Indigenous Agroforestry Systems in Amazonia: From Prehistory to Today

Understanding the historical development of indigenous systems will provide valuable information for the design of ecologically desirable agroforestry production systems. Such studies have been relatively few, especially in Amazonia. The agroforestry systems in Amazonia follow a trail that begins with the arrival of the first hunter-gatherers in prehistoric times, followed by the domestication of plants for agriculture, the development of complex societies rich in material culture, the decimation of these societies by European diseases, warfare, and slavery, the introduction of exotic species, and finally, the present-day scenario of widespread deforestation, in which agroforestry is ascribed a potential role as an alternative land use. Despite the upheavals which occurred in colonial times, greatly reducing the population of native tribes, a review of anthropological and ethnobiological literature from recent decades indicates that a great variety of indigenous agroforestry practices still exist, ranging from deliberate planting of trees in homegardens and fields to the management of volunteer seedlings of both cultivated and wild species. These practices result in various configurations of agroforestry systems, such as homegardens, tree/crop combinations in fields, orchards of mixed fruit trees, and enriched fallows. Together they constitute a stock of knowledge developed over millenia, and represent technologies that evolved along with the domestication of native forest species and their incorporation into food production systems. This knowledge is the basis for the principal agroforestry practice employed by farmers in Amazonia today, the homegarden, and has potential to contribute to the development of other agroforestry systems.     

Agroforestry landscapes and global change: landscape ecology tools for management and conservation

Forest ecosystems are impacted by multiple uses under the influence of global drivers, and where landscape ecology tools may substantially facilitate the management and conservation of the agroforestry ecosystems. The use of landscape ecology tools was described in the eight papers of the present special issue, including changes in forested landscapes due to agricultural and forestry activities, landscape changes due to recent intensification of agriculture, and the impacts of agroforestry as compared to natural forest ecosystems. Landscape ecology can improve the economic, environmental and social values of agroforestry, and this knowledge should help to develop new management alternatives for agroforestry. We believe that these papers will inform management at the landscape level, especially in agroforestry landscapes, offering new tools for management and conservation.     

Fire intensity effects on seed germination of native and invasive Eastern deciduous forest understory plants

Low-intensity fires were important for maintaining the structure of Eastern deciduous forests (EDFs) for thousands of years before European settlement of North America, though fire suppression became a standard management practice in the 1930s. More recently, prescribed fires have been reintroduced to EDF habitats to aid in the restoration of native plant diversity, but invasions of non-native species such as Microstegium vimineum (Japanese stiltgrass) may increase prescribed fire intensity and suppress colonization of native species. As fire becomes a more common management tool in these habitats, it is vital to predict fire temperature effects on the native and non-native species present in the system. In this study, we found that prescribed fires in areas invaded by Microstegium can be 250-300 °C hotter than fires in nearby native-dominated areas. We then compared the effects of fire on germination rates of six native and three non-native EDF understory species representing the range of functional groups common in this habitat. We manipulated both fire intensity (temperature and length of exposure) and type of fire effect (direct flame and indirect furnace heat) to generate germination curves and make predictions about potential prescribed fire effects on populations of these species. There were very different responses among species to both direct (flame) and indirect (furnace) heating. Germination of three native species, Lycopus americana (American water horehound), Verbesina alternifolia (wingstem), and Vernonia gigantea (tall ironweed), showed signs of being stimulated by heating at low temperatures, while germination of all non-native species (M. vimineum, Elaeagnus umbellata, and Schedonorus phoenix) were inhibited at these lower intensities. High fire intensity (temperatures above 300 °C) effectively killed most species, though one native species, Senna hebacarpa (American senna) and one non-native species, E. umbellata (autumn olive), were capable of tolerating 500 °C temperatures. We conclude that high-intensity prescribed fires in habitats invaded by Microstegium may reduce seed germination of some non-native species, but may also inhibit the regeneration of native understory species.     

Agroforestry for soil health

Healthy soil is one of the most critical resources for the health and sustainability of ecosystems, including agroecosystems. Although the agroforestry community has long been convinced of the soil health benefits of agroforestry practices, many of such practices remain to be fully accepted by the mainstream agriculture community. Agroforestry, as a sustainable land management practice, has shown solid evidence of its role in improving soil quality and health based on at least four decades of data gathered from the world over. This thematic issue presents 28 papers that add further to the body of knowledge to reaffirm that agroforestry can improve the major measurable soil metrics that define soil health. Collectively, these papers show that agroforestry has the ability to (1) enrich soil organic carbon better than monocropping systems, (2) improve soil nutrient availability and soil fertility due to the presence of trees in the system, and (3) enhance soil microbial dynamics, which would positively influence soil health. It is imperative that agroforestry, as part of a multifunctional land-use strategy, should receive increased attention in our policy discussion for the future of soil and soil health.     

Selection of native trees for intercropping with coffee in the Atlantic Rainforest biome

A challenge in establishing agroforestry systems is ensuring that farmers are interested in the tree species, and are aware of how to adequately manage these species. This challenge was tackled in the Atlantic Rainforest biome (Brazil), where a participatory trial with agroforestry coffee systems was carried out, followed by a participatory systematisation of the farmers experiences. Our objective was to identify the main tree species used by farmers as well as their criteria for selecting or rejecting tree species. Furthermore, we aimed to present a specific inventory of trees of the Leguminosae family. In order to collect the data, we reviewed the bibliography of the participatory trial, visited and interviewed the farmers and organised workshops with them. The main farmers’ criteria for selecting tree species were compatibility with coffee, amount of biomass, production and the labour needed for tree management. The farmers listed 85 tree species; we recorded 28 tree species of the Leguminosae family. Most trees were either native to the biome or exotic fruit trees. In order to design and manage complex agroforestry systems, family farmers need sufficient knowledge and autonomy, which can be reinforced when a participatory methodology is used for developing on-farm agroforestry systems. In the case presented, the farmers learned how to manage, reclaim and conserve their land. The diversification of production, especially with fruit, contributes to food security and to a low cost/benefit ratio of agroforestry systems. The investigated agroforestry systems showed potential to restore the degraded landscape of the Atlantic Rainforest biome.     

Are horses responsible for introducing non-native plants along forest trails in the eastern United States?

Non-native plant species pose a serious ecological and economic threat to managed and natural ecosystems; therefore, there is a great need to identify sources for the introduction of non-native species and develop management plans to reduce or eliminate their introduction. Horses have been suggested to be an important source for the introduction of non-native plant species along trails, but the conclusions were based on anecdotal evidence. In this study, horse hay, manure, and hoof debris samples were collected from 12 to 24 horses at five endurance ride events in North Carolina, Kentucky, Illinois, Wisconsin, and Michigan. One sub-sample of each material from each horse was sown in pots and grown under ideal conditions to determine if horse hay, manure, and hoof debris samples contained seeds from non-native species. A second sub-sample of each material from each horse was placed back on their respective trail to determine what plants would germinate and establish on the trail. Vegetation surveys were also conducted along 50 m transects perpendicular to horse and hiking (horses not permitted) trails at three of the five sites to compare species composition of native and non-native plant species. On average, non-native plant species germinated in 5.2% of the hay samples in the pots, but non-native species did not germinate from the manure or hoof debris samples. Only 3 of the 288 (≈1% of total samples) hay, manure, and hoof debris plots established on horse trails at the five sites contained plants, all of which were native plants, at the end of the first growing season and no plants were observed at the end of the second growing season. Non-native species composition and percent of total plants species did not differ significantly (p = 0.56) between horse and non-horse trails, and non-native plant species were only found within 2 m of the trail. The results of this and another study [Campbell, J.E., Gibson, D.J., 2001. The effect of seeds of exotic species transported vie horse dung on vegetation along trail corridors. Plant Ecology 157, 23–35] demonstrate that horse hay and manure does contain seeds of non-native plant species, but native and non-native plant species rarely become established on horse trails because of the harsh environmental conditions. Management and policy implication of this study are discussed.     

Potential of indigenous multistrata agroforests for maintaining native floristic diversity in the south-eastern Rift Valley escarpment, Ethiopia

Most studies undertaken in the field of agroforestry have focussed on system design, soil fertility management, and system interactions. Less emphasis has been placed on biodiversity aspects. The aim of this study is to investigate the potential of indigenous, multistrata agroforests for maintaining native woody species diversity in the south-eastern Rift Valley escarpment, Ethiopia. A total of 60 farms, representing three agroforest types (enset-AF, enset-coffee-AF and fruit-coffee-AF), were randomly selected along altitudinal gradients. Enset (Ensete ventricosum) is a perennial, herbaceous monocarpic banana-like plant which serves as a food plant in Ethiopia. The three agroforests are results of the domestication of natural forests and intensification of the landuse systems centuries ago. Sample-based assessment protocols were employed to place sample quadrats and to measure all individuals in the quadrats. A total of 58 woody species, belonging to 49 genera and 30 families, was recorded. Of all woody species identified, 86% were native. The highest proportion of native woody species was recorded in enset-AF (92%), followed by enset-coffee-AF (89%) and fruit-coffee-AF (82%). Among native tree species, Millettia ferruginea and Cordia africana were the most widespread. In all, 22 native woody species were recorded as of interest for conservation, acccording to IUCN Red lists and local criteria. Among them, Pygeum africanum and Rhus glutinosa were categorised as vulnerable in the wild, and in need of conservation priority. The introduction of non-native fruit trees in agroforests can be a threat to maintenance of native woody species. Management strategies favoring enset and coffee will also put other native tree species at risk. A smaller number of native woody species was recorded in fruit-coffee-AF, but a higher mean basal area and stem number. The mean basal area and stem number ranged from 5.4?±?0.5 to 11.7?±?1.0?m^2?ha^?1 and 625?±?84 to 1,505?±?142 stems?ha^?1, respectively. Altitude explained 68 and 71% of the variation in species richness and abundance, respectively. Finally, it is concluded that recognition of the indigenous agroforestry system as an option for maintaining native woody species should be given more attention, to counteract the local threat of these species from the wild.     

Multipurpose leguminous trees and shrubs for agroforestry

These are various ways in which farmers deliberately incorporate trees and shrubs on farm production fields. Many of the species so incorporated are legumes. The role of such woody perennials in agroforestry systems can be productive and/or protective. Legumes offer by far the maximum range of choice of woody species for agroforestry in terms of their economic uses as well as ecological adaptibility. In addition to the several leguminous woody species that are well known in agroforestry, there are many more whose potentials have not yet been fully understood. An evaluation is presented of the agroforestry potentials of a few leguminous species from the point of view of their growth characteristics, ecological adaptability, combining ability with other species and uses/functions. The science of agroforestry is still in its infancy. There exists no research data on the various management aspects of these potentially promising group of plants. ICRAF, in its capacity as an international research council, has assembled several multipurpose leguminous trees and shrubs of agroforestry potential at the Council's recently-established Field Station in Machakos, Kenya, primarily for demonstration and training purposes. Initial results from these trials are presented in the paper.Adapted from a paper presented at the International Symposium on Nitrogen Fixing trees in the Tropics, 19–24 September, 1983 Rio-de-Janeiro, Brazil.     

A review of belowground interactions in agroforestry, focussing on mechanisms and management options

This review summarises current knowledge on root interactions in agroforestry systems, discussing cases from temperate and tropical ecosystems and drawing on experiences from natural plant communities where data from agroforestry systems are lacking. There is an inherent conflict in agroforestry between expected favourable effects of tree root systems, e.g. on soil fertility and nutrient cycling, and competition between tree and crop roots. Root management attempts to optimise root functions and to stimulate facilitative and complementary interactions. It makes use of the plasticity of root systems to respond to environmental factors, including other root systems, with altered growth and physiology. Root management tools include species selection, spacing, nutrient distribution, and shoot pruning, among others. Root distribution determines potential zones of root interactions in the soil, but are also a result of such interactions. Plants tend to avoid excessive root competition both at the root system level and at the single-root level by spatial segregation. As a consequence, associated plant species develop vertically stratified root systems under certain conditions, leading to complementarity in the use of soil resources. Parameters of root competitiveness, such as root length density, mycorrhization and flexibility in response to water and nutrient patches in the soil, have to be considered for predicting the outcome of interspecific root interactions. The patterns of root activity around individual plants differ between species; knowing these may help to avoid excessive competition and unproductive nutrient losses in agroforestry systems through suitable spacing and fertiliser placement. The possibility of alleviating root competition by supplying limiting growth factors is critically assessed. A wide range of physical, chemical and biological interactions occurs not only in spatial agroforestry, but also in rotational systems. In a final part, the reviewed information is applied to different types of agroforestry systems: associations of trees with annual crops; associations of trees with grasses or perennial fodder and cover crops; associations of different tree and shrub species; and improved fallows. This revised version was published online in June 2006 with corrections to the Cover Date.     

Species-specific responses to environmental stress on germination and juvenile growth of two Bolivian Andean agroforestry species

Integrating native trees in farmland can support soil, water and biodiversity conservation. This is particularly important in regions characterized by long periods of drought and soil erosion, such as the Bolivian Andes, where agroforestry with native woody species is rarely applied. Better knowledge on the effects of environmental stress on propagation and establishment of such native plants is needed to optimize their cultivation. In our study, we tested the effects of temperature and scarification on seed germination, and assessed seedling survival and juvenile growth of two potential agroforestry species (Prosopis laevigata var. andicola, Schinus molle) under diverse soil and water conditions. Temperatures above 30 °C accelerated germination, but they increased fungi infestation in the case of S. molle. The application of acid and mechanical scarification significantly improved the germination capacity of P. laevigata var. andicola. Medium to high moisture levels in sand provided the most favourable conditions for plant growth. S. molle was more sensitive to dry and P. laevigata var. andicola more vulnerable to water-saturated clay loam. Mulching enhanced the survival and growth of S. molle juveniles, but increased P. laevigata var. andicola’s growth in sand and dry soils only. Our results may facilitate guidance on improving propagation of these two potential agroforestry species under environmental stress conditions. More generally, our study shows that easily applicable treatments, such as mulching, can significantly improve the cultivation of native species, provided that their habitat requirements and limiting factors are well known. This highlights the relevance of identifying and closing such knowledge gaps for native trees and shrubs in order to promote their potential for use in agroforestry.     

Post-wildfire seeding in forests of the western United States: An evidence-based review

Broadcast seeding is one of the most widely used post-wildfire emergency response treatments intended to reduce soil erosion, increase vegetative ground cover, and minimize establishment and spread of non-native plant species. We conducted an evidence-based review to examine the effectiveness and effects of post-wildfire seeding treatments on soil stabilization, non-native species invasion, and plant community recovery in the western U.S. We reviewed 94 scientific papers and agency monitoring reports identified using a systematic search protocol. As sampling designs have become more rigorous in recent years, evidence that seeding is effective in reducing erosion has decreased. Of highest and high quality studies evaluating soil erosion, 92% (11 of 12) were published since 2000, none of which showed an effective result. Before 2000, the majority of the studies (71%) fell into the lowest quality categories, of which 72% showed seeding to be effective. The majority of studies (20 of 27, 74%) evaluating soil erosion in seeded versus unseeded controls showed that seeding did not reduce erosion relative to unseeded controls. Even when seeding significantly increased vegetative cover, seeded sites rarely supported plant cover levels considered sufficient to stabilize soils within the first and second year post-wildfire. Of the 11 studies evaluating seeding effectiveness for curtailing invasions of non-native plant species, an almost equal percentage found seeding treatments to be either effective (54%, 6 studies) or ineffective (45%, 5 studies). However, the majority of effective and ineffective treatments (83% and 80%, respectively) used non-native species. Sixteen of 26 studies (62%) evaluating seeding effects on plant communities reported that seeding suppressed recovery of native plants, although data on long-term impacts of this reduction are limited. The literature suggests that post-wildfire seeding does little to protect soil in the short-term, has equivocal effect on invasion of non-native species, and can have negative effects on native vegetation recovery, although long-term studies are needed to assess lasting impacts of seeded species.     

Nature vs. nurture: managing relationships between forests,agroforestry and wild biodiversity

Many agroforestry systems are found in places that otherwise would be appropriate for natural forests, and often have replaced them. Humans have had a profound influence on forests virtually everywhere they both are found. Thus ‘natural’ defined as ‘without human influence’ is a hypothetical construct, though one that has assumed mythological value among many conservationists. Biodiversity is a forest value that does not carry a market price. It is the foundation, however, upon which productive systems depend. The relationship between agroforestry and the wild biodiversity contained in more natural forests is a complicated one, depending on the composition of the agroforestry system itself and the way it is managed. Complex forest gardens are more supportive of biodiversity than monocrop systems, shade coffee more than sun coffee, and systems using native plants tend to be more biologically diverse. Nonnative plants, especially potentially invasive alien species, threaten biodiversity and need to be avoided. The relationship between forests, agroforestry and wild biodiversity can be made most productive through applying adaptive management approaches that incorporate ongoing research and monitoring in order to feed information back into the management system. Maintaining diversity in approaches to management of agroforestry systems will provide humanity with the widest range of options for adapting to changing conditions. Clear government policy frameworks are needed that support alliances among the many interest groups involved in forest biodiversity.

     

The role of disturbance severity and canopy closure on standing crop of understory plant species in ponderosa pine stands in northern Arizona,USA

Concerns about the long-term sustainability of overstocked dry conifer forests in western North America have provided impetus for treatments designed to enhance their productivity and native biodiversity. Dense forests are increasingly prone to large stand-replacing fires; yet, thinning and burning treatments, especially combined with other disturbances such as drought and grazing, may enhance populations of colonizing species, including a number of non-native species. Our study quantifies plant standing crop of major herbaceous species across contrasting stand structural types representing a range in disturbance severity in northern Arizona. The least disturbed unmanaged ponderosa pine stands had no non-native species, while non-native grasses constituted 7–11% of the understory plant standing crop in thinned and burned stands. Severely disturbed wildfire stands had a higher proportion of colonizing native species as well as non-native species than other structural types, and areas protected from grazing produced greater standing crop of native forbs compared to grazed unmanaged stands. Standing crop of understory plants in low basal area thinned and burned plots was similar to levels on wildfire plots, but was comprised of fewer non-native graminoids and native colonizing plants. Our results also indicate that size of canopy openings had a stronger influence on standing crop in low basal area plots, whereas tree density more strongly constrained understory plant standing crop in dense stands. These results imply that treatments resulting in clumped tree distribution and basal areas <10 m² ha⁻¹ will be more successful in restoring native understory plant biomass in dense stands. Multiple types and severity of disturbances, such as thinning, burning, grazing, and drought over short periods of time can create greater abundance of colonizing species. Spreading thinning and burning treatments over time may reduce the potential for non-native species colonization compared to immediately burning thinned stands.     

Toward an understanding of tropical home gardens

Tropical home gardens are an agroforestry practice found worldwide. From an analytical perspective little is known about this practice. The universality of their complex structure would indicate the existence of common objectives. The objectives and resulting implementation strategies will dictate the form, layout, species composition and management style of each home garden. Understanding the interrelationships between these various elements is one step toward utilising the advantages of home gardens in a range of agroforestry practices.     

Shifting from simple to complex agroforestry systems: an example for buffer zone management from Kerinci (Sumatra,Indonesia)

Kerinci is a densely populated valley surrounded by a national park in western central Sumatra, Indonesia. Indigenous agroforestry systems include important cash crops like coffee (Coffea canephora var.robusta) and cinnamon (Cinnamomum burmani), and range from alternate cycles of cash crop monocultures or simple associations, to multispecies and multi-storey gardens; these may include as many as 100 common useful species, comprising many fruit trees and indigenous timber species.After analysing the trends of forest conversion and its causes in the area of Kerinci Seblat National Park, a case study of one particular village is presented in order to describe the evolution of cyclic agroforestry systems (ladang) into complex agroforestry systems (pelak). The composition, structure and management of the various systems have been studied through interviews, botanical surveys and the method of profile diagrams.It is suggested that locally developed complex agroforestry systems evolve partly in response to changes in land availability and labour constraints. Finally the interest of such systems when designing projected buffer zones and their development in relation to new market incentives are discussed.     

Local knowledge helps select species for forest restoration in a tropical dry forest of central Veracruz, Mexico

Species for restoration forestry on degraded lands in the tropics are often restricted to a few well-known exotic timber species. This selection frequently leads to failed projects, as local people expect trees to cover a number of uses, not only timber. We studied local knowledge of the usefulness, scarcity and importance for wildlife of native tree species in central Veracruz, Mexico, a region with mainly secondary vegetation and remnants of tropical dry forest. Data were obtained from several workshops, in depth interviews of 40 key informants, field walks with informants, and botanical collections. Analysis included indices for cultural importance, scarcity and wildlife relevance. We documented 76 species in one or more of the categories, from primary, secondary, agroforestry and riparian habitats. Fabaceae was the most important family. All of the species were useful for humans, mainly for rural construction, food, fence posts and fuel. Two-thirds of the species were considered scarce though they were not necessarily rare??some were highly useful, overexploited species with populations insufficient for demand; this category included five of the ten most important species culturally. Also, two-thirds of the tree taxa were considered important for wildlife, especially species of Moraceae. The study shows that the local population is highly aware of the varying functions of trees in the landscape. However, few of the important species are available from regional nurseries. We propose a number of species for restoration forestry, agroforestry systems and enrichment plantings that would be valued by landowners.     

Concepts of resource sharing in agroforestry systems

Although there are very few specific data on management techniques for agroforestry systems, there are important concepts to consider for the design of effective management. One of these is the sharing of resource pools (e.g., light, water, nutrients) between and among the different crop components. With this knowledge, and with the spatial and temporal coordination of growth responses of the crops, effective management for agroforestry systems can be developed.     

Improved management of fruit trees in West African parklands

West African agroforestry systems are changing because agricultural intensification and a changing climate put the tree component at risk. Since local fruit trees play an important role in human nutrition and income generation, this is critical for rural livelihoods. This special issue presents a range of papers devoted to local fruit trees and their potential to improve local livelihoods. The topics cover studies of regeneration, use of mycorrhiza, tree/crop interactions, pollination, variation in fruit quality and genetic variation in adaptability. It is shown that there are many possibilities to improve benefits from trees. Some are likely to have immediate effect on livelihoods, such as cultivation of shade-tolerant crops under trees or improved management of pollinators. Others will require long term efforts, such as using natural variability of trees in breeding programmes to improve adaptation, quality and yield. In any case, to maintain the benefit from trees in the long run it will be necessary to identify appropriate strategies for regeneration of species that are currently in decline.     

Assessment of small mammal diversity in coffee agroforestry in the Western Ghats,India

Coffee agroforestry is a conservation strategy that has shown promise to support the diversity of bird, bat, and insect communities, but few studies have focused on non-volant mammals in coffee farms. We assessed mammal diversity within coffee agroforestry systems in Kodagu, India and investigated the impacts of the non-native shade tree species, Grevillea robusta, on mammal diversity. Twenty farms, with varying amounts of G. robusta planted within the coffee farm, were sampled throughout three rainfall zones during the 4-month study period. We captured six species of small mammals, with indirect methods yielding an additional five species, totaling 11 mammal species. Contrary to current ecological thought, we found that increased amounts of G. robusta did not have a negative impact on either abundance or richness of mammals. Small mammal abundances were higher at farms with greater amounts of herbaceous ground cover and larger, mature shade trees, while small mammal species richness was found to increase with an increase in tree species richness as well as greater amounts of herbaceous ground cover. Additionally, small mammal abundance was higher at coffee farms closer to forested areas. Based on these findings, we suggest the maintenance or cultivation of shade tree richness, mature shade trees, and herbaceous ground cover within coffee farms and preservation of forested areas within the landscape to enhance coffee agroforestry habitat for non-volant mammals. We hope that these habitat requirements will be incorporated into conservation strategies for the promotion of biodiversity within coffee agroforestry systems.