Annual rings of perennial forbs and mature oaks show similar effects of climate but inconsistent responses to fire in the North American prairie-forest ecotone

For the prairie-forest ecotone of central North America, research of the effects of climate and fire on the annual growth of nonwoody plant types is currently needed to compliment dendrochronological research used for predicting the stability of this ecotone in the future. Using cores of Quercus stellata Wangenh. and collars of taproots of Asclepias viridis Walter from central Oklahoma, as well as cores from Quercus macrocarpa Michx. and Lespedeza capitata Michx. collars in central Minnesota, we aimed to distinguish the response towards annual precipitation and temperature, as well as fire regime, between these co-existing plant types through patterns in annual ring growth. The effect of spring fire on the annual growth increment was only consistently significant for one of the forbs, with a positive relationship. The strong negative effect of summer temperature was consistent between forbs and Q. stellata, while the positive effect of either growing season precipitation was consistent between plant types. Furthermore, we found stronger patch-specific annual ring patterns in forbs in comparison with trees when patches are separated based on unique fire histories. Overall, such efforts could be used in further studies to better predict growth rates of dominant plant types in landscapes susceptible to significant environmental change. Key words: annual rings, Asclepias viridis, climate, dendrochronology, fire, forbs, herb chronology, Lespedeza capitata, prairie-forest ecotone, Quercus stellata, Quercus macrocarpa. Dans le cas de l'ecotone prairie-foret du centre de l'Amerique du Nord, la recherche concernant les effets du climat et du feu sur la croissance annuelle des types de plantes non ligneuses est actuellement necessaire pour completer la recherche dendrochronologique utilisee pour predire la stabilite future de cet ecotone. A l'aide de carottes de Quercus stellata Wangenh. et de collets racinaires d'Asclepias viridis Walter provenant du centre de l'Oklahoma ainsi que de carottes de Quercus macrocarpa Michx. et de collets racinaires de Lespedeza capitata Michx. provenant du centre du Minnesota, nous avons cherche a distinguer la reaction a la precipitation et a la temperature annuelles ainsi qu'au regime de feu de ces types de plantes coexistantes a l'aide des patrons dans les cernes annuels. L'effet des feux de printemps sur l'accroissement annuel etait constamment significatif pour seulement une des plantes herbacees non graminoides et la relation etait positive. L'effet negatif important de la temperature estivale etait constant chez les plantes herbacees non graminoides et Q. stellata tandis que l'effet positif des precipitations durant chaque saison de croissance etait constant parmi les types de plantes. De plus, nous avons observe des patrons plus nets dans les cernes annuels, specifiques aux Hots de plantes herbacees non graminoides, comparativement aux arbres lorsque les Hots etaient separes sur la base de leur historique de feu particulier. Dans l'ensemble, de tels efforts pourraient etre utilises dans le cadre d'etudes ulterieures pour mieux predire le taux de croissance des types vegetaux dominants dans les paysages sujets a un changement environnemental important. [Traduit par la Redaction] Mots-cles : cernes annuels, Asclepias viridis, climat, dendrochronologie, feu, plantes herbacees non graminoides, dendrochronologie des herbacees, Lespedeza capitata, ecotone prairie-foret, Quercus stellata, Quercus macrocarpa.
Introduction The prairie-forest ecotone of central North America is responsive to environmental changes, leading to dramatic shifts of vegetation boundaries (Umbanhowar et al. 2006; Camill et al. 2003). Differential responses [...]