How Big Is the Global Weed Patch?

7 Pages·2003·5.5 MB·English

by  Clinton N Jenkins

HOW
THE GLOBAL
BIG
IS
WEED
PATGH?
1
ccics arc a major glohal lineal lo Inodiversilv and agriculture and
l..,||, llu
Governments
science. icco-mi/.- this ami aie devoting increasing resources
lo\
as lend lo lie verv favorable lo in\asi\es. e-peeiallv the ueedv We
-|ieeies.
i
The
simplest answer
question "ever
to this
umbers is
and with sued speed as today. Musi are
where"! Consider
the flora ol Urilaui: mclud<
enign. Itul a dangerous few cause major environ- It
Polygonum
amplcxicaulc Don
from Him,
the
I).
piohlems.
lenlal Invasive species
inav thrive
in
Dianthus
lavas. caryophyllus from southern
L. Ki
new environment and
leir dramatically change
the
sommlcnim
M.pe. I'a/miri from western
Asi
I,,
vnanues and composition
of die eco~v
-tern. Ih ^
'"'"'""'"" *""''"'
'«""
,aus, of our k of v.plau,,, w, now
la. suffer '"rr'l
la,,,-
"l' !""f'
imnir-zrlamliur knk \e«
from /ealan
>''»''/./
)nnn n ^ I.
. . , •
, | i i ^
^
^
^^
W,™„
^^
Iruusport „,
(,.. B ,,a ,,,us,,.| ,,,,/, r,, ,„> ^ ^ ^
.
^
Asian clam (
(Corhiculu
flii>„„,<<,,.
,, include species from around the urn
uu Id.
.. . .
2(,MM)). and witness t,he d,egrad,ati. on even
or
re-
u
,, _ natjve flom
s[)( . s |)OU|.
r
" (e.g., purple loose-
a Species can he
flora. introduced
l
{Lythrum Thompson
strife saliraria L).
1987;
et al.,
to "aannyywwhheerree,^ would seem. That
J* it
"
Pimentel Growth
et al.. 2(HM)). of the glohal trade
more
, [m| sn||I<1 S|)(J are likely
; t,
species than
others.
:
prohlem
ihe inherently glohal. we musl
> is
ur
() arguI11Ptlt is lnal
IL
prime
! ' habitats invasive specu-s. l{ecogniz
I,,,
h focuses on iden-
absence we
le of an ideal database, selected
,| a
sties of s that enahle them
species from Worlds
the Worst
f Invasive
() Al
The
who
ade. idea
is to identify will invade Species compiled Lowe
hv
list el al. (2001) to
:
V
ill.'
I, i I I,
approach
vital to solving the top three plants, and the
i
L. [51
per takes an alternative approach. We attempt Chmmoluvim mta &&
lo odorata R. MM.. KKiinngg Koh.
h
\{. IIII.. |88|.
identify where they will invade rather than who the and h-uruetm Irucoocreepphhaallaa ((LLaamm..)) ddee WWiitt
|,T7|.
ders will he. The
counts
of
c
"' "lin.nl ol c..l„g\ „d KwlulionaiA |;i„|„p. mv.-ilv ,1 lenne.-ee. knovu
l> I :l | .,(,<> l);il.n,\ Hall.
Wo.
.5. I ..S.A. Present .,,1.1, e.-: I.', \alural lo- ,ii„ -.. )e,,ai tl.lent ol 'Fisheries and Michigan
, I \\ ildlile. Si
I'm
Landing. Michigan
IS5H2 1-1222. |enk,ns(«,nsu.edu.
.S. \.
I
Nicholas rimmnmenl
School
Ihe and Sciences. Duke
,,1 .nil, Univcrsilv. Uos ham.
I' <><).',2o. '
27708. U.S.A. Stnartlm»m(«aol.eom.
Ann.
Missouri Hoi. Gard.
172-178.
90: 2003.
have
species
Nonetheless, three
nations. all
i>l;iiul
Chromohicna odorata. native
large areas.
in\ I.mI
.)•
(Holm
America and Caribbean
the et al.,
tropical
to
Holm invades
212-216; 1979:
1977: et al.. 85).
much
pastures and croplands in of tropical Africa
landeover change provide
Global assessments of
and
and Asia, the Southeast Asian island nations,
somewhat overlapping estimates of dis-
series of
71
Mm
A rough estimate of the size of the
SuXXm. 299-302: turbed habitats.
1077:
(Holln
'rTra 'l
of(D
widespread
1979: 207). a
et is
al.,
and
degraded grazing lands,
croplands, with (3)
(2)
South
turelands
in
areas of cleared forests
the- t
southern
Weed of National Significance), parts of
U. n uu an, and ex-
\ln, a uid \1 u _ Ik liih
about 129
Of land surface of
the ice-free r
(1)
h-iuanui
treme southern parts of the United States,
(Holm
\merica
h-ticoccphala native to tropical et
i-
km- were converted
Ml million
but
the planet.
Lowe non- I
1979: 214; et al.. 2001). but in its
al..
ecosystems
wooded
from naturally or forested
aim
native range can form dense,
(Pimm,
2001).
stands render large areas uni
that
The drylands cover roughly 61 million
world's
(2)
The from au-
and savannas. area varies
shriiblanils.
species occur heavily disturbed ar-
All three in
depending on what one means by
author
thor
to
do many other widely distributed invasive
as
as,
Olson
(Pimm, 2001; Vitousek 1986: el
"dry" et al..
Mimosa pi«m various species
such
peeies. as
I...
1983).
al..
omniums
\nother way
AOnunlia. and
liirinus
I., dn
Most of the world"- lands suffer from desert-
_
problem survey (hs.urbed areas.
view to
to this is moslK human-caused
ifi( . atioii a|.g( , |(()| .|i() in „,
t| , |
expenence
Throughout the tropics, ,s our that Some 23
it
|)m|)|rms ss |)|aM n>(luc tivity.
|h;|| (|^( , |)n .
^.^ , ,,
and
have n
disturbed habitats will at least o...- oil, damaged
^ ^ ., . vhm(ls vegeta-
, ,,.„,,.
o{ .
(||
several of these listed spec.es. Often they will be 986) „<„.„ means the spre ad
. gM(1 T|l s
(|)l ,
( _ , ;
dominant spe-
common; sometimes they be the
will ^
species following
n as unpalatable plant
11( . . ,. () f
j
Searching for "worst weeds" on the World ^ am
cies. her livestock
gnals
o^ver^ ,^ ratlU ot
a/i )V ._
. |
,
Web oiled, &
Wide produces peal that
a list ol r. - & (m W() 199 Bahre
,| ;m< . .X ,,.| ie r, 4;
|_
, |
economic harm croplands and pastures.
cause to She jc,^. an Auken. 2000). Those will some-
ton
\
] ^
Most are exotics, but not all. mes i nal Vr species, for instance, mesquite (na-
)e
t
j j
In short, these and oilier examples suggest that dramatically increased in
|jv( . />roSl)pis s|)|)-) uls
|
predominantly disturbed
invasive species occur in miu southwestern United
nv „f
Msilv [|ie
. ,. r .j,
( | (
we mean major eco-
ecosystems. By "disturbed." (Bahre Shelton. 1993; Archer, 1994; Van
Stales'
c\
system changes, such as conversion to croplands. More weeds be
\uken. 2000). often, the will exotic-
grazing lands, urban areas, or anthropogenic ones. such Opuntia Australia and Africa,
nvas as in
v
«-s
i
j
such as grasslands where there was once forest. 3 Another 40 million knr of the land surface
)
(
We connection be-
will not further belabor this has or an( s of one kind or another.
fort s s U()()(
|[
, , ]
well-established and n bviously wetlands and urban areas (Olson et
tats, for is er . s
it ( II( .l ll( | (
| j
we connection and
Rather, accepl the
controversial. £., 1983).
move the problem of estimating how large a frac- The conversion of forests to other habitats is
to
of the Earth's land surface humans have mod- more complicated, since most of the world's crop-
tion
—
been
Since invasive species in these disturbed lands were once forests and so have already
ified.
deemed be weeds, we can re- counted above as croplands. Most of the converted
habitats are often to
phrase our question How big is the global weed forests are in temperate regions. About 2 million
to:
km been converted
2 of these forests have also to
patch?
We proceed by estimating the size of the weed grazing lands (Pimm. 2001).
Modern human actions have shrunk the world's
Globally.
then regional levels.
patch global,
at first
from
humid from an original area of
Regionally. tropical forests
area of disturbed habitats is large.
the-
km
km 2
we our global estimates are too small, for 14 to 18 million 2 to about 7 million at
find that
Pimm, Again.
(Myers 2000; 2001).
much disturbance thai thev miss. is not present el al..
there
is It
the exact numbers depend somewhat
on what one
to identify landcover in ca. I9<>2. As the primary
means
"humid."
by Yel only about 2 million km- concern
of onr study disturbance
areas
is (i.e.. vul-
of croplands are what was humid
in formerly, nerable we
for- to invasion), locus on disturbed
tin-
Some 5-9
ests. million km- of humid forests have classes of the GI.CC (croplands, mosaics
of crop-
been
converted
nominally
to grazing land, though lands and natural vegetation, and urban The
areas).
much
(.1 il ha- \e,\ |„w slocking rales (I'nnni. lesoluli ihi- map approximately one
is km-'
al
I'
2001).
the equator.
Summing
these three pieces suggests We
that also identify areas have changed
that land-
l.->
in. 1 ion km-' o| present-day croplands. 2.i million cover, but not necessarily into croplands or urban
1
km-
of drylands. km-
2 million of temperate
forest areas. For example, the conversion of
forests into
converted
to grazing lands, and from 5 9
to million grasslands lor grazing will „ot appear as disturbed.
km-
nl additional forested laud not producing crops
but obviouslv [Grasslands
are natural type
is. a
it
have
sustained changes
sufficient
to their vegeta- of vegetation, but not where the original vegetation
make
them
lion In target areas invasive species. was humid We
lot a tropical do
forest.) this to assess
The combined
under
total is just half the ice-free potential error causes and means of improving on
The
weed
irface. potential patch huge. our main
is analysis.
approach
approximate
is inevitjibly a
and
plete detailed analysis landcovei hauges
ol of
<
iere these disturbed 1. inds are. To both refi all ecosystem types. The BIOMF and GI.CC maps
•stimates and provide check on
a their use schemes
different classification
for vegetation
• i
mm
we
will exploit detailed estimates make matching
that corresponding classes between
;
We
ter. so a global scale, then them somewhat CFCC
.1., first at For example,
arbitrary. the
Our
map open
scales. analyses relate primarily has an shrubland"
.1 to class that corre-
i t
once-loresled
half of the planet since the remote sponds BIOME
to souk- grassland the map. How-
in
sensing imagery on which we does
rely not so read- ever, open shrubland
also includes areas are
that
damage
ily detect the (Inlands.
to obviouslv not grassland, such as central Australia.
which BIOMF. map
the
classifies as hot desert.
It
A
Sl'VTiM.l Fm-I.KIT Cl.niui. \ssi:ss\1K\t is uncertain thai these changes represent land deg-
\
(il-
CoWKKTKI) more
FoUKSts radalion: hkelv. thev represent differences
in
schemes.
classification
For we
the global analysis, use Geographic
a
In-
BDAS
formation System Imagine com-
(I 8.5) to
v K
s| ,,,, VN|) )|S(;|SS1()N
,,
|
map
bine presumed
a ol original vegetation with an
estimate of current landcover. The
result is a global Not surprisingly, the global analysis confirms
map
where each
pixel has information about that humanitv has disturbed
its a large fraction of the
original vegetation and has changed,
if it or not world (Fig. I). Of the ca. 129 million km-' of ice-
changed,
into a different type of landcover. free land. ca. 27 million km- appear have been
to
The
map
original vegetation from
is the bite- converted to croplands, mosaics of croplands and
grated Model Assess
to the Global Environment natural areas, and urban areas. Table
(IMAGK) &
project (Feema.is van den
Born. 1994;
Aleamo IMAGF
1998:
et
al..
t
17%
of the laud. Disturbance concentrates
in leni-
ror
ties, a detailed description of this model, see perate climates (temperate warm mixed
forests,
for-
md
Prentice et al. (19)2) II van d grassland/steppe) and
est. the drier subtropical and
Born The map
(1994). resolution of this one-half
is tropical vegetation (scrubland, savanna). Again,
not
degree
and maps
of latitude longitude. Color are surprisingly, most of this disturbance coincides with
Aleamo IMAGF
available from (1998) and human
et al. the world populal d croplands,
n.nsl-
.
team
(2001).
the Northern Hemisphere.
in
| y
The map
current landcover from
is the Global Grasslands, scrublands, and savannas have
lost
band Cover
Characterization (GI.CC) (Foveland
from
et a fourth to a third of their original area (Table
A
al., 2000). digital version is available al (l.ttp:// I), but these numbers may be misleading. Dislur-
edcdaac.usgs.gov/glce/glee.ht,nl). This project used bance from
livestock grazing on such ecosystems
is
AVHKK
one-year sequence
a of imagery
satellite
difficult to detect by satellite. Most of the very cold
Mack mosaics croplands and natural u-uelaliou.
arras include croplands,
..i
,.
OLCC map
map. This uses geographic projection
landcoxer from the a
rent
is
U.CC
and the very dry However, the data do not include separate
areas (tundra boreal forest) anil
habitats (such as grasslands) that
escape major disturbance. categories for dr>
(deserts)
have been (Love-
Of combined disturbed area.. 1,2 million are purported to originally forest
the
1
What happens we assume
sum that
km oneedon-led land 2000).
2 from area- (fable of et al., if
are I.
We
temp, mixed these are also converted landscapes? approxi-
disturbed boreal forest, cool conifer,
dryland conversion by
and deeid. forest, warm mixed forest, and tropical male the area of lores! to
woodlands and forests that are
woodland and This seems be esti- identifying tropical
forest). In a lov\
The
woody savannas.
we should compare with the million now ,ma»lan<l-. -ax annas, or
mate,
for
it 1 1
km
2 Adding piece
km2 are now croplands plus a further area is about 2.4 million in this
of forests that
.
km
minimum km 2 cleared Hop- suggests that 16.6 million 2 of forest have been
estimate of 5 million of
dose 16
lower estimate of
croplands (above and converted. This to the
ical forests not converted to i<
km' based on combining independent es-
imm million
2001).
|»
.
and
mosaics croplands natural
lands, of
each talmn ro|.
Table Original area of <,.,,
I. (
UIOVI K
woodlands
opical or tropical forests
vegetation, and as urban areas. Drylands are (
M|ua,c
map), but are now grasslands, savannas, or vv All areas are expressed as l<M)0> ol
.
;;o2t
mixed
Temp, forest
27
11
2719
Warm
mixed
forest
IOJ!.-»
(irassland/sleppe
The
area
le.
7525
km-, which
is slill less than two-thirds o
TRFIC
Kven
estimate.
after correcting the
C,
ma|) lor unnatural drylands, misses
still a
it
of the disturbed
area.
For the Atlantic Forest example, we map
f
FTM
edge disturbed cover 1999 using Landsat +
in 7
satellite
agery. sing standard
.supervised
classilic;
I
we
techni(|ues, classify seven Landsat images
We
and
lores! non-forest classes. do
not
(listing-
specific plantations eucalyptus)
(e.g.. are not a
I
The W
World Fund map
obs.). eeoregion
ildlife pro-
vides an estimate &
of original cover (Olson
forest
Dinerstein.
1998).
In the Atlantic Forest example, the analyses of
Landsat imagery show 91.993 km-
thai of forest, of
an original 127.850 km', has been
defores-
lost to
The
tation. area disturbed lands (d(.C
ol the
in
map
is just 51.851 km-. 56<7r of the Landsat-de-
However,
rive<l .•sinuate. adding Ibiesi- eonverl-
in
ed to drylands increases the area 1,000 km'.
to
I I
We
selected two
tropical forest areas in Rraz.il In both examples, the best of estimates from
lit
Hen
with disturbance
di histories CA.CC
lit to try to idenlifv data to detailed regional estimates comes
what the global analysis missing. when we
is only recognize the conversion
forests
ol |o
The Amazon
is relatively intact but has had high obviously disturbed
habitats (such as croplands)
rales of recent deforestation (i.e.. within the last 30 and less obvious categories (such as grasslands and
years. Skole Tucker. 1993). Northern Mato Cros-
cK sav.uuiasl could be
thai natural os\ stems,
ei but are
so Amazon
stale, in the southeastern our
liasin.
is
example
such
ol recent anthropogenic disturbance. Two
factors contribute to these deficiencies the
ol
In contrast, most ol the Atlantic Forest was defor- CAXIC map. One. AVHRR
the imagery used
in
ested more than 30 years ago (Fundaeao SOS Mala making GLCC
the has
limited
abilitv to discrimi-
The
Atlantica, 1998). state of Kio de Janeiro and nate vegetation types. The AYHHK sensors spee-
the surrounding area our example
is of such his- tral bands are loo wide and poorly positioned
for
mapping
vegetation, yielding inevitable errors. This
Amazon
For the example, we
calculate defores- appears
contribute ove
to to the [estimation of de-
tation using forest cover maps from
the Tropical
forestation in the Atlantic Forest example. The
re-
Rain Forest Information (TKFK We
ienlei 2002). maining
( i. lores) is simply misclassilied. The second
maps
use 1992 match
for to the year of the GI.CC
laclor is thai the resolution ol the regional analyses
We
map.
also simulate the undisturbed condition (0.0000 km') much GLCC
is liner than the dala
(I
by replacing the deforested class in the 1902 map km') in the global analysis. This
finer resolution
enables
better detection ol small areas of defores-
This
tation. likely contributes to the underestimate
small patches
of deforestation.
We
do know
not these error rales are general
if
for ihe global analysis. These are only Iwo examples
analysis
significantly underestimates from W
il relatively small areas. do
hal they indicate
According
in this region. to the CA.CC, need mapping
is a for belter global of landcover.
example shows 3913 km
2 GLCC
jusl of dis- At the lime of writing, the was ihe best glob-
only about
hill is a third of the re- al dala set available, but g prospects
. I exist for
I
late in the previous paragraph. Another
refining our results. FITorts are under way using
*
html) and Landsal
n
'i
I i -
map
imagery
ellite lo
'
30-meter resolutions. respeelbeb. \egetalion map- global
ping primary consideration those sensor"-,
is a in
maps should Conci.
designs, so the resulting hotter
(lis-
eliminate vegetation pes and their level of dis-
l\
isi\e species are a growing problem lor the
The improved should
turbance. spatial resolution
.
, both ecologically and economically. In re-
islurbanee.
mi
I i ' I i i I the problem, governments are devoting
to
sing amounts of resources toward the preven-
The Edges
Missing
many
and
ontrol, eradication of invasives in
the world. To enable efficient use of these
)f
We mapped
have disturbed areas as best possi
icre invasives arc likely to be a problem or
wood pateh missing Irom our estimates
is still
problem
a in the future.
ie
Laurance (1997) found forest e.lges to be vulnera-
Imbed ecosystems arc often favorable for in-
imasbes
ble because of "edge effects"" disturb
to
ion confirmed by comparing our
*
'
commiii cannot
ing the forest iir'. as-
i \ 1 i i i < ma
iii disturbed
P
'»'
-i .1
i . . .
some the worst invaders. These disturbed areas.
<>f
. .
weed one ,km-,
pateh. the resoli ution loo eo,
is
the global weed patch, occupy least 29. million
at
1
we can estimate for the Amazon and Atl;
it
km-' (23<7r) of the ice-free land surface. Other than
Forest examples.
the overgrazed dr\ lands, which our analyses arc
The maps have some
regional forest errors
numbers
detect, the broadly agree with
we must correct. They have small gaps of nuu-
first
"
,M
foresl. some of which ma\ be natural, but main of "'' '" '
Tihi«e, «ad«vvaarntage of our approach is that sin
it
l " :_
...i .. ..I....":*":.'..!".:"' .1
"""
""'\'' """ Jl VI "
• where those dislui icd area- are and thus where
I
6
be Combining
invaders arc likeb in tin— \Mlh
. . "
.
—I , ,
dge.
lo "
i.
- " < - ' * ' I" » i - lormali. on on who .invaders are 1l-i1 keb .
T I to
llie
.„
m
,
even that ed,ge . a si. ngle ,10- pixeli, lo account.
is
it
should help allocating resources
in efficiently
I
we
for this, replace patches of iion-forest smaller
than 2 hectares with The use of 2 hectares
forest.
sification errors, ma\ also include some truly
bill
&
Leemans
Kreileman. 1998. Global
R. K.
The
delorested areas and natural gaps. result a
is
(Jiang,- Scenarios tlir 21-1 lirsulls Inim llie
,,l < ill ii v
edge < i :
probable underestimate of lores,.
'&
IMAGE
Model. IVrgamon Klsevier Sc,
2.1
Amazon
In the example. 17.801 km- of forest
is
300
within meters of an edge (fable the distance
2).
com-
Laurance (1998. 2000) detected
that et al.
munity changes \inazoniaii forest fragments.
in
&
cock R. D. Pieper
(
However, in the original state this region already
had 1986 km- edge due
of natural forest to rivers
and savannas, \dding the edge forest, minus nat-
ural edge, to the earlier estimate of disturbed area
yields 24.760 knr of disturbed area (Table ap-
2),
km
example. 29.373 2
In the Atlantic Forest of
the remaining forest within 300 meters of an
is
edge, \dding the delorested area yields
this to
121.366 knr of disturbed area, leaving just 6484
The
Netherlands,
knr of un(ddiissttuurrbbeedd floorreesstl.. TThhee mmaapp oolf oorriiggiinnaall ffoorr-- lumlirao SOS Mala -Vllantica/INPE/Instituto Socioam-
(WWF
da Evolucao
est F eeccoorreeggiioonn)) ttoooo ggeenneerraall ttoo rreelliiaabbllvy ccaall-- hiental. 1998. Atlas d(
iiss
Ecossistemas \ss,,ciados
' "natural"* amoiinl of edge as done for the
1990-1W5.
Perfodo de Sao Paulo. Brasil.
Amazon.
Pancho K
I'lueknell.
I,. J. \. J. P. II,-,
When
we
incorporate these regional estimates of
p
)(M.gt .„ >77 Th( , World's Worst
|
edges into the calculations of disturbed area, then and Biology. Univ. Press of Hawaii. Honolulu.
(.e.mapliical \tlas d' World Weed-. John Wi- -oiisenal mi, prioril - Nature I'M-}
I«»7<). \ 10.,; ;.>{}.
i,
.
lev & Sons. New York. Olson. I). \1. * K. |)in.-M<-m l«*K5 Hi.- dol.al 2(K
VI \(,K learn. 2001. The |\1 \(,K 2.2 Implementation ol representation approach to rons.-miif- thr KarthV .
I
„„-,,„
lnuln^„,,IK valuable ocoro^,o„s.
iheHJKS Scenarios: \con,p,dic,,s,w anaKs.s.donns- t,„|.
I
.-.02-.il.).
sions climate elian-e and imi.acls ihe •> ce
In 1st
\
X
Olson. S... Walls Allison. '){«. iarbn
.,- .... \.
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