2019-09-19_Estimating_Capacity_for_Horses_in_the_Lower_Salt_River_Area_DyessJ__1_.pdf

United States Department of Agriculture

8/15/2019Forest Service Southwestern Region

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Estimating Capacity for Horses in the Lower Salt

River Area

Judith Dyess, Assistant Director of Rangeland Management August 19, 2019

Salt River Horse Collaborative Meeting

Three information sources utilized:

1) University of Arizona Forage Assessment of the Lower Salt River Recreation Area

Information presented at previous collaborative meeting,

2) Analysis of the Goldfield Grazing Allotment, (of which a portion is the area the horses use)

3) Production Analysis and Estimate of Capacity Utilizing Satellite Remote Sensing Considering

Average Annual Production for 35 years.

What is NDVI?

The normalized difference vegetation index (NDVI) is a simple graphical indicator that can be used to analyze remote sensing measurements, typically from a space platform, and assess whether the target being observed contains live green vegetation or not.

Comparison in reflective greenness measured via NDVI across the season of the 2017 study conducted by the University of Arizona

The report provided the following information:

Horses are heavily dependent on seasonally available forage in the form of annual herbaceous plant material

This forage is available with prolonged seasonal precipitation events such as winter rainfall and somewhat summer monsoons

Once these annual plants are consumed or die, horses increasingly consume woody browse species of reduced nutritional value.

University of Arizona Forage Assessment of the Lower Salt River Recreation Area and the Horse Fecal Analysis

Complicating factors based on fecal analysis:

~ 38% of all production is utilized by horses.

Of what they selected for: 20% is annual forb and grass species, 80% woody species

Upland areas lack the desired forage species much of the time and this focuses horse activity in the mesquite bosque’s and the riparian corridor.

56, 487 Acre Goldfield Allotment

Salt River Horse Recreation Area 26,030 Acres

Additional Work with Rocky Mountain Research Station (RMRS)

Matt Reeves, PhD, Research Ecologist

1) Looked at average annual herbaceous production over 35 years utilizing NDVI (The Rangeland Production Monitoring Service; RPMS, https://www.fs.fed.us/rmrs/projects/development-rangeland-production-monitoring-service-could-improve-rangeland-management )

2) Again determined a great deal of variability in in production and green vegetation available throughout the year.

https://www.fs.fed.us/rmrs/projects/development-rangeland-production-monitoring-service-could-improve-rangeland-management

Approximately June 2001- Dec 2002

Severe Drought

Approximately Nov 2010- May 2012

Drought- historic fire year in AZ

Winter 2016/Spring 2017 Average to above average precipitation And forage production

UOA Study Period

Drought Conditions of 2018

Winter 2018/Spring 2019 Above average precipitation And forage production

Monsoon 2017 Somewhat Above average precipitation And forage production

January 2000 to April 2019

Feb 2017

Dec 2017

UOA Study Feb 2017- Dec 2017 (green arrows) Drought 2018 and did not start recovery until approximately Dec 2018

Feb 2018

Feb 2019

February

February

February

Demonstrates Extreme Variability year to year.

Spring

Winter

Monsoon

Pre-monsoon

Demonstrates Extreme Variability within the year with spring being best forage time.

Extremes range 2200 lbs/ac to < 50 lbs/ac

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

Mean Total Production Across All Sites

Analysis of diet content indicates that a majority (~64%) of potential forage species measured across all sample sites were not actively consumed by horses, regardless of what was available.

Average Annual Herbaceous Production based on the 5 Terrestrial Ecosystem Unit Inventory Map Units

What about riparian vegetation for the horses?

Peak consumption of aquatic or riparian obligate species occurred concurrently with peak periods of spring time annual production (Feb- April) and reduced with the onset of the dry season.

Consumption of aquatic/ riparian obligate species correlates positively with diet quality and comprises the bulk of herbaceous material per fecal sample from July- December 2017.

Data derived from fecal content analysis, however, suggests that the majority of riparian obligate species consumed are reeds, cattails and willows with only trace amounts of bermuda grass (Cynodon dactylon) no detection of Zosteracae spp. (eelgrass) in any of the fecal contents sequenced.

However… High dependence on woody vegetation in the diet, even with the availability of riparian vegetation suggests that the current arrangement likely lacks the capacity to meet the long term nutritional requirements of the herd at the given population numbers.

Therefore how does this information assist in estimating capacity for the horses in the Lower Salt River Area?

Goldfield Allotment The Goldfield Allotment had an Estimated Capacity of 600 AUMs equating to 50 Cow/Calf Pairs year round. This could be roughly looked at as 42 horses, however only approximately half of the allotment is used by the horses so therefore can estimate 21 horses year round.

UOA available forage production analysis and diet based on fecal analysis provided information demonstrating what is available and what the horses use.

UOA sampled approximately 11000 acres between the 2 highways. Their information applied across the 26,030 acres in the area the horses use.

Let’s look at the UOA 2017 data relative to estimating a capacity for horses

Accessible production- 324 lbs./Acre X 26,060 Acres = 8,433,720 lbs. of production

Fecal analysis demonstrated 38% of that is used by the horses 8,433,720 lbs. X 0.38 = 3,204,814 lbs. used production selected by horses

Herbaceous portion of that is 20%. This is most nutritious, highly preferred forage 3,204,814 X 0.20 = 640,963 lbs. of accessible selected for herbaceous forage

Allowable Use to maintain plant physiological needs, soil productivity, watershed Stability is 35%.

640,963 lbs. X 0.35 = 224,337 lbs. of forage allowable for use

Approximately 11,388 lbs. of forage needed per horse per year.

224,337 / 11,388 = 20 Horses

The RMRS work with the stated assumptions also informs the Estimated capacity. The estimate of herbaceous forage produced annually is 409,972.5 pounds in the area the horses occupy.

409,972.5 lbs./11,388 lbs. per year = 36 Horses a year estimate

Why the difference?

Both studies based on the premise that forage is always available and accessible which the data shows is not the case.

UOA-- 1 year worth of production data for herbaceous actually used.

RMRS--Range of animals was 28 to 44 horses a year.

35 years worth of production data for all herbaceous, used or not.

Other Evidences

Per Arizona Department of Agriculture, Jackie Hughes

Supplemental feeding started in April of 2018 and was conducted until November of 2018. Approximately 500 horses were fed 12 semi-trucks of hay over approximately 7 months, with the amount per month tapering down over the last 2 months.

February 2018 April 2018

Forage March 2019 After wet winter

Forage April 2019 Forage May 2019

2019:

Started feeding in June 2019.

Late commencement of the monsoon rains.

Many thanks to the people who have assisted with data collection and analysis and photos

Sarah Noelle, Brett Blum, George Ruyle, Jackie Hughes, Matt Reeves, Brice Hanberry and others.