A Snapshot of Maryland’s Forestry Sector
Forest Cover. Maryland has 39% forest cover and a continued trend of slow loss of forest land. When all tree canopy is considered, including patches smaller than an acre, tree canopy covers almost 50% of the state. Trends correlate with the pace of development, constrained but not stopped by existing laws, policies, and programs.
Carbon Sequestration. In a year, Maryland’s forests absorb 4.3 million metric tons of carbon dioxide equivalent (MMtCO2e) emissions. Urban trees and forests also contribute to carbon sequestration and store an additional 2.2 MMtCO2e per year.
Forest Age. Maryland is well-positioned to provide mature forests, which now make up 78% of Maryland’s forest cover; 40% of forests are over 80 years old. The benefits of more mature forests for recreation, timber supply, interior forest habitat, and sustained carbon storage also come with the trend of slower annual net growth rates and increasing natural mortality. The related decrease in young forests has reduced early successional habitats needed for a variety of species now in decline, and increased the potential for future high carbon sequestration rates.
.
Ownership. A quarter of Maryland’s forests are publicly owned, and over 41% of that forest is considered reserved from forest harvesting, about 10% of the forest area. Renewable resource-based industries, important for stable rural economies and watersheds, source more wood from private lands.
Tree Planting. 16.9 million trees have been planted through ten planting programs in the last 14 years. The Backyard Buffer program has expanded to 20 counties, the Marylanders Plant Trees coupons continue to be available, and state funding for residential plantings in priority areas has increased. Pine seedling planting has decreased, while hardwood seedling planting has increased.
Bay Restoration. Planting and maintaining forested riparian buffers is an integral strategy for protecting water quality. Since 1996, over 1,400 acres of riparian buffers have been planted in Maryland. 57% of Maryland’s streams are fully buffered, and another 27% are partially buffered.
Health Concerns. Forest health concerns are expanding as many forests age, combined with continued new introductions of invasive, exotic pests, such as the emerald ash borer and spotted lantern fly. Gypsy moth (exotic) and southern pine beetle (native) continue to pose significant risks of interacting with seasonal weather, biocontrol organisms, and drought stress.
Sustainable Management. The area of sustainably certified forests has expanded since 2010. Over 800,000 acres are certified and audited, including private lands certified though the American Tree Farm System, dual certified State Forests, and other Sustainable Forestry Initiative certified private forests.The sustainable forestry certification on State Forest Lands includes protection of old-growth systems and plans for managing significant additional areas as Old-Growth Ecosystem Management Areas, where old-growth characteristics can develop over time.
Fire Risk. Wildfire acres burned has declined, which is correlated with trends in increased rainfall and increased use of prescribed fire to restore fire-adapted ecosystems and manage wildfire risk.
Industry. Markets for locally sourced forest products are decreasing due to several factors including the loss of the fumigation capability at the Port of Baltimore, decline of log truck driving capacity, and closure of saw and paper mills. The Luke Paper Mill, Maryland’s last remaining paper mill, located on the Potomac River in Allegany County, closed in 2019. Before its closure, it was capable of producing 450,000 tons of freesheet paper products annually.
Economic Impact. Declining markets have impacted forestry’s contribution to the economy. From 2005 to 2015, the economic impact of forestry in Maryland declined from $4.7 billion to $3.5 billion. Investing in existing markets, like poultry bedding, and new markets, like woody biomass for thermal and electrical energy, could help revitalize the forest products industry, and provide income to landowners and sustainable management of forests.
Harvesting. Forest harvest best management practices (BMPs) are widely used and are properly implemented at a rate of 88% during forest harvest, with 97% implementation on public lands. The natural land cover in Maryland is predominantly forest, and with wide use of good BMPs, forests are the most protective land use for water quality and watershed function.
Forest Types. Most Maryland forest types, dominated by oaks and yellow-poplar, are considered to have moderate to high adaptive capacity in the face of climate change, but red spruce habitats are more at risk. Faster growth has been documented for many tree species and is expected to continue with the higher carbon dioxide levels (needed for photosynthesis), and observed trends of warmer, wetter conditions, especially in winter and spring. However, all forest types, regardless of climate change adaptive capacity, require climate informed management to address threats that may be exacerbated by climate change.
Saltwater Intrusion. Coastal maritime forests, where saltwater intrusion is a particular concern, are at risk. Maritime forests face increasing levels of saltwater, and a 2016 survey by MDA found that 50,406 acres had been affected by saltwater intrusion. This was an increase from 18,117 acres of forest in 2013.
Measuring Forests
Often the terms Forest and Tree Canopy (or Tree Cover) are used interchangeably, but this is incorrect, and they have two very unique definitions. Tree Canopy is any area covered by trees when viewed from above. This includes forests, trees in a yard or park, trees in an urban setting, orchards, and trees where animal grazing or other agricultural operations may be taking place below. On the other hand, Forest is a subtype of tree canopy, and is defined by the US Forest Service as: An area of trees with at least 10% tree canopy cover that is at least 1 acre in size, is at least 120 feet wide when measured from stem to stem.
Forest land includes transition zones, such as areas between forest and nonforest lands that meet the minimal tree stocking/cover and forest areas adjacent to urban and built—up lands. Roadside, streamside, and shelterbelt strips of trees must have a width of at least 120 feet and continuous length of at least 363 feet to qualify as forest land. Unimproved roads and trails, streams, and clearings in forest areas are classified as forest if they are less than 120 feet wide or less than an acre in size. Tree-covered areas in agricultural production settings, such as fruit orchards, or tree—covered areas in urban settings, such as city parks, are not considered forest land.
--US Forest Service, National Core Field Guide, Version 6.0, October, 2012
Figure 1: Shows examples of how forest and tree canopy are similar and different. The green ground represents area under trees that is mowed or grazed. Orchards and silvapasture areas are not considered forest.
Figure 2: Shows the types of openings that can occur that will change a forest designation. Water bodies are generally considered part of the forest.
Figure 3: Shows a cut-over area within a forest. This area has had the tree canopy removed, but is still considered part of the forest, as its land-use designation has not changed — it is being managed as a new forest. However only the surrounding areas are counted as tree canopy, until a tree canopy develops in the cleared area.
University of Maryland Analysis of Tree Canopy for 2011
This data estimates that there is nearly 3.095 million acres of tree canopy in Maryland, or nearly 50% of total land area.
This data is intended to make maps, identify trees and tree canopy, very precisely at many scales, but primarily at the county level. It was created as a byproduct of the Carbon Monitoring System project by the Geography Department of the University of Maryland, funded by a grant from NASA. This data can be placed on a map to depict individual or groups of trees and tree canopy. This data utilizes LiDAR data from 2003 to 2012, and 2011 NAIP Imagery, to produce a 1 meter resolution tree canopy binary raster data layer for each county in the state. This is done using an “object based analysis”, utilized by Jarlath O’Neil-Dunne and the Department of Geography at the University of Vermont. LiDAR provides the height, while NAIP Imagery from 2013 provides the background color information. Thus a tall, green object has a high probability of being a tree. The tree canopy analysis represents a very accurate and precise “snapshot” of tree canopy in the year 2011. The data takes the form of a binary raster that can be used by commercial mapping software.
Figure 4 A binary raster used as a digital map image. “1” represent trees and “0” represents other land-uses. Cells are 1 meter x 1 meter square.
Figure 5: A view of the tree canopy (red) around Clarksville, Maryland in 2007 from the University of Maryland tree canopy assessment.
Figure 6: A view of the various land cover types around Clarksville, Maryland in 2013 from the Chesapeake Conservancy High Resolution Land cover Project. Major tree canopy types are shown as dark green and yellow.
Chesapeake Conservancy High Resolution Land Cover Assessment for 2013
The tree canopy estimate from this data is approximately 3.168 million acres, or 51% of total land area.
This data is also intended to make maps, identify trees and tree canopy very precisely at many scales, primarily at the county level. This data can be placed on a map to depict individuals or groups of trees and tree canopy. It is a raster dataset with 1 meter resolution land cover assessment with 11 land classes, and was created using the same basic methodology as the UMD tree canopy data; an “object based analysis”. Tree canopy is a class, with additional tree canopy classes including “tree canopy over impervious”, “tree canopy over structure”, and “tree canopy over impervious roads”. These are grouped together to provide an estimate of total tree canopy. This data utilizes LiDAR data from various years, but generally 2012 to 2015, and sometimes in combination with other years. More information is available in the User Guide.
Figure 7: The relative percent of 6 different land cover types in Maryland. If all of the land cover types were placed together, this is what it would look like. Based on the Chesapeake Conservancy Land Cover Assessment for 2013.
US Forest Service Inventory and Analysis (FIA) Annual Summary of Permanent Plots in Maryland
Forest area from this data is estimated at 2.462 million acres in 2016 or nearly 40% of total land area.
Since 1929, the US Forest Service has been periodically collecting information about America’s forests, and this task falls to the Forest Service’s Forest Inventory and Analysis unit. The 1998 Farm Bill now requires the US Forest Service to collect data every year. This inventory is different from the digital data described above; field crews collect data from sample plots arranged across the state. It is not capable of measuring the tree canopy, but instead focuses on forest area, and collecting information about the forest.
There are over 900 permanent sample plots across the state, and the trees in these plots are measured at least every 7 years. Using statistics, the information for each plot is expanded to represent 6,000 acres of the surrounding forest. For example, if 2 of the plots were forested on a previous survey have been developed into houses, it can be interpreted as 12,000 acres of forest loss. Keep in mind, the UMD and Chesapeake Conservancy data sets are measures of tree canopy area, and FIA only measures forest. The data collected by FIA crews is invaluable, and tells us about the forest’s composition, age, structure, health, value, and much more. FIA derived data for Maryland can be accessed through the US Forest Service’s Design and Analysis Toolkit, or DATIM tool. Reports about the FIA forest sample data can be selected or created using the tool.
Figure 8: A graph of the forest cover area over time in Maryland. The FIA data (light green) is compared to estimates of forest area from the Maryland Department of Planning. Note the largely stable trend between 2008 and 2016, thought to have been caused by the financial crisis of 2008, and subsequent slowing of new construction.
Additional Resources
Forests of Maryland, 2021 Snapshot (USDA-FS FIA)
National Agricultural Imagery Program (USDA)
Maryland Forest Technical Study (Chesapeake Conservancy)
