Sampling method and sample size affect diversity and indigenous dominance estimates in a mixed grassland community

Abstract

Abstract:Estimates of vegetation attributes measured by sampling often inform scientific inference, management actions, and policy decisions. However, different sampling methods and sample sizes (i.e. number of plots) can yield significantly different estimates of vegetation attributes. This occurs because the abundance distributions and spatial distributions of species in the plant community influence their probabilities of detection and estimates of their abundances. We predicted that different sampling methods and sample sizes would produce significantly different estimates not only of vascular plant species diversity, but also of indigenous dominance (the level of indigenous influence) in mixed vegetation where indigenous and exotic floras have different abundance or spatial distributions. To test our predictions we applied three sampling methods to 24 plots in grassland and cushion vegetation in a 1058-ha scientific reserve in the Upper Waitaki (Mackenzie) Basin, New Zealand. Our methods sampled ground areas from 0.65 to 400 m 2 , and included two variants of common 'subsampling' approaches, which assessed only discrete subunits within larger plots. Indigenous plant species were both less abundant on average and more spatially-clustered (i.e. less evenly dispersed across plots) than exotic species. The two subsampling methods were less likely to detect less abundant and more spatially clustered species, leading to lower ratios of indigenous to exotic species recorded, and lower estimates of indigenous dominance of composition (% of species indigenous). Numbers of indigenous species accumulated more rapidly with increasing sample size than numbers of exotic species, so that indigenous dominance also increased with the number of plots sampled. We conclude that properly measuring species diversity and indigenous dominance in mixed indigenous-exotic plant communities requires both the searching of sizeable plots and use of rarefaction rather than plot-averaging of statistics. We suggest greater use of rarefaction and more consideration of species' detection probabilities in sampling New Zealand's mixed indigenous-exotic plant communities should improve the reliability, transparency and comparability of measures of diversity and may also provide new ecological insights.

Impact of seasonal changes on the vegetation composition of some selected areas in Lagos state, Nigeria

“…Our diversity index analysis (Dominance, Evenness, Equitability, Shannon-wiener and Simpson's indices) were conducted using Palaeontological Statistics (PAST) software (v 2.17c, Hammer et al, 2001). Also, our study presented percentage plant family (APG, 2009) and habit (Life-form) distribution Walker et al, 2016). We evaluated similarities and differences among the selected studied sites using Jaccard correlation (statistical function in PAST software) based on species occurrence during the study.…”

Evaluating outcomes of restoration ecology projects on limited budgets: assessment of variation in sampling intensity and sampling frequency for four habitat types

“…Furthermore, they are faced with the challenge of determining what minimum sampling effort (e.g., the number of sampling quadrats and frequency of sampling) is required for assessing changes over time in key metrics such as plant species diversity and richness. Beyond the context of restoration, different vegetation sampling strategies have been evaluated extensively for herbaceous communities, with considerable emphasis placed on the optimization of sampling techniques (Stohlgren et al ; Walker et al ) and quadrat sizes (Goodall et al ; Hackett et al ). Although, for multiyear sampling efforts, the scope and intensity of sampling is often limited by budgetary and time constraints (Tille & Ecker ), high sampling resolution can be essential for detecting problems in the context of restoration (Franson et al ).…”

What effects must be avoided, remediated or mitigated to maintain indigenous biodiversity?

“…> 20% of species or plant cover) is problematic because it would exclude ecosystems and habitats important for indigenous biota. Many ecosystems and plant communities dominated by non-indigenous plant species are essential for maintaining indigenous species, for example dryland plants (Walker et al 2016), wētā in gorse (Sherley & Hayes 1993), endangered black-billed gulls Larus bulleri in non-indigenous pasture (Mischler 2018), dotterels on motorway margins (Judd 2007), kiwi, bats, Peripatus and land-snail species in plantation forests, and geckos and skinks in urban areas.…”