The loneliest trees are at most risk of extinction

Globally more than 20% of tree species are threatened with extinction, particularly through changes in land use. Worldwide forest land is being increasingly removed due to deforestation, urbanisation and other man-made causes, often forming fragmented, patchy populations of forest-land.

Our reliance on forests, for timber, environmental services and food, can’t be understated. As a result, the understanding of how to improve conservation of forests, and the endangered species within them, is of utmost importance.

Gene flow, which is the exchange of genetic material either between populations or between individuals in a population, helps to maintain genetic diversity. Genetic diversity is something that often contributes to the likelihood that a species or population will survive in response to external challenges, or its risk of going extinct - this is known as viability.

Gene flow is more limited between populations (or individuals within a population) when they are more isolated. Increased fragmentation between forest populations increases isolation, which can have detrimental consequences on population resilience because of increased levels of inbreeding and a reduction in the ability to combat threats such as pathogens.

Research undertaken by the University of Oxford’s Department of Plant Sciences has investigated the extent to which isolation can reduce genetic flow between tree populations or individuals, and reduce population viability. Particular areas of research interest included:

• Showing the importance of trees on agricultural land for bridging the gap between different forest populations
• Demonstrating that no forest is ‘too small’ for conservation – even the smallest patch of woodland can help contribute to effective breeding between threatened tree species
• Assessing how different land uses, such as crops, or cattle pasture, can affect the genetic connectivity between forest patches more than the distance between patches does
• Developing models that can assess the chances of survival of tree species, based on associated land use, accessible habitat and distance between trees and forests

These studies developed understanding of fundamental genetic processes in tree reproduction and the importance of fragmented tree populations in conservation.

This has ultimately helped to inform policies and strategy implemented by the UN Food and Agriculture Organisation, and the Chilean, Canadian and UK governments around forest conservation, as well as leading training and forest management practice in new directions internationally.