Landscape phenology, vegetation condition, and relations with climate at Colorado National Monument, 2000–2019

Thoma, David

doi:10.36967/nrr-2293476

Quantitatively linking satellite observations of vegetation condition and climate data over time provides insight to climate influences on primary production, phenology (timing of growth), and sensitivity of vegetation to weather and longer-term patterns of weather referred to as climate. This in turn provides a basis for understanding potential climate impacts to vegetation—and the potential to anticipate cascading ecological effects, such as impacts to forage, habitat, fire potential, and erosion, as climate changes in the future. This report provides baseline information about vegetation production and condition over time at Colorado National Monument (NM), as derived from satellite remote sensing. Its objective is to demonstrate methods of analysis, share findings, and document historic climate exposure and sensitivity of vegetation to weather and climate as a driver of vegetation change. This report represents a quantitative foundation of vegetation–climate relationships on an annual timestep. The methods can be modified to finer temporal resolution and other spatial scales if further analyses are needed to inform park planning and management. For this analysis, vegetation alliance groups were derived from vegetation-map polygons by lumping vegetation types expected to respond similarly to climate. Relationships between vegetation production and phenology were evaluated for each alliance map unit larger than a satellite pixel (~300 × 300 m). We used a water-balance model to characterize the climate experienced by plants. Water balance translates temperature and precipitation into more biophysically relevant climate metrics, such as soil moisture and drought stress, that are often more strongly correlated with vegetation condition than temperature or precipitation are. By accounting for the interactions between temperature, precipitation, and site characteristics, water balance helps make regional climate assessments relevant to local scales. During the study period (2000–2019), there were dry years, as well as dry periods extending for several years, that resulted in substantial declines in vegetation cover. At the end of the study period, vegetation condition at Colorado NM was close to the long-term average after rebounding from a three-year drought. Key findings: The patterns of pivot points and responses can serve as a guide to anticipate what, where, when, and why vegetation change may occur. Multiple indicators suggest production has increased in all vegetation alliance groups at Colorado National Monument since 2000. Non-native grasslands declined in production, but none of the native alliance groups decreased in production. Increases in production occurred everywhere in the park, except in non-native grasslands. Annual precipitation and annual production were generally among the most strongly correlated variables, suggesting that increases in annual precipitation may have caused the increase in production over the study period. Perennial and annual exotic grasslands and dry shrublands were more drought-tolerant than juniper or pinyon-juniper woodlands. Mixed montane shrublands were the least drought-tolerant alliance group. Annual exotic grasslands were most sensitive to interannual variation in precipitation. Two-to-three years of annual average soil moisture was the best indicator of annual production at the park scale. This was also generally true at the alliance-group scale. By the end of the study period, the growing season was starting earlier for all alliance groups except annual exotic grasslands and wet shrublands. By the end of the study period, the growing season was ending earlier for some alliance groups (perennial exotic grasslands and dry shrublands) but later for others (annual exotic grasslands). By the end of the study period, the timing of peak growth was occurring later in the calendar year. Date of complete snowmelt, actual evapotranspiration, and temperature were the most...

Landscape phenology, vegetation condition, and relations with climate at Colorado National Monument, 2000–2019

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