Rangeland Analysis Platform

New data source for In-Season NDVI:  Rangeland Analysis Platform. (RAP) https://rangelands.app/rap/ 

RAP allows mapping of Cover and Biomass, and generates reports for an Area of Interest for Cover, Annual biomass, and 16-day biomass.  I'm hopeful they will upgrade the map to include 16-day biomass.  If they did, I could add it to the comparisons of the other NDVI sources.  Mapping would allow in-season management decisions based on forage production.

Case Example: Dugas, AZ

This series of years from 2018-2023 shows the variability in biomass production by season in a desert grassland at mid-elevation (4,000 ft) in AZ:

2018 shows a drought year, when there was little to no spring green-up due to a lack of winter precipitation, and a low green-up in response to summer monsoons.

2019 and 2020 were the "nonsoon" years, when the summer monsoons failed to materialize.  However, because the winter rains were good in 2019 and exceptional in 2020, total production was high.

2021 and 2022 show the potential for growth in years of good monsoon rains.  2023 shows a "normal" year with bimodal peaks in production corresponding to the spring green-up peaking in late March, and the summer monsoons peaking in mid-August.  However, for some reason this year had almost no annual biomass production associated with the monsoon.  Each year is different!

----

Case Example: Congress, AZ

This series from around Congress, AZ shows the extreme variability of plant growth in the Sonoran desert (2,500 ft).

In drought years like 2018 and 2022, there is almost no plant growth, whereas the extreme winter precipitation year of 2020 annuals produced almost 130 pounds/acre of spring growth.  None of the years hadmuch perennial herbaceous production, and monsoons inconsistently produce up to 40 pound/acre of growth in good years.  

----

Case Example:  Grand Canyon Junction 

SR-64 and SR 180 intersection, just south of Grand Canyon high-elevation grassland (6,000 ft).

Maximum production compared to the lower elevation sites is lower, only reaching 50 pounds/acre in good years.   However, total annual production is usually more consistent.  There is still the potential for bimodal production peaking in the late spring (early June) (2023 and 2017, not shown) and in the monsoons.  The monsoon peak seems to be most consistent, except in 2019 and 2020 when the monsoons failed - luckily those years had relatively good spring growth.   

In contrast to the low desert site, annual production (red) is usually less important than perennial production (green) at this site:

Fence Line Contrasts

Sitting on the fence has become a metaphor for ambivalence, but actual fence lines are some of the clearest lessons in land management.  Fencelines can be the best place to study ecology, because most fences divide two different land management histories.  The easiest places to learn from fence line contrasts is where the land management history is known.  For example, along highway right-of-ways (ROWs), the strip of land between the road and the fence is almost never grazed, whereas the private or public alotment on the other side of the fence has almost certainly been grazed and/or farmed.

However, just because the ROW hasn't been grazed doesn't mean that it has escaped disturbance. While comparing two disturbed areas can yield some insights, the multiple factors at work will make cause and effect deductions extremely difficult. To find a good comparison, look for areas that are relatively far from the road; immediately adjacent to the road is a zone of disturbance, which can include vehicle traffic, trash, mowing, and runoff from the road (i.e. increased moisture).

The best comparison areas occur where the ROW is relatively higher than road (so there is no possibility of runoff and little chance of other human disturbance).  However, areas with cutbanks below them are not good for comparisons, because of excess erosion, different microclimates around bare rock or exposed subsoil, and lowered water table.   A zone of depression in soil moisture can also occur around ditches, trenches, gullies, roadcuts, etc.

The actual fence-line itself may have different species due to fence-line drip of dew and the ability of fences to catch seeds, especially tumbleweeds. (photo).

On the ground immediately beyond the fence there may be an area of extra disturbance due to cattle trails, etc, and any areas near stock tanks or gates are also likely more heavily used (and hence a more extreme contrast).  In cases with less grazing on the private land, such as on steep hill slopes, vegetation and soils may look quite similar across fence-lines.  Of course, there will always be variable disturbance on both sides of the fence, but that is part of the challenge and opportunity of observing fence-line contrasts.

The best comparisons are between areas relatively far from disturbance, close to but not immediately adjacent to the fence-line.  With a good undisturbed ROW as a control, the vegetation on the other side of the fence can be compared to the potential climax community of the site.  

Case Example:

I was recently watching fence-lines along NM highway 285 from Vaughn to Clines Corners, and noticed that typical overgrazed areas are Grama Grass (Bouteloua gracilis) monocultures or low-stature annuals with large amounts of bare dirt.  The ungrazed roadsides still have bare ground, but the vegetation has a starkly different structure and composition:  multiple grass species occur with different growth forms.  But even more noticeable than the grass growth is the shrub encroachment in an area that is pure grassland.  Without fire or grazing, woody growth, especially saltbush (Atriplex canescens) and  Chimisa (Ericameria nauseosa) increases markedly.

While some trees and shrubs (e.g. E. nauseosa) are resistant to grazing when mature, their seedlings are highly palatable.  Cows can completely eliminate woody overstories from riparian areas in a single generation simply be eliminating recruitment (through both grazing and trampling) of Cottonwood and Willow seedlings.  Grazing pressure on seedlings is important, but easily overlooked: as long as there are trees, we describe an ecosystem as a forest. And it may seem strange to say that cows are eating a forest. But without seedling regeneration, no ecosystem is sustainable.

That grazing impacts woody growth as much or more than herbaceous growth is well-known along rivers and wetlands, but I think has been less remarked on in uplands.  From this brief study of fence-line contrasts, it appears that even more of our grasslands would support shrublands were it not for either grazing or fire limiting woody plant establishment.

25 Years Without Cows: Hart Mountain National Antelope Refuge

From an article about a recent publication documenting changes on the Refuge:

"By comparing the new photos with the historical ones, the researchers determined that following 23 years of passive recovery after cattle were excluded from the Hart Mountain National Antelope Refuge, stream channels narrowed, woody vegetarian increased, and there was a noticeable reduction in eroding stream banks. Nearly all sites displayed a decrease in bare soil, resulting in an overall 90% increase in plant cover, mainly thanks to grasses, sedges, forbs, and willow. Willow and rush cover increased fourfold. "

The conclusion is clear: “Simply removing cattle from areas may be all that is required to restore many degraded riparian areas in the American West.”

Range Monitoring on Chihuahan Desert Grasslands

We helped out with a long-term monitoring project at a ranch in Southwestern New Mexico.

Diverse plots contained upwards of 30 perennial grass and forb species, plus half a dozen shrubs.  Degraded areas might contain only three or four annual, weedy species.  We found evidence of ecosystem engineers like termites and banner-tailed kangaroo rats.  Also, the remains of last year's grasshoppers were thick in the better grasslands.  Interestingly, the only mole we found was in the one of the most degraded sites, an area with only sparse annual grasses -- not much roots for a mole to munch!

Reading a vegetation transect line in a thick Giant Sacaton (Sporobolus wrightii) flat.  More photos.  

Cows eat grass...and Rain grows grass (!)

Grasslands can recover from grazing, provided there is sufficient moisture to grow.  Arid environments often lack moisture, so recovery can be extremely slow (Valone et al) or nonexistent.  That is the overarching conclusion of several long-term vegetation studies in Arizona and New Mexico.  Shrub removal can increase grass cover, but at low levels shrubs do not seem to compete with grasses.  At the Santa Rita experimental range, south of Tucson, invasive species pushed aside native grasses, but then all vegetation cover decreased during the following 20-year drought.  

Figure from Mashiri et al.  Basal cover of perennial grasses on the Santa Rita Experimental Range from 1972 through 2006.  SR = Seasonal Rotation grazing; YL= Year Long grazing.  Following the wet 1980's, grass cover increased to the peak in the center of the graph, but has been falling ever since.

It may sound obvious that grazing can decrease grass cover and that it may take several wet years to regain aboveground growth.  Range science has long advocated for differential season of grazing, or intensive grazing, or other management alternatives, but some studies such as Mashiri et al find no long-term differences between management methods.

A recent study from Bestelymeyer et al did find some slight differences between winter- and summer-season grazing, but they were the opposite differences that traditional range science manuals would predict for Black Grama grass! 

Figure from Bestelmeyer et al.  Black Grama grass cover on the Jornada Experimental Range decreased with grazing and increased following grazing.

References:

Bestelmeyer, Brandon T., Duniway Michael C., James D.K., Burkett L.M., and Havstad Kris M. A test of critical thresholds and their indicators in a desertification-prone ecosystem: more resilience than we thought.  Ecology Letters, 01/2013, Volume 16, p.339-345, (2013)

Mashiri, F., M. McClaran, and J.S. Fehmi. 2008. Short- and Long-term Vegetation Change Related to Grazing Systems, Precipitation and Mesquite Cover. Rangeland Ecology and Management 61:368-379.

Valone, T. J., Meyer, M., Brown, J. H. and Chew, R. M. (2002), Timescale of Perennial Grass Recovery in Desertified Arid Grasslands Following Livestock Removal. Conservation Biology, 16: 995–1002.

An Important Point about Grazing-based Land Restoration

"Allan Savory's holistic resource management [was described] as a "promising option," even though there is no science to back up claims about intensive grazing schemes.  The truth is that grasslands are relatively arid environments, and livestock don't make the grass grow: rain does.  And rain doesn't follow the hoof."
--Jeff Burgess, reader response in the November/December 2013 Nature Conservancy magazine

Addendum:  read this comprehensive response to Allan Savory's claims, or this recent direct rebuttal:

The Savory Method can not green deserts or reverse climate change, Briske, David D., Bestelmeyer Brandon T., Brown Joel R.,Fuhlendorf Samuel D., and H. Polley Wayne , Rangelands, Volume 35, Issue 5, p.72-74, (2013)

and this follow-up:

Forest Fires versus Forest Restoration

At ESA this year, one discussion turned to the elephant in the room of forest restoration thinning projects: the certainty that thinning will have some deleterious effects versus the probability that a thinned area would actually encounter a forest fire during the approximately 25-year window of restoration effectiveness.  Forest restoration typically involves thinning forests to lower stand densities to discourage the spread of stand-replacement crown fires in historically low-intensity fire regimes.  Yet,  absent the return to presettlement semi-annual burn patterns (i.e. an end to the total suppression paradigm), tree seedlings will recruit and form high density stands within a couple decades.  

What are the odds that a given patch of forest will encounter a mega-fire over a 25-year time span?  According to some participants in the discussion, the odds are quite low.  But that may depend on the forest.  Take, for example, the fire-prone semi-arid mountains of the southwest:

Representative map of burned areas in SE Arizona and SW New Mexico over the last decade.  The Wallow Fire (538,000 acres in the White Mtns) and the Horseshoe Two (223,000 acres in the Chiricahua Mtns) fire, are visible as large yellow areas.

Shaded areas indicate official MTBS 2000-2009 burned area polygons.  Yellow areas are provisional "fire detection" areas from MODIS.  This map was generated using the U.S. Forest Change Assessment Viewer (FCAV), which can map a large number of forest disturbance types, utilizing historical to contemporary GIS layers and current satellite imagery.

Perhaps the ESA discussion participants should read:


Rhodes, J.J. and Baker, W.L., 2008. Fire probability, fuel treatment effectiveness and ecological
tradeoffs in western U.S. public forests. Open Forest Science Journal, 1: 1-7.

Grazing Optimization

McNaughton SJ. Grazing as an Optimization Process: Grass-Ungulate Relationships in the Serengeti. The American Naturalist. 1979 May 1;113(5):691–703.

McNaughton lists 9 possible mechanisms by which productivity of herbivore affected plant tissues may be compensated or stimulated:
1. Increased photosynthetic rates in residual tissue;
2. Reallocation of substrates from elsewhere in the plant;
3. Mechanical removal of older tissues functioning at less than a maximum
photosynthetic level;
4. Consequent increased light intensities upon potentially more active underlying
tissues;
5. Reduction of the rate of leaf senescence, thus prolonging the active photosynthetic period of residual tissue;
6. Hormonal redistributions promoting cell division and elongation and activation of remaining meristems, thus resulting in more rapid leaf growth and promotion
of tillering;
7. Enhanced conservation of soil moisture by reduction of the transpiration
surface and reduction of mesophyll resistance relative to stomatal resistance;
8. Nutrient recycling from dung and urine;
9. Direct effects from growth promoting substrates in ruminant saliva

Theoretical work by Claire Mazancourt (1998 and 1999):




But how much difference can herbivory make when ecosystem ecologists so routinely ignore it when calculating NPP?


Relationship between average aboveground annual NPP and average annual precipitation for 100 ecological regions within the central grassland region of the USA . Sala,O. E., Parton, W. J., Joyce, L. A. and Lauenroth, W. K. (1988b) Primary production of the central grassland region of the United States. Ecology 69, 40-45. More info, including soil carbon relationships.

One possibility is that there isn't much wiggle-room, and even that is dependent on nutrient concentrations:

Cebrian J, Williams M, McClelland J, Valiela I. The dependence of heterotrophic consumption and C accumulation on autotrophic nutrient content in ecosystems. Ecology Letters. 1998;1(3):165–170.