A Bird’s Eye View Can Measure Woody Plant Encroachment to Assess Carbon Consequences

Newswise — Rangeland Ecology & Management – While invasions of unwanted plant species are easy to see in a single location, gauging the impact on a regional or continental level is difficult. As woody plants encroach onto grasslands, they could potentially impact the continental carbon budget. Measuring large-scale encroachment of species such as juniper is vital to understanding its influence on carbon budgets of ecosystems. Aerial photography and satellite imagery offer opportunities for measurement at these larger scales.

A paper in the current issue of the journal Rangeland Ecology & Management examines whether the removal of woody species by various control methods or wildfires can offset the regional consequences of juniper encroachment on carbon sequestration in vegetation. These authors concluded that efforts to eradicate or slow expansion in select areas may be sufficient to negate the overall impact of juniper expansion of carbon accumulation.

The rates of above-ground carbon accumulation due to the expansion of woody plants are small compared to that of forest production. However, high rates of carbon accumulation in forest is balanced by carbon losses associated with natural disturbance or timber harvest, while woody encroachment has typically been considered as a continuous process of carbon accumulation.

To assess rates of encroachment across eastern Oregon, aerial photos and satellite images from 1985–1986 and 2005 were compared. About two-thirds of the 92 randomly selected aerial photographs showed increases in juniper crown cover, while satellite imagery showed that approximately 27 percent of the study area experienced an increase in woody plant cover. These methods showed promise in identifying patterns of vegetation change. However, correlating changes in juniper encroachment among techniques for a single woody species is difficult. The carbon accumulation attributed to juniper encroachment in Oregon appears to be very small compared to forest growth or even wildfire emissions.

Full text of the article, “Assessing the Carbon Consequences of Western Juniper (Juniperus occidentalis) Encroachment Across Oregon, USA,” Rangeland Ecology & Management, Vol. 65, No. 3, May 2012, is available at http://srmjournals.org/toc/rama/65/3