Virtual Mt. Lemmon Field Trip

The Santa Catalinas are one of the "Sky Island" mountain ranges of the southwestern United States and northern Mexico. Because of their extreme changes in elevation, these ranges have remarkable environmental and biological diversity. The Catalinas rise more than 2100 m (6890 feet) above central Tucson and the University of Arizona campus. This virtual field trip will take you up the General Hitchcock Highway, which is also locally known as the Catalina Highway and the Mt. Lemmon Highway. It begins on the south (Tucson) side of the range and goes for about 48 km (30 miles) from the cacti and shrub-dominated arid environments at the base to the much moister temperate forests at the summit of Mt. Lemmon at an elevation of 2791 m. We will be talking about individual plants but also about how various species of plants occur together at a particular location, what is known as vegetation.

This field trip is best viewed on a laptop or desktop computer at full screen. Some of the maps and imagery will not display if viewed on a mobile device. Additionally, some web browsers do not support all of the graphics that are embedded in this field trip. If it doesn't work in your browser, try a different one (Chrome may be best, Firefox the next best, Safari the third best) and make sure you have the most recent version installed. There are times when the server where this file is located may be down. If this happens, just wait an hour and try again.

We will begin with information on using contour maps and other geographical tools to visualize the environment. Then, as we proceed up the highway, we will stop at various points, and with images and explanation learn about plants there, how to identify them, and the environments that they inhabit, why this matters, and how they are changing. Certain terms are in bold text. These should become part of your botanical lexicons. You should record at least six of these terms (not including plant common names) and provide a definition for them in your Field Notebook. You may build your definition from information presented here, but you may also want to consult resources on the Internet. There is another exercise for you to complete within this trip, which you will also include in your Field Notebook.

There are lots of linked images and associated text. You should slowly explore both. Some buttons will lead to detailed descriptions of particular plant species. Take a close look at these, not with the goal of memorizing anything, but just to learn more about the amazing diversity of plants you can encounter in this mountain range and how they are described. A major goal here is to prepare yourself to better understand natural environments so that you can function effectively and enjoy them more when you're next in them.

Our focus will be mostly on larger, easier to see woody plant species. This is always a good starting point as you learn about plants in a particular area. Once you're on the ground, it's easier to then focus on the smaller, less conspicuous species. We will use common names for all organisms while on this field trip. A list of common names and their scientific names is available  here . (Some links will only be available to students registered in RNR 230L.)

The Catalina Highway quickly climbs along slopes and canyons with the grade averaging about 5-8% (5-8 m rise for every 100 m covered on the road). We will encounter many different landforms (a natural feature of the earth's surface) including arroyos, ridges, drainages, cliffs, marshes, canyons, streams, hills, and summits. In order to function effectively as field botanists, we need to visualize the landforms we work in and be able to accurately describe our location. This is especially important when making a plant collection and our work may require that we read and interpret contour (topographic) maps. We will prepare for our journey by learning about these maps and what they tell us about the natural environment using topography of Sabino Canyon on the south side of the Santa Catalinas as a platform.

Wherever you are on land in the world, climate is the primary factor determining vegetation that occurs there. Your experience has already convinced you of this. For example, you probably accept that the vegetation of the Amazon Basin is what it is because the environment there is consistently relatively wet and warm. Plants adapted to those sort of environments occur there. Similarly, deserts of the southwestern United States have vegetation that reflect the fact that it is relatively dry and warm in these environments. Climate is also the major factor driving the vegetation changes we’ll experience as we go up the Catalina Highway. And this climate changes very rapidly here since elevation does the same. Average annual precipitation is about 300 mm at Tucson (elevation 728 m) but it is 751 mm at Summerhaven (elevation 2500 m), which is near the summit. The image below shows the south face or southern aspect of the mountain range and predicted mean annual precipitation.

As anyone who has ever driven up the Catalina Highway from Tucson will tell you, temperature also changes with increasing elevation. Weather instruments tell us that the annual average temperature is about 12° C (21.6° F) higher in Tucson than Summerhaven. This is a reflection of a physical characteristic of the atmosphere called the lapse rate, which is the change in temperature with change in altitude. While meteorologists have many ways of defining the lapse rate, depending mostly on the amount of water in the atmosphere, a good average lapse rate is about 6.5° C per 1000 m. The difference in elevation between Tucson and Summerhaven is 1772 m, thus 1.772 m x 6.5° C per 1000 m = 11.5° C, which is very close to the actual average temperature difference between the two locations from the instrument record. Lapse rate can tell us a lot about how vegetation will change with changes in elevation, but again there are many other geographical features to consider when trying explain vegetation on the ground.

Below is a 3D representation of an aerial image of Bear Canyon with the Catalina Highway winding through the fore- and middle ground. The image has been rotated so that we can look up the canyon along the highway. The Middle Bear Parking Area (elev. 1791 m), which has rest rooms, is located at the "star."

Note the vegetation differences between the slopes to the right and left of the portion of the highway that runs along Bear Canyon, shown in red. Vegetation on the cooler, moister north-facing slope is both more abundant and of a different type than that on the south-facing slope to the left of highway.

As we often say in Arizona, "it's cooler in the shade." Have you ever noticed that it is blistering hot standing outside near a south-facing wall of a building, but much cooler on the north side of the building? Wherever you live, go outside and find, photograph, and describe a location that shows obvious differences in plant growth, health, or composition as a result of aspect. Places with topographic relief are good places to look, but <big hint> you probably don't have to go far from home, wherever your home might be. Include all of your observations in your Field Notebook, of course with a  header page  describing the location as always.

The image below is aspect raster (raster: digital image) of the aerial scene, above. The raster was created by analyzing 1 km x 1 km grids containing elevation data. Each color represents a compass direction that the slope faces. Although such fine-scale data manipulations are not necessary for day-to-day field botany work, this technology and others are regularly used by land and watershed managers, wildlife biologists, botanists, fire ecologists, and others to categorize landscapes in order to understand current conditions and predict future changes, such as how a landscape will respond to fire, and how changes in vegetation will affect watershed properties, or threatened and endangered plant and animal species. From the aspect raster, we see that the cool side of the canyon is predominately northwest facing and the opposite side is south-southeast facing.

Mt. Lemmon is named for the California botanist and artist  Sara Plummer Lemmon  who explored the Santa Catalina Mountains on her honeymoon in 1881 with her husband John Gill Lemmon and rancher Emerson Stratton. They climbed the north side of the range to the summit approaching from the town of Oracle.

They explored the Southwest in an era when the going was rough. A very interesting  article  based on the Lemmons' letters to friends and family gives us a glimpse of what southern Arizona was like in the 1880s. Many plant species have been named in their  honor .

As we head back, we hope you have a chance to review what we've learned and think about how you might apply this when you are next in the field. For many of you, this next field experience might actually be into the Santa Catalina Mountains. Regardless, our hope is that you may apply this knowledge anywhere.

Remember to complete the two activities described during the field trip (defining terms in bold text, and describing and photographing an example of an aspect effect on plant growth). Include your responses in your Field Notebook.