Succession 15.1 Intro Change 1. Long-term (geol time) - climate, soils ... Physical Environ 2. þ Genetic - "Evolution"/Natural Selection 3. þ Types, #'s, groupings of organisms Assoc þ's in environ (soils, micro ...) "Succession" - sequence of communities ... over time, e.g., past Mt. St. Helens. Also the process(es) of change in communities & physical environment. "Sere" - characteristic sequence of communities that successively occupy and replace each other in a particular environment following disturbance or formation of a new environ: seral stage(s) (JB: successional stage) early successional - "pioneer" mid successional ... Primary Succession from "raw" geol Secondary succession in environments previously occupied/modified by vegetation animals clearcuts, ag. fields ? clearcut, burn and erosion!?? 1ø or 2ø? implications xerarch - xeroseres "xeric" mesarch - meseseres "mesic" hydrarch "hydric" psammoseres!! haloseres lithoseres oligotrophic - nutrient poor mesotrophic eutrophic "Driving force" for succession??! Changes in physical environment caused by organisms "autogenic" Changes due to geol processes "allogenic" "biogenic" sudden biotic cause, e.g., insect or disease alteration of plant community or herbivores overwhelming ... Rates of change/succession - variable!! - among environments - among seral stages "Climax" - prolonged, stable seral stage ?! "Linear" progression of succession?? Does it happen? How often? vs. "partial setbacks" ..., "loops" K15.2 Concepts & Classical Models of Succession Monoclimax Theory "Successional Convergence" toward climatic climax, e.g., K illus Fig. 15.2 Polyclimax Theory pyral/pyric climax edaphic climax biotic climax ** mosaic of "climax" communities "Climax Pattern" Hypothesis Veg'n is a complex pattern of integrating communities rather than a mosaic of distinct communities. þ Succession will result in a complex pattern of individualist climax communities. Some ecologists have concluded that "climax" concepts and arguments have outlived their usefulness. (I agree.) Usefulness: * Differences between successional stage & self-maint' comm' - Basis for comparisons - Means of identifying types of environments ... 15.3Mechanisms of Successional Change Colonization * What's a good pioneer? Invasion Survival Pop'n biology - Propagule # and "germination" dispersal, e.g., BCD for 1125 seeds/m2 69% alder 30% "new" 22% "don't exist" - stored seeds - sprouting - variation in germin w/in a species - "rate of invasion" - propagules, growth ... - ? "Relay floristics" - "current colonization" vs - initial vegetative composition Image for competition/control ... Alteration of Physical Site Characteristics - Light/shade - Temp - H2O - Soil: om pH, elem avail ... N-fix biotic (parts of succession) - Glacial recession - Mt. St. Helens - Landslides - Mud flows - Mt. Shasta/Mt. Rainier - River bars/terraces - Microclimate - Soils - Community - plants/animals N-slopes on interior AK (Text) Birch/alder blk/wht spruce w/ mosses  T  permafrost sphagnm peat less sp. open bog ? Retrogressive succession? ? Reduced avail of N & P due to  T &  decomp Ugolini & Mann Succession acid O podzolization iron pan impeded drainage sphag bog organic acid removal of pan, but still bog. Displacement of Species Antibioasis Autotoxicity Competition !? Kalmia heath sere climax in E. Canada Callena heath (heather) - Scotland - inhib' mycorr! Grasses N þ's?! (Rice, OK) !? Salmonberry & salal? Tapp & Zasada Succession fh: Invasion rate Shade tolerance Allelopathy Autotoxicity Environ modification Competition for nutrients - H2O Age/senescence Seed longevity & avail) Sprouting ... Signif of physiol adaptations Rates of Successional Change 1. ? "Degree" of environ change necessary for "next" stage ? light, H2O, nutrients (N fix, weathering, accum dust ...) 2. Productivity of organisms & rates at which they cause changes, e.g., lichens vs grasses/shrubs 3. "Longevity" of organisms in a stage Alder/aspen/salmonby/D'fir!! 4. Site "occupance" & domination by a community Generalizations about succession 1. Rates of þ: primary < 2ø 2. Rates in research > xerarch or hydarch succ'n 3. Xero, hydro - slow early Meso - "faster" early 4. Duration of a stage fh invasion by next 5. Faster on climates w/high NPP & biomass accum K15.5 Three Major Types of Sere A. Xerarch Succession - xerosere B. Meso Succession ... C. Hydarch - hydro ... Note diff's Study Sec 15.5 & Fig. 2! K15.6 Linear & Cyclic Succession The problem w/ "climax" concept * "Shifting mosaic steady state" K15.7 Recent models: Reference Only A. Markov ... "random" Replacement probabilities B. Stand models - detail - spatial distribution, e.g., Reed & Clark, Fig 15.10 C. Thru-Pathway Model (Fig. 15.11) D. Multiple Pathway Model (Fig 15.12) Read and Be Aware K15.8 Changes in Ecosystem Function During Succession Changes þ's in: Life form & longevity of dominant plants Community structure Community productivity Ratio of green to woody biomass Result in ecosystem "function" changes * Energetics - E "flows"/webs ... Biomass - living/dead - 1ø producers (autotrophs) Roots!! - herbivores - detritovores * Biogeochemistry Geochem: ppt, dust, weathering, leaching, erosion, ?pollutants Biogeochem: N-fix Nut' elem "turnover" Decomp ... Biochemical/Internal "Conservation" of elements - w/drawal from foliage Uptake from O horizons? Internal storage JB Add: Hydrology - effects on: soil H2O, stream flow, T ... K15.9 Ecosystem Stability & Successional Stage * ? What determines "stability"? What "is" stability? Constancy/Persistence Resilience/Elasticity vs Inertia "Trajectory", e.g., effects of fire vs windthrow K15.10 Hubbard Brook Model ref "Pattern & Process", B & L Secondary succession Reorganization Decomp & erosion - ? site specific Aggradation Transition "Steady-state" - dynamic patches K15.11 Animal Community Succession Read, e.g., Fig. 15.9 * Think about for forests of our field labs K15.12 Forest Mgt. & Succession **Study** Clearcutting ? Removal ? Fire ? Herbicides - Microclimate Desyncronized for - Forest floor desired species - Mineral soils - Microbes - Insects - Birds & animals - Shrubs - Trees - Hydrology: rain/snow What "seral stage" is desired? What's needed to get it? ? Microclimate ? Forest floor ? Competition ? Herbivores ? Pathogens ? Too much disturbance?? ? Enough?? e.g., forest floor, competitors **Study** Slashburning - Forest floor, mineral soil, and fauna - Microclimate Forestry: "Manipulating Succession"