Effect of succession gaps on the understory water‐holding capacity in an over‐mature alpine forest at the upper reaches of the Yangtze River

The water‐holding capacity (WHC) of the understory in the headwater regions of major rivers plays an important role in both the capacity of the forest water reservoir and water quality and quantity in the butted rivers. Although forest gaps could regulate water‐holding patterns in the understory by redistributing coarse woody debris (CWD), fine woody debris (FWD), non‐woody debris (NWD) and understory vegetation, little information is available on the effects of forest gaps on understory WHC. Therefore, we investigated the WHCs of CWD, FWD, NWD, herbaceous vegetation, mosses, epiphytes (including fern and lichen growing on the surface of logs) and soils from the gap centre to the adjacent closed canopy in an alpine forest at the upper reaches of the Yangtze River. The total WHC of the alpine forest understory components was approximately 300 mm. Soil layer had the largest contribution to the total understory WHC (90%), and among the aboveground components, CWD and mosses contributed 5% and 4% to the aboveground WHC, respectively. With the exception of that of the herbaceous layer, the WHC of the forest floor increased from the gap centre to the closed canopy. Although mosses had the lowest biomass allocation on the alpine forest floor, the water‐holding ratio (k) of mosses reached 485%. In conclusion, biomass is the parameter that most strongly and positively correlated with the WHC of the alpine forest understory, and forest gap formation decreases the understory WHC of alpine forest resulting from a decrease in organic soils, CWDs and mosses. Copyright © 2015 John Wiley & Sons, Ltd. Highlights

• The effects of gaps on the understory WHC were examined in an alpine forest.
• Gaps decreased the understory WHC by decreasing the amounts of the larger WHC components.
• The contribution of CWD and mosses to the aboveground WHC was large.
• The WHC of dead debris was higher than that of the vegetation.

     

Schmidt‐hammer exposure‐age dating (SHD) of snow‐avalanche impact ramparts in southern Norway: approaches,results and implications for landform age,dynamics and development

Schmidt‐hammer exposure‐age dating (SHD) was applied to the problem of dating the diachronous surfaces of five distal river‐bank boulder ramparts deposited by snow avalanches plunging into the Jostedøla and Sprongdøla rivers in the Jostedalsbreen region of southern Norway. Approaches to local high‐precision linear age calibration, which controlled in different ways for boulder roundness, were developed. The mean age (SHD_mean) and the maximum age (SHD_max) of surface boulders were estimated for whole ramparts, crests and distal fringes. Interpretation was further assisted by reference to R‐value distributions. SHD_mean ages (with 95% confidence intervals) ranged from 520 ± 270 years to 5375 ± 965 years, whereas SHD_max ages (expected to be exceeded by <5% of surface boulders) ranged from 675 to 9065 years. SHD ages from the Jostedøla ramparts tended to be older than those associated with the Sprongdøla, rampart crests were younger than the respective distal fringes, and use of relatively rounded boulders yielded more consistent SHD ages than angular boulders. The SHD_mean ages indicate differences in recent levels of snow‐avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and, in smaller numbers, on the distal fringes. SHD_max ages provide minimum age estimates of rampart age (i.e. the time elapsed since the ramparts began to form) and suggest that at least some of the ramparts have been developing since the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd.