[rec.backcountry] Snags: Impact of Widespread Removal

cmyles@milton.acs.washington.edu (Cathy Myles) (01/03/90)

My nephew is doing a project on 'snags' and has asked me to gather 
information for him.

Snags are a home for many different types of birds, bugs, and other
animals. At the same time they are a hazard to people walking around
underneath them, especially loggers. The result of them being a 
hazard is that the British Columbia Worker's Compensation Board 
(injury insurance for workers) penalises loggers for not cutting them 
down.

In the project my nephew wants to consider whether cutting the snags 
down is a good or bad idea. I would like mail about: what is done 
about them where you live, opinions on what should be done, what 
animals might be threatened by widespread snag removal, and anything 
else you can think of.

Thanks in advance.    Jamie

jimh@qtc.UUCP (Jim Hurst) (01/05/90)

In article <1220@milton.acs.washington.edu> you write:
>I would like mail about: what is done 
>about them where you live, opinions on what should be done, what 
>animals might be threatened by widespread snag removal, and anything 
>else you can think of.
>
>Thanks in advance.    Jamie

	Mail to your site bounced.  Here's what I thought of.

	Snags are an important part of the undisturbed forest ecosystem.
They provide a unique structural component of the forest, which is home to
many different species of bugs and fungi with very narrow ecological niches.
There are several species of birds and mammals dependent on snags for primary 
habitat, that is, habitat where they can reproduce, not just survive.  Amongst 
the species that need cavities or standing snags are (this is from the appendix 
in Larry Harris' book listed below):

	saw-whet owl				pygmy owl
	screech owl 				pileated woodpecker
	northern three-toed woodpecker 		hairy woodpecker
	tree swallow 				purple martin
	western bluebird 			mountain bluebird
	yellow-bellied sapsucker 		black-capped chickadee
	downy woodpecker 			chestnut-backed chickadee
	red-breasted nuthatch 			white-breasted nuthatch
	brown creeper 				Vaux's swift
	California myotis 			Yuma myotis
	little brown myotis 			fringed myotis   (myotis ~= bat)
	long-legged myotis 			silver-haired bat
	big brown bat 				racoon
	marten 					fisher
                              and of course 
	spotted owl   <------ that famous million dollar bird

	This list looks to me like there are degrees of need:  there aren't 
many snags in my neighborhood, but lots of chickadees and several racoons.  
On the other hand, pileated woodpeckers, some owls, martens, fishers, and bats 
absolutely need snags to survive and reproduce.  Snags aren't really an isolated
feature, , they are part of the continuum of the forest.  Conifers that sustain 
damage to the crown often begin a slow death from heart rot even as the lateral 
branches begin growing upward form an enclosure protected from the elements 
that is used by cavity nesting birds along with holes in dead trees.  So by 
the time the tree dies (which can take decades or even centuries) and becomes a 
snag, it is home to a diverse community of birds, mammals, bugs, and 
sapprophytes.

	Snags indirectly protect the forest from insect damage by providing
habitat for natural insect predators.  Insect infestation tends to occur in
isolated outbreaks, particularly in areas where the forest is stressed by
drought, poor soil, fire damage, altitude, etc.  In forests maintaining healthy
populations of insect eating birds, woodpeckers and their friends home in on
outbreaks early in their occurrence, usually preventing infestation from 
becoming large scale.  On the other hand, snag can also provide an environment
that allows the survival of large numbers of insects, and so can actually
help facilitate insect infestation.

	What is done in our area?  We litigate, wrangle, lobby and generally
fight over snags and associated structurally diverse forests.  The presence of 
snags is subsumed in the larger controversy over forest management and old 
growth in the Northwest.  Preservation of the structural diversity of the 
forest, and its accompanying biological diversity has become the major issue 
on the agenda of the environmentalists in the region.  They (we) are gradually 
gaining power and influence as the timber industry becomes a less dominant 
part of the regional economy.  Traditional forest management has been based 
on clearcutting, and therefore on the removal of all snags, although leaving
"wildlife" trees and snags has been practiced on occasion.  Recent court 
decisions, combined with the Forest Service's stated intention of changing 
forestry practice with regard to ancient forest, indicate that snags and 
structural diversity in US forests will be handled more carefully in the future.  
	Calls for a "new forestry" involving more snags and downed wood
have begun to show results in the national forests of Oregon.  The Blue River 
Ranger district of Willamette National Forest has done shown leadership in 
experimentation with timber harvest techniques that preserve structural 
divesity, including snags.  Exactly how public forests will be managed after 
the timber compromise (aka the Appropriations Rider from Hell) of 1989 remains
to be seen, but clearly more snags will be left in the future.

	What do I think should be done?  I believe there are no simple 
generalizations as to the correct manner to manage the 10 million or so
acres of federal forest in Oregon, although the hardline environmentalists in
the Native Forest Council would tell you otherwise.  So would the hardline
timber industry folks, of course.  (What did Newton say about equal and opposite
forces?)  An intelligent management program will combine a wide array of 
different techniques, and make an effort to apply those techniques best suited 
to the local conditions.

	That said, if I were king of the forest, I would require clearcuts no
larger than some small threshold, say 10 acres.  This threshold should probably
actually be a function of the topography and local conditions.  In silviculture 
speak, this becomes small selection cuts, rather than clearcuts.  Leave all 
snags.  

	Here's what Elliot Norse, past Public Policy Director of the Ecological 
Society of America, says about snags in his book:  (note that this is in the 
context of the ancient forests of the Pacific Northwest.  Your mileage may
vary.)

	"Standing dead trees and fallen ones have different ecological roles.
Snags offer sloughing slabs of bark, chimneylike cavities and vantages out of
reach of ground-dwelling predators.  They also attract birds whose droppings
contain seeds of blackberries, salmonberries, thimbleberies, huckleberries,
and other plants that colonize clearcuts and burns.  Some plants, fungi, and
invertebrates use both snags and logs, but most vertebrates use mainly one of
the other.

	Snags are particularly important for birds, bats, and carnivorous 
mammals.  Raptors (hawks and owls) use them for lookout and plucking posts;
many birds use them for courtship display, nesting, feeding, and roosting
sites and for thermal protection at night, during heavy rains, and in cold
weather.  Loose sheets of bark on snags are major breeding sites for brown
creepers and for several kinds of bats.  Cavities at the base of snags serve
as dens for mammals as large as black bears, cavities higher up are nesting
sites for 30-45 percent of Nortwest forest bird species and dens for squirrels,
martens, and bobcats.

	In general, smaller snags can be used by some smaller species, but large
snags are essential for larger species and some small ones too.  Wood ducks, 
great horned owls, pileated woodpeckers, and fishers generally need snags more 
than 25 inches in diameter, but so do some smaller species, such as Vaux's 
swift.  Height is also important; far more cavity-nesting species use tall snags
than low-cut stumps.  Although young forests often have more snags, the larger
snags in ancient forests are far more valuble to cavity-dwelling wildlife.

	Most cavities in hard (younger) snags are excavated by woodpeckers 
preparing to nest.  Chickadees and nuthatches also excavate cavities in soft
(older) snags.  When excavators move out, a wide variety of other birds and 
mammals can move in.  By providing a crucial limiting resource, excavators 
function as keystone species, ones whose activites disproportionately influence
other forest dwellers.

	Most excavators, in turn, depend on insects and fungi to soften snags.
Wood boring beetles tunnel into trees soon after they die, providing entry for
decomposing fungi.  This allows woodpeckers and bears to shred the softened 
wood as they forage for beetle larvae.  People who automatically consider 
insects and fungi to be pests might be supriessed to learn of their essential
service to all cavity dwellers, from furbearing mammals and gamebirds to rare 
species such as spotted owls.

	As decomposition and shredding weaken a snag, it first loses its needles
and twigs, then upper branches, bark, and the top of its trunk, then wood 
further down the bole.  Some snags are firm when they fall, but many just
disintegrate and collapse.  Size affects their longevity, small ones decompose
faster.  In western Oregon, small Douglas fir snags characteristic of eighty
year old stands fall within two decades.  The large Douglas fir snags of ancient
forests usually last more than 125 years.  The species of snag affects longevity
as well.  Western redcedar and Douglas fir snags outlast western hemlocks and
silver firs.  So diameter, height, species, degree of decomposition, and numbers
all affect the value of snags to forest wildlife.

	Entire trees need not die to provide essential vertial dead wood 
habitat for forest wildlife.  The tops of many ancient conifers are dead,
victims of wind, freezing, lightning strikes, bark beetles, or pathogenic
fungi.  Although dead tops - often the top 10%, sometimes even the top half -
are difficult to see from the ground (and hence, are often missed in surveys),
canopy dewllers use them in the same ways that they use snags.

End quote.

	For more information, the following have some bearing on the general 
subject of snags:

The Fragmented Forest     Larry Harris   University of Chicago Press  1984
The Redesigned Forest     Chris Maser    R & E Miles, San Pedro, CA   1988
Forest Primeval           Chris Maser    Sierra Club Books            1989
Ancient Forests of the Pacific Northwest   Elliot Nourse   Island Press,
					 Covelo, CA/Washington DC     1989

	Other recent books that might be of interest on other aspects of 
forests and forestry.

Fragile Majesty              Keith Ervin        Sierra Club Books         1989
The Forest and the Trees     Gordon Robinson    Island Press              1988
Reforming the Forest Service Randall O'Toole    Island Press              1988

	Hope this helps,

					JimH