Levels Of Soil Disturbance Research Articles

Do harvest methods and soil type impact the regeneration and growth of black spruce stands in northwestern Quebec?

Machinery traffic restrictions during forest harvest have been adopted to minimize soil damage and protect tree regeneration. However, this practice is questioned for paludifying black spruce ( Picea mariana (Mill.) BSP) stands in which severe soil disturbance by wildfire restores forest productivity. The objective of this study was to determine, 8 years after harvest, how soil disturbance created by clearcutting and careful logging affected black spruce natural regeneration and growth and how this effect varied by soil type. While regeneration density was higher following careful logging, stocking was not influenced by harvest method. Regenerating stands were taller following clearcutting despite potentially greater damages to preestablished regeneration. Compared with careful logging, clearcutting also resulted in reduced cover of Sphagnum spp. and ericaceous shrubs. Spruce stem density and stocking were both higher on organic and subhydric soils and lower on mesic soils. No significant interactions were observed between harvest method and soil type, indicating that the observation of taller black spruce stands and adequate stocking with clearcutting may be applicable to all soil types considered in this study. These results suggest that an adequate level of soil disturbance is an important part of forest regeneration, particularly in ecosystems where an autogenic reduction in productivity occurs.

Contrasting effects of season and method of harvest on soil properties and the growth of black spruce regeneration in the boreal forested peatlands of eastern Canada

It has been suggested that without sufficient soil disturbance, harvest in boreal forested peatlands may accelerate paludification and reduce forest productivity. The objectives of this study were to compare the effects of harvest methods (clearcutting vs. careful logging) and season (summer vs. winter harvest) on black spruce regeneration and growth in boreal forested peatlands of eastern Canada, and to identify the soil variables that favour tree growth following harvest. Moreover, we sought to determine how stand growth following harvest compared with that observed following fire. The average tree height of summer clearcuts was greater than that of summer carefully logged stands and that of all winter harvested sites. Summer clearcutting also resulted in a higher density of trees > 3 m and > 4 m tall and in a 50% reduction in Rhododendron groenlandicum cover, a species associated with reduced black spruce growth. Height growth of sample trees was related to foliar N and P concentrations, and to soil total N, pH and available Ca and Mg but not to harvest method or season. Our results also indicate that summer clearcutting could produce stand productivity levels comparable to those observed after high-severity soil burns. These results suggest that summer clearcutting could be used to restore forest productivity following harvest in forested peatlands, and offer further support to the idea that sufficient levels of soil disturbance may be required to restore productivity in ecosystems undergoing paludification.

Impact of disturbance from roadworks on Pteleopsis suberosa regeneration in roadside environments in Burkina Faso, West Africa

The seedling population structure of Pteleopsis suberosa and their regeneration mechanisms were investigated in four roadside environments (graded, adjacent, intermediate and ungraded areas) along paved and unpaved roads in West Africa. A total of 203 quadrats of 2 m × 5 m in size were surveyed and placed along transects parallel to the roads. Within each quadrat, the total number of seedlings and the number of living shoots per seedling base were recorded. Regeneration mechanisms were determined by assessing basal and aerial sprouts and excavating the root systems below ground level. The results show that the total seedling density and the densities of single- and multi-stemmed individuals varied significantly (p < 0.05) among the four roadside environments. However, all seedlings were produced asexually; root suckers were predominant (98%) compared to water sprout (1%) and coppices (less than 1%). This study demonstrates that an intermediate level of soil disturbance from grading along paved and unpaved roads may stimulate P. suberosa regeneration by root suckering. Road type (paved and unpaved) did not affect seedling density, but was a highly significant variable in relation to the coppicing ability of P. suberosa populations in roadside sites. In conclusion, P. suberosa is a disturbance-tolerant species which can proliferate mainly by root suckering after roadwork disturbance.

Spatial impacts of soil disturbance and residual overstory on density and growth of regenerating aspen

We examined spatial aspects of harvesting impacts on aspen regeneration at 25 sites in northern Minnesota. These sites had been clearcut or partially harvested 4–11 years ago. At each site, residual overstory, which was composed of trees other than aspen, soil disturbance, and tree regeneration were determined along transects leading away from skid trails into the neighboring stand. We characterized spatial extent of soil disturbance as soil strength using an Eijkelkamp soil cone penetrometer. Soil disturbance dropped off very quickly at the edge of skid trails, suggesting that the impact of harvesting traffic on areas adjacent to skid trails is minor. On skid trails, disturbance levels were higher on sites harvested in summer than on sites harvested in winter. Even after adjustment for differences in soil disturbance, stands harvested in winter had higher regeneration densities and greater aspen height growth than stands harvested in summer, suggesting that aspen regeneration was more sensitive to a given level of soil disturbance on summer-harvested sites versus on winter-harvested sites. Soil disturbance and residual overstory interactively reduced aspen regeneration densities and height growth, indicating that avoidance of soil disturbance is even more critical in partially harvested stands. Predictions based in the spatial patterns of impact found in this study indicated that harvesting conditions may have a great impact in future productivity of a site.

Effects of Strip Tillage and Production Inputs on Soil Biology across a Spatial Gradient

Strip tillage results in soil disturbance levels similar to those of conventional tillage systems in the row locations (strip) and properties of no‐till in the interrow (between‐row) locations. In this study, biological and physical soil properties in the region spanning the row to interrow were investigated and results were compared among strip–tillage systems utilizing different inputs (conventional fertilizer and pesticides vs. USDA‐approved organic inputs) and rotation regimes (continuous tomato [Lycopersicon esculentum Mill.] vs. a 3‐yr vegetable rotation). Bulk density was significantly greater in the interrow locations. Soil respiration potential was greatest in the interrow and least in the row locations, and greater in treatments receiving organic inputs relative to synthetic inputs. No differences in soil N mineralization potential were determined. Microbial biomass C and N were greatest in interrow and least in row locations. Total soil C and N values did not vary from row to interrow locations or as a result of synthetic vs. organic inputs. The data suggest that organically managed production systems are less biologically stratified than conventional input systems under strip‐tillage management. Although net C mineralization was similar between chemical and organically managed systems, greater microbial biomass values in the organic treatment systems may have been the result of continuous additions of weed biomass during the summer. The hypothesis of a gradient effect for biological activity in strip‐tillage systems from row to interrow appears to be true in systems managed with synthetic fertilizers and pesticides, but not true of organically managed systems.

Variation in soil seed bank species composition of a dry coniferous forest: spatial scale and sampling considerations

In order to assess the effects of disturbance on soil seed bank spatial structure, variation in seed bank species composition was analyzed at two spatial scales in mature (undisturbed) and recently disturbed stands of Interior Douglas-fir forest in south-central British Columbia. Coarse-scale analysis among stands 10–100 km apart using Multi-Response Permutation Procedures showed that individual mature stands were mainly characterized by unique seed bank species compositions. Disturbance had an homogenizing effect on seed bank species composition at the coarse scale––there was less variability among stands following disturbance by both low and high severity fires, and by non-salvage logging. In contrast, finer scale analysis among sampling units c. 10 m apart showed that heterogeneity in seed bank species composition was greater on severely burned and logged sites, commensurate with greater levels of soil disturbance, than on lightly burned and undisturbed sites. Despite the high intensity of seed bank sampling (sixty 25 cm2 soil samples from each of 16 sites), species-area curves leveled off only when infrequent species were removed from the dataset. The number of seed bank samples required to account for the common species ranged from 84 on severely burned sites, to 196 on undisturbed sites; more than the 240 samples collected per disturbance class in this study would have been required to account for the remaining infrequent species. Overall, this study highlights the importance of sampling intensively within multiple stands to capture the variation in species composition inherent to these dry coniferous forest soil seed banks.

Efeitos de sistemas de preparo do solo na erosão e na produtividade da acácia-negra (&lt;i&gt;Acacia mearnsii&lt;/i&gt; de Wild.).

Os plantios homogêneos de acácia-negra nem sempre são feitos em solos adequados às exigências da espécie, seja pelo valor da terra ou proximidade da indústria. Diferentes sistemas de preparo podem melhorar as condições do solo, evitar problemas de erosão e diminuir custos de implantação. Em áreas de propriedade da TANAGRO S.A e da SETA S.A., nos municípios de Piratini e Butiá, RS, em dois tipos de solos distintos - Neossolo Litólico e Argissolo Vermelho-Amarelo, foram testados sistemas de preparo do solo com diferentes níveis de movimentação para plantio de acácia-negra: plantio de mudas em covas e plantio após subsolagens com duas, três e cinco hastes e uso de gradagens. Foram avaliados o crescimento em DAP e altura, anualmente, e produção de biomassa aérea no corte raso. Os solos foram caracterizados química e fisicamente em seus horizontes superficiais. Nas plantas, após sete anos, foram coletadas amostras de discos em seis posições no tronco para avaliação das densidades básicas. Preparo do solo com subsolador de cinco hastes apresentou maiores perdas de solo, que foram mensuráveis apenas até 18 meses após o plantio. Essas perdas de solo são extremamente importantes na sustentabilidade da produção do Neossolo Litólico, composto em 80% de calhaus e cascalho. O preparo reduzido do solo, com a abertura de covas manual e mecanicamente para plantio da acácia negra, não diminuiu o crescimento das plantas em ambos os solos estudados. No entanto, o desenvolvimento inicial das plantas de acácia negra, plantadas em sistema de preparo reduzido, foi mais lento (altura e DAP), defasagem que permaneceu até os 24 meses após o plantio.

The effect of the glyphosate, 2,4-D, atrazine e nicosulfuron herbicides upon the Edaphic collembola (Arthropoda: Ellipura) in a no tillage system

The use of herbicides is a common and intensive practice in no tillage systems. The herbicides can influence, directly or indirectly, the population of edaphic arthropods. Collembola is a group that functions as a bio-indicator of soil conditions. The degree of abundance and diversity of Collembola provides the level of soil disturbance provoked by agricultural practices. This experiment was designed to compare the influence of herbicides on the population fluctuation of Collembola in a no-till soil preparation system. The work was conducted in a non irrigated no-till area at the Núcleo Experimental de Ciências Agrárias of the Universidade Federal de Mato Grosso do Sul (UFMS), Campus de Dourados, in soil planted with corn as a surface covering, during the period of December, 2002 to December, 2003. The data were analyzed according to a completely randomized model, in a split plot design. The plots received four types of herbicides: glyphosate, atrazine, 2,4-D and nicosulfuron. A fifth plot did not receive any herbicide (control), for a total of five treatment types. The sub plots were represented by their collection times (10, 20, 30 and 40 days after the herbicide applications). Both the type of herbicide and the time of data sampling influenced the Collembola population fluctuaction. The treatments with atrazine and 2,4-D caused the most reduction of the population of Collembola, depending on the time of application.

Effect of nitrogen fertilizer rate, herbicide rate, and soil disturbance at seeding on the productivity of a wheat-pea rotation

Rotational productivity is a function of the rotational crops and their interactions, as well as the management employed. Understanding the functioning of the overall production system, as well as its component parts, may contribute to improved management. Effects of nitrogen fertilizer rate (25, 50, 75, 100 kg N ha-1 as urea) and herbicide rate (66 or 100% of recommended) applied to wheat, and of the level of soil disturbance at seeding, on the productivity and N status of a 2-yr rotation of spring wheat (Triticum aestivum L.) and field pea (Pisum sativum L.) were assessed over two rotation cycles at two locations in southwestern Manitoba. Management factors typically acted independently to influence the cropping system. In both wheat and pea, high soil disturbance at seeding reduced or tended to reduce plant density in most site-years, resulting in reduced yields in about half of site-years. In 2 site-years where weed pressure was high, wheat yields for high disturbance treatments were less than 60% of low disturbance seeding, demonstrating the importance of adequate plant stands under sub-optimal growing conditions. The herbicide rate applied to wheat had few significant effects on wheat and pea. In most site-years, N fertilization had limited or negative effects on wheat yields due partly to relatively high soil NO3-N levels. Soil NO3-N levels declined over the years of the study, suggesting that N contributions from peas did not exceed crop N removal and/or N losses from the wheat-pea rotation. The N rate applied to wheat typically did not affect pea yields. Key words: Wheat, pea, rotation, herbicide, nitrogen, soil disturbance

Different Restoration Thinning Treatments Affect Level of Soil Disturbance in Ponderosa Pine Forests of Northern Arizona, USA

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Tillage systems affect trifluralin bioavailability in soil

Trifluralin is widely used for control of rigid ryegrass in no-till grain crops in southern Australia. Trifluralin must be incorporated into soil to be effective. Several field studies were conducted to evaluate the effect of different tillage systems on vertical seed distribution and efficacy and rate of loss of bioavailable trifluralin. Experiments were conducted during the growing seasons of 2004 and 2005 at two sites in South Australia: on the Roseworthy Campus farm of the University of Adelaide and near Minlaton on the Yorke Peninsula. The tillage systems at the Roseworthy Campus were minimum tillage (MinTill) and no-till using narrow points, whereas four direct-drill-seeding systems were used at Minlaton. Plastic beads were spread on the soil surface to simulate weed seeds. MinTill sowing buried more plastic beads than no-till, indicating that greater soil disturbance was caused by the MinTill system. Trifluralin efficacy was lower under no-till as compared to MinTill. A bioassay, based on response of oat roots, was used to quantify the concentrations of bioavailable trifluralin under different tillage systems. In both years at the Roseworthy Campus, loss of bioavailable trifluralin was greater under no-till than under MinTill; however, the rate of loss under both systems was much faster in 2004 than in 2005. In 2004, bioavailable trifluralin at 12 d after sowing under MinTill and no-till was 55 and 33% of the initial concentration, respectively. In 2005, bioavailable trifluralin remaining at 23 d after sowing was 86% under MinTill and 54% under no-till. At Minlaton in both years, bioavailable trifluralin was greater under tillage systems that provided the highest level of soil disturbance. These results demonstrate that reduced bioavailability of trifluralin occurs in no-till seeding systems, which could result in reduced weed control.

Influence of tillage systems on vertical distribution, seedling recruitment and persistence of rigid ryegrass (Lolium rigidum) seed bank

Several studies were conducted to evaluate the effects of different tillage systems on the vertical seed distribution, seedling recruitment pattern, and persistence of the rigid ryegrass seed bank. Experiments were conducted in South Australia at two locations (Roseworthy Campus and Minlaton, a site on the Yorke Peninsula) in 2003 and 2005. The distribution of surface seeds through the soil profile was associated with the level of soil disturbance. The low–soil-disturbance tillage systems left more seed on the soil surface, whereas the high–soil-disturbance systems buried most of the seeds. The seedling recruitment of rigid ryegrass was lower under the low–soil-disturbance tillage systems than under the high–soil-disturbance tillage systems at both locations. The seedling recruitment was two- to fourfold greater under minimum tillage than under no-till. Not only was the seedling recruitment lower under the low–soil-disturbance tillage systems, biomass accumulation by rigid ryegrass seedlings was also lower under these systems. The carryover of residual viable seeds from one season to the next was similar between the tillage systems. However, seed decay under no-till (48 to 60%) was much greater than under minimum tillage (12 to 39%).

Influence of soil scarification on reindeer foraging and damage to planted Pinus sylvestris seedlings

The effects of soil scarification on reindeer lichen cover and re-establishment, reindeer foraging and damage possibly caused by reindeer to planted Scots pine seedlings were studied during six growing periods in a field experiment established in a reindeer lichen site that was grazed by a herd of 500–600 reindeer each winter. Seedlings (at a density equivalent to 2000 ha−1) were planted in mounds with mineral soil on top, in tracks with exposed mineral soil, in tracks with mixed organic material and mineral soil and in intact lichen mat (control) with no soil disturbance. The disturbed area varied from 0 to 28%. After six growing periods, the reindeer lichen cover and volume were 10–20% lower in the scarified plots than in the control plots. There was no clear evidence that the reindeer avoided foraging even in plots with the highest levels of soil disturbance. However, the behaviour of the reindeer during winter grazing seemed to be affected by both coverage of reindeer lichen (positively) and the proportion of exposed mineral soil (negatively). Damage possibly caused by reindeer trampling affected 8.2% of the living seedlings each year and approximately 50% of these seedlings were subsequently infected by fungal diseases (compared with 20% of viable undamaged seedlings). Scarification treatments that exposed mineral soil mildly resulted in higher survival and growth rates than the other treatments, especially the control.

Composition and function of biological soil crust communities along topographic gradients in grasslands of central interior British Columbia (Chilcotin) and southwestern Yukon (Kluane)

Grasslands in the rainshadow of the Chilcotin (British Columbia) and St. Elias (Kluane, Yukon) mountain ranges of western Canada are characterized by widely spaced clumps of bunchgrass and sage, between which can be found lichen-dominated biological soil crusts (BSC). Our examination of Chilcotin and Kluane grasslands showed differential BSC development along topographic gradients, favoring those sites with lower levels of soil disturbance. Lichen species richness was greatest in upper topographic positions, that is, on valley side terraces in the Chilcotin and esker slopes in Kluane. Common BSC lichens in both grasslands included Acarospora schleicheri, Caloplaca tominii , Collema tenax , Diploschistes muscorum , Fulgensia bracteata , Phaeorrhiza nimbosa , Placidium squamulosum , and Psora decipiens . Chilcotin BSC additionally contained many Cladonia species (e.g., C. carneola , C. chlorophaea , C. pyxidata ), particularly where vegetation had encroached on BSC. The potential for nitrogen fixation by Collema -dominated crusts in Kluane was examined using acetylene reduction assays (ARA) and soil surface microclimate monitoring. ARA activity was highly dependent upon the duration of wetting events, reaching C2H4 levels up to 63 μmol·m–2·h–1after 40 h of hydration. Given the abundance of Collema-dominated crusts in Kluane and the optimal conditions for ARA activity that are reached during wetting–drying transitions, we hypothesized that BSC communities potentially make an important contribution to ecosystem nitrogen budgets. Enrichment in total and mineralizable N, as well as 15N natural abundance values, was consistent with N fixation making an important contribution to soil N pools in these ecosystems. Both Chilcotin and Kluane BSC had similar spongy microstructures that contrasted with the platy microstructures of the underlying surface mineral soils, but only the latter site showed micromorphological evidence of burial of mosses and other BSC components by continuing loess deposition. BSC may have performed similar roles in analogous steppe-like ecosystems that existed under full-glacial conditions in the unglaciated areas of eastern Beringia in Alaska and Yukon.

Persistence of Glyphosate‐Resistant Canola in Western Canadian Cropping Systems

Canola (Brassica napus L.) is the most important oilseed crop in western Canada. Its prevalence across the Canadian Prairies influences the occurrence and impact of canola volunteers as weeds. Here we determined the persistence of canola seed in cropping systems so effective volunteer management strategies can be developed. In mid‐ to late‐October of 2000, approximately 770 seeds m−2 of glyphosate [N‐(phosphonomethyl)glycine]–resistant (GR) canola were scattered on plot areas at seven western Canadian sites. From 2001 to 2003 the plots were seeded to a wheat (Triticum aestivum L.)–field pea (Pisum sativum L.)–barley (Hordeum vulgare L.) rotation or a fallow–field pea–fallow rotation in five different seeding systems involving seeding dates and soil disturbance levels, and monitored four times each year for canola plant density. Crop seeding date did not consistently influence volunteer canola density. With some exceptions, higher levels of soil disturbance led to higher volunteer canola densities. The vast majority of canola seedlings were recruited in the year following seed dispersal (2001). Across all locations, rotations, and seeding systems, and averaged over preplanting (PREP) and in‐crop prespray (PRES) intervals, canola densities were 6.2, 0.7, and 0.0 plants m−2 in 2001, 2002, and 2003, respectively. Canola volunteers were usually most abundant at PREP and PRES intervals; total recruitment at those intervals averaged across all seeding systems in the continuous cropping rotation was 3% (25 plants m−2). Preventing seed production in new canola volunteers in 2001 reduced canola densities in subsequent years (2002 and 2003) below those required to mitigate weed–crop competition influences in most crops.

Glyphosate-resistant wheat persistence in western Canadian cropping systems

Abstract As a weed, wheat has recently gained greater profile. Determining wheat persistence in cropping systems will facilitate the development of effective volunteer wheat management strategies. In October of 2000, glyphosate-resistant (GR) spring wheat seeds were scattered on plots at eight western Canada sites. From 2001 to 2003, the plots were seeded to a canola–barley–field-pea rotation or a fallow–barley–fallow rotation, with five seeding systems involving seeding dates and soil disturbance levels, and monitored for wheat plant density. Herbicides and tillage (in fallow systems) were used to ensure that no wheat plants produced seed. Seeding systems with greater levels of soil disturbance usually had greater wheat densities. Volunteer wheat densities at 2 (2002) and 3 (2003) yr after seed dispersal were close to zero but still detectable at most locations. At the end of 2003, viable wheat seeds were not detected in the soil seed bank at any location. The majority of wheat seedlings were recruited i...

Soil disturbance in integrated logging operations and the potential impacts on a fossorial Australian frog

Forestry practices have been shown to impact on amphibian species to varying degrees. Burrowing amphibian species may be of less concern as they may be able to escape the direct impacts of a logging operation. The giant burrowing frog Heleioporus australiacus is a threatened frog species in south-eastern Australia. Logging is currently excluded from known habitat of this species. We examine aerial photographs to determine the extent of soil disturbance in 15 coupes in which integrated logging has occurred and 15 unlogged coupes. We then examine the extent of soil disturbance in a standard operation in a simple field experiment to assess the potential for a logging operation to affect H. australiacus . Approximately 65% of a coupe experiences medium to high levels of soil disturbance during an integrated logging operation. These disturbances appear to be at a level which would be disruptive to an individual H. australiacus occupying such sites. Alternate logging practices result in varying levels of disturbance and therefore are likely to have varying impacts on individuals. Active management of an area following a logging operation may improve the habitat for H. australiacus and other soil organisms.

Grassland species response to soil disturbance and nutrient enrichment on the Northern Tablelands of New South Wales

An experiment was established in an area of long-grazed temperate grassland on the Northern Tablelands of New South Wales to investigate individual species response to mechanical soil disturbance and nutrient enrichment. Grazing was excluded for the duration of the experiment. The total species pool available in the experiment included 56 native and 24 exotic species recorded in the plots, as well as seven exotic species that were artificially introduced (i.e. sowing treatment). Eighteen months after treatment, total species richness was significantly lower under high soil disturbance (mean of 14.7 ± 0.85 species m–2) than under low (21.1 ± 0.67 species m–2) and moderately (21.7 ± 0.77 species m–2) disturbed conditions. Total species richness was not significantly affected by nutrient enrichment or sowing. Most of the annuals analysed were exotic and their relative cover increased with nutrient enrichment (Aira cupaniana Guss., Briza minor L. and Vulpia spp.), but was unresponsive to soil disturbance. Perennials showed varied responses, with the abundance of most decreasing with high soil disturbance and being unaffected by moderate soil disturbance levels. All four perennials favoured by high soil disturbance were exotic (Dactylis glomerata L., Lolium perenne L., Hypochaeris radicata L. and Sanguisorba minor Scop.); three of these were sown. Most perennials showed no significant response to nutrient enrichment, although the occurrence of a small number was either reduced (Aristida ramosa R.Br., A. warburgii Mez., H. radicata and S. minor) or increased (Carex inversa R.Br., D. glomerata, Fimbristylis dichotoma (L.) Vahl., Sporobolus creber De Nardi and Tricoryne elatior R.Br.). Most interactions (i.e. species response to one experimental factor depends on another experimental factor) occurred because few individuals survived on the severely soil-disturbed plots to respond to nutrient enrichment. However, in this particular grassland, the short-term response of most species to soil disturbance was independent of the level of nutrient enrichment.

Orangutan Nesting Behavior in Disturbed Forest of Sabah, Malaysia: Implications for Nest Census

High concentrations of orangutans remain in the multiple-use forests of the Lower Kinabatangan, Sabah, Malaysia. Compared to primary forest, the habitat is highly fragmented, characterized by a low tree density (332 stems/ha), small tree size (83.6% of trees are <20 m high), low basal area (18 m2/ha), abundance of canopy gaps and high level of soil disturbance. The forest structure and composition influence orangutan nesting patterns, and thus directly influence the results of nest surveys used to determine orangutan population size. In logged forests, tall and large trees are the preferred nesting sites of orangutans. The scarcity of suitable nesting sites in the logged-over forests of Kinabatangan, could partly explain the lower daily rate of nest construction (r = 1.00) versus those of other orangutan populations. The nest decay rate t recorded at the study site (average ± SD = 202 ± 151 days) strongly depends on the species of tree in which a nest is built. Our results illustrate that the nest-related parameters used for orangutan censuses fluctuate among habitat types and emphasize the need to determine specific values of r for specific orangutan populations and of t for different tree species in order to achieve accurate analysis of census data.

The use of alkalinity as a conservative tracer in a study of near-surface hydrologic change in tropical karst

Water shortages commonly increase in frequency following forest clearance on lands overlying karst in the tropics. The mechanism underlying this hydrologic change is likely to depend on the land use which follows forest cover. To determine the flow paths which prevail for a progression of land uses common to the uplands of Leyte, Philippines, samples of interflow were collected during the rainy season and titrated to determine their alkalinities. The ratio of the measured alkalinity to the value predicted by equilibrium calculations for each sample was used as an indication of the contact time of the water with the limestone. The responses of the alkalinity saturation ratio and the runoff depth to increasing rainfall depth were used to substantiate the hypothesis that epikarst infilling and changing soil structure create throttles to percolation and infiltration. The forest site was found to generate interflow primarily as pipe flow, with the infiltration and percolation throttles rarely exceeded. Similarly, infiltration was not limiting for the slash/mulch site; however, the level of soil disturbance was adequate to initiate a throttle at the epikarst which increased the volume of interflow generated. The total percolation was similar for the plowed and slash/mulch sites; however, the interflow was decreased at the plowed site by reduced infiltration at the soil surface. The throttles to surface infiltration and epikarst percolation were even greater at the pasture sites, resulting in high runoff generation. However, comparatively greater infiltration was observed in the pasture having contour-hedgerows.