Ontario Forest Biomonitoring Network: 
The Ontario Ministry of Environment, Conservation and Parks (Ministry) conducted this work through the Ontario Forest Biomonitoring Network (OFBN) in 1986-2017. 

Any use of these data should acknowledge the Ontario Ministry of the Environment, Conservation and Park's Ontario Forest Biomonitoring Network program. The Ministry is not liable for any interpretation or conclusions made with the data.All data were quality control checked. Despite this effort, some errors or issues with the data may have been missed. Please inform michele.williamson@ontario.ca of any issues discovered.

In 1985, the Ministry established the OFBN, a long-term monitoring program that monitors hardwood forest health. The program was initiated in response to widespread reports of forest decline in North America and Europe, and the implication that air pollution was a causal factor. The main objective of the OFBN has been to establish and maintain a province-wide database on the visual symptoms of forest health for the province’s mixed hardwood forests (McIlveen et al. 1989). In total, 110 permanent forest observation plots were established in 1986 across the range of the mixed hardwood forests in southern and central Ontario. A new site was added in 2010. Currently, 93 plots are monitored as sampling has been discontinued in 18 plots for various reasons. The plots have been sampled in 1986, 1987, 1989, 1990-2006, 2008, 2011, 2014, 2016 and 2017 years.

The plots are located on lands owned either privately by individuals or businesses, First Nations, Conservation Authorities, Ontario provincial or national parks, and the Niagara Parks Commission. The Ministry thanks these land owners for their continued cooperation and permission to conduct monitoring in the forest plots on their lands. 

The initial objectives of the forest health monitoring were:
1. “to establish a network of permanent observation plots in which baseline data can be obtained regarding the condition of the hardwood forest tree species (sugar maple was the primary target species).
2. to develop a rating system to assess the condition of hardwood trees with respect to the symptomatology experienced in Ontario.
3. to evaluate the assessment data and determine if regional differences are apparent in forest tree condition” (McIlveen et al. 1989).  

The current program has the same objectives, and is able to assess changes over the years. Each tree is marked in the plot and is monitored over the years. 

OFBN Permanent Monitoring Plots
The following criteria that were used to select sugar maple stands for plots (McIlveen et al. 1989):  

1. “A mature forest stand, approximately 60 to 200 years old, representative of an area over 10 hectares in size, to allow for buffering of the plot from edge effects. 

2. Species composition should consist of dominantly sugar maple with at least 20% associated hardwood species, including yellow birch, white birch, white ash, beech, black cherry and poplar.

3. Stands should be adequately stocked and relatively free of disease and injury.

4. A relatively undisturbed area without cutting, grazing or tapping within the past 20 years.

5. Good access from an all-weather road within 1.0 km of the plot location should be available.

6. Stands located on public lands or agreement forests are preferred.

7. Stands should be located at least ten kilometres from urban areas or point sources of air pollution.

8. Parts of southern Ontario have a history of extensive forest clearing, harvesting, fuel wood cutting, tapping and other management activities. The remaining sugar maple forest typically occurs as small stands, often on private woodlots or in Conservation Authorities.  The criteria for site selection may have to be expanded to accommodate the establishment of plots in these areas.

9. Within the selected forest stands or woodlots, the baseline plots should be chosen in uniform conditions representative of the stand as a whole.  Plots should be located at least 50 metres from any edge effects.

10. Wherever possible, preference is given to areas close to existing weather monitoring stations or MOE atmospheric monitoring stations.”

Initially, plots contained 100 trees that had diameters greater than 10 cm at breast height (DBH) and were closest to the post in the centre of the plot.  In 1991, the plots were changed to square quadrats (50 m X 50 m).  Some of the initial 100 trees were outside the 50 m x 50 m quadrats and monitoring continued on them.  The plots contain between 93 and 307 trees greater than 10 cm in DBH, for a total of over 18,000 trees in the program. A total of 34 hardwood and conifer species have been found in plots. 

Decline Index
The Decline Index is the metric developed by the Ministry to assess hardwood forest decline patterns to quantify tree stress symptoms that have been observed to respond to air pollution and other stressors. The Decline Index is a weighted measure of four stress parameters for every mature hardwood stem (> 10 cm of Diameter at Breast Height) inside the plot or the initial 100 trees outside the plot. 

DI = CD + (A * UL) + (A * ST) + (A * SL/2)  

Where
DI = Decline Index
CD = % Crown Dieback (percent cover of branches with no live foliage in crown)
A = ([100-CD]/400
UL = % Undersized leaves of remnant live foliage
ST = % leaves with strong chlorosis i.e., dark yellow throughout leaves of remnant live foliage
SL = % leaves with slight chlorosis of light yellow-pale green throughout leaves or leaf edges of remnant live foliage

Chlorosis and undersized leaves are excellent indicators of short-term stress within a year whereas persistent stress across years is measured by crown dieback.  Thus, crown dieback is weighted more heavily in the DI than the foliage short-term stress indicators.  Strong chlorosis is also weighted more heavily than slight chlorosis; highly stressed trees have a larger influence on the DI.  Conifer softwoods were not assessed for decline as their needles do not respond the same way to stresses as hardwood foliage. The Decline Index is calculated to the nearest whole number and ranges from 0 for a tree stem with no stress symptoms to 100 for a stem with maximum decline.  The Decline Index is divided into five classes of decline incidence to indicate the severity of decline for plot averages:  

Very Low (< 11), 
Low (11-15), 
Moderate (16-20), 
High (21 - 25) and 
Severe (> 25) (MOE 1989).  

These decline incidence classes were determined by forest experts to provide a measure of tree or forest stand health. 

The Decline sampling was conducted by the following organizations over the years:  Ecological Services for Planning Ltd. in 1986-1987, Beak Consultants in 1989-1991, Boreal Resources in 1994-2006, TECO Timber Natural Resource Group Ltd in 2008 and 2011, and Ministry staff and Watters Environmental Group Inc. in 2014, 2016 and 2017.
 
Individual Mature Tree Metrics
The Decline Index is only one of many measures of tree stress that have been measured on individual trees within OFBN plots. Stress measures have varied over the years and include forest canopy cover, tree crown cover, crown vigour, tree damage/defects, insect defoliation, disease, etc. Tree mortality, diameter at breast height and heights has also been measured. Tree species have been identified. 

Tree Regeneration Data:
Forest health is indicated by the amount of regeneration of new trees. Numbers of individuals were counted for five height classes of seedlings and saplings of each tree species that were found in 2 metre X 2 metre regeneration plots.

Woody Debris Data:
Forest health is indicated by the amount of woody debris fallen onto the ground. Amounts of woody debris were measured along the western, northern, and eastern borders of the 50 metre X 50 metre tree plots. If possible, the species, decomposition, condition, and cause of mortality were identified for fallen debris. 

Invasive Plant Species:
Invasive plants have the potential to stress other vegetation species. Presences of invasive species were recorded if they were observed inside or outside of the main 50 metre X 50 metre tree plot. 

Salamander Data:
Salamanders are sensitive to multiple stresses e.g., climate conditions. Counts of individuals of each species were made on sampling boards that were located adjacent to the main 50 metre X 50 metre tree plot.

Plant Phenology Photos:
The timing of leaf emergence and flowering has been found to indicate climate conditions and potential climate change. Photos have been made throughout the spring for each year to provide the potential to identify when leaves and flowers first emerge for mature trees or ground y vegetation.

Sound Recordings:
The timing of bird songs or other animal sounds in the spring has been found to indicate climate conditions and potential climate change. Sounds recordings have been made to provide the potential to identify when songbirds or other animals start vocalizing in the spring. 

Reference
McIlveen, W.D., McLaughlin, D.L., and Arnup, R.W. 1989. A survey to document the decline status of the sugar maple forest of Ontario. Ontario Ministry of Environment, December 1989. ISBN 0-7729-6253-7. Queen’s Printer for Ontario. www.archive.org