Bug Communities and Forest Structure Modification

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Bug Communities and Forest Structure Modification

• Andy Moldenke
• Carolyn Ver Linden

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Bugs, bugs, bugs and more bugs!Bugs rule!!
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Shade versus sun

• On an individual species preference basis
• Climatic
• Bombus mixtus
• Thermoregulation easier to locomote in
  open-canopy environment
• Eukiefferiella spp (flying adults)
• Visibility easier to find mate in open-canopy
  environment
• Resource
• For both, easier to find more food

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• Individual species preference basis
• Is this interesting only for endangered
  species?
• (after all who cares about a single species of
  arthropod?)
• Bombus mixtus is probably a keystone species

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Shade versus sun

• On a functional guild preference basis
• Herbivores prefer sunny conditions
• More photosynthesis
• More young leaves
• More broadleafed plants
• Higher caloric status
• Lower poisonous secondary compounds
• (but less nitrogen)
• (but higher vertebrate predator populations)

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Shade versus sun

• A whole taxon preference basis
• Bees
• Nesting requirement sunny bare ground
• Jumping spiders
• Wolf-spiders
• Visual pursuit hunting diurnal predators
• Butterflies

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• Whole taxon basis
• Bees
• Responsible for pollination
• Responsible for fruit/seed resource (vertebrate
  food)
• Diurnal activity
• Responsible for shift from mammals amphibian
  predators to birds and reptiles

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Shade versus sun

• Total community species richness basis
• On a localized basis, much higher in early
  succession
• Basic reason
• Nearly all closed-canopy taxa PLUS open-canopy
  obligates too (if not trashed)

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Shade versus sun

• Continental-scale distribution of
• Madrotertiary and Arctotertiary biota
• Glacial cycles of migration of taxa

Add north america map
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Californian biota summer-dry adapted
thermophilic largely open-canopy preference

• Prefer
• open-canopy meadows
• savanna (oak ponderosa)
• Willamette Valley grasslands
• (often disturbance fire-adapted)
• (not very important in mesic west-side
  Douglas-fir forests)

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• The macroevolutionary scale
• Evolutionary plug for open-canopy species
• Small populations
• Rapid local extinctions
• Northern edge of species distributions
• Important for adaptation to climatic changes
• exposure to novel biotic
  interactions
• (with both native introduced taxa)

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Ecosystem function changes with clearcutting

• 1 Changing the position of the photosyn-
• thetic biomass (canopy to herb/shrub
  layer)
• and changing the edibility of the
  photosynthetic biomass (awful distasteful
  evergreen needles to short-term edible deciduous
  leaves)

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• This change in plant species composition
  results in a HUGE change in the species
  composition of animals and their biomass
  increases (because of increased edibility of food)

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Opening the canopy
Open-canopy Forest
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• Functional guild basis
• Herbivorous caterpillars
• Joans birds run on herbivorous caterpillars
• Collector/gatherer aquatic midges
• Flycatchers and bats and fish too
• (and more important things like web-spinning
  spiders too)

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Opening the canopy
Open-canopy versus closed-canopy foodwebs
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How open is open?

• Effect of 1 acre gap openings
• Forest Canopy
• Indicator Species 11
• Open Canopy
• Indicator Species 42
• The presence of open canopy species is logical
  (even though the gap is very small but the is
  surprisingly high!)

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Ecosystem function changes with clearcutting

• 2 Fundamental alteration of soil water
• relations
• Trees (all plants, but especially trees) are like
  fountains pumping water out of the ground and
  back into the atmosphere

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Remove the trees (w of the mountains) and there
is plenty of water to go around during the summer
months

• Plants can fix photosynthetic carbon all summer
  long (instead of shutting down in
  August-September)
• Soil microbes have water so they can metabolize
  all summer long (and the bugs that eat them also)
  so they can provide nutrients for plant growth
  all summer long
• (no stop/start as in control forested sites)

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You have to judge by ecological function

• In a thinning the flush of annual vegetation is
  initially mineralized (decomposed) at the start
  of the fall rainy season the pulse of soluble
  nutrients are picked up by the remaining tree
  roots and mycorrhizae
• (more available nothing lost good
  good)
• In the clearcut (especially if followed by a hot
  burn and herbicides) there are few/no live roots
  to absorb the fall nutrient flush nutrients are
  lost to ground water
• (more available most lost good bad)

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Opening the canopy

• Open versus closed canopy faunas
• 1. many years of Andrews Forest studies reveals
  that the two are nearly entirely distinct
• 2. both faunas VERY diverse
• 3. about 50 of species of total arthropod fauna
  of forested regions is restricted to the short
  temporal windows (15-30 yrs.) of open canopy
• WOW! Surprising!

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Opening the canopy

• Species Richness
  Total Abundance
• Forested Canopy 318 9575
• Clearcut 489 7942
• (per 250 samples each)
• Clearcuts are unsightly--
• but clearcuts very speciose
• clearcuts very productive

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• Total species richness basis
• Spiders ½ of total fauna only in first 15 years
  post-harvest
• Bees 1-2 under closed-canopy versus 250
  post-harvest (other groups too butterflies,
  grasshoppers, etc.)
• Pitfall-trapping fauna richness increases 1.5
  2.0x.

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Aquatic environments

• Density and biomass of emergent aquatics
  increases (1.5-2.5x)(fixed sunlight)
• Biggest response is in Diptera (esp. midges, not
  EPTs)
• Richness shows very modest increase
• (few, if any, forest canopy taxa are lost
  entirely)
• (in contrast with terrestrial fauna, little
  turnover in species)
• (more emergent biomass results in higher
  percentage of predaceous species)

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Ecosystem function changes with clearcutting
3 Pollination of the flora ( reproduction)

• Canopy removal increases light
• Allows plants to fix more energy
• Allows plants to make flowers fruits
• Canopy removal increases light
• Allows air temperature to increase for
  cold-blooded
• insect activity of pollinators
• Logging disturbance provides nesting
  opportunities
• Plants get pollinated
• Seeds fruits provide additional resources for
  vertebrates

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Soopen- and closed-canopy bugs are different

• What makes any one open-canopy stand better
  than any other?

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• Predaceous species respond in basically the same
  manner to all types of canopy openings (probably
  the same as most vertebrates species)
• The driving environmental variable is
  productivity (total photosynthetic biomass
  deciduous/conifer ratio)
• native predators introduced predators
  individual plant species present no difference

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• For herbivores and shredders it is a different
  story
• Amount and species of CWD and types of individual
  plant species are crucial for determining insect
  assemblages.

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Lets hear it for clearcuts!

• industrial-grade clearcuts with low-to-moderate
  burn site prep have the highest diversity of
  insects (esp. if some slash is piled)
• Usually highest herbaceous component
• (burn removes litter)
• Greatest growth rate of shrubs
• (burn mineralizes nitrogen)
• Best pollination and seed set
• (burn produces bee nesting sites)

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However,

• If burn is too hot
• If legacy of dead wood is not left
• If herbicides are used
• then legacy is gone
• introduced weeds/pests flourish
• erosion ensues

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Caveat

• Nearly all post-harvest changes have short
  half-lives, BUT
• 1) Natural post-harvest foodweb change
  shifts system towards more bacterial-based energy
  flow.
• 2) If soil ecosystem is shifted too far
  towards a bacterial-based foodweb, then a certain
  class of microbes may develop which prevents the
  recolonization of ectomycorrhizal fungi and
  subsequent conifer recolonization.

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Riparian Zone Fauna Composition

• How far does riparian influence extend away from
  stream?

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Riparian Hotspots

• Species Richness Total Abundance
• Forest Floor 13.6c 32.6c
• Veg break 15.8b 44.4b
• Riparian 19.0a 65.6a
• (p lt0.004) (plt0.00001)
• (Green Peak August)

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Riparian Zone Fauna Composition
Forest floor Riparian
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Riparian Zone Fauna Composition

• Indicator species numerous
• Example Pterostichus crenicollis

• Big, easy to identify, abundant, widespread
• geographically, active most of the year
• With several such indicator species, can assay
  for
• effect of management activities in riparian
  zone
• (extra margin of safety for aquatic
  portion)
• (fish lobby
  drinking water)

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Forest-floor invertebrates
Millipedes
Beetles
Spiders
Mollusks
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• Individual species preference basis
• Is this interesting only for endangered
  species?
• (after all who cares about a single species of
  arthropod?)
• Bombus mixtus is probably a keystone species

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Forest (97 species)
F. Köhler
1 m
5-70 m
(2 species)
(1 species _at_ 20 m)
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Management treatments
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Management treatments (134 species)
Total r2 .84 Axis 1 .18 Axis 2 .51
Buffer/Forest (9 species)
Clearcut (19 species)
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Buffer vs. Forest edge effects?