Kidman Springs Long Term Exclosure Study - Vegetation Changes 1973-2002 

The data are herbage biomass (dry weight, gram per square metre) and density of trees and shrubs (number per transect) measured inside cattle-proof exclosures and on adjacent grazed areas on two sites of different soils at Kidman Springs, Northern Territory between 1973 and 2002. 

We at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging. 

Initially, in the 1970s and 1980s, to test the effectiveness of destocking, using exclosures, as a means of promoting pasture recovery on two important rangeland types of the semi-arid tropics of north west Australia. Subsequently, to determine the longer-term (30+ years) dynamics of these red-soil and black-soil vegetation communities. 

The use of destocking as a means of promoting pasture recovery was evaluated on two important rangeland types of the semi-arid tropics of north west Australia.

Fenced areas approximately 500-m square were established in 1973 on Victoria River Research Station, Kidman Springs, Northern Territory. One site, called Black Soil, was located on a cracking clay soil with shrubs (mainly Carissa lanceolate, conkerberry) and trees (Lysiphyllum cunninghamii, bauhinia and Terminalia volucris, rosewood) on the margins. The herbage layer was dominated by Chrysopogon fallax (ribbon grass) and Iseilema fragile (Flinders grass). This site was minimally affected by past grazing and was deemed in good condition. Two exclosures were constructed on red calcareous soils; one site eroded (Red Soil, eroded) and the other not (Red Soil, not eroded). When data collection commenced, the red-soil sites had an open tree and shrub layer of Eucalyptus pruinose (silver leaf gum), E. terminalis (bloodwood) and C. lanceolata. The herbage layer at the good site was dominated by biennial Enneapogon spp. (limestone grass) with sparse Brachyachne convergens (native couch), Sporobolus australasicus (fairy grass) and Aristida spp. (wire grasses) present in the degraded state.

Six permanent plots (45 m by 30 m) were randomly located inside and outside of each of the three exclosures.

Herbage biomass was measured by clipping individual species. Species were harvested within five randomly placed 1-m square quadrats at each plot. Samples were oven dried to obtain dry weight. Additional biomass data were obtained in two years (1989 and 1994) by estimating yield and composition using BOTANAL (Tothill et al. 1992) within 15 randomly placed 1-m square quadrats at each of the six permanently marked sampling locations.

Trees and shrubs, categorised by lifeform (juvenile or mature), were counted within fixed 0.14-ha areas at each of the permanent sampling locations used to collect herbage biomass data. These numbers were multiplied by 7.14 to give the number per hectare (i.e. density).

For analysis, the dry-weight biomass of individual species was sequentially grouped into functional groups: annual or perennial grasses and forbs, total grass and forb, and total herbage biomass. The data are provided by functional group and the biomass of dominant species for each soil type. Similarly, the densities of tree and shrub species by lifeform were aggregated to juvenile trees or shrubs and mature trees or shrubs and, from there, total trees or total shrubs. Data are provided by species with the user to aggregate to lifeform and age groups if required.

Two separate analyses were conducted based on time since exclosure. In the first (Foran et al. 1985), analysis of variance was conducted on the herbage biomass and woody density data to examine the effect of destocking and year (essentially, prior wet-season rainfall). Stepwise multiple linear regression analysis was used to define the influence of different factors such as rainfall, stocking rate and shrub density on the levels of standing biomass in the grazed treatments. For the red-soil sites in their second reporting period (Bastin et al. 2003), repeated-measures analysis of variance was used to explore whether there was a significant change (slope) across time (years since exclosure) and, if so, whether changes across time differed for inside and outside the exclosures (treatments). If changes across time appeared to be non-linear, quadratic and cubic polynomials were explored.