Doctoral Dissertation Research: The Effects of Climate and Disturbance Variation on Post-Fire Regeneration of Madrean Pine-Oak Forests in Mexico's Sierra Madre Occidental

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

The ecological effects of anthropogenic global climate change are of increasing concern for understanding and predicting climate driven vegetation change. Global circulation models exist that predict future climates and changes in coarse scale vegetation patterns. However, the efficacy of these models is limited by temporal and spatial scale problems and a poor understanding of how climate variation and human land use changes influence disturbance regimes and subsequent vegetation patterns. This doctoral dissertation research project will help to understand how annual to decadal scale climatic variation interacts with human influences on the landscape in north-central Mexico to effect changes in the fire regime and subsequently affect the regeneration success and species distributions of Madrean pine-oak ecosystems after fire. The specific objectives are: 1) to assess how climate variation and changes in human land use practices influence the fire regime in Madrean pine-oak ecosystems, 2) how climate variation and alterations to the fire regime interact to regulate seedling establishment and success, and 3) to test if ecosystem/community responses to climate and land use identified in other regions of North America are general ecological responses or are dependent on the life history traits of specific taxa. Standard tree-ring study techniques will be used to derive tree establishment dates, tree age frequencies, and reconstruct past fire regimes in a set of study sites that have been repeatedly disturbed by humans within a context of pronounced climatic variability. A combination of correlation analysis and regression analysis techniques will be used to identify temporal patterns of tree establishment at different spatial and temporal scales. The results of this study will be used to test the general hypothesis that seedling establishment in Madrean pine-oak ecosystems is related to climate variation and variations in the fire regime. Seedling establishment is predicted to occur during multi-annual to decadal periods of above average precipitation that follow widespread, biologically severe fires. Widespread fire years are predicted to occur during annual to multi-annual periods of below-average precipitation and above-average temperature. Humans are predicted to influence the occurrence and severity of fires by altering fuel quantity and continuity and serving as ignition sources. Ultimately, the site specific ecosystem/community responses to climate and land use variation identified in north-central Mexico will be compared with previous results from studies in other regions to test if these are general ecological responses, or if they are dependent on the life history traits of specific taxa. The study of how climate variation and human land use affect the fire regime and subsequent vegetation patterns has important consequences for predicting the ecological effects of global change. This study will provide basic information concerning how climate and human interactions with the fire regime affect the success of seedling establishment after fires in north-central Mexico. This research has broad ecological significance in that it will test previous hypotheses of climatic influences on fire, tree establishment, and tree mortality that were developed in other regions of North America with taxonomically different ecosystems under different precipitation and temperature trends. This study will also provide additional information to clarify the roles of climatic and human influences on vegetation change due to the climatic differences, and the differences in the timing of human migrations and subsequent land use practices throughout North America. Moreover, the differences in ecosystem characteristics between our sites in Mexico and other areas of North America will allow us to test whether the ecosystem responses to climate and land use changes identified in previous studies are general ecological responses or are if they dependent on the life history traits of specific taxa. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.