The data used in this study was collected from the Southern Alps of Canterbury, New Zealand. The study area consists of two adjacent stream basins (Broken River and Craigieburn) within the Craigieburn range, located at approximately 43.13 S 171.71 E. Six primary habitats have been identified in these catchments; forest, forest creek, canopy gap (treefall gaps), alpine creek, tussock grassland, and scrub. The forest, forest creek, and forest gap habitats occupy lower elevations within the stream catchments, gen- erally ranging from approximately 800 to 1400m AMSL. These three habitats coexist in a matrix which consists primarily of forest habitat. The forest habitat is typified by a dense canopy of mountain beech (N. solandri), and is interspersed with occasional windfall gaps (forest gap habitat), typically caused by the loss of a single tree or small group of trees. The forest creek habitat reflects the more open conditions which occur adjacent to the creeks which dissect the catchment, and is comprised largely of stream banks or open gravel. Above approximately 1400m, the catchment is dominated by tussock grasslands, which consist primarily of long-lived Chionochloa species with a mixture of alpine herbs and grasses that occupy the inter-tussock spaces. Intermixed with the tussock grassland are patches of scrub habitat, dominated by low-growing (approximately 30-100cm) woody shrubs. The alpine creek habitat are those areas directly adjacent to the creeks that dis- sect these upper reaches of the catchment, and are also comprised largely of stream banks and open gravel.
Four field experiments were performed to obtain demographic data on H. lepidulum. These data were used to parameterise the models which describe the probability of a H. lepidulum individual transitioning between di↵erent stages of its life cycle. These field experiments included 1) a field survey of existing H. lepidulum distribution, 2) monitoring of tagged individuals of H. lepidulum, 3) a seed sowing trial, and 4) a seed burial experiment. These experiments were initially established by Alice Miller as part of her PhD thesis (Miller 2006); subsequent years of data collection were performed by myself and others. The use of multiple data sources allowed for the demographic model to reflect the full life cycle of H. lepidulum; however, this approach also introduced a few shortcomings. Observations of adult mortality did not account for the density or size of conspecifics, and therefore does not incorporate the density-dependent regulatory mechanisms which are included in the models of juvenile survival. In addition, the seed sowing experiments from which the observations of juvenile survival collected from were even-aged cohorts and did not
produce adults until the final two years. As such, the density-dependent mechanisms incorporated into the models of juvenile survival reflect the influence of similarly sized individuals. In application, the models of juvenile survival account for the total number of individuals present in a cell across all life stages, but assume that they have similar influences, as opposed to attributing a larger influence to the adult individuals. This e↵ectively results in a conservative estimation of the density dependent mechanisms by downplaying the influence of adult individuals.
Field survey
Survey data were collected for a previous investigation in the austral summer of 2003/04 to describe the distribution and abundance of H. lepidulum in these catchments (Miller 2006). Ten (10) randomly chosen creeks from two adjacent catchments within the Craigieburn Range were chosen for survey. Transects were placed perpendicular to the creek every 100m (side chosen at random) until the creek was no longer identifiable, and extended into the adjacent habitats for 100m. Five 2x3m plots were located randomly along the transect and surveyed for H. lepidulum abundance. Counts of abundance were performed at six 1x1m subplots within each plot. Mean abundances across these subplots are used to estimate density per m2, and summarised by the six habitat types for analysis. Mea-
surements reflecting the number of individuals present were recorded for a total of 1068 plots.
Tagged individuals
Five patches of H. lepidulum in each of the six habitats were randomly selected from those identified during the field survey. In each patch 40 flowering individuals were selected for monitoring. Four of the patches contained less than 40 individuals; in these patches all of the plants were monitored. Overall, a total of 1355 individuals were tagged and monitored. These individuals were surveyed in January 2004 and then again the following year. During each survey the number of flowers on each individual were counted, seed production was estimated from a subset of mature flowering heads, and any mortality was recorded.
Seed sowing trial
Additional demographic data were obtained from a seed sowing experiment established in the Craigieburn basin in 2003. Sowing density treatments consisted of a control with no seed addition, and seed addition at rates of 25, 125, 625, 3125 and 15625 seeds per 30x30cm plot. Each treatment was replicated three times in each block, and each block was replicated six times in each habitat. Blocks were located a random distance up the catchment’s primary creek; forest creek and alpine creek blocks were located directly
adjacent to the creek, forest and tussock habitats were randomly located between 20 and 200m from the creek, and forest gap blocks were located at a gap greater than 25m2 nearest
to a randomly located point between 20 and 200m from the stream. Scrub habitats were randomly selected from all scrub patches within the catchment. The entire experiment was replicated the following year, with the new blocks sown adjacent to those from the previous year, resulting in a total of 1512 individual sowing trials. Seed was collected in the field immediately prior to sowing from the lower reaches of the Avoca River, close to the study area. Seed was collected from a single location to minimise potential variation in seed viability. These plots were revisited annually through 2008 to survey the number of individuals recruited from seed and to record any occurrences of flowering over that five year period. This resurveying provided size years of data for one replicate and five for the other; five years of data from each replicate were used to equilibrate their influence.
Seed burial
In addition to the seed sowing, seed burial trials were performed at each of the blocks to determine the viability of the seed bank after one year, and how this varied among habitats. The survival of seed in the soil in each block was assessed by burying 100 seeds in mesh bags at a depth of 3 cm. Bags were buried at a random location within three metres of the plot, and were removed after 1 year. Seed survival was assessed by counting empty and filled seeds on exhumation, and determining the proportion of filled seeds which germinated by placing them on moist filter paper.