The Need for Forest Surveys
Forest surveys are used to obtain information on the condition of the forest, identifying the various trees, their ages, heights and growth rate, and other information on diseases and pests that are depleting the forest. They also help to keep track of logging activities and trees that have fallen because of wind or soil conditions. This type of survey also helps to get an idea of the topography, slopes, and soil conditions that are prevalent to determine whether they have any relevance to the forest and its development or depletion.
Forest surveys give an idea of the resources available and other aspects that can affect the ecological health of the country. Conducting surveys at regular intervals helps governments and concerned authorities to establish trends and make decisions for implementing additional tree cover. A comparison with previous surveys and a statistical analysis is always useful.
Image Source: Wikimedia: Forests
Methods for Present Day Forest Survey
Forests cover large areas of a country’s area. Because of the terrain and accessibility, it is quite often not very easy to conduct any surveys and even modern methods like GPS are defeated by the tree cover which prevents proper penetration of satellite signals. One of the most common methods of initializing a forest survey is to take aerial photographs of the forested area. These photographs are taken from special survey aircraft that will fly on predetermined routes quite often in a grid pattern with the aircraft also flying at a fixed height. Very high precision cameras are used to take millions of photographs that are then scaled down to a fixed scale of about 1:15000. It is possible for specially trained interpreters who view the photographs stereoscopically to make some judgments on the tree species, composition, and heights. Special software is then used to make special cartographical maps from the photographs.
Image Source: Wikimedia: Forest
Making Sense Out Of Forest Surveys
Now that an overall assessment has been made, it is then necessary to verify the data and its accuracy. Sample plots are identified on the maps and areas of about 5000 square feet are marked at selected spots. Each plot is then physically assessed by surveyors and foresters and the trees in that area are identified and counted. The age, condition and species are all noted. During the survey soil samples are also obtained and a further detailed survey made so that slopes, altitude, drainage, and run off conditions are noted. During every survey sample plots would measure in the hundreds of thousands, and out of these some representative ones are chosen as permanent plots which are surveyed during every survey operation. These permanent plots are used for comparisons with subsequent surveys to assess the efficiency of any forest management plan in action.
The data from the sample plots is then used as a representative for the particular areas surrounding it and extrapolations are made to transfer the data to larger areas, until the entire forest area is covered. Forestry officials will then be able to provide a complete picture of the forest and its resources. This then allows them to determine the areas where logging operations can be conducted without seriously depleting forest cover.
Forests are classified in 28 different categories that broadly cover temperate forests and tropical forests. Each forest would again have a separate classification depending on the vegetation and trees in it and may vary from evergreen, deciduous, sparse, parkland, and swamp forests among others.
Some surveys may also be linked up with wildlife departments and simultaneous surveys of fauna may also be made. These surveys allow scientists to link up this wildlife with forest cover and determine any need for protection and hunting restrictions. Local authorities also take advantage of such surveys to understand how to survey property in woods forests.
Forest Surveys in the United States
Forest surveys are also used to assess greenhouse gases and the effect they have on forest cover. The year 2011 has been declared as an International Year of Forests and experts from around the world are expected to decide on a definition for sustainable forest management based on the FAO guidelines for a national forest program. The Forest Survey program in the United States has a history of more than 100 years with the first recorded inventory being made in 1830. The US Forest Service has changed over to conducting annual surveys instead of periodic surveys and this means that they have foresters on the job at all times.
canadianencyclopedia.ca: Forest Survey
un.org: Forum on Forests
fia.fs.fed.us: Forest Inventory
fs.fed.us: A history of forest survey
museum.state.il.us: Classification of forests