6 results for Arnold, Greg

  • Automatic Recognition of Light Microscope Pollen Images

    Allen, Gary; Hodgson, Bob; Marsland, Stephen; Arnold, Greg; Flemmer, Rory; Flenley, John; Fountain, David (2006)

    Journal article
    Massey University

    This paper is a progress report on a project aimed at the realization of a low-cost, automatic, trainable system "AutoStage" for recognition and counting of pollen. Previous work on image feature selection and classification has been extended by design and integration of an XY stage to allow slides to be scanned, an auto focus system, and segmentation software. The results of a series of classification tests are reported, and verified by comparison with classification performance by expert palynologists. A number of technical issues are addressed, including pollen slide preparation and slide sampling protocols.

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  • Native bird abundance after Australian magpie (Gymnorhina tibicen) removal from localised areas of high resource availability

    Morgan, Dai K.J.; Waas, Joseph R.; Innes, John G.; Arnold, Greg (2012)

    Journal article
    University of Waikato

    Many reports exist of Australian magpies (Gymnorhina tibicen) attacking and sometimes killing other birds. One study concluded that magpies had little impact on the abundance of other birds at landscape scales, but another found that birds (mainly exotic species) avoided flying or landing close to them. We assessed whether continuously removing magpies for 6 weeks from localised areas of high resource availability (e.g. bush remnants or private gardens with fruit- or nectar-producing trees) in rural areas increased visitations by native birds compared with similar sites where magpies were not removed. Three count methods were used to estimate bird abundance: five-minute bird counts and ‘slow-walk’ transects in bush remnants, and five-minute bird counts and ‘snapshot’ counts in gardens. Generally, the abundance of native birds did not increase in treatment areas after magpie removal. In bush remnants, transect counts were typically better at detecting the presence of most species compared with five-minute bird counts. In gardens, snapshot counts were better at detecting tui (Prosthemadera novaeseelandiae) while five-minute bird counts were better at detecting magpies. Despite these differences, the different bird counting methods were generally in agreement and revealed that magpies had little impact on native birds at the scale we examined.

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  • Using five-minute bird counts to study magpie (Gymnorhina tibicen) impacts on other birds in New Zealand

    Innes, John G.; Spurr, Eric B.; Arnold, Greg; Morgan, Dai K.J.; Waas, Joseph R.; Watts, Corinne (2012)

    Journal article
    University of Waikato

    We used five-minute bird counts to investigate whether introduced Australian magpies (Gymnorhina tibicen) influence the abundance of other birds in rural New Zealand. Over 3 years, magpies were removed from five c. 900-ha study blocks, one in each of Northland, Waikato, Bay of Plenty, Wellington and Southland. Birds were counted in both the treatment blocks and paired non-treatment blocks for the 3 years of removal and also 1 year before. To minimise problems raised elsewhere with index counts we (1) selected treatment blocks and count stations using randomisation procedures, (2) used trained observers who spent equal time in paired treatment and non-treatment blocks, and (3) counted all blocks at the same time of year and only in good weather. On average, 548 magpies were removed from each treatment block each year, with magpie counts reduced by 76% relative to non-treatment blocks. Our results suggest magpies may restrict the movements of some birds (including kererū and tūī) in rural areas, but are less important than pest mammals at limiting population abundance at a landscape scale. We submit that five-minute bird counts were appropriate for our objectives, but that more research to examine their relationship to absolute densities is needed.

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  • Correcting bulk density measurements made with driving hammer equipment

    Parfitt, R.L.; Ross, C.W.; Schipper, Louis A.; Claydon, J.J.; Baisden, W. Troy; Arnold, Greg (2010)

    Journal article
    University of Waikato

    Accurate measurement of dry bulk density is critical for determining stocks of elements such as carbon or nitrogen, in soils. During investigations of changes of soil carbon with time, we resampled soil profiles for bulk density using two methods, namely the driving hammer method and the carving method. The carving method involves gently pressing a metal ring down into a carved pedestal of soil while the hammer method uses percussion to insert a metal ring into the top of a soil layer. We consider the carving method to be more accurate because the soils are less disturbed using carving. The hammer method generally underestimated bulk density by about 5% in comparison with the carving method – depending on soil order and horizon. Most of the bulk density data in the New Zealand National Soils Database (originally collected in moist soils for water release characterisation) were obtained with the hammer method and can now be corrected to the equivalent of data obtained by carving. With data from 44 soil profiles comprising 388 horizons, we showed that a greater correction is needed for soils in the Allophanic (+ 10%) and Melanic soil orders than for other soil orders. The Brown Soils were separated from the remaining soils and a correction factor of about + 9% was required for their A and AB horizons and + 3% for their subsoil horizons. The remaining soils required a correction factor of + 6% for their A and AB horizons and + 3.5% for their subsoil horizons. The correction factor for the A horizons for the Allophanic Soils was similar to their subsoil horizons, suggesting that the influence of aluminium and allophane was overriding that of soil carbon. The Melanic Soils required a correction factor of + 13% for their A horizons but their subsoil horizons responded differently to other soils possibly because of high smectite contents. These differences in bulk density, attributed to change in sampling method, were often greater than changes in soil carbon that would be considered important. Although we used New Zealand soils, we believe that our conclusions will apply to many soils world-wide because most of our soils have equivalents within the FAO and USDA systems of soil classification. This study shows the importance of assessing bulk density methodology, and the possible need for other workers to amend the carbon stocks calculated from the hammer method.

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  • Effect of grazing on ship rat density in forest fragments of lowland Waikato, New Zealand

    Innes, John G.; King, Carolyn M.; Bridgman, Lucy Jade; Fitzgerald, Neil; Arnold, Greg; Cox, Neil R. (2010)

    Journal article
    University of Waikato

    Ship rat (Rattus rattus) density was assessed by snap-trapping during summer and autumn in eight indigenous forest fragments (mean 5 ha) in rural landscapes of Waikato, a lowland pastoral farming district of the North Island, New Zealand. Four of the eight were fenced and four grazed. In each set of four, half were connected with hedgerows, gullies or some other vegetative corridor to nearby forest and half were completely isolated. Summer rat density based on the number trapped in the first six nights was higher in fenced (mean 6.5 rats ha–1) than in grazed fragments (mean 0.5 rats ha–1; P = 0.02). Rats were eradicated (no rats caught and no rat footprints recorded for three consecutive nights) from all eight fragments in January–April 2008, but reinvaded within a month; time to eradication averaged 47 nights in fenced and 19 nights in grazed fragments. A second six-night trapping operation in autumn, 1–3 months after eradication, found no effect of fencing (P = 0.73). Connectedness to an adjacent source of immigrants did not influence rat density within a fragment in either season (summer P = 0.25, autumn P = 0.67). An uncalibrated, rapid (one-night) index of ship rat density, using baited tracking tunnels set in a 50 × 50 m grid, showed a promising relationship with the number of rats killed per hectare over the first six nights, up to tracking index values of c. 30% (corresponding to c. 3–5 rats ha–1). The index will enable managers to determine if rat abundance is low enough to achieve conservation benefits. Our results confirm a dilemma for conservation in forest fragments. Fencing protects vegetation, litter and associated ecological processes, but also increases number of ship rats, which destroy seeds, invertebrates and nesting birds. Maximising the biodiversity values of forest fragments therefore requires both fencing and control of ship rats.

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  • Trends in soil carbon and nutrients of hill-country pastures receiving different phosphorus fertilizer loadings for 20 years

    Schipper, Louis A.; Dodd, M.B.; Fisk, L.M.; Power, I.L.; Parenzee, Jacinta; Arnold, Greg (2010)

    Journal article
    University of Waikato

    There are few records of long-term trends in soil C and N in grazed pasture systems but recent measurements have demonstrated unexplained losses on New Zealand lowlands. To determine whether losses were also occurring in hill country pastures, we analyzed archived soil samples collected between 1983 and 2006 from two slope classes (steep and easy) at the Whatawhata Research Centre. Soils were Ultic Hapludand and Typic Haplohumult on the easy slopes (10–20°), and Typic Haplohumult on the steeper slopes (30–40°). Soil samples (0–75 mm) had been collected from paddocks that were fertilized with six different loading rates of P (ranging from 0 to 100 kg P ha⁻¹ year⁻¹ since 1985). This range of P loadings allowed us to determine whether P inputs would regulate trends in soil C and N. While there were significant temporal trends in C and N (P < 0.05), these were not unidirectional and trends were not dependent on P loading rate. On average, soil C initially increased during the first 6 years of the trial at 0.270% C year⁻¹ (1.56 t ha⁻¹ year⁻¹) and 0.156% C year⁻¹ (1.06 t ha⁻¹ year⁻¹) on easy and steep slopes, respectively. Subsequently, there was no significant trend in soil C on the easy slopes but soil C declined at −0.066% year⁻¹ (0.45 t ha⁻¹ year⁻¹) on the steep slopes. Similarly, soil N increased between 1983 and 1989 at 0.025% N year⁻¹ (144 kg ha⁻¹ year⁻¹) and 0.012% N year⁻¹ (82 kg ha⁻¹ year⁻¹) on easy and steep slopes, respectively. Post-1989, small but significant losses of total N were measured on the steep slopes of 0.004% year⁻¹ (27 kg N ha⁻¹ year⁻¹) (P < 0.05) with no trend on the easy slopes. Two potential causal factors for these decadal-scale patterns were identified, operating via changes in primary productivity. These were lower S inputs from 1989 due to a change in fertilizer type, and a series of relatively dry summers during the 1990s. These significant inter-annual trends in soil C and N complicate attempts to measure long-term changes in soil organic matter associated with land use change and management practices. This study has demonstrated the potential error associated with infrequent soil sampling to determine long-term trends in soil C and N; large gains or losses could have been detected at Whatawhata depending on when sampling started and finished. Understanding these long-term trends in soil organic matter dynamics and driving factors requires more long-term sampling trials.

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