Radiocarbon Dating Informs Tree Fern Population Dynamics and Disturbance History of Temperate Forests in Southeast Australia

Abstract

Tree ferns are slow-growing and long-lived components of temperate forests; however, these characteristics make determining size-age and population dynamics through mensuration approaches problematic while dendroecological approaches cannot be used. In this study, we use radiocarbon (14C) dating of Cyathea australis and Dicksonia antarctica to (1) determine their age-to-size relationships, (2) reconstruct the age distribution of tree fern species, and (3) test if predicted ages align with the ages of the co-occurring tree community and observed disturbance history. We used the best age-size models to reconstruct the population structure of tree ferns sampled in five paired rainforest and old-growth eucalypt stands and compared these to the age structure of co-occurring tree species. The species had similar growth allometry; however, C. australis grew four times faster than D. antarctica. The age class structures of tree ferns were congruent with the associated tree species and reflected known fire history and snowfall events in the region. Tree fern abundance increased with increasing time-since-fire and post canopy disturbance. The study demonstrates that 14C dating of tree ferns provides a means of investigating tree fern demographics and the role of disturbance in shaping their population structure in forests of southeast Australia.

The hare, tortoise and crocodile revisited: Tree fern facilitation of conifer persistence and angiosperm growth in simulated forests

“…The model produced realistic and plausible dynamics, with individual C. dealbata attaining heights of up to 10 m and ages between 300 and 500 years (Brock et al, ; Bystriakova et al, ; Mueck et al, ). Ageing understorey tree ferns is challenging, and there are no published age data for New Zealand species, and few globally (Fedrigo et al, ; Mueck et al, ). While the occasional individual tree fern in the treatments achieved a longevity in excess of 500 years, which is older than any field measurements, the problem of unexpectedly long individual persistence under low‐light levels is not restricted to the tree ferns and is something that previous similar models have struggled with (Hall & Hollinger, ; Morales & Perry, ).…”

“…Conducting manipulative field‐based experiments to evaluate such hypotheses, however, is impractical because tree fern sporophytes can persist in forest communities for upwards of 250 years, and associated angiosperms and conifers often longer (Bystriakova, Bader, & Coomes, ; Fedrigo et al, ; Morales, ; Mueck, Ough, & Banks, ; Ogden & Stewart, ). One solution to this challenge is to experiment in silico and many forest models have been developed to explore vegetation dynamics over broad spatial and temporal extents (Scheller & Mladenoff, ).…”

“…Furthermore, age‐growth data are difficult to obtain for tree ferns as, similar to monocotyledons, tree fern structures leave few indications of an individual's age (Brock et al, ). Attempts to age tree ferns have used long‐term remeasurement data, radiocarbon dating from basal tissues (destructive), stipe‐scar counting and fire scars as historic markers to calculate recent growth rates (Ash, ; Blair, Blanchard, Banks, & Lindenmayer, ; Bystriakova et al, ; Fedrigo et al, ; Mueck et al, ; Tanner, ). However, there is no universal cross‐species method with which to accurately estimate the age of tree ferns.…”

Predictive Ecosystem Mapping of South-Eastern Australian Temperate Forests Using Lidar-Derived Structural Profiles and Species Distribution Models

“…Airborne lidar data were commissioned by the state environment department and were acquired from late 2007 to early 2008 over a subset of the Central Highlands region (Figure 1) from a fixed wing aircraft (Data agreement number DQ201206071138; see Table 1 for flight details and sensor settings). There should be limited impact of the date discrepancy between the lidar capture and floristic sampling due to the slow change in forest structure of these mature stand types (>100 years old) and the exclusion of disturbed field sites in the study [45,51,73,74]. This is further supported by a previous study where a time lag of six years between field-data collection and lidar acquisition only had a minimal influence on the predicted distribution of bird species modelled using structural variables in an undisturbed coniferous forest [74].…”

Dead frond “skirts” as tree fern defence: what is the evidence?

“…Tree ferns are a prominent feature of many tropical and southern warm temperate forests (Page & Brownsey 1986;Brock et al 2016;AVH 2020;Manaaki Whenua -Landcare Research 2020), and in New Zealand and south-eastern Australia tree ferns also occur in regions that regularly experience sub-zero temperatures (Wiser et al 2011;Brock et al 2016;Fedrigo et al 2019). In several taxa, dead fronds or frond stipes are retained in a fringe, encircling the top of the trunk of the tree fern like a skirt.…”