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 activityResponsible 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 sunContinental-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 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)

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-canopyForest

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 canopyOpen-canopy versus closed-canopy foodwebs

How open is open?

Effect of 1 acre gap openings

Forest CanopyIndicator Species 11%

Open CanopyIndicator 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 318 9575

• Clearcut 489 7942 (per 250 samples each)

Clearcuts are unsightly--

but clearcuts very speciose

clearcuts very productive

• 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

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

#3 – Pollination of the flora (& reproduction)

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-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)

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 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.

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) (p=<0.00001)

(Green Peak – August)

Forest floorRiparian

Riparian Zone Fauna Composition

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:

Spiders

Beetles

Mollusks

Millipedes

• 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(97 species)

1 m 5-70 m(2 species) (1 species @ 20 m)

F. Köhler

Distance from stream

1m5 m10 m20 m50-70 m

Total r2 = .92Axis 1 = .12Axis 2 = .66

DISTANCE

ELEVATION

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

Management treatments

Cool/humid(6 species)

Warm/dry(16 species)

AIR TEMP

SOIL TEMP% RH

Buffer/Forest(9 species)

Clearcut(19 species)

Management treatments(134 species) Buffer

Clearcut Forest

Total r2 = .84Axis 1 = .18Axis 2 = .51

2G

SP

MM

Edge effect

Stream effect

TC

BP

Buffer vs. Forestedge effects?

Buffer

Forest