Timing of climate variability and grassland productivity

Abstract

Future climates are forecast to include greater precipitation variability and more frequent heat waves, but the degree to which the timing of climate variability impacts ecosystems is uncertain. In a temperate, humid grassland, we examined the seasonal impacts of climate variability on 27 y of grass productivity. Drought and highintensity precipitation reduced grass productivity only during a 110-d period, whereas high temperatures reduced productivity only during 25 d in July. The effects of drought and heat waves declined over the season and had no detectable impact on grass productivity in August. If these patterns are general across ecosystems, predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing.Konza | net primary production | streamflow | critical climate periods F uture climates are likely to include more frequent droughts, high-intensity precipitation patterns, and heat waves, (i.e., periods of elevated air temperatures) (1, 2). At their most severe, extreme climate events, such as the mid-American heat waves of 1980 and 2011 and the 2003 European heat wave, involve months of hot, dry weather (3, 4), increasing mortality in humans and wildlife (5, 6) while reducing agricultural and natural-systems productivity (7-10). An increase in climate extremes would have unambiguously negative effects on ecosystems. However, most climate variability would not be considered extreme and occurs on much shorter time scales throughout the growing season with temperature and precipitation frequently disassociated. The response of ecosystems to short-term climate variability at different times of year is thought to vary (11-16), but we know little about how the timing of short-duration climate variability impacts key ecosystem dynamics such as plant productivity.To understand better how the timing of climate variability affects grassland productivity, we applied the critical climate period approach (17, 18) to long-term measurements of grass productivity in a humid, temperate grassland. Aboveground net primary productivity of grass (ANPP G ) was measured at the time of peak standing biomass from 1984-2010 in both shallow-soil upland and deep-soil lowland topographic positions in an annually burned, ungrazed watershed that is dominated by grasses with the C 4 photosynthetic pathway. In attempting to understand how the timing of climate variability affects grass productivity, we analyzed long-term records of precipitation, stream discharge, and air temperature to examine how variation in drought, precipitation intensity, and heat waves affect grass productivity at different times of the growing season. Results and DiscussionAcross 27 y, drought reduced grass productivity over a wide range of dates but had declining effects as the season progressed. ANPP G decreased with decreasing precipitation summed from April 15 to August 2 [day of year (DOY) 105-214] (Fig. 1). ANPP G declined 0.60 ± 0.12 g·m −2 for each millimeter decline in p...

Anticipating changes in variability of grassland production due to increases in interannual precipitation variability

“…Furthermore, under the nonlinear models, ANPP will be decreasing more in dry years than it is increasing in wet years, increasing the frequency of low production years more than the frequency of high production years despite a symmetric increase in the frequency of wet and dry years. These increases in ANPP variability will make primary production more difficult to forecast and could exacerbate existing challenges for natural resource management, especially when combined with alterations in ANPP caused by changes in the annual mean of precipitation (Hsu et al 2012) as well as the intra-annual variability and timing of precipitation (Swemmer et al 2007, HeislerWhite et al 2009, Craine et al 2012.…”

“…Our work continues the tradition of applying statistical techniques to long-term data sets to characterize relationships between climate and primary production (e.g., Hulett and Tomanek 1969, Le Houerou et al 1988, Laurenroth and Sala 1992, Craine et al 2012, Sala et al 2012. Like previous studies, we use simple statistical models to explain historical variation in ANPP as a function of historical variation in precipitation.…”

Temperature and Precipitation Affect Steer Weight Gains Differentially by Stocking Rate in Northern Mixed-Grass Prairie

“…These models, however, were not founded on data that originally and directly linked long-term cattle weight gains to corresponding climatic variability. Climatic variability and timing of precipitation influences productivity of grasslands (Craine et al 2012), as well as bison weight gains in tallgrass prairie (Craine et al 2009). Inclusion of relationships between climatic variability and beef production from long-term data would increase the accuracy and reliability of predicted cattle weight gains.…”

Diverse responses of forest growth to drought time‐scales in theNorthernHemisphere

“…Different techniques have been used to determine the response times of vegetation to water deficit and drought (e.g., Craine et al, 2012). A robust approach is to relate multiscalar drought indices with different variables as tree-ring width or vegetation activity measured from satellite imagery (Ji & Peters, 2003;Pasho et al, 2011).…”