Term Ecological Research Site Research Articles

Climatic factors and the occurrence of vesicular stomatitis in New Mexico, United States of America

Vesicular stomatitis (VS) outbreaks occurred in the southwestern United States of America in 1995, 1997 and 1998. The epidemiology of VS is not understood completely and some of the epidemiologic aspects of this disease are currently under investigation. In this study, daily maximum temperature, daily minimum temperature, daily mean temperature, daily mean relative humidity and daily total precipitation were collected at the Sevilleta Long Term Ecological Research site in central New Mexico. Discriminant analysis was used to identify the climatic variables best able to classify in which months VS would occur. The study found that the amounts of precipitation occurring two, ten, eleven and twelve months prior to the month in which cases were diagnosed, were the climatic variables that best described the occurrence of VS cases. The association of VS cases and precipitation suggests that, like numerous other arthropod-borne diseases, transmission of the disease-causing pathogen is linked to variations in climate.

Changes in the grassland-forest boundary at Ta-Ta-Chia long term ecological research (LTER) site detected by stable isotope ratios of soil organic matter

The carbon isotope analysis [δ 13C values] of organic samples can be a useful research in ecological studies because δ 13C values are indicative of the plant source. This study investigated the changes in plant communities along the grassland-forest boundary in the alpine forest at Ta-Ta-Chia long term ecological research (LTER) site in central Taiwan using carbon isotope data. The aim of this study was focused on the forest fire affected the change of vegetation community. Four pedons from grassland dominated by Miscanthus transmorrisonensis (pedons 1 and 2), transition zone by Tsuga and Yushania nittakeyamensis (pedon 3), and forest zone by Tsuga and nittakeyamensis (pedon 4) were examined. Soil organic matter (SOM) δ 13C values in the upper soil horizon were similar to δ 13C values of the overlaying vegetation types. This indicates that the boundary between these plant communities remained the same in the past decades. The δ 13C values of the grassland SOM ranged from −19.4‰ to −24.1‰, showing decrease with soil depth. This suggests that C 4 plants ( transmorrisonensis) have replaced C 3 plants of Tsuga and nittakeyamensis. The δ 13C values of the Tsuga forest area (pedon 4) range from −27.0‰ to −23.5‰ and showed only slight change with soil depth, implying that C 3 plants have remained the major species in the forest.

LUMBRICUS FRIENDI COGNETTI, 1904 A NEW EXOTIC EARTHWORM IN NORTH AMERICA

Soil fauna of the Baltimore-Washington Metropolitan Area, MD was assessed as part of the Baltimore Ecosystem Study Long Term Ecological Research Site. The majority of earthworm species were European exotics, and one of them Lumbricus friendi Cognetti, 1904 proved to be a new species to the fauna of North America. The species is very similar to L. terrestris, thus a comparative description of the two species is given.

Soil characteristics at a long-term ecological research site in Taylor Valley, Antarctica

Soils at a Long Term Ecological Research site near Lake Hoare in Taylor Valley, Antarctica, were investigated during November/December 1999. The soils alongside 6 experimental plots at the research site were described, repeatedly sampled over a 17-day period, and the gravimetric water content, particle size, and conductivity determined daily. At one nearby location, the soil water content was repeatedly measured after a plot irrigation, while at another, the water content of soil adjacent to a snow patch was repeatedly measured to determine the rate of water loss during thawing of snow. Soils at 2 sites at higher elevations outside the research area were also examined for comparison.The soils at the experimental plots were generally similar but differed in stoniness, the presence of occasional silty layers, and the depth to ice-cemented ground. Water contents (gravimetric) of surface horizons were <0.5% and increased with depth through the active layer to 12% or greater in the ice-cemented permafrost. There were small variations in the water content of surface horizons over the 17-day sampling period with larger variations at depth. A few siltier horizons had higher water contents. The water content profiles and <2 mm% particle size trends were broadly similar for all the sites. Conductivities were low, except in silty horizons where values were markedly higher. At the irrigated site, water was progressively lost over the first 9 days, after which values were close to those at unirrigated sites. There was a less marked loss of water from the soil alongside the thawing snow patch but an increased loss after all snow had thawed. The higher elevation soils outside the experimental area were more weathered and had higher salinities indicating a significantly greater soil age.Small changes in water content in the surface horizons appeared to be related to changing weather conditions, whereas at greater soil depth, changes in the water content corresponded with the increasing thawing depth. The results illustrate the dynamic nature of soil moisture over short periods of time in Antarctic Cold Desert soils.

Monitoring urban land cover change: An expert system approach to land cover classification of semiarid to arid urban centers

The spatial and temporal distribution of land cover is a fundamental dataset for urban ecological research. An expert (or hypothesis testing) system has been used with Landsat Thematic Mapper (TM) data to derive a land cover classification for the semiarid Phoenix metropolitan portion of the Central Arizona-Phoenix Long Term Ecological Research (CAP LTER) site. Expert systems allow for the integration of remotely sensed data with other sources of georeferenced information such as land use data, spatial texture, and digital elevation models (DEMs) to obtain greater classification accuracy. Logical decision rules are used with the various datasets to assign class values to each pixel. TM reflectance data acquired in 1998 [visible to shortwave infrared (VSWIR) bands plus a vegetation index] were initially classified for land cover using a maximum likelihood decision rule. In addition, spatial texture of the TM data was calculated. An expert system was constructed to perform postclassification sorting of the initial land cover classification using additional spatial datasets such as texture, land use, water rights, city boundaries, and Native American reservation boundaries. Pixels were reclassified using logical decision rules into 12 classes. The overall accuracy of this technique was 85%. Individual class user's accuracy ranged from 73% to 99%, with the exception of the commercial/industrial materials class. This class performed poorly (user's accuracy of 49%) due to the similarity of subpixel components with other classes. The results presented here indicate that the expert system approach will be useful both for ongoing CAP LTER research, as well as the planned global Urban Environmental Monitoring (UEM) program of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument.

Prevalence of Eimeria (Apicomplexa: Eimeriidae) in Reintroduced Gunnison's Prairie Dogs (Cynomys gunnisoni)

Fecal samples from 54 Gunnison's prairie dogs (Cynomys gunnisoni) from Albuquerque, NM were analyzed for the presence of coccidia and all were positive. They were then relocated to an abandoned prairiedog town on the Sevilleta Long Term Ecological Research (LTER) site. Six Eimeria species, E. callospermophili, E. cynomysis, E. pseudospermophili (new host record), E. spermophili, E. ludoviciani and E. vilasi (new host record) were found in Albuquerque animals, but only 2 species, E. callospermophili and E. vilasi were present in relocated hosts. A significant (P < 0.05) reduction was seen in the prevalence of E. vilasi (72% vs. 13%) and in the prevalence of infections (P < 0.05) with 2 or more Eimeria species (39% vs. 4%) in pre- and postrelocation animals. To assess the impact of the introduction of C. gunnisoni on the resident rodent population, feces were collected from 6 species of rodents. Five Eimeria species, E. arizonensis (Reithrodontomys), E. chobotari (Dipodomys, Perognathus), E. liomysis (Dipodomys), E. mohavensis (Dipodomys) and E. reedi (Perognathus) were found. We found no evidence of coccidia transfer among introduced and resident rodent species.

Modelling Watersheds as Spatial Object Hierarchies: Structure and Dynamics

The generation, transport and fate of non‐point source pollutants in surface water systems is recognized as a major threat to water supplies, aquatic and coastal ecosystems. The transformation and movement of water, carbon and nutrients through watersheds integrates a set of ecosystem processes along hydrologic flowpaths. Human individual and institutional interactions with these processes involve direct addition or abstraction of these substances, or the alteration of land cover and drainage systems. In natural and developed catchments, these processes often vary at granularities ranging from below the level of a hillslope, up through regional watersheds. This suggests the need for the development of hierarchical analysis tools that can address the integration of a set of biophysical, biogeochemical and socioeconomic processes over a spectrum of scales. We describe and illustrate the use of a watershed model implemented as a spatial object hierarchy, representing successively contained landform classes associated with class specific processes as member functions. The model has been linked in a range of looser and tighter couplings with GRASS and ArcView, supplemented by specific terrain analytical functions. We illustrate the data and model system for an instrumented catchment monitored as part of the Baltimore Ecosystem Study (BES), a Long Term Ecological Research (LTER) site centering on integrated carbon, water and nutrient cycling.

EFFECTS OF FERTILIZER ADDITION AND DEBRIS REMOVAL ON LEAF-LITTER SPIDER COMMUNITIES AT TWO ELEVATIONS

This study investigates the indirect effects of primary productivity enhancement via fer- tilization, and the direct effects of environmental differences at two elevations, on the density and species richness of leaf-litter spiders. Litter was sampled in tabonuco forest (340-360 m elevation) and elfin forest (1051 m elevation) within the Luquillo Experimental Forest Long Term Ecological Research (LTER) site in Puerto Rico. Treatments consisted of three blocks with fertilization and control plots at both sites, and a one time removal of hurricane generated debris at tabonuco forest only. Treatments had no significant effect on spider density, species diversity, and species richness at either elevation. Elfin forest showed lower densities and lower species richness than tabonuco forest due to harsh environmental conditions. The thin litter layer and similar standing litter in the tabonuco forest suggest that spiders are limited by habitat, and also that they have successfully recolonized the debris cleared areas at this elevation. Harsh environmental conditions at elfin forest seem to be strong enough to counteract the effects of fertilizer addition on the measured variables. However, the high biomass of grasses in the fertilization plots at elfin forest could have caused an underestimation of spider densities. This study suggests that habitat availability is an important variable in bottom-up models for food web link control.

PLANT CARBON–NUTRIENT INTERACTIONS CONTROL CO2EXCHANGE IN ALASKAN WET SEDGE TUNDRA ECOSYSTEMS

We explored the long-term (8-yr) effects of separate field manipulations of temperature and nutrient availability on carbon balance in wet sedge tundra near the Arctic Long Term Ecological Research (LTER) site at Toolik Lake, Alaska. Our goals were (1) to assess the relative importance of chronic warming (with field greenhouses) and increased N and P availability (by fertilization) in controlling gross ecosystem photosynthesis, ecosystem respiration (plant plus heterotrophic respiration), and ultimately ecosystem C balance; and (2) to attempt to partition ecosystem responses to these treatments between plant and soil contributions. We present results of the effects of these manipulations on whole-system CO2 exchange over seasonal and diel cycles, and on nonrhizosphere soil microbial respiration using in situ soil incubations. Wet sedge control plots were, at best, a weak sink for carbon even during the peak growing season. Chronic nutrient additions of N + P shifted wet sedge carbon balance to a strong sink throughout the growing season; nutrient availability regulated seasonal and diel CO2 exchanges in these two wet sedge ecosystems. The N + P plots had significantly higher photosynthesis and ecosystem respiration in spite of the unanticipated effect of ∼30% reduction in thaw depth in these plots, apparently due to a twofold increase in litter accumulation insulating the soil surface and/or possible shading from greater plant cover in these plots. These results highlighted the prevailing importance of nutrient–carbon interactions in controlling ecosystem processes and ecosystem C balance in arctic tundra. In contrast, warming had only subtle effects on CO2 exchanges. Increased temperatures in the warmed plots had little effect on instantaneous rates of photosynthesis or respiration. After eight years of chronic warming with an average 5.6°C higher air temperature over the growing season and a 40–200% increase in net N mineralization rate, it was surprising that warming did not have more profound effects on CO2 exchange and plant cover. If there were an effect of warming, increased temperatures might cause early canopy development and lengthen the growing season, rather than directly affect instantaneous rates of photosynthesis. Based on photosynthesis–light response curves developed from the early- and late-season diel measurements, we demonstrated that the main effect of warming was to accelerate the development of the canopy early in the season. By midseason, however, there were no significant differences in C exchange between warmed and control plots. Perhaps the most important and novel result emerging from this study is the prevailing importance of plant C exchange, not soil processes, in driving ecosystem C fluxes. First, nonrhizosphere soil microbial respiration as estimated CO2 flux from in situ soil incubations was a small fraction of whole-system respiration and did not vary among treatments. This suggests that anaerobic conditions or some other factor may limit soil microbial respiration more than do temperature or nutrients. Second, plant respiration contributed most (90%) of the ecosystem respiration in fertilized plots. This unanticipated and large contribution from plant respiration highlights the critical importance of understanding the response of plant respiration to global environmental change in these wet sedge ecosystems.

Impacts of logging on autumn bird populations in the southern forests of Tasmania

Bird assemblages were documented in different forest types in the Warra Long Term Ecological Research Site in Tasmania's southern forests. Sampling was undertaken in areas immediately after clearfelling and burning, in regrowth up to 26 years after this treatment, in selectively logged forest, in regrowth following wildfire, and in old-growth forest. It was found that areas subjected to clearfelling and burning supported assemblages which were distinct from areas with other histories, in that they comprised fewer species and individuals. This adverse impact of silvicultural practices on bird populations was apparent in all strata of the forest; canopy, mid-layer and ground. Immediately after clearfelling and burning, coupes were colonised by ground-feeding insectivores more typical of open country than of the surrounding wet sclerophyll forests, but these were quiddy displaced with the advent of young regrowth, which was gradually colonised by forest-inhabiting species. However, these assemblages were still depauperate as much as 26 years after clearfelling. Comparisons with previous studies suggest that this deleterious impact of forestry operations on birds may be ameliorated by the retention of patches in logging coupes. This is supported by the absence of significant impacts on birds in parts of the area which were selectively logged 25 years earlier.

Cross-site comparison of soil microbial biomass, soil nutrient status, and nematode trophic groups

Summary Soil microbial biomass, soil nutrient status, and nematode trophic groups were examined at the Coweeta, Harvard Forest, and Hubbard Brook Long Term Ecological Research (LTER) sites. Soils were divided into standardized depths (0–5 cm and 5–10 cm) for all analyses. Microbial biomass, nematode abundance and labile soil phosphorus levels were significantly higher in the 0–5 cm soil than in the 5–10 cm soil. Overall, both Harvard Forest and Hubbard Brook had greater nematode abundance and soil phosphorus than Coweeta, while Harvard Forest had the highest levels of microbial biomass. Bacterial feeders, followed by fungal feeders and Tylenchidae were the dominant nematode trophic groups at all three sites. Soil factors such as organic matter, root biomass and total soil C and N contributed to increased levels of microbial biomass, nematode abundance and soil phosphorus levels. In contrast, litter quality and climatic factors such as temperature and moisture apparently had little effect upon the parameters measured. This study illustrates the complex interrelationships between decomposer communities, climate, litter quantity, litter quality, soil nutrients, and site specific ecosystem processes. Continued long-term, cross-site ecosystem studies remain necessary to better understand the complex and dynamic processes causing variability both within and between ecosystems.

THE EFFECTS OF DISTURBANCE EVENTS ON LABILE PHOSPHORUS FRACTIONS AND TOTAL ORGANIC PHOSPHORUS IN THE SOUTHERN APPALACHIANS

Changes in labile soil phosphorus pools, together with changes in organic matter and total organic soil phosphorus levels, were measured following rhododendron harvest and hurricane windthrow events at the Coweeta Long Term Ecological Research (LTER) site. Seasonal soil samples were taken every 3 months from June 1996 to September 1997. Soil cores were taken along four transects within each study area at distances approximately 1, 5, and 15 m upslope from the stream channel. Levels of resin P were low for all sites and sampling dates (<5 μg PO4-P g soil−1). Levels of bicarbonate inorganic P were <8 μg PO4-P g soil−1 for all sites and sampling dates, whereas bicarbonate organic P levels were somewhat higher and ranged from 6.5 to 26.6 μg PO4-P g soil−1. Microbial P levels were the most variable and ranged from 4.5 to 25.8 μg PO4-P g soil−1. In contrast, total organic P levels were high, 149 to 348 μg PO4-P g soil−1. For the 3 years after the disturbance events, there were no significant changes in labile phosphorus pools or in total organic phosphorus levels in the soil. This lack of significant differences is likely attributable to the low phosphorus, high P-sorbing status of the soils at Coweeta and the lack of erosion that followed these disturbance events.

Grassland Precipitation-Use Efficiency Varies Across a Resource Gradient

Aboveground net primary production (ANPP) is positively related to mean annual precipitation, an estimate of water availability. This relationship is fundamental to our understanding and management of grassland ecosystems. However, the slope of the relationship between ANPP and precipitation (precipitation-use efficiency, PUE) has been shown to be different for temporal compared with spatial precipitation series. When ANPP and precipitation are averaged over a number of years for different sites, PUE is similar for grasslands all over the world. Studies for two US Long Term Ecological Research Sites have shown that PUE derived from a long-term dataset (temporal model) has a significantly lower slope than the value derived for sites distributed across the US central grassland region (spatial model). PUE differences between the temporal model and the spatial model may be associated with both vegetational and biogeochemical constraints. Here we use two independent datasets, one derived from field estimates of ANPP and the other from remote sensing, to show that the PUE is low at both the dry end and the wet end of the annual precipitation gradient typical of grassland areas (200–1200 mm), and peaks around 475 mm. The intermediate peak may be related to relatively low levels of both vegetational and biogeochemical constraints at this level of resource availability.

An improved methodology for predicting the daily hydrologic response of ungauged catchments

In order to model fluxes of water from the land surface to the atmosphere, and from one grid cell to another in climate models, predictions of hydrologic response are required for catchments where hydrologic data are not available. A methodology has been presented previously that has the capability of producing estimates of catchment scale hydrologic response for ungauged catchments on a daily timestep ( Post and Jakeman, 1998, Ecol. Mod. submitted). In the present paper, it is demonstrated that these daily predictions of hydrologic response can be improved by incorporating information about the hydrologic response of the catchment on a longer timestep. This is because the influence of large scale phenomena such as climate and vegetation may produce a similar water yield in nearby catchments, even though their daily hydrologic response may be different, due for example, to differences in drainage density. Thus, the water yield of an ungauged catchment is inferred on an inter-annual timestep, and this information is used to balance the water budget of a daily timestep rainfall-runoff model. It was found that using tree stocking densities to predict water yields for small experimental catchments in the Maroondah region of Victoria produced better results than those obtained by inferring the water balance parameter of a daily timestep rainfall-runoff model from channel gradient and catchment elongation. Good predictions of inter-annual water yield were also obtained for small experimental catchments in the H. J. Andrews, Hubbard Brook, and Coweeta long term ecological research (LTER) sites in the United States, indicating that it may be possible to produce high quality predictions of daily hydrologic response for ungauged catchments in these regions also.

Root decomposition across a barrier island chronosequence: Litter quality and environmental controls

A root decomposition study using the litterbag approach was conducted along a dune and swale chronosequence on the Virginia Coast Reserve-Long Term Ecological Research Site in Virginia, USA to evaluate how environmental and substrate quality factors influence belowground decay and associated nutrient dynamics. Gradients in moisture levels and nitrogen availability associated with the chronosequence provided the experimental framework. Spartina patens roots were buried at all sites as a standard substrate to evaluate environmental influences. Roots native to each site were buried to evaluate community decay dynamics and the influence of litter quality. Spartina decay was reduced in the wet, anoxic soils of swale sites (k = 0.21–0.33 yr-1) relative to decay in dunes soils (k = 0.52–0.72 yr-1). Increasing soil nitrogen availability from younger to older sites had no effect on the rate of Spartina root decay. Native root decay across the Hog Island chronosequence exhibits certain trends expected in response to nitrogen limitation and moisture availability. Increased nitrogen content of root material corresponds to increased soil nitrogen availability. Among dune sites, native root decay increased in concert with increased root nitrogen (6 year k = 0.34 yr-1, 120 year dune: k = 0.97 yr-1). Litter quality, alone, does not explain this trend since Spartina roots decayed more slowly than native dune roots and had a higher initial nitrogen content. Among swales, increased moisture levels and associated soil anoxia inhibited native root decomposition and minimized the effects of litter quality on decay. In general, phosphorus was rapidly lost from decaying roots while nitrogen immobilization was low to nonexistent. The low nitrogen immobilization of decaying roots in a nitrogen limited ecosystem warrants further study and may reveal that belowground decay increases the rate of nutrient cycling relative to decay aboveground.

Top‐Down Impacts on Creosotebush Herbivores in a Spatially and Temporally Complex Environment

I studied top—down effects on creosotebush (Larrea tridentata) insect herbivores by protecting them from bird and arthropod predation. The purpose of my study was to investigate experimentally the differential and/or interactive effects of two predator guilds on herbivore densities. I performed my experiments on 24 creosotebushes at each of three sites within the Jornada Long—Term Ecological Research Site in the Chihuahuan Desert of southwestern New Mexico, USA. At each site the experiment consisted of: six creosotebushes from which birds were excluded with nylon mesh cages; six creosotebushes from which arthropod predators were removed by hand or aspirator; six creosotebushes from which both birds and arthropod predators were removed; and six control creosotebushes from which neither birds nor arthropod predators were removed. I conducted nondestructive nocturnal visual censuses of herbivores on each creosotebush at the beginning of the experiments in mid—May, 6 wk after the start of the experiment in late June, and 12 wk after the start of the experiment in early August. I conducted these experiments and censuses in 1993 and again in 1994. In both years the herbivore densities became significantly higher in experimental than in control creosotebushes. The effects of bird and arthropod predation on herbivore densities were additive in 1993, but they were compensatory in 1994. In 1994 arthropod predator densities became lower in creosotebushes from which birds had been removed than in creosotebushes from which birds had not been removed, but this result did not obtain in 1993. These results may be due to a combination of factors including: avian and arthropod predation on herbivores, “intraguild” predation of birds on arthropod predators, and competition within the herbivore community. The relative numerical impacts of the predator—removal experiments varied among seasons and among sites within either year, but temporal and spatial variation in predator impacts did not correlate strongly with known gradients of climatic or bottom—up heterogeneity in this system. The results of this study confirm the important direct and cumulative effects of multiple predator guilds, even against a complex background of temporal and spatial heterogeneity.

The effect of nitrogen fertilization on the phenology of roots in a barrier island sand dune community

Little work has been done on the phenology of root growth and senescence largely due to methodological difficulties. The application of minirhizotron technology has enabled the tracking of individual roots through an entire growing season. As a result, direct measures of mortality, root growth, and an analysis of cohorts can be obtained. This study examined the belowground response of vegetation in a nutrient limited system to nitrogen addition. Small plots on a 36 year old dune on Hog Island, a barrier island in the Virginia Coast Reserve Long Term Ecological Research Site, were fertilized with nitrogen. Minirhizotron tubes were installed in each fertilized and control plot. Each tube was sampled monthly for nine months, March through October of 1992. Root length density increased throughout the growing season with the greatest root length density in the top 20 cm of the soil profile. The fertilized plots had greater root length densities (14.1 mm cm-2) than the unfertilized plots (2.9 mm cm-2). There was no significant depth × treatment interaction. Root mortality did not significantly change with fertilization. The largest loss of roots for a cohort occurred within the first month. The dune grassland community did not respond to fertilization with large changes in root distribution or increases in mortality in this study.

Fine-Root Biomass Distribution and Production Along a Barrier Island Chronosequence

-Fine roots are important in community development on barrier islands. Fine roots can influence nutrient losses from the soil environment along with regulating water loss based on their distribution and concentration. A sequential coring method was used to determine live fine-root biomass along a barrier island dune and swale chronosequence on the Virginia Coast Reserve-Long Term Ecological Research Site. Fine-root production and the effects of nitrogen fertilization were also examined using an in-growth core method along the chronosequence. Variation in biomass was associated with topographic position and the interaction with nitrogen and water availability along the chronosequence. The swales had significantly larger accumulations (16 to 180 g/m2) of live fine-root biomass (LFRB) than the dunes (4 to 13 g/m2). Higher LFRB was probably due to higher nitrogen levels and moister conditions in the swales. LFRB changed very little across the dune chronosequence but LFRB in the swales generally decreased from the 6-yr to the 120-yr site. However, the 6yr swale had significantly lower biomass than the other swales. LFRB was concentrated in the upper 10-20 cm of soil in dune and swale sites across the chronosequence, with swales having proportionally more (70%) in the upper 10 cm of soil than dunes (29%). Root nitrogen concentration in LFRB was higher in the older dunes and swales. Root phosphorus concentrations increased from the 6-yr to the 120-yr dune but were not different in the swales. Fineroot production increased significantly with N-fertilization in the dune communities, 1.5 times to 2.5 times the reference sites. Nitrogen fertilization also increased nitrogen concentrations in live fine roots.

Response of root and cotton strip decay to nitrogen amendment along a barrier island dune chronosequence

The influence of nitrogen amendment on fine root decomposition was evaluated on sites located along a barrier island chronosequence (24-, 36-, and 120-year-old dunes). The degree to which exogenous nitrogen limits decay at each site was evaluated through a fertilization experiment. Decay substrates included native roots and cotton strips that differed in carbon and nitrogen chemistries. Root decay on younger sites (24 and 36 years old) showed a slight but significant increase in native root decay in response to fertilization. Cotton strips decayed significantly faster in response to fertilization on all sites during three different time periods except on the oldest site in the winter–spring. Nitrogen mineralization and soil nitrogen availability responded to fertilization in a manner consistent with nitrogen limitation. Nitrogen immobilization potential was low in unfertilized plots and increased on younger sites as a result of fertilization. Suppressed lignin degradation in 120-year-old dune roots suggested possible negative fertilization effects. Pure cellulose (cotton strips) did not demonstrate this suppression. It was concluded that nitrogen was a limiting factor during root decay in younger sites but not on the older 120-year-old dune site. Keywords: cotton strips, decomposition, lignin, Long Term Ecological Research Site, nitrogen, phosphorus, roots.

Regional Climatic Similarities in the Temperate Zones of North and South America

We performed an analysis of the climatic patterns of the temperate zones in North and South America using a global database of monthly precipitation and temperature. Three synthetic variables, identified by a principal component analysis (PCA) of the monthly data, were used: mean annual precipitation, mean annual temperature and the proportion of the precipitation falling during summer. We displayed the spatial gradient of the three variables by constructing a com- posite colour raster image. We used a parallelepiped classification algorithm to locate areas in both continents that are climatically similar to five North American Long Term Ecological Research sites and to two South American long- term ecological research sites. The same algorithm was used to identify areas in South America which are climatically similar to some of the major grassland and shrubland types of North America. There is substantial overlap between the climates of North and South America. Most of the climatic patterns found in South America are well represented in North America. How- ever, there are certain climates in North America that are not found in South America. An example is a climate with relatively low mean annual temperature and high summer precipitation. The climatic signatures of three North American LTER sites (Cedar Creek, CPER and Sevilleta) were not found in South America. The climatic signatures of two LTER sites (Konza and Jornada) had some representation in South America. Two South American research sites (Rio Mayo and Las Chilcas) were well represented climatically in North America. The climates of six out of seven selected North American grassland and shrubland types were represented in South America. The northern mixed prairie type was not represented climatically in South America. Our analysis sug- gests that comparisons of North and South America can provide a powerful test of climatic control over vegetation.