Ecological Archives A024-029-A2
R. J. Fensham, J. L. Silcock, J. Firn. 2014. Managed livestock grazing is compatible with the maintenance of plant diversity in semidesert grasslands. Ecological Applications 24:503–517. http://dx.doi.org/10.1890/13-0492.1
Appendix B. Method for assessing herbarium collecting trends.
Here we describe survey methodology for rare or poorly known species potentially threatened by grazing. It is expected that species that have declined dramatically because of grazing may exhibit a shallower slope (flat trend) of collections through time relative to the collections for Australia as a whole. Herbarium collecting records were extracted from the Australian Virtual Herbarium (http://www.chah.gov.au/avh/). All records were assigned to a decade of collection. The entire record consists of 3,843,222 records of which only 1.6% are pre-1990. All pre-1900 records were assigned to a single bin and every post 1900 decade was given a bin with a total of 12 ‘time bins’ until 2010. This ‘transformation’ effectively weights the pre-1990 record on the assumption that this period best represents Mitchell grasslands before there were dramatic impacts of domestic livestock grazing. The number of records from the entire Australian record for each time bin were converted to a proportion of the total number of records and regressed against time as represented by the 12 bins and yielded an equation of the form:
(Eq. B.1) CP = 0.0193T-0.0422;
where CP is the proportion of the collections; and T is a Time bin (1-12).
The R² for this relationship is 0.775; P < 0.001. This analysis was repeated for candidate species that could be decreaser species and the coefficient of slope divided by 0.0193, the slope for the collecting effort overall from Eq. B.1. For species where this proportion is low (relatively flat trend), there has been a lower proportion of collections in recent times than in the early period of pastoral grazing relative to collection returns from Australia overall.
[Back to A024-029]