My PhD project is endorsed by the Global Land Project.

It has been featured in the Oct. 2008 GLP Newsletter.

A more complete description of PhD project can be downloaded here.

Context 

Pastures and rangelands are the most extensive land uses on earth, and are expected to undergo rapid intensification to meet the forecasted doubling in global food demand by 2050. Because agricultural intensification is one of the main drivers of global biodiversity loss and environmental change, there is a crucial need to explore how long-term changes to biodiversity brought on by land use affect the functioning of ecosystems, their resilience in the face of unexpected environmental change, and the services they provide to humanity.

This research project explores the long-term impacts of agricultural intensification on plant functional diversity, ecosystem functioning, ecosystem services, and resilience in New Zealand high country rangelands. To do so, we use 32 8×50-m grassland plots from a rangeland improvement trial which have been over-sown with a mixture of 25 exotic pasture species and then experimentally subjected to different levels of agricultural inputs (fertiliser and irrigation) and sheep grazing intensity for over 25 years.

Research objectives

1) Long-term dynamics of plant functional diversity
How functional diversity is affected by land-use change is an important research question. In this project, vegetation cover of the ten most-abundant species has been evaluated annually (each November, after spring regrowth period) since the start of the experiment in 1982. In addition, a range of plant functional traits will be measured on all ~56 vascular plant species which are found within the study plots. This will allow us to analyse the long-term responses of plant functional diversity to agricultural intensification in those grasslands.

2) Links between agricultural intensification, plant functional diversity, and ecosystem functioning
Because most biodiversity-ecosystem function experiments to date have randomly manipulated species richness, there is a need for more realistic research that assesses how land-use change affects plant biodiversity, and how this feedbacks to ecosystem functioning. Using our study plots, we will analyze how agricultural intensification has impacted plant functional diversity, and how this turns affects aboveground net primary production (ANPP), belowground net primary production (BNPP), litter decomposition, and soil respiration. Structural equation modeling will be used to assess the links between those variables. This will allow us to quantify the relative strength of external factors (i.e. fertilisation, grazing, irrigation) vs. biotic factors (i.e. plant functional diversity) on ecosystem functioning. Moreover, this will enable us to assess which component of plant functional diversity (value, range, or relative abundance) best predicts land use-induced changes in ecosystem functioning.

3) Quantifying trade-offs among ecosystem services
A key research goal is to quantify the inherent trade-offs among ecosystem services that are associated with land-use intensification in production systems to better inform policy and management. We will assess three important ecosystem services in this project: 1) native biodiversity conservation (native species richness, native tussock grass density and height), 2) economic production values (forage quality, forage quantity, belowground production, sheep production), and 3) carbon sequestration (soil organic matter, above and belowground plant organic matter pools). This will allow us to quantify particular trade-offs among ecosystem services associated with different land-use scenarios in New Zealand high country rangelands.

4) Assessing ecosystem resilience through plant functional traits
One of the major challenges that humanity faces in the coming decades is how to increase the production of ecosystem goods while ensuring that production systems stay resilient to unexpected change. Resilience critically depends on response diversity, which is defined as the diversity of responses to environmental change within groups of species that contribute to the same functions or services (i.e. functional effect groups). Although this issue has been well developed conceptually, empirical studies remain scarce. Using our grassland study plots, we will explore here how the diversity of response traits (mostly regenerative traits) varies within particular functional effect groups along an agricultural intensification gradient. This analysis will allow us to explore whether agricultural intensification makes the resulting ecosystems, and the services they provide, more vulnerable to future disturbances.