Optimum Management of White Cypress Pine ('Callitris glaucophylla'): Individuals to Landscapes

Abstract

Woody vegetation thickening and encroachment is a global issue of both environmental and economic significance. On the North Western Slopes and Plains of New South Wales, Australia, the indigenous conifer Callitris glaucophylla Joy Thomps. & L.A.S. Johnson (White Cypress Pine) regenerates prolifically, especially in previously cleared agricultural landscapes. The species is recognised in state legislation as 'Invasive Native Scrub' and strategies to manage the species in a manner that improves or maintains on-farm environmental condition are now required by law. The primary objective of this study was to address some of the present knowledge gaps that exist regarding the role and function of the species in a range of configurations in agricultural landscapes of the region. A secondary objective was to draw upon data resulting from this project to suggest optimum management strategies for the species under a variety of scenarios. The investigative approach taken in this study employed a combination of field surveys, field experiments and glasshouse trial, each of which were concerned with describing and/or manipulating the effects of the species on soil and vegetation parameters. As a prelude to this project, a small pilot study was used to identify soil and vegetation parameters most likely to respond to changes in the management of the species. This study used a paired site approach to revisit sites thinned or maintained as controls since 2000 by Greening Australia and compared them with adjacent cleared areas as yet un-colonised by C. glaucophylla. In general, soil and vegetation parameters varied due to site and land-use or their interaction. There was a general trend of increased litter cover from cleared zones through to control zones across all sites, whilst vegetative groundcover decreased with increasing tree cover. The diversity of vegetative groups was linked to site effects. Soil C, N, S and ext. P were generally more abundant in the mineral soil of treed areas and were significantly less abundant in cleared zones, although soil pH was significantly more acid in control plots than thinned or cleared areas. The study also identified two possible economic benefits of the species for landholders. The growth of trees in thinned plots in the five years since management suggested that it may have farm-forestry potential. This growth, in conjunction with the carbon content of all other site components resulted in an estimated total site carbon that was much higher in thinned and control plots than cleared areas and hence the carbon trading potential for the species in a agricultural setting was also suggested. The results of this study indicated that, for the parameters studied, thinning maintained environmental condition.