Climatic determinants of berry crops in the boreal forest of the southwestern Yukon

Berry crops in the southwestern Yukon were quantified from 1997 to 2008 at 10 locations along 210 km of the Alaska and Haines highways. We tested the hypothesis that the size of berry crops could be predicted from spring and summer temperature and rainfall of years t, t-1 (1 year prior), and t-2 (2 years prior). Six common species were studied in the boreal forest of the Kluane region: Arctostaphylos rubra (Rehd. & Wils.) Fern., Arctostaphylos uva-ursi (L.) Spreng. s.l., Empetrum nigrum L., Vaccinium vitis-idaea L., Geocaulon lividum (Richards) Fern, and Shepherdia canadensis (L.) Nutt.. For the first five species we counted berries on fixed 40 cm x 40 cm quadrats to obtain an index of berry production for the Kluane region for each of the 12 years, and for S. canadensis we counted berries on two tagged branches of 10 bushes at each location. Stepwise multiple regressions were utilized to predict the size of berry crops for each species. For all species, predictive equations could explain statistically 80%-96% of the variation in berry crops. Different weather variables characterized each plant species, and there was no common weather regression that could explain the variation in berry crops in all species. Rainfall and temperature from years t-1 and t-2 were typically the significant predictors. There was no indication of a periodicity in berry production, and 43%-60% of the quadrats counted had large berry crops at one year intervals, while other quadrats never had a high crop during the study interval. Key words: berry production, Yukon, climate, Kluane, dwarf shrubs. Les auteurs ont quantifie les recoltes de baies dans le sud-ouest du Yukon de 1997 a 2008, a 10 endroits sur 210 km le long des autoroutes d'Alaska et de Haines. Its ont verifie l'hypothese qu'on pourrait predire l'importance des recoltes de petits fruits a partir des temperatures estivales des annees t, t-1 et t-2. Its ont etudie six especes communes de la foret boreale dans la region de Kluane: Arctostaphylos rubra (Rehd. & Wils.) Fern., Arctostaphylos uva-ursi (L.) Spreng. s.l., Empetrum nigrum L., Vaccinium vitis-idaea L., Geocaulon lividum (Richards) Fern et Shepherdia canadensis (L.) Nutt. Chez les 5 premieres especes, on a compte les baies sur des quadrats fixes de 40 cm x 40 cm afin d'obtenir un index de la production des baies dans la region de Kluane pour chacune des 12 annees, et pour le S. canadensis on a compte les baies sur deux branches marquees chez 10 bosquets sur chaque site. Les auteurs ont utilise la regression multiple progressive pour predire la dimension des recoltes de petits fruits pour chaque espece. Chez toutes les especes, les equations predictives peuvent expliquer statistiquement 80-96 % de la variation des recoltes de petits fruits. Differentes variables climatiques caracterisent chaque espece de plante, et on n'observe pas de regression commune qui pent expliquer la variation des recoltes de baies chez toutes les especes. La precipitation et la temperature des annees t-1 et t-2 constituent des pronostiques significatifs. Il n'y a pas d'indication qu'il existerait une periodicity dans la production des baies, et 43-60 % des quadrats enumeres montrent de fortes productions de baies a un an d'intervalles, alors que les autres quadrats n'ont jam ais montre de fortes recoltes tout an long de l'etude. Mots-cles : production de baies, Yukon, climat, Kluane, arbustes nains. [Traduit par la Redaction]
Introduction Berry crops in the boreal forest region vary dramatically from year to year. A combination of soil factors and climatic events are usually put forward to explain these variations [...]