fbpx
Wikipedia

Snag (ecology)

For other uses, see Snag (disambiguation).
This article needs additional citations for verification. Please help improve this article by . Unsourced material may be challenged and removed.
Find sources: "Snag" ecologynews · newspapers · books · scholar · JSTOR
(October 2016) ()

In forest ecology, a snag refers to a standing, dead or dying tree, often missing a top or most of the smaller branches. In freshwater ecology it refers to trees, branches, and other pieces of naturally occurring wood found sunken in rivers and streams; it is also known as coarse woody debris. When used in manufacturing, especially in Scandinavia, they are often called "dead wood" and in Finland "kelo wood".

A fir tree snag among living fir trees

Contents

Snags are an important structural component in forest communities, making up 10–20% of all trees present in old-growth tropical, temperate, and boreal forests. Snags and downed coarse woody debris represent a large portion of the woody biomass in a healthy forest.

In temperate forests, snags provide critical habitat for more than 100 species of bird and mammal, and snags are often called 'wildlife trees' by foresters. Dead, decaying wood supports a rich community of decomposers like bacteria and fungi, insects, and other invertebrates. These organisms and their consumers, along with the structural complexity of cavities, hollows, and broken tops make snags important habitat for birds, bats, and small mammals, which in turn feed larger mammalian predators.

A coast Douglas-fir snag provides nest cavities for birds

Snags are optimal habitat for primary cavity nesters such as woodpeckers which create the majority of cavities used by secondary cavity users in forest ecosystems. Woodpeckers excavate cavities for more than 80 other species and the health of their populations relies on snags. Most snag-dependent birds and mammals are insectivorous and represent a major portion of the insectivorous forest fauna, and are important factors in controlling forest insect populations. There are many instances in which birds reduced outbreak populations of forest insects, such as woodpeckers affecting outbreaks of southern hardwood borers and Engelmann spruce beetles.

Successional stages of a snag from death of a tree to final decomposition.

Snag creation occurs naturally as trees die due to old age, disease, drought, or wildfire. A snag undergoes a series of changes from the time the tree dies until final collapse, and each stage in the decay process has particular value to certain wildlife species. Snag persistence depends on two factors, the size of the stem, and the durability of the wood of the species concerned. The snags of some large conifers, such as Giant Sequoia and Coast Redwood on the Pacific Coast of North America, and the Alerce of Patagonia, can remain intact for 100 years or more, becoming progressively shorter with age, while other snags with rapidly decaying wood, such as aspen and birch, break up and collapse in 2–10 years.

Snag Forests, or Complex Early Seral Forests, are ecosystems that occupy potentially forested sites after a stand-replacement disturbance and before re-establishment of a closed-forest canopy. They are generated by natural disturbances such as wildfire or insect outbreaks that reset ecological succession processes and follow a pathway that is influenced by biological legacies (e.g., large live trees and snags downed logs, seed banks, resprout tissue, fungi, and other live and dead biomass) that were not removed during the initial disturbance.

Water hunting birds like the osprey or kingfishers can be found near water, perched in a snag tree, or feeding upon their fish catch.

In freshwater ecology in Australia and the United States, the term snag is used to refer to the trees, branches and other pieces of naturally occurring wood found in a sunken form in rivers and streams. Such snags have been identified as being critical for shelter and as spawning sites for fish, and are one of the few hard substrates available for biofilm growth supporting aquatic invertebrates in lowland rivers flowing through alluvial flood plains. Snags are important as sites for biofilm growth and for shelter and feeding of aquatic invertebrates in both lowland and upland rivers and streams.

A Canada goose feeds near a snag in the Nisqually River

In Australia, the role of freshwater snags has been largely ignored until recently, and more than one million snags have been removed from the Murray-Darling basin. Large tracts of the lowland reaches of the Murray-Darling system are now devoid of the snags that native fish like Murray cod require for shelter and breeding. The damage such wholesale snag removal has caused is enormous but difficult to quantify, however some quantification attempts have been made. Most snags in these systems are river red gum snags. As the dense wood of river red gum is almost impervious to rot it is thought that some of the river red gum snags removed in past decades may have been several thousand years old.

Also known as deadheads, partially submerged snags posed hazards to early riverboat navigation and commerce. If hit, snags punctured the wooden hulls used in the 19th century and early 20th century. Snags were, in fact, the most commonly encountered hazard, especially in the early years of steamboat travel. In the United States, the U.S. Army Corps of Engineers operated "snagboats" such as the W. T. Preston in the Puget Sound of Washington State and the Montgomery in the rivers of Alabama to pull out and clear snags.[citation needed] Starting in 1824, there were successful efforts to remove snags from the Mississippi and its tributaries. By 1835, a lieutenant reported to the Chief of Engineers that steamboat travel had become much safer, but by the mid-1840s the appropriations for snag removal dried up and snags re-accumulated until after the Civil War.

"Kelo wood" ("dead wood") used in Finland in the manufacture of rustic furniture products.

In Scandinavia and Finland, snags, invariably pine trees, known in Finnish as kelo and in Swedish as torraka, are collected for the production of different objects, from furniture to entire log houses. Commercial enterprises market them abroad as "dead wood" or in Finland as "kelo wood". They have been especially prized for their silver-grey weathered surface in the manufacture of vernacular or national romantic products. The suppliers of "dead wood" emphasise its age: the wood has developed with dehydration in the dry coldness of the subarctic zones, the tree having stopped growing after some 300–400 years, and the tree has remained upright for another few hundred years. "Dead wood" logs are easier to transport and handle than normal logs due to their lightness.

Wikimedia Commons has media related to Snag.
  1. Nilsson, Sven G; Niklasson, Mats; Hedin, Jonas; Aronsson, Gillis; Gutowski, Jerzy M; Linder, Per; Ljungberg, Håkan; Mikusiński, Grzegorz; Ranius, Thomas (2002). "Densities of large living and dead trees in old-growth temperate and boreal forests". Forest Ecology and Management. 161 (1–3): 189–204. doi:10.1016/S0378-1127(01)00480-7.
  2. Delaney, Matt; Brown, Sandra; Lugo, Ariel E.; Torres-Lezama, Armando; Quintero, Narsizo Bello (1998-03-01). "The Quantity and Turnover of Dead Wood in Permanent Forest Plots in Six Life Zones of Venezuela1". Biotropica. 30 (1): 2–11. doi:10.1111/j.1744-7429.1998.tb00364.x. ISSN 1744-7429.
  3. Vázquez, Leopoldo; Renton, Katherine (2015-01-23). "High Density of Tree-Cavities and Snags in Tropical Dry Forest of Western Mexico Raises Questions for a Latitudinal Gradient". PLOS ONE. 10 (1): e0116745. Bibcode:2015PLoSO..1016745V. doi:10.1371/journal.pone.0116745. ISSN 1932-6203. PMC4304802. PMID 25615612.
  4. Raphael, Martin G.; White, Marshall (1984-01-01). "Use of Snags by Cavity-Nesting Birds in the Sierra Nevada". Wildlife Monographs (86): 3–66. JSTOR 3830575.
  5. "Region 6 – Resource Management". www.fs.usda.gov. Retrieved2016-10-22.
  6. Thomas, Jack W., Ralph G. Anderson, Chris Maser, and Evelyn L. Bull. 1979. Snags. p.60-77. In Wildlife habitats in managed forests the Blue Mountains of Oregon and Washington, USDA Forest Service. Ag. Hand. No. 553, 512p.
  7. Keen, F. P. 1955. The rate of natural falling of beetle-killed ponderosa pine snags. Journal of Forestry 53(10):720–723.
  8. Swanson, Mark E; Franklin, Jerry F; Beschta, Robert L; Crisafulli, Charles M; DellaSala, Dominick A; Hutto, Richard L; Lindenmayer, David B; Swanson, Frederick J (2011-03-01). "The forgotten stage of forest succession: early-successional ecosystems on forest sites". Frontiers in Ecology and the Environment. 9 (2): 117–125. doi:10.1890/090157. hdl:1885/60278. ISSN 1540-9309.
  9. Franklin, Jerry F.; Lindenmayer, David; MacMahon, James A.; McKee, Arthur; Magnuson, John; Perry, David A.; Waide, Robert; Foster, David (2000-01-01). "Threads of Continuity". Conservation in Practice. 1 (1): 8–17. doi:10.1111/j.1526-4629.2000.tb00155.x. ISSN 1552-5228.
  10. Donato, Daniel C.; Fontaine, Joseph B.; Robinson, W. Douglas; Kauffman, J. Boone; Law, Beverly E. (2009-01-01). "Vegetation response to a short interval between high-severity wildfires in a mixed-evergreen forest". Journal of Ecology. 97 (1): 142–154. doi:10.1111/j.1365-2745.2008.01456.x. ISSN 1365-2745.
  11. MacNally, Ralph; Parkinson, Amber; Horrocks, Gregory; Young, Matthew (2002). "Current Loads of Coarse Woody Debris on Southeastern Australian Floodplains: Evaluation of Change and Implications for Restoration". Restoration Ecology. 10 (4): 627–635. doi:10.1046/j.1526-100X.2002.01043.x. ISSN 1526-100X.
  12. Hunter, Lewis C. (1977). Steamboats on the Western Rivers. New York: Dover Publications. pp. 193–272.

Snag (ecology)
Snag ecology Language Watch Edit For other uses see Snag disambiguation This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Snag ecology news newspapers books scholar JSTOR October 2016 Learn how and when to remove this template message In forest ecology a snag refers to a standing dead or dying tree often missing a top or most of the smaller branches In freshwater ecology it refers to trees branches and other pieces of naturally occurring wood found sunken in rivers and streams it is also known as coarse woody debris When used in manufacturing especially in Scandinavia they are often called dead wood and in Finland kelo wood A fir tree snag among living fir trees Contents 1 Forest snags 2 Freshwater snags 3 Maritime hazard 4 Dead wood products 5 See also 6 ReferencesForest snags EditSnags are an important structural component in forest communities making up 10 20 of all trees present in old growth tropical temperate and boreal forests 1 2 3 Snags and downed coarse woody debris represent a large portion of the woody biomass in a healthy forest 1 2 3 In temperate forests snags provide critical habitat for more than 100 species of bird and mammal and snags are often called wildlife trees by foresters 4 5 Dead decaying wood supports a rich community of decomposers like bacteria and fungi insects and other invertebrates These organisms and their consumers along with the structural complexity of cavities hollows and broken tops make snags important habitat for birds bats and small mammals which in turn feed larger mammalian predators 6 A coast Douglas fir snag provides nest cavities for birds Snags are optimal habitat for primary cavity nesters such as woodpeckers which create the majority of cavities used by secondary cavity users in forest ecosystems Woodpeckers excavate cavities for more than 80 other species and the health of their populations relies on snags Most snag dependent birds and mammals are insectivorous and represent a major portion of the insectivorous forest fauna and are important factors in controlling forest insect populations 6 There are many instances in which birds reduced outbreak populations of forest insects such as woodpeckers affecting outbreaks of southern hardwood borers and Engelmann spruce beetles 6 Successional stages of a snag from death of a tree to final decomposition Snag creation occurs naturally as trees die due to old age disease drought or wildfire A snag undergoes a series of changes from the time the tree dies until final collapse and each stage in the decay process has particular value to certain wildlife species 7 Snag persistence depends on two factors the size of the stem and the durability of the wood of the species concerned The snags of some large conifers such as Giant Sequoia and Coast Redwood on the Pacific Coast of North America and the Alerce of Patagonia can remain intact for 100 years or more becoming progressively shorter with age while other snags with rapidly decaying wood such as aspen and birch break up and collapse in 2 10 years Snag Forests or Complex Early Seral Forests are ecosystems that occupy potentially forested sites after a stand replacement disturbance and before re establishment of a closed forest canopy 8 They are generated by natural disturbances such as wildfire or insect outbreaks that reset ecological succession processes and follow a pathway that is influenced by biological legacies e g large live trees and snags downed logs seed banks resprout tissue fungi and other live and dead biomass that were not removed during the initial disturbance 9 10 Water hunting birds like the osprey or kingfishers can be found near water perched in a snag tree or feeding upon their fish catch Freshwater snags EditIn freshwater ecology in Australia and the United States the term snag is used to refer to the trees branches and other pieces of naturally occurring wood found in a sunken form in rivers and streams Such snags have been identified as being critical for shelter and as spawning sites for fish and are one of the few hard substrates available for biofilm growth supporting aquatic invertebrates in lowland rivers flowing through alluvial flood plains Snags are important as sites for biofilm growth and for shelter and feeding of aquatic invertebrates in both lowland and upland rivers and streams A Canada goose feeds near a snag in the Nisqually River In Australia the role of freshwater snags has been largely ignored until recently and more than one million snags have been removed from the Murray Darling basin Large tracts of the lowland reaches of the Murray Darling system are now devoid of the snags that native fish like Murray cod require for shelter and breeding The damage such wholesale snag removal has caused is enormous but difficult to quantify however some quantification attempts have been made 11 Most snags in these systems are river red gum snags As the dense wood of river red gum is almost impervious to rot it is thought that some of the river red gum snags removed in past decades may have been several thousand years old Maritime hazard EditAlso known as deadheads partially submerged snags posed hazards to early riverboat navigation and commerce If hit snags punctured the wooden hulls used in the 19th century and early 20th century Snags were in fact the most commonly encountered hazard especially in the early years of steamboat travel 12 In the United States the U S Army Corps of Engineers operated snagboats such as the W T Preston in the Puget Sound of Washington State and the Montgomery in the rivers of Alabama to pull out and clear snags citation needed Starting in 1824 there were successful efforts to remove snags from the Mississippi and its tributaries 12 By 1835 a lieutenant reported to the Chief of Engineers that steamboat travel had become much safer but by the mid 1840s the appropriations for snag removal dried up and snags re accumulated until after the Civil War 12 Dead wood products Edit Kelo wood dead wood used in Finland in the manufacture of rustic furniture products In Scandinavia and Finland snags invariably pine trees known in Finnish as kelo and in Swedish as torraka are collected for the production of different objects from furniture to entire log houses Commercial enterprises market them abroad as dead wood or in Finland as kelo wood They have been especially prized for their silver grey weathered surface in the manufacture of vernacular or national romantic products The suppliers of dead wood emphasise its age the wood has developed with dehydration in the dry coldness of the subarctic zones the tree having stopped growing after some 300 400 years and the tree has remained upright for another few hundred years Dead wood logs are easier to transport and handle than normal logs due to their lightness See also EditWikimedia Commons has media related to Snag Coarse woody debris Complex early seral forest Large woody debris Stream restoration Tree hollowReferences Edit a b Nilsson Sven G Niklasson Mats Hedin Jonas Aronsson Gillis Gutowski Jerzy M Linder Per Ljungberg Hakan Mikusinski Grzegorz Ranius Thomas 2002 Densities of large living and dead trees in old growth temperate and boreal forests Forest Ecology and Management 161 1 3 189 204 doi 10 1016 S0378 1127 01 00480 7 a b Delaney Matt Brown Sandra Lugo Ariel E Torres Lezama Armando Quintero Narsizo Bello 1998 03 01 The Quantity and Turnover of Dead Wood in Permanent Forest Plots in Six Life Zones of Venezuela1 Biotropica 30 1 2 11 doi 10 1111 j 1744 7429 1998 tb00364 x ISSN 1744 7429 a b Vazquez Leopoldo Renton Katherine 2015 01 23 High Density of Tree Cavities and Snags in Tropical Dry Forest of Western Mexico Raises Questions for a Latitudinal Gradient PLOS ONE 10 1 e0116745 Bibcode 2015PLoSO 1016745V doi 10 1371 journal pone 0116745 ISSN 1932 6203 PMC 4304802 PMID 25615612 Raphael Martin G White Marshall 1984 01 01 Use of Snags by Cavity Nesting Birds in the Sierra Nevada Wildlife Monographs 86 3 66 JSTOR 3830575 Region 6 Resource Management www fs usda gov Retrieved 2016 10 22 a b c Thomas Jack W Ralph G Anderson Chris Maser and Evelyn L Bull 1979 Snags p 60 77 In Wildlife habitats in managed forests the Blue Mountains of Oregon and Washington USDA Forest Service Ag Hand No 553 512p Keen F P 1955 The rate of natural falling of beetle killed ponderosa pine snags Journal of Forestry 53 10 720 723 Swanson Mark E Franklin Jerry F Beschta Robert L Crisafulli Charles M DellaSala Dominick A Hutto Richard L Lindenmayer David B Swanson Frederick J 2011 03 01 The forgotten stage of forest succession early successional ecosystems on forest sites Frontiers in Ecology and the Environment 9 2 117 125 doi 10 1890 090157 hdl 1885 60278 ISSN 1540 9309 Franklin Jerry F Lindenmayer David MacMahon James A McKee Arthur Magnuson John Perry David A Waide Robert Foster David 2000 01 01 Threads of Continuity Conservation in Practice 1 1 8 17 doi 10 1111 j 1526 4629 2000 tb00155 x ISSN 1552 5228 Donato Daniel C Fontaine Joseph B Robinson W Douglas Kauffman J Boone Law Beverly E 2009 01 01 Vegetation response to a short interval between high severity wildfires in a mixed evergreen forest Journal of Ecology 97 1 142 154 doi 10 1111 j 1365 2745 2008 01456 x ISSN 1365 2745 MacNally Ralph Parkinson Amber Horrocks Gregory Young Matthew 2002 Current Loads of Coarse Woody Debris on Southeastern Australian Floodplains Evaluation of Change and Implications for Restoration Restoration Ecology 10 4 627 635 doi 10 1046 j 1526 100X 2002 01043 x ISSN 1526 100X a b c Hunter Lewis C 1977 Steamboats on the Western Rivers New York Dover Publications pp 193 272 Retrieved from https en wikipedia org w index php title Snag ecology amp oldid 1045343372, wikipedia, wiki, book,

books

, library,

article

, read, download, free, free download, mp3, video, mp4, 3gp, jpg, jpeg, gif, png, picture, music, song, movie, book, game, games.