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Agroforestry systems provide important ecosystem functions and services. They have the potential to enrich agricultural monocultures in central Europe with structural elements otherwise absent, which is expected to be accompanied by a surplus of ecosystem functions. Here we used quantitative measures derived from terrestrial laser scanning in single-scan mode to describe the structural complexity, the canopy openness, the foliage height diversity and the understory complexity of four common agroforest systems in central Europe. We accessed silvopasture systems with grazing ponies and cattle as well as fellow deer, short rotation forests with agricultural use between the tree rows, tree orchards with grazing sheep and Christmas tree plantations on which chickens forage. As a reference, we used data for 65 forest sites across Germany, representing different forest types, various dominant tree species, stand ages and management systems. We found that overall stand structural complexity is ranked as follows: forest > silvopasture systems > short rotation forest > tree orchard > Christmas tree plantation. Consequently, if overall structural complexity of an agricultural landscape shall be enriched, there is now strong evidence on how this may be achieved using agroforests. However, if the focus lies on selected structures that serve specific functions, e.g. dense understory to provide animal shelter, specific types of agroforests may be chosen and the ranking in overall structural complexity may be less important.

[Background and Aims] Plant physiological traits and their relation to soil N availability was investigated as regulators of the distribution of understory shrub species along a slope in a Japanese cedar (Cryptomeria japonica) plantation in central Japan. [Methods]At the study site, previous studies demonstrated that both net and gross soil nitrification rates are high on the lower slope and there are dramatic declines in different sections of the slope gradient. We examined the distributions of understory plant species and their nitrate (NO3[-]-N) use traits, and compared the results with the soil traits. [Results]Our results show that boundaries between different dominant understory species correspond to boundaries between different soil types. Leucosceptrum stellipilum occurs on soil with high net and gross nitrification rates. Hydrangea hirta is dominant on soil with high net and low gross nitrification rates. Pieris japonica occurs on soil with very low net and gross nitrification rates. Dominant understory species have species-specific physiological traits in their use of NO3[-]-N. Pieris japonica lacks the capacity to use NO3[-]-N as a N source, but other species do use NO3[-]-N. Lindera triloba, whose distribution is unrelated to soil NO3[-]-N availability, changes the extent to which it uses NO3[-]-N in response to soil NO3[-]-N availability. [Conclusions]Our results indicate that differences in the physiological capabilities and adaptabilities of plant species in using NO3[-]-N as a N source regulate their distribution ranges. The identity of the major form of available soil N is therefore an environmental factor that influences plant distributions.

The diversification model proposed in Chapter 1 emphasizes ecological change after a few decades of quasi-monoculture. Is it also a primary determinant of diversification for the world's leading producer of cocoa? In the early-to-mid 2010s, cocoa production in Côte d'Ivoire is above 1.5 million tonnes per year. This growth dynamic is mainly explained by the universal model of cocoa economies: new migrations leading to massive clearing of forests. The decline of the old cocoa farms rarely appears in statistics due to the massive new planting mostly at the expense of the last pockets of forests. However, in the old cocoa and coffee regions, the lure of rubber and oil palm cultivation has increasingly gone hand in hand with lower cocoa yields, the fight against insect damage and diseases, and difficulties of replanting. It has led to the clearing of cocoa plantations or the cultivation of rubber in the understory of old cocoa trees waiting to be felled. In addition to factors of price and public policy (for example, the creation of a hybrid oil palm and clonal rubber sectors in the 1960s), the process of diversification was partly driven by deforestation and exhaustion of the forest rent. For many smallholders, even more than markets and cocoa prices which need a serious stimulus, and besides the land conflicts, the answer rests on the ability of research and the chocolate industry to come up with technological advances applicable at low cost to help them to solve the universal problems of cocoa replanting.

Gall-forming insects reach highest diversity, abundance and survivorship on sclerophyllous vegetation. This pattern was recently reviewed and shown as a habitat rather than ecosystem effect. We tested the hypothesis that upper forest canopies are probably the best suitable habitat for gall-forming insects in any tropical vegetation, comparing the wet rainforest of Panama (Neotropical), and the subtropical forest of Australia (Australian). We further tested whether foliage/plant community traits could influence this gall distribution pattern, and we investigated the effect of host family size and evolutionary age. Foliage traits, leaf chewing herbivory, and gall abundance and survivorship were measured using vertical cylindric transects from the understorey to the canopy. In both Panama and Australia, leaf sclerophylly increased significantly with sampling height, while free-feeding herbivory decreased inversely. Gall distribution and survivorship responded significantly to sclerophylly, but distribution between understorey and canopy varied between study sites. The probability of gall survivorship increased with increasing leaf sclerophylly as death by fungi, parasitoids or accidental chewing were greater in the non-sclerophyllous vegetation in the understorey of both study sites. However, number of galls, proportion of infected sampled plants, and proportion of host species against total sampled species were all greater in Panama than in Australia. On the other hand, the Australian forest had a fauna much more concentrated on fewer hosts, with 80 % of galls infesting six host species. The present study supports the existence of a global positive effect of sclerophylly on gall establishment and survivorship in the upper canopy of tropical and subtropical forests.

A key issue for sustainable management of oak woodlands is understanding the complex overstory-understory relationships that influence ecosystem productivity and stability. Oak removal is traditionally practiced in Californian ranches and Spanish oak dehesas to increase forage for grazing, but the response of the understory, and subsequently of the trees, is not fully understood. Existing knowledge of the effects of trees on understory forage production and the effects of the understory on tree production and recruitment is reviewed to synthesize from what is known and to identify knowledge gaps. Emphasizing the few published manipulative experiments to clarify the importance of facilitation and competition, plant to plant interactions are analyzed to examine three aspects of the relationship between trees and the understory: understory production, tree growth and production, and tree regeneration. First, we find that understory production is related to canopy-caused gradients of aboveground and belowground resources such as light, nutrients, and water. Second, the consequences of tree density and understory structure on oaks are analyzed, including competitive use of belowground resources. Third, the importance of the understory for oak seedling survival is discussed for its effect on the stability and sustainability of Spanish and Californian oak woodlands. While dehesa shrub encroachment is certainly favorable for oak seedling regeneration, it does not maintain longer-term stand functions and profitability from livestock, wildlife, and cork production. We conclude by proposing a future research agenda for the study of plant-to-plant relationships.

Ponderosa Pine Forest is the lowest-elevation, most extensive forest in the American Southwest. It occurs in an elevational band below Mixed Conifer Forest and above Pinyon-Juniper vegetation, Gambel Oak Shrubland, and Interior Chaparral Shrubland. Stands are dominated by ponderosa pine, and are divided into moist, mesic, and dry stand types with decreasing elevation and moisture availability. A historical fire regime of frequent, low-severity surface fires is widely documented, but there is growing evidence of historical mixed-severity and high-severity fires, especially for steep slopes in areas of heterogeneous topography. Other important natural disturbances include insect outbreaks and drought. Late nineteenth century livestock grazing initiated fire exclusion, which was continued by fire management through most of the twentieth century. Other anthropogenic drivers are modern climate change, invasive species, recreation, and nearby land use. Vegetation dynamics are dominated by tree regeneration, thinning, and succession. Historical conditions ranged from open-canopied stands with a well-developed, often grass-­dominated understory – more woodland than forest – to denser stands. Stand densities increased during the twentieth century because of the exclusion of surface fires. Vegetation dynamics are illustrated in a nested, three-tiered set of conceptual models. Key conclusions and challenges for researchers and land managers are summarized.

Bulk deposits of aeolian sand accumulated over recent timescales provide instructive systems for examining effects of colonising vegetation on soil development. The two contrasting case studies presented here are eucalypt woodland in a dune system in southwest Australia and the rubified sand seas of the United Arab Emirates. In the former, clay pavements forming under the lateral root catchments of the eucalypts are shown to be constructed from iron, aluminium and other mineral elements abstracted from ground waters by deep roots. The pavements concerned have a marked restrictive influence on understorey density and biodiversity while also having an overall role in maximising effectiveness of usage of water and nutrients by the trees in question. Timescales and amounts of iron uplifted in this manner are estimated for the system. In the Arabian example, the occurrence of intense reddening (rubification) of sand towards the mountains of Oman is well known, and abiotic processes have been implicated in the phenomenon. In this chapter, we invoke involvement of a biotic component, having demonstrated a relationship between vegetation density and extent of rubification as seen in a positive correlation between increased reddening and cumulative vegetation encountered as one moves from coast to mountains. We hypothesise that uplift of iron by deep-rooted shrubs/trees might be the agent responsible for progressive reddening. Definitive testing of this hypothesis is required, particularly by analysing for iron in xylem sap flowing up through taproots and looking for evidence of its subsequent release into superficial layers of sand surrounding lateral roots of the trees.

The application thermal analysis and stable isotope mass spectrometry together to the study of soil organic matter (SOM) has received limited attention to quantify its heterogeneous nature and function within an ecosystem context. We analysed surface soils (0–30 cm) from forest plantations in Northern California with thermogravimetry-differential scanning calorimetry (TG-DSC) and 13C- and 15N-labelled litters combined with long-term incubations to quantify affects of diverse litter and fertiliser inputs on SOM energetic properties and the stability of SOM. For the thermal analysis, replicate sample data was processed to develop summary models of DSC thermograms for the range of sampling depths and treatments along with subsoils with comparable particle size and mineralogy. The models estimate ‘mineral-free’ SOM energy density and the proportion of energy from the three primary regions of exothermic activity corresponding to carbohydrates and lipids (150–350°C), aromatic and condensed polymers (400–460°C) and refractory/mineral associated C (500–550°C). Calculated energy budgets show soils that receive diverse litter inputs (pine and evergreen hardwood litter & roots) have greater SOM energy density than soils with pine only inputs. Fertiliser (NPK) additions to these systems enhanced these signals with ‘energetic enrichment’ in fertilised-mixed litter soil and ‘energy depletion’ in fertilised-pine litter soils. Long-term incubations following the fate of 13C/15N-labelled litters showed that increased diversity in the form of more understory shrub species increased the stability of recently added litter C and N. The treatment effects show changes in the stability of SOM with reduced diversity leading to less energy and less C being stabilised where understory was removed, a common practice in the forest industry. The results suggest plant diversity increases the stability of SOM showing that diverse species affect the stability and likely the function of SOM.

Many traditional land-use systems in Europe involved agroforestry in the pre-industrial era, but, over the years, increased mechanization led to the development of increasingly specialized crop, animal and wood production systems. As a consequence, the area under agroforestry declined in many regions of Europe, and agroforestry systems became confined to situations where understorey primary production is restricted due to cold temperatures (Boreal and Alpine areas) or drought (Mediterranean areas) and to plots that are hard to reach or too small for cultivation with modern machinery, as in Spain, Italy and the lower altitude mountain regions in southern and central Germany. On the whole, agroforestry continued to be practised only where it enabled farmers to obtain economic returns from lands that were otherwise relatively unproductive and mostly limited to silvopastoral practices. Since the mid-1990s, however, European policies have encouraged land management systems that combine production, environmental services (biodiversity, carbon sequestration, nutrient cycling and water quality) and social benefits, and this has created a new interest in agroforestry systems. Today, the major agroforestry practices in Europe include silvopasture and silvoarable. However, the benefits and opportunities offered by agroforestry can only be realized with substantial investments and coordinated efforts in research, education, knowledge transfer and appropriate national policies across Europe.

The rapid rate of global deforestation, estimated at an average of 6.4 million ha per annum between 2000 and 2010, draws attention to the need to minimize future loss of forest cover. This chapter outlines potential afforestation and reforestation strategies that could improve the state of tropical forest management by conserving biological diversity and increasing potential economic benefits to local communities. Forest plantations provide many of the benefits associated with natural forests, including timber and non-timber forest products, erosion control, stabilization of hydrologic processes, carbon sequestration, and wildlife habitats. Native species plantations will more closely mimic natural forests and provide many of the non-timber forest products that could be marketed beyond their current range. Continuing research on establishment of forest plantations using native species has provided a strong argument for their use based on stand productivity. Use of native species in place of exotics for plantation establishment could result in less negative impacts, both ecologically and economically, over time. Based on experiences of countries with extended histories of plantation forestry, the following recommendations should be considered as targeted guidelines for tropical forest plantation establishment: (1) use native species, within their native range and on suitable sites, (2) use multiple species to allow access to diverse markets, (3) select species that facilitate, or at least do not restrict, native understory development, and (4) consider the ability of species to sequester carbon. Implementation of these practices, whenever and wherever possible, should lead to more sustainable land use in tropical regions.

Largely a legacy of stand-replacing human disturbances, today’s central hardwood forests exhibit a narrower range of stand ages and structures than those in the presettlement landscape. Although natural disturbance types and frequencies vary within the region, large stand-replacing natural disturbances have always been infrequent; typical return intervals in excess of 100 years are longer than current forests have existed. Many present-day stands are dominated by early to mid-successional species in the overstory and late successional species in the understory; natural disturbances often serve to increase dominance of the understory late successional species, unless they are severe enough to disturb the canopy, forest floor, and soil. In any case, only the most severe natural disturbances or combinations of disturbances (including human disturbance) initiate large patches of early successional vegetation. Will the amount and spatial arrangement of early successional habitats created by natural disturbances be sufficient to meet management goals? We do not have the information to answer this question at present; the answer is further complicated by the potential effects of climate change on the rates and intensities of natural disturbances.

Terrestrial fossils from Late Miocene sediments in the Mokollsdalur area are mainly known for their insect fauna. Plant fossils and the sedimentological context suggest that most of the macrofossils deposited at Mokollsdalur originate from trees and shrubs that grew on the slopes around a caldera lake in the highlands. Abundant fossils of aquatic crustaceans, insects, and plants suggest that the lake and adjacent areas were a diverse ecosystem at the time of deposition. Forests covering the slopes were dominated by Fagus with a few evergreen elements in the understorey (Ilex, Rhododendron). In contrast, the palynological record points to the presence of mixed oak forests in areas behind the mountain ridge surrounding the caldera. The poor representation of herbaceous elements in the pollen record may point to a filter effect against pollen influx from surrounding areas into the lake. Slope exposure may have determined the presence of Fagus or Quercus as is also seen today in cool temperate regions of the northern hemisphere. Overall, the climate appears to be more diversified than in the older floras with relatively warmer humid conditions windward of the mountains or in sheltered areas close to the lake and cooler more continental conditions leeward of the mountains.

Theobroma cacao (cacao) is a tropical understory tree with sensitivity to drought. Cacao responds to drought by decreases in net photosynthesis, PS II efficiency, stomatal conductance, water potential and changes in leaf florescence. Drought also alters cacao gene expression as well as leaf glucose and free amino acid content. In recent years an incredible diversity of fungal endophytes has been identified in association with cacao. These endophytes are being studied for the benefits they provide to cacao including tolerance to biotic and abiotic stresses. During establishment of the endophytic association between cacao and fungal endophytes both plant and fungal gene expression are altered. The endophytic Trichoderma hamatum isolate DIS 219b delays the onset of drought stress in cacao. This delay manifests itself through enhanced root growth, maintenance of stomatal conductance, water potential, net photosynthesis, and PSII efficiency, changes in free amino acid concentrations, and a delay in drought-induced changes in leaf gene expression. The cacao plant and DIS 219b adapt to each other and this adaptation may contribute to the observed plant growth promotion and the delay in onset of drought stress. The increase in root growth is thought to increase water uptake and availability, delaying the time point where the water supply becomes limiting and drought stress occurs.

Studies in postagricultural forests have suggested that the effect of land use overrides that of environmental factors in defining the present forest composition. This study demonstrates that the effect of land use history in the composition of postagricultural forests can be reduced by exposure to frequent disturbance. The study was undertaken in a rural landscape of the Peruvian Amazon floodplain with a history of land use and periodic river disturbance. The history of land use for the region was reconstructed using a set of remote sensing images dating from 1948. Trees above 2.5 cm DBH were identified and measured in 46 plots of 600 m2 in postagricultural forests older than 10 years. For each plot, I measured its distance to other landscape features (river, swamps, lowland forest, upland forests) and its elevation above sea level. In this region, elevation correlates to the probability of a site being exposed to flooding. Correlations of the explanatory variables to a nonmetric multidimensional scaling (NMDS) ordination were used to evaluate the relative effect of elevation, distance to landscape features, and time since abandonment in the canopy and understory composition of the plots. Correlations to the NMDS ordination show that both canopy and understory species compositions are better explained by flood exposure for older plots. It also indicates that the distance to forest patches affects the composition of postagricultural forests. In general, the results show that land use in the Amazonian floodplain has not erased the natural environmental gradients of the landscape.

Wildland fire has been a key selective force through evolutionary time, influencing the development of characteristic adaptations of forest trees ranging from the serotinous cones of lodgepole pine (Pinus contorta) to the vigorous sprouting of Canary Island pine (Pinus canariensis) (Keeley and Zedler 1998). In the semi-arid southwestern United States, forest fires play complex ecological and social roles. Ecologically, the southwestern U.S. encompass forests adapted to severe, stand-replacing fires, those adapted to frequent surface fires, and forests with a mixture of fire intensities. Overlaid on this natural mosaic, however, modern industrial society has consistently sought to suppress fire (Pyne 1982). An unintended consequence of fire exclusion, however, is the accumulation of fuel horizontally across contiguous tree canopies and vertically through the crowns of small understory trees. Coupled with warming climate, more droughts, less snow, and longer fire seasons, there is little doubt that severe fires will increase (Westerling et al. 2006). For forest ecosystems not adapted to severe burning and already stressed by non-native species, human impacts, and climate change, the likelihood of substantial irreversible degradation appears high (Savage and Mast 2005; Strom and Fule 2007). Early proponents of taking an ecological approach to fire, such as Leopold (1924) and Weaver (1951), were lonely voices in their time. Today, however, the attention of scientists and forest managers is focused on the restoring of the naturally fire-resilient characteristics of native ecosystems (Falk 2006). In order to have a chance to accomplish this goal, it is vital that we have the best possible understanding of historical forest characteristics: fire regimes, forest structure, species composition, and dynamics.

The last 50 years or so have seen a steady increase in the rate of destructive wildfires across the world, partly as a result of climate change and partly as a result of encroachment of human settlement on fire-based ecosystems (Russell et al. 2004; Westerling et al. 2006). Years of active fire suppression in such areas has inevitably led to the build-up of hazardous fuel loads, creating ideal conditions for destructive wildfires (Johnson et al. 2001). Recently, serious wildfires have occurred in Australia, southeast Asia and the Mediterranean, as well as those occurring in the USA in California, Montana, Idaho and Alaska. Current thinking on fire management is very much focused on re-instating natural fire regimes and allowing fire, as nearly as possible, to function in its natural ecological role (Miller 2006), thereby reducing the occurrence of destructive fires. Mechanical fuel treatments (e.g. thinning) and prescribed burning are being used to reduce fuel loads to near natural conditions, after which natural fire regimes can be allowed to operate. There are two main types of thinning that either remove selected trees to create a more widely spaced forest consisting of trees of different sizes/ages or remove all smaller trees and brush within the understory to leave a more uniform forest of more widely spaced older trees. Prescribed burning uses small managed fires, rather than mechanical means, to achieve the latter. This is a long and involved process and often has the potential to create conflict between the different management regimes associated with adjacent lands and between the different inhabitants and stakeholders affected in the short to medium term. This requires a high degree of collaboration and participatory planning if acceptable fuel reduction strategies and management plans are to be developed.

Early farming activity migrated originally from forests. A high rate of cultivation led to almost complete degradation of Dutch forests. To conserve them it was necessary to prohibit grazing of forests. Since a few decades, grazing has been used as a measure to improve the natural values of forests. An agroforestry system, which existed for a long period in the Netherlands, was high-growing fruit trees (boguards) with an underlayer of grass, which was mowed or grazed by cows and sheep. Recently there has been an increased interest in combining trees as multipurpose natural elements with agricultural activities. Research and demonstration projects have been established in different parts of the Netherlands. Walnut (Juglans regia L.) is the most widely planted tree species. Density varies between 25 and 100 trees per hectare. Understorey vegetation is mostly grass, which is grazed by sheep, cows or horses/ponies or is mowed and ensiled. Other combinations of tree species with understorey are explored. Some research has been carried out regarding the attitude of modern farmers. Farmers from different regions had different attitudes. The needs of an urbanising countryside seem to favour chances for agroforestry.

The impact of human disturbance on colonisation dynamics of vascular epiphytes is poorly known. We studied abundance, diversity and floristic composition of epiphyte seedling establishing on isolated and adjacent forest trees in a tropical montane landscape. All vascular epiphytes were removed from plots on the trunk bases of Piptocoma discolor. Newly established epiphyte seedlings were recorded after 2 years, and their survival after another year. Seedling density, total richness at family and genus level, and the number of families and genera per plot were significantly reduced on isolated trees relative to forest trees. Seedling assemblages on trunks of forest trees were dominated by hygrophytic understorey ferns, those on isolated trees by xerotolerant canopy taxa. Colonisation probability on isolated trees was significantly higher for plots closer to forest but not for plots with greater canopy or bryophyte cover. Seedling mortality on isolated trees was significantly higher for mesophytic than for xerotolerant taxa. Our results show that altered recruitment can explain the long-term impoverishment of post-juvenile epiphyte assemblages on isolated remnant trees. We attribute these changes to a combination of dispersal constraints and the harsher microclimate documented by measurements of temperature and humidity. Although isolated trees in anthropogenic landscapes are considered key structures for the maintenance of forest biodiversity in many aspects, our results show that their value for the conservation of epiphytes can be limited. We suggest that abiotic seedling requirements will increasingly constitute a bottleneck for the persistence of vascular epiphytes in the face of ongoing habitat alteration and atmospheric warming. peerReviewed

Species richness and composition of the Chrysomelidae (Coleoptera) were studied in larch (Larix kaempheri [Lamb.] Carriere) plantations, secondary forests, and primary forests. In addition, the effects of forest management practices, such as thinning and long rotation, were examined in the larch plantation. The species richness of Chrysomelidae was higher in the larch plantation than in the secondary forest or in the primary forest. Among the larch plantations, the species richness in old-aged plantations was higher than that in middle-aged plantations. The composition of the beetle assemblages in the larch plantation differed from that in the secondary forest or in the primary forest. Exosoma akkoae (Chujo), Batophila acutangula Heikertinger, and Calomicrus nobyi Chujo were caught with a bias toward the larch plantation. Longitarsus succineus (Foudras) and Sphaeroderma tarsatum Baly were caught more in the secondary forest and the primary forest, respectively. More B. acutangula and S. tarsatum were caught in stands where their host plants occurred at higher rates. Species richness of understory plants was an important factor for chrysomlid species richness, and frequency of host occurrence affected the number of individuals of leaf beetles examined. It seems that forest types and forest management practices affect host plants as well as Chrysomelidae, and that these effects on the host plants also influence chrysomelid assemblages.