Plant diversity and climate change

Conserving and promoting plant diversity plays an important role in limiting global warming. Global climate change is mediated from a precious resource: the soil organic carbon. Plant diversity generally increases the absorbtion of carbon and other nutrients in live plants. For example, clover roots are home to bacteria that provide nitrogen to the plant,  increasing soil fertility.  With regard to water, a common example is the tap root of a dandelion, absorbing water from deep in the soil compared with the shallow roots of a daisy.  Grasslands with different species are more resilient to climate change effects, such as to severe drought events.

Cultivation and environment

Monoculture has several effects on the environment: the loss of soil productivity and fertility, risks of promoting pests and diseases, and higher risks of adverse effects of storms and fire.

A mixture of species, instead, can maximise the use of resources, and consequently increase soil productivity and carbon sequestration (absorbtion), becoming more resistant to damage caused by storms, insects, or diseases; furthermore, they could be more efficient in filtering of atmospheric pollutants (e.g., sulphur and chlorine) in the areas with heavy precipitation.

Benefits of plant diversity in grasslands

There are also co-benefits to the use of multispecies grasslands, including higher protein content of such swards, which can improve animal nutrition and reduce the need for concentrated animal feed, as well as providing increased resistance to weeds, which may reduce the need for herbicide application. Grazing trials in Ireland indicate that the performance of ewes and lambs is improved under multispecies grassland systems compared with perennial ryegrass monocultures.

Effects on biodiversity

The use of multispecies grasslands offers many additional benefits such as enabling more forage to be produced using less nitrogen fertiliser whilst improving biodiversity. Today, biodiversity is threatened by climate change, pollution, over-exploitation of natural resources, and habitat loss. Loss of biodiversity impacts the interdependency of different species and damages the ecosystem, leading sometimes to extinction of local populations, for example, pollinators such as insects, birds, and bats. Declines in honey bee populations result in negative impacts on ecology and the economy for fruit crops and flowers. Research from the ‘Smartgrass’ project at University College Dublin demonstrates that both beetle and wasp numbers increased with multispecies swards and it was found an increase in 300% of the earthworm population (an indicator species for soil health and biodiversity) under multispecies grasslands compared to monoculture ryegrass.

Diversity in forests

More than one genotype is necessary for planted forests in order to address biodiversity and climate change issues. Forestry plantations have a fundamental role in conserving natural forests by reducing deforestation, improving and restoring degraded lands, and sequestering carbon dioxide. Furthermore, they are important for connected populations, improving connectivity between forest patches and buffer edges across natural forests and non-forest lands.

In conclusion, it is important to select different species with complementary structural and functional traits, such as shade tolerance, height growth rate, crown structure, foliage and root phenology, and root depth. With careful design and appropriate management, mixed-species plantations with three or four species can be more productive and have more advantages than disadvantages. As a result, mixed-species plantations and agroforestry should be broadly promoted and adopted as they can produce more economic and ecological gains, and contribute to food security.

Several studies demonstrate that conserving or promoting plant diversity in natural and managed systems is an integral part to limit global warming. Soil organic carbon (SOC) is a valuable resource for mediating global climate change. The plant diversity generally increases the carbon sequestration of live plants due to complementary resource utilisation among constituent species in species-rich ecosystems. Findings suggest that SOC content is on average 5 and 8% higher in species mixtures than in monocultures.

Single-species monocultural plantations have several effects on the environment:the loss of soil productivity and fertility, disruption of hydrological cycles, risks of promoting pests and diseases, and higher risks of adverse effects of storms and fire. Species mixtures, instead, can maximise the use of resources, and consequently increase soil productivity and carbon sequestration, becoming more resistant to damage caused by storms, insects, or diseases; furthermore they could be more efficient in filtering of atmospheric pollutants (e.g., sulphur and chlorine) in the areas with heavy precipitation.

There are also co-benefits to the use of multispecies grasslands, including higher protein content of such swards, which can improve animal nutrition and reduce the need for concentrated animal feed, as well as providing increased resistance to weeds, which may reduce the need for herbicide application. Grazing trials in Ireland indicate that the performance of ewes and lambs is improved under multispecies grassland systems compared with perennial ryegrass monocultures.

Furthermore, multispecies grasslands are more resilient to climate change effects, such as to severe drought events. The use of multispecies grasslands offers many additional benefits such as enabling more forage to be produced using less nitrogen fertiliser whilst improving biodiversity. Today, biodiversity is threatened by climate change, pollution, overexploitation of natural resources, and habitat loss. Loss of biodiversity weakens species connections and impairs the ecosystems, leading to extinction of species and local populations, for example, pollinators such as insects, birds, and bats. Declines in honey bee populations may result in a loss of pollination services with negative impacts on ecology and economy for fruit crops and flowers, which will eventually affect the maintenance of wild plant diversity, wider ecosystem stability, agricultural production, human welfare, and global food security. A research from the ‘Smartgrass’ project at University College Dublin demonstrates that both beetle and wasp numbers increased with multispecies swards compared to ryegrass swards and it was found an increase in 300% of the earthworm population (an indicator species for soil health and biodiversity) under multispecies grasslands compared to monoculture ryegrass, thus indicating that multispecies grasslands can enhance soil health and biodiversity.

Also for planted forests is necessary more than one genotype in order to address the biodiversity and climate change issues. Forestry plantations have a fundamental role in conserving natural forests by relieving deforestation, improving and restoring degraded lands, and sequestering carbon dioxide. Furthermore, they are important for metapopulations, because they improve connectivity between forest patches and buffer edges across natural forests and non-forest lands.

A great number of studies have indicated that it is important to select species in mixtures with complementary structural and functional traits, such as shade tolerance, height growth rate, crown structure, foliar and root phenology, and root depth. With careful design and appropriate management, mixed-species plantations with three or four species can be more productive and have more advantages over disadvantages. As a result, mixed-species plantations and agroforestry should be broadly promoted and adopted as they can produce more economic and ecological gains, and contribute to food security.

Written by Mariangela Difilippo

Sources:

(1) https://www.gasnetworks.ie/biomethane-sustainability-report-2021.pdf

(2) https://www.epa.ie/publications/research/climate-change/Research_Report_371.pdf

(3) https://www.sciencedirect.com/science/article/pii/S235198941830088X

(4) https://eds.p.ebscohost.com/eds/pdfviewer/pdfviewer?vid=3&sid=5c0e5866-d3dd-46fd-af35-9869d1aa9d2e%40redis