Insect and Disease Disturbances Correlate With Reduced Carbon Sequestration in Forests of the Contiguous United States

Abstract

Major efforts are underway to harness the carbon sequestration capacity of forests to combat global climate change. However, tree damage and death associated with insect and disease disturbance can reduce this carbon sequestration capacity. We quantified average annual changes in live tree carbon accumulation associated with insect and disease disturbances utilizing the most recent (2001 – 2019) remeasurement data from National Forest Inventory plots in the contiguous United States. Forest plots recently impacted by insect disturbance sequestered on average 69% less carbon in live trees than plots with no recent disturbance, and plots recently impacted by disease disturbance sequestered on average 28% less carbon in live trees than plots with no recent disturbance. Nationally, we estimate that carbon sequestration by live trees, defined as the estimated average annual rate of above- and belowground carbon accumulation in live trees (diameter at breast height ≥ 2.54 cm) on forest land, has been reduced by 9.33 teragrams carbon per year (95% confidence interval: 7.11 to 11.58) in forests that have experienced recent insect disturbance and 3.49 teragrams carbon per year (95% confidence interval: 1.30 to 5.70) in forests that have experienced recent disease disturbance, for a total reduction of 12.83 teragrams carbon per year (95% confidence interval: 8.41 to 17.28). Strengthened international trade policies and phytosanitary standards as well as improved forest management have the potential to protect forests and their natural capacity to contribute to climate change mitigation.

Trends in forest carbon offset markets in United States

“…Our results further highlight that a significant portion of existing forest carbon offsets face a risk of reversal through wildfire, including all the existing projects in California. Future research and partnerships could build a body of evidence for not only how these improved forest management strategies impact carbon, but also the extent to which they mitigate or exacerbate risk from disturbances such as wildfire 31,38,39 and pest outbreaks 29 . For example, some improved forest management strategies such as thinning reduce fuel loads, but thinning only represented around 10% of credits, whereas no management of projects could increase exposure to risk of catastrophic carbon losses and was the dominant practice in 34% of certified projects (Table 1).…”

“…As a result, wildfires could threaten carbon offsets from forests across the U.S. -not just in the flammable West. Increasing demand for forest based offset credits could also drive the expansion of projects further into fire-prone landscapes, where fuel conditions are further exacerbated by the unpresented drought [27][28][29] . Finally, predictions of future wildfire occurrence and outcomes are inherently uncertain 30 , adding to the uncertainty associated with forest carbon offset permanence.…”

Carbon stored in live ponderosa pines in the Sierra Nevada will not return to pre-drought (2012) levels during the 21st century due to bark beetle outbreaks

“…Major efforts are underway to better understand the effects of disturbances on C sequestration and storage capacities in U.S. forests. For example, Quirion et al (2021) used remeasurement data from national FIA plots and found those plots recently impacted by forest insects sequestered ~69% less C in trees than plots with no recent disturbance. Nationally, they estimated that C sequestration is reduced by ~9.3 Tg C yr -1 in forests that have experienced insect disturbance.…”

Mapping Tree Mortality Caused by Siberian Silkmoth Outbreak Using Sentinel-2 Remote Sensing Data

“…These include the displacement of native tree species, widespread defoliation, and mortality [10,11]. This reduces the ability of forests to capture and store carbon dioxide, and causes carbon emission release due to wood and canopy decomposition in dead stands [12]. Global warming may promote insect population growth, increase outbreak frequencies, and encourage the geographic expansion of some insect species [13][14][15], violating the global carbon balance.…”