Uncleared Pastures Research Articles

Biodiversity responses to land‐use and restoration in a global biodiversity hotspot: Ant communities in Brazilian Cerrado

AbstractGiven that land‐use change is the main cause of global biodiversity decline, there is widespread interest in adopting land‐use practices that maintain high levels of biodiversity, and in restoring degraded land that previously had high biodiversity value. In this study, we use ant taxonomic and functional diversity to examine the effects of different land uses (agriculture, pastoralism, silviculture and conservation) and restoration practices on Cerrado (Brazilian savanna) biodiversity. We also examine the extent to which ant diversity and composition can be explained by vegetation attributes that apply across the full land management spectrum. We surveyed vegetation attributes and ant communities in five replicate plots of each of 13 land‐use and restoration treatments, including two types of native vegetation as reference sites: cerrado sensu stricto and cerradão. Several land‐use and restoration treatments had comparable plot richness to that of the native reference habitats. Ant species and functional composition varied systematically among land‐use treatments following a gradient from open habitats such as agricultural fields to forested sites. Tree basal area and grass cover were the strongest predictors of ant species richness. Losses in ant diversity were higher in land‐use systems that transform vegetation structure. Among productive systems, therefore, uncleared pastures and old pine plantations had similar species composition to that occurring in cerrado sensu stricto. Restoration techniques currently applied to sites that were previously Cerrado have focused on returning tree cover, and have failed to restore ant communities typical of savanna. To improve restoration outcomes for Cerrado biodiversity, greater attention needs to be paid to the re‐establishment and maintenance of the grass layer, which requires frequent fire. At the broader scale, conservation planning in agricultural landscapes, should recognize the value of land‐use mosaics and the risks of homogenization.

Soil respiration rate and its sensitivity to temperature in pasture systems of dry-tropics

Tree clearing is a topical issue the world over. In Queensland, the high rates of clearing in the past were mainly to increase pasture production. The present research evaluates the impact of clearing on some soil biological properties, i.e. total soil respiration, root respiration, microbial respiration, and microbial biomass (C and N), and the response of soil respiration to change in temperature. In-field and laboratory (polyhouse) experiments were undertaken. For in-field studies, paired cleared and uncleared pasture plots were selected to represent three major tree communities of the region, i.e. Eucalyptus populnea, E. melanophloia, and Acacia harpophylla. The cleared sites were chosen to represent three different time-since-clearing durations (5, 11–13, and 33 years; n=18 for cleared and uncleared plots) to determine the temporal impact of clearing on soil biological properties. Experiments were conducted in the polyhouse to study in detail the response of soil respiration to changes in soil temperature and soil moisture, and to complement in-field studies for estimating root respiration. The average rate of CO2 emission was 964 g CO2/m2/yr, with no significant difference (P<0.05) among cleared and uncleared sites. Microbial respiration and microbial biomass were greater at uncleared compared with those at cleared sites. The Q 10-value of 1.42 (measured for different seasons in a year) for in-field measurements suggested a small response of soil respiration to soil temperature, possibly due to the limited availability of soil moisture and/or organic matter. However, results from the polyhouse experiment suggested greater sensitivity of root respiration to temperature change than for total soil respiration. Since root biomass (herbaceous roots) was greater at the cleared than at uncleared sites, and root respiration increased with an increase in temperature, we speculate that with rising ambient temperature and consequently soil temperature, total soil respiration in cleared pastures will increase at a faster rate than that in uncleared pastures.

IMPACT OF TREE CLEARING ON SOIL ATTRIBUTES FOR A PASTORAL PROPERTY IN CENTRAL QUEENSLAND, AUSTRALIA

Impacts of tree clearing on soil properties in grazing systems of Queensland largely remain undetermined. In the past, most of the land was cleared to develop pastures to enhance pasture production. The present research highlights how tree clearing affects soil attributes over time on a pastoral property in the semiarid zone of central Queensland, Australia. Paired cleared and uncleared pasture systems were selected to represent three different times since clearing (5, 11-13, and 33 years). Three woodland plant communities, which are common in the region, were studied: poplar box (Eucalyptus populnea), ironbark (Eucalyptus melanophloia), and brigalow (Acacia harpophyllla). Soil macronutrients and micronutrients and exchangeable cations were studied down the profile for 0-5, 5-10, 10-20, 20-30, and 30-60 cm depth. The results suggest that tree clearing initially increased concentration of some nutrients (such as total N in the topsoil) that consequently augmented pasture production. However, this scenario changes with increased time since clearing: concentrations of some soil nutrients increased, whereas some decreased, thus disturbing the equilibrium in soil functions that further impacts upon pasture yield. The impacts of clearing on soil properties were more apparent at deeper layers of soils. Increase in concentrations of Na at 30-60 cm in cleared pastures of E. populnea and E. melanophloia raises concern for sodicity. Results from this study support other findings in the region that changing native woodlands to introduced grass pastures is likely to have consequences on soil nutrients, which can affect cattle production gains and the sustainability of pasture systems.

Litter production, decomposition and nutrient release in cleared and uncleared pasture systems of central Queensland, Australia

The temporal impact of clearing trees on litter production, litter decomposition and on C, N and P release through decomposition of litter was examined in the pasture systems of a semi-arid zone of central Queensland. Paired sites for cleared pastures (developed from clearing woodlands) and uncleared (intact woodland) pastures were selected to represent three dominant tree communities of the region i.e. Eucalyptus populnea, E. melanophloia and Acacia harpophylla, with three different time-since-clearing (5, 11–13 and 33 y) treatments. Yearly litter production was greater at uncleared sites (1732–1948 kg ha−1 y−1 for eucalypt and 2596 kg ha−1 y−1 for acacia communities) compared with cleared sites (1038–1282 kg ha−1 y−1 for eucalypt and 1100 kg ha−1 y−1 for acacia communities averaged over three time-since-clearing treatments). Rates of litter decomposition and of release of C, N and P from decomposing litter were higher at cleared than uncleared sites for all three tree communities. The cleared and uncleared sites did not differ significantly in total amount of C and N released per year since the concentrations of C and N were greater in litter from uncleared sites but the rate of release was less than that at cleared sites. Slow but continuous release of nutrients in eucalypt and acacia woodlands may be an adaptation of these communities to maintain the nutrient cycle and to avoid leaching of nutrients in the nutrient-poor soils of the region.

Pasture composition in cleared and uncleared woodlands

Land clearing in Queensland is often practised to enhance pasture production, and hence, increase financial returns from beef production. The benefits of clearing have been quantified in terms of short-term gains in pasture yield but have not adequately accounted for possible medium- or longer-term impediments that may be attributed to clearing. Therefore, impacts of clearing and the subsequent sowing of exotic grasses such as Cenchrus ciliaris L. on pasture composition and production were studied. To achieve this, paired sites were selected representing cleared and uncleared pastures across three different times since clearing (i.e. 5, 11–13 and 33 years since clearing) for the three dominant tree communities of central Queensland (i.e. Eucalyptus populnea F.Muell. (poplar box), E. melanophloia F.Muell. (silver-leaved ironbark) and Acacia harpophylla F.Muell. ex. Benth. (brigalow)). The results demonstrated that species diversity declined with clearing and sowing of exotic pastures. Species diversity and pasture production were negatively related. Although pasture yield was 2–3 times greater 13 years after clearing of E. populnea and A. harpohylla, the gains in pasture yield were not consistent over time, yields being only 1.5 times greater after 33 years of clearing. In E. melanophloia, an increase in the yield of only 1.5–1.8 times occurred 5 years after clearing compared with uncleared pastures, whereas 33 years after clearing, yield was 3/4 of that in uncleared pastures. The initial gains in pasture yield were accompanied by a loss of plant diversity that may affect ecosystem functions such as nutrient cycling or soil mineralisation, and the longer-term production gains.

Benefits or Losses from Clearing Trees to Develop Pastures in Central Queensland, Australia?

Clearing trees to develop land for exotic pastures that enhance pasture production and hence the financial gains, is an important issue in Queensland. Gains from clearing woodlands are questioned. Three tree communities i.e. Acacia harpophylla, Eucalyptus melanophloia and Eucalyptus populnea were selected at three different ages of clearing i.e. 5 yr, 11-13 yr and 33 yr to collect the data on pasture production, soil properties (biological and physicochemical), litter production and nutrient recycling and pasture plant diversity over 2-3 year period of the study. The net economic gains from clearing in terms of pasture production were compared to uncleared pastures and assessed against the tradeoffs of ecological services. The increase in pasture production post-clearing was not consistent with age of clearing. A bioeconomic model, applied to predict pasture production over the 50 years of time of clearing, though suggested economic benefits, however, it is difficult to predict how the loss in ecosystem functions in cleared pastures (> 30 years of clearing), by implication, affect pasture yield over time.

Tradeoffs between pasture production and plant diversity and soil health attributes of pasture systems of central Queensland, Australia

The clearing land of trees and introduction of exotic pastures to enhance pasture production and associated monetary gains has been a common practise in Queensland. Previous studies on tree clearing emphasised the gains in pasture production, but over periods of less than 10–15 years after clearing, thus potentially misleading land managers who plan to continue grazing beyond that time. The present research follows an integrated approach to quantify the pasture yield and the effects of tree clearing on pasture species composition, soil properties (organic carbon, available N (NO 3 − ), pH w and microbial biomass (C and N)), and litter production over time-since-clearing on a grazing property in central Queensland, and to evaluate the implications of our findings for the region. The cleared pasture systems were taken at <5, 11–13 and >33 year age of clearing in comparison to their paired uncleared pastures for three major tree communities representative of the region: Eucalyptus populnea , Eucalyptus melanophloia and Acacia harpophylla . The paper evaluates the effects of clearing on individual attributes as well as an integrated effect of these attributes, i.e. overall ecological services. Pasture production generally increased with clearing but plant diversity, litter production and potential return of N and P through litter decreased. Among soil attributes, clearing of trees adversely impacted upon soil pH and microbial biomass, which play an important role in nutrient availability and mineralisation. This, the initial gains in pasture production are not sustainable over time. The multivariate analysis for such ecological attributes suggests that at the >33 year age of clearing, the ecological state of pasture systems changed compared to that at 5 year or 11–13 year or to the uncleared system. A disturbed pasture system will most likely take longer to revert to the original state compared to the time that would have taken to harvest the benefits. The results are important for landholders and policy makers to comprehend the real gains and losses following tree clearing for pasture development over the long term.

Impact of tree clearing on soil pH and nutrient availability in grazing systems of central Queensland, Australia

In Queensland, land is cleared at high rates to develop pastures for enhanced production and the associated monetary gains. However, pasture production declines over time in cleared pastures until a new equilibrium is reached. The present study focussed on elucidating the reasons for decline in pasture production and finding the key soil properties that are affected due to clearing. Paired sites for cleared and uncleared pastures were selected to represent 3 dominant tree communities of the semi-arid tropics in central Queensland, i.e. Eucalyptus populnea, E. melanophloia, and Acacia harpophylla. The cleared pastures were chosen to represent 3 different durations of time since clearing (5, 11–13, and 33 years) to evaluate the temporal impact of clearing on soil properties. Various soil parameters were studied: macronutrients—available N (NH4+and NO3–), total N, and available P; micronutrients—Cu, Fe, Zn, and Mn; exchangeable cations—Ca, Mg, Na, and K (also macronutrients); pHw; and electrical conductivity. Of these, pHw showed a significant response to time of clearing for all 3 tree communities. Soil pHw increased significantly at cleared sites relative to uncleared (native woodland) pastures, and the increase was highly correlated with concentrations of exchangeable Ca, Mg, and Na. The change in soil pHw and exchangeable cations was more evident at &gt;0.30 m soil depth. The increase in soil pHw in cleared pastures decreased the availability of soil nutrients for plant growth and, hence, pasture productivity. The interactions of different soil properties down the profile as a result of changes caused by clearing are important when interpreting the effects of clearing on soil properties.

The effect of exotic pasture development on floristic diversity in central Queensland, Australia

Floristic diversity was compared across boundaries where the trees have been cleared in semi-arid brigalow ( Acacia harpophylla), gidgee ( A. cambagei) and eucalypt ( Eucalyptus populnea, E. melanophloia) woodland and forest in central Queensland. The cleared treatments included Exotic pasture (uncultivated, exotic grasses having more than 10% total cover) and Native pasture (uncultivated, not dominated by exotic grasses). An ordination of presence–absence data did not distinguish the floristic composition of the uncleared pasture and native pasture treatments, however, these treatment types were floristically distinct from the exotic pasture treatment in all three land types. Declines in species richness and diversity were substantial between uncleared and exotic pastures for brigalow and eucalypt lands. Differences were far less substantial for the same comparison in gidgee lands, and between uncleared and native pasture for all three land types. These trends reflected differences in most perennial lifeform groups and the species that show significant declines are identified. There was no significant relationship between native diversity and the age of clearing. This study draws attention to the negative impacts on plant diversity posed by deliberate and inadvertent spread of exotic perennial grasses in tropical forests and woodlands.

Preliminary studies on the establishment of Townsville lucerne (Stylosanthes humilis) in uncleared pasture at Katherine, N.T

The effects of surface treatments, soil type and type of seed sown on the early establishment of Townsville lucerne (Stylosanthes humilis H.B.K.) in native pastures at Katherine, N.T., were studied on microplots in the 1965-66 wet season. In experiment 1, six soil surface treatments were compared in burnt and unburnt native perennial pastures on Tippera clay loam on three occasions. In experiment 2, seeds were compared with pods, cleared cultivated land with uncleared uncultivated land, and Tippera clay loam with Cockatoo sand on two occasions. The results indicate that, given favourable weather conditions, Townsville lucerne can be established on untreated soil surfaces in uncleared native pastures, either annual or perennial ; that weather conditions affect early establishment, presumably through the length of the period that the soil surface remains wet ; that seeds perform two to three times better than pods ; and that early establishment is approximately three times better in the presence of growing native pasture than in its absence, possibly because of the higher atmospheric humidity within the protective grass cover.