A set of simple decision matrices for prioritizing collection of rare plant species for ex situ conservation

Because it is virtually impossible to collect seed or tissue for ex situ conservation banks from every known population of rare plant species, it is important to rank populations systematically in terms of their priority for collection. The New England Wild Flower Society, which maintains a regional seed bank, developed a set of three complementary decision matrices in spreadsheet form by which to prioritize all occurrences of all state-listed rare plant species in New England in terms of their urgency and feasibility for collection. Data on 4333 occurrences, spanning 456 taxa, were collated from six state Natural Heritage Programs. The first decision matrix ranked taxa in terms of their amenability to storage or propagation at ex situ institutions, and determined whether any known New England occurrences were reproductive. The second matrix further ranked taxa in terms of their global and regional rarity and the viability and genetic and geographic representation of collections already present in the bank. The third matrix scored individual occurrences within each taxon in terms of the presence of imminent threat, reproductive status, vigor, protection status, potential genetic distance from other occurrences, availability of landowner permission, and their current status in the bank. Occurrences were then sorted in ascending order by total matrix score; those with low scores were at the top of the list for collection priority. 3743 occurrences were deemed eligible for collection. Scores ranged from 14.5 to 182, and were influenced most strongly by the number of occurrences per taxon. Clear breakpoints were apparent in the distribution of scores, with clusters of uncommon taxa at the low end of the scale and a long tail created by taxa with more numerous occurrences in New England. These breakpoints could potentially be used to prioritize groups of occurrences that should receive the first attention for collection, while postponing collection of higher-scoring groups. Fewer than 1% of occurrences were misclassified, according to post hoc inspection. This simple set of decision matrices can be adapted by a wide range of institutions involved in ex situ conservation.     

Hydrologic regime and the conservation of salmon life history diversity

Life history diversity of imperiled Pacific salmon Oncorhynchus spp. substantially contributes to their persistence, and conservation of such diversity is a critical element of recovery efforts. Preserving and restoring diversity of life history traits depends in part on environmental factors affecting their expression. We analyzed relationships between annual hydrograph patterns and life history traits (spawn timing, age at spawning, age at outmigration, and body size) of Puget Sound Chinook salmon (Oncorhynchus tshawytscha) to identify environmental indicators of current and historic diversity. Based on mean monthly flow patterns, we identified three hydrologic regimes: snowmelt-dominated, rainfall-dominated, and transitional. Chinook populations in snowmelt-dominated areas contained higher proportions of the stream-type life history (juvenile residence >1 year in freshwater), had older spawners, and tended to spawn earlier in the year than populations in rainfall-dominated areas. There are few extant Puget Sound populations dominated by the stream-type life history, as several populations with high proportions of stream-type fish have been extirpated by construction of dams that prevent migration into snowmelt-dominated reaches. The few extant populations are thus a high priority for conservation. The low level of genetic distinction between stream-type and ocean-type (juvenile residence <1 year in freshwater) life histories suggests that allowing some portion of extant populations to recolonize habitats above dams might allow re-expression of suppressed life history characteristics, creating a broader spatial distribution of the stream-type life history. Climate change ultimately may limit the effectiveness of some conservation efforts, as stream-type Chinook may be dependent on a diminishing snowmelt-dominated habitat.     

The distribution of disturbance-dependent rare plants in a coastal Massachusetts sandplain: Implications for conservation and management

Rare plants in coastal New England sandplains are often restricted to anthropogenically disturbed sites including plowed and mowed firelanes at the Manuel F. Correllus State Forest on Martha’s Vineyard. Little is known about pre-colonial rare plant habitat or how modern management impacts these species. To understand the factors influencing rare plant distribution, we examined the influence of vegetation structure, species composition, environmental characteristics and disturbance history on rare plant populations and potential natural habitat in the 2100-ha Forest. We sampled >100, 100 m² plots - in firelanes and forested/shrubland areas - and conducted extensive searches for rare plants.Linum intercursum and Scleria pauciflora var. caroliniana were frequent in firelanes including in recently plowed areas, whereas Nabalus serpentarius, Sisyrinchium fuscatum, and Aristida purpurascens generally occurred in isolated, locally-abundant patches in firelanes not plowed for many decades. The former group may be characterized by an ability to rapidly establish following disturbances while the latter may take longer to establish and develop large populations. In some respects, rare plants were associated with environmental conditions reflecting the disturbance histories of sites they occupied (e.g., L. intercursum with lower duff depth and N. serpentarius with greater litter cover/depth).In forests and shrublands undisturbed for decades, rare plants only occurred on well-worn paths. Although scrub oak stands supported conditions more similar to those found in firelanes than other native vegetation types, disturbances - far more severe than those in forests/shrublands of the past century - are probably required to create suitable rare plant habitat in sandplain forests and shrublands.     

Grouping and prioritization of vascular plant species for conservation: combining natural rarity and management need

National and International Red Lists and Legal Acts specify species with conservation needs, mainly on the basis of personal experiences. For effective conservation we need scientifically justified prioritization and grouping of these species. We propose a new combined approach where species are grouped according to the similar activities needed for their conservation. We used the national list of vascular plant species with conservation need for Estonia (301 species), and linked these species to eight qualitative conservation characteristics, four reflecting natural causes of rarity (restricted global distribution; restricted local distribution within a country; always small populations; very rare habitat type), and four connected with nature management (species needing the management of semi-natural grasslands; species needing local disturbances like forest fires; species needing traditional extensive agriculture; species which may be threatened by collecting). Only one positive association occurred among the characteristics - between restricted local distribution and small size of populations. Thus, natural causes of rarity and management aspects are not overlapping, and both should be used in conservation activities. Species grouping by different conservation characteristics allows one to focus on species groups with similar conservation needs instead of individual species. Prioritization of species with conservation needs can be based on the number of conservation characteristics that are associated with a particular species. Our prioritization did not correlate with the categories of the national Red Data Book, but a positive association was found with legal protection categories. The legislation, however, covers only the natural causes of rarity. We propose a new combined approach for plant species’ conservation planning that starts by considering human induced rarity and progresses through to natural rarity causes.     

The influence of life history attributes and fishing pressure on the efficacy of marine reserves

Two key questions regarding “no-take” marine reserves are: (1) how effective are reserves likely to be, and (2) how does effectiveness vary with life history attributes and the relative size of reserves. To investigate these questions, we use a simple Ricker model that includes fishing, larval dispersal, and larval loss while in a planktonic pool, and that tracks protected and unprotected populations. We applied two different measures of reserve effectiveness to our simulation results. One metric was intended to reflect goals oriented towards conservation and the second was intended to reflect fishery enhancement goals. Both metrics compare the situation before reserves are established to after the reserve has been in place and a new equilibrium was reached. Yield effectiveness is defined as the total equilibrium annual harvest after reserves are established divided by the total annual harvest before reserves are established. Conservation effectiveness is defined as the average adult density inside the reserve divided by the average density in the same area prior to reserve establishment. A substantial fraction of the 5120 simulated parameter combinations representing different harvest rates and life history attributes went extinct in the absence of a reserve, and these scenarios leading to extinction could be predicted accurately (85% aptly classified) simply on the basis of exploitation rate and population growth rate. Of the cases that did not go extinct, we compared the performance of reserves as measured by each effectiveness metric. Few of the cases (less than 8%) produced effective reserves as measured in terms of increased harvest; whereas over half of the cases resulted in effective reserves as measured by conservation effectiveness. Moreover, the two measures of reserve effectiveness were only weakly correlated. Simple linear regression or polynomial regression could explain at most 23% of the variation in reserve effectiveness as measured by either metric. As expected, the size of the reserve area had a marked and typically negative effect on total annual yield, which suggests that while marine protected areas may do a good job of conserving protected populations, there will generally be pressure from the fishing community to keep them small because of their tendency to reduce total catch.     

Risk assessment: Simultaneously prioritizing the control of invasive plant species and the conservation of rare plant species

Although the consequences of the homogenization of Earth’s flora and fauna are not well understood, experts agree that biological invasions pose hazards to rare species. As a result, there is a need for a systematic approach to assess risks from invasive species. The Relative Risk Model can be adapted to assess combinations of rare species, invasive species, and regions. It also can be applied to different taxonomic groups and at different spatial scales. This flexibility makes it a promising tool for invasive species risk assessment. We used the Relative Risk Model to quantify risks posed to endangered plant species by non-indigenous invasive plant species in Nebraska.We modeled the suitable habitats for eight invasive plant species, which we subsequently compared to documented occurrences of endangered plant species in a Geographic Information System. We combined this data with an assessment of the ecological impacts of each invasive species in a regional risk assessment framework to simultaneously calculate relative risk scores for invasive plant species, imperiled plant species, and subregions. We assessed uncertainty with Monte Carlo simulations.The results of this assessment are discrete values indicating the relative threat posed by invasive species to rare species, the relative risk posed to the rare species, and the relative risk in subregions. Results indicate that the invasive species Elaeagnus angustifolia and Rhamnus cathartica pose the greatest risks to endangered plants in Nebraska. The rare species Panax quinquefolius and the subregion Western Corn Belt Plains show the highest risk scores.     

Recovery of native plant communities after the control of a dominant invasive plant species, Foeniculum vulgare: Implications for management

The control and/or removal of a dominant invasive species is expected to lead to increases in native species richness and diversity. Small pilot studies were performed on Santa Cruz Island (SCI), California, in the early 1990s to test the efficacy of different methods on the control of Foeniculum vulgare (fennel) and management’s effects on native species recovery. We chose a treatment that showed significant native species recovery, applied it at the landscape scale, and followed its effects on fennel infested plant communities. We tested the hypothesis that results from small-scale studies translate to the landscape level. We found that although the control of fennel translated from the small to landscape scale, decreasing from an average of 60% to less than 3% cover, native species recovery did not occur in the landscape study as it did in the pilot studies. Invasive fennel cover was replaced by non-native grass cover over time. Unexpectedly, fennel cover in untreated fennel plots decreased significantly (though not as drastically) from over 60% cover to just under 40% cover while native species richness in untreated areas increased significantly. The correlation between precipitation and changes in native and non-native species richness and abundance in this study imply that changes in species abundances were highly correlated with environmental fluctuations. The lack of a native seedbank and the accumulation of non-native grass litter likely prevented the recovery of native species in treated areas. Greater vertical complexity found in fennel communities, which increased visitation by frugivorous birds and likely increased native seed dispersal, may have been responsible for the increase in native species richness in the untreated areas. These results suggest that successful invasive species control and native species recovery experiments conducted at small scales may not translate to the landscape level, and active restoration should be an organic component of such large-scale projects.     

Natural history collections and the conservation of poorly known taxa: Ecological niche modeling in central African rainforest genets (Genetta spp.)

Natural history collections are crucial resources for conservation biology, particularly given the development of the ecological niche modeling (ENM) approach. We combined ENM with taxonomic investigations to address ecological, geographic, and phenotypic variation in the poorly known central African rainforest genets (Genetta cristata, Genetta servalina, Genetta victoriae) to provide new insights into their conservation status. Taxonomic identification was based on four discrete morphological characters. ENMs were developed using the Genetic Algorithm for Rule-Set Prediction (GARP), 10 environmental data layers and 310 georeferenced localities extracted from 667 museum specimens and 22 literature sources. Re-assessed taxonomic identifications allowed us to expand significantly the known range and ecological limits of the three genets. We suggested limited hybridization between G. cristata and G. servalina, in a zone of sympatry likely to cover central Cameroon, northwestern Gabon and Congo. ENM showed that almost all known occurrences were connected geographically by suitable ecological conditions, suggesting continuous potential distributions between supposedly isolated populations of the three genets. Our investigations indicated that G. cristata is distinct from G. servalina in morphology, geographic ranges and ecological niches, indicating species status for G. cristata, which, as such, should be the subject of appropriate conservation attention. Areas of predicted connectivity and actual zones of occurrence falling outside current forest cover should be surveyed to re-assess the status of the rainforest genets. Our study shows that combining ENM and taxonomic investigations can substantially improve data utilization from natural history collections, especially in the case of poorly known species.     

Questions and possible new directions for research into the biology of terrestrial isopods

New directions for research identified during the final plenary discussion of the Sixth Symposium on the Biology of Terrestrial Isopods included: locating enzymes buffering pleon fluids during excretion of ammonia and the use of isopods in ecotoxicology including how they adapt to or tolerate high contaminant levels; how they interact with free living and endosymbiotic microbiota and how Wolbacchia avoids the immune response of isopods. New analyses of mating behaviour raised questions concerning mate choice while new microsatellite techniques may help resolve issues of multiple paternity and sperm competition. In relation to their ecology and biogeography new questions included how does the ability to learn the location of high quality food patches in spatially heterogeneous environments and the existence of an Allee effect, influence the population biology of isopods in the field and how do patterns of invasion and colonisation vary between species with different motility and life history strategies?     

Responses of cycads with different life histories to the impact of plant collecting: simulation models to determine important life history stages and population recovery times

Collection of plants and seeds from wild populations threatens a large number of cycad species. We investigated to what extent individual life history stages contribute to population growth (λ) and compared two species with major differences in life histories in the African genus Encephalartos: Encephalartos cycadifolius, a highly persistent grassland species that resprouts after fire, and Encephalartos villosus, a relatively fast growing, non-sprouting forest species. Several harvesting scenarios impacting different sized individuals were simulated to determine the sensitivity of the two functional types to harvesting. In both species λ was most sensitive to changes in abundance of adult plants. The harvesting of seeds had minimal impact on population growth rates, whereas harvesting of adult plants led to rapid population decline. This response from two very different functional types suggests that the conservation of adult plants is critical for all cycad species. Despite similar responses to adult mortality, the two species had substantially different population growth rates. This determined recovery time after harvesting of adult individuals. Encephalartos cycadifolius is typical of highly persistent plant species associated with low levels of recruitment and unable to recover from even small losses of adults within a reasonable conservation time frame (<100 years). Our results suggest that the ability to recover from loss of individuals is an important factor that should be considered when assessing the vulnerability of wild populations to threats.     

Understanding mental constructs of biodiversity: Implications for biodiversity management and conservation

The participation of the public in environmental decision-making and management is increasingly seen as essential for the success of conservation initiatives. Ecological scientists and conservation practitioners have, however, argued that a lack of understanding of biodiversity issues by the public is a barrier to their effective participation in decision-making processes. These arguments are often based on studies where scientific knowledge is used as the sole measure of public understanding of biodiversity, and therefore fail to account for individuals’ constructs of biodiversity and related issues such as biodiversity management.We examined individuals’ mental constructs of biodiversity, and their conceptual contexts, through a series of focus group discussions with members of the general public in Scotland. To gain a fuller picture of public understanding of biodiversity, we distinguished between mental associations with the term ‘biodiversity’, and the meanings associated with biodiversity-related concepts independent of scientific terminology.We found participants to express rich mental concepts of biodiversity, irrespective of their scientific knowledge. These included notions of balance, food chains and human-nature interactions, and showed strong normative dimensions that were used to define desirable or ideal states of nature. These concepts of biodiversity were, in turn, strongly related to their attitudes towards how best to manage biodiversity.This study highlights that a better understanding of individuals’ mental constructs of biodiversity, which are linked to their attitudes towards biodiversity management, is essential for the design of biodiversity-related policies that are supported by the public.     

Fluazifop-p-butyl herbicide: Implications for germination, emergence and growth of Australian plant species

Five experiments were implemented to collect information related to the effects of fluazifop-p-butyl (active chemical in grass selective herbicides, Fusilade^® and Fusilade Forte™) on seed germination, seedling emergence, growth and health of species native to southwest Australia (a grass and non-grasses), together with several co-occurring introduced species (grasses and a non-grass). Experiments investigated effects of herbicide concentrations, seed burial depths, seed-sowing times since herbicide application and application locations (foliage versus soil). Both herbicides, at half to quadruple strength of recommended field application concentrations, adversely affected development of native and introduced species, both grasses and non-grasses. Herbicidal effects were observed during the seed germination phase, and if germination had occurred, during seedling emergence and, finally, during plant establishment. However, effects were more pronounced after seed germination, particularly on development of seedlings and plants, with retardation and/or discoloration of either radicles or shoots. Not unexpectedly, seedlings from seeds buried deeper in the sand medium (20 mm) struggled to emerge. Both herbicides demonstrated residual characteristics by impeding seedling emergence and growth from seeds sown at various dates (up to maximum test duration of 3 weeks) following exposure of the sand medium to the herbicides. Further, herbicide application to sand only, produced effects on 5-6 months old plants that were similar as application to foliage only, demonstrating herbicide uptake from sand. While the findings support independent research, they contradict the purported herbicide characteristics by commercial sources - grass selective, post-emergent, non-residual, rapid breakdown and active through foliar application only. Implications of these herbicides for biodiversity conservation are discussed.     

Linking the gaps between conservation research and conservation management of rare dipterocarps: A case study of Shorea lumutensis

To conserve a rare plant, conservation programs must be guided by the biological attributes of the species. What constitutes the most critical biological information for plant conservation has been the issue of discussion for the last 30 years. Most scientists promote an approach that is either ecological or genetic in emphasis. Ecological and genetic processes will often interact synergistically to influence the population viability and to determine the persistence of populations in the long run. Consequently, conservation management of plant species, in addition to ecological information, requires a robust understanding of underlying genetic processes as well as the variation within and between populations. Conservation has a cost and the resources available for conservation programs are always limited. Therefore, conservation management strategies should not only be scientifically justified but also practical in terms of resource availability. Shorea lumutensis is a rare and endemic dipterocarp in Peninsular Malaysia. A comprehensive research activity was initiated to assess the population ecology and population genetics of S. lumutensis to elucidate specific ecological and genetic requirements and subsequently to set conservation strategies and priorities. This paper is apparently the first attempt at applying both the ecological and genetic approaches into conservation management of a rare dipterocarp. In addition, this paper also attempts to link the gaps between conservation research and conservation management in a realistic manner. It is our hope that this study will serve as a model for the study of other rare dipterocarps which should be given priority for conservation.     

Social perceptions of the impacts and benefits of invasive alien species: Implications for management

Research on biological invasions has traditionally focused on the ecological component of invasive alien species, either without considering or by considering in a restricted way, the knowledge of the social component. An understanding of the human dimension of invasions is critical to effectively tackle the problems associated with invasive alien species. We distributed questionnaires to evaluate the social perceptions and attitudes of different stakeholder groups affected by invasive alien species in the Doñana social-ecological system (SW Spain). Our analysis served to characterize respondents based on their knowledge and perceptions of the impacts of invasive alien species, and the attitudes toward their introduction and eradication. Hierarchical cluster and principal component analyses identified five categories of respondents, and potential support of eradication programs was assessed using a contingent valuation approach. The five stakeholder groups differed in their degree of knowledge, perceptions, attitudes, and willingness to pay for eradication. The fact that different stakeholders have remarkably different perceptions about the impacts and benefits caused by invasive alien species, and different attitudes toward their introduction or eradication should be considered in any decision-making process regarding their management, particularly when developing appropriate educational and informative programs. Consultation with different stakeholders should also be encouraged from the onset of any decision-making process. In this way, trade-offs involved in IAS management are directly addressed and successful implementation of management practices is facilitated.     

The effect of turf cutting on plant and arbuscular mycorrhizal spore recolonisation: Implications for heathland restoration

In two natural heathland vegetations, we analysed the effect of turf cutting on spore numbers of arbuscular mycorrhizal fungi (AMF). Next to this, we performed a controlled factorial experiment to examine the role of AMF for germination and establishment of Arnica montana in both turf cut and non-turf cut situations. AMF spore numbers decreased with soil depth, and, along with the topsoil, almost all AMF spores were removed with the removal of the acidified and/or eutrophied organic layer. Recolonisation of AMF spore numbers after turf cutting was slow: spore numbers of approximately 60-95 spores g⁻¹ dry soil were found two and a half years after turf cutting, corresponding with 55-70% of AMF spore numbers found in natural field populations of A. montana. Since AMF colonisation increased establishment and biomass, and decreased mortality of A. montana, it was suggested that lack of AMF after turf removal might complicate the establishment of this herbaceous species. Removal of organic material as a management measure should therefore carefully be applied, taking in consideration the low recolonisation rates of AMF as this can markedly effect the success of restoration.     

Arthropod responses to harvesting and wildfire: Implications for emulation of natural disturbance in forest management

Although natural disturbance has been widely adopted as a template for forest management that protects biodiversity, this hypothesis has not been adequately tested. We compared litter-dwelling arthropod assemblages (Coleoptera: Carabidae and Staphylinidae; Araneae) in aspen-dominated stands originating as clear-cuts or wildfires across three age classes (1-2, 14-15, and 28-29 years old) to test whether the post-harvest and post-fire assemblages converged following disturbances, and to compare faunal succession. These findings were compared to data about epigaeic arthropods in old and mature pyrogenic aspen stands (>70 years old) to determine whether diversity and community composition of arthropods from the younger age-classes approached what may have been typical pre-disturbance conditions. The resulting data-set of almost 27,000 arthropods and 230 species showed convergence in most taxa, and some general similarities between 28- and 29-year-old stands and old and mature stands. However, not all taxa responded similarly, and faunal succession following clear-cutting appeared to progress more rapidly than following wildfire. Rarefaction-estimated diversity was elevated in 1-2-year-old stands, compared to unharvested stands, reflecting a mix of closed-canopy and open-habitat species. Non-metric multi-dimensional scaling ordinations showed that samples from young wildfire disturbed stands (1-2 years old) included more variable assemblages than all other study sites, and contained species that may depend on unique post-fire habitat characteristics. The fauna of old and mature stands exhibited low diversity, but contained species with limited dispersal abilities, and species tied to old-growth habitats such as dead wood. Harvesting systems that do not allow adequate recovery following a first harvesting pass, or do not maintain microhabitat features associated with older fire-origin forests, may threaten persistence of some elements of boreal arthropod faunas.     

Historical influences on the vegetation and soils of the Martha’s Vineyard, Massachusetts coastal sandplain: Implications for conservation and restoration

Both disturbance history and previous land use influence present-day vegetation and soils. These influences can have important implications for conservation of plant communities if former disturbance and land use change species abundances, increase colonization of nonnative plant species or if they alter soil characteristics in ways that make them less suitable for species of conservation interest. We compared the plant species composition, the proportion of native and nonnative plant species, and soil biogeochemical characteristics across seven dominant land use and vegetation cover types on the outwash sandplain of Martha’s Vineyard that differed in previous soil tillage, dominant overstory vegetation and history of recent prescribed fire. The outwash sandplain supports many native plant species adapted to dry, low nutrient conditions and maintenance of native species is a management concern. There was broad overlap in the plant species composition among pine (Pinus resinosa, P. strobus) plantations on untilled soils, pine plantations on formerly tilled soils, scrub oak (Quercus ilicifolia) shrublands, tree oak (Q. velutina, Q. alba) woodlands, burned tree oak woodlands, and sandplain grasslands. All of these land cover categories contained few nonnative species. In contrast, agricultural grasslands had high richness and cover of nonnative plants. Soil characteristics were also similar among all of the woodland, shrubland and grassland land cover categories, but soils in agricultural grasslands had higher pH, extractable Ca²⁺ and Mg²⁺ in mineral soils and higher rates of net nitrification. The similarity of soils and significant overlap in vegetation across pine plantations, scrub oak shrublands, oak woodlands and sandplain grasslands suggests that the history of land use, current vegetation and soil characteristics do not pose a major barrier to management strategies that would involve conversion among any of these vegetation types. The current presence of high cover of nonnative species and nutrient-enriched soils in agricultural grasslands, however, may pose a barrier to expansion of sandplain grasslands or shrublands on these former agricultural lands if native species are not able to outcompete nonnative species in these anthropogenically-enriched sites.     

Inter-annual variability in the home range of breeding turtles: Implications for current and future conservation management

We assessed home range size for breeding loggerhead turtles (Caretta caretta) near the limit of the species range at the Greek island of Zakynthos in the Mediterranean. Thirteen adult females and seven adult males were tracked using GPS units (loggers and transmitters) during May and June of 2006, 2007 and 2008. Kernel analysis indicated that core home range sizes (50% estimator; range: 2.9-19.7 km²) for both males and females were restricted to a 7.5 km tract of coastline. 15% of GPS locations fell outside of the national park protection zones, while within the protected breeding area 88% of GPS locations occurred in zones of minimal protection. Female home ranges were 64% larger in 2008 than in 2006 and 2007, indicating that several years monitoring may be required for the most effective designation of marine protected areas (MPAs). Ten of the tracked females departed the core breeding area on 15 occasions for periods of 1-15 days travelling distances of 10-100 km, although none nested at alternative breeding sites. The inter-annual variability of breeding area home range size and likelihood of incidence of forays appeared be correlated with barometric pressure. The movement responses of loggerheads to environmental conditions implicates an ability to switch nesting areas over small scales in response to climate change. However, such behaviour suggests the protection of existing core breeding sites may be inadequate, with policy makers being required to consider the protection of broader areas to encompass potential changes in the habitat needs of this species.     

Field-scale spatial variability of soil calcium in a semi-arid region: Implications for soil erosion and site-specific management

Excess calcium(Ca) in soils of semi-arid and arid regions has negative effects on soil structure and chemical properties, which limits the crop root growth as well as the availability of soil water and nutrients. Quantifying the spatial variability of soil Ca contents may reveal factors influencing soil erosion and provide a basis for site-specific soil and crop management in semi-arid regions. This study sought to assess the spatial variability of soil Ca in relation to topography, hydraulic attributes, and soil types for precision soil and crop management in a 194-ha production field in the Southern High Plains of Texas,USA. Soils at four depth increments(0–2, 0–15, 15–30, and 30–60 cm) were sampled at 232 points in the spring of 2017. The Ca content of each sample was determined with a DP-6000 Delta Premium portable X-ray fluorescence(PXRF) spectrometer. Elevation data was obtained using a real-time kinematic GPS receiver with centimeter-level accuracy. A digital elevation model(DEM) was derived from the elevation data, and topographic and hydraulic attributes were generated from this DEM. A generalized least-squares model was then developed to assess the relationship between soil Ca contents of the four layers and the topographic and hydraulic attributes. Results showed that topographic attributes, especially slope and elevation, had a significant effect on soil Ca content at different depths(P 0.01). In addition, hydraulic attributes, especially flow length and sediment transport index(STI), had a significant effect on the spatial distribution of soil Ca. Spatial variability of soil Ca and its relationships with topographic and hydraulic attributes and soil types indicated that surface soil loss may occur due to water or wind erosion, especially on susceptible soils with high slopes. Therefore, this study suggests that the application of PXRF in assessing soil Ca content can potentially facilitate a new method for soil erosion evaluation in semi-arid lands. The results of this study provide valuable information for site-specific soil conservation and crop management.     

Chemical composition and diversity influence non-additive effects of litter mixtures on soil carbon and nitrogen cycling: Implications for plant species loss

Diverse plant litter mixtures frequently decompose differently than expected compared to the average of the component species decomposing alone, and it remains unclear why decomposition may respond non-additively to diversity. Here, we hypothesized that litter chemical composition and chemical diversity would be important determinants of the strength and direction (synergistic versus antagonistic) of non-additive soil carbon (C) and nitrogen (N) cycling responses to litter mixtures. To test this, we performed a soil incubation experiment using litter mixtures comprised of up to four plant species, and we measured three components of decomposition: respiration, net N mineralization, and microbial biomass N accumulation. We used nine chemical traits to calculate the chemical composition and diversity of the litter mixtures. First, we found that respiration responded as the average of the individual species in the mixture (i.e. additively), rather than non-additively as initially predicted. Second, litter mixtures stimulated significantly more net N immobilization than expected in 64% of cases, and non-additive responses were highly dependent on mixture chemical composition, and were influenced to a lesser degree by chemical diversity. Specifically, concentrations of tannins and certain low molecular weight phenolics in the mixtures were positively correlated with greater N immobilization than expected. Non-additive N mineralization responses were poorly correlated with traditional measures of litter chemistry like N concentration, C:N, lignin:N, and phenolic:N. Our results also show that non-additive N mineralization responses were affected by loss of some species significantly more than others, and the effects of species loss could depend on 1) whether a species contains compounds with strong effects on non-additive responses; and 2) whether those compounds are also found in other species. Finally, litter mixtures stimulated more microbial biomass N than expected in 45% of cases, but non-additive responses were only weakly dependent on the litter chemistry variables that we measured.