White Cypress Pine Callitris Glaucophylla Research Articles

Ecological outcomes for multiple taxa from silvicultural thinning of regrowth forest

Management of forest regrowth is a key issue globally, particularly where it occurs as high densities of small-sized stems and where there is little to no self-thinning. Thinning can reduce stem density to accelerate tree growth and potentially restore forest-structural complexity. Yet, in some forest types, it remains unclear how biodiversity responds to thinning, especially over longer periods. White cypress pine Callitris glaucophylla is geographically widespread in Australia and has history of silvicultural thinning in parts of its distribution. We used a chronosequence approach to assess the short- and longer-term responses of multiple taxa (bats, birds, invertebrates, reptiles, non-volant mammals, and plants) to thinning of C. glaucophylla in the dry Pilliga forests of New South Wales. We recorded data from a total of 227 taxa. The short (<8 years)- and longer-term (>20 years) responses to thinning of C. glaucophylla regrowth were mostly positive or neutral for the taxa considered. Bat activity and diversity were comparable to levels in long-undisturbed reference forest, though this was influenced by time since thinning. Reptile diversity and abundance was positively associated with thinning at an intermediate time since thinning (8–20 years), with both metrics greater than unthinned regrowth and long-undisturbed reference forest. Bird diversity was greater in recent and old thinning treatments when compared to unthinned forest regrowth, although species composition was not affected by thinning. Though thinning did not affect volant invertebrate biomass, it was associated with a relatively more even distribution among size classes >8 years post-thinning, and a greater representation of beetles to overall insect biomass. The activity, diversity and composition of non-volant mammals did not differ among treatments, nor did understorey plant diversity or composition. Combining these multiple taxa into a composite ‘biodiversity’ index demonstrated a 16–22% increase with thinning relative to index values in long-undisturbed reference forests. Overall these results indicate that thinning has neutral to positive effects on biodiversity, but responses are species-specific and likely to be dependent on forest-type and the broader landscape of a site. Given unthinned forest represented habitat of similar value to thinned forest for some taxa, we recommend that that regrowth patches of varying size are retained across the landscape to provide a mosaic forest structure suitable for a diverse suite of flora and fauna.

Modelling the dynamics of white cypress pine Callitris glaucophylla woodlands in inland south-eastern Australia

White cypress pine Callitris glaucophylla is an important native tree widespread in heavily cleared savanna woodlands of the south-east Australian wheat-sheep belt. C. glaucophylla woodlands have been the focus of vigorous debate regarding their structure and dynamics during Aboriginal times and following European settlement, and the causes of structural changes are poorly understood. Management of contemporary woodland remnants is therefore controversial, and has so far lacked a predictive, process-based approach. We sought to determine whether a simple process model with recruitment, growth and survival mediated by rainfall and competition, could accurately simulate medium-term dynamics of C. glaucophylla woodlands in which fire has typically been excluded. Model parameters were optimised using reference data from 6- to 36-year silvicultural trials in central-western New South Wales (NSW). Predictions of the calibrated model compared favourably to actual growth, survival and recruitment of C. glaucophylla in the reference data, as well as in an independent dataset not used in optimisation. We tested whether remaining differences between predictions and actual data were related to variation in site productivity (a function of moisture availability as influenced by soil and landscape factors not modelled). Growth was overestimated in low-productivity sites and underestimated in high-productivity sites. Growth predictions were improved by using site-specific expected maximum heights to reflect site productivity. We also tested whether the model and parameter set produce dynamics consistent with those observed over the last half century. Modelled growth, survival, recruitment and competition processes were consistent with data and observations in previous studies on historical dynamics and stand behaviour of C. glaucophylla. The model has a wide range of potential applications for understanding past and predicting future stand dynamics. To illustrate an application of the model to thinning, a strategy currently being implemented to manage tree densities in inland NSW, we compared predicted stand structures in simulations of different thinning treatments. The simulations showed that without careful manipulation of existing canopy cover, stands can re-fill to pre-thinning densities within relatively short periods of time.

Impacts of logging, fire and grazing regimes on bird species assemblages of the Pilliga woodlands of New South Wales

We investigated the composition and distribution of bird assemblages in the continuous Pilliga woodlands of north-west New South Wales in relation to floristic assemblages and disturbance (logging, fire and grazing) patterns. Box-ironbark woodlands contained high densities of White Cypress Pine Callitris glaucophylla and Narrow-leaved Ironbark Eucalyptus crebra, had a sparse, depauperate understorey, and were associated with frequent, intense logging and infrequent fires (due to fire exclusion and the use of grazing for fuel reduction). Box-ironbark woodlands were characterized by high frequencies of 12 bird species that occurred throughout the Pilliga and low frequencies of many other species. Blakely's Red Gum E. blakelyi woodlands typical of creeks and Broad-leaved Ironbark E. fibrosa woodlands typical of poor soils contained lower densities or smaller trees of C. glaucophylla and E. crebra, had a moderately dense, diverse understorey, and were associated with infrequent low-intensity logging and moderately frequent wildfire. Bird species assemblages of Broad-leaved Ironbark woodlands were similar to those of box-ironbark woodlands. Blakely's Red Gum woodlands were characterized by 36 bird species that were virtually absent from box-ironbark and Broad-leaved Ironbark woodlands, including 10 threatened and declining species. The 10 are among 48 woodland species that are known or thought to be declining and that are dependent on woodlands with mature trees and grassy or patchy grass/shrub understorey. We conclude that these species have declined in the Pilliga and will continue to decline under existing disturbance regimes, particularly in box-ironbark woodlands. We suggest adaptive management strategies for maintaining and rehabilitating their habitats.