Plant phenological responses to extreme events - A long term perspective from the Chihuahuan Desert
Abstract
Arid and semi-arid regions of the southwestern USA are especially sensitive to changes in temperature as well as drought frequency and intensity. Timing of periodic life cycle events (i.e., phenology) is an integrated and salient indicator of plant responses to climate change. We examine an 18-year dataset of monthly observations of plant phenology for two species of perennial grasses and a deciduous shrub (honey mesquite) distributed across three upland grassland sites and three mesquite-dominated sites on the Jornada Basin USDA-LTER in southern New Mexico, USA. Precipitation is highly variable between years and across space. Long-term phenology data collection spanned a multi-year drought (1994-2003) followed by a sequence of years with average to very high rainfall (2004 - 2008). Our objective was to compare and contrast responses to extreme dry and wet cycles in the timing and duration of first leaf and fruit production for two grasses (Bouteloua eriopoda [black grama], Sporobolus flexuosus [mesa dropseed]) with one co-existing shrub that has displaced grasses in this system (Prosopis glandulosa [honey mesquite]). Monthly field observations yield estimates of phenological status and abundance for 18 growing seasons from 1993 to 2010. All three species most commonly initiated new growth prior to onset of the monsoon rains (March or April). Timing of first growth for mesquite was less variable (standard deviation = 0.47) than for black grama (SD = 1.42) and mesa dropseed (SD = 1.22) grasses. Initial growth for grasses was delayed to September in 2006 following twelve months of deficit values for PDSI. The appearance of first fruit for grasses occurred consistently in August or September, although the number of plants producing fruit was highly variable from year to year. The largest numbers of fruit-bearing grasses were observed in late fall 2008 in response to heavy monsoon rains in 2006 and 2008. Mesquite demonstrated remarkable synchrony in the production of flowers (May), and fruit (June) across four sites that ranged from 1.2 to 14.4 km apart. The appearance of first fruit and peak fruit production was most often in the same month for mesquite and mesa dropseed whereas this time period for black grama was one month at two sites and in the same month at a third, suggesting local variability in rainfall or soil moisture dynamics play a role in fruit production. Future analyses will examine relationships between the amount and seasonal distribution of rainfall with timing and abundance of fruit production. Understanding the role of abiotic factors in influencing the timing and success of reproductive events is especially relevant to the conservation and restoration of species of concern. Elucidating the role of extreme events in structuring plant populations is paramount to predicting plant responses to changes in climate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.B43A0282B
- Keywords:
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- 0439 BIOGEOSCIENCES / Ecosystems;
- structure and dynamics;
- 0476 BIOGEOSCIENCES / Plant ecology;
- 1605 GLOBAL CHANGE / Abrupt/rapid climate change;
- 1632 GLOBAL CHANGE / Land cover change