An analysis of year-to-year changes in native and non-native vegetation abundance in response to climate and soil variability

Background/Question/Methods

Fine-scale climatic and soil variability in vegetation communities can significantly alter the community structure and species distributions from season to season. The biological intertia of communities can mask the effects that climate has. Therefore, studies that have the ability to monitor these variations over several years may be able to separate climate effects from other effects. The current research evaluated the response of vegetation change to climatic variability within two communities over a three year period (2009-2011). In order to evaluate this, three 25 meter transects were established at two locations along the Front Range of Colorado near Boulder and Golden respectively. Soil temperature sensors were buried at 5cm depths at meter intervals along each transect and soil moisture sensors at 5-10cm depth at 6.25m intervals. Vegetation abundance was monitored using the line intercept method for each transect once per growing season. To assess the variability of climate and soil conditions, correlation analyses were performed using both native and non-native vegetation abundance and cover; soil temperature; and moisture.

Results/Conclusions

Soil temperature and moisture varied greatly depending on the season with spring highs and lows ranging from -2-5°C; 12-30°C in summer; and -2-18°C in the fall. Soil moisture further ranged from 0.001-0.300 m³xm³ VMC. The variability of these conditions from year to year in relation to exceptionally variable climatic conditions of 2009-2011 determined which species emerged each spring. At the Boulder site, fall 2009 soil moisture had a negative relationship (R= -0.36) with non-native cheatgrass (Bromus tectorum) abundance in 2010 and a weaker relationship between fall 2010 moisture and 2011 abundance (-0.02). Fall 2009 temperature at the same site had a negative relationship with cheatgrass (-0.38) and a positive relationship in 2010 (0.19). Native abundance varied from 72% in 2009 to 58% in 2010 and 84% in 2011, which may be attributed to the variations in soil temperature and precipitation during those growing seasons. Total native abundance in 2010 showed a positive relationship with fall 2009 moisture and spring 2010 temperature (0.19 and 0.10 respectively), while in 2011 native abundance had a positive relationship with fall 2010 moisture (0.07) and a negative relationship to spring 2011 temperature (-0.22). The results from these correlations show that soil conditions and local climate may be important drivers of both native and non-native species distribution each season. This research contributes to the understanding of the resilience of these communities in the face of future climate change.