Seasonal Dynamics of Nitrogen Compounds in a Disturbed Forest in Northern Mexico

Pine and oak forests have great relevance worldwide since they are recognized for the benefits and services they provide. Grazing can affect nitrogen reserves in forest trees in complex ways, the effects manifest through changes in the soil, vegetation, and the nitrogen cycle. Nature tourism can have negative impacts on tree physiology. These impacts affect vital processes such as photosynthesis, respiration, water relations, and metabolism. This study was developed in order to determine whether natural populations of pine (Pinus cembroides Zucc.) and oak (Quercus grisea Liebm.) are affected physiologically by grazing and tourism during the stages of development and dormancy, specifically in nitrogenous compounds (Total Soluble Proteins [TSP] and Total Amino Acids [TAA]) stocked in perennial organs (stem and roots) and leaves. The results showed that grazing and tourism have both negative and favorable effects on the concentrations of nitrogen compounds. The highest concentration of nitrogenous compounds was found in oak compared to pine. The root, trunk, and leaves in the grazed and non-impacted sites showed the highest concentrations of nitrogen compounds compared to the tourism-impacted site. Pine is the species most affected by anthropogenic processes (grazing and tourism) in the stages of development and dormancy, since the concentrations of nitrogenous compounds were lower compared to oak.