A summary of responses to my query last month:
On Dec 16, 2017, at 2:57 AM, David Inouye<[email protected]> wrote:
Can anyone comment on the validity of this statement about effects of grazing?
"Suggesting that landscapes will return to natives by removing livestock is not
substantiated by research."
It's from a letter from my county commissioners in response to a draft National
Forest management plan.
Thanks.
David
I wrote an article in Conservation Biology in 2002 entitled Grazing, Rest, and
Restoration (attached below) that reviews the arguments that landscape recover
following grazing. Of course this is just a small piece of a very large and
complex issue, I tried to succinctly address the core ideas in a short and
pithy article. The bottom line is, especially in light of climate change,
landscapes typically do not recover on their own and sometimes judicious use of
practices such as fire and grazing can speed recovery. Of course every
landscape is somewhat different, for the Southwest D. Milchunas wrote a review
for the Forest Service in 2006 that exhaustively considers this topic. There
are a number of other reviews out.
*****************
Although I am not an expert in rangeland ecology, a quick scan of the literature is
enough to allow me to answer your question with another. What time scale do you
(they) have in mind? It appears that, in semi-arid grasslands, change post-grazing
is slow and multiple trajectories are possible. Trajectories depend on local
conditions (edaphic parameters, degree and duration of grazing pressure, nature of
grazing community and, perhaps, climate change pressure), so no unqualified blanket
statement (such as you quote) seems justified unless you are cherry-picking to
support a foregone conclusion. One factor that might be applicable is this. Will
the rangeland affected be managed for restoration post-grazing or will it be subject
to “benign neglect."
*****************
From my own personal experience, removing disturbances such as livestock from
an area does, indeed, result in the return of native plants and animals. It
does also, however, provide an opportunity for invasive plants to become
established, so assisting the colonization of native plants helps establish a
community less prone to invasives.
*****************
Welcome to the vociferous debate about 'regenerative grazing',
'intensively managed grazing', 'holistic management', Alan Savory,
Richard Teague vs. Brisk & Holloway, and others.
There seems to be plenty of traditional research to indicate that
grazing livestock destroy rangelands, and a growing body of
anecdotal/rancher-led evidence (and active research) in development that
is suggesting otherwise. Kristina Wolf in Sonoma County could likely
comment further based on work at Pepperwood Preserve where cattle are
used specifically to restore native California bunch grasses. I have
worked with targeted goat graziers in Alberta to slow/stop spread of
invasives and support return of native grasses, but nothing published.
There are many other examples but careful documentation is rarer.
It depends on which natives, in part - woody species may recover when
protected from grazing; bunch and other perennial grasses seem to suffer
from a lack of /appropriately timed /grazing impact. That is - grazed
once or twice a year to remove biomass, but protected from overgrazing
by removing livestock before they get a 'second bite' chance that cuts
into young and growing tissue still in a recovery phase.
I think I'd like to leave it there and catch up on my background
research before going further, but this is definitely an active
discussion and there is be evidence on both sides. It seems largely to
amount to how we manage (or don't manage) livestock grazing - timing
(duration, time of year, timing of rain/precipitation and plant
phenology), number of animals, species, and native ecology - and
experimental set-up, i.e. using an adaptive management, whole-landscape
and context-driven approach or a small plot, context-independent approach.
I'm pretty sure that doesn't help clarify but may give you a start...
****************
Usually rehabilitation of a landscape that has been over grazed is more
involved than merely removing the initial degradation factor (livestock
grazing). The complexities of restoring an ecosystem to its natural
state depends on the current state of the landscape; native plants
present, invasive noxious weeds present, native animals present, the
condition of the soil, etc.
******************
That statement is simplistic. In some cases removing livestock could allow
natives to recover. As I suppose you would imagine, the consequence of removing
livestock would depend on the biome type, the composition of the native
vegetation in the location, and also the history of livestock grazing,
including how long the area had been grazed and how intensively it had been
grazed.
I manage a prairie restoration, but I don't have a history of publishing on the
effects of livestock grazing on plant community structure. I imagine that you
have received messages from others who have much more experience.
Thanks for all you do for ecology and ecologists.
******************
This may or may not be applicable, but removing horse grazing resulted
in the return of natives in this study:
Beever, E., Tausch, R. and Thogmartin, W. 2008. Multi-scale responses of
vegetation to removal of horse grazing from Great Basin (USA) mountain
ranges. Plant Ecology 196:163-184.
Hope this helps.
********************
--
Dr. David W. Inouye
Professor Emeritus
Department of Biology
University of Maryland
Principal Investigator
Rocky Mountain Biological Laboratory
