Quantification of state-and-transition model components utilizing long-term ecological response data following one-seed juniper treatment on a deep sand savannah ecological site Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/j098zd73d

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  • A proposed state-and-transition model (STM) for the Deep Sand Savannah ecological site in central New Mexico was developed using historical data and expert knowledge. This STM was tested utilizing data from short and long term one-seed juniper (Juniperus monosperma (Engelm.) Sarg.) control experiments initiated in 1981 and 1985. Utilizing data from the individual plots within the identified states, the proposed model was refined with definitions of specific processes and indicators associated with each state and transition. At-risk community phases, feedback mechanisms and threshold values were identified and described for soil aggregate stability and vegetative cover variables. Short term response data were collected in 1984 and long term response data from 1985 through 1989 and in 2003. Soil moisture data indicated the treated plots contained significantly (α=0.05) more available moisture than control plots especially during the drought year of 1989. The treated plots were significantly (α=0.05) different from controls for all the vegetation and soil variables. Vegetation measurements were repeated in 2003 along with additional vegetation attributes and soil aggregate stability. Eighteen years after treatment, data analysis indicated significantly (α=0.05) different treatment effects in most variables and significant (α=0.05) ranch by treatment interactions for many others. Linear regression showed expected correlations and several weak (r²<0.30) but significant (α=0.05) relationships. Results suggest soil aggregate stability variables provided the best integrator of long term ecological responses to change in vegetation production, soil moisture, cover, bare ground, litter accumulation and bare patch size. Surface soil stability was a reliable indicator and predictor of state membership and provided indication of value ranges within states for itself and other data elements. The STM includes feedback mechanisms that build resilience into each of the three identified states, at-risk community phases within the Reference and Juniper States and threshold values between the three states. This model will assist managers with identification of potential ecological thresholds and at-risk community phases, thus providing information to plan actions that facilitate the maintenance of ecological and economic sustainability while providing the broadest array of ecosystem services possible within the potential of the ecological site.
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