ABSTRACT
Temperate grasslands and woodlands are the focus of extensive restoration efforts worldwide. Reintroduction of locally extinct soil-foraging and burrowing animals has been suggested as a means to restore soil function in these ecosystems. Yet little is known about the physical and chemical effects of digging on soil over time and how these effects differ between species of digging animal, vegetation types or ecosystems. We compared foraging pits of a native reintroduced marsupial, the eastern bettong (Bettongia gaimardi) and that of the exotic European rabbit (Oryctolagus cuniculus). We simulated pits of these animals and measured pit dimensions and soil chemical properties over a period of 2 years. We showed that bettong and rabbit pits differed in their morphology and longevity, and that pits had a strong moderating effect on soil surface temperatures. Over 75% of the simulated pits were still visible after 2 years, and bettong pits infilled faster than rabbit pits. Bettong pits reduced diurnal temperature range by up to 25 °C compared to the soil surface. We did not find any effects of digging on soil chemistry that were consistent across vegetation types, between bettong and rabbit pits, and with time since digging, which is contrary to studies conducted in arid biomes. Our findings show that animal foraging pits in temperate ecosystems cause physical alteration of the soil surface and microclimatic conditions rather than nutrient changes often observed in arid areas.
ABSTRACT
The eastern bettong (Bettongia gaimardi), a medium-sized digging marsupial, was reintroduced to a predator-free reserve after 100 years of absence from the Australian mainland. The bettong may have the potential to restore temperate woodlands degraded by a history of livestock grazing, by creating numerous small disturbances by digging. We investigated the digging capacity of the bettong and compared this to extant fauna, to answer the first key question of whether this species could be considered an ecosystem engineer, and ultimately if it has the capacity to restore lost ecological processes. We found that eastern bettongs were frequent diggers and, at a density of 0.3-0.4 animals ha-1, accounted for over half the total foraging pits observed (55%), with echidnas (Tachyglossus aculeatus), birds and feral rabbits (Oryctolagus cuniculus) accounting for the rest. We estimated that the population of bettongs present dug 985 kg of soil per ha per year in our study area. Bettongs dug more where available phosphorus was higher, where there was greater basal area of Acacia spp. and where kangaroo grazing was less. There was no effect on digging of eucalypt stem density or volume of logs on the ground. While bettong digging activity was more frequent under trees, digging also occurred in open grassland, and bettongs were the only species observed to dig in scalds (areas where topsoil has eroded to the B Horizon). These results highlight the potential for bettongs to enhance soil processes in a way not demonstrated by the existing fauna (native birds and echidna), and introduced rabbit.
ABSTRACT
Revegetation plantings have been established to ameliorate the negative effects of clearing remnant vegetation and to provide new habitat for fauna. We assessed the vegetation development of revegetation established on agricultural land in Gippsland, southeastern Australia. We compared (1) woodlot plantings (overstory eucalypts only) and (2) ecological plantings (many species of local trees, shrubs, and understory) with remnants and paddocks for development of vegetation structural complexity and colonizing plant species. We also assessed structural complexity and plant species composition in response to several site parameters. Structural complexity increased with age of planting, toward that of remnants, even when very few species were planted at establishment. Richness of all plants and native plants, however, did not increase with age. Native ground cover plants were not included at establishment in either planting type, and their richness also did not increase with age of planting. This indicated that colonization did not occur through time, which does not support the "foster ecosystem hypothesis." Weed species richness was unrelated to native plant richness, which does not support the "diversity-resistance hypothesis". Weed cover increased with age of planting in woodlot plantings but decreased with age in ecological plantings. Richness of all plants and native plants in plantings did not increase with planting size or with the presence of old remnant trees and was greater in gullies and where vegetation cover in the landscape was greater. Structural complexity was unaffected by planting size but was positively correlated with floristic richness. Ecological plantings had higher condition scores, greater shrub cover, more plant life-forms and fewer weeds than woodlot plantings indicating a possible greater benefit as habitat for wildlife. We conclude that ecological plantings can achieve similar overall structural complexity as remnant vegetation within 30-40 years but will not gain a native ground layer and will not necessarily contain some important structural features by this age. Ecological plantings may provide habitat for the conservation of fauna (through the development of structural complexity), but they may not provide for the conservation of non-planted flora (given the absence of re-colonizing smaller life-forms).
