Owing to high precipitation, low fuel load, and forest type, the Lower Mississippi Alluvial Valley (LMAV) has very low fire frequency and intensity. In fact, the US Forest Service has designated much of the region as “non-burnable.” The LMAV receives among the highest average annual precipitation of any region in the US, with Louisiana and Mississippi consistently ranking as the country’s first and second wettest states respectively, and the region’s many rivers act as fire breaks to help further limit fire spread (GreenTrees’ project area is bifurcated by the Mississippi River whose width is too large to be jumped by fire). When they do occur in the Southern US, fires are primarily restricted to dry, upland pinelands — not the wet, low-lying floodplains that GreenTrees forests occupy.

Historically, the vast Mississippi alluvial floodplain experienced seasonal flooding each spring associated with spring rains and snowmelt from the northern Mississippi River watershed, helping bring sediments and nutrients to the expansive bottomland hardwood forests of the LMAV. Despite channelization and other flood control measures, flooding still occurs in the project area, but it needs to be long in duration and severe in intensity to induce tree mortality. GreenTrees mostly plants flood-adapted tree species that are tolerant of periodic inundation. Longer-term flooding can deprive trees of oxygen and slow growth but rarely causes death, meaning trees retain the biomass carbon they’ve already sequestered. Importantly, flooding is only a risk during the growing season when trees are actively engaging in oxygen uptake as part of respiration; since dormant trees have little or no oxygen needs, they are unaffected by prolonged inundation. GreenTrees has experienced multiple historic floods since the project’s inception, and none have resulted in a meaningful loss of biomass.

Disease and pest outbreaks occur across the project area with variable spatiotemporal frequency, though most target specific species and leave non-host species unaffected. GreenTrees project lands are planted with 27+ species of native hardwoods in part to confer resistance against species-specific pathogens. According the USDA, most monitored disease-related tree mortality in the United States is attributable to outbreaks affecting conifers in the western US, not hardwoods in the Southeast. It’s further worth noting that trees often take years to succumb to disease, during which time they’re still sequestering carbon that can be counted towards the project’s buffer pool.

Hurricanes moving north into the project area from the Gulf of Mexico quickly deteriorate as they track inland after making landfall. With 95% of project lands lying over 100 miles from the coast and the project’s southernmost parcel being located in Avoyelles Parish, Louisiana 88 miles north of the nearest coastline, GreenTrees is far removed from the worst impacts of landfalling storms. Moreover, the hurricane-force winds capable of causing tree damage are typically restricted to a small windfield surrounding the hurricane’s eye, and with GreenTrees forests dispersed over such a broad area, it’s exceedingly improbable that hurricane-force winds could impact a meaningful portion of project lands. As an example, the strongest hurricane to impact the LMAV, category 5 Hurricane Katrina, affected 1.3 million acres of forest — equivalent to only 12.38% of the 10.5 million-acre area occupied by GreenTrees parcels. Furthermore, hurricanes only impact aboveground biomass, typically causing crown damage but leaving tree trunks partially or wholly intact, allowing for future regeneration and preserving the carbon stored in belowground biomass and the trunk.

Based on analysis of historical frequency and intensity data, the resulting expected loss for all four selected perils is 0.00%. Given the expectation of increasingly frequent and severe natural disasters in the future, a 0.1% (i.e., 1/1000) uncertainty factor was applied to each peril, resulting in an implied expected loss of of 0.4% (i.e., 1/250) for the project.