Feb	12,	2012

The	comments	regarding	the	use	of	certain	species	for	bioenergy	production	(via	

the EPA	ruling)	has	raised	concern	regarding	the	promotion	of	potentially	invasive	

species,	which	would	be	in	violation	of	Executive	Order	13112.	The	damage	caused	

by	invasive	species	is	well	documented	and	should	not	be	overlooked	when	

considering	bioenergy	crop	selection	and	production.	However,	it	is	my	opinion	that	

use	of	known	invasive	species	should	not	be	allowed in	areas	where	they	are	known	

to	be	problematic	(eg,	kudzu	in	the	Southeast),	but	that	outside	of	those	areas	the	

issue	becomes	much	more	complex.	Below	I	specifically	address	the	issue	of	giant	

reed	(Arundo	donax,	hereafter	Arundo),	but	the	same	principle	applies	to	all	species.	

Arundo is	a	state	listed	noxious	weed	in	Texas	and	California.	However,	several	

other	states	consider	Arundo	to	be	invasive,	or	potentially	invasive	(eg,	Tennessee).	

The	distinction	between	the	two	listing	types should	be	clarified:	noxious is	a	

regulated	taxon	in	that	state,	whereas	any	other	listing,	such	as	invasive,	is	an	unregulated	listing	by	an	unofficial	listing	organization	(unofficial	in	the	sense	that	the	

state	does	not	recognize	that	listing).		For	example,	the	Tennessee	Exotic	Pest	Plant	

Council	lists	Arundo	as	an	invasive	species,	but	this	listing	does	not	carry	any	legal	

restrictions	on	trade	or	control.		This	is	not	to	say	that	the	listed	“invasive”	species	is	

not	causing	economic	or	ecological	harm,	but	that	it	is	not	regulated	in	that	state.

Weed	Risk	Assessments	(WRA)	have	been	conducted	for	Arundo	in	some parts	of	

the	US,	including	Florida,	which	have	generally	resulted	in	“reject”,	which	means	it	

has	a	high	risk	of	invasion.	However,	it	should	be	noted	that	the	current	WRA	

system	(Pheloung	et	al	1999)	has	no	way	of	distinguishing	different	climates,	

regions,	or	ecosystems,	which	will	have	varying	levels	of	susceptibility	to	risk

(Barney	and	DiTomaso	2008).	The	“high	risk”	or	“reject”	outcome	for	Arundo	is	

driven	by	the	presence	of	invasive	populations	in	California	and	Texas,	where	

Arundo	is	displacing	native	flora	and	have	negative	ecosystem	impacts along	

riparian	corridors. For	example,	the	same	WRA	result	of	“reject”	would	be	found	for	

Arundo	in Texas,	where	it	is	a	state	listed	noxious	weed,	and	Maine,	where	it	is	not	

known	to	occur.	Therefore,	WRA	results	should	be	interpreted	in	the	context	of	their	

limitations.	Additionally,	the	WRA	was designed	as	a	pre-introduction	(ie,	the	plant	

is	not	in	this	country	yet)	screen,	which	of	course	is	not	the	case	for	Arundo.	My	

2008	(Barney	and	DiTomaso	2008)	paper	has	been cited	as	an	example	

demonstrating	that	Arundo	is	a	high	risk	in	Florida,	which	was	a	result	of	the	WRA.	

That	WRA	analysis was	done	as	a	first	step	in	evaluating	the	risk	of	three	bioenergy	

crops,	and	should	be	interpreted	in	the	context	of	the	screening	process	we	

proposed,	of	which	the	WRA	is	only	one	component	(Barney	and	DiTomaso	2008).	

WRAs are	good	first	steps	in	evaluating	invasiveness,	but	should	not	be	used	

exclusively	without	the	insight	of	field	tests,	which	that	paper,	and	others,	argues.

It	should also be	noted	that	invasiveness	is	not	a	universal	character,	and	that	

species	are	not	invasive,	rather	populations	of	species	are	invasive.	Also,	all	

populations	of	an	“invasive	species”	are	not	invasive.	For	example,	kudzu	is	a	
harmful	invasive	species	of	the	southeast,	but	populations in	New	England are	not	

invasive	or	threatening	to	become	invasive.	Additionally,	Arundo	is	harmful	in	

California	and	Texas	almost	exclusively	along	riparian	corridors	where	it	makes	

mono-clonal	stands (Ahmad	et	al	2008).	However,	in	the	drier	uplands	of	both	

states	Arundo	is	less	abundant.	Arundo	spreads	exclusively	via	vegetative	fragments	

(stems	and	rhizomes),	which	are	primarily	water	dispersed.	Therefore,	upland	

populations are	far	less	likely	to	spread. The	ability	to	spread	when	growing	along	a	

riparian	area	is	far	greater	than	when	growing	in	a	field	far	from	a	dispersal

corridor (Boose	and	Holt	1999).	

As	stated	above,	invasiveness	is	not	exhibited	by	all	populations	or	in	all	locations	

within	a	taxon.	Arundo	was	actively	planted	along	riparian	corridors	of	California	

for	bank	stabilization and	erosion	control (Boose	and	Holt	1999),	just	as	kudzu	was	

planted	along	roadsides	in	the	Southeast.	The	active	cultivation	along	dispersal	

corridors	led	to	the	large-scale	spread	of	both	species.	In	contrast,	the	active	

cultivation	and	management	of	a	bioenergy	crop	within	field	boundaries	will	

dramatically	decrease	the	likelihood	of	unintentional	escape.	This	is	especially	the	

case	for	Arundo,	which	does	not	produce	seeds,	and	is	therefore	relegated	to	

dispersing	via	vegetative	fragments,	which	greatly	reduces	the	probability	of	

moving	offsite,	especially	when	far	from	a	riparian	area.

All	species	present	a	non-zero	risk	of	becoming	invasive.	The	vast	majority	of	

species	present	a	very	low	risk,	but	that	risk	is	still	not	zero.	For	a	successful	

invasion	to	occur	several	components	must	be	present:	an	introduction	event(s),	a	

susceptible	habitat,	an	available	(favorable)	microsite,	and	sufficient	time

(Theoharides	and	Dukes	2007).	Management	of	bioenergy	crops	will	include	best	

practices	to	minimize	several	of	these	components	to	reduce	the	likelihood	of	

invasion (NC	BC 2011).	

Lastly,	several	of	the	locations	where	Arundo	is	being	discussed	for	cultivation	is	far	

outside	of	the	warm	climates	where	Arundo	is	currently	problematic.	Cold-tolerance	

is	largely	unknown	in	Arundo,	and	it	should	not	be	assumed	that	behavior	exhibited	

in	one	region	represents	eventual	behavior	everywhere.	Much	research	must	be	

done	of	Arundo	biology	and	ecology	in	these	cooler	climates.

In	conclusion,	while	I	fully	recognize	the	dramatic	Arundo	invasions	in	California	

and	Texas,	and	the	consequences	on	native	species	and	ecosystem	properties,	it	

should	not	be	assumed	that	Arundo	will	become	invasive	in	all	circumstances	and	

locations.	Nearly	all	research	on	Arundo	has	been	conducted	in	California	and	Texas,	

and	we	know	little	about	Arundo	in	the	Southeast or	many	other	regions.	The	

intentional	planting	of	Arundo	along	riparian	corridors	was	also	likely	its	downfall,	

which	should	not	be	the	case	for	bioenergy	production.	The	precautionary	principle	

would	advise	us	against	using	Arundo	or	similar	species,	but	the	potential	benefits	

must	be	weighed	against	the	risks	(known	and	unknown).	We	have	learned	much	

about	how	Arundo	spreads,	and	can	use	this	information	to	guide	best	management	

practices	to	reduce	the	probability	of	unintentional	escape.
I	am	certainly	in	favor	of	reducing	the	promotion	of	invasive	species	in	any	context,	

and	am	interested in	protecting	our	natural	resources.	I	am	arguing	for	invasiveness	

to	be	viewed	in	the	context	of	each	species	and	location.	Invasions	are	an	extremely	

complex	phenomena,	and	due	diligence	should	be	done	to	protect	our	natural	

resources	while	also	supporting	bioenergy	production.

Respectfully,

Jacob Barney,	PhD

Assistant	Professor	of	Invasive	Plant	Ecology

Department	of	Plant	Pathology,	Physiology,	and	Weed	Science

Virginia	Tech

Blacksburg,	VA	24061

Ahmad	R,	Liow	PS,	Spencer	DF,	Jasieniuk	M.	2008.	Molecular	evidence	for	a	single	

genetic	clone	of	invasive	Arundo	donax in	the	United	States.	88:	113-120.

Barney	JN,	DiTomaso	JM.	2008.	Nonnative	species	and	bioenergy:	Are	we	cultivating	

the	next	invader?	BioScience	58:	64-70.

Boose	AB,	Holt	JS.	1999.	Environmental	effects	on	asexual	reproduction	in	Arundo	

donax.	Weed	Research	39:	117-127.

North	Carolina	Biofuels	Center.	2011.	Voluntary	best	management	practices	for	

energy	crops:	Minimizing	the	risk	of	invasiveness.	

Pheloung	PC,	Williams	PA,	Halloy,	SR.	1999.	A	weed	risk	assessment	model	for	use	

as	a	biosecurity	tool	evaluating	plant	introductions.	57:	239-251.

Theoharides	KA,	Dukes	JS.	2007.	Plant	invasion	across	space	and	time:	factors	

affecting	nonindigenous	species	success	during	four	stages	of	invasion.	New	

Phytologist	176:	256-273.