Annual Seedfall Variation in Nothofagus solandri (Fagaceae), Canterbury, New Zealand

Abstract

Annual seed production was measured over 23 yr for a Nothofagus solandri stand at Mount Thomas Forest (foothill forest) and over 24 yr for three stands along an elevation gradient (montane to subalpine forest) in the Craigieburn Range, Canterbury, New Zealand. Total and viable annual seedfall were strongly correlated between stands, with highest correlations between adjacent stands. Periodicity of heavy seed production was greatest near timberline. For all stands, maximum seed viability occurred when total seed production exceeded ca. 7000 nuts ml2, indicating that pollination success was maximized in heavy seed years. Seed crop size was related to five predisposing variables. Mean daily temperature at the time of floral primordia formation (summer) was positively correlated with seed production. Seed crop size was negatively correlated with the previous 3 years' seedfall in montane and subalpine forest, but only with the previous year's seedfall in foothill forest. This suggests that high elevation forest needs a longer recovery period than lower elevation forest. Increased precipitation and extreme minimum temperature at the time of flowering were negatively correlated with seed production in montane and subalpine forest, but not in foothill forest. Increased daily temperatures at the time of flowering were positively correlated with seed production in montane and subalpine forest. Multiple linear regression showed that these five variables accounted for most variation in total and viable seed production within each stand. For the Craigieburn elevation gradient, these variables accounted for less variation with increasing elevation, indicating that the predictability of seed production declined near the elevation limit of the species.