Just sayin'

We all suspected as much.

Sarah K.

I grew up in the midwest, but am in love with the desert. I have worked in the Great Basin as well as the Mojave, and am ever so excited to see what the Sonoran has to offer. I have an innate love of plants and am fascinated with desert species. I like hula hooping, my favorite color is pink, and I enjoy eating avocados, a lot. My favorite home has always been my tent and a desert sunset just isn't the same without a Tecate in hand.

Team Member: Steven Sesnie

Currently, I am a research professor at NAU. I have been a desert rat since 1985 when I led an expedition of several thousand individuals into the Grand Canyon, along the Bright Angel trail. At least, I felt like I was leading thousands of individuals down the trail. Since that time I've been exploring deserts from northern Mexico to Peru as a recreational pursuit. I have primarily been focused on studying tropical and tropical forest ecology since 1992 in the southwestern US and Central and South America. The Sonoran Desert Research Program is a new undertaking with NAU and other research partners, where I hope to deepen my understanding of southwestern desert ecosystems and contribute novel methods and approaches to biodiversity conservation in these systems. I greatly look forward to meeting the many new members of our research team and sharing this tremendous opportunity with all of you!

A Taste of the Desert

This Newsletter on Organ Pipe's website should give you a taste of the desert, even if it is about 6 years old. I especially like the section called, "How do you say that word?"

http://www.nps.gov/orpi/parknews/upload/newspaper2005.pdf

Study Area

By now Luke probably told most of you that we will start at Organ Pipe Cactus National Monument (ORPI). This is just one of many land units that we will be visiting this spring and we are working hard to finalize study permits and logistics. I thought it would be helpful to share with you the study area boundaries and the potential land owners we will be working with. Here is a map showing the study area boundary in black and the diversity of potential land owners in different colors. The map is zoomed in to central and southwestern AZ. We will not be working on private lands but all other lands are potential sites for plots (pending research approval in some cases). ORPI, our starting location, is shown in turquoise.

Touching briefly on the methods and science behind this project

For those of you wondering what the plots might look like, here is one from the fall sampling. Click on the photo to get a larger version in which you can see the plot boundary (large square) and subplot boundaries (small squares). Point sampling is performed where the yellow lines (transects) intersect subplot boundaries or other transects. Thus, there are 25 point intercepts per subplot. The subplots are 30m by 30m (the size of a Landsat TM pixel). The plots are 250m by 250m (the size of a MODIS pixel). These satellite sensors are considered moderate resolution and you can see from the image that there is a lot of spatial heterogeneity at a scale smaller than what either a Landsat TM or MODIS TM pixel can see. Here is a photo taken at the furthest right subplot in the image above to give you a sense of the community structure and diversity:

For comparison, I've included a crude map showing what the same place on the ground looks like in a single Landsat TM image below. The outline of a single MODIS pixel is shown in black.

There are two hypotheses being tested. The first hypothesis is that invaded pixels have a different spectral signature. Landsat TM has 6 reflective bands, so each pixel can be described by a set of 6 values. One of the more famous derivatives of Landsat data (and many other satellite imagery) is the Normalized Difference Vegetation Index, or NDVI. NDVI utilizes the fact that vegetation has strong absorption in the red wavelength due to chlorophyll activity while and highly reflective in the near-infrared wavelengths due to cell structures. These characteristics are unique to vegetation, so NDVI is used to quantify the amount or health of vegetation. NDVI utilizes two of the six Landsat TM bands, so ostensibly, more information can be obtained from the full set of Landsat bands. Of course, the spectral "signature" of vegetation and other materials change over the course of season due to factors such as green-up and senescence, the wetting and drying of soils, and the presence of snow. Therefore, we seek to find an optimal timing in which invaded pixels are distinguishable from uninvaded pixels.

The second hypothesis is that the phenology of invasive species in the desert differ from native species. This has been demonstrated already for many species, including cheatgrass (Bromus tectorum), and one of our study species, Sahara mustard (Brassica tournefortii). The premise is that these species are more aggressive in their water usage, green up earlier, and senesce earlier. Additional evidence suggests that invasive grasses mute bimodal growing seasons.

What makes our approach viable is the incorporation of long time series of these satellite images. Shown below is a time series of MODIS NDVI over the course of 10 years. The goal is to match unique phenological signals in the time series with invasive species and biomass estimates gained in the field this spring and develop models that predict invasive species occurrence, abundance, and biomass at other locations.

Team Member: Aaryn Olsson

I am a desert rat. I have been intimate with glochids and retrorsely barbed spines many more times than I can remember. I know the thrill of seeing the broken tip of an embedded agave thorn surface weeks after it first entered my skin. I can weave through a patch of chainfruit cholla at the same pace that most people walk along a sidewalk. My contortions of navigating a cluster of jumping cholla could be used to train pole vaulters and high jumpers. I have broken icicles off saguaros and gathered snow from prickly pears to make desert snowballs. I have waited for Gila Monsters to cross my path and given sidewinders a wide berth. I listen to thunder and then I yell back. I have chewed on Ephedra and drunk from tinajas. I kissed a Canyon tree frog and it didn't turn into a prince (or a princess). I part the slime in canyon pools. I picked up a Colorado River toad and didn't get warts. My favorite smell is creosote right before it rains. I run through puddles and I always root for desert rain. I love flash floods and eat wild greens. I have a love-hate relationship with Kearney and Peebles. So will you. Yes, I have hugged a saguaro.

I grew up in Tucson, AZ, and received degrees from the University of Arizona, the last being a PhD in Arid Lands Resource Sciences. I started work at the NAU Lab of Landscape Ecology and Conservation Biology in June, 2010. I am a desert ecologist and remote sensing specialist with a strong interest in invasive species and the "grass-fire cycle". The grass-fire cycle, as termed by Carla D'Antonio and Peter Vitousek (1992), describes a positive feedback between invasive grasses in arid ecosystems that have historically experienced infrequent fires or no fires at all. Arid ecosystems are typically characterized by little to no fine fuel connectivity and are resistant to fire. Invasive grasses fill the interstitial spaces and allow a fire cycle that destroys natives and promotes further invasion by grasses. This is happening in my own backyard.

I now live in Flagstaff with my wife and son. We are expecting #2 in March and as a result I will not be in the field for the duration. When the day comes, I hope you will drink a Tecate for our little one.