Part of assessing forest condition is to carefully document current conditions. We have completed a detailed characterization of soil properties and plant nutrient status that can serve as a baseline for future reference. In addition we can also draw some conclusions about the susceptibility of these forests to acid (particularly N) deposition. We have analyzed stem, weed, litter, leaf and needle samples from Ponderosa Pine (Pinus Ponderosa Laws.), black oak (Quercus kelloggii) and white fir (Abies Conculor). We also collected and analyzed combined samples of roots. All tissues were tested for concentrations of N, P, S, Ca, Mg, K, Mn and Zn. No nutrient deficiencies are apparent. Nutrient concentrations were not normally distributed except for K.
Soils at the Barron Flats are relatively young. This is reflected in the relatively low clay content and the absence of significant clay movement (no argillic horizon) and the high base saturation of the exchange complex. Previous classification of the soils in this area included the finding of clay translocation and hence the presence of an argillic horizon. Based on our measured soil characteristics, these soils are insensitive to short-term pH influences associated with acid deposition. This is a result of the high base saturation and abundance of weatherable minerals in these soils. Hence, acute effects of acid deposition like aluminum toxicity should not be a problem.
Forests have evolved under conditions that are typically N-limited. This is evidenced by the response of most forests to N fertilizers. There is not an unlimited response to N additions. Hence, chronic deposition of N can produce N-saturation. Given the relatively young nature of these soils (relatively coarse texture, low clay content and low caution exchange capacity), the total capacity of the soil to immobilize continued N deposition will have limits. One good indicator of the change in N loading in these soils will be C: N ratio.
Chronic deposition of N has occurred in the Los Angeles Basin for at least the last 40 years. Elevated stream water NO3 concentrations have recently been reported for chaparral watersheds exposed to chronic N deposition in the San Gabriel mountains near Los Angeles. The high N losses from these chaparral ecosystems are an indication of N-saturation. A number of nutritional parameters across spatial and temporal gradients in the San Bernardino mountains support the hypothesis that the mixed conifer forests in the highly exposed western.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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