North American tropical deciduous forest (TDF) is severely threatened by deforestation for livestock production and agriculture. Integrating cattle and forests, silvo-pastoral systems are an alternative to forest conversion to pasture, but the impact of cattle on TDF tree community diversity and structure in forested ranches is poorly understood. Furthermore, no research to date has quantified cattle foraging biases toward or against woody forage plant species in TDF, in order to isolate the role of cattle browsing from other variables contributing to impacts on woody vegetation. Here, I describe the foraging behavior and movements of free-ranging cattle in TDF, and differences in statistically paired TDF with and without cattle, on ranches with low stocking rates and an adjacent conservation preserve in the foothills of the Sierra Madre Occidental, Sonora, Mexico.
In Chapter 1, I introduce CowPro, an animal-mounted time-lapse video, GPS and data logging system I designed and used throughout this study. CowPro units require no human intervention for periods up to seven days, allowing researchers to unobtrusively collect quantitative behavioral data on leery, forest-dwelling cattle or other large terrestrial animals. For Chapter 2, I tested hypotheses on cattle bias toward or against food resources at the plant- species level and at the plant-community level. Using CowPro, I generated a database of woody plant species and frequencies of those species occurring in cow diets. I then quantified tree community structure in TDF with arrays of 5-meter by 5-meter plant census plots on known cow foraging paths and across all available cattle habitat within ranches in the TDF, and compared species frequencies and community diversity. Cows are selective at both the individual-plant scale as well as the landscape-level, habitat scale, though the best predictor of cow preference for woody plant species overall is the prevalence of that species in foraging habitat. Additionally, repeat-visit foraging habitat is more diverse than all habitat available to cows. For Chapter 3, I tested hypotheses on the effect of cattle on TDF woody plant species abundances, species im