Canopy Patches Research Articles

The influence of canopy patch mosaics on understory plant community composition in boreal mixedwood forest

We assessed the composition of understory vascular plant communities in relation to the mosaic of canopy patch types, and their associated structure and environment, within unmanaged, mature boreal mixedwood forests in western Canada. Within a 30 km 2 area, we sampled patches of four different canopy types: conifer-dominated, broadleaf-dominated, mixed conifer-broadleaf, and canopy gaps (total n = 98). There were significant differences in understory composition among the four patch types (based on multi-response permutation procedure (MRPP)) and these were mainly due to differences in relative abundances of understory species. The understory communities of conifer patches were characterized by low abundances of shade intolerant species while shade-tolerant and evergreen species were indicators (based on an indicator species analysis (ISA)). Understory communities under gap and broadleaf patches were characterized by higher abundances of grasses and shade intolerant species. Gap, broadleaf, and mixed patches had higher abundances of certain shrub species than did conifer patches. The patch types also differed in terms of their environmental conditions. Conifer patches had drier, cooler soils and the lowest understory light. Broadleaf patches had the warmest soils while understory light during the leaf-off period was similar to that of canopy gaps. Gap patches had the lowest litter cover and PO 4 − availability and the highest light. Seven environmental variables (soil moisture, soil temperature, total light during the leaf-off period, cover of coarse and fine downed woody material, and availability of NH 4 + and Ca 2+) were significantly related to understory species composition (in a constrained ordination by means of a distance-based redundancy analysis (db-RDA); 16.5% of variation in understory community data explained). Even within a single patch type, there was substantial environmental variation that was related to understory species composition. Our study suggests that the mosaic of canopy patches within mixedwood forests supports coexistence of both early and late successional understory plant species in mixedwood stands. Maintaining the mixture of canopy patch types within mixedwood stands will be important for conserving the natural patterns of understory plant composition in boreal mixedwood forests.

Ecohydrological controls of soil evaporation in deciduous drylands: How the hierarchical effects of litter, patch and vegetation mosaic cover interact with phenology and season

Soil evaporation, a critical ecohydrological process in drylands, can exhibit substantial spatio-temporal variation. Spatially, ecohydrological controls of soil evaporation may generally depend on a hierarchical structure spanning from the presence or absence of litter, through canopy patches of woody plants and intercanopy patches separating them, up to the overall vegetation mosaic characterized by density of woody plant cover in the landscape, although assessment of these factors in concert is generally lacking. Temporally, ecohydrological controls can be further complicated by not only seasonal climate, but also phenology, particularly in seasonally deciduous drylands. We experimentally assessed the interactive controls on soil evaporation along a gradient of mesquite cover ( Prosopis velutina) within the North American monsoon region, with respect to such hierarchical structure and seasonality/phenology. Our results indicate that presence of litter exerts a dominant control on soil evaporation, independent of seasonality; in absence of litter, both patch and mosaic attributes influence soil evaporation variably with season/phenology. Correlations from related measures of incoming energy suggest energy limits evaporation in many cases, although other factors such as wind may potentially influence hierarchical and seasonal/phenological combinations. Our results highlight the need to account for both hierarchical vegetation structure and seasonal/phenological variability to improve ecohydrological predictions of soil evaporation.

Soil carbon heterogeneity in piñon–juniper woodland patches: Effect of woody plant variation on neighboring intercanopies is not detectable

Soil carbon often varies significantly among vegetation patch types, but less known is how the size and species of plants in the tree canopy patches and the cover types of the intercanopy patches affect the carbon storage, and whether vegetation characteristics affect storage in adjacent patches. To assess this, we measured fine-fraction soil carbon in a semiarid woodland in New Mexico USA for canopy patches of two co-dominant woody species, Pinus edulis and Juniperus monosperma that were paired with intercanopy patch locations covered by herbaceous grass ( Bouteloua gracilis) or bare ground. Soil carbon at shallow depths was greater in canopy than intercanopy patches by a factor of 2 or more, whereas within intercanopy patches soil carbon in grass locations exceeded that in bare locations only after accounting for coarse-fraction carbon. Hypothesized differences among canopy patches associated with species or size were not detected (although some size-depth interactions consistent with expectations were detected), nor, importantly, were effects of species or size of woody plant on intercanopy soil carbon. The results are notable because where applicable they justify estimates of soil carbon inventories based on readily observable heterogeneity in above-ground plant cover without considering the size and species of the woody plants.

Horizontal heterogeneity in the frequency of plant‐available water with woodland intercanopy–canopy vegetation patch type rivals that occuring vertically by soil depth

AbstractSoil moisture integrates and drives ecohydrological processes in dryland ecosystems. However, despite the central importance of soil moisture, relevant field studies have not holistically assessed key inter‐related aspects of ecohydrological spatiotemporal variation: the threshold‐like manner in which soil texture controls the frequency at which soil water is readily available for plants, assessment of horizontal heterogeneity associated with vegetation patches in addition to vertical heterogeneity associated with depth, seasonal variation associated with precipitation type (snow vs rain) and inter‐annual variation spanning notably wet and dry periods. We measured soil water content by neutron probe in a semiarid piñon‐juniper woodland (Pinus edulis and Juniperus monosperma) in northern New Mexico, USA, over 15 years and evaluated an ecohydrological metric–plant‐available water, estimated as the percentage of time that soil water content was sufficiently wet to be generally available to plants. The frequency of plant‐available water varied significantly across all variables assessed: precipitation amount (across years or seasons), precipitation type, vertically with soil depth and horizontally with vegetation patch type (canopy patches beneath trees, intercanopy patches between trees and edges between the two patch types). Notably, in many cases, horizontal heterogeneity in plant‐available water associated with vegetation patch was as substantial as vertical heterogeneity associated with depth, yet such horizontal heterogeneity is not included in most ecological or hydrological models. Our results highlight spatiotemporal variation in the frequency of plant‐available water that is substantial, often overlooked, and may need to be explicitly considered for predicting dryland vegetation responses to land use and climate change. Copyright © 2009 John Wiley & Sons, Ltd.

Population distribution and conservation of the four-horned antelope (Tetracerus quadricornis) in the tropical forest of Southern India

Population density, distribution patterns and conservation problems of the four-horned antelope (Tetracerus quadricornis) were assessed in the Mudumalai Wild Life Sanctuary, Southern India. The antelopes were found to be restricted to dry deciduous and dry thorn forests in the northern and eastern areas of the sanctuary in an area of approximately 79 km 2 . The ecological density of the antelope was 0.88 individual/km 2 and the crude density was ~0.22 individual/km 2 . Within the dry deciduous forest, the antelopes were further restricted to flat short grass patches and hilly areas with open canopy patches of tall grass. The antelopes were relatively more abundant in the dry deciduous short grass habitat than in the dry deciduous tall grass and dry thorn forests. They also seemed to have higher preference for hill slopes with semi-open canopy (>70%). Antelopes and evidence of their presence have not been seen in recent years in some eastern areas of the sanctuary where antelopes were seen until 1990. We attribute the range decline to the overgrazing by cattle and the resultant weed invasion in the recent years.

Soil disturbance by animals at varying spatial scales in a semi-arid Australian woodland

We studied soil disturbance by rabbits, echidnas, goannas, ants and termites at three different spatial scales across four vegetation communities (dense woodland, open woodland, shrubland, grassland) in semi-arid rangeland in western NSW. For analyses, bare and litter-covered surfaces (micro-scale) were nested within canopy and open patches (intermediate scale), which were nested within vegetation communities (landscape scale). Landscape-scale disturbances (rabbit warrens) were six and three times more abundant in open woodlands and shrublands, respectively, than in dense woodlands. Although individual warrens had a similar mass of excavated soil across all vegetation communities, in total, more soil was excavated in the grasslands than in the dense woodlands or shrublands. There were four times as many intermediate-sized disturbances (foraging pits and resting sites) under canopies than out in the open, and this was consistent across all vegetation communities. Echidna foraging pits and kangaroo resting sites dominated the canopy patches. Intermediate-sized disturbances scaled up to the landscape scale were marginally more abundant in the dense and open woodlands than in grasslands and shrublands. However, total mass of soil moved by all species did not differ among vegetation communities. The density of small-scale disturbances (ant nests, termite foraging galleries) did not differ at the landscape-, intermediate- or micro-scales. Our study documents the extent of animal activity in the semi-arid woodlands, and reinforces the notion that, as soil disturbance is scale-dependent, differences among species, habitats and communities will depend on the scale at which disturbances are examined.

Ecohydrological controls on soil moisture and hydraulic conductivity within a pinyon‐juniper woodland

The impact of pinyon‐juniper woodland encroachment on rangeland ecosystems is often associated with a reduction of streamflow and recharge and an increase in soil erosion. The objective of this study is to investigate vegetational control on seasonal soil hydrologic properties along a 15‐m transect in pinyon‐juniper woodland with biocrust. We demonstrate that the juniper tree controls soil water content (SWC) patterns directly under the canopy via interception, and beyond the canopy via shading in a preferred orientation, opposite to the prevailing wind direction. The juniper also controls the SWC and unsaturated hydraulic conductivity measured close to water saturation (K(h)) under the canopy by the creation of soil water repellency due to needle drop. We use this information to refine the hydrologic functional unit (HFU) concept into three interacting hydrologic units: canopy patches, intercanopy patches, and a transitional unit formed by intercanopy patches in the rain shadow of the juniper tree. Spatial autoregressive state‐space models show the close relationship between K(h) close to soil water saturation and SWC at medium and low levels, integrating a number of influences on hydraulic conductivity.

Re-envisioning the structure of last glacial vegetation in New Zealand using beetle fossils

A series of 18 fossil beetle assemblages are used to reconstruct the paleoenvironment of the northwest West Coast, New Zealand, over the period of the last interstadial–stadial transition (ca. 37,000–21,300 cal yr BP). The samples were recovered from an in-filled hollow within a dune field ca. 9 km south west of Westport (41°47′S, 171°30′E). This fossil beetle reconstruction is compared to an existing palynological reconstruction from the same site. The beetle assemblages indicate an environment of marshy shrubland interspersed with closed canopy coastal vegetation prior to glacial onset, and a mosaic of closed canopy patches and open tussock grassland during full glacial conditions. These interpretations, contrast with the palynologically based interpretation which indicates subalpine shrubland prior to glacial onset and widespread grassland with little woody vegetation during the period of maximum glacial cooling. This study is consistent with other non-pollen studies in New Zealand and indicates that the palynological interpretation of the paleoenvironment of the Westport region downplays the importance of closed canopy vegetation in the area during the transition from interstadial to full glacial (stadial) conditions. It challenges the interpretation of open vegetation at low elevations during glacial periods from pollen studies.

Retention time and dispersion associated with submerged aquatic canopies

The shear layer at the top of a submerged canopy generates coherent vortices that control exchange between the canopy and the overflowing water. Unlike free shear layers, the vortices in a canopy shear layer do not grow continuously downstream but reach and maintain a finite scale determined by a balance between shear production and canopy dissipation. This balance defines the length scale of vortex penetration into the canopy, δe, and the region of rapid exchange between the canopy and overflow. Deeper within the canopy, transport is constrained by smaller turbulence scales. A two‐box canopy model is proposed on the basis of the length scale δe. Using diffusivity and exchange rates defined in previous studies, the model predicts the timescale required to flush the canopy through vertical exchange over a range of canopy density and height. The predicted canopy retention times, which range from minutes to an hour, are consistent with canopy retention inferred from tracer observations in the field and comparable to retention times for some hyporheic regions. The timescale for vertical exchange, along with the in‐canopy velocity, determines the minimum canopy length for which vertical exchange dominates water renewal. Shorter canopies renew interior water through longitudinal advection. Finally, canopy water retention influences longitudinal dispersion through a transient storage process. When vertical exchange controls canopy retention, the transient storage dispersion increases with canopy height. When longitudinal advection controls water renewal, dispersion increases with canopy patch length.

Soil respiration response to experimental disturbances over 3 years

Soil respiration is a major pathway for carbon cycling in terrestrial ecosystems yet little is known about its response to natural and anthropogenic disturbances. This study examined soil respiration response to prescribed burning and thinning treatments in an old-growth, mixed-conifer forest on the western slope of the Sierra Nevada Mountains. Experimental treatments were applied in 2001 using a full factorial design consisting of two levels of burning and three levels of thinning, and included: unburned–unthinned (UN), unburned–overstory thinned (US), unburned–understory thinned (UC), burned–unthinned (BN), burned–understory thinned (BC), and burned–overstory thinned (BS). We measured soil respiration rate (SRR), soil moisture ( M S), soil temperature ( T S), and litter depth (LD) for three replicates of each of three dominant patch types (closed canopy, open canopy, and ceanothus shrub) within each of the six treatments ( n = 54). The same sampling points were measured from May to August in 2000 (pre-treatment) and in 2002, 2003, and 2004 (post-treatment). Within our sampling period there was as much as 37% variation ( p = 0.0005) between years in the undisturbed patches, which appeared to be driven by changes in precipitation. SRR also varied by year in all treated plots (US: p = 0.0516; UC: p = 0.0006; BN: p = 0.0158; and BC: p = 0.0040), with the exception of BS ( p = 0.3344). SRR response to disturbance varied with patch type, year, and treatment type. In most cases, burning and the combination of burning and thinning had less of an effect on mean SRR than thinning alone. Ceanothus patches appear to have recovered fastest, while treatment effects remained 3 years after thinning in closed canopy ( p = 0.0483 and 0.0333 in UC and US, respectively) and open canopy patches ( p = 0.0191 in US). Open canopy patches showed no response to any treatment aside from US. Both UC and US increased SRR in closed canopy and ceanothus patches, and US decreased SRR in open canopy patches. BS increased SRR in 2004 in closed canopy patches ( p = 0.0108), but no significant changes occurred in any patch type in response to BN or BC treatments. Across all treatments, the relationship of SRR with temperature, moisture, and litter depth changed in post-disturbance years. The results of this study can be used to help understand how management of Sierran mixed-conifer forests affects soil carbon sequestration.

The grassland–forest continuum: trends in ecosystem properties for woody plant mosaics?

Many ecosystems can be viewed as lying within a continuum between grassland and forest, where ground coverage by woody plants (trees and shrubs) ranges from non-existent to complete. Patterns of energy, water, and biogeochemistry are often heterogeneous between canopy patches beneath woody plants and the intercanopy patches that separate them. Notably, connectivity between patch types is produced by processes such as shading, root uptake of resources, and redistribution of runoff. Patch-scale connectivity is hypothesized to influence trends in energy, water, and biogeochemistry as a function of woody plant canopy coverage. When connectivity is strong, the mean for an ecosystem property is expected to change in a more curvilinear than linear fashion along the continuum. Associated variance is expected to be greatest not midway along the continuum, as might be expected, but rather at a site with substantially less than 50% canopy coverage. These hypotheses collectively provide a framework for future researc...

Neighborhood interactions influencing tree population dynamics in nonpyrogenous boreal forest in northern Finland

Open-canopy moss-rich woodlands dominated by Picea abies and Betula pubescens in northern Finland may undergo cyclic development with reciprocal replacement of the tree species due to the positive feedbacks on soil conditions. Although relations to the abiotic environment are well understood, intra- and interspecific interactions during development of sparse boreal forests have received less attention. We studied tree regeneration, growth and survival with respect to size and density of neighboring trees in four stands representing roughly four stages of the Picea–Betula forest cycle. We conducted spatial analysis (Ripley’s K-function) of mapped locations of live and dead stems to reconstruct the distribution of stems prior to mortality, and to infer possible causes of tree population decline. The prevalence of standing dead stems enabled us to test if mortality was associated with density and size of neighboring trees. Logistic regression was used to test for relationships between tree survival and local crowding indices. We also examined spatial autocorrelations of individual size characteristics to determine the mode and spatial extent of tree interactions. Picea abies had reduced recruitment in open areas occupied by mosses and dwarf-shrubs, and preferentially regenerated near B. pubescens, whereas B. pubescens formed small clumps (and occasionally these consisted entirely of stems from a single tree) that showed local repulsion from large P. abies trees. Size of neighboring trees was the primary determinant of individual growth and survival, whereas neighborhood density per se had only a weak effect. Picea abies had negatively correlated sizes among close neighbors (0–4 m radius) indicating that dominant trees suppress their smaller neighbors. Negative autocorrelations prevailed at the transition stages where the patches of smaller trees were concentrated around evenly spaced large trees. Tree sizes became spatially independent at the mature phase. We hypothesize that both low light and soil nutrient availability causes the P. abies population decline. Dominant trees in this high latitude forest have large light depletion zones and shallow root system to promote strong above- and below-ground competition with younger trees. Higher mortality rates within canopy patches were not compensated for by recruitment in gaps, causing P. abies population to decline steadily.

Effects of Vegetation Patches on Soil Nutrient Pools and Fluxes within a Mixed-Conifer Forest

Abstract At a spatially heterogeneous mixed-conifer forest in the central California Sierras, we quantified total carbon (C) and nitrogen (N), inorganic N, and net N mineralization in organic (O) and surface (0–15 cm) mineral soils, and in situ fluxes of inorganic N and ortho-phosphate using resin lysimeters under three patch types: closed canopy conifer, sparsely vegetated open canopy, and Ceanothuscordulatus thickets. In O horizons, total N and C pools ranked: closed canopy > Ceanothus > open canopy. In mineral soils, total N pools under Ceanothus exceeded those under closed canopy patches by about 30%. For 2 years, nitrate concentrations and rates of net N mineralization in O horizons were 4× greater under Ceanothus than under the other patch types. Similarly, ammonium concentrations and net N mineralization in mineral horizons were more than 80 and 200% greater, respectively, under Ceanothus than under the other patch types. In situ fluxes of nitrate were 4× greater beneath Ceanothus for 1 year, and no differences were found among the patch types for another year. Despite the interannual variability, our data suggest that Ceanothus contributes to a greater proportion of total N mineralized than based on cover alone, and may be important for forest nutrition under current conditions and after forest burning. FOR. SCI. 51(3):211–220.

Bryophyte (moss and liverwort) conservation under remnant canopy in managed forests

Management of forest for timber values presents potential threats for forest floor bryophytes, as localized disturbances are applied across landscapes. Dispersal limitation may exacerbate local extirpation, by preventing recolonization within a cut-block rotation period. Populations of forest floor bryophytes that persist under those patches of tree canopy remaining after clear-cutting could reduce dispersal distances and thereby contribute to conservation of species across the landscape. We examined bryophyte guilds (liverworts, forest-habitat mosses and colonist–pioneer mosses) and community composition in relation to habitat quality (microclimate and substrate) in five treatment classes in New Brunswick Acadian forest, 4 years after harvest. Four potential refugium classes with intact substrate were examined: three were characterized by remnant canopy height, one was treeless. These were compared to clear-cut areas with substrate disturbance. Microclimate (temperature, total daily photosynthetically active radiation and vapour pressure deficit) differed significantly between areas with and without remnant canopy, but differed little among refugium classes. This suggests that any remnant canopy moderates microhabitat relative to treeless areas. Liverworts and forest-habitat mosses were more frequent under remnant canopy than in open and clear-cut areas, with 25 species present only under remnant canopy. Environmental variation explained approximately 24% of bryophyte pattern, highlighting the potential influence of the pre-harvest community, which we could not document. In the absence of substrate disturbance, patches of remnant canopy provide potential refugia for some forest-habitat bryophytes. Characteristics of effective refugia (size and shape) should be determined by assessments of their impacts on: (i) change in bryophyte communities in refugia relative to natural dynamics and (ii) recolonization of adjacent areas.

Precipitation pulses and carbon fluxes in semiarid and arid ecosystems.

In the arid and semiarid regions of North America, discrete precipitation pulses are important triggers for biological activity. The timing and magnitude of these pulses may differentially affect the activity of plants and microbes, combining to influence the C balance of desert ecosystems. Here, we evaluate how a "pulse" of water influences physiological activity in plants, soils and ecosystems, and how characteristics, such as precipitation pulse size and frequency are important controllers of biological and physical processes in arid land ecosystems. We show that pulse size regulates C balance by determining the temporal duration of activity for different components of the biota. Microbial respiration responds to very small events, but the relationship between pulse size and duration of activity likely saturates at moderate event sizes. Photosynthetic activity of vascular plants generally increases following relatively larger pulses or a series of small pulses. In this case, the duration of physiological activity is an increasing function of pulse size up to events that are infrequent in these hydroclimatological regions. This differential responsiveness of photosynthesis and respiration results in arid ecosystems acting as immediate C sources to the atmosphere following rainfall, with subsequent periods of C accumulation should pulse size be sufficient to initiate vascular plant activity. Using the average pulse size distributions in the North American deserts, a simple modeling exercise shows that net ecosystem exchange of CO2 is sensitive to changes in the event size distribution representative of wet and dry years. An important regulator of the pulse response is initial soil and canopy conditions and the physical structuring of bare soil and beneath canopy patches on the landscape. Initial condition influences responses to pulses of varying magnitude, while bare soil/beneath canopy patches interact to introduce nonlinearity in the relationship between pulse size and soil water response. Building on this conceptual framework and developing a greater understanding of the complexities of these eco-hydrologic systems may enhance our ability to describe the ecology of desert ecosystems and their sensitivity to global change.

Effect of light availability on the carbon gain of beech (Fagus crenata) seedlings with reference to the density of dwarf bamboo (Sasa kurilensis) in an understory of Japan Sea type beech forest

AbstractIn the understory of Japan Sea type beech (Fagus crenata Bl.) forests, a beech seedling bank persists at the forest floor where the seedlings are shaded by dwarf bamboo (Sasa kurilensis Makino et Shibata). The culm density of dwarf bamboo is reduced by shading from the overstory. To determine the effect of the dwarf bamboo on the photosynthetic productivity of beech seedlings, we evaluated the leaf carbon gain of the beech seedlings with respect to the spatiotemporal variation in light regimes and CO2 concentration in a forest at Buna‐Daira, Fukushima Prefecture, central Japan. In midsummer, we measured photosynthetic photon flux density (PPFD) and air CO2 concentration (Camb) at the beech seedling height in the understory beneath the forest canopy with less dwarf bamboo, and in a canopy gap with dense dwarf bamboo. A frequency distribution of log10‐transformed PPFD showed that the mode PPFD class was greater beneath the closed canopy patch than in the gap (51–109 µmol/m2 per s vs 24–52 µmol/m2 per s), which was close to the estimated mean background PPFD (diffuse light) in each understory. The total sunfleck period during the midday hours and the mean PPFD of each sunfleck were also greater beneath the closed canopy than in the gap. From the diurnal course of PPFD and Camb, we simulated the midday carbon gain of beech seedlings using the CO2 assimilation (A)–PPFD and A–CO2 curves of beech leaves in the closed canopy patch. The total carbon gain of beech leaves beneath the canopy was 2.35‐fold greater than that in the gap, whether the simulation incorporated photosynthetic induction responses to sunflecks or not. High Camb at the forest floor (380–420 µmol/mol) enhanced the total carbon gain 1.12‐fold. The simulation indicated that an increase in diffuse light under sparse dwarf bamboo, which could accelerate the photosynthetic responses to sunflecks and high Camb, contributed to the photosynthetic carbon gain of beech leaves beneath the forest canopy. These findings suggest that the light environment of the understory can be determined by the effects of forest canopy structure on the density of understory dwarf bamboo and that the photosynthetic productivity of beech seedlings mainly depends on the diffuse light intensity.

Interaction between introduced rats and a frugivore bird-plant system in a relict island forest

The seed dispersal system formed by the fleshy-fruited shrub Viburnum tinus L. (Caprifoliaceae) and the bird Erithacus rubecula L. is known to occur in both the Mediterranean basin and the laurel forest of the Canary Islands. The latter is invaded by the ship rat Rattus rattus L. This situation allows (1) the comparison of oceanic island and mainland situations for the bird-plant interaction, and (2) quantification of the possible effects of an invading species on the plant, and thus on the whole seed dispersal system. Fruit removal by birds and rats was studied for V. tinus in a laurel forest of Tenerife during a fruiting season to assess patterns of disperser and predator's use of the plant. Fruits were persistent in time and spontaneous fruit loss rate was low. It was exploited by a reduced frugivorous community. Its fruits were dispersed almost exclusively by E. rubecula at extremely low rates, whereas R. rattus rapidly predated the bulk of the crops. Fruit removal by E. rubecula was influenced by vegetation structure and fruit crop size (higher removal rates from gaps or sparse and low canopy patches, and from larger fruit displays). Fruit predation by R. rattus was not related to microhabitat or individual plant traits. Fruit removal by R. rattus had no apparent influence on the pattern of bird frugivory. However, later in the fruiting season, heavy fruit depletion by rats restrained fruit availability for birds. The mainland (Mediterranean) V. tinus-E. rubecula dispersal system is strikingly different from this island counterpart in: (1) the virtual irrelevance of rodent seed predation, and (2) the comparatively high incidence of bird frugivory by the exclusive seed disperser, E. rubecula.

Temporal and Spatial Variation of Episodic Wind Erosion in Unburned and Burned Semiarid Shrubland

Redistribution of soil, nutrients, and contaminants is often driven by wind erosion in semiarid shrublands. Wind erosion depends on wind velocity (particularly during episodic, high-velocity winds) and on vegetation, which is generally sparse and spatially heterogeneous in semiarid ecosystems. Further, the vegetation cover can be rapidly and greatly altered due to disturbances, particularly fire. Few studies, however, have evaluated key temporal and spatial components of wind erosion with respect to (i) erosion rates on the scale of weeks as a function of episodic high-velocity winds, (ii) rates at unburned and burned sites, and (iii) within-site spatial heterogeneity in erosion. Measuring wind erosion in unburned and recently burned Chihuahuan desert shrubland, we found (i) weekly wind erosion was related more to daily peak wind velocities than to daily average velocities as consistent with our findings of a threshold wind velocity at approximately 7 m s(-1); (ii) greater erodibility in burned vs. unburned shrubland as indicated by erosion thresholds, aerodynamic roughness, and nearground soil movement; and (iii) burned shrubland lost soil from intercanopy and especially canopy patches in contrast to unburned shrubland, where soil accumulated in canopy patches. Our results are among the first to quantify post-fire wind erosion and highlight the importance of accounting for finer temporal and spatial variation in shrubland wind erosion. This finer-scale variation relates to semiarid land degradation, and is particularly relevant for predictions of contaminant resuspension and redistribution, both of which historically ignore finer-scale temporal and spatial variation in wind erosion.

Plant species effect on the spatial patterns of soil properties in the Mu-us desert ecosystem, Inner Mongolia, China

Although Artemisia ordosica Krasch. and Sabina vulgaris Ant. are the dominant shrub species in the Mu-us desert ecosystem, they differ in their botanical traits. We investigated the spatial patterns of soil properties using geostatistical analysis to examine the effect of plant species on these spatial patterns. Comparison among three microsite types (under A. ordosica, under S. vulgaris, and the opening between vegetation) showed that A. ordosica generally had less effect than S. vulgaris on local soil properties. The long life-span, prostrate life-form, and evergreen leaf-habit of S. vulgaris may lead to a higher accumulation of organic and fine materials under S. vulgaris. The range of spatial autocorrelation found in the mass of organic matter on the soil surface was smaller than that of the coverage of S. vulgaris (11.5 m) which corresponded to the canopy patch size of this species, and was longer than the canopy patch size of A. ordosica. The ranges of total C and N, and pH (11.7–15.6 m) were similar to that of S. vulgaris. The range of available P (106.3 m) was comparable to that of the coverage of A. ordosica (86.2 m) considered to be the scale of the distribution of this species. The ranges of silt+clay and exchangeable K, Ca, and Mg (31.0–46.7 m) were not related to plant presence, and were similar to that of topography (43.1 m).

Ecological Restoration of Coastal Sage Scrub and Its Potential Role in Habitat Conservation Plans.

Extensive acreage loss of coastal sage scrub (CSS), isolation of surviving stands, and the federal listing of several animal species with obligate relationships to this plant community, particularly the threatened California gnatcatcher (Polioptila californica), have led to attempts to create CSS to mitigate habitat lost to urban development and other causes. Many of these creations lie within habitat conservation plan (HCP) sites, and they could play a more prominent role by being repositories for plants taken from a single site having site-specific genetics. Among others, one technique that increases initial resemblance to natural stands uses digitized, to-scale photography, which has been ground-truthed to verify vascular plant associations, which appear as mosaics on a landscape. A combination of placing patches of salvaged, mature canopy plants within larger matrices of imprinted or container plant plots appears to significantly enhance immediate use by CSS obligate bird species, accelerate "spread" or expansion of CSS, and can also introduce many epiphytic taxa that otherwise would be slow or unable to occupy developing CSS creations. Reptile, amphibian, butterfly, and rodent diversity in a salvaged canopy restoration case study at the University of California, Irvine, showed CSS species foraging and inhabiting transplanted canopy patches. Using restoration techniques to expand existing CSS stands has more promise than creating isolated patches, and the creation of canopies resembling CSS mid-fire cycle stands is now common. Gnatcatchers and other birds use restorations for foraging and occasional nesting, and in some cases created stands along "biological corridors" appear to be useful to bird movement. Patches of transplanted sage scrub shrubs along habitat edges appear to break up linear edge effects. There are no data on which long-term survival, succession, or postfire behavior can be predicted for CSS restoration sites, and postfire community changes are not part of either mitigation or restoration planning at present. Long-term planning including burning is needed so that a fire-adapted habitat will develop. Restoration is important in retaining genetic resources, for ameliorating edge effects, as habitat extenders in buffer zones around HCP sites, and by providing areas into which natural stands can expand.