Forest Floor Soil Research Articles

Influence of nutrients, disturbances and site conditions on carbon stocks along a boreal forest transect in central Canada

The interacting influence of disturbances and nutrient dynamics on aboveground biomass, forest floor, and mineral soil C stocks was assessed as part of the Boreal Forest Transect Case Study in central Canada. This transect covers a range of forested biomes—from transitional grasslands (aspen parkland) in the south, through boreal forests, and into the forested subarctic woodland in the north. The dominant forest vegetation species are aspen, jack pine and spruce. Disturbances influence biomass C stocks in boreal forests by determining its age-class structure, altering nutrient dynamics, and changing the total nutrient reserves of the stand. Nitrogen is generally the limiting nutrient in these systems, and N availability determines biomass C stocks by affecting the forest dynamics (growth rates and site carrying capacity) throughout the life cycle of a forest stand. At a given site, total and available soil N are determined both by biotic factors (such as vegetation type and associated detritus pools) and abiotic factors (such as N deposition, soil texture, and drainage). Increasing clay content, lower temperatures and reduced aeration are expected to lead to reduced N mineralization and, ultimately, lower N availability and reduced forest productivity. Forest floor and mineral soil C stocks vary with changing balances between complex sets of organic carbon inputs and outputs. The changes in forest floor and mineral soil C pools at a given site, however, are strongly related to the historical changes in biomass at that site. Changes in N availability alter the processes regulating both inputs and outputs of carbon to soil stocks. N availability in turn is shaped by past disturbance history, litter fall rate, site characteristics and climatic factors. Thus, understanding the life-cycle dynamics of C and N as determined by ageclass structure (disturbances) is essential for quantifying past changes in forest level C stocks and for projecting their future change.

Trends in Water Chemistry in a Maple Forest on a Steep Slope

Year-to-year variation in SO42-,NO3-, Ca2+, K+, and Mg2+concentrations in forest floor and mineral soil percolatefrom a forested, podzolic soil at the Turkey Lakes Watershedon the Precambrian Shield was assessed for monotonic trendsbetween 1986 and 1995. Our objective was to examine howrapidly ion concentrations in soil percolate equilibratedafter stabilization of SO42- concentrations inprecipitation. Significant negative trends were detected inmonthly Ca2+, and Mg2+ concentrations in forestfloor and SO42-, Ca2+, and Mg2+ inmineral soil percolate during the 10-year-period. Thedecline in Ca2+ and Mg2+ was greater than annualdecreases in SO42- and NO3- in forestfloor percolate and proportional to the reduction inSO42- in mineral soil percolate. Response ofmineral soil percolate to a 15 μmolc L-1SO42- decrease in wet-only precipitation between1985 and 1986 was a gradual decline in SO42-concentration through 1995. The five-year meanSO42- concentration in bulk precipitation, forestfloor percolate, and mineral soil percolate decreased 8, 9and 18 μmolc L-1 from 1986–90 to 1991–95.Microbial (mineralization of organic S) and sorption(release from and/or retention in the pool of insolubleSO42-) processes in the soil were logicalexplanations for the observed changes in SO42- inmineral soil percolate.

Comparison of arboreal and terrestrial soil characteristics in a lower montane forest, Monteverde, Costa Rica

Summary In many tropical and temperate forests, live and dead components of canopy-held organic matter (COM) form communities that are distinct from terrestrially rooted plant and forest floor soil communities, but that interact with whole-forest processes. We quantified some of the soil characteristics of dead organic matter held within the canopy of mature trees in a tropical lower montane forest of Monteverde, Costa Rica, and compared them to soils from the upper horizons on the ground. The concentration of canopy organic matter was significantly higher than terrestrial soil, but similar for P and Ca. Canopy humus had very low pH compared to terrestrial soils. The terrestrial soil had a tenfold greater amount of extractable cations, but the C/N ratios and cation exchange capacity of COM and the upper soil horizon did not differ significantly. Canopy organic matter has rarely been considered in forest ecosystem studies due to its inaccessibility, the lack of rigorous sampling and extrapolation methods, and because its mass is small relative to total forest soil mass. However, in habitats where COM is large, a canopy root-humus mat occurs on branch and trunk surfaces, similar to that which occurs on the forest floor. Organic matter in the forest canopy may thus have more ecological importance than its mass implies, as the nutrient-retaining capacity of the root-humus mat layer could play an important role in nutrient conservation for the individual trees and epiphytes whose roots are imbedded within the mats, and for the forest ecosystem as a whole.

Cadmium and copper release kinetics in relation to afforestation of cultivated soil

Afforestation of cultivated soils causes soil acidification and elevated concentrations of dissolved organic matter (DOC) in the soil solution, and hence, aggravate the risk of heavy metal leaching. The kinetics of cadmium and copper release from an unpolluted arable soil applied with forest floor soil solution was investigated in the laboratory, and the release rates correlated to pH and DOC in solution through log–log equations. The soil solution was isolated from Norway spruce ( Picea abies (L.) Karst.) by centrifugation, and the solution passed a cation-exchange column to remove metal cations and to protonate the DOC. Soil samples from an arable Ap horizon were placed in completely mixed flow cells, and influent solutions with 0 to 5 mM DOC were applied. The solution pH was adjusted to achieve effluent pH values in the range 3.6 to 6.9 in the flow cells at steady-state conditions. Cadmium release rates were very low at pH > 5 and increased exponentially as pH decreased to <5. The release rate was correlated to solution pH in a simple model: log(cadmium release rate) = −0.21 pH − 15.28 ( R 2 = 0.48), and no significant effect of DOC was observed. The kinetics of copper release from the soil was more complicated with effects of both pH and DOC. In experiments without DOC, the release rate of copper was slightly lower at high pH than at low pH. In experiments above pH 5, the presence of 5 mM DOC in the solution increased the release rate of copper. However, the copper release was retarded by DOC in the range pH 3.8 to 5.0, which coincided with a maximum retention of DOC in the flow cells. The release rate of copper was correlated to solution pH and concentration of DOC, including an interaction of pH and DOC: log(copper release rate) = 0.86 pH − 1.26 logDOC + 0.24 pH · logDOC − 19.26 ( R 2 = 0.60). If the changes in soil chemical conditions after afforestation influence the cadmium and copper release rates in a similar way as observed in the flow cell experiments, then the release rate of cadmium will increase exponentially at soil solution pH < 4.5. The inhibition of copper release by DOC observed at pH 3.8 to 5.0 indicates that copper is retained in the soil by interactions with adsorbed organic matter.

Relationships between net nitrogen mineralization, properties of the forest floor and mineral soil, and wood production in &lt;i&gt;Pinus radiata&lt;/i&gt; plantations

Relationships between net nitrogen mineralization, properties of the forest floor and mineral soil, and wood production in &lt;i&gt;Pinus radiata&lt;/i&gt; plantations

Composition and reactivity of DOC in forest floor soil solutions in relation to tree species and soil type

Metal coordinating propertiesof DOC (dissolved organic carbon), and henceits influence on heavy metal release andmineral weathering, depend on the compositionand properties of DOC. Tree species producelitter with different chemical composition anddegradability, and these differences mightinfluence the composition and reactivity of DOCin soil solutions. Accordingly, analysis ofcomposition and reactivity of DOC in soilsolution samples collected by centrifugationfrom 16 forest soil O horizons from the fourtree species beech (Fagus sylvatica L.),oak (Quercus robur L.), grand fir (Abies grandis Lindl.), and Norway spruce (Picea abies (L.) Karst.) on two clayey and twosandy soils were carried out. The compositionand properties of DOC were determined bycapillary zone electrophoresis, acid-basetitration, Cu ion titration, total elementalanalysis, IR and UV spectroscopy, and metalrelease assays. Concentrations of DOC rangedfrom 20 to 163 mM with pH ranging from 4.6 to7.3. Norway spruce produced the highest DOCconcentration, and the lowest pH. Carbon inlow-molecular-weight aliphatic carboxylic acids(LACA) accounted for less than 6% of DOC withformic and acetic acids as the most abundantLACAs. The DOC was cation exchanged and protonsaturated to obtain comparable forms of DOC.Titratable carboxylic acid and phenolic groupswere in the range 51 to 82 and 20 to64 mmol·mol−1 C, respectively, with fewerphenolic groups in grand fir DOC as the onlysignificant difference. Infrared spectra offreeze-dried DOC samples suggest low contentsof aromatic C in the DOC especially from grandfir stands. Stability constants, log K of Cu-DOC complexes, determined by Cu ion titrationof DOC samples with fitting of the data to atwo-site binding model, were in the range 5.63to 6.21 for the strong binding sites and 3.58to 4.10 for the weak sites, but with nosignificant effects of tree species or site.Freeze-dried DOC samples were found to consistof 41 to 45% C, 38 to 49% O, 4.4 to 5.4% Hand 1.2 to 2.0% N and C/N ratios in the range26 to 42. Reactivity of DOC in terms of releaserates of Cd, Cu and Fe cations from a soilsample (flow cell experiments) showed nosignificant differences among DOC samples fromdifferent tree species and soil types.Apparently, only minor differences occur inchemical composition and reactivity ofequivalent concentrations of DOC in forestfloor soil solutions irrespective of origin,i.e. four tree species and two soil types. Soilsolution pH and the concentration of DOCproduced by various tree species are thecritical parameters when distinguishing amongtree species in relation to heavy metal releaseand mineral weathering.

Comparative fate of glyphosate and triclopyr herbicides in the forest floor and mineral soil of an Acadian forest regeneration site

Comparative fate of glyphosate and triclopyr herbicides in the forest floor and mineral soil of an Acadian forest regeneration site

Changes in Soil Chemical and Physical Characteristics in Japanese Cypress (Chamaecyparis obtusa Endl.) Stands by Mixture of Deciduous Broad-leaved Trees in the Northern Kanto Region of Japan

In order to clarify the effects of a mixture of deciduous broad-leaved trees on soil fertility, we investigated litter biomass accumulation, mineral soil chemical and physical characteristics, characteristics of nitrogen mineralization, and the mutual relationships between them in Japanese cypress (Chamaecyparis obtusa) stands mixed with deciduous broad-leaved trees at different ratios (mixture ratio; MR = 0, 16, 33, 43, 100% by basal area) in the northern Kanto region of Japan. Litter biomass in the forest floor and mineral soil was 19.1 Mg ha−1 in MR 0% and decreased approximately 60 % in MR 33%, MR 43% and MR100%. The permeability at 0–5 cm soil depth in MR100% was twice as much as that in MR 0%. Increases in soil permeability were likely due to larger soil pores in the higher MR with much accumulated deciduous broad-leaves. At 0–5 cm soil depth, the differences in carbon concentration among the plots were not clear. On the other hand, carbon concentrations at 5–10 cm depth increased from 90 g kg−1 to 147 g kg−1 with increases in MR from 0% to 100%. Concentrations of exchangeable bases increased two to four times with increases in MR from 0 to 100% at 0–10 cm depth. Soil pH (H2O) generally increased with increases in MR at each depth. The rates of net nitrogen mineralization at 0–5 cm depth in vitro increased from 25 to 87 mg kg−1 2 weeks−1 with increases in MR from 0 to 100%. However, increases in nitrification with increases in MR were not clear compared with nitrogen mineralization. These results indicated that a mixture of deciduous broad-leaved trees in a Japanese cypress stand was effective in preventing soil fertility decline.

Spruce growth response specificity after treatment with plant growth-promoting Pseudomonads

Naturally regenerating hybrid spruce seedlings (Picea glauca (Moench) Voss beta Picea engelmannii Parry) were collected from sites near Mackenzie, Salmon Arm, and Williams Lake, British Columbia, Canada. Bacteria were isolated from roots and screened in greenhouse trials for their ability to enhance spruce growth. Three strains belonging to the genus Pseudomonas were selected for study based on their disparate geographic origins and their capacity to consistently stimulate spruce seedling growth in screening trials. Factorial experiments were performed in the greenhouse to evaluate the effectiveness of these Pseudomonas strains with different spruce ecotypes. Factors tested were spruce seed sources, Pseudomonas isolates, and forest floor soils originating from different sites. Three levels of each factor were studied: one spruce seedlot, one Pseudomonas isolate, and one forest floor type each originated from a site at Mackenzie, Salmon Arm, and Williams Lake, British Columbia. Fourteen weeks after treatments were established, spruce biomass accumulation was greatest when spruce ecotypes were inoculated with bacteria originating from the same geographical area as spruce seed. However, Pseudomonas strains originating from sites other than the seed collection area also stimulated seedling growth significantly, rendering the difference in growth promotion between bacterial treatments small and insignificant. In addition, spruce growth promotion was not enhanced when seed was treated with combinations of Pseudomonas strains and forest floor soils originating from the same forest ecosystem. We conclude that specificity between spruce ecotypes and plant growth-promoting rhizobacteria strains can be detected under carefully controlled conditions, thereby supporting the hypothesis that growth-promoting bacteria may adapt to their plant hosts. However, the growth advantage accruing to seedlings treated with bacteria originating from the same ecosystem is small and suggests that it is not necessary to match Pseudomonas strains with spruce ecotypes and soil types for effective seedling growth promotion.Key words: Pseudomonas, spruce, specificity, growth promotion.

The use of laboratory measurements to predict nitrogen mineralization and nitrification in Pinus radiata plantations after harvesting

We tested whether laboratory estimates of net N mineralization and nitrification (subsequently termed N mineralization and nitrification) could be used to predict these processes in the field after harvesting nine Pinus radiata D. Don. plantations. Laboratory rates of N mineralization and nitrification were measured by aerobic incubation (20°C) of intact cores. Annual rates of these processes in the field were measured using a sequential coring procedure. Rates of N mineralization in the laboratory were 1.1-6.6 and 0.019-0.525mg·kg-1·day-1 for forest floor and mineral soil, respectively (nitrification accounted for 6-71 and 8-93% of N mineralization). Annual N mineralization by forest floor in the field was 5.2-23.9kg·ha-1·year-1and was not correlated with N mineralized in the laboratory. Annual N mineralization in mineral soil in the field was 16-74kg·ha-1·year-1and was highly correlated (r2 = 0.97) with N mineralized in the laboratory. Annual nitrification in forest floor in the field ranged from 3 to 45% of annual N mineralization, and in mineral soil from 4 to 27%, both were correlated with relative nitrification measured in the laboratory.

Pine and spruce seedling growth and mycorrhizal infection after inoculation with plant growth promoting Pseudomonas strains

Pine and spruce seeds were inoculated with antibiotic-resistant plant growth promoting fluorescent Pseudomonas strains Sm3-RN, Ss2-RN and Sw5-RN for evaluation of bacterial root colonization and seedling growth responses under greenhouse conditions. Mycorrhizal inoculum was introduced to seedling containers by placing 2 cc of forest floor soil around seeds at the time of sowing. Mycorrhizal roots were detected on 39% of pine and 30% of spruce seedlings treated with forest soil 13–15 weeks later. Most mycorrhizae were formed by Wilcoxina sp. (E-strain) (89% for spruce and 69% for pine); some Amphinema-like, Mycelium radicis atrovirens, Suillus-like, Thelephora-like, and Tuber-like mycorrhizae were also detected. In the absence of bacterial inoculum, spruce seedling biomass was positively correlated with the number of mycorrhizal root tips. This trend was obscured following inoculation with strains Ss2-RN and Sw5-RN. Pine seedling growth was weakly correlated with mycorrhizal root tip development only after treatment with strain Sm3-RN. Bacterial inoculation did not influence the mycorrhizal status of seedlings, but all three Pseudomonas strains stimulated biomass accumulation of spruce and pine seedlings, up to 19% (P < 0.05). Non-mycorrhizal seedlings tended to support smaller root-associated Pseudomonas populations, but inoculant bacteria colonized seedlings with a minimum of 6.3 × 103 colony forming units per gram of rhizosphere soil regardless of their mycorrhizal status. For spruce, growth effects due to bacterial inoculation were similar in both mycorrhizal and non-mycorrhizal seedlings. However, statistically significant gains in pine biomass by inoculation with strains Sm3-RN and Ss2-RN occurred only in mycorrhizal seedlings, whereas strain Sw5-RN caused significant growth promotion only in non-mycorrhizal pine. Our results suggest that these fluorescent pseudomonad strains enhanced spruce seedling growth through mechanisms unrelated to increased mycorrhizal colonization, but growth promotion of pine by strains Sm3-RN and Ss2-RN was facilitated by an interaction with mycorrhizae.

Pine and spruce seedling growth and mycorrhizal infection after inoculation with plant growth promoting Pseudomonas strains

Pine and spruce seeds were inoculated with antibiotic-resistant plant growth promoting fluorescent Pseudomonas strains Sm3-RN, Ss2-RN and Sw5-RN for evaluation of bacterial root colonization and seedling growth responses under greenhouse conditions. Mycorrhizal inoculum was introduced to seedling containers by placing 2 cc of forest floor soil around seeds at the time of sowing. Mycorrhizal roots were detected on 39% of pine and 30% of spruce seedlings treated with forest soil 13–15 weeks later. Most mycorrhizae were formed by Wilcoxina sp. (E-strain) (89% for spruce and 69% for pine); some Amphinema-like, Mycelium radicis atrovirens, Suillus-like, Thelephora-like, and Tuber-like mycorrhizae were also detected. In the absence of bacterial inoculum, spruce seedling biomass was positively correlated with the number of mycorrhizal root tips. This trend was obscured following inoculation with strains Ss2-RN and Sw5-RN. Pine seedling growth was weakly correlated with mycorrhizal root tip development only after treatment with strain Sm3-RN. Bacterial inoculation did not influence the mycorrhizal status of seedlings, but all three Pseudomonas strains stimulated biomass accumulation of spruce and pine seedlings, up to 19% ( P < 0.05). Non-mycorrhizal seedlings tended to support smaller root-associated Pseudomonas populations, but inoculant bacteria colonized seedlings with a minimum of 6.3 × 10 3 colony forming units per gram of rhizosphere soil regardless of their mycorrhizal status. For spruce, growth effects due to bacterial inoculation were similar in both mycorrhizal and non-mycorrhizal seedlings. However, statistically significant gains in pine biomass by inoculation with strains Sm3-RN and Ss2-RN occurred only in mycorrhizal seedlings, whereas strain Sw5-RN caused significant growth promotion only in non-mycorrhizal pine. Our results suggest that these fluorescent pseudomonad strains enhanced spruce seedling growth through mechanisms unrelated to increased mycorrhizal colonization, but growth promotion of pine by strains Sm3-RN and Ss2-RN was facilitated by an interaction with mycorrhizae.

Effect of Plant Growth Promoting BacillusStrains on Pine and Spruce Seedling Growth and Mycorrhizal Infection

Rifamycin-resistant derivatives of plant growth promoting Bacillus polymyxastrains L6, Pw-2, and S20 were used to evaluate the interaction of bacterial–mycorrhizal co-inoculation on pine and spruce seedling growth. We were particularly interested in determining if the mechanism by which bacteria stimulated seedling growth depended on the presence of ectomycorrhizae. Mycorrhizal inoculum was introduced by adding 2ml of one of six forest floor soil types originating from different spruce and pine stands to seedling containers. Mycorrhizal roots developed in 34% of pine and 27% of spruce seedlings treated with forest soil, but no differences between forest soils were detected. Most mycorrhizae were formed by Wilcoxinasp. (E-strain) (98% for spruce and 67% for pine); small numbers of Amphinema-like, Mycelium radicis atrovirens, Suillus-like, Thelephora-like, and Tuber-like mycorrhizae were also found on pine (27% in total). Thelephora-like fungi comprised 2% of spruce mycorrhize. In the absence of bacterial inoculum, spruce seedling biomass was positively correlated with the number of mycorrhizal root tips, but this trend was not detected in spruce inoculated with bacteria or in pine. Bacterial inoculation did not influence the mycorrhizal status of seedlings, but all three Bacillusstrains stimulated growth of both conifer species. Root biomass, in particular, was significantly enhanced by up to 18% compared with uninoculated controls. Mycorrhizal fungi improved the growth of spruce seedlings, but plant growth promotion by Bacilluswas similar for mycorrizal and non-mycorrhizal seedlings of both species. Our results suggest that Bacillusstrains L6-16R, Pw-2R, and S20-R enhance conifer seedling growth through a mechanism unrelated to mycorrhizal fungi.

A new mechanism for calcium loss in forest-floor soils

CALCIUM is the fifth most abundant element in trees, and is an essential component for wood formation and the maintenance of cell walls. Depletion of Ca from the rooting zone can result in acidification of soil1 and surface water2 and possibly growth decline and dieback of red spruce3,4. During the past six decades, concentrations of root-available Ca (exchangeable and acid-extractable forms) in forest-floor soils have decreased in the northeastern United States5,6. Both net forest growth and acid deposition have been put forth as mechanisms that can account for this Ca depletion5,6. Here, however, we present data collected in red spruce forests in the northeastern United States that are inconsistent with either of these mechanisms. We propose that aluminium, mobilized in the mineral soil by acid deposition, is transported into the forest floor in a reactive form that reduces storage of Ca, and thus its availability for root uptake. This results in potential stress to trees and, by increasing the demand for Ca, also decreases neutralization of drainage waters, thereby leading to acidification of lakes and streams.

Moisture and Temperature Patterns of Canopy Humus and Forest Floor Soil of a Montane Cloud Forest, Costa Rica

Accumulations of organic material can be found in the crowns of trees in tropical wet forests. We investigated moisture and temperature patterns of dead organic matter in the canopy and of soil in the upper horizons of the forest floor over a 42-month period. Temperatures of the canopy material and forest floor soil fluctuated throughout the year (range = 11.5?C to 21.0?C), but remained within an average of 1?C of each other. Both canopy material and forest floor soils were moist throughout the wet and misty seasons (over 70% water content). Although canopy organic substrate experienced periods of rapid and severe dehydration during the dry season (20%-40% water content), forest floor soils remained at a consistently high water content (60%-70%). The more extreme and fluctuating moisture conditions of canopy organic material may be important in determining the distribution and activity of epiphytic plants and associated canopy organisms.

Wildfire Effects on Forest Floor and Surface Soil in a Table Mountain Pine-Pitch Pine Forest

Wildfire plays a dominant role in creating die environmental and biological conditions necessary for the natural regeneration of mixed Pinus pungens Lamb. (Table Mountain pine)-Pinus rigida Mill. (pitch pine) forests. This study of forest floor and surface soil properties following a mid-July wildfire in these forests in the Shenandoah National Park revealed significant reductions in nutrient contents. Prolific regeneration of the pines occurred following the fire, with over 9,000 seedling/ha tallied in high severity areas, compared with less than 800 seedlings/ha in unburned areas. It is hypothesized that fire degrades site quality and sets back the site succession process so that the pines are better able to compete with invasive, xeric-site deciduous species like oaks and maples. Adjacent, unburned xeric-site oak forests dominate on more moist and fertile sites.

The Significance of Grasslands in Absorption of Atmospheric Methane and Emission of Nitrous oxide

Presented here are measurements of methane (CH4) uptake by, and nitrous oxide (N2O) emissions from established grassland and neighboring forest-floor soils in Japan. Grassland and forest sods act as a sink of atmospheric CH4 under aerobic conditions. From ours and other data, we estimated that the uptake of CH4 by 14 ecosystem types throughout the world vary between 7 and 78 TgCH4 per year. The sink strength of grasslands would represent a maximum of about 8.5% for the total CH4 consumption by soil and other land uses.

Empirical relationships between temperature and nitrogen availability across North American forests

Published data were analyzed to examine whether nitrogen (N) availability varies along macroclimatic gradients in North America. Extractable N produced during 8-week aerobic laboratory incubation was used as an index of potential net N mineralization. Mean extractable N during the growing season in the forest floor plus top mineral soil was used as an index of the available N pool. Using multiple regression, potential net N mineralization was shown to increase with available N and with litter-fall N (R2 = 0.722). Available N increased with increasing total soil N and with decreasing mean January and July air temperatures (R2 = 0.770). These relationships appeared to hold also for deciduous and coniferous forests separately across regions. Results suggest that net N mineralization output under uniform temperature and moisture conditions can be generally expressed by variations of N input (litter fall) and the available soil N pool, and that the available soil N pool is predictable along a temperature gradient at a regional scale.

Forest floor characteristics and soil nitrogen availability on slash-burned sites in coastal British Columbia

Organic forest floor materials were surveyed on spring and fall slash-burned sites in the Sproat Lake region of Vancouver Island 2 years after burning. Dominant organic matter types, distinguished according to morphological criteria, were sampled and incubated in the laboratory for 26 weeks with periodic leaching and measurement of mineral N. Mineralization data closely fit a first-order kinetic model. Field mineralization, estimated using mass of each organic matter type in the field and first-order model parameters corrected for local temperature, ranged from 2 to 6 g N•m−2•year−1, depending on burn severity, suggesting that slash burning did not reduce N availability below levels required to support early plantation growth, except in situations of severe burns on coarse-textured soils. Differential consumption of forest floor organic matter types increased spatial variability in N mineralization and resulted, at the most severely burned site, in 50% of mineralizable N being derived from materials covering only 5% of the site. Significant correlation between N mineralization and codes and indices of the Canadian Forest Fire Weather Index System indicated that predictions of slash-burn impacts on site fertility may be made from weather conditions prior to and during burning.

Diversity of soil fauna in the canopy and forest floor of a Venezuelan cloud forest

ABSTRACTArboreal and terresterial soil and lilter were sampled for macro-and microinvertebrates at two locations in a Venezuelan cloud forest. Fauna were most abundant in forest floor soil and associated litter. However, media suspended in the canopy and particularly those trapped in bromeliad shoots were most densely populated, while the diversities of the arboreal and terrestrial soil fauna were indistinguishable. Rates of leaf litter decomposition in the arboreal and terrestrial soils were similar, but the arboreal soils contained higher concentrations of mineral nutrients and carbon. Implications of these findings for the definition of soil in humid tropical forests, and related differences between temperate and tropical forests are discussed. The similarities in diversity and differences in species composition between arboreal and terrestrial soil fauna raise questions concerning the evolution of tropical soil fauna, as well as the estimate of global biotic diversity.