Download Insects in Early Seral Habitats

Bug Communities and Forest
Structure Modification
Andy Moldenke
Carolyn Ver Linden
Bugs, bugs, bugs and more
bugs!
“Bugs rule!!”
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
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’
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)
Shade versus sun
A whole taxon preference basis:
– Bees
• Nesting requirement = sunny bare ground
– Jumping spiders
– Wolf-spiders
• Visual pursuit hunting diurnal predators
– Butterflies
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
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)
Shade versus sun
Continental-scale distribution of
Madrotertiary and Arctotertiary biota:
Glacial cycles of migration of taxa
Add north america map
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)
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)
Ecosystem function changes with
clearcutting
#1 – Changing the position of the photosynthetic biomass (canopy to herb/shrub layer)
and changing the edibility of the
photosynthetic biomass (awful distasteful
evergreen needles to short-term edible
deciduous leaves)
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)
Opening the canopy
Open-canopy
Forest
Functional guild basis:
– Herbivorous caterpillars
• Joan’s birds run on herbivorous caterpillars
– Collector/gatherer aquatic midges +
• Flycatchers and bats; and fish too
– (and more important things like web-spinning spiders
too)
Opening the canopy
Open-canopy versus closed-canopy foodwebs
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!)
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
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)
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)
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!
Opening the canopy
Species Richness Total Abundance
• Forested Canopy
• Clearcut
318
489
(per 250 samples each)
Clearcuts are unsightly-but clearcuts very speciose
clearcuts very productive
9575
7942
• 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.
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)
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
So…
open- and closed-canopy bugs are different
What makes any one open-canopy stand
‘better’ than any other?
• 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
• 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.
Let’s hear it for ‘clearcuts’!
• industrial-grade clearcuts with low-tomoderate 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)
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
Caveat:
• Nearly all post-harvest changes have short halflives, 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.
Riparian Zone Fauna Composition
• How far does riparian influence extend
away from stream?
Riparian Hotspots
Species Richness
Total Abundance
Forest Floor
13.6c
32.6c
Veg break
15.8b
44.4b
Riparian
19.0a
65.6a
(p = <0.004)
(Green Peak – August)
(p=<0.00001)
Riparian Zone Fauna Composition
Forest floor
Riparian
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)
Forest-floor invertebrates:
Beetles
Millipedes
Mollusks
Spiders
• 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’
Forest
ELEVATION
(97 species)
DISTANCE
F. Köhler
1m
(2 species)
Distance from stream
1m
5m
10 m
20 m
50-70 m
Total r2 = .92
Axis 1 = .12
Axis 2 = .66
5-70 m
(1 species @ 20 m)
Management treatments
Microclimate classes
18.0-23.9 C
45-93% RH
24.0-31.9 C
31-61% RH
32.0-44.1 C
16-36% RH
AIR TEMP
% RH
Cool/humid
(6 species)
SOIL TEMP
Warm/dry
(16 species)
Management treatments
(134 species)
Total r2 = .84
Axis 1 = .18
Axis 2 = .51
Buffer
Clearcut
Forest
Buffer/Forest
(9 species)
Clearcut
(19 species)
Buffer vs. Forest
edge effects?
Stream effect
MM
Buffer
Forest
Edge effect
2G
BP
TC
SP