Geographic versus environmental space: Patterns of potential native and exotic woody propagule pressure on New Zealand's indigenous grasslands

Hua, Xiaobin; Ohlemüller, Ralf

doi:10.1111/nzg.12187

Cited by 2 publications

(2 citation statements)

References 42 publications

(82 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Aerial and/or satellite imagery are powerful tools for assessing broad changes in tussock cover or woody thickening, at least of larger shrubs, over decades (Weeks et al 2013;Hua & Ohlemüller 2018). Some species are able to be differentiated using satellite imagery, such as matagouri, a widely distributed yet understudied native nitrogen-fixer (Day 2020).…”

Section: Research Needsmentioning

confidence: 99%

“…Tussock cover is relatively easy to measure either on the ground or using remote sensing technology. Relating tussock cover to other components of biodiversity and ecosystem functions could enhance understanding of impacts of vegetation change at spatial scales larger than plots or transects (Hua & Ohlemüller 2018;West 2019). For instance, there may be non-linear relationships between tussock cover and native plant diversity where high cover provides microclimates for native plants but too much cover may reduce diversity due to competition for soil resources (Adair et al 2019) or shading effects (Rodrigues et al 2017).…”

Section: Tussock Cover As a Potential Indicator Of Biodiversity And E...mentioning

confidence: 99%

See 1 more Smart Citation

Predicting ecological change in tussock grasslands of Aotearoa New Zealand

Day,

Barratt,

Christensen

et al. 2023

NZJE

View full text Add to dashboard Cite

Natural grasslands are among the most threatened biomes on Earth. They are under pressure from land cover change including afforestation, farming intensification, invasive species, altered fire regimes, and soil amendments, all of which impact native biodiversity and ecosystem functioning. In Aotearoa New Zealand, tussock-dominated native grasslands expanded due to increased fire activity during waves of human settlement. These areas have subsequently been maintained as modified grasslands by agricultural pastoral land management practices and effects of introduced feral mammals. Despite many decades of research on biodiversity in tussock grasslands, we need greater fundamental understanding of many processes causing change in their biodiversity and ecosystem functioning in order to predict how future global change will impact this important and increasingly threatened biome. In this perspective forum article, we present five key research questions that, if answered, would greatly enhance our understanding of connections between tussock grassland biodiversity, ecosystem functioning, and associated ecosystem services: (1) What are the relative impacts of domesticated and non-domesticated mammals on indigenous biodiversity in grasslands? (2) Where will invasive plants undergo range expansion? (3) Will future fires tip tussock grasslands into alternative vegetation states? (4) What are the implications of woody thickening by native or non-native species? (5) What are the impacts of global change, and vegetation change in particular, on soil processes and ecosystem functioning? We provide recommendations for research to address and integrate across these questions using both existing and new data. This work would build on our current knowledge and lead to a framework to better understand the ecological impacts of ongoing global change in tussock grasslands.

show abstract

Section: Research Needsmentioning

confidence: 99%

Section: Tussock Cover As a Potential Indicator Of Biodiversity And E...mentioning

confidence: 99%

Predicting ecological change in tussock grasslands of Aotearoa New Zealand

Day,

Barratt,

Christensen

et al. 2023

NZJE

View full text Add to dashboard Cite

show abstract

Spatial dynamics and drivers of recent changes in grass and shrub cover in submontane grassland plant communities

Hua,

Ohlemüller,

Sirguey

2024

COMMUNITY ECOLOGY

View full text Add to dashboard Cite

Shrub encroachment into grassland ecosystems has been increasingly observed and documented worldwide in recent years. A grass–shrub transition can affect the diversity, abundance and functional integrity of grassland plant communities and understanding the drivers behind these processes is therefore crucial. While potential environmental drivers are often investigated, the role of spatial patterns of neighbouring shrub density in local shrub encroachment has been less well studied. The aim of this study is to investigate the relative role of neighbouring shrub density and topography as potential key drivers of shrub encroachment in a typical montane grassland ecosystem in New Zealand. We used the SPOT (Satellite Pour l’Observation) 6/7 multispectral imagery captured on one day in 2013 and in 2017 to calculate recent changes in shrub/grass cover during this period. Using the Normalised Difference Vegetation Index (NDVI), we classified the study area into grassland and shrubland and quantified the extent and change in these two land-cover types over the study period. We then investigated the relationships between changes in land cover and neighbourhood shrub density, elevation and aspect. Between 2013 and 2017, there was an overall shrubland increase of + 0.35% of the study area per year, and grassland decrease of −0.43% per year. Locations at which any change in vegetation type occurred were more likely to be at mid-elevation (c. 600–1,000 m a.s.l.) and on west-facing slopes. Highest shrub expansion rates were observed on areas that were on warmer, north-facing slopes and at elevations below 900 m a.s.l.; this is consistent with areas below the pre-human, natural treeline which is estimated to be at very similar elevations. We found a marked threshold in the degree to which neighbourhood shrub density correlated with local shrub encroachment: local shrub encroachment only occurred when shrub cover in the neighbourhood exceeded 40% and peaked at c. 60% indicating the potential for a sudden grass–shrub regime shift once shrub cover reaches a certain level. Our study provides new evidence from the Southern Hemisphere of a measurable and interacting effect of topography and neighbourhood shrub density on recent shrub encroachment rates in montane grasslands even over short time periods.

show abstract

Geographic versus environmental space: Patterns of potential native and exotic woody propagule pressure on New Zealand's indigenous grasslands

Cited by 2 publications

References 42 publications

Predicting ecological change in tussock grasslands of Aotearoa New Zealand

Predicting ecological change in tussock grasslands of Aotearoa New Zealand

Spatial dynamics and drivers of recent changes in grass and shrub cover in submontane grassland plant communities

Contact Info

Product

Resources

About