Flower-heads, herbivores, and their parasitoids: food web structure along a fertility gradient

Abstract. 1. The ways in which a soil fertility gradient affects three trophic level food webs defined by plants of the family Asteraceae, flower‐head herbivores, and their parasitoids was investigated. It was tested how the fertility gradient alters: (i) the abundance and richness of plants, herbivores, and their parasitoids, (ii) the herbivore–plant ratio, and (iii) the connectance of the plant–herbivore community matrix. 2. From April to May 2000, plants and insects were sampled in 16 Brazilian Cerrado (sensu stricto) sites along a physiognomic gradient varying from open shrublands (cerrado) to closed woodlands (cerradão). Sites were objectively positioned along the physiognomic gradient by a single index, tree density. Sixty‐seven per cent of the variation in tree density among sites was correlated to two principal components of a PCA, representing gradients of soil fertility. 3. Asteraceae abundance, richness, and flower‐head availability were negatively related to tree density due to their preference for sunny environments, despite the surplus of soil nutrients. The abundance and richness of Diptera and Lepidoptera, the most important flower‐head herbivores, were also negatively related to tree density. Parasitoid abundance decreased with tree density; however, the number of parasitoids per hosts was lower in cerrado, suggesting that top‐down forces are not getting stronger in more productive sites, as could be expected. 4. Community allometry analyses showed that the herbivore to plant ratio was independent of community richness and did not respond to tree density. 5. Connectance of the plant–herbivore matrix was dependent on the community matrix size. Proportionally, species‐rich cerrado sites had fewer interactions than their species‐poor counterparts. Nevertheless, after removing the effect of the matrix size, connectance was not related to tree density. 6. Soil fertility, as the primary cause of the cerrado–cerradão physiognomic gradient, strongly affected the abundance and richness of plants, herbivores and their parasitoids; however, it had little effect on important community attributes, such as the herbivore–plant ratio and the connectance of the plant–herbivore matrix.     

Native forest metacommunity structures in Uruguay shaped by novel land‐use types in their surroundings

We explore the effect of land‐use change from extensively used grasslands to intensified silvi‐ and agricultural monocultures on metacommunity structure of native forests in Uruguay. We integrated methods from metacommunity studies, remote sensing, and landscape ecology to explore how woody species distribution was influenced by land‐use change from local to regional scale. We recorded richness and composition of adult and juvenile woody species from 32 native forests, created land‐use maps from satellite image to calculate spatial metrics at landscape, class, and patch levels. We also analyzed the influence of land use pattern, climate, topography, and geographic distance between sites (d) on metacommunity, and created maps to visualize species richness and (dis)similarity between communities across the country. Woody species communities were distributed in a discrete pattern across Uruguay. Precipitation and temperature seasonality shaped species distribution pattern. Species richness and community dissimilarity increased from West to East. Latitude did not influence these patterns. Number of patches, landscape complexity, and interspersion and juxtaposition indexes determine woody species distribution at landscape level. Increasing areas covered by crops and timber plantation reduced species richness and increased community dissimilarity. The spatial metrics of native forest fragments at patch level did not influence metacommunity structure, species richness, and community dissimilarity. In conclusion, Uruguayan native forests display a high range of dissimilarity. Pressure of neighborhood land uses was the predominant factor for species assemblages. Conserving landscape structures that assure connectivity within and among native forest patches is crucial. On sites with rare target species, the creation of alliances between governmental institution and landowner complemented by incentives for biodiversity conservation provides opportunities to advance in species protection focused on those less tolerant to land‐use change.     

Species traits and abundance influence the organization of liana–tree antagonistic interaction

The interaction among species can be influenced by neutral processes, in which more abundant species have high effect on the structure of interaction, or can be influenced by trait matching. Despite both variables (abundance and species traits) influencing the interaction of species in mutualistic networks, few studies showed their importance in antagonistic networks. Here, we posed the question: what are the main predictors of the liana–tree interactions: species abundance, biological traits or both? In a savanna woodland fragment in south‐eastern Brazil, we sampled lianas and trees in 1 ha, where we recorded the abundance, maximum height and bark roughness of tree species, as well as abundance, maximum diameter and climbing system of liana species. For each species, we calculated their contribution to nestedness (n_i), which is a measure of network structure, and performed simple linear regressions between n_i and abundance and species traits. Abundant species contribute more to n_i than rare species, indicating that neutral processes affect interactions between lianas and trees, probably because lianas are opportunistic and climb trees in their neighbourhood. The only trait related to n_i was tree height, which can indicate that light availability can have a considerable role on network structure between both growth forms. Therefore, the importance of species abundance and tree height can be related to opportunism of lianas on climbing the most suitable tree in their neighbourhood.     

Fertilisers and insect herbivores: a meta‐analysis

Despite the importance of a thorough understanding of the effect of synthetic fertiliser on insect population dynamics, existing literature is conflicting and an area of intense debate. Here, a categorical random‐effects meta‐analysis and a vote count meta‐analysis are employed to examine the effects of nitrogen (N), phosphorus (P), potassium (K) and NPK fertiliser on insect population dynamics. In agreement with the general consensus, insects were found to respond positively, overall, to fertilisers. Sucking insects showed a much stronger response to fertilisers than chewing insects. The environment in which a study is conducted can have a marked effect on insect responses to fertiliser, with natural environments showing the potential for buffering effects of nitrogen fertilisers in particular. As well as highlighting the potential shortfall in the amount of research investigating particularly the effects of potassium and phosphorus, this study provides an invaluable flag post in the ongoing research investigating fertiliser effects on ecosystems.     

Downscaling land‐use data to provide global 30″ estimates of five land‐use classes

Land‐use change is one of the biggest threats to biodiversity globally. The effects of land use on biodiversity manifest primarily at local scales which are not captured by the coarse spatial grain of current global land‐use mapping. Assessments of land‐use impacts on biodiversity across large spatial extents require data at a similar spatial grain to the ecological processes they are assessing. Here, we develop a method for statistically downscaling mapped land‐use data that combines generalized additive modeling and constrained optimization. This method was applied to the 0.5° Land‐use Harmonization data for the year 2005 to produce global 30″ (approx. 1 km²) estimates of five land‐use classes: primary habitat, secondary habitat, cropland, pasture, and urban. The original dataset was partitioned into 61 bio‐realms (unique combinations of biome and biogeographical realm) and downscaled using relationships with fine‐grained climate, land cover, landform, and anthropogenic influence layers. The downscaled land‐use data were validated using the PREDICTS database and the geoWiki global cropland dataset. Application of the new method to all 61 bio‐realms produced global fine‐grained layers from the 2005 time step of the Land‐use Harmonization dataset. Coarse‐scaled proportions of land use estimated from these data compared well with those estimated in the original datasets (mean R²: 0.68 ± 0.19). Validation with the PREDICTS database showed the new downscaled land‐use layers improved discrimination of all five classes at PREDICTS sites (P < 0.0001 in all cases). Additional validation of the downscaled cropping layer with the geoWiki layer showed an R² improvement of 0.12 compared with the Land‐use Harmonization data. The downscaling method presented here produced the first global land‐use dataset at a spatial grain relevant to ecological processes that drive changes in biodiversity over space and time. Integrating these data with biodiversity measures will enable the reporting of land‐use impacts on biodiversity at a finer resolution than previously possible. Furthermore, the general method presented here could be useful to others wishing to downscale similarly constrained coarse‐resolution data for other environmental variables.     

Partitioning taxonomic diversity of aquatic insect assemblages and functional feeding groups in neotropical savanna headwater streams

Biological diversity can be divided into: alpha (α, local), beta (β, difference in assemblage composition among locals), and gamma (γ, total diversity). We assessed the partitioning of taxonomic diversity of Ephemeroptera, Plecoptera and Trichoptera (EPT) and of functional feeding groups (FFG) in neotropical savanna (southeastern Brazilian cerrado) streams. To do so, we considered three diversity components: stream site (α), among stream sites (β₁), and among hydrologic units (β₂). We also evaluated the association of EPT genera composition with heterogeneity in land use, instream physical habitat structure, and instream water quality variables. The percentage of EPT taxonomic α diversity (20.7%) was smaller than the β₁ and β₂ diversity percentages (53.1% and 26.2%, respectively). The percentage of EPT FFG collector-gatherer α diversity (26.5%) was smaller than that of β₁ diversity (55.8%) and higher than the β₂ (17.7%) diversity. The collector-gatherer FFG was predominant and had the greatest β diversity percentage among stream sites (β₁, 55.8%). Our findings support the need for implementing regional scale conservation strategies in the cerrado biome, which has been degraded by anthropogenic activities.     

Environmental performance of gasified willow from different lands including land‐use changes

A life‐cycle assessment (LCA) of a low‐input, short rotation coppice (SRC) willow grown on different Danish lands was performed. Woodchips are gasified, producer gas is used for cogeneration of heat and power (CHP), and the ash–char output is applied as soil amendment in the field. A hybrid model was developed for the estimation of greenhouse gas (GHG) emissions from indirect land‐use changes (iLUC) induced by willow cropping on arable land (iLUC_food). For this, area expansion results from a general equilibrium economic model were combined with global LUC trends to differentiate between land transformation (as additional agricultural expansion, in areas with historical deforestation) and occupation (as delayed relaxation, DR, in areas with historical land abandonment) impacts. A biophysical approach was followed to determine the iLUC_feed emissions factor from marginal grassland. Land transformation impacts were derived from latest world deforestation statistics, while a commercial feed mix of equivalent nutritive value was assumed to substitute the displaced grass as fodder. Intensification effects were included in both iLUC factors as additional N‐fertilizer consumption. Finally, DR impacts were considered for abandoned farmland, as a relative C stock loss compared to natural regeneration. ILUC results show that area related GHG emissions are dominant (93% of iLUC_food and 80% of iLUC_feed), transformation being more important (82% of iLUC_food) than occupation (11%) impacts. LCA results show that CHP from willow emits 4047 kg CO₂‐eq (or 0.8 gCO₂‐eq MJ^?1) when grown on arable land, while sequestering 43 745 kg CO₂‐eq (or ?10.4 gCO₂‐eq MJ^?1) when planted on marginal pastureland, and 134 296 kg CO₂‐eq (or ?31.8 gCO₂‐eq MJ^?1) when marginal abandoned land is cultivated. Increasing the bioenergy potential without undesirable iLUC effects, especially relevant regarding biodiversity impacts, requires that part of the marginally used extensive grasslands are released from their current use or energy cropping on abandoned farmland incentivized.     

The transparency,reliability and utility of tropical rainforest land‐use and land‐cover change models

Land‐use and land‐cover (LULC) change is one of the largest drivers of biodiversity loss and carbon emissions globally. We use the tropical rainforests of the Amazon, the Congo basin and South‐East Asia as a case study to investigate spatial predictive models of LULC change. Current predictions differ in their modelling approaches, are highly variable and often poorly validated. We carried out a quantitative review of 48 modelling methodologies, considering model spatio‐temporal scales, inputs, calibration and validation methods. In addition, we requested model outputs from each of the models reviewed and carried out a quantitative assessment of model performance for tropical LULC predictions in the Brazilian Amazon. We highlight existing shortfalls in the discipline and uncover three key points that need addressing to improve the transparency, reliability and utility of tropical LULC change models: (1) a lack of openness with regard to describing and making available the model inputs and model code; (2) the difficulties of conducting appropriate model validations; and (3) the difficulty that users of tropical LULC models face in obtaining the model predictions to help inform their own analyses and policy decisions. We further draw comparisons between tropical LULC change models in the tropics and the modelling approaches and paradigms in other disciplines, and suggest that recent changes in the climate change and species distribution modelling communities may provide a pathway that tropical LULC change modellers may emulate to further improve the discipline. Climate change models have exerted considerable influence over public perceptions of climate change and now impact policy decisions at all political levels. We suggest that tropical LULC change models have an equally high potential to influence public opinion and impact the development of land‐use policies based on plausible future scenarios, but, to do that reliably may require further improvements in the discipline.     

Land suitability for energy crops under scenarios of climate change and land‐use

Bioenergy is expected to play a critical role in climate change mitigation. Most integrated assessment models assume an expansion of agricultural land for cultivation of energy crops. This study examines the suitability of land for growing a range of energy crops on areas that are not required for food production, accounting for climate change impacts and conservation requirements. A global fuzzy logic model is employed to ascertain the suitable cropping areas for a number of sugar, starch and oil crops, energy grasses and short rotation tree species that could be grown specifically for energy. Two climate change scenarios are modelled (RCP2.6 and RCP8.5), along with two scenarios representing the land which cannot be used for energy crops due to forest and biodiversity conservation, food agriculture and urban areas. Results indicate that 40% of the global area currently suitable for energy crops overlaps with food land and 31% overlaps with forested or protected areas, highlighting hotspots of potential land competition risks. Approximately 18.8 million km² is suitable for energy crops, to some degree, and does not overlap with protected, forested, urban or food agricultural land. Under the climate change scenario RCP8.5, this increases to 19.6 million km² by the end of the century. Broadly, climate change is projected to decrease suitable areas in southern regions and increase them in northern regions, most notably for grass crops in Russia and China, indicating that potential production areas will shift northwards which could potentially affect domestic use and trade of biomass significantly. The majority of the land which becomes suitable is in current grasslands and is just marginally or moderately suitable. This study therefore highlights the vital importance of further studies examining the carbon and ecosystem balance of this potential land‐use change, energy crop yields in sub‐optimal soil and climatic conditions and potential impacts on livelihoods.     

Hotspots of uncertainty in land‐use and land‐cover change projections: a global‐scale model comparison

Model‐based global projections of future land‐use and land‐cover (LULC) change are frequently used in environmental assessments to study the impact of LULC change on environmental services and to provide decision support for policy. These projections are characterized by a high uncertainty in terms of quantity and allocation of projected changes, which can severely impact the results of environmental assessments. In this study, we identify hotspots of uncertainty, based on 43 simulations from 11 global‐scale LULC change models representing a wide range of assumptions of future biophysical and socioeconomic conditions. We attribute components of uncertainty to input data, model structure, scenario storyline and a residual term, based on a regression analysis and analysis of variance. From this diverse set of models and scenarios, we find that the uncertainty varies, depending on the region and the LULC type under consideration. Hotspots of uncertainty appear mainly at the edges of globally important biomes (e.g., boreal and tropical forests). Our results indicate that an important source of uncertainty in forest and pasture areas originates from different input data applied in the models. Cropland, in contrast, is more consistent among the starting conditions, while variation in the projections gradually increases over time due to diverse scenario assumptions and different modeling approaches. Comparisons at the grid cell level indicate that disagreement is mainly related to LULC type definitions and the individual model allocation schemes. We conclude that improving the quality and consistency of observational data utilized in the modeling process and improving the allocation mechanisms of LULC change models remain important challenges. Current LULC representation in environmental assessments might miss the uncertainty arising from the diversity of LULC change modeling approaches, and many studies ignore the uncertainty in LULC projections in assessments of LULC change impacts on climate, water resources or biodiversity.     

Effect of land‐use and land‐cover change on mangrove blue carbon: A systematic review

Mangroves shift from carbon sinks to sources when affected by anthropogenic land‐use and land‐cover change (LULCC). Yet, the magnitude and temporal scale of these impacts are largely unknown. We undertook a systematic review to examine the influence of LULCC on mangrove carbon stocks and soil greenhouse gas (GHG) effluxes. A search of 478 data points from the peer‐reviewed literature revealed a substantial reduction of biomass (82% ± 35%) and soil (54% ± 13%) carbon stocks due to LULCC. The relative loss depended on LULCC type, time since LULCC and geographical and climatic conditions of sites. We also observed that the loss of soil carbon stocks was linked to the decreased soil carbon content and increased soil bulk density over the first 100 cm depth. We found no significant effect of LULCC on soil GHG effluxes. Regeneration efforts (i.e. restoration, rehabilitation and afforestation) led to biomass recovery after ~40 years. However, we found no clear patterns of mangrove soil carbon stock re‐establishment following biomass recovery. Our findings suggest that regeneration may help restore carbon stocks back to pre‐disturbed levels over decadal to century time scales only, with a faster rate for biomass recovery than for soil carbon stocks. Therefore, improved mangrove ecosystem management by preventing further LULCC and promoting rehabilitation is fundamental for effective climate change mitigation policy.     

The fate of European breeding birds under climate,land‐use and dispersal scenarios

Many species have already shifted their distributions in response to recent climate change. Here, we aimed at predicting the future breeding distributions of European birds under climate, land‐use, and dispersal scenarios. We predicted current and future distributions of 409 species within an ensemble forecast framework using seven species distribution models (SDMs), five climate scenarios and three emission and land‐use scenarios. We then compared results from SDMs using climate‐only variables, habitat‐only variables or both climate and habitat variables. In order to account for a species’ dispersal abilities, we used natal dispersal estimates and developed a probabilistic method that produced a dispersal scenario intermediate between the null and full dispersal scenarios generally considered in such studies. We then compared results from all scenarios in terms of future predicted range changes, range shifts, and variations in species richness. Modeling accuracy was better with climate‐only variables than with habitat‐only variables, and better with both climate and habitat variables. Habitat models predicted smaller range shifts and smaller variations in range size and species richness than climate models. Using both climate and habitat variables, it was predicted that the range of 71% of the species would decrease by 2050, with a 335 km median shift. Predicted variations in species richness showed large decreases in the southern regions of Europe, as well as increases, mainly in Scandinavia and northern Russia. The partial dispersal scenario was significantly different from the full dispersal scenario for 25% of the species, resulting in the local reduction of the future predicted species richness of up to 10%. We concluded that the breeding range of most European birds will decrease in spite of dispersal abilities close to a full dispersal hypothesis, and that given the contrasted predictions obtained when modeling climate change only and land‐use change only, both scenarios must be taken into consideration.     

Senescence‐feeders: a new trophic sub‐guild of insect herbivores

Herbivorous insects that have evolved to feed on senescing tissues of plants, or the phloem flowing from those tissues, comprise a distinct sub‐guild of the major trophic guilds, the senescence‐feeders. Some senescence‐feeders have evolved the capacity to accelerate the rate at which the tissues they feed on senesce, thus enhancing the quantity and quality of their food. Other species prolong their access to good food by feeding alternatively on both senescing and flushing tissues. Senescing plant tissues release a poorer quality food more slowly than the rapid inflow to new growth. As a result, senescence‐feeders grow more slowly than equivalent flush‐feeders. Any environmental stress of a plant that hastens its rate of senescence results in faster growth and higher survival of senescence‐feeders. Senescence‐feeders therefore succeed best on damaged or stressed plants and frequently reach outbreak levels on drought‐stressed trees. If the distinctive ecology of senescence‐feeders and the way in which they differ from flush‐feeders in their response to the condition of their host plants are to be recognized and understood, it is important to identify species that belong to this separate trophic sub‐guild. Such understanding is also necessary if attempts to control or manage their attacks on crops and forests are to succeed.     

Changes in phytophagous insect host ranges following the invasion of their community: Long‐term data for fruit flies

The invasion of an established community by new species can trigger changes in community structure. Invasions often occur in phytophagous insect communities, the dynamics of which are driven by the structure of the host assemblage and the presence of competitors. In this study, we investigated how a community established through successive invasions changed over time, taking the last invasion as the reference. The community included four generalist and four specialist species of Tephritidae fruit flies. We analyzed a long‐term database recording observed numbers of flies per fruit for each species on 36 host plants, over 18 years, from 1991 to 2009. Community structure before the last invasion by Bactrocera zonata in 2000 was described in relation to host plant phylogeny and resource availability. Changes in the host range of each species after the arrival of B. zonata were then documented by calculating diversity indices. The flies in the community occupied three types of niches defined on the basis of plant phylogeny (generalists, Solanaceae specialist, and Cucurbitaceae specialists). After the arrival of B. zonata, no change in the host range of specialist species was observed. However, the host ranges of two generalist species, Ceratitis quilicii and Ceratitis capitata, tended to shrink, as shown by the decreases in species richness and host plant α‐diversity. Our study shows increased host specialization by generalist phytophagous insects in the field following the arrival of an invasive species sharing part of their resources. These findings could be used to improve predictions of new interactions between invaders and recipient communities.     

Community structure of insect herbivores on introduced and native Solidago plants in Japan

We compared community composition, density, and species richness of herbivorous insects on the introduced plant Solidago altissima L. (Asteraceae) and the related native species Solidago virgaurea L. in Japan. We found large differences in community composition on the two Solidago species. Five hemipteran sap feeders were found only on S. altissima. Two of them, the aphid Uroleucon nigrotuberculatum Olive (Hemiptera: Aphididae) and the scale insect Parasaissetia nigra Nietner (Hemiptera: Coccidae), were exotic species, accounting for 62% of the total individuals on S. altissima. These exotic sap feeders mostly determined the difference of community composition on the two plant species. In contrast, the herbivore community on S. virgaurea consisted predominately of five native insects: two lepidopteran leaf chewers and three dipteran leaf miners. Overall species richness did not differ between the plants because the increased species richness of sap feeders was offset by the decreased richness of leaf chewers and leaf miners on S. altissima. The overall density of herbivorous insects was higher on S. altissima than on S. virgaurea, because of the high density of the two exotic sap feeding species on S. altissima. We discuss the importance of analyzing community composition in terms of feeding guilds of insect herbivores for understanding how communities of insect herbivores are organized on introduced plants in novel habitats.     

Inter‐regional comparison of land‐use effects on stream metabolism

1. Rates of whole‐system metabolism (production and respiration) are fundamental indicators of ecosystem structure and function. Although first‐order, proximal controls are well understood, assessments of the interactions between proximal controls and distal controls, such as land use and geographic region, are lacking. Thus, the influence of land use on stream metabolism across geographic regions is unknown. Further, there is limited understanding of how land use may alter variability in ecosystem metabolism across regions. 2. Stream metabolism was measured in nine streams in each of eight regions (n = 72) across the United States and Puerto Rico. In each region, three streams were selected from a range of three land uses: agriculturally influenced, urban‐influenced, and reference streams. Stream metabolism was estimated from diel changes in dissolved oxygen concentrations in each stream reach with correction for reaeration and groundwater input. 3. Gross primary production (GPP) was highest in regions with little riparian vegetation (sagebrush steppe in Wyoming, desert shrub in Arizona/New Mexico) and lowest in forested regions (North Carolina, Oregon). In contrast, ecosystem respiration (ER) varied both within and among regions. Reference streams had significantly lower rates of GPP than urban or agriculturally influenced streams. 4. GPP was positively correlated with photosynthetically active radiation and autotrophic biomass. Multiple regression models compared using Akaike’s information criterion (AIC) indicated GPP increased with water column ammonium and the fraction of the catchment in urban and reference land‐use categories. Multiple regression models also identified velocity, temperature, nitrate, ammonium, dissolved organic carbon, GPP, coarse benthic organic matter, fine benthic organic matter and the fraction of all land‐use categories in the catchment as regulators of ER. 5. Structural equation modelling indicated significant distal as well as proximal control pathways including a direct effect of land‐use on GPP as well as SRP, DIN, and PAR effects on GPP; GPP effects on autotrophic biomass, organic matter, and ER; and organic matter effects on ER. 6. Overall, consideration of the data separated by land‐use categories showed reduced inter‐regional variability in rates of metabolism, indicating that the influence of agricultural and urban land use can obscure regional differences in stream metabolism.     

Initial soil C and land‐use history determine soil C sequestration under perennial bioenergy crops

In the UK and other temperate regions, short rotation coppice (SRC) and Miscanthus x giganteus (Miscanthus) are two of the leading ‘second‐generation’ bioenergy crops. Grown specifically as a low‐carbon (C) fossil fuel replacement, calculations of the climate mitigation provided by these bioenergy crops rely on accurate data. There are concerns that uncertainty about impacts on soil C stocks of transitions from current agricultural land use to these bioenergy crops could lead to either an under‐ or overestimate of their climate mitigation potential. Here, for locations across mainland Great Britain (GB), a paired‐site approach and a combination of 30‐cm‐ and 1‐m‐deep soil sampling were used to quantify impacts of bioenergy land‐use transitions on soil C stocks in 41 commercial land‐use transitions; 12 arable to SRC, 9 grasslands to SRC, 11 arable to Miscanthus and 9 grasslands to Miscanthus. Mean soil C stocks were lower under both bioenergy crops than under the grassland controls but only significant at 0–30 cm. Mean soil C stocks at 0–30 cm were 33.55 ± 7.52 Mg C ha^?1 and 26.83 ± 8.08 Mg C ha^?1 lower under SRC (P = 0.004) and Miscanthus plantations (P = 0.001), respectively. Differences between bioenergy crops and arable controls were not significant in either the 30‐cm or 1‐m soil cores and smaller than for transitions from grassland. No correlation was detected between change in soil C stock and bioenergy crop age (time since establishment) or soil texture. Change in soil C stock was, however, negatively correlated with the soil C stock in the original land use. We suggest, therefore, that selection of sites for bioenergy crop establishment with lower soil C stocks, most often under arable land use, is the most likely to result in increased soil C stocks.