Using spatial models to establish climatic limiters of plant species’ distributions

Plant species’ climatic range limiters provide clues to reconstruct past climates, restore ecosystems, and manage agricultural systems. However, precise climatic limiters are unknown for many important species, and determining them typically involves long-term autecological studies. A new method presented here automatically and quantitatively infers limiters for a plant species using its documented, digitized distribution. The method uses available and accessible elevation and climate datasets from the US Geological Survey (USGS) and NOAA, along with common off-the-shelf (COTS) geographic information software technology (GIS) to determine which variables in the plant distribution climate space are actually limiting the range by restricting its movement into surrounding territory. The method utilizes precision climate interpolation allowing for independent variables in addition to latitude and longitude, via a software package developed at Australian National University (ANUSPLIN). For this first run, elevation and slope were included as independent variables for interpolating precipitation and temperature surfaces. The model defined limits for five Sonoran Desert plant species: Carnegiea gigantea, Cercidium microphyllum, Encelia farinosa, Ferocactus acanthodes, and Larrea tridentata. Results were tested against environmental factors outlined in autecological studies. Important model-derived climatic constraints to the distribution of C. gigantea include insufficient monsoon precipitation, low winter and monsoon temperatures, and excessive monsoon and fall precipitation. The distribution of C. microphyllum is constrained by cold winter and fall temperatures, excessive spring and summer precipitation and insufficient fall precipitation. E. farinosa is restricted by frigid winter temperatures and too much summer rainfall. Key factors limiting F. acanthodes are cold winter temperatures and inadequate fall and monsoon precipitation. An inordinate amount of precipitation during the summer, monsoon, and fall constrict the range of L. tridentata, along with an abnormally cool summer or monsoon. Results indicate that the method adequately resolves plant range limiters consistent with the autecological record. Future changes to the model are offered to improve results.