Vegetation Canopy Cover Research Articles

Evaluation of a Global Positioning System backpack transmitter for wild turkey research

AbstractRadiotelemetry is the standard method for monitoring wild turkey (Meleagris gallapavo) movements and habitat use. Spatial data collected using telemetry‐based monitoring are frequently inaccurate due to triangulation error. However, new technology, such as Global Positioning Systems (GPS) has increased ecologists' ability to accurately evaluate animal movements and habitat selection. We evaluated the efficacy of micro‐GPS backpack units for use on wild turkeys. We tested a micro‐GPS developed specifically for avian species that incorporated a GPS antenna with a lightweight rechargeable battery and a very high frequency (VHF) transmitter. We conducted a series of static tests to evaluate performance in varying types of vegetative canopy cover and terrain. After static testing, we deployed micro‐GPS on 8 adult male Rio Grande wild turkeys (M. g. intermedia) trapped in south Texas and 2 adult females trapped in the Texas panhandle. Micro‐GPS units collected 26,439 locations out of 26,506 scheduled attempts (99.7% fix rate) during static testing. Mean distance error across all static tests was 15.5 m (SE = 0.1). In summer 2009, we recovered micro‐GPS from 4 tagged males and both females to evaluate data collection. Units on males acquired approximately 2,500 locations over a 65‐day test period (94.5% fix rate). We recovered units from the 2 females after 19 days and 53 days; those units acquired 301 and 837 locations, respectively, for a 96% fix rate. Cost analysis indicated that VHF will be cost effective when 1 location per day is required up to 181 days, but micro‐GPS becomes less expensive as frequency of daily locations increases. Our results indicate that micro‐GPS have the potential to provide increased reliable data on turkey movement ecology and habitat selection at a higher resolution than conventional VHF telemetric methods. © 2011 The Wildlife Society.

Restoration of Ecosystem Carbon Stocks Following Exclosure Establishment in Communal Grazing Lands in Tigray, Ethiopia

Degraded lands are common in human‐influenced tropical semiarid areas, and the potential for C sequestration through rehabilitation of these areas is substantial. In this study, we investigated changes in ecosystem C stocks (ECS) after establishing exclosures on degraded communal grazing lands, and identified easily measurable biophysical and management‐related factors that can be used to predict ECS restoration in the highlands of Tigray, Ethiopia. We selected replicated (n = 3) 5‐, 10‐, 15‐, and 20‐yr‐old exclosures and paired each exclosure with an adjacent communal grazing land. All exclosures displayed higher ECS than the communal grazing lands. Differences in ECS between exclosures and grazing lands varied between 29 (±4.9) and 61 (±6.7) Mg C ha−1 and increased with exclosure duration. In exclosures, much of the variability in ECS was explained by a combination of the following variables: precipitation, clay content, vegetation canopy cover, woody biomass, and exclosure duration (R2 = 0.77–0.90). Precipitation and vegetation canopy cover also explained much of the variability of ECS in communal grazing lands (R2 = 0.48–0.55). Our results help to establish baseline information for C sequestration projects and to predict the expected ecosystem C sequestration under exclosures. Expansion of exclosures would increase grazing pressure on the remaining communal grazing area. Therefore, the decision to establish additional exclosures should also include an economic analysis and an evaluation of the social consequences.

The spatial extent of termite influences on herbivore browsing in an African savanna

Termite mounds form islands of fertility in savanna landscapes and create foraging hotspots for herbivores, but the magnitude and spatial extent of these influences is unknown. We mapped terrain, termite mound and woody vegetation three-dimensional (3-D) structure at 56 cm resolution across a large-scale (254 ha), long-term (34 years) herbivore exclusion experiment in the Kruger National Park, with the Carnegie Airborne Observatory (CAO). We compared vegetation 3-D structure in areas protected from herbivores with those accessible to herbivores, both on termite mounds and in the landscape matrix between termite mounds. Termite mound density was 1.1 ha −1 across the study area and mound size did not differ between protected and accessible areas. Woody vegetation canopy cover was ∼100% greater on protected than accessible mounds, but was only ∼20% greater in the protected inter-mound matrix when compared to the accessible matrix. Woody canopy height class distributions differed significantly between protected and accessible areas, with the tallest vegetation (>10 m) occurring on protected termite mounds. The impacts of herbivore browsing were evident at distances of up to 20 m from termite mound centres. Spatial analysis of mound distribution revealed that the sphere of termite mound influence constitutes ∼20% of the total landscape. Termite influences on herbivore browsing operate at scales much larger than the spatial extent of their mound building activities.

Estimating vegetation height and canopy cover from remotely sensed data with machine learning

High quality information on forest resources is important to forest ecosystem management. Traditional ground measurements are labor and resource intensive and at the same time expensive and time consuming. For most of the Slovenian forests, there is extensive ground-based information on forest properties of selected sample locations. However there is no continuous information of objectively measured vegetation height and canopy cover at appropriate resolution. Currently, Light Detection And Ranging (LiDAR) technology provides detailed measurements of different forest properties because of its immediate generation of 3D data, its accuracy and acquisition flexibility. However, existing LiDAR sensors have limited spatial coverage and relatively high cost of acquisition. Satellite data, on the other hand, are low-cost and offer broader spatial coverage of generalized forest structure, but are not expected to provide accurate information about vegetation height. Integration of LiDAR and satellite data promises to improve the measurement, mapping, and monitoring of forest properties. The primary objective of this study is to model the vegetation height and canopy cover in Slovenia by integrating LiDAR data, Landsat satellite data, and the use of machine learning techniques. This kind of integration uses the accuracy and precision of LiDAR data and the wide coverage of satellite data in order to generate cost-effective realistic estimates of the vegetation height and canopy cover, and consequently generate continuous forest vegetation map products to be used in forest management and monitoring. Several machine learning techniques are applied to this task: they are evaluated and their performance is compared by using statistical significance tests. Ensemble methods perform significantly better than single- and multi-target regression trees and are further used for the generation of forest maps. Such maps are used for land-cover and land-use classification, as well as for monitoring and managing ongoing forest processes (like spontaneous afforestation, forest reduction and forest fires) that affect the stability of forest ecosystems.

Stream Temperature Response to Three Riparian Vegetation Scenarios by Use of a Distributed Temperature Validated Model

Elevated in-stream temperature has led to a surge in the occurrence of parasitic intrusion proliferative kidney disease and has resulted in fish kills throughout Switzerland's waterways. Data from distributed temperature sensing (DTS) in-stream measurements for three cloud-free days in August 2007 over a 1260 m stretch of the Boiron de Merges River in southwest Switzerland were used to calibrate and validate a physically based one-dimensional stream temperature model. Stream temperature response to three distinct riparian conditions were then modeled: open, in-stream reeds, and forest cover. Simulation predicted a mean peak stream temperature increase of 0.7 °C if current vegetation was removed, an increase of 0.1 °C if dense reeds covered the entire stream reach, and a decrease of 1.2 °C if a mature riparian forest covered the entire reach. Understanding that full vegetation canopy cover is the optimal riparian management option for limiting stream temperature, in-stream reeds, which require no riparian set-aside and grow very quickly, appear to provide substantial thermal control, potentially useful for land-use management.

Soil erosion and runoff in different vegetation patches from semiarid Central Mexico

article i nfo Vegetation patches in arid and semiarid areas are important in the regulation of surface hydrological processes. Canopy and ground covers developed in these fertility islands are a natural cushion against the impact energy of rainfall. Also, greater levels of organic matter improve the soil physicochemical properties, promoting infiltration and reducing runoff and soil erosion in comparison with the open spaces between them. During the 2006 rainy season, four USLE-type plots were installed around representative vegetation patches with predominant individual species of Huisache (Acacia sp), Mesquite (Prosopis sp), Prickly Pear or Nopal (Opuntia sp) and Cardon (Opuntia imbricata), to evaluate soil erosion and runoff, in semiarid Central Mexico. A comparative bare surface condition (Control) was also evaluated. Vegetative canopy and ground cover were computed using digital images. Selected soil parameters were determined. Soil erosion was different for the studied vegetation conditions, decreasing as canopy and ground cover increased. There were not significant differences in runoff and soil erosion between the Control and O. imbricata surfaces. Runoff was reduced by 87%, 87% and 98% and soil loss by 97%, 93%, and 99% for Acacia farnesiana, Prosopis laevigata and Opuntia sp, respectively, as compared to the Control. Soil surface physical conditions were different between the low vegetation cover conditions (Control and O. imbricata surfaces) and the greater vegetation cover conditions (A. farnesiana, P. laevigata and Opuntia sp), indicating a positive effect of vegetation patches on the regulation of surface hydrological processes.

Interaction of geomorphic and ecologic features across altitudinal zones in a subarctic landscape

Vegetation is often considered to stabilize geomorphic processes. An increasing abundance of vegetation may cause negative feedbacks within a periglacial system. In this study, we explored the importance of vegetation on the occurrence of active cryoturbation-dominated feature fields in subarctic Finland on a landscape scale. The vegetation–cryoturbation interaction was studied across three altitudinal zones by applying hierarchical partitioning (HP) and variation partitioning (VP) methods that overcome collinearity problems in multivariate analysis. Firstly, our results showed that vegetation factors, especially the canopy cover of the field-layer vegetation and the total above ground biomass, were among the most important environmental variables affecting the occurrence of active cryoturbation features. Moreover, vegetation factors were for the most part positively associated with cryoturbation. Under the predicted global warming, the ‘greening’ of arctic and subarctic regions may, therefore, decrease and also increase the activity of the periglacial processes in sparsely vegetated terrain. Secondly, our analyses gave contrasting results of the environmental factors of the periglacial processes across altitudinal zones, although the relative importance of the vegetation group was rather constant throughout the zones. Thus, we stress the importance of the spatial study setting in geomorphic studies in topographically varying relief. We recommend either taking the altitudinal zonation of the landscape into consideration or studying the features within a predetermined zone to decrease misinterpretations in environment–process relationships. Methodologically, our results encourage wider applications of partitioning methods in multivariate settings in geomorphology.

Characterizing forest succession with lidar data: An evaluation for the Inland Northwest, USA

Quantifying forest structure is important for sustainable forest management, as it relates to a wide variety of ecosystem processes and services. Lidar data have proven particularly useful for measuring or estimating a suite of forest structural attributes such as canopy height, basal area, and LAI. However, the potential of this technology to characterize forest succession remains largely untested. The objective of this study was to evaluate the use of lidar data for characterizing forest successional stages across a structurally diverse, mixed-species forest in Northern Idaho. We used a variety of lidar-derived metrics in conjunction with an algorithmic modeling procedure (Random Forests) to classify six stages of three-dimensional forest development and achieved an overall accuracy > 95%. The algorithmic model presented herein developed ecologically meaningful classifications based upon lidar metrics quantifying mean vegetation height and canopy cover, among others. This study highlights the utility of lidar data for accurately classifying forest succession in complex, mixed coniferous forests; but further research should be conducted to classify forest successional stages across different forests types. The techniques presented herein can be easily applied to other areas. Furthermore, the final classification map represents a significant advancement for forest succession modeling and wildlife habitat assessment.

Is 'vegetation thickening' occurring in Queensland's mulga lands? A 50-year aerial photographic analysis

Changes in the density of woody vegetation in arid and semiarid rangelands have the potential to dramatically reduce productivity as well as adversely affect ‘natural’ ecosystem processes. Many parts of Australia are believed to have experienced thickening of woody vegetation since European occupation and the associated changes to fire and grazing regimes that followed. Unfortunately there is little empirical evidence to support a widely held perception of thickening. This study analyses the available historical aerial photographic coverage for the mulga lands bioregion of south-western Queensland, Australia; a record spanning the second half of the twentieth century. Changes in woody vegetation canopy cover were assessed for 190 sites. More than half of the sites had no evidence of mechanical disturbance and thus reflected general, or background trends in woody vegetation cover. The region-wide average extent of change on these undisturbed sites was estimated to be approximately a 3.6% increase in canopy cover over the study period. Thus, a trend toward vegetation thickening was detected. However, large variation was observed depending on the land systems and rainfall zone where sites were located. The results are discussed in the context of century scale climate variability and perceptions of vegetation change and a tentative explanatory model is presented to account for the observed data.

Effects of Livestock Grazing on Vegetation Composition and Soil Moisture Properties in Grazed and Non-Grazed Range Site

Studies of vegetation and soil dynamics on grazed and non-grazed rangelands are important prerequisites for improving range management. For this reason, the effects of excluding grazing animals for 26 years were studied on vegetation and soil dynamics at two rangeland condition sites (enclosure and exclosure) in Isfahan province, Iran. The vegetation cover and edaphic characteristics were studied simultaneously in both grazed and non-grazed range sites. In this study vegetation characteristics, as well as vegetation floristic, canopy cover, plant density, botanical composition, plant biodiversity and soil moisture infiltration were recorded during the grazing seasons of 2006 to 2007. Vegetation characteristics, in particular vegetation cover and plant density, differed significantly between the non-grazed (enclosed) and grazed sites and increased significantly in the non-grazed range site. The vegetation cover in the non-grazed site consisted mainly of class I and II plants while class III plants predominated in the grazed site. There was no significant difference in the botanical composition of the two areas. There was a significant increase in Gramineae in the enclosure site compared to the SWTOllllding grazed site, but there was a considerable decrease in forb species. We also observed a significant decrease in soil infiltration rates in the grazed range site compared to the enclosed range site. Litter content was higher inside and exposed bare soil greater outside the enclosure. Infiltration rates were higher in the enclosed area than in the grazed exclosure area throughout the grazing season. A comparison of vegetation and soil infiltration within the enclosure showed that vegetation condition and soil infiltration were good and that removal of grazing animals, as in the enclosure, causes an improvement in rangeland condition in this region.

Impacts of Overgrazing in a Long Term Traditional Grazing Ecosystem on Vegetation Around Watering Points in a Semi-Arid Rangeland of North-Eastern Iran

In this study, the effects of livestock overgrazing on vegetation of the critical area around livestock watering points in a traditional grazing ecosystem was investigated on a semi-arid rangeland in North-East of Iran. Transects were placed in 8 geographical directions around watering points and samples were taken systematically. In each experimental plot, 4 m2, percentage of canopy cover, abundance, density and species richness of vegetation were calculated. The results of this study showed that the percentage of canopy cover, density and species richness were changed with distance from watering points. Critical area immediately adjacent to watering points was dominated by unpalatable Peganum harmala and contained of ruderal species such as Sophora sp. Adjacent to this was a zone dominated by species of low palatability such as Acantholimon sp. and Hulthemia persica. In areas most distant from watering points relative importance of moderately palatable species such as Artemisia herba-alba increased. These results show the negative impacts of overgrazing on vegetation and palatability in a traditional grazing ecosystem, which may indicate the necessity of a monitoring programme, to manage livestock grazing and watering points in North-East of Iran.

Rethinking Avian Response toTamarixon the Lower Colorado River: A Threshold Hypothesis

AbstractMany of the world’s large river systems have been greatly altered in the past century due to river regulation, agriculture, and invasion of introducedTamarixspp. (saltcedar, tamarisk). These riverine ecosystems are known to provide important habitat for avian communities, but information on responses of birds to differing levels ofTamarixis not known. Past research on birds along the Colorado River has shown that avian abundance in general is greater in native than in non‐native habitat. In this article, we address habitat restoration on the lower Colorado River by comparing abundance and diversity of avian communities at a matrix of different amounts of native and non‐native habitats at National Wildlife Refuges in Arizona. Two major patterns emerged from this study: (1) Not all bird species responded toTamarixin a similar fashion, and for many bird species, abundance was highest at intermediateTamarixlevels (40–60%), suggesting a response threshold. (2) InTamarix‐dominated habitats, the greatest increase in bird abundance occurred when small amounts of native vegetation were present as a component of that habitat. In fact,Tamarixwas the best vegetation predictor of avian abundance when compared to vegetation density and canopy cover. Our results suggest that to positively benefit avian abundance and diversity, one cost‐effective way to rehabilitate larger monocultureTamarixstands would be to add relatively low levels of native vegetation (∼20–40%) within homogenousTamarixhabitat. In addition, this could be much more cost effective and feasible than attempting to replace allTamarixwith native vegetation.

Rapid assessment of habitat quality in riparian rainforest vegetation

GIS and aerial photographic techniques were applied to assessing riparian vegetation quality in an agricultural landscape formerly covered in lowland rainforest. Canopy cover and width of woody riparian vegetation, both easily determined from remotely sensed data, were investigated as indicators of riparian quality. High correlations between field measurements of canopy cover and width of woody riparian vegetation with several other vegetation attributes indicative of vegetation quality (weed abundance, debris, human disturbance, native species richness) demonstrated that these two habitat attributes were suitable field vegetation quality surrogates. Desktop quality analysis combined GIS measurement of riparian width with aerial photographic analysis of canopy cover. Desktop quality equalled field quality in 78% of cases, with a further 13% showing errors due to clearing or thickening of vegetation after aerial photographs were taken. Bird communities in higher vegetation quality areas comprised mainly rainforest-dependent species, whereas poor quality areas mostly supported birds of open habitats. Bird community diversity and rainforest-dependent bird diversity increased significantly both with increasing levels of canopy cover and greater riparian width, but a combination of these factors explained more variance than each factor separately. Desktop riparian vegetation quality therefore proved a satisfactory indicator of habitat quality for birds in rainforest riparian zones. This quick and efficient desktop method of riparian habitat quality assessment can determine conservation values of rainforest riparian areas with minimal field validation, thereby allowing more effective targeting of appropriate management practices, identification of areas of conservation concern and prioritisation of revegetation and rehabilitation efforts.

Ecosystem impacts of disturbance in a dry tropical forest in southern India

AbstractIndian forests provide a multitude of services to vast populations. Common human activities including livestock grazing, fuelwood extraction and burning have the potential to impact forest ecosystem structure and function. The effects of these activities on vegetation, ecology and soil properties were investigated in Bandipur National Park (BNP) in southern India. Data were collected from 200 sites in four watersheds within the park. Sample sites spanned a degradation gradient measured by a field disturbance index (FDI). This paper focusses on the impacts on vegetation structure, diversity and composition, and integrates impacts on soil. Shrub and tree species were inventoried and evaluated in plots 10‐m in diameter. The tree layer was dominated by Anogeissus–Emblica–Tectona species. The understory was dominated by invasives Chromolaena odorata and Lantana camara, and native Gymnosporia emarginata. Vegetation plot heights, canopy cover and tree diameters were negatively correlated with field disturbance resulting in stunted forest stature in degraded sites. Vegetation composition in degraded watersheds was dominated by small woody tree species and a greater diversity of shrub species. Ordination analysis was used to integrate soil data with vegetation and disturbance, revealing that deciduous forest in the park is degrading to scrub forest along with negative impacts on soil characteristics. Consequences of services currently enjoyed by local populations are discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Differentiating wheat varieties with different leaf angle distributions using NDVI and canopy cover

Ten winter wheat varieties (Triticum aestivum L.) with different leaf angle distributions (LAD) were used in this experiment. Results showed that varieties with planophile LAD had a leaf orientation value (LOV) ranging from 25.12 to 40.33 while varieties with erectophile LAD had LOV ranging from 67.5 to 73.25. The canopy spectral reflectance was measured using a ground‐based spectroradiometer. Normalised difference vegetation index (NDVI) and canopy cover were compared for the two types. The results indicate that at the jointing stage, the planophile varieties presented higher canopy spectral reflectance than the erectophile ones in the near infrared region. However, in the visible wavebands, the erectophile varieties had higher reflectances than the planophile ones. The difference between the two types was greatest at the jointing stage for canopy spectral reflectance, NDVI and canopy cover. Discriminant analysis validated the results that simultaneous measurements of NDVI and cover can be used to differentiate leaf angle distribution of wheat at the jointing stage.

Evaluation of Herbicides for Restoring Native Grasses in Buffelgrass‐Dominated Grasslands

Abstract Buffelgrass (Pennisetum ciliare) is an exotic grass that threatens arid and semiarid ecosystems. The objective of this study was to determine effectiveness of several herbicides at reducing competition from buffelgrass to enhance establishment of planted native grasses. In Duval County, Texas, plots were delineated in two experiments in a buffelgrass‐dominated pasture and mowed on 2 September 2002. On 18 September 2002 and 7 October 2002, a 41% glyphosate (N‐(phosphonomethyl) glycine) herbicide was applied to all plots. A mixture of three native grasses—green sprangletop (Leptochloa dubia), plains bristlegrass (Setaria leucopila), and four‐flower trichloris (Chloris pluriflora)—was planted on 8 October 2002. On 9 October 2002, 1.12 and 2.24 kg/ha of a 80% tebuthiuron (N‐[5‐(1,1‐dimethyethyl)‐1,3,4‐thiadiazol‐2‐yl]‐N,N’‐dimethylurea) herbicide was applied preemergence to the first experiment, and all other herbicides were applied postemergence on 27 July 2003 to the second experiment. Percent canopy cover of vegetation was estimated with a 20 × 50–cm sampling frame during April, June, and October 2003 and August 2004. Postemergent herbicides had no significant effect on canopy cover of buffelgrass or planted species (p≥ 0.05). Canopy cover of native grasses did not exceed 8% on any treatment or sampling date, and buffelgrass cover returned to pre‐treatment conditions in less than 1 year; however, the 2.24 kg/ha rate of tebuthiuron suppressed (p < 0.05) canopy cover of buffelgrass compared with controls and increased (p < 0.05) native grasses almost 2 years past application. Tebuthiuron may have potential value in reducing buffelgrass canopy cover and increasing cover of native grasses, particularly Chloris spp.

Post-Fire Burn Severity and Vegetation Response Following Eight Large Wildfires Across the Western United States

Vegetation response and burn severity were examined following eight large wildfires that burned in 2003 and 2004: two wildfires in California chaparral, two each in dry and moist mixed-conifer forests in Montana, and two in boreal forests in interior Alaska. Our research objectives were: 1) to characterize one year post-fire vegetation recovery relative to initial fire effects on the soil surface that could potentially serve as indicators of vegetation response (and thus, ultimately longer-term post-fire ecosystem recovery), and 2) to use a remotely-sensed indicator of burn severity to describe landscape patterns in fire effects. We correlated one-year post-fire plant species richness and percent canopy cover to burn severity and to soil surface cover immediately after the fires. For all eight wildfires, plant canopy cover and species richness were low and highly variable one year post-fire. We found a greater number of forbs when compared to other plant life forms, independent of burn severity. Plant cover was dominated by grasses in chaparral systems, by forbs in mixed-conifer forests, and by shrubs in boreal forests, similar to the unburned vegetation. Fine-scale variability in post-fire effects on soils, the diversity of pre-fire vegetation, and the resilience of plants to fire likely explain the high variation observed in post-fire vegetation responses across sites and burn severities. On most low and moderate burn severity sites, >30% of the soil surface was covered with organic material immediately post-fire, and one year later, the canopy cover of understory vegetation averaged 10% or more, suggesting low risk to post-fire erosion. In California chaparral and the two Montana mixed conifer sites, 5% or less of the area within the fire perimeter burned with high severity, while in Alaska, 58% was mapped as high burn severity; we think this is characteristic in Alaska, but uncharacteristic of chaparral fires, especially given the high proportion of non-native species post-fire in our chaparral sites. All fires had a mosaic of different burn severities (as indicated by delta Normalized Burn Ratio, dNBR) with highly variable patch size (mean 1.3 ha to 14.4 ha, range from <1 ha to over 100,000 ha).

View angle effects on relationships between MISR vegetation indices and leaf area index in a recently burned ponderosa pine forest

While nadir-viewing passive multispectral sensors have limited utility for characterizing the full dimensionality of forest canopies, multi-angle remote sensors such as the Multi-angle Imaging SpectroRadiometer (MISR) may improve detection of canopy architecture, canopy cover, and leaf area index (LAI) of forest canopy versus understory vegetation. Our objective was to determine whether data from the MISR sensor could improve estimates of LAI across a post-fire ponderosa pine forest located in the Black Hills of South Dakota. We measured LAI during the 2002 and 2003 growing seasons and created continuous LAI maps using Landsat TM and ETM+ data (mean R 2 = 0.81). We fit linear regression models of total and canopy LAI, using a series of MISR at-nadir and off-nadir or anisotropic vegetation indices as predictor variables, for each of five sampling periods. We found the best LAI model fits using either a new hotspot-adjusted normalized difference vegetation index, NDVI HS, NDVI calculated from the − 60° view angle, or NDVI at-nadir and either the Hotspot–DarkSpot Index (HDS) or the normalized difference anisotrophic index (NDAX) ( R 2 = 0.56–0.91). However, differences in fits of these best models and those including NDVI at-nadir ranged from only 1 to 8%. Reflectance anisotropy patterns related strongly to understory vegetation phenology. We found that the relationships among NDVI or the enhanced vegetation index (EVI) and canopy or total LAI showed little variation across view angles when the understory vegetation was senesced and significant anisotropy when understory green LAI was greatest. These findings demonstrate the value of multi-temporal measurements during periods of understory phenological change, even if the overstory LAI is relatively stable. We also evaluated the performance of the MISR LAI product and found moderate fits between the MISR LAI and our field- and Landsat-derived canopy LAI ( R 2 = 0.21–0.44).

Establishing Vegetation on Migrating Inland Sand Dunes in Texas

Migration of sand dunes damages range improvements in the Texas Coastal Sand Plain. We determined effects of mulching with native prairie hay and an open weave geotextile fabric, seeding, fertilization, and transplanting on plant species canopy cover on inland sand dunes. We compared applying native hay vs. a synthetic geotextile material to inhibit wind erosion, seeding ‘Alamo’ switchgrass (Panicum virgatum L.), ‘Mason’ sandhill lovegrass (Eragrostis trichodes [Nutt.] Wood), and partridge pea (Chamaecrista fasciculata [Michx.] Greene) vs. no seeding, and fertilization with 468 kg·ha−1 of 45:45:90 (N:P:K) vs. no fertilization. The same treatments were compared in a second experiment except that switchgrass, sandhill lovegrass, vetiver (Vetiveria zizanoides [L.] Nash ex Small), and giant reed (Arundo donax L.) were transplanted rather than seeded. Treatments were applied during March and April 1994 and canopy cover of vegetation in each experimental unit was estimated in October 1994, 1995, and 2004. Livestock were excluded from the study sites. The geotextile fabric degraded within 4 months and was replaced with coastal Bermuda (Cynodon dactylon [L.] Pers.) hay. Fertilization plus native hay mulch resulted in greater (P < 0.05) canopy cover of purple sandgrass (Triplasis purpurea [Walt.] Chapm.), sandbur (Cenchrus incertus M. A. Curtis and C. echinatus L.), and snakecotton (Froelichia spp.) than other treatments in 1994. In 1994 and 1995, canopy cover of switchgrass and sandhill lovegrass was greater (P < 0.05) with a combination of geotextile fabric and commercial hay, seeding, and fertilization than in other treatments. Vegetation composition and canopy cover were similar (P > 0.05) across treatments in 2004 in both experiments. Fertilization, seeding, and transplanting appear unnecessary to establish vegetation on dunes protected from livestock grazing when mulch is applied to inhibit sand movement. El movimiento de dunas de arena perjudica las prácticas de mejoramiento de agostaderos en la región del Texas Coastal Sand Plain. El objetivo del presente estudio fue determinar los efectos del acolchado con heno de pastos nativos y una malla textil además de la fertilización, trasplante, y siembra directa sobre la cobertura aérea de la vegetación en las dunas. Se comparó la malla textil contra el uso de heno para evitar la erosión eólica, la siembra directa de ‘Alamo’ switchgrass (Panicum virgatum L.), ‘Mason’ sandhill lovegrass (Eragrostis trichodes [Nutt.] Wood), y partridge pea (Chamaecrista fasciculata [Michx.] Greene) contra no siembra, y la fertilización con 468 kg·ha−1 de 45:45:90 (N:P:K) contra no fertilización. Los mismos tratamientos se compararon en un segundo experimento con la excepción de que se trasplantaron switchgrass, sandhill lovegrass, vetiver (Vetiveria zizanoides [L.] Nash ex Small), y carrizo (Arundo donax L.) en lugar de sembrados directamente. Los tratamientos se aplicaron en Marzo y Abril de 1994 y la cobertura aérea de la vegetación en cada unidad experimental se estimó en Octubre de 1994, 1995, y 2004. Los sitios se mantuvieron excluidos de pastoreo. La malla textil se degradó en los primeros 4 meses del estudio y se reemplazo con heno de zacate Bermuda (Cynodon dactylon [L.] Pers.). La fertilización en combinación con el acolchado con heno de pastos nativos presentó la cobertura aérea mas alta (P < 0.05) de purple sandgrass (Triplasis purpurea [Walt.] Chapm.), sandbur (Cenchrus incertus M. A. Curtis y C. echinatus L.), y snakecotton (Froelichia spp.) comparado con el resto de los tratamientos en 1994. En 1994 y 1995 la cobertura aérea de switchgrass y sandhill lovegrass fue mas alta (P < 0.05) en la combinación de malla textil, siembra directa, y fertilización comparado con el resto de los tratamientos. La composición de la vegetación y la cobertura aérea fueron similares (P > 0.05) entre tratamientos en 2004 en ambos experimentos. La fertilización, siembra directa, y el trasplante son aparentemente innecesarios para establecer vegetación en las dunas protegidas del pastoreo de ganado cuando se utiliza el acolchado para inhibir el movimiento de las dunas.

English

A model of soil erosion and sediment transport on hillslopes is used to illustrate the role of process understanding in determining dominant processes as a function of spatial scale. Erosion and sediment yield from hillslopes are primarily determined by surface runoff, topography, vegetative canopy cover, ground surface cover, soil erodibility, and sediment properties. In areas where winter processes (snow, snowmelt, soil frost, etc.) are important, erosion and sediment yield also determined by these factors. The Hillslope Erosion Model (HEM) incorporates these factors in simulating erosion and sediment yield. The world's largest rainfall simulator database for arid and semiarid areas and data from small hillslope-scale watersheds are used to calibrate and validate the spatially distributed, processed-based HEM. Spatially distributed estimates of sediment transport and yield along hillslopes from the HEM are used with an understanding of dominant processes as a function of spatial scale as the scientific basis to determine stability of slopes at plot to hillslope scales. Interrill processes of raindrop splash and thin sheetflow transport are diffusive. Concentrated flow (rill erosion) processes are advective. Spatial loci of transition from diffusive to advective processes are inherently zones of landscape instability and channel formation. The HEM is used to define these areas of instability on hillslopes. Stability criteria for hillslopes are in turn used as criteria for geomorphic designs. Field data taken on a mine rehabilitation site in Queensland, Australia and at the Yakima Training Center in Washington State were used to extend the erosion model to disturbed site rehabilitation problems. These example applications from natural and designed slopes are used to illustrate model predictions and their applications in scaling and geomorphic designs.