Postscript 2

Questions that research needs to address concerning the South Texas mesquite grassland ecosystem:

Questions about the nitrogen cycle

a. In the natural economy of the South Texas range, what are the avenues by which nitrogen becomes available in fixed form?

b. What is the relative importance of woody legumes, such as mesquite, in determining the rate at which nitrogen becomes available to the biological system?

c. Put in terms of greatest interest to the producer, what fraction of the nitrogen in beef protein enters the system via woody legumes such as mesquite?

d. What conditions are optimal for biological fixation of nitrogen, or, what factors limit this process in South Texas?

Questions about other macronutrients and micronutrients

a. Which macronutrients limit production and under what conditions: How do they enter the system?

b. To what extent do deeply rooted plants, such as woody legumes, transport nutrients from deep below the root zone of grasses?

c. To what extent do variations in plant productivity among sites reflect patterns of micronutrient deficiency or excess?

d. How do micronutrient deficiencies, excesses, or interaction impact the health of grazing animals?

e. How do different species of grasses, woody plants and forbes differ in macro- and micro-nutrient accumulation? That is, what does biodiversity of plant species mean to nutrient availability?

Questions about vegetative patterns

a. How stable are open, grass-dominated areas in unmanipulated areas? Why do they exist in the first place?

b. What are the patterns of vegetative succession with respect to soil type?

c. To what degree does competition for water establish observed patterns among woody plants and between brush and grassland?

A sample of questions on animal-plant interaction

a. How does plant nutritive value, palatability, and toxicity vary with stress (i.e., from drought, defoliation, etc.)?

b. Are defensive compounds (allelochemicals) induced by herbivory among the set of significant forage plants? If so, what are the physiological consequences to animals and when are such interactions expected?

c. Are there interactions between levels of particular nutrients in the overall diet and the abilities of animals to detoxify allelochemicals in forage plants?