Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 5, 1998
Publication Date: N/A
Technical Abstract: Degree-day models can be used to compare the relative thermal response of different seed populations. When the objective is to compare different species or seed-lots, the modeling approach typically involves some simplifying assumptions. These assumptions make model equations easier to calculate and allow for the generation of thermal indices for ranking population response. An alternative approach is to minimize modeling assumptions, optimize model accuracy, and evaluate population differences based upon predicted response under various measured or simulated temperature regimes. The objective of this experiment was to measure thermal response of 5 range grass species under a range of constant temperature conditions; to derive a cumulative-thermal-response model for each species; to evaluate potential species response under field-simulated thermal regimes; and to compare potential-population response based upon different types of model assumptions. Bluebunch wheatgrass, thickspike wheatgrass, bottlebrush squirreltail, sandberg bluegrass and cheatgrass seeds were germinated under 21 constant temperature regimes and 18 field-variable temperature regimes. Linear and non-linear thermal response models were developed from the constant- temperature data and a linear model for each species from the variable- temperature data. Historical field-temperature simulations were used to compare potential seedlot-germination response under a wide range of field-temperature scenarios. Probabilistic profiles of potential germination response may provide a more ecologically relevant basis for comparing seed populations for thermal response characteristics.