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 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)
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)
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 Canopy3189575 Clearcut4897942 (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.
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)
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.
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)