The Experimental Control

Every experiment in science has a control which can be thought of as a test where nothing is done, no treatment, no manipulation, really just a base line for the experiment allowed to run concurrently with experimental treatments.  The grassland restoration project at the Painted Pony Resort has an experimental control.  It is an area marked off by railroad ties at the north end of the property enclosing an area of about 12' x 12'.  This area started as bare earth when the main complex was built and the former estate manager placed the railroad ties to create a planting area but did nothing further.  I have left this area alone to see what would happen if there was no intervention on the landscape (only cutting back tumbleweed occasionally so I don't get any 5' high plants).  While it may appear I have not been diligent in keeping the area free of weeds and other woody shrubs this plot shows what happens if a barren area is left to naturally recover.  The plot is dominated by tumbleweed but also has woody shrubs including mesquite, Indian tea, amaranth, and rubber rabbitbrush and 1 unidentified thick stemmed weed.  Two species of annual grass have grown and one species of a perennial bunch grass has appeared but little else.  This suggests that a passive management strategy of only removing grazers and allowing the land to rest for several seasons is no longer adequate for the landscape recovery when starting from bare ground.  Rather it takes an active management strategy to restore the grassland in this heavily modified desert landscape.  For the estate that means interventions to manage water, soil, vegetation, and animals. 

The question arises as to why simple rest no longer appears to be adequate to recover the grasslands on the estate.  Several factors may be involved with the appearance of only a single perennial grass within the test plot shown below.  It may require longer periods of rest (a couple of years is not sufficient) to recover grasses within the test plot and is a reflection of my inexperience with restoration in the desert.  Or it may be a result of succession in the grassland, that is with enough time the perennial grasses will out compete the other plants.  Or it may be related to changes in climate.  About 20 years ago The Portal Project (a long term desert ecology project in the area) published a paper on the changes within their test plots, noting a shift from grasses to woody shrubs within their enclosures they suggested changes in rainfall were resulting in a shift away from grasses and to woody shrubs.  The Malpai Borderlands group also noted this shift away from grasses and towards woody shrubs with the exclusion of grazers and the loss of fire as a tool for managing grasslands, see their historical photo archives and click on a tag to view historical and recent repeat images.  Changes in climate, especially short term ones, have a particularly large effect on minimally productive desert landscapes and periods of drought in combination with human activity are known to have altered the landscape particularly the drought of 1891-93 in the area.  But are long term changes also having an effect?  Changes in rainfall patterns, especially increasing winter rains favor woody shrubs over perennial grasses making it more difficult to restore grasslands and is one reason the river bottom grasses are currently isolated so grass seed production will continue unabated.  The yearly mean temperature in New Mexico has increased 2 degrees since 1970 and marginal landscapes like the high desert may be the first to respond this change.  Whatever the source it is clear that active management as opposed to passive management techniques are required to create and sustain a productive landscape.

Control plot of vegetation with out any intervention.  Tumbleweed predominates followed by woody shrubs.

Harvester Ants as a Rangeland Indicator Species

Ants, especially harvester ants utilize seeds as a food source and might be a useful indicator species for the grassland restoration efforts at the Painted Pony Resort.  A number of reports suggest that both soil composition and grazing intensity can alter harvester ant colony frequency on the landscape (1, 2, 3). Variation in ant colony density across the estate was noted while preparing a previous post on indicator minerals in ant colony mounds so a small comparative study was designed to test the hypothesis that harvester ant colonies varied with the grazing intensity on the estate.  A 3 km transect across the estate from west to east, starting on grazed New Mexico State land was chosen and at 14 stations a 30 m diameter circle (area = 730 meters²) was examined for harvester ant colony entrances.  A colony was defined on the basis of a circular pile of small (1-2 mm) stones, and an entrance hole with or without harvester ants on the surface. Although other ant species were observed along the transect these were not included in the colony totals.
Constantly grazed land had a average of 1 colony/730 m² while ungrazed land averaged 4 colonies/730 m² and there was a significant difference in the frequency of harvester ant colonies between the 2 grazing regimes, P = 0.003, single tailed t-test.  Since soil type also varies across the estate the number of colonies by soil type was also tested. Forest-Pinleno association is found on the west side of the estate while Eba very gravelly loam predominates the eastern portion of the estate. There was no significant difference in harvester ant colony density between these 2 soil types, P = 0.12, single tailed t-test. This suggests that soil composition, and secondarily plant species diversity, are not a major contributor to harvester ant colony frequencies on the estate in the semi-arid southwest, but rather the frequency of grazing (constantly grazed versus ungrazed land) is the more important determinant of harvester ant colony frequency in and around the estate.

Satellite view of the 756 acre Painted Pony Resort showing 3 km transect and locations of test sites.  The red line indicates the property boundary but no fencing and accessible to cattle, while the white line indicates fencing around the estate where cattle are excluded.  The 3 stations furthest west lie on New Mexico State land which is grazed year round.

Frequency of harvester ant nest colonies.

Soil map of the Painted Pony Resort.

Rangeland Rehabilitation: Stabilizing Arroyos

Arroyos in the desert southwest are major conduits of water across the landscape and during the rainy seasons can be major sources of erosion on a lightly vegetated landscape.  On the 756 acres of the Painted Pony Resort just several arroyos contribute to the majority of erosional damage on the estate.  These arroyos collect water from the west flanks of the Peloncillo mountains which is concentrated into 3 arroyos by bridges along the old El Paso and Southwestern Railroad running along the base of the mountains.  The water collected on the up slope side of the railroad bed is funneled through the bridges and across the property down these 3 arroyos eventually reaching the San Simon Riverbed.  The concentrated and rapidly flowing water erodes both down through the soils and also moves the arroyos laterally.  The high velocity water makes roads on the east side of the estate impassible and washes out culverts and crossings which require significant repair work.  While the changes in drainage patterns as a result of the railroad bridges is beyond one persons ability to easily change, the arroyos resulting from a century of landscape modification can be managed to reduce the damage caused by concentrated high velocity water.  

One of several arroyo management techniques in use requires stabilization of the arroyo banks.  Over 10' deep in places on the estate, arroyo banks frequently collapse and stabilization would reduce the amount of soil eroded during the rains.  But what sort of stabilization technique is applicable?  Being in favor of utilizing low cost materials that are available on the landscape this is the approach most frequently chosen.  Many times people toss in whatever garbage is available into arroyos to slow water flow and protect the banks, but this approach results in an arroyo strewn with leftover wood and metal products which randomly catch sediment and is unsightly (the out of sight out of mind approach).  An alternative approach is to utilize plants for stabilization.  In this case, a native species of ground spreading gourd Cucurbita sp.. 

Members of this genus are low growing ground covering annuals and perennials, in many species the fruit is edible and include cultivars of squash and pumpkin.  Adapted to arid climates and growing well in sandy soils they can be found along roadsides and the gourds may be collected in the late summer.  Producing about 300 seeds/gourd, 3 species of Cucurbita are found on the estate, Cucurbita digitata , Cucurbita foetidissima, and an unidentified species.  The green developing gourds turn yellow when dried and are easily spotted on the landscape for collection.  Arroyo stabilization requires harvesting the gourds and extracting the seeds which are then planted high along the edges of arroyos.  The gourd produces a taproot allowing it anchor itself deeply in soil ensuring it will not wash out with periodic high water and hold the soil.  The long vines it produces cover the ground, absorbing energy and slowing water, and will hang along vertical surfaces allowing its large leaves to protect the underlying soil, reducing soil loss.

Previous tests with planted Cucurbita along the entrance driveway resulted in plant coverage over areas of barren ground which has allowed additional grass to establish itself.  So this is being expanded to treat problem arroyos on the estate.  Collected seeds were planted at about 50 locations along a segments of 2 deep arroyos at the bottom to the top at a depth of 1-2".  Starting at the old bridge, quarter sections of gourds were cut and planted along the banks for a distance of several hundred feet.  Next years crop of gourds should spread downstream with the goal of creating more plants that will stabilize these problem arroyos.

Fruit from C. digitata, C. foetidissima, and an unknown species harvested from the estate.

Looking downstream along a problem arroyo, treated by planting native gourds .

Looking upstream at an old El Paso and Southwestern railroad bridge that funnels water creating problem arroyos.

Native Cucurbita along an arroyo showing how the vines and leaves provide cover for developing grasses.

New Mexico Rangeland Restoration

The grassland restoration project at the Painted Pony Resort continues to bear fruit.  In many areas the topsoil is completely removed due to poor range management techniques in the past and as a result large swaths of landscape are completely barren of vegetation leading to additional erosion problems.

These eroded areas are generally surrounded by terracettes, individual plants or low woody shrubs which hold topsoil and sit up to 18" above the surrounding subsoil.  While observing these naturally occurring terracettes and noting how the plants hold the topsoil an artificial terracette was found.  This artificial terracette was the result of several pieces of hog fence left laying on the ground.  The mesh work held the top soil, creating a micro habitat for new plant growth.  The plants and mesh work would also catch additional windblown seeds and soils continuing the process of topsoil regeneration.  In an attempt to replicate this process an experiment in topsoil restoration was started.  The first treatment utilized weeds pulled around the estate and this material was laid in widely spaced rows perpendicular to the dip, to catch water, or if the ground was level, perpendicular to the prevailing winds.  With the arrival of the monsoons new grass has sprouted along these test barriers and additional soil has accumulated.  The placement of biological material in rows on the landscape creates not only a micro habitat for new plant growth but also slows water running across the landscape decreasing soil loss and in combination with the seed reservoir will help heal the landscape naturally and continue to restore the landscape to its' original condition.

Untreated state land showing soil movement and little grass.

An artificial terracette of hog fencing.

Black lines denote new growth along test topsoil barriers.

A close up of new grass growth along one topsoil test barrier.  Note the accumulation of soil around the line of grass.