Herbage response to precipitation in central Alberta boreal grasslands

The dependence between grassland herbage production and precipitation within the Boreal region of central Alberta was evaluated. Additional objectives were to compare current year growing season (e.g., April or May, to August) precipitation with 12 and 16 month water gear (e,g,, dormant and growing season) precipitation for use in predicting herbage growth, and determine whether lowland and upland grasslands differ in their response to precipitation. Lowland herbage production averaged 6,053 kg ha(-1), nearly twice the 3,153 kg ha(-1) found on upland grasslands during the study. In general, herbage production correlated significantly with precipitation, but the magnitude and direction of that relationship varied depending on grassland type. Uplands displayed a positive linear relationship with precipitation (r = 0.76; p < 0.01), while lowland communities displayed a negative curvilinear (R-2 = 0.65; P < 0.05) relationship. Furthermore, while herbage production on uplands was better predicted by current year precipitation, lowland production appeared more heavily dependent on precipitation falling during the water year, the latter of which included fall and winter moisture recharge. We hypothesize that these differences are linked to water redistribution within the landscape, along with subsequent soil temperature regimes and the length of effective growing season. Given the influence of topography in regulating water availability and use, rangeland managers within the Boreal region should use caution when determining rangeland carrying capacity from meteorological data.