Carbon sequestration potential of five tree species in a 25-year-old temperate tree-based intercropping system in southern Ontario,Canada

Carbon (C) sequestration potential was quantified for five tree species, commonly used in tree-based intercropping (TBI) and for conventional agricultural systems in southern Ontario, Canada. In the 25-year-old TBI system, hybrid poplar (Populus deltoides × Populus nigra clone DN-177), Norway spruce (Picae abies), red oak (Quercus rubra), black walnut (Juglans nigra), and white cedar (Thuja occidentalis) were intercropped with soybean (Glycine max). In the conventional agricultural system, soybean was grown as a sole crop. Above- and belowground tree C Content, soil organic C, soil respiration, litterfall and litter decomposition were quantified for each tree species in each system. Total C pools for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and a soybean sole-cropping system were 113.4, 99.4, 99.2, 91.5, 91.3, and 71.1 t C ha^?1, respectively at a tree density of 111 trees ha^?1, including mean tree C content and soil organic C stocks. Net C flux for hybrid poplar, white cedar, red oak, black walnut, Norway spruce and soybean sole-crop were 2.1, 1.4, 0.8, 1.8, 1.6 and ?1.2 t C ha^?1 year^?1, respectively. Results presented suggest greater atmospheric CO₂ sequestration potential for all five tree species when compared to a conventional agricultural system.     

Tree establishment and growth using forage ground covers in an alley-cropped system in Midwestern USA

The integration of forage crops in an alley-cropped system was examined as a method of encouraging tree planting to increase farm income, improve soil quality, and enhance biodiversity on Midwestern U.S. farms. Crop and tree performance were evaluated in an alley-cropped system using four forage intercrops grown in tree alleyways to simulate a potential hay crop – oat (Avena sativa L.) and red clover (Trifolium pratense L.); oat, red clover, and red fescue (Festuca rubra L.); oat, red clover, and orchardgrass (Dactylis glomerata L.); and oat and hairy vetch (Vicia villosa Roth) – compared to a herbicide, mowing and control (no management) treatment. Five tree species, divided into fast-growing hardwoods of two poplar (Populus spp.) clones [Crandon (P. alba L. × P. grandidentata Michx.) and Eugenei (P. deltoids Bartr. × P. nigra L.)], and silver maple (Acer saccharinum L.) were compared with two high-value, slow-growing hardwoods planted from seed and as seedlings: red oak (Quercus rubra L.) and black walnut (Juglans nigra L.). Tree survival in the first year was greater for the fast-growing species, and by the fourth year, tree height among the four forage treatments was equivalent for all upland locations. The oat/hairy vetch ground cover was associated with the shortest trees in the bottomland site. Herbicide-treated trees were taller than the average of the four forage treatments for all four planting conditions. Tree height in the mowing and the control treatments was not significantly different for all four planting conditions. The nutritive value of the forage crop was excellent in the second year of tree establishment, with crude protein content and digestibility at 17 and 71%, respectively, in the oat/red clover/red fescue treatment, suggesting the viability of forage crops as alternatives to herbicides in alley-cropped systems.     

Allelopathic Interactions Between Herbaceous Species and Trees Grown in Topsoil and Spoil Media

Dried foliage (litter) of several herbaceous species was mixed with either vermiculite or two minesoils (topsoil and spoil) in containers planted with black locust (Robinia pseudoacacia), white ash (Fraxinus americana) or sweetgum (Liquidambar styraciflrua) seedlings in a greenhouse. Also, germinated seed of northern red oak (Quercus rubra) was planted in containers previously seeded with herbaceous species. In vermiculite, black locust growth was inhibited by 12 g litter additions of ranger alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus), tall fescue (Festuca arundinacea), and Kentucky bluegrass (Poa pratensis), but stimulated by red clover (Trifolium pratense) litter. White ash growth was strongly inhibited by alfalfa and trefoil added to vermiculite at 12 and 18 g levels. In topsoil, sweetgum was strongly inhibited by alfalfa litter. Both sweetgum and red oak grew poorly in spoil, but seeded perennial ryegrass (Lolium perenne), orchardgrass (Dactylis glomerata) and fescue grew well. Some aspects of red oak growth were inhibited if grown in containers seeded with alfalfa, ryegrass, orchardgrass, red clover or fescue. Although isolation and identification of allelopathic compounds was not attempted, these results demonstrate that there may be important allelopathic interactions between herbaceous species and trees planted on minelands.     

Oak mortality associated with crown dieback and oak borer attack in the Ozark Highlands

Oak decline and related mortality have periodically plagued upland oak–hickory forests, particularly oak species in the red oak group, across the Ozark Highlands of Missouri, Arkansas and Oklahoma since the late 1970s. Advanced tree age and periodic drought, as well as Armillaria root fungi and oak borer attack are believed to contribute to oak decline and mortality. Declining trees first show foliage wilt and browning, followed by progressive branch dieback in the middle and/or upper crown. Many trees eventually die if severe crown dieback continues. In 2002, more than 4000 living oak trees ≥11 cm dbh in the relatively undisturbed mature oak forests of the Missouri Ozark Forest Ecosystem Project (MOFEP) were randomly selected and inventoried for tree species, dbh, crown class, crown width, crown dieback condition (healthy: <5% crown dieback, slight: >5–33%, moderate: 33–66%, and severe: >66%) and number of emergence holes created by oak borers on the lower 2.4 m of the tree bole. The same trees were remeasured in 2006 to determine their status (live or dead). In 2002, about 10% of the red oak trees showed moderate or severe crown dieback; this was twice the percentage observed for white oak species. Over 70% of trees in the red oak group had evidence of oak borer damage compared to 35% of trees in the white oak group. There was significant positive correlation between crown dieback and the number of borer emergence holes (p < 0.01). Logistic regression showed oak mortality was mainly related to crown width and dieback, and failed to detect any significant link with the number of oak borer emergence holes. Declining red oak group trees had higher mortality (3 or 4 times) than white oaks. The odds ratios of mortality of slightly, moderately, and severely declining trees versus healthy trees were, respectively, 2.0, 6.5, and 29.7 for black oak; 1.8, 3.8, and 8.3 for scarlet oak; and 2.6, 6.5 and 7.1 for white oaks.     

Influences of woody encroachment and restoration thinning on overstory savanna oak tree growth rates

Midwestern savannas historically covered >10 M ha in central North America, but are now rare due to agricultural conversion and anthropogenic modifications to disturbance regimes - particularly fire suppression. Throughout this range, Midwestern savannas are characterized by scattered overstory trees; however, with fire suppression, these systems are invaded by non-savanna trees. Restoration of encroached savannas involves removal of invading trees, yet little is known about the impacts of encroachment or encroachment removal on the relict savanna overstory trees, which define these systems. Here, we use tree ring analysis to investigate savanna tree growth rates in encroached, non-encroached, and experimentally restored Midwestern oak savannas in central Iowa. We found that woody encroachment led to pronounced declines in growth rate (ring width) of relict overstory white oak (Quercus alba), relative to Q. alba trees in competition-free, open-grown conditions, or in an encroachment-free remnant woodland. To further understand effects of encroachment removal on relict Q. alba savanna trees, we conducted a large-scale restoration experiment, where encroaching trees were mechanically removed from four encroached savannas, with an additional four savannas retained as encroached controls. Restoration led to elevated tree growth rates, with these changes generally persistent through 7 years post-restoration (2003-2009). Over the course of this post-restoration study period, ring width, basal area increment, and relative basal area increased by 49%, 59%, and 55%, respectively, in trees from restored sites, relative to trees from encroached, control sites. These results suggest that woody encroachment has strong influence on overstory savanna trees, through increased competitive dynamics; however, woody encroachment removal may help to restore relict savanna tree growth rates, even after prolonged periods of encroachment (>40 years). To restore the oak savannas at our sites, and perhaps elsewhere, we advocate a three step process: (1) mechanical woody encroachment removal, (2) maintenance of the encroachment-free state through prescribed fire, and (3) promotion of a diverse understory layer, characteristic of oak savanna in our region. While promoting oak regeneration will be important for the long-term maintenance of these sites as oak savanna, relict savanna trees appear responsive to restoration and should maintain overstory conditions through the near-term.     

Osmotic potential of several hardwood species as affected by manipulation of throughfall precipitation in an upland oak forest during a dry year

Components of dehydration tolerance, including osmotic potential at full turgor (Psi(pio)) and osmotic adjustment (lowering of Psi(pio)), of several deciduous species were investigated in a mature, upland oak forest in eastern Tennessee. Beginning July 1993, the trees were subjected to one of three throughfall precipitation treatments: ambient, ambient minus 33% (dry treatment), and ambient plus 33% (wet treatment). During the dry 1995 growing season, leaf water potentials of all species declined to between -2.5 and -3.1 MPa in the dry treatment. There was considerable variation in Psi(pio) among species (-1.0 to -2.0 MPa). Based on Psi(pio) values, American beech (Fagus grandifolia Ehrh.), dogwood (Cornus florida L.), and sugar maple (Acer saccharum Marsh.) were least dehydration tolerant, red maple (A. rubrum L.) was intermediate in tolerance, and white oak (Quercus alba L.) and chestnut oak (Quercus prinus L.) were most tolerant. During severe drought, overstory chestnut oak and understory dogwood, red maple and chestnut oak displayed osmotic adjustment (-0.12 to -0.20 MPa) in the dry treatment relative to the wet treatment. (No osmotic adjustment was evident in understory red maple and chestnut oak during the previous wet year.) Osmotic potential at full turgor was generally correlated with leaf water potential, with both declining over the growing season, especially in species that displayed osmotic adjustment. However, osmotic adjustment was not restricted to species considered dehydration tolerant; for example, dogwood typically maintained high Psi(pio) and displayed osmotic adjustment to drought, but had the highest mortality rates of the species studied. Understory saplings tended to have higher Psi(pio) than overstory trees when water availability was high, but Psi(pio) of understory trees declined to values observed for overstory trees during severe drought. We conclude that Psi(pio) varies among deciduous hardwood species and is dependent on canopy position and soil water potential in the rooting zone.     

Effect of gap size on mid-rotation stand structure and species composition in a naturally regenerated mixed broadleaf forest

This paper is an assessment of the effect of gap size on stand structure and species composition 48 years following treatment in a mixed broadleaf upland forest. Established in 1960, the study tests three circular openings, 15.2 m (0.02 ha), 45.7 m (0.16 ha), and 76.2 m (0.46 ha). Forty-eight years following treatment (2008) basal area, top height, and quadratic mean diameter were significantly lower in 15.2 m openings. Maple (Acer spp.) species had the highest mean importance value across treatments (0.40). Trends suggest that species composition of dominant and codominant trees among opening sizes may have been influenced by shade tolerance adaptations of the species groups present. Whereas 15.2 m openings were dominated by shade tolerant maple species, 45.7 and 76.2 m openings produced a mixture of commercial species including shade intolerant species such as yellow-poplar (Liriodendron tulipifera L.), trees of intermediate shade tolerance like oak (Quercus spp.), and shade tolerant maple. Data further suggest the density of overstory oak was highest in the intermediate opening size (45.7 m), while yellow-poplar increased in the larger opening sizes. Evaluation of species shifts between 1981 and 2008 showed that relative basal area of maple increased across all treatments. Relative basal areas from 45.7 to 76.2 m openings suggest declines in yellow-poplar and other non-commercial species were balanced by increases in oak and maple.     

Effects of soil fauna on leaf litter decomposition under different land uses in eastern coast of China

Soil fauna decompose litter, whereas land use changes may significantly alter the composition and structure of soil fauna assemblages. However, little is known of the effects of land-use on the contribution of soil fauna to litter decomposition. We studied the impacts of soil fauna on the decomposition of litter from poplar trees under three different land uses (i.e. poplar-crop integrated system, poplar plantation, and cropland), from December 2013 to December 2014, in a coastal area of Northern Jiangsu Province. We collected litter samples in litterbags with three mesh sizes (5, 1 and 0. 01 mm, respectively) to quantify the contribution of various soil fauna to the decomposition of poplar leaf litter. Litter decomposition rates differed significantly by land use and were highest in the cropland, intermediate in the poplar-crop integrated system, and lowest in the poplar plantation. Soil fauna in the poplar-crop integrated system was characterized by the highest numbers of taxa and individuals, and highest Margalef’s diversity, which suggested that agro-forestry ecosystems may support a greater quantity, distribution, and biodiversity of soil fauna than can single-species agriculture or plantation forestry. The individuals and groups of soil fauna in the macro-mesh litterbags were higher than in the meso-mesh litterbags under the same land use types. The average contribution rate of meso- and micro-fauna to litter decomposition was 18.46%, which was higher than the contribution rate of macro-fauna (3.31%). The percentage of remaining litter mass was inversely related to the density of the soil fauna (P < 0.05) in poplar plantations; however, was unrelated in the poplar-crop integrated system and cropland. This may have been the result of anthropogenic interference in poplar-crop integrated systems and croplands. Our study suggested that when land-use change alters vegetation types, it can affect species composition and the structure of soil fauna assemblages, which, in turn, affects litter decomposition.     

Structure of pollarded oak forest in relation to aspect in Northern Zagros,Iran

We analyzed the structure of pollarded oak forest and biometric indices of pollarded oak species in relation to aspect in northern Zagros forests, western Iran. A number of 319 circular plots (0.1 ha) were established using a systematic random method over the study area. In each plot, for all trees (diameter at breast height ≥5 cm) diameter was measured and tree species was recorded. Total height, trunk height, and major and minor diameter axis of the crown of two trees in each plot (nearest tree to the center of the plot and the largest tree in term of diameter) were measured. As the dispersion of slope and altitude classes in the study area were identical, the effect of these factors was assumed to be constant. To evaluate the effect of aspect on biometric indices of oak trees a comparison was used for each oak species separately. The results indicated that the forest species composition differed statistically significant in main aspects except for easterly and westerly aspects (P < 0.01). The diameter of similar oak trees was significantly different except for Lebanon oak in northerly and southerly and Gall oak in easterly and westerly aspects (P < 0.01), but there was no significant difference between the total height and crown area of similar oak species in different aspects. Differences in diameter, height, and crown area distributions showed a significant difference in main aspects. The basal area and tree density in northerly and southerly aspects were significantly different (P < 0.05).     

Intercropping trees’ effect on soil oribatid diversity in agro-ecosystems

The benefits of tree-based intercropping (TBI) compared to conventional agro-ecosystems in North America could include climate change mitigation and adaptation, although enhancing resilience to climate change through increasing soil diversity remains poorly explored. Diversity of soil microarthropods supports a series of ecological services that may be altered by soil desiccation due to climate change. Here we study the effect of red oak and hybrid poplar TBI on soil oribatid mite species assemblages associated to forage crops (mix of Timothy-grass and red clover). Abundance and species density of oribatids were affected by treatment, depth and the interaction of both variables. Abundance of oribatid mites was significantly lower in the oak TBI, showing a homogeneous vertical distribution in opposition to a decreasing with depth distribution under poplar TBI and conventional crops. Species density was significantly higher in the conventional crop, showing again significant differences in depth that were not present in both TBI treatments. Distance to tree did not affect mite abundance nor species density. TBI increased oribatid richness (obtained by sample-based rarefaction and extrapolation) only in the presence of oaks. The distribution of oribatids was strongly associated to tree fine root biomass and stress the importance of underground organic resources for the oribatid fauna and their ecological functions. If increasing drought associated with climate change desiccates superficial levels of agro-ecosystem soils, deeper sources of organic resources, such as tree roots, should become crucial in the maintenance of diverse microarthropod communities.     

Biotic interactions in a Mediterranean oak forest: role of allelopathy along phenological development of woody species

Plant–plant chemical interactions in forests can have a strong impact on the biodiversity and dynamics of these ecosystems, particularly in Mediterranean forests where plants exhibit a high secondary metabolite diversity. Allelopathic interactions in Mediterranean ecosystems have been mostly studied in the first stages of ecosystem dynamics, shrublands and pine forests, but little is known about these interactions in mature oak forests. In this study, the allelopathic effect of three main woody species of downy oak forests (Quercus pubescens, Acer monspessulanum and Cotinus coggygria) on germination and growth of two herbaceous species (Festuca ovina and Linum perenne) was tested through aqueous extracts obtained from different leaf phenological stages (green, senescent and litter). The germination velocity of the two target species was inhibited by the aqueous extracts of senescent leaves from all the woody species. The growth of F. ovina seedlings was affected by aqueous extracts of green leaves of all the woody species, while the growth of L. perenne was only affected by aqueous extracts of green leaves of A. monspessulanum. This shows that (i) allelochemicals released by leaf leachates of the dominant woody species could control the dynamic of the herbaceous species, and then their potential competition with trees and (ii) allelopathic effects of woody species are related to their phenological stage and seem consistent with the development stage of target species.

     

Seed bank and regeneration dynamics of <Emphasis Type="Italic">Emmenopterys henryi</Emphasis> population on the western side of Wuyi Mountain,South China

Emmenopterys henryi Oliv. (Rubiaceae) is an endangered tree species that is native to China. The wild populations of E. henryi have declined rapidly because of its poor natural regeneration, but the actual regeneration processes are not yet understood. In field tracking surveys and experiments in the Wuyishan Nature Reserve in Southeast China to determine the most important stage that affects the regeneration process, seed bank characteristics, seed germination, and seedling growth dynamics were studied in the typical habitats of E. henryi, Phyllostachys pubescens and broad-leaved forests. Results showed that in both P. pubescens and broad-leaved forests, more than 70% of the E. henryi seeds were distributed in moss and litter layers, and few were found in the soil beneath them. However, seed germination in the soil layer was significantly higher than in the moss and litter layers. Seed density, overall seed quality, and germination rate in the broad-leaved forest were significantly higher than in P. pubescens forest. Seed germination was highest in the microsites around the edge of the crown projection area of E. henryi mother trees. The order of survival rate of the seedlings on different ground surfaces was soil > moss > litter. In both habitats, the average seed density was 24.9 seeds m^?2, and the total germination rate was less than 3.5‰. However, seedlings developed from only 1% of the germinated seeds, indicating that the seed germination is the most important stage in the natural regeneration of E. henryi.     

Relationships between advance oak regeneration and biotic and abiotic factors

Relationships between advance regeneration of four tree species (red maple (Acer rubrum L.), white oak (Quercus alba L.), chestnut oak (Q. montana Willd.) and northern red oak (Q. rubra L.)) and biotic (non-tree vegetation and canopy composition) and abiotic (soil series and topographic variables) factors were investigated in 52, mature mixed-oak stands in the central Appalachians. Aggregate height was used as a composite measure of regeneration abundance. Analyses were carried out separately for two physiographic provinces. Associations with tree regeneration were found for all biotic and abiotic factors both in partial models and full models. Red maple was abundant on most of the sites, but high red maple abundance was commonly associated with wet north-facing slopes with little or no cover of mountain-laurel (Kalmia latifolia L.) and hay-scented fern (Dennstaedtia punctilobula (Michx.) Moore). Regeneration of the three oak species was greatly favored by the abundance of overstory trees of their own kind. White oak regeneration was most abundant on south-facing, gentle, lower slopes with soils in the Buchanan series. Chestnut oak regeneration was more common on south-facing, steep upper slopes with stony soils. There was a positive association between chestnut oak and huckleberry (Gaylussacia baccata (Wangh.) Koch) cover classes. Northern red oak was more abundant on north-facing wet sites with Hazleton soil, and was associated with low occurrence of mountain-laurel and hay-scented fern.     

Die Wirkung wäßriger Streuextrakte verschiedener Waldbäume auf Mycelwachstum und Konidiosporenkeimung von Fomes annosus (Fr.) Cke.

The effect of water extracts of leaf and needle litter from different forest trees on the mycelial growth and the germination rate of conidia of Fomes annosus (Fr.) Cke. Litter extracts from various forest trees and stands have distinct effects on mycelial growth and germination rate of conidia of Fomes annosus. The effects depend on concentration of the extract, period of extraction and on date of collecting the litter samples.     

Forage legumes as living mulches for trees in agroforestry practices -- preliminary results

Successful establishment and growth of tree seedlings in an agroforestry practice is dependent on the control of competing herbaceous vegetation. Conventional weed control methods (i.e., chemical, mechanical, and physical suppression) are effective but can be costly in terms of time, damage to non-target vegetation, or increased soil erosion. Alternatively, some living mulches can exclude undesirable vegetation, protect the soil, compete minimally with associated trees, and supplement soil nitrogen. In this study, small and large white clover (Trifolium repens L.), red clover (T. pratense L.), kura clover (T. ambiguum Bieb.), strawberry clover (T. fragiferum L.), birdsfoot trefoil (Lotus corniculatus L.), hairy vetch and ’AU Early‘ hairy vetch (Vicia villosa Roth) were selected for evaluation as living mulches. These species were established in 9 m ×9 m replicated plots along with two controls [tall fescue (Festuca arundinacea Schreb.) and bare soil kept vegetation free using glyphosate]. The controls represent ’high competition‘ and ’no competition‘, respectively. Eastern black walnut (Juglans nigra L.), honeylocust (Gleditsia triacanthos L.), and hybrid pitch × loblolly pine (Pinus rigida L. × P. taeda L.) seedlings were planted in association with each living mulch. Tree seedling heights and diameters were measured during the first two years and forage performance evaluated. All seedlings grew better in the absence of competition. Tall fescue greatly reduced the growth of hardwood seedlings. Red clover and ladino clover showed the greatest promise as living mulches for use with the hardwood and pine seedlings, respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

Microclimate of a natural pasture under planted Robinia pseudoacacia in central Appalachia, West Virginia

The conditions under which forages yield more under tree canopies than in open fields are not well understood. This study was conducted to determine how microclimate experienced by forages in central Appalachia is modified by black locust (Robinia pseudoacacia L.) tree canopies. The effect of tree row location relative to forage growing point was evaluated for its impact on soil water, photosynthetically active radiation (PAR), red/far-red ratio, and surface soil temperature. There was no consistent spatial dependency relating tree rows to soil water levels. While daily PAR decreased as the time under shade increased, the level of PAR under tree canopies nearly doubled as cloud cover increased from 0 to 25%. The red/far-red ratio decreased from 1.16 to 0.2 over forage growing between tree rows compared to forage within tree rows. Surface soil temperature remained nearly constant (1.5–2 °C increase) during sunny days under tree canopies but increased 8–12 °C by mid afternoon at unshaded sites depending on soil water levels. Forages under black locust trees experienced less extreme variation in both daily PAR and temperature than unshaded forages, thus reducing the metabolic cost of adaptation to extreme conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phenological responses of juvenile pecan and white oak on an upland site

Pecan (Carya illinoiensis) and white oak (Quercus alba) produce multiple products and wildlife values, but their phenological responses to N fertilization have not been well characterized. We compared tree growth at planting and for six consecutive growing seasons during establishment (2003–2008, Test 1), and determined if phenology of budburst, leaf area index (LAI), quantum yield of photosystem II (Fv/Fm), radial growth, and total chlorophyll concentration (a, b) responded to poultry litter fertilization supplying 0, 50, and 100 kg ha^?1 N (2010–2012, Test 2) in a mixed-species orchard on an upland site near Booneville, Arkansas. Species did not differ significantly in height in Test 1. Budburst was 9 days earlier for white oak than pecan in 2010. Budburst for both species could be predicted by accumulating chilling and forcing units throughout the dormant season. Maximum predicted radial growth was comparable for pecan (2.19 mm) and white oak (2.26 mm), and peaked 28 days earlier for white oak (3 June) than pecan (1 July). White oak LAI generally exceeded that of pecan during the growing season. Senescence began about 27 October regardless of species, and was better characterized by decreasing Fv/Fm or total chlorophyll concentration than LAI. Phenology was generally not responsive to N fertilization, perhaps because of adequate soil and foliar N. The study provides additional information on growth responses of these high-valued species to supplemental fertilization on an upland site.     

Five-year radial growth of red oaks in mixed bottomland hardwood stands

We studied the relationships among 5-year radial (diameter and basal area) growth of red oak (genus Quercus, subgenus Erythrobalanus) crop trees and predictor variables representing individual tree vigor, distance-dependant competition measures, and distance-independent competition measures. The red oaks we examined are representative of the commercially and ecologically important oak species of the bottomland hardwood forests of the southeastern US. The crown class score, a quantitative measure of crown class and tree vigor, performed best in accounting for the variability in tree diameter growth. Plot-level variables failed to account for a significant proportion of the variability in tree radial growth. The basal area of the first-order neighbors that were taller than the crop trees and located within 2.4 times the mean overstory crown radius had the highest negative correlation with crop tree 5-year radial growth. Red oaks were a major part of these competitors and likely exerted the greatest competitive pressure. However, crop tree radial growth was positively associated with the basal area of the red oaks which were indirect (second order) neighbors and which were taller than the crop trees. It is possible that indirect neighbors do not compete with the crop trees, but they likely compete with the direct competitors of the crop trees, thus having an indirect positive influence on crop tree growth. Such reasoning is consistent with previously observed spatial dependence up to four times the mean overstory crown radius. The findings may have implications for thinning hardwoods stands and crop tree management in that foresters need to take into account (1) oak intra-genus competition, (2) the negative competitive effect of direct neighbors, and (3) the potentially positive effect of the indirect neighbors, the competitors’ competitors.     

Establishment and production from thinned mature deciduous-forest silvopastures in Appalachia

Small Appalachian hill farms may benefit economically by expanding grazing lands into some of their under-utilized forested acreages. Our objective was to study the forage production potential of forest to silvopasture conversion. We thinned a white oak dominated mature second growth forested area establishing two orchardgrass-perennial ryegrass-white clover silvopasture replications for comparison with two nearby open pasture replications. After thinning trees, silvopastures were limed, fertilized and seeded. Sheep were fed hay and corn scattered across the area to facilitate removal of residual understory vegetation, disruption of litter layer and incorporation of applied materials into surface soil. Each area was divided into multiple paddocks and rotationally grazed by sheep. Two 1 m² herbage mass samples were taken from each paddock prior to animal grazing. There was no significant difference in soil moisture between silvopastures and open pastures however, there was adequate rainfall to prevent drought all 3 years. The two silvopastures received 42 and 51% of total daily incident PAR compared to the open field. Total dry forage mass yield from open pasture over the 3 years averaged 11,200 kg ha⁻¹ y⁻¹ and from silvopasture 6,640 kg ha⁻¹ y⁻¹. Silvopastures, however, had a higher PAR use efficiency (PARUE) than open pasture. Hill farms could increase grazing acreages without sacrificing all benefits from trees on the landscape by converting some areas to silvopasture.     

Relationships of overstory trees and shrubs with forage species portray ecosystem service interactions in smallholder fallows

Interactions among ecosystem services are increasingly perceived as important to ecosystem service delivery. Synergies and trade-offs among ecosystem services arise through direct ecological interactions or indirectly through correlated responses to other factors. To investigate whether and how interactions of overstory trees and shrubs with livestock forage species growing beneath generate ecosystem service interactions, overstory and forage species were examined in smallholder fallows in western Kenya. In 18 grazed and 21 improved fallows, we estimated biomass and quantified soil properties. We assessed whether the overstory reduces forage biomass and quality through competition, and whether overstory niche complementarity ameliorates competition or enhances facilitation. In improved fallows, forage biomass declined with overstory biomass, indicating competition and a wood-forage trade-off. In grazed fallows, biomass of higher quality forage species increased with overstory biomass, indicating a synergy, likely indirect. Niche complementarity, quantified as taxonomic and functional diversity, did not appear influential. Forage quality was not associated with overstory characteristics, but declined with grazing intensity. The contrasting relationships between overstory and forage species among fallow types appear ultimately attributable to the presence and intensity of grazing and the dense overstory in improved fallows.