Tuesday, February 04, 2014

Passion-flower Distribution in the Sonoran Ecoregion

Source: SEINet

Passiflora (Passion flower vine) is a tropical genera of vines, which reach their northernmost distribution with P. mexicana in the Santa Teresa mountains, North of the Gila River.  They produce edible passion fruits, but the herbiage is extremely unpalatable to animals, to the point that (reportedly) starving horses will not eat P. foetidius due to the stinky sticky hairs.

I have never seen these monsoon-bloomers in the wild in Arizona, but hope springs eternal in the Sky Islands...there are three species in Arizona:  P. arizonica, P. bryonoides, and P. mexicana:

P. arizonica ca 4-5.5 cm in diameter, whitish, the corona white or purplish.

P. bryonioides ca. 2.5-4.5 cm in diameter, whitish with purplish bands on corona. 

P. mexicana ca. 2-3 cm in diameter, light green or yellowish green, the corona red or reddish purple.

There are two more species in the Sonoran Desert south of the border:

P. palmeri (no description available)

P. suberosa (no description available)

Monday, February 03, 2014

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.  

Monarch Decline Blamed on Changing US Agriculture

Graph of returning migration Monarch Butterflies from MonarchWatch.org

CBS quoted entymologist Lincoln Brower: "The main culprit," he wrote in an email, is now genetically modified "herbicide-resistant corn and soybean crops and herbicides in the USA," which "leads to the wholesale killing of the monarch's principal food plant, common milkweed."

The website MonarchWatch.org has the best in-depth analysis of the triple threat of habitat loss.  What to do?  Plant milkweed!

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.


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.