replace natural fynbos vegetation. Surface-active
arthropods were selected as they are species rich,
relatively immobile, and occur in high abundance.
We hypothesized that the impact of the two types of
land cover transformation would produce similar
qualitative and quantitative effects on the arthropods.
We also compared the results in the transformed and
natural areas with those in areas cleared of alien trees.
Arthropod species richness in cleared areas was
higher than in vineyards and more similar to that in
natural fynbos, while alien trees had the lowest.
Overall abundance scores were highest in cleared
areas, closely followed by fynbos, then vineyards and
lowest in alien trees. Several species were restricted to
each vegetation type, including alien trees. In terms of
assemblage composition, all vegetation types were
significantly different, although fynbos and vineyards
grouped, suggesting that vineyards have less impact on
the arthropod community than do alien trees. When
rare species were excluded, vineyards and cleared sites
grouped, indicating some recovery but only involving
those species that were common and habitat tolerant.
Our results suggest that vineyards retain a greater
complement of indigenous species than alien trees, but
that clearing of these aliens soon encourages estab-
lishment of indigenous species. Although there were
significant differences in soil moisture and litter depth
within and between vegetation types, we did not record
them as significantly affecting species richness or
abundance, even in alien vegetation, an encouraging
sign for restoration.
Keywords Alien vegetation Agricultural
conversion Restoration Arthropods Cape Floristic
Region
Introduction
Invasion by alien tree species is a global environ-
mental problem (Mack et al. 2000; Richardson and
Pys
ˇ
ek 2006), affecting movement patterns of animals,
including insects (Wood and Samways 1991), and
threatening their habitats (Armstrong and van
Electronic supplementary material The online version of
this article (doi:10.1007/s10530-011-9994-x) contains
supplementary material, which is available to authorized users.
R. N. Magoba M. J. Samways (&)
Department of Conservation Ecology and Entomology,
and Centre for Invasion Biology, University
of Stellenbosch, P/Bag X1, Matieland 7602, South Africa
e-mail: samways@sun.ac.za
123
Biol Invasions
DOI 10.1007/s10530-011-9994-x

Hensbergen 1996; Samways et al. 1996; Richardson
and van Wilgen 2004; Samways and Taylor 2004).
However, different ecosystems vary considerably in
their susceptibility to invasion (Chytry
´
et al. 2008),
with the impacts of alien tree species in natural
systems being dependent on invader attributes and on
characteristics of the invaded community (Mason and
French, 2008). Invasive alien trees (IATs) are wide-
spread in the Cape Floristic Region (CFR), South
Africa, and their success attributed to their good
colonizing abilities, especially in disturbed areas
(Holmes and Richardson 1999). In many parts of the
world, alien trees are the main component of
commercial forestry, with these trees often spreading
from planting sites (Simberloff et al. 2010). IATs
such as Pinus, Acacia and Eucalyptus species are of
major commercial importance in South Africa, but
they are also a threat to water supplies and biodiver-
sity (Wittenberg and Cock 2001; Le Maitre et al.
2004), especially in the CFR (Macdonald and
Richardson 1986).
Another impact on natural systems is conversion
to agriculture, which changes ecosystem composition
and function (Donald and Evans 2006), and its
biodiversity (Turin and den Boer 1988; Newton 2004;
Gaigher and Samways 2010). Agriculture is one of
the most significant human-induced disturbances that
threatens terrestrial biodiversity (Sala et al. 2000;
Tilman et al. 2001), affecting the availability of
suitable terrestrial habitats (Feber et al. 1996; Warren
et al. 1997; Jeanneret et al. 2003; Kleijn and van
Langevelde 2006). For example, vegetation structure
is important to some arthropods because it can affect
their ability to thermoregulate and reproduce (Holl
1996). However, vegetation loss for agricultural
purposes does not threaten all arthropods equally
(Fleishman et al. 1999), with some relatively small-
scale agriculture maintaining open, early seral bio-
topes favoured by some arthropod species (Shreeve
and Mason 1980; Sibatani 1980).
The regional focus for this study is the CFR, a
global biodiversity hotspot (Mittermeier et al. 2005)
and a world centre of plant diversity and endemism
(Linder 2005; Proches¸ and Cowling 2006), with 67%
of plant species endemic to the region (Linder 2005
).
It is also an important area for many rare and
endemic arthropod species (Johnson 1992; Picker and
Samways 1996; Wright and Samways 1998;
Giliomee 2003; Proches¸ and Cowling 2006; Proches¸
et al. 2009). Of significance here is that both invasive
alien trees (IATs) and agriculture, especially vine-
yards, have an impact on this biodiversity (Rouget
et al. 2003). Yet there is little knowledge on the
comparative impact, or footprint, of these two types
of human-induced land transformations on this bio-
diversity, so we investigate here the comparative
impact of IATs and vineyards on soil-surface arthro-
pod diversity, and compare it with patches where
IATs had been removed. We chose this group of
arthropods as it is species-rich, occurs in high
abundance, and most species are relatively immobile
(therefore allowing spatially-explicit interpretation of
the arthropod data). We hypothesized that the quan-
titative and qualitative adverse footprint in its entirety
(interior and edge) of IATs and vineyards on
arthropod diversity is the same, as they are both, at
least to the human eye, major transformations of
landscape matrix at the spatial scale of the patch.
Study area and methods
Study sites
Sampling was in three nature reserves and seven wine
estates within the CFR (Table 1). At each of these ten
localities, transects were established, so that the focal
land cover/land use types (hereafter referred to as
‘vegetation type’) were adjacent to each other. In
total, there were 36 transects, each 256 m in length.
Half of the transect, i.e. 128 m, was on either side of
the boundary of land use/land cover types, with the
exception of two transects (128 m in length) that
were established across native vegetation and small
IAT fragments (Table 1). Vegetation type was in four
categories: natural fynbos (evergreen schlerophyllous
shrublands characterized by graminoids of the Res-
tionaceae, and shrubs of the Ericaceae and Protea-
ceae), IATs, cleared of invasive alien trees (CIATs),
and vineyards. These resulted in six different pairs of
vegetation types (Table 1).
Natural fynbos was relatively untransformed by
human activity and selected from the nature reserve
and the wine farms with less than 10% alien tree
vegetation. Natural fynbos was predominantly moun-
tain fynbos, with common plant species being geo-
phytes Watsonia borbonica, Cyphia phyteuma and
Chasmanthe aethiopica; herbs Gymnodiscus capillaris
R. N. Magoba, M. J. Samways
123

and Dimorphotheca pluvialis; shrubs Aspalathus forb-
esii, A. aspalathoides, Lebeckia sepiaria, Lotononis
prostrata, Hymenolepis crithmoides, Protea compacta,
P. repens, P. neriifolia, and Salix species, as well
as various ericas. IATs was considered a vegetation
type with more than 90% alien trees, mainly Acacia
Table 1 Details of the study sites and transects
Category Site name Locality Pair of vegetation Transect
length (m)
No. pitfall
traps
Vineyards Vergelegen E: 34.09206
S: 18.89851
Cleared IATs Natural Fynbos 256 28
Cleared IATs Natural Fynbos 256 28
Cleared IATs Natural Fynbos 256 28
Cleared IATs Natural Fynbos 256 28
IATs Natural Fynbos 256 28
IATs Cleared IATs 256 28
IATs Cleared IATs 256 28
Bilton E:34.01431
S:18.87259
Vineyard IATs 256 28
Vineyard IATs 256 28
Vineyard IATs 256 28
Vineyard Natural Fynbos 256 28
Vineyard Natural Fynbos 256 28
Stellenzicht-Driekoppen E:34.98575
S:18.95216
Vineyard Cleared IATs 256 28
Vineyard Cleared IATs 256 28
Waterford E: 34.06625
S: 18.87626
Vineyard IATs 256 28
IATs Cleared IATs 256 28
Rustenberg E: 33.96862
S: 18.9354
Vineyard Cleared IATs 256 28
Vineyard Cleared IATs 256 28
Vineyard Natural Fynbos 256 28
Vineyard Natural Fynbos 256 28
Vineyard Natural Fynbos 256 28
Vineyard Natural Fynbos 256 28
Vineyard IATs 256 28
Dornier E: 34.01731
S: 18.86607
Vineyard IATs 256 28
Waterford-Driekoppen E: 34.0063
S: 18.87639
Vineyard Cleared IATs 256 28
Vineyard Cleared IATs 256 28
Nature Reserves Jonkershoek E: 33.98317 IATs Natural Fynbos 256 28
S: 18.94967 IATs Natural Fynbos 256 28
IATs Natural Fynbos 128 24
IATs Natural Fynbos 128 24
Helderberg E: 34.00535 IATs Cleared IATs 256 28
S: 18.8748 IATs Natural Fynbos 256 28
Hottentots Holland E: 34.06436 IATs Cleared IATs 256 28
IATs Cleared IATs 256 28
S: 18.87469 Cleared IATs Natural Fynbos 256 28
Cleared IATs Natural Fynbos 256 28
Total number of pitfall traps 1000
IATs invasive alien trees
Comparative footprint of alien, agricultural and restored vegetation
123

mearnsii, A. longifolia, A. saligna, Hakea sericea,
H. drupacea, Pinus Pinaster, P. radiata, Eucalyptus
lehmannii, E. diversicolor and Populus trees, with an
understorey of grasses and forbs. Since 2000, farmers
together with government authorities started clearing
these invasive alien trees, with follow-up clearing
undertaken at least every 3 years. Physical or manual
and chemical control methods were applied during IAT
clearing. In essence, IATs were cut and herbicides
applied to the remaining mainstem. Only organic
vineyards were considered. Organic vineyard manage-
ment involves no application of artificial fertilizers as
the soils are relatively fertile through permanent cover
crop (i.e. wheat), and only apply pesticides when
absolutely necessary. One application of chemical
agent chlorpyrifos was applied during early August to
control mealybugs which are the vectors of a viral
disease of the vines.
The 9800 ha Jonkershoek nature reserve com-
prises the Jonkershoek mountains and portions of the
upper Jonkershoek valley where large Radiata pine
(Pinus radiata) plantations are a distinctive feature
bordering fynbos vegetation. This reserve was con-
sidered due to the presence of mountain fynbos
adjacent to invasive alien trees (i.e. Pinus and Hakea
spp.). The 286 ha Helderberg nature reserve has
mountain fynbos dominated mainly by protea spe-
cies. This site was chosen for its IATs adjacent to a
site cleared of IATs (i.e. Pinus spp.). The Hottentots
Holland nature reserve is 42 000 ha and comprises
the Hottentots Holland mountains with the presence
of pristine mountain fynbos adjacent to IATs (i.e.
P. radiata).
Sampling
Sampling of the arthropods was on three occasions
(August-October 2006, May–July 2007 and Novem-
ber 2007–January 2008), when soil surface charac-
teristics (i.e. soil moisture with radioactive moisture-
density gauge (Troxler 3411-B) and leaf litter depth
by inserting a steel rod, 4 mm in diameter, into the
leaf-litter until the harder soil layer was reached)
were also measured. Pitfall traps were used to sample
arthropods as this method is particularly good for
comparative studies of soil-surface active arthropods
(Samways et al. 2010). The 256 m transects consisted
of a trap-set of two individual pitfall traps, 1 m apart,
placed at log 2 intervals: 2, 4, 8, 16, 32, 64 and 128 m
on either side of the boundary between two adjoining
vegetation types to ensure all species across
the whole vegetation type were accounted for. The
reason for this layout of traps was because the
‘footprint’ of any one patch has both interior and
edge, with a cross over at approximately 30 m
(Samways and Moore 1991; J.S. Pryke unpublished
data). The aim was to give approximate equal
weighting to both interior and edge, while at the
same time having a sampling programme that was
practical in terms of time, hence the log 2 intervals.
This is a study of a land mosaic consisting of
patchwork of land use types, making a reference site
of a small-sized patch of fynbos being more appro-
priate than an extensive nature reserve so as to
compare different types of patches of comparative
size. Furthermore, beta diversity is very high in
extensive natural habitats and we did not want to
invoke another variable into the data. It was not the
intention here to unpack all the complex details of
edge effects for the different taxa but rather to
compare patches in their entirety in a variety of
landscape contexts (see Wiens et al. 1993). However,
two transects, between IATs and fynbos, were each
four traps short, owing to unavailability of extensive
sites (Table 1). The total was 1000 pitfall traps (two
per set, fourteen sets per transect, six transects per
vegetation type pair and six vegetation pairs from
four vegetation types, minus eight traps) (Table 1).
Pitfall traps for sampling arthropods were 500 ml
plastic honey jars, each containing a replaceable
paper cups, 8 cm diameter, 12 cm deep. Each trap
was one-third filled with 70% ethylene glycol. Traps
remained closed during non-sampling periods, and
opened for five consecutive days without rain
(Borgelt and New 2006). Samples then were washed
in water, and transferred to 70% ethanol.
Sampling in vineyards was under vine rows to
minimize impact of disturbance by farm activity. All
pitfall traps were established three months prior
initial sampling to eliminate ‘digging effects’.
Arthropod samples from each trap set were com-
bined, resulting in one sample per sampling station
(i.e. 1000 pitfall traps gave 500 samples per sam-
pling period, making 1 500 samples over the three
sampling periods).
Arthropods were identified to species, or where
this was not possible, assigned to morphospecies.
Voucher specimens are in the Entomology Museum,
R. N. Magoba, M. J. Samways
123

Stellenbosch University, although spiders are in the
National Collection of Arachnida, National Museum,
Pretoria. Identification was by keys and expert
opinion.
Data analyses
Species accumulation curves, using EstimateS
version 8.0.0 with samples randomized 50 times
(Colwell 2006), were produced for all vegetation types
separately, and for all combined. Non-parametric
species estimators were used to provide the best
overall arthropod species estimates for all vegetation
types (Hortal et al. 2006). The incidence based
Coverage Estimator (ICE) is a robust and accurate
estimator of species richness (Chazdon et al. 1998),
whereas Chao2 and Jackknife estimators provide the
least biased estimates should insufficient sampling be
an issue (Colwell and Coddington 1994), and were
calculated here using EstimateS (Colwell 2006) for
all vegetation types separately and for all combined.
As arthropod species richness was normally dis-
tributed and variance homogeneous, one-way analy-
sis of variance (ANOVA) was performed on species
richness data. However, log transformations were
used for abundance data. Multiple comparisons of the
means were made using Bonferroni methodology
(Legendre and Legendre 1998). ANOVA was used to
test for differences between means of populations.
ANOVAs were performed on the selected envi-
ronmental variables in the different vegetation types
using SPSS v17 software (SPSS Inc. 2006), and
significance level was set at a P-value [0.05. Where
the ANOVAs were not significant, the analysis was
terminated. However, where the result was signifi-
cant, it was investigated further using multi-compar-
ison tests.
Classification trees, using CHAID growth limits
(SPSS Inc. 2006) determined the relationship
between the vegetation types in terms of species
richness and abundance relative to environmental
variables. Significance level for splitting nodes and
merging categories was 0.05, and the significance
values were adjusted using Bonferroni methodology.
Correlations between species richness and abundance
with environmental variables for all vegetation types,
separately and collectively, were calculated using
Spearman’s Rank Order Coefficient, since the data
were not normally distributed.
Multivariate analysis, using Primer Ver. 5 (Clarke
and Gorley 2001), was used to detect trends and to
explore the differences in arthropod assemblages
between different vegetation types. Bray-Curtis sim-
ilarity coefficients were used to derive similarity
matrices of arthropod data, then clustering dendro-
grams and non-metric, multi-dimensional scaling
(NMDS) ordination plots to detect trends in similar-
ity. The main advantage of NMDS is its greater
ability to represent complex relations accurately in
low-dimensional space (Clarke and Warwick 2001).
Joint absences in the NMDS were ignored to
emphasize similarity in common or rare species,
comparing only percentage composition (Clarke and
Warwick 2001). The dendrograms were group-aver-
age linking on Bray-Curtis species similarities from
standardized abundance data.
Principal Components Analysis (PCA) was used to
determine whether arthropods from the different
vegetation types fell into distinct groups (Clarke
and Warwick 2001). PCA considers a different
starting point by making different assumptions about
the definition of (dis)similarity of samples being
compared. Rare species were excluded from the PCA,
so that the species retained were more comparable
with the number of samples (Clarke and Warwick
2001). Distances between vegetation types on the
ordination attempt to match the corresponding dis-
similarities in arthropod assemblage composition i.e.
similar vegetation types would have very similar
arthropod assemblages, while vegetation types that
are dissimilar would have few species in common, or
the same species at very different levels of abun-
dance. However, PCA can produce inconclusive
results, so the data were further analyzed using
cluster analysis for determining how the vegetation
types varied, and how they grouped in terms of their
arthropod assemblages. Cluster analysis produces
results that broadly agree with PCA (Clarke and
Warwick 2001), and usually it is much easier to
observe grouping in cluster analysis than in PCA.
Nevertheless, it may be easier to understand what the
groupings indicate if they have been produced by
PCA. Therefore, using a combination of cluster
analysis and PCA is an effective approach.
Analysis of similarity (ANOSIM) tests the hypoth-
esis that there are no assemblage differences between
groups of samples specified, here vegetation type
(Clarke and Warwick 2001). R is approximately zero
Comparative footprint of alien, agricultural and restored vegetation
123

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Abstract: Bioindicators, as taxa or functional groups, are widely used as indicators of environmental change, specific ecological factors or taxonomic diversity. The use of ecological, environmental and biodiversity indicators, is reviewed here. Although indicator taxa are considered to be generally unreliable as broad indicators of biodiversity, they may serve a useful function in identifying ecological characteristics or monitoring the effects of habitat management. Use of only a narrow range of taxa may be unreliable, and is particularly vulnerable to distortion by a small number of invasive species. Taxa also need to be selected to reflect the specific ecosystem being studied. It is recommended that isopods be used for soil systems (if there is sufficient local diversity), in some areas earthworms or mites may be useable but are generally too difficult to identify to be practically useful. In the ground layer indicator sets could include ants, millipedes, molluscs (snails in particular), ground beetles, harvestmen and gnaphosid spiders. Foliage-inhabiting indicators could comprise ants, chrysomelid leaf beetles, theridiid spiders and arctiid moths. Ants, orthopterans and butterflies may be appropriate for use in open habitats. These basic sets should be supplemented by other taxa where appropriate resources and taxonomic expertise are available.

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References
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Journal ArticleDOI
01 Oct 2004-Ibis
TL;DR: The main aspects of agricultural intensification that have led to population declines in farmland birds over the past 50 years are reviewed, together with the current state of knowledge, and the effects of recent conservation actions.
Abstract: In this paper, the main aspects of agricultural intensification that have led to population declines in farmland birds over the past 50 years are reviewed, together with the current state of knowledge, and the effects of recent conservation actions. For each of 30 declining species, attention is focused on: (1) the external causes of population declines, (2) the demographic mechanisms and (3) experimental tests of proposed external causal factors, together with the outcome of (4) specific conservation measures and (5) agri-environment schemes. Although each species has responded individually to particular aspects of agricultural change, certain groups of species share common causal factors. For example, declines in the population levels of seed-eating birds have been driven primarily by herbicide use and the switch from spring-sown to autumn-sown cereals, both of which have massively reduced the food supplies of these birds. Their population declines have been associated with reduced survival rates and, in some species, also with reduced reproductive rates. In waders of damp grassland, population declines have been driven mainly by land drainage and the associated intensification of grassland management. This has led to reduced reproductive success, as a result of lowered food availability, together with increased disturbance and trampling by farm stock, and in some localities increased nest predation. The external causal factors of population decline are known (with varying degrees of certainty) for all 30 species considered, and the demographic causal factors are known (again with varying degrees of certainty) for 24 such species. In at least 19 species, proposed causal factors have been tested and confirmed by experiment or by local conservation action, and 12 species have been shown to benefit (in terms of locally increased breeding density) from options available in one or more agri-environment schemes. Four aspects of agricultural change have been the main drivers of bird population declines, each affecting a wide range of species, namely: (1) weed-control, mainly through herbicide use; (2) the change from spring-sown to autumn-sown cereal varieties, and the associated earlier ploughing of stubbles and earlier crop growth; (3) land drainage and associated intensification of grassland management; and (4) increased stocking densities, mainly of cattle in the lowlands and sheep in the uplands. These changes have reduced the amounts of habitat and/or food available to many species. Other changes, such as the removal of hedgerows and ‘rough patches’, have affected smaller numbers of species, as have changes in the timings of cultivations and harvests. Although at least eight species have shown recent increases in their national population levels, many others seem set to continue declining, or to remain at a much reduced level, unless some relevant aspect of agricultural practice is changed.

618 citations


"Comparative footprint of alien, agr..." refers background in this paper

  • ...Another impact on natural systems is conversion to agriculture, which changes ecosystem composition and function (Donald and Evans 2006), and its biodiversity (Turin and den Boer 1988; Newton 2004; Gaigher and Samways 2010)....

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25 Jun 1998
TL;DR: In this article, the authors compared the performance of various estimation techniques within individual sites as well as across a range of sites differing in successional status and in woody species abundance and spatial distribution.
Abstract: The study of plant communities requires a basic understanding of the abundance, distribution, and number of species present Yet, in obtaining this information, scientists can rarely sample the entire community or area of interest In practice, data from numerous small sub-samples provide a basis for extrapolating to a larger area, Such extrapolating must take into account the well-supported observation that estimates of local species richness depend strongly on the number of individuals and the area sampled (Gleason, 1922; Preston, 1948) Although researchers must rely heavily on extrapolations for many kinds of ecological studies, relatively little attention has been focused on improving the accuracy, applicability, and accessibility of species-richness estimators in vegetation studies, particularly in higly diverse tropical ecosystems If robuts and accurate statistical estimators of species richness that are reasonably insensitive to sample size can be found, they can serve to provide a quantitative basis for identifying conservation priorities, for comparative biogeographic or regional studies, and for assessing long-term changes in species richness Bunge and Fitzpatrick (1993) and Colwell and Coddington (1994) provided a broad overview of statistical approaches for estimating species richness form samples Here, we evaluated the performance of several of these methods in estimating species richness of young woody regeneration in six tropical forest sites We compared the performance of various estimation techniques within individual sites as well as across a range of sites differing in successional status and in woody species abundance and spatial distribution We focused specifically on two size classes of wood regeneration: 1) established seedlings 1m in height, but

615 citations


"Comparative footprint of alien, agr..." refers background in this paper

  • ...The incidence based Coverage Estimator (ICE) is a robust and accurate estimator of species richness (Chazdon et al. 1998), whereas Chao2 and Jackknife estimators provide the least biased estimates should insufficient sampling be an issue (Colwell and Coddington 1994), and were calculated here using…...

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Journal ArticleDOI
TL;DR: It is concluded that most species richness estimators may be useful in biodiversity studies and a decision framework is proposed to assess which estimator should be used to compare species richness scores of different sites, depending on the grain size of the original data, and of the kind of data available.
Abstract: Summary 1 Fifteen species richness estimators (three asymptotic based on species accumulation curves, 11 nonparametric, and one based in the species–area relationship) were compared by examining their performance in estimating the total species richness of epigean arthropods in the Azorean Laurisilva forests. Data obtained with standardized sampling of 78 transects in natural forest remnants of five islands were aggregated in seven different grains (i.e. ways of defining a single sample): islands, natural areas, transects, pairs of traps, traps, database records and individuals to assess the effect of using different sampling units on species richness estimations. 2 Estimated species richness scores depended both on the estimator considered and on the grain size used to aggregate data. However, several estimators (ACE, Chao1, Jackknife1 and 2 and Bootstrap) were precise in spite of grain variations. Weibull and several recent estimators [proposed by Rosenzweig et al. (Conservation Biology, 2003, 17, 864–874), and Ugland et al. (Journal of Animal Ecology, 2003, 72, 888–897)] performed poorly. 3 Estimations developed using the smaller grain sizes (pair of traps, traps, records and individuals) presented similar scores in a number of estimators (the above-mentioned plus ICE, Chao2, Michaelis–Menten, Negative Exponential and Clench). The estimations from those four sample sizes were also highly correlated. 4 Contrary to other studies, we conclude that most species richness estimators may be useful in biodiversity studies. Owing to their inherent formulas, several nonparametric and asymptotic estimators present insensitivity to differences in the way the samples are aggregated. Thus, they could be used to compare species richness scores obtained from different sampling strategies. Our results also point out that species richness estimations coming from small grain sizes can be directly compared and other estimators could give more precise results in those cases. We propose a decision framework based on our results and on the literature to assess which estimator should be used to compare species richness scores of different sites, depending on the grain size of the original data, and of the kind of data available (species occurrence or abundance data).

505 citations


"Comparative footprint of alien, agr..." refers methods in this paper

  • ...Non-parametric species estimators were used to provide the best overall arthropod species estimates for all vegetation types (Hortal et al. 2006)....

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Journal Article
TL;DR: The ecological evidence for the impacts of invasive alien plants on South African ecosystems is examined and a framework to suggest the main challenges for research is suggested that will address critical gaps in knowledge and that will serve explicit management needs is suggested.
Abstract: .South Africa has a long history of problems with invasive alien species, and of research and management of biological invasions (Table 1). The Working for Water programme 26–28 was started in 1995 to conduct and coordinate alien-plant management throughout South Africa. The programme initially worked only in watersheds and riparian areas, but now leads alien-plant management initiatives in all natural and semi-natural ecosystems. It has grown into one of the world’s biggest programmes dealing with invasive alien species. The enterprise’s success has been attributed to its multi-faceted and cross-disciplinary nature that has enabled it to leverage local and international funding and continuing political support. The programme is driven by multi-disciplinary ecological, hydrological, social and economic goals. In practice it has focused on hydrological and social concerns (as embodied in the name of the programme), and its ecological goals are less clearly defined. The extent to which the aim of improving the ecological integrity of natural ecosystems through the control of invasive alien plants has therefore not always been clear to both programme participants and other stakeholders. In this paper, we examine the ecological evidence for the impacts of invasive alien plants on South African ecosystems. We begin with a brief review of what is known about the extent of invasions and influences of these plants, and then discuss the consequences for the delivery of ecosystem goods and services to people. However, the emerging field of invasion ecology addresses issues beyond the effects of invasive species. The different aspects of invasion ecology can be related to the critical stages of invasion, and these stages also provide a useful framework for classifying the management interventions that are required to deal with the problem (Box 1). Our understanding of many of the broader aspects of invasion ecology needs to improve, and we use this framework to suggest the main challenges for research that will address critical gaps in knowledge and that will serve explicit management needs. Components of impact

504 citations

Journal ArticleDOI
TL;DR: In this paper, a database of 52 480 vegetation plots from three regions of Europe: Catalonia (Mediterranean-submediterranean region), Czech Republic (subcontinental) and Great Britain (oceanic) was used to classify plant species into neophytes, archaeophytes and natives, and calculated the proportion of each group in 33 habitats described by the EUNIS classification.
Abstract: Summary 1. Although invasions by alien plants are major threats to the biodiversity of natural habitats, individual habitats vary considerably in their susceptibility to invasion. Therefore the risk assessment procedures, which are used increasingly by environmental managers to inform effective planning of invasive plant control, require reliable quantitative information on the extent to which different habitats are susceptible to invasion. It is also important to know whether the levels of invasion in different habitats are locally specific or consistent among regions with contrasting climate, flora and history of human impact. 2. We compiled a database of 52 480 vegetation plots from three regions of Europe: Catalonia (Mediterranean‐submediterranean region), Czech Republic (subcontinental) and Great Britain (oceanic). We classified plant species into neophytes, archaeophytes and natives, and calculated the proportion of each group in 33 habitats described by the European Nature Information System (EUNIS) classification. 3. Of 545 alien species found in the plots, only eight occurred in all three regions. Despite this large difference in species composition, patterns of habitat invasions were highly consistent between regions. None or few aliens were found in environmentally extreme and nutrient-poor habitats, e.g. mires, heathlands and high-mountain grasslands. Many aliens were found in frequently disturbed habitats with fluctuating nutrient availability, e.g. in man-made habitats. Neophytes were also often found in coastal, littoral and riverine habitats. 4. Neophytes were found commonly in habitats also occupied by archaeophytes. Thus, the number of archaeophytes can be considered as a good predictor of the neophyte invasion risk. However, neophytes had stronger affinity to wet habitats and disturbed woody vegetation while archaeophytes tended to be more common in dry to mesic open habitats. 5. Synthesis and applications. The considerable inter-regional consistency of the habitat invasion patterns suggests that habitats can be used as a good predictor for the invasion risk assessment. This finding opens promising perspectives for the use of spatially explicit information on habitats, including scenarios of future land-use change, to identify the areas of highest risk of invasion.

485 citations


"Comparative footprint of alien, agr..." refers background in this paper

  • ...However, different ecosystems vary considerably in their susceptibility to invasion (Chytrý et al. 2008), with the impacts of alien tree species in natural systems being dependent on invader attributes and on characteristics of the invaded community (Mason and French, 2008)....

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  • ...However, different ecosystems vary considerably in their susceptibility to invasion (Chytrý et al. 2008), with the impacts of alien tree species in natural systems being dependent on invader attributes and on characteristics of the invaded community (Mason and French, 2008)....

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Frequently Asked Questions (1)
Q1. What are the contributions in "Comparative footprint of alien, agricultural and restored vegetation on surface-active arthropods" ?

The authors studied here the comparative impact of these two types of land transformation on a wide range of surface-active arthropod species using pitfall traps, with evergreen sclerophyllous natural vegetation ( fynbos ) as the control. The study was in the Cape Floristic Region, a global biodiversity hotspot, where alien trees are of major concern and where vineyards replace natural fynbos vegetation. In terms of assemblage composition, all vegetation types were significantly different, although fynbos and vineyards grouped, suggesting that vineyards have less impact on the arthropod community than do alien trees. Their results suggest that vineyards retain a greater complement of indigenous species than alien trees, but that clearing of these aliens soon encourages establishment of indigenous species. Although there were significant differences in soil moisture and litter depth within and between vegetation types, the authors did not record them as significantly affecting species richness or abundance, even in alien vegetation, an encouraging sign for restoration.