Age‐states, population structure, and seedling regeneration of Chionochloa pallens in Canterbury alpine grasslands, New Zealand

Abstract

Abstract. Age‐states, population structure, and seedling regeneration of the grass Chionochloa pallens were investigated in eight alpine grassland stands representing the range of canopy cover (ca. 5–75 %) and basal area (112 ‐ 3889 m2/ha‐1) in the headwaters of the Avoca catchment, Canterbury, New Zealand. In open‐canopy stands (< 50 % canopy cover, < 2000 m2/ha‐1 basal area) C. pallens individuals were clearly distinguishable. Rela‐tionshipsbetweenbasal diameter, number of tillers, height, and % crown death suggested four putative age‐states: ‘seedlings‘, ‘juvenile tussocks’, ‘mature tussocks’ and ‘senescent tussocks’. Four types of population structure were identified depending onthe proportions of seedlings and juvenile and mature tussocks. C. pallens seedlings were present in seven stands at densities ranging from 0.6 to 123.4 / m2. They were most frequent on microsites protected from frost‐heave by short herbaceous vegetation or litter, but with little competition from taller vegetation. Differences in seedling densities between stands partly reflected the proximity and abundance of seed sources and degree of protection from frost‐heave. C. pallens population structures appear to be influenced by the frequency and magnitude of geomorphic disturbances and browsing by introduced animals.

Effect of climate change on mast‐seeding species: frequency of mass flowering and escape from specialist insect seed predators

“…There are 22 species of Chionochloa endemic to New Zealand, and most species have mass flowering and mast seeding (Connor 1966;Mark 1968;Kelly et al 1992). The plants grow as long-lived tussocks (Connor 1991), with only occasional regeneration from seed (Rose & Platt 1990;Lee et al 1993).…”

Pattern of natural regeneration of narrow-leaved snow tussockChionochloa rigidassp.rigidain Central Otago, New Zealand

“…In New Zealand Journal of Botany, 1993, Vol. 31 climatically stressed habitats, intertussock swards contain many openings for tussock regeneration, which are rare in dense natural tall tussock grassland where tussocks are large and canopies coalesce (Rose & Platt 1990). In the latter, in the absence of burning, regeneration is probably limited by the availability of suitable establishment microsites.…”

“…A similar approach was used by Rose & Platt (1990) in their study of population structure of Chionochloa pallens. Although some of the immature plants may be seedlings, others are probably at least 5-10 years old and are more correctly termed juveniles; it is not known what proportion are reproductively active.…”

“…rigida with and without grazing after fire was examined by Mark (196Sa), but nothing has been published about recruitment of seedlings in the absence of burning, although Rose & Platt (1990) have investigated natural recruitment in Chionochloa pallens (Connor 1991). The main focus of our investigation is the spatial distribution of seedlings around isolated tussocks; that is, the "regeneration shadow" of the individual parent plants.…”

Is vegetation inside Carex sempervirens tussocks highly specific or an image of the surrounding vegetation?

“…Many ecosystems, including wetlands, arctic tundra and high-altitude grasslands, are dominated by caespitose grasses and sedges that form well-delineated tussocks (Chapin et al 1979;Rose & Platt 1990;Jónsdóttir & Watson 1997;Klimeš et al 1997;Körner 1999;Mark & Wilson 2005). In tussocks of some of these graminoids other plant species can grow, forming small communities (Nichols 1915;Costello 1936;Rutter 1955;Jervis 1969;Fetcher 1985;Yabe 1985;Niering 1987;Lord & Lee 2001;Levine 2001;Yu et al 2004Yu et al , 2006.…”