Auckland's green volcanic heart: groundcover vegetation and soils of the Auckland volcanic cone reserve network

Abstract

The volcanic cones of Auckland are distinctive landmarks of that city, currently realized as an 'archipelago' of grassy reserved hills. Most of these cones were modified as hill forts during former occupation by Māori. Here, we review the Auckland volcanic reserve network and survey the current groundcover vegetation and soils of four large representative examples. Forty-eight reserves currently occur on remnant volcanic features. As well as two inshore island reserves (2372 ha), the other 46 reserves total 1241 ha. Most of the volcanic reserves support exotic grassland with rare forest patches. Groundcover vegetation follows a topographic sequence from flatter, fertile sites dominated by Lolium perenne, Trifolium repens and Pennisetum clandestinum, to moderately steep sites dominated by a diverse range of exotic grasses, to steep, lower fertility sites dominated by Microlaena stipoides. Pennisetum clandestinum is a major component of groundcover vegetation on many sites across all slope classes, its abundance varying in relation to soil N levels rather than to changes in slope. Soil analyses indicate that soils are nutrient-rich with high soil carbon and phosphorus. Future management should restore some native forest and introduce more herbaceous native species where low groundcover vegetation is desirable. Decreasing soil nutrient levels through strategies such as cessation of fertilizer application may assist these processes.

Restoration of indigenous dominance in exotic grassland by the establishment of juvenile Microlaena stipoides plants

“…In addition, substantial human trampling occurred on some of the plots, and we suspect this also contributed to plant losses. The initial vegetation survey (Burns et al 2013) showed that Microlaena was largely absent on this topographical unit, probably due to high levels of competition from other species on high-fertility soils Esler and Esler (2010). This absence was the reason for locating Experiment II on these terrace sites, but they also presented the greatest challenge to revegetation with Microlaena, given the early results of Experiment I (Table 1).…”

“…The existing grassland cover of these cones is dominated by exotic pasture species that form a number of different community assemblages based on environmental factors such as slope, soil properties, grazing intensity and tree cover (Burns et al . ). Dominant species include Perennial Ryegrass, Kikuyu, bromes ( Bromus spp.…”

“…The flatter ‘terrace’ sites on the cones were chosen because of their vigorous resident plant growth and the absence of Microlaena in the resident swards (Burns et al . ).…”

Dilemma of Geoconservation of Monogenetic Volcanic Sites under Fast Urbanization and Infrastructure Developments with Special Relevance to the Auckland Volcanic Field, New Zealand

“…In the present day, they are mostly protected as parks and recreational spaces well utilized by inhabitants of the city. However, they offer very little geologically unique aspects mostly due to the fact that they are grass covered with no exposures preserved or readily accessible [55][56][57]. In the southern part of the city, volcanoes are typically phreatomagmatic volcanoes, and explosion craters (shallow maars) surrounded by tuff rings are common [58].…”

Some agricultural characteristics of soils in eastern-northeastern slopes of a volcanic cone: Şebinkarahisar Dikmen Hill (Giresun, Turkey) example

“…Also, unlike Maungawhau and Maungarei cones, comprising especially high organic matter and soil nitrogen, the Maungakiekie cone has the highest P levels. While the soils in the plane and slightly gradient areas contain higher C, N and P than the gradient areas, the slopes in the north have a higher P content than the slopes in the south (Burns et al, 2013). Şenol et al (2014) investigated the elemental losses (i.e., Ca, Mg, K, Na, Si, Al and Fe) of soils in Isparta Çünür Hill containing geologically volcanic sand, limestone and andesite/trachyandesite and weathering products.…”