Forest gap formation and closure along an altitudinal gradient in Tongariro National Park, New Zealand

Abstract

24 treefall gaps accumulated over a 10 year period along an altitudinal transect covering 4.6 ha on Mt. Hauhungatahi, Tongariro National Park, New Zealand were described quantitatively in terms of the area of damage ('expanded gap'), the canopy opening ('light-gap') and the size of the root mound. Tree mortality and branch loss following cyclone Bola, 1988, were recorded. In each gap saplings were ranked by species according to their vigour. Pre-gap and post-gap vertical and horizontal branch growth rates were calculated. Effects in the subalpine forest (> 1050 m) were compared with those in the montane zone.Tree mortality was highly episodic, associated with major storms, and patchy. Falling canopy trees destroyed, on average, 1.3 additional trees (> 10 cm diameter at 1 m). About half the trees were uprooted and the remainder broken off. Uprooted angiosperm (canopy) trees frequently resprouted from their bases, gymnosperms rarely. Expanded gap area averaged 56 m 2 in the sub-alpine forest and 88 m 2 in the montane zone. Median expanded gap areas were about twice those of light gaps. Gap size frequency distribution was highly skewed. The largest gap was formed by a single Dacrydium cupressinum which destroyed six other trees creating a gap of ca. 0.03 ha.Expanded gaps, light gaps, and root mounds comprised 4.5, 2.8 and 0.l % of the forest area in the sub-alpine zone, and 3.8, 2.5 and 0.06 % in the montane forest. These values represent 10 years of accumulation, and imply light gap 'return times' of 360 years for the sub-alpine and 400 years for the montane forest. These periods are in agreement with the known longevities of the canopy and emergent trees.Vertical shoot growth rate was about twice that in the horizontal plane, and both increased following gap formation. The relative increase was greatest in the subalpine forest. Using the measured growth rates it is estimated that gaps of median dimensions are filled by lateral extension growth in 31 -44 yr. Saplings require longer to reach the mean canopy height and consequently require large (multiple tree) gaps or sequential gap events.

Patterns of species composition, recruitment, and growth within canopy gaps in two New Zealand kauri (Agathis australis) forests

“…After 5 years it was apparent that gap closure would result mostly from lateral expansion of canopy trees around the gap edge, and the rapid vertical growth of plants damaged, but not killed, by the tree-fall. The estimated rate of lateral closure (33 cm/yr) is slightly higher than those obtained for some northern hardwood forests in North America, which range from 6 to 26 cm/yr (Hibbs 1982), and for montane forests of central North Island, New Zealand (Ogden et al 1991), perhaps owing to a longer growing season.…”

Microclimatic differences between and within canopy gaps in a temperate rainforest

“…The large gap measured here falls near the upper end of the range of gap sizes described by Ogden et al (1991) for montane forests in the central North Island of New Zealand. The small gap had estimated areas of 12.6 m 2 and 12 m 2 respectively.…”

Gap closure process by lateral extension growth of canopy trees and its effect on woody species regeneration in a temperate secondary forest, Northeast China

“…Previous studies usually estimated gap closure process by supposing a constant lateral extension growth rate (Rentch et al 2003) because continuously long term monitoring is not easy (Bekker et al 2007). However, this assumption may not be realistic (Webster and Lorimer 2005) because the decrease of gap size due to lateral extension growth could not continue indefinitely (Ogden et al 1991). Resource availabilities, mainly light and space, which are the limiting factors, decrease with time.…”

“…We found that the mean lateral extension growth rate (48 cm a -1 , varied from 13 cm a -1 to 79 cm a -1 ) in our study area was great higher than sub-alpine coniferous forests and some other temperate broad-leaved forests, but lower than tropical rain forests. For example, Ogden et al (1991) claimed that canopy gaps with a radius of 7 m in a sub-alpine forest predominated by coniferous species Dacrydium biforme (Hook.) Pilg.…”