Vegetation Stature Research Articles

Use of principal components of UAV-acquired narrow-band multispectral imagery to map the diverse low stature vegetation fAPAR

The fraction of absorbed photosynthetically active radiation (fAPAR) is an important plant physiological index that is used to assess the ability of vegetation to absorb PAR, which is utilized to sequester carbon in the atmosphere. This index is also important for monitoring plant health and productivity, which has been widely used to monitor low stature crops and is a crucial metric for food security assessment. The fAPAR has been commonly correlated with a greenness index derived from spaceborne optical imagery, but the relatively coarse spatial or temporal resolution may prohibit its application on complex land surfaces. In addition, the relationships between fAPAR and remotely sensed greenness data may be influenced by the heterogeneity of canopies. Multispectral and hyperspectral unmanned aerial vehicle (UAV) imaging systems, conversely, can provide several spectral bands at sub-meter resolutions, permitting precise estimation of fAPAR using chemometrics. However, the data pre-processing procedures are cumbersome, which makes large-scale mapping challenging. In this study, we applied a set of well-verified image processing protocols and a chemometric model to a lightweight, frame-based and narrow-band (10 nm) UAV imaging system to estimate the fAPAR over a relatively large cultivated land area with a variety of low stature vegetation of tropical crops along with native and non-native grasses. A principal component regression was applied to 12 bands of spectral reflectance data to minimize the collinearity issue and compress the data variation. Stepwise regression was employed to reduce the data dimensionality, and the first, third and fifth components were selected to estimate the fAPAR. Our results indicate that 77% of the fAPAR variation was explained by the model. All bands that are sensitive to foliar pigment concentrations, canopy structure and/or leaf water content may contribute to the estimation, especially those located close to (720 nm) or within (750 nm and 780 nm) the near-infrared spectral region. This study demonstrates that this narrow-band frame-based UAV system would be useful for vegetation monitoring. With proper pre-flight planning and hardware improvement, the mapping of a narrow-band multispectral UAV system could be comparable to that of a manned aircraft system.

Ideas and perspectives: how coupled is the vegetation to the boundary layer?

Abstract. Understanding the sensitivity of transpiration to stomatal conductance is critical to simulating the water cycle. This sensitivity is a function of the degree of coupling between the vegetation and the atmosphere and is commonly expressed by the decoupling factor. The degree of coupling assumed by models varies considerably and has previously been shown to be a major cause of model disagreement when simulating changes in transpiration in response to elevated CO2. The degree of coupling also offers us insight into how different vegetation types control transpiration fluxes, which is fundamental to our understanding of land–atmosphere interactions. To explore this issue, we combined an extensive literature summary from 41 studies with estimates of the decoupling coefficient estimated from FLUXNET data. We found some notable departures from the values previously reported in single-site studies. There was large variability in estimated decoupling coefficients (range 0.05–0.51) for evergreen needleleaf forests. This is a result that was broadly supported by our literature review but contrasts with the early literature which suggests that evergreen needleleaf forests are generally well coupled. Estimates from FLUXNET indicated that evergreen broadleaved forests were the most tightly coupled, differing from our literature review and instead suggesting that it was evergreen needleleaf forests. We also found that the assumption that grasses would be strongly decoupled (due to vegetation stature) was only true for high precipitation sites. These results were robust to assumptions about aerodynamic conductance and, to a lesser extent, energy balance closure. Thus, these data form a benchmarking metric against which to test model assumptions about coupling. Our results identify a clear need to improve the quantification of the processes involved in scaling from the leaf to the whole ecosystem. Progress could be made with targeted measurement campaigns at flux sites and greater site characteristic information across the FLUXNET network.

Near‐surface turbulence as a missing link in modeling evapotranspiration‐soil moisture relationships

AbstractDespite many efforts to develop evapotranspiration (ET) models with improved parametrizations of resistance terms for water vapor transfer into the atmosphere, estimates of ET and its partitioning remain prone to bias. Much of this bias could arise from inadequate representations of physical interactions near nonuniform surfaces from which localized heat and water vapor fluxes emanate. This study aims to provide a mechanistic bridge from land‐surface characteristics to vertical transport predictions, and proposes a new physically based ET model that builds on a recently developed bluff‐rough bare soil evaporation model incorporating coupled soil moisture‐atmospheric controls. The newly developed ET model explicitly accounts for (1) near‐surface turbulent interactions affecting soil drying and (2) soil‐moisture‐dependent stomatal responses to atmospheric evaporative demand that influence leaf (and canopy) transpiration. Model estimates of ET and its partitioning were in good agreement with available field‐scale data, and highlight hidden processes not accounted for by commonly used ET schemes. One such process, nonlinear vegetation‐induced turbulence (as a function of vegetation stature and cover fraction) significantly influences ET‐soil moisture relationships. Our results are particularly important for water resources and land use planning of semiarid sparsely vegetated ecosystems where soil surface interactions are known to play a critical role in land‐climate interactions. This study potentially facilitates a mathematically tractable description of the strength (i.e., the slope) of the ET‐soil moisture relationship, which is a core component of models that seek to predict land‐atmosphere coupling and its feedback to the climate system in a changing climate.

Biodiversity of Sri Lanka

This paper reviews the information available on the biodiversity of Sri Lanka, the causes of its degradation and the policies, legal instruments and strategies developed both nationally and internationally for its conservation and sustainable use. In the first part of this paper, the biodiversity of Sri Lanka at the ecosystem, species and genetic levels is reviewed. At ecosystem level, each major ecosystem is introduced by giving its distribution, vegetation stature where relevant, dominant plant taxa, endemic component, some information on the fauna and finally, a few references to sites studied for that ecosystem. At the species level, the number of taxa in each group, the proportions of endemics and threatened species are highlighted. At the genetic level, genetic variation within and between populations of some indigenous species for which data are available are given, along with a brief overview of genetic diversity in cultivated species. The second part examines causes of loss of biodiversity at the ecosystem level; the third presents information on the policies, legislation and national strategies related to biodiversity conservation in the country and in meeting the international obligations for conservation, sustainable development and sharing of benefits arising from conservation. A strong plea is made on both formal and non-formal education at all levels for using the protected area network as learning laboratories for testing and demonstrating innovative approaches to reconcile the conservation of biodiversity with social and economic development in line with the Man and the Biosphere concept.

Airborne lidar remote sensing applications in non-forested short stature environments: a review

Lidar (light detection and ranging) remote sensing technology provides promising tools for 3D characterization of the earth’s surface. In ecosystem studies, lidar derived structural parameters relating to vegetation and terrain have been extensively used in many applications and are rapidly expanding. Yet, most of the lidar applications have focused on tall, woody vegetation in forested environments and less research attention is given to non-forest, short stature vegetation dominated ecosystems. Similar to the lidar developments in forestry, novel methodological approaches and algorithm developments will be necessary to improve estimates of structural and biophysical properties (i.e. biomass and carbon storage) in non-forested short stature environments. Under changing climate scenarios, the latter is particularly useful to improve our understanding of their future role as terrestrial carbon sinks. In an attempt to identify research gaps in airborne lidar remote sensing application in short stature vegetation studies, in this review article we provide a comprehensive overview on the current state of airborne lidar applications. Our focus is mainly on the levels of accuracies and errors reported, as well as the potentials and limitations of the methods applied in these studies. We also provide insights into future research needs and applications in these environments.

Silurian vegetation stature and density inferred from fossil soils and plants in Pennsylvania, USA

Silurian fossil plants range from small vascular plants (rhyniophytes) to moderately large fungi (nematophytes), but give little idea of the stature, rooting depth and plant density of vegetation on land. Silurian to earliest Devonian palaeosols from the Bloomsburg Formation show unusually deep bioturbation of several distinct kinds. Surface ground-parallel rhizomes of vascular land plants (to 20 cm deep) are penetrated by burrows like those of millipedes (to 80 cm), but the deepest stratum (down to 2 m below the surface) has features interpreted as bioturbation by fungal hyphae and rhizines. Plant-like axes associated with palaeosols are evidence of vegetation with three distinct tiers above ground as inferred from diameters using allometric scaling equations. Nematophytes ( Germanophyton psygmophylloides ), up to 1.3 m tall, formed a tier above herbaceous vascular land plants (30 cm) and ground cover (<2 cm tall) of thallose organisms and litter. Drab haloed plant bases in the surface of palaeosols demonstrate that nematophytes grew densely (up to 51 m −2 ) with spacing (20 cm) that closed canopy in seasonally dry wetland palaeosols, comparable with modern marsh vegetation. Vascular land plants of well-drained soils in contrast were scattered, with bare earth between. Wetland ground cover was thus more extensive than cover of well-drained soils, and precursor lichens facilitated early evolution of vascular land plants. Supplementary Material: Tables of mineral and grain-size proportions, major-element chemical analyses, and plant spacing and size are available at http://www.geolsoc.org.uk/SUP18848 .

How will the greening of the Arctic affect an important prey species and disturbance agent? Vegetation effects on arctic ground squirrels.

Increases in terrestrial primary productivity across the Arctic and northern alpine ecosystems are leading to altered vegetation composition and stature. Changes in vegetation stature may affect predator-prey interactions via changes in the prey's ability to detect predators, changes in predation pressure, predator identity and predator foraging strategy. Changes in productivity and vegetation composition may also affect herbivores via effects on forage availability and quality. We investigated if height-dependent effects of forage and non-forage vegetation determine burrowing extent and activity of arctic ground squirrels (Urocitellus parryii). We collected data on burrow networks and activity of arctic ground squirrels across long-term vegetation monitoring sites in Denali National Park and Preserve, Alaska. The implications of height-specific cover of potential forage and non-forage vegetation on burrowing behaviour and habitat suitability for arctic ground squirrels were investigated using hierarchical Bayesian modelling. Increased cover of forbs was associated with more burrows and burrow systems, and higher activity of systems, for all forb heights. No other potential forage functional group was related to burrow distribution and activity. In contrast, height-dependent negative effects of non-forage vegetation were observed, with cover over 50-cm height negatively affecting the number of burrows, systems and system activity. Our results demonstrate that increases in vegetation productivity have dual, potentially counteracting effects on arctic ground squirrels via changes in forage and vegetation stature. Importantly, increases in tall-growing woody vegetation (shrubs and trees) have clear negative effects, whereas increases in forb should benefit arctic ground squirrels.

Vegetation controls on northern high latitude snow‐albedo feedback: observations and CMIP5 model simulations

The snow-masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large-scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow-albedo feedback is controlled largely by the contrast between snow-covered and snow-free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, we compare satellite observations and coupled climate model representations of albedo and tree cover for the boreal and Arctic region. Our analyses reveal consistent declines in albedo with increasing tree cover, occurring south of latitudinal tree line, that are poorly represented in coupled climate models. Observed relationships between albedo and tree cover differ substantially between snow-covered and snow-free periods, and among plant functional type. Tree cover in models varies widely but surprisingly does not correlate well with model albedo. Furthermore, our results demonstrate a relationship between tree cover and snow-albedo feedback that may be used to accurately constrain high latitude albedo feedbacks in coupled climate models under current and future vegetation distributions.

Multi-scale Analysis of Environmental Conditions and Conifer Seedling Distribution Across the Treeline Ecotone of Northern Manitoba, Canada

Treeline represents not only an important physiognomic boundary but also an important transition between disjunct mesoclimates and environmental limitations on establishment of tree species. The circumboreal treeline is controlled by some still to be understood physiological mechanism dependent on air temperatures, though younger life stages are increasingly influenced by numerous other biotic and abiotic factors at finer spatial and temporal scales. The goal of this study was to evaluate environmental and reproductive characteristics across treeline around Churchill, Manitoba, and to determine which factors are most important for successful seedling establishment by tamarack, white spruce and black spruce. We examined mid-winter snowpack, soil characteristics, seed viability, seedling establishment, and dominant vegetation at sites within forest and at treeline. Growing season was longer at treeline due to less snow accumulation, though soil temperatures were more variable throughout the year when compared with forest. Conifer seed germination was greater than 88% for most of the region and total seedling density was relatively consistent between sites. Seedlings were negatively associated with other plants within the forest, but low stature vegetation seemed to facilitate establishment at treeline. The associations between seedling establishment and habitat availability observed at several sites suggest that treeline advance in the Churchill area could be contingent on the facilitative effects of plants at and beyond treeline. The results of this study support the premise that fine-scale biotic and abiotic patterns and processes such as snowpack and facilitation by neighboring vegetation certainly cannot be overlooked in analyses of patterns at treeline in a changing Subarctic.

Habitat Occupancy and Detection of the Pacific Sheath-Tailed Bat (Emballonura semicaudata) on Aguiguan, Commonwealth of the Northern Mariana Islands

Occupancy analysis was used to quantify Pacific sheath-tailed bat (Emballonura semicaudata) foraging activity and its relationship to forest structure and proximity to cave roosts on Aguiguan Island in the Commonwealth of the Northern Mariana Islands. Bat occurrence was most closely associated with canopy cover, vegetation stature and distance to known roosts. The metrics generated by this study can serve as a quantitative baseline for future assessments of the status of this endangered species following changes in habitat due to management activities (e.g., feral goat control) or other factors (e.g., typhoon impacts). Additionally, we provide quantitative descriptions of the echolocation calls of E. semicaudata. Search-phase calls were characterized by a relatively narrow bandwidth and short pulse duration typical of insectivores that forage within vegetative clutter. Two distinctly characteristic frequencies were recorded: 30.97 ± 1.08 kHz and 63.15 ± 2.20 kHz

Infrared heater arrays for warming field plots scaled up to 5-m diameter

As Earth continues to warm globally, there is a need to conduct ecosystem plot warming experiments under conditions as representative of open fields in the future as possible. One promising approach is to use hexagonal arrays of infrared heaters such as described by [Kimball, B.A., Conley, M.M., Wang, S., Lin, X., Luo, C., Morgan, J., Smith, D., 2008. Infrared heater arrays for warming ecosystem field plots. Global Change Biology 14, 309–320]. However, their plots were only 3 m in diameter (7.1 m 2), which limits the stature of vegetation to shorter than about 1 m and also limits the amount of plant material that can destructively harvested. Therefore, we tested a larger hexagonal 5-m diameter array of infrared heaters, which provided a near tripling of useable area (19.6 m 2). The number of heaters was tripled from 6 to 18, and their height above the vegetative (wheat) canopy was scaled with the diameter (0.4 times diameter = 2.0 m). Distributions of down-going thermal radiation and of the resultant warming of the vegetation were quite uniform across the plot. Moreover, the same equation previously determined from 3-m diameter plots to describe the thermal radiation efficiency as a function of wind speed was still applicable. Thus, no problems were encountered in tripling the area of the infrared heater-warmed plots.

Long-term steady state <sup>13</sup>C labelling to investigate soil carbon turnover in grasslands

Abstract. We have set up a facility allowing steady state 13CO2 labeling of short stature vegetation (12 m2) for several years. 13C labelling is obtained by scrubbing the CO2 from outdoors air with a self-regenerating molecular sieve and by replacing it with 13C depleted (−34.7±0.03‰) fossil-fuel derived CO2 The facility, which comprises 16 replicate mesocosms, allows to trace the fate of photosynthetic carbon in plant-soil systems in natural light and at outdoors temperature. This method was applied to the study of soil organic carbon turnover in temperate grasslands. We tested the hypothesis that a low disturbance by grazing and cutting of the grassland increases the mean residence time of carbon in coarse (>0.2 mm) soil organic fractions. Grassland monoliths (0.5×0.5×0.4 m) were sampled from high and low disturbance treatments in a long-term (14 yrs) grazing experiment and were placed during two years in the mesocosms. During daytime, the canopy enclosure in each mesocosm was supplied in an open flow with air at mean CO2 concentration of 425 µmol mol−1 and δ13C of −21.5±0.27‰. Fully labelled mature grass leaves reached a δ13C of −40.8 (±0.93) and −42.2‰ (±0.60) in the low and high disturbance treatments, respectively, indicating a mean 13C labelling intensity of 12.7‰ compared to unlabelled control grass leaves. After two years, the delta 13C value of total soil organic matter above 0.2 mm was reduced in average by 7.8‰ in the labelled monoliths compared to controls. The isotope mass balance technique was used to calculate for the top (0–10 cm) soil the fraction of 13C labelled carbon in the soil organic matter above 0.2 mm (i.e. roots, rhizomes and particulate organic matter). A first order exponential decay model fitted to the unlabelled C in this fraction shows an increase in mean residence time from 22 to 31 months at low compared to high disturbance. A slower decay of roots, rhizomes and particulate organic matter above 0.2 mm is therefore likely to contribute to the observed increased in soil carbon sequestration in grassland monoliths exposed to low disturbance.

Mapping Burn Severity of Mediterranean-Type Vegetation Using Satellite Multispectral Data

Knowledge of the spatial distribution of burn severity immediately following a fire is needed to locate areas requiring management for environmental impacts and timber salvage, and for validation of fire risk and fire behavior models. We evaluated methods for mapping post-fire burn severity in southern California Mediterranean-type ecosystems using satellite images calibrated and validated by field-collected data. The effects of spectral transforms, temporal dimensionality, classifiers, and sensor type on the accuracy of burn severity classification were analyzed. We mapped and analyzed the distributions of five categories of burn severity or land cover for two southern California wildfires based primarily on classification of Landsat TM/ETM+ data, with IKONOS MS data also being evaluated. Map accuracy was assessed relative to field-based classification of burn severity of randomly located plots, using the Composite Burn Index approach. Maps based on the multi-temporal Kauth Thomas transform of Landsat TM/ETM+ data and maximum likelihood classifier had the highest overall accuracy (64 and 55%) and kappa values (0.51 and 0.37) for the two study areas. Forested lands were classified at a much higher level of accuracy (overall accuracy near 80%), while accurate classification of burn severity in shrublands was more challenging (overall accuracy less than 50%). The lower stature vegetation of shrublands typically experiences crown-burning fires, such that range of burn severity for shrublands is more limited.

CO2 flux from soil in pastures and forests in southwestern Amazonia

AbstractStocks of carbon in Amazonian forest biomass and soils have received considerable research attention because of their potential as sources and sinks of atmospheric CO2. Fluxes of CO2 from soil to the atmosphere, on the other hand, have not been addressed comprehensively in regard to temporal and spatial variations and to land cover change, and have been measured directly only in a few locations in Amazonia. Considerable variation exists across the Amazon Basin in soil properties, climate, and management practices in forests and cattle pastures that might affect soil CO2 fluxes. Here we report soil CO2 fluxes from an area of rapid deforestation in the southwestern Amazonian state of Acre. Specifically we addressed (1) the seasonal variation of soil CO2 fluxes, soil moisture, and soil temperature; (2) the effects of land cover (pastures, mature, and secondary forests) on these fluxes; (3) annual estimates of soil respiration; and (4) the relative contributions of grass‐derived and forest‐derived C as indicated by δ13CO2. Fluxes were greatest during the wet season and declined during the dry season in all land covers. Soil respiration was significantly correlated with soil water‐filled pore space but not correlated with temperature. Annual fluxes were higher in pastures compared with mature and secondary forests, and some of the pastures also had higher soil C stocks. The δ13C of CO2 respired in pasture soils showed that high respiration rates in pastures were derived almost entirely from grass root respiration and decomposition of grass residues. These results indicate that the pastures are very productive and that the larger flux of C cycling through pasture soils compared with forest soils is probably due to greater allocation of C belowground. Secondary forests had soil respiration rates similar to mature forests, and there was no correlation between soil respiration and either forest age or forest biomass. Hence, belowground allocation of C does not appear to be directly related to the stature of vegetation in this region. Variation in seasonal and annual rates of soil respiration of these forests and pastures is more indicative of flux of C through the soil rather than major net changes in ecosystem C stocks.

GIS‐analysis of tree‐line elevation in the Swiss Alps suggests no exposure effect

Abstract. Counter intuition, an analysis of tree‐line position across the Swiss Alps based on a geographical information system (GIS) with a spatial resolution of 100 m (2.5 million points) revealed no difference in climatic tree‐line altitude with slope exposure. Through step wise discrimination procedures our analysis accounts for anthropogenic tree‐line depression. Any land cover bias affects the frequency of GIS‐points corresponding to tree‐line forests rather than the mean elevation of such points, captured by our analysis. We explain this phenomenon (1) by the absence of significant drought effects in the Alps (no disadvantages for southwest slopes), (2) by the fact that tree tops, unlike low stature vegetation, do not profit from greater radiation warming on south slopes during the growing season but are thermally coupled to free air circulation, and (3) by preliminary data for root zone temperatures during the growing season, which do not differ between south and north slopes, as long as the soil is screened by a closed forest canopy. The overall difference in season length and snow cover, often seen between south and north slopes, does not seem to affect tree‐line position but explains greater natural forest fragmentation on north slopes. It is this greater fragmentation and patchiness (avalanche tracks, snow beds etc.) which seem to have nourished the idea of a generally lower limit of tree growth and tree lines at northern slopes. These results are in line with a recently developed theory, which suggests that tree‐line elevations in humid climates correspond to similar isotherms, irrespective of latitude and thus, season length.

Community structure on unusual habitat islands: quartz-fields in the Succulent Karoo, South Africa

Quartz fields are edaphically arid, azonal habitats occurring under different macroclimatic conditions in several arid regions of southern Africa. They are the exclusive home of 142 plant species of which ca. 70% are local or regional endemics. This paper is an analysis of the quartz-field floras and growth form-soil relationships in two quartz field regions: the Knersvlakte in the Namaqualand-Namib Domain of the Succulent Karoo, and the western Little Karoo in the Southern Karoo Domain. The Knersvlakte supported 52 quartz-field specialists of which 39 were endemic to the region. Corresponding data for the Little Karoo were 11, and 10 species, respectively. In both regions, the average canopy cover on the quartz-field releves was ca. 8%, and more than half of this comprised contracted, succulent nanochamaephytes. Cover and vegetation stature were markedly higher on adjacent zonal habitats. Quartz fields in both regions supported a similar array of compact, subglobose and subterranean nanochamaephytes, as evidenced by convergent patterns in two distantly related genera (Argyroderma N. E. Brown and Gibbaeum (Haworth) N. E. Brown, both Mesembryanthemaceae), endemic to the Knersvlakte and largely restricted to the Little Karoo, respectively. Analyses of vegetational and edaphic data of quartz fields and adjacent, zonal habitats were carried out using multivariate direct gradient analysis (Canonical Correspondence Analysis) in order to identify those factors that control the peculiar composition of growth forms on quartz fields. The results revealed highly similar patterns of growth form composition in relation to similar edaphic gradients in both regions. In general, the soils of quartz fields were shallower compared to those of adjacent zonal habitats. In both regions, two different groups of quartz-field edaphic habitats, representing extremes of a continuum, were identified. Group 1 was characterized by high salt content, neutral to slightly acid soil pH, and low stone content. Group 2 was characterized by low salt content, low soil pH, and high stone content. Group 1 quartz fields are the most edaphically arid habitats and support the highest relative cover and diversity of subglobose and subterranean chamaephytes. The combination of reduced competition from larger growth forms, shallow soils and high soil salinity, represents a regionally unusual selective regime. Some succulent lineages in the Mesembryanthemaceae have undergone diversification which has resulted in the fine-scale discrimination of subtle edaphic gradients within the saline quartz-patch habitats. Reliable seasonal rainfall and reduced thermal stress have also played a role in the evolution of quartz patch specialists.

Screen-aided CO 2 control (SACC): a middle ground between FACE and open-top chambers

We have developed a novel CO 2 exposure system for natural vegetation that is a middle ground between Free Air CO 2 Enrichment (FACE) and traditional open-top chambers (OTC). Screen-Aided CO 2 Control (SACC) technology uses much less CO 2 per experiment and per replicate than FACE and is superior to OTCs in terms of its effects on microclimate. A SACC unit consists of a thin metal frame, a clear plastic “screen”, and a pipe at the base of the screen through which CO 2 enriched jets of air are directed into the unit. There is a gap between the ground and the bottom of the pipe and the screen is relatively short in comparison to the maximum height of the vegetation. Our SACC units are hexagonal and enclose a ground area of 1.27 m 2. SACC works in the following way: 1) the screen breaks the wind and creates turbulent mixing within the unit, 2) the mixing of the outside air with the CO 2 enriched jets of air generates relatively uniform CO 2 concentrations within the screened-in vegetation, and 3) a fully automated system monitors CO 2 concentrations and adjusts CO 2 injection rates for each unit every ca. 10 minutes to maintain preset CO 2 concentrations. Twenty-four hour means of CO 2 concentrations in the middle of a unit are typically maintained within 1 μl l −1 of their set points. Spatial variation and short-term fluctuations in CO 2 concentration are similar to those in OTCs and FACE. CO 2 consumption at our site is 5 kg CO 2 day −1 replicate −1 for a total of ca. 30 tons per year for 20 elevated CO 2 SACC units. Compared to OTCs, SACC units have reduced temperature peaks at full sunlight, minimal effects on solar radiation, reduced rainfall interception by chamber walls, and freer access of small animals to experimental plots. We believe that SACC is the best method for exposing short stature vegetation to elevated CO 2 when financial constraints do not allow for a properly replicated FACE experiment.

Experimental trampling of vegetation. II. Predictors of resistance and resilience : D. N. Cole, Journal of Applied Ecology, 32(1), 1995, pp 215–224

1. Experimental trampling was conducted in 18 vegetation types in five separate mountain regions in the United States. Each type was trampled 0-500 times and vegetation response was assessed 2 weeks and 1 year after trampling. 2. The response of vegetation to trampling is expressed in terms of three indices: resistance, tolerance and resilience. Resistance and tolerance are determined from the vegetation surviving 2 weeks and 1 year after trampling. respectively. Resilience compares the change over the remainder of the year with that during the first 2 weeks after trampling. 3. Plant morphological characteristics explained more of the variation in response to trampling than the site characteristics that were assessed: altitude, overstorey canopy cover or total groundlayer vegetation cover. 4. Resistance was primarily a function of vegetation stature, erectness and whether plants were graminoids, forbs or shrubs. The most resistant plants were caespitose or matted graminoids; the least resistant plants were erect forbs. 5. Resilience was primarily a function of whether plants were chamaephytes, with perennating buds located above the ground surface. Chamaephytes were much less resilient than other plants. 6. Tolerance, which measures the ability of vegetation to withstand a cycle of disturbance and recovery, was correlated more with resilience than resistance. Consequently, the least tolerant plants were the chamaephytes. The most tolerant plants were caespitose, matted and rosette hemicryptophytes, and geophytes. 7. The resistance and resilience of individual species were negatively correlated, particularly for chamaephytes and graminoids. For herbaceous species with perennating tissues located at or below ground level, tolerance was more highly correlated with resilience than with resistance. For chamaephytes, tolerance was more highly correlated with resistance.

Experimental Trampling of Vegetation. II. Predictors of Resistance and Resilience

1. Experimental trampling was conducted in 18 vegetation types in five separate mountain regions in the United States. Each type was trampled 0-500 times and vegetation response was assessed 2 weeks and 1 year after trampling. 2. The response of vegetation to trampling is expressed in terms of three indices: resistance, tolerance and resilience. Resistance and tolerance are determined from the vegetation surviving 2 weeks and 1 year after trampling. respectively. Resilience compares the change over the remainder of the year with that during the first 2 weeks after trampling. 3. Plant morphological characteristics explained more of the variation in response to trampling than the site characteristics that were assessed: altitude, overstorey canopy cover or total groundlayer vegetation cover. 4. Resistance was primarily a function of vegetation stature, erectness and whether plants were graminoids, forbs or shrubs. The most resistant plants were caespitose or matted graminoids; the least resistant plants were erect forbs. 5. Resilience was primarily a function of whether plants were chamaephytes, with perennating buds located above the ground surface. Chamaephytes were much less resilient than other plants. 6. Tolerance, which measures the ability of vegetation to withstand a cycle of disturbance and recovery, was correlated more with resilience than resistance. Consequently, the least tolerant plants were the chamaephytes. The most tolerant plants were caespitose, matted and rosette hemicryptophytes, and geophytes. 7. The resistance and resilience of individual species were negatively correlated, particularly for chamaephytes and graminoids. For herbaceous species with perennating tissues located at or below ground level, tolerance was more highly correlated with resilience than with resistance. For chamaephytes, tolerance was more highly correlated with resistance.

Aboveground:Belowground Phytomass Ratios in Venezuelan Paramo Vegetation and Their Significance

Phytomass determinations were made for the pairamo vegetation at five sites between 3530 and 4700 m altitude in the Venezuelan Andes. Aboveground values (living vascular plant parts only) were 59.5 to 377.5 g m-2, and aboveground:belowground (A:B) ratios were 1:0.4 to 1:1.0 at four sites and 1:1.4 at a site showing effects of grazing. These ratios are far higher than those typical of arctic and alpine vegetation, but they confirm similarly high values found in two earlier studies in tropicalpine vegetation. A model is proposed in which A:B ratio variations between vegetation types are explained in terms of two unquantified parameters: total annual stress is inversely related to vegetation stature, controlling A:B ratios through the requirement for supporting roots; predictable periodic stress or seasonality necessitates belowground storage of energy reserves. Vegetation types are located on a figure, in accord with available A:B ratio data. Tropicalpine vegA:Bet ration, being short and not growing in pronounced seasonal environments, is portrayed as having the highest ratio of all vegetation.