Identifying forest ecosystem regions for agricultural use and conservation

ABSTRACT Balancing agricultural needs with the need to protect biodiverse environments presents a challenge to forestry management. An imbalance in resource production and ecosystem regulation often leads to degradation or deforestation such as when excessive cultivation damages forest biodiversity. Lack of information on geospatial biodiversity may hamper forest ecosystems. In particular, this may be an issue in areas where there is a strong need to reassign land to food production. It is essential to identify and protect those parts of the forest that are key to its preservation. This paper presents a strategy for choosing suitable areas for agricultural management based on a geospatial variation of Shannon's vegetation diversity index (SHDI). This index offers a method for selecting areas with low levels of biodiversity and carbon stock accumulation ability, thereby reducing the negative environmental impact of converting forest land to agricultural use. The natural forest ecosystem of the controversial 1997 Ex-Mega Rice Project (EMRP) in Indonesia is used as an example. Results showed that the geospatial pattern of biodiversity can be accurately derived using kriging analysis and then effectively applied to the delineation of agricultural production areas using an ecological threshold of SHDI. A prediction model that integrates a number of species and families and average annual rainfall was developed by principal component regression (PCR) to obtain a geospatial distribution map of biodiversity. Species richness was found to be an appropriate indicator of SHDI and able to assist in the identification of areas for agricultural use and natural forest management

Leaf nutrients, not specific leaf area, are consistent indicators of elevated nutrient inputs

Leaf traits are frequently measured in ecology to provide a ‘common currency’ for predicting how anthropogenic pressures impact ecosystem function. Here, we test whether leaf traits consistently respond to experimental treatments across 27 globally distributed grassland sites across 4 continents. We find that specific leaf area (leaf area per unit mass)—a commonly measured morphological trait inferring shifts between plant growth strategies—did not respond to up to four years of soil nutrient additions. Leaf nitrogen, phosphorus and potassium concentrations increased in response to the addition of each respective soil nutrient. We found few significant changes in leaf traits when vertebrate herbivores were excluded in the short-term. Leaf nitrogen and potassium concentrations were positively correlated with species turnover, suggesting that interspecific trait variation was a significant predictor of leaf nitrogen and potassium, but not of leaf phosphorus concentration. Climatic conditions and pretreatment soil nutrient levels also accounted for significant amounts of variation in the leaf traits measured. Overall, we find that leaf morphological traits, such as specific leaf area, are not appropriate indicators of plant response to anthropogenic perturbations in grasslands

Soil net nitrogen mineralisation across global grasslands

Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net Nmin) varies with soil properties and climate. However, because most global-scale assessments of net Nmin are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We find that realised Nmin is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised Nmin, but contributes to explain realised net Nmin when combined with soil and climatic variables. We provide novel insights of global realised soil net Nmin and show that potential soil net Nmin data available in the literature could be parameterised with soil and climate data to better predict realised NNational Science Foundation Research Coordination Network; Long-Term Ecological Research; Institute on the Environment at the University of Minnesota.http://www.nature.com/ncommspm2020Mammal Research InstituteZoology and Entomolog

Potential benefits of biodiversity to Australian vegetation projects registered with the Emissions Reduction Fund—is there a carbon‐biodiversity trade‐off?

Global assessments show biodiversity has already declined beyond ‘safe limits’ across most biomes, calling for large‐scale conservation and restoration interventions. At the same time, the potential and emerging catastrophic impacts of accelerated climate change have led to increasing investment in climate change mitigation efforts through maintaining or sequestering carbon in vegetation biomass, particularly woodlands and forests. This raises the challenge of whether these climate change mitigation investments can concurrently contribute to ameliorating the biodiversity crisis. However, the assumption of industry observers is that tree monocultures will sequester more carbon than biodiverse plantings, that is, there is a carbon‐biodiversity trade‐off. Here, we review experimental and observational evidence to examine whether a biodiversity trade‐off is necessary to maximise carbon credits. We apply the findings to the four types of Australian vegetation projects that have been registered with the Australian Government’s Emissions Reduction Fund since 2012: avoided deforestation, managed regeneration, farm forestry and tree planting. We find limited evidence in the biodiversity‐ecosystem function literature for a trade‐off between biodiversity and carbon stored in above‐ground vegetation biomass; rather we find evidence for neutral or positive relationships. Further, additional benefits of plant diversity to carbon storage, rarely accounted for in vegetation projects, include increased soil carbon storage, stability and ecological resilience to disturbances. Our findings suggest opportunities for enhancing biodiversity in vegetation projects, for example through more diverse plantings, or manipulation of herbivores or plant propagules in avoided deforestation and managed regeneration projects. More research is needed to understand the contribution of faunal diversity to ecosystem functions and to manage fire in vegetation projects. We conclude that vegetation projects can aim to benefit biodiversity without compromising carbon credits

P is for persistence: Soil phosphorus remains elevated for more than a decade after old field restoration

Understanding constraints to ecological restoration on former agricultural land has become increasingly important due to agricultural land degradation in the developed world, and growing evidence for enduring agricultural legacies that limit native species recovery. In particular, the removal of native plant biomass and subsequent disturbance of soil properties through farming activities can alter soil ecosystem processes. Planting of native plant species is a common approach to restoring native vegetation on agricultural land and is assumed to benefit soil ecosystem processes, but the degree to which altered soil chemical processes recover is poorly documented. We investigated recovery of soil chemical properties after restoration in semiarid Western Australia, hypothesizing that elevated nutrient concentrations would gradually decline post planting, but available phosphorus (P) concentrations would remain higher than reference conditions. We used a space-for-time substitution approach, comparing 10 planted old field plots with matched fallow cropland and reference woodlands. Sampling on planted old fields and reference woodland plots was stratified into open patches and under tree canopy to account for consistent differences between these areas. The most prominent legacy of cropping was significantly and substantially higher concentrations of soil available P in fallow croplands and restored old fields compared with reference woodlands. Soil mineral nitrogen (N) concentrations were elevated in fallow croplands compared to open patches in reference woodlands (ammonium and nitrate) and under the tree canopy (ammonium). However, in restored old fields, mineral N concentrations were similar to woodland sites, providing evidence for amelioration over time. No significant differences in nutrient concentrations under tree canopies compared with open patches had developed in the planted old fields, despite a distinction between open patches and he under ttree canopy in reference woodlands for total N. We conclude that soil P legacies in old fields may inhibit the recolonization of native species that are sensitive to, or uncompetitive at, elevated P concentrations. To achieve full recovery, further research is required to test restoration practices aimed at reducing soil P concentrations to facilitate native plant establishment and persistence

Recovery of woody but not herbaceous native flora 10 years post old‐field restoration

Vegetation recovery in old fields towards mature reference states is often limited by abiotic and biotic thresholds resulting from agricultural land use legacies, as commonly highlighted using state and transition models. Old-field restoration may include interventions (e.g. planting of vegetation) to overcome these thresholds and assist transition between states. However, our understanding of the effectiveness of these interventions is limited. Using a point-intercept transect method, we surveyed nine sites, each comprising a triplet of fallow cropland, planted old field and woodland reference plots to reflect states of old-field restoration, from the degraded state to the reference state. We compared ground cover attributes, and richness and cover of woody and herbaceous flora species, using ANOVA and multivariate analyses. We found that a decade after planting, cover of leaf litter and woody debris in planted old fields were significantly higher than in the fallow croplands; however, woodland reference conditions were not achieved. Cover of logs was similar to the fallow cropland. Woody species cover and richness were similar in planted old fields and woodland reference plots, with planted old fields having more than 60% of the shrub species richness and cover, and similar tree species richness, to the woodland reference plot. In contrast, whilst herbaceous species contributed more than half the plant species richness in reference woodland plots, there were significantly fewer herbaceous species in the planted old fields, which were more similar to the fallow croplands. Cover of exotic annual forbs in planted old fields was about half that of fallow cropland, and exotic annual grass cover was similar to the reference woodland. Our results show that active restoration of old fields increased leaf litter, woody debris and cover and richness of trees and perennial shrubs. However, native herbaceous species richness, and to some extent cover, remained similar to the fallow cropland. To effect transitioning of the herbaceous layer to the woodland reference state, further intervention such as removal of exotics, followed by sowing or planting native herbaceous species, may be necessary

Abiotic and biotic responses to woody debris additions in restored old fields in a multi‐site Before‐After‐Control‐Impact experiment

Ecological restoration of former agricultural land can improve soil conditions, recover native vegetation, and provide fauna habitat. However, restoration benefits are often associated with time lags, as many attributes, such as leaf litter and coarse woody debris, need time to accumulate. Here, we experimentally tested whether adding mulch and logs to restoration sites in semi-arid Western Australia can accelerate restoration benefits. All sites had been cropped and then planted with native trees and shrubs (i.e., Eucalyptus, Melaleuca, and Acacia spp.) 10 years prior to our experiment, to re-establish the original temperate eucalypt woodland vegetation community. We used a Multi-site Before-After-Control-Impact (MBACI) design to test the effects on 30 abiotic and biotic response variables over a period of 2 years. Of the 30 response variables, a significant effect was found for just four variables: volumetric water content, decomposition, native herbaceous species cover and species richness of disturbance specialist ants. Mulch addition had a positive effect on soil moisture when compared to controls but suppressed growth of native (but not exotic) herbaceous plants. On plots with log additions, decomposition rates decreased, and species richness of disturbance specialist ants increased. However, we found no effect on total species richness and abundance of other ant species groups. The benefit of mulch to soil moisture was offset by its disbenefit to native herbs in our study. Given time, logs may also provide habitat for ant species that prefer concealed habitats. Indeed, benefits to other soil biophysical properties, vegetation, and ant fauna may require longer time frames to be detected. Further research is needed to determine whether the type, quantity, and context of mulch and log additions may improve their utility for old field restoration and whether effects on native herbs are correlated with idiosyncratic climatic conditions

Old‐field restoration improves habitat for ants in a semi‐arid landscape

Many old fields are undergoing ecological restoration aiming to return lost biodiversity and ecosystem functions. However, there is scant evidence that this outcome is achieved. Here we investigate the effects of tree planting following cessation of cropping on ant communities. Ants are a dominant faunal group, functionally important for ecosystem recovery and widely used as indicators of ecosystem restoration. Using a space-for-time approach, we surveyed eight fallow croplands, 10-year-old planted old fields, and reference woodlands in semi-arid south-western Australia. We tested the extent ant communities in planted old fields diverged from those of fallow cropland and converged with those of reference woodlands, distinguishing areas under tree canopies and open patches to account for a direct tree effect. We analyzed ant community data at species, genus, and functional-group levels. Ant species composition in planted old fields substantially converged from fallow croplands toward reference woodlands. Abundance and richness of genera in the tree-associated functional group Subordinate Camponotini was higher under trees than in open areas in planted old fields and reference woodlands. Unlike in reference woodlands, abundance and richness of Hot Climate Specialists was not higher in open areas than under trees in planted old fields, indicating that planted trees did not yet strongly impact the microclimate beneath them. Although old field restoration had positive effects on ant assemblages, full convergence to reference woodlands had not been achieved after 10 years. This was particularly evident for functional groups. Research on older plantings is needed to test if and when full convergence occurs

Ecological interactions among microbial functional guilds in the plant-soil system and implications for ecosystem function

Background Soils harbour a remarkable diversity of interacting fungi, bacteria, and other microbes: together these perform a wide variety of ecological roles from nutrient cycling and organic matter breakdown, to pathogenic and symbiotic interactions with plants. Many studies demonstrate the role of microbes in plant-soil feedbacks and their interactions with plants. However, interactions among microbes are seldom addressed, and there is no consensus regarding the nature and outcomes of interactions among microbial functional guilds. Scope Here, we critically review what is known about microbe-microbe interactions among functional guilds within the plant-soil system, with the aim to initiate a path to disentangling the “microbe black-box”. Our review confirms that the nature of microbial interactions among major functional guilds is explained by niche theory. This means that, among microbes, a competitive relationship is likely when their benefits to plants, source of carbon and nutrients, or nutrient scavenging mechanisms overlap, while a neutral-to-facilitative relationship is likely when these microbial traits differ or complement each other. Conclusions We highlight the numerous knowledge gaps and provide a framework to characterise microbe-microbe interactions that offers insight into the contributions of microbes to key ecosystem functions such as carbon sequestration and nutrient cycling

Global meta‐analysis reveals incomplete recovery of soil conditions and invertebrate assemblages after ecological restoration in agricultural landscapes

Restoration of old fields in agricultural landscapes has become increasingly important for conservation of species and their habitats owing to habitat destruction and rapid environmental change. Studies examining the outcomes of old field restoration predominantly focus on plant, and sometimes, vertebrate communities. Fewer studies have systematically investigated the effects of restoration efforts on soil properties or ground‐dwelling invertebrates and there is limited synthesis of these data. We conducted a global meta‐analysis of published studies to assess the effects of old field restoration on soil properties and soil invertebrate abundance and richness. We anticipated increased vegetation cover would improve soil properties towards reference condition and in turn, this would promote invertebrate abundance and richness. Studies were included if field sites had a history of cropping or livestock grazing. We identified 42 studies (1994–2019) from 16 countries that met our criteria. More studies assessed passive restoration methods than active planting, and native species were more commonly planted than exotic species. Results showed that restoration improved soil conditions with respect to total nitrogen, magnesium, soil carbon, bulk density and porosity when compared to controls; however, conditions similar to those in reference ecosystems were generally not achieved, even 50+ years after restoration had been initiated. Moderator analyses showed few significant tends, however, bulk density improved with age, and in passively restored versus reference ecosystems. Outcomes for soil carbon and bulk density were most predominant in the top soil when compared to the degraded ecosystem. We detected no consistent trends for the effect of restoration on soil invertebrate richness and abundance compared to the control or reference ecosystems. Synthesis and applications. Our global meta‐analysis found strong evidence that old field restoration in agricultural landscapes had positive effects on soil condition but did not lead to full recovery when compared to a reference ecosystem. We detected few and idiosyncratic effects for invertebrates. Further research is needed to understand effects of restoration on soil invertebrate functional groups and to develop management interventions that accelerate the restoration of soil condition