Advancing and reversing succession as a function of time since fire and insect outbreaks: An 18 year in situ remeasurement of changes in forest composition

AbstractThe impacts of insect outbreaks on tree mortality, productivity, and stand development in Canada are reviewed, emphasising spruce budworm (Choristoneura fumiferana(Clemens), Lepidoptera: Tortricidae) and mountain pine beetle (Dendroctonus ponderosaeHopkins, Coleoptera: Curculionidae). Reduced growth and survival are a function of insect population and defoliation level. It is feasible to make short-term (annual) predictions of insect population and defoliation based upon sampling, but long-term, multi-year predictions are problematic. Given the historical record, it is expected that outbreaks will occur with relatively predictable frequency and basic host relationships and abiotic constraints will not change dramatically. However, the precision of predictions at fine scales is variable and reduced over time. Relationships between tree growth reduction, survival, and cumulative defoliation or beetle population level are available for major insect species. Understanding insect outbreak effects hinges on mortality, changes in interspecies competition, regeneration, and succession. Altered stand dynamics caused by insects can be interpreted for indicators such as wildlife habitat, old forest, riparian buffer cover, viewscapes, and connectivity. Anthropogenic changes are altering impacts via range expansions, northward shifts, and changes in forest composition. We can better understand effects of insect outbreaks and how best to ameliorate damage through a combination of empirical permanent plot studies, modelling, and manipulative experiments.

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Stratigraphy and floristics of Eocene swamp forests from Axel Heiberg Island, Canadian Arctic Archipelago

Canadian Journal of Earth Sciences ◽

10.1139/e93-169 ◽

1993 ◽

Vol 30 (9) ◽

pp. 1914-1923 ◽

Cited By ~ 17

Author(s):

David R. Greenwood ◽

James F. Basinger

Keyword(s):

Canadian Arctic ◽

System Structure ◽

Forest Community ◽

Forest Composition ◽

Small Scale ◽

Canadian Arctic Archipelago ◽

Lake Formation ◽

Axel Heiberg Island ◽

Density And Biomass

A record of polar Eocene forests is preserved as in situ tree-stump fields and leaf-litter mats in Buchanan Lake Formation sediments on Axel Heiberg Island, in the Canadian Arctic Archipelago. Stratigraphic examination at the centimetre to metre scale of peat–coal lithology and macrofossil floristics in two levels of these fossil forests reflects small-scale changes in forest composition and swamp hydrology horizontally and temporal variation vertically. Root system structure and tree base stratigraphy suggest that exposed tree stumps may not include only coeval individuals of a single forest stand, but rather also individuals representing different phases of the forest through one cycle of the hydrological development of this Eocene polar forest community. Earlier calculations of stand density and biomass, based upon the assumption that all stumps represent coeval trees, may therefore be greatly overestimated. A mosaic of Alnus – fern bog, mixed coniferous community, and taxodiaceous (Metasequoia–Glyptostrobus) swamp appears to have produced both the leaf mats and the in situ stumps, with the taxodiaceous swamp the dominant peat-accumulating phase.

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Geographic variation in forest composition and precipitation predict the synchrony of forest insect outbreaks

Oikos ◽

10.1111/oik.04388 ◽

2017 ◽

Vol 127 (4) ◽

pp. 634-642 ◽

Cited By ~ 3

Author(s):

Kyle J. Haynes ◽

Andrew M. Liebhold ◽

Ottar N. Bjørnstad ◽

Andrew J. Allstadt ◽

Randall S. Morin

Keyword(s):

Geographic Variation ◽

Forest Composition ◽

Insect Outbreaks ◽

Forest Insect

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Coarse woody debris in the southeastern Canadian boreal forest: composition and load variations in relation to stand replacement

Canadian Journal of Forest Research ◽

10.1139/x99-256 ◽

2000 ◽

Vol 30 (5) ◽

pp. 674-687 ◽

Cited By ~ 63

Author(s):

C Hély ◽

Y Bergeron ◽

M D Flannigan

Keyword(s):

Boreal Forest ◽

Coarse Woody Debris ◽

Structural Characteristics ◽

Woody Debris ◽

Decay Rates ◽

Forest Composition ◽

Stand Age ◽

Time Since Fire ◽

Clay Deposits ◽

Canopy Composition

Quantities and structural characteristics of coarse woody debris (CWD) (logs and snags) were examined in relation to stand age and composition in the Canadian mixedwood boreal forest. Forty-eight stands originating after fire (from 32 to 236 years) were sampled on mesic clay deposits. The point-centered quadrant method was used to record canopy composition and structure (living trees and snags). The line-intersect method was used to sample logs of all diameters. Total log load, mean snag density, and volume per stand were similar to other boreal stands. Linear and nonlinear regressions showed that time since fire and canopy composition were significant descriptors for log load changes, whereas time since fire was the only significant factor for snag changes. Coarse woody debris accumulation models through time since fire were different from the U-shaped model because the first initial decrease from residual pre-disturbance debris was missing, the involved species had rapid decay rates with no long-term accumulation, and the succession occurred from species replacement through time.

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Canopy Disturbances Catalyse Tree Species Shifts in Swiss Forests

Ecosystems ◽

10.1007/s10021-021-00649-1 ◽

2021 ◽

Author(s):

Daniel Scherrer ◽

Davide Ascoli ◽

Marco Conedera ◽

Christoph Fischer ◽

Janet Maringer ◽

...

Keyword(s):

Species Composition ◽

Tree Species ◽

Management Practices ◽

Environmental Changes ◽

Species Turnover ◽

Castanea Sativa ◽

National Forest Inventory ◽

Forest Composition ◽

Insect Outbreaks ◽

Tree Species Composition

AbstractWidely observed inertia of forest communities contrasts with climate change projections that suggest dramatic alterations of forest composition for the coming decades. Disturbances might be a key process to catalyse changes in tree species composition under environmental change by creating opportunities for ‘new’ species to establish. To test this assumption, we compared two assessments (1993–1995, 2009–2017) from the Swiss National Forest Inventory to evaluate which forests were opened by natural canopy disturbance (that is, wind, insect outbreaks, fire and drought) and if these disturbances altered tree species composition both in terms of species-specific basal area and recruitment densities. Natural disturbances affected 14% of the Swiss forests within 25 years, with wind and insect outbreaks being the most frequent (75%) and fire and drought being rare (< 1.5%). Disturbances led to a shift from conifer to broadleaf tree species at low elevation, in particular in dense Picea abies stands, but no change was observed at higher elevations. The composition of undisturbed sites persisted during the same period. Our results demonstrate that undisturbed forests widely resist changes in tree species composition as an effect of direct ingrowth by stand-forming species. Disturbance events seem necessary to create opportunities for climatically ‘better suited and site-adapted’ species to (re-)establish and therefore potentially catalyse tree species turnover under environmental changes. We detected a reduction of tree species that were—centuries ago—cultivated outside their primary natural range, in particular P. abies, or depended on traditional management practices (Pinus sylvestris, Castanea sativa), which may inform us on how the projected increase in disturbance frequency and severity might filter tree species composition and hereby alter forest structure.

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Rendez vous with Saturn's rings

International Astronomical Union Colloquium ◽

10.1017/s0252921100101885 ◽

1984 ◽

Vol 75 ◽

pp. 743-759 ◽

Cited By ~ 2

Author(s):

Kerry T. Nock

Keyword(s):

Solar Energy ◽

Electric Propulsion ◽

Power Source ◽

Propulsion System ◽

Low Thrust ◽

Ring Plane ◽

The Earth ◽

Total Impulse ◽

Saturn's Rings

ABSTRACTA mission to rendezvous with the rings of Saturn is studied with regard to science rationale and instrumentation and engineering feasibility and design. Future detailedin situexploration of the rings of Saturn will require spacecraft systems with enormous propulsive capability. NASA is currently studying the critical technologies for just such a system, called Nuclear Electric Propulsion (NEP). Electric propulsion is the only technology which can effectively provide the required total impulse for this demanding mission. Furthermore, the power source must be nuclear because the solar energy reaching Saturn is only 1% of that at the Earth. An important aspect of this mission is the ability of the low thrust propulsion system to continuously boost the spacecraft above the ring plane as it spirals in toward Saturn, thus enabling scientific measurements of ring particles from only a few kilometers.

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