http://newzealandecology.org/nzje/3276

Abstract

Fire, pastoral farming and exotic species have been major drivers of vegetation change in the eastern South Island high country since human arrival. More recently, fire frequency and grazing intensity have declined allowing regeneration of previously suppressed woody elements in some areas, such as our 1775 ha Cass study site. We collected vegetation and abiotic data from 117 Recce plots (10 × 10 m) using an objective grid-based network to classify the vegetation, determine factors influencing vegetation pattern, discuss long-term vegetation changes and assess the role of exotic species. Hierarchical cluster analysis and ordination on compositional data revealed seven broad vegetation types: grassland, mixed shrubland, mānuka shrubland, mountain beech forest, gorse shrubland, wetlands and subalpine vegetation. Within four of these types (mixed shrubland, grassland, subalpine, wetlands) distinct subtypes were also identified. There was evidence for compositional structuring based on altitude and slope. Two vegetation types were characterised by exotic species (gorse shrubland, grassland), with exotic species more common at lower elevations and on gentle slopes. While short tussock grassland dominated the Cass landscape in the early twentieth century, having been induced by burning and grazing, it only dominates 8% of the landscape today. Native woody vegetation (predominantly shrubland) is now the dominant land cover at Cass. As long as fire is excluded, grazing is limited (but not necessarily eliminated) and exotic woody species are controlled, is it likely that these transitional shrublands will be replaced by mountain beech forest in the longer-term. Similar patterns of recovery of native woody elements are likely to occur more widely in similar high country environments in the absence of fire and with careful management of grazing and exotic woody plants.

Root diameter, host specificity and arbuscular mycorrhizal fungal community composition among native and exotic plant species

“…Interestingly, contrary to our hypothesis that exotic plants will associate with generalist arbuscular mycorrhizal fungi, we did not find a significant difference between native and exotic plants in the frequency of associations with generalist fungi. The lower elevations of the Cass Mountain Research Area, from which we sampled, are dominated by exotic grasses which have been present for over a 100 yr (Young et al ., 2016). A meta‐analysis by Bunn et al .…”

“…We tested these hypotheses in a New Zealand montane grassland/shrubland ecosystem (Young et al ., 2016). Our understanding of arbuscular mycorrhizal communities in New Zealand grasslands is limited, with current knowledge based on visual quantification of presence and abundance (Weijtmans et al ., 2007) and of arbuscular mycorrhizal fungal species obtained via direct wet sieving methods (Williams et al ., 2012).…”

“…Our understanding of arbuscular mycorrhizal communities in New Zealand grasslands is limited, with current knowledge based on visual quantification of presence and abundance (Weijtmans et al ., 2007) and of arbuscular mycorrhizal fungal species obtained via direct wet sieving methods (Williams et al ., 2012). Furthermore, these ecosystems are highly invaded by a range of exotic grass and shrub species (Day & Buckley, 2013; Young et al ., 2016). The use of next‐generation sequencing to characterize arbuscular mycorrhizal fungal communities will provide valuable insights into the kind of mutualistic associations exotic plants form and how these differ from native plants.…”

Predicting ecological change in tussock grasslands of Aotearoa New Zealand

“…Exclosure studies across grassland types suggest there is no substantial impact on plant community structure when grazing is removed over relatively short time frames of 5-16 years (Primack 1978;McIntosh & Allen 1998;Grove et al 2002;Rose & Frampton 2007; and no significant changes in soil chemical properties (Lord 1990;McIntosh & Allen 1998). Increases in native woody cover after many decades of low or no domesticated grazing have been observed in short- (Rose et al 2004) and tall-tussock grasslands (Young et al 2016). However, 30 years without grazing at Black Rock Reserve showed woody thickening was highly localised, resulting in a grassland-shrubland mosaic (Mark & Dickinson 2003); this emphasises the importance of spatial scale and environmental gradients when assessing impacts of grazing removal.…”

Knowing when native regeneration is for you, and what you should do about it. The Aotearoa New Zealand context

“…Specific examples of regeneration have been documented over tens to hundreds of hectares on disturbed land following exotic plantation clear-fell (Lambie & Marden 2020;Forbes et al 2021;Forbes 2021b) or on retired livestock pastures (Allen et al 1992;Wilson 1994;Young et al 2016). In contrast, native tree plantings have been established at comparatively small scales and often in contexts where regeneration processes are dysfunctional, such as where regeneration sites lack sufficient natural propagule sources (Overdyck & Clarkson 2012), are extremely dry (Dollery et al 2018), are weed infested (Wallace et al 2017), or where fundamental biotic impacts such as altered soil hydrology or soil compaction exist (Sullivan et al 2009).…”