Interior Trees Research Articles

Brief windows with more favorable atmospheric conditions explain patterns of Polylepis reticulata tree water use in a high-altitude Andean forest.

Polylepis trees occur throughout the Andean mountain region, and it is the tree genus that grows at the highest elevation worldwide. In the humid Andes where moisture is rarely limiting, Polylepis trees must adapt to extreme environmental conditions, especially rapid fluctuations in temperature, ultraviolet radiation and vapor pressure deficit (VPD). However, Polylepis' water-use patterns remain largely unknown despite the importance of understanding their response to microclimate variation to determine their capacity to maintain resilience under future environmental change. We conducted a study in a Polylepis reticulata Kunth forest in the Ecuadorian Andes to evaluate its tree water-use dynamics and to identify the main environmental drivers of transpiration. Tree sap flow was monitored simultaneously with soil volumetric water content (VWC) and microclimate during 2 years for trees growing in forest edge and interior locations. We found that sap flow was primarily controlled by VPD and that VWC exerted a secondary role in driving sap flow dynamics. The highest values for sap flow rates were found when VPD>0.15kPa and VCW<0.73cm3cm-3, but these threshold conditions only occurred during brief periods of time and were only found in 11% of our measurements. Moreover, these brief windows of more favorable conditions occurred more frequently in forest edge compared with forest interior locations, resulting in edge trees maintaining 46% higher sap flow compared with interior trees. Our results also suggest that P. reticulata has a low stomatal control of transpiration, as the sap flow did not decline with increasing VPD. This research provides valuable information about the potential impacts of projected future increases in VPD due to climate change on P. reticulata water-use dynamics, which include higher sap flow rates leading to greater transpirational water loss due to this species' poor stomatal control.

Effects of permanent and temporary edges onPinus clausa(sand pine) architecture and stand conditions

Effects of permanent (i.e., maintained) and temporary edges with north- and south-facing exposures were studied in sand pine (Pinus clausa var. clausa (Chapm. ex Engelm.) Vasey ex Sarg.) scrub, an open-canopied forest type in Ocala National Forest, Florida. On edges and interiors of four stands of each type, we measured canopy tree architecture in 5 m × 100 m plots and stand density and basal area in 5 m × 200 m plots. Edge effects were modest but often stronger on south- than north-facing edges and along permanent forest roads than temporary edges of clearcuts that were allowed to regrow. Compared with interior trees, those on edges were typically shorter, retained branches lower on their boles, oriented their first branches more towards the edge, and produced more asymmetrical crowns with the long axis extending into the opening; these trends were greater on south- than north-facing edges and along permanent than temporary edges. Contrary to expectations, there were no edge effects on total basal area, dead tree densities, proportions of sand pine trees with leaning trunks, directions of lean, or angles of lean. Instead of an edge effect, most trees leaned towards the southwest, which seems related to the northeastern origin of prevailing winds and wind gusts.

Edge creation changes the timing and intensity of phenological reproductive patterns and species activities in forest tree communities

Abstract Environmental characteristics are among the most important triggers and regulators of plant phenophases, so that the abiotic and biotic changes driven by habitat loss and fragmentation can result in alterations of plant phenological patterns. We investigated whether forest edge and interior have differences in phenological pattern of tree communities. We followed the reproductive phenologies of tree communities in seven forest fragments on a monthly basis for two years (in 200 m² edge and interior plots per fragment). We sampled a total of 0.28 ha of anthropic forest fragments, comprising 313 trees (180 in edge, 133 in interior) belonging to 103 species and 34 families. Our results evidenced reproductive phenological changes between edge and interior tree communities, with: (i) phenological activities differing temporally between the two habitats (edge and forest interior) in all tree communities; (ii) greater phenological intensity at the forest edge than in the forest interior among tree species common to both habitats; (iii) more tree species showed phenological activity at the forest edge in 2010 and interior in 2011, when considering only those exclusive to each habitat. Habitat fragmentation can therefore alter microenvironmental characteristics and influence biologic processes, including the reproductive phenologies of trees, through edge formation.

The short-term effect of sudden gap creation on tree temperature and volatile composition profiles in a Norway spruce stand

Higher solar radiation leads to higher crown temperatures, sap flow, and airborne volatile concentrations as well as altered bark chemical composition in trees at fresh forest edge. Spruce bark beetles are likely to attack trees that are at newly opened forest edges after wind disturbance due to higher temperatures and higher emission of primary attractants. The mechanisms behind these phenomena are still not fully known. We investigated how sudden gap creation affects tree physiology parameters related to induced defence processes in Norway spruce trees 2 months after the disturbance driven gap formation. We hypothesized that the sudden sun exposure of mature spruce trees would increase: (1) bark and crown temperatures, (2) sap flow rates, and (3) the phloem and airborne concentration of terpenes. Using a terrestrial and airborne thermal camera, sap flow sensors, and chromatography, we confirmed that trees at the forest edge had significantly higher (1) mean tree crown temperature, (2) mean sap flow rates (2-fold higher) and (3) airborne concentration of α-pinene (αP, 12.2-fold higher) and β-pinene (βP, 7.9-fold higher) close to the bark. We observed a significant positive correlation (R2 = 0.77) between the measured sap flow rates and terpene concentrations in airborne samples. Bark temperatures were not significant. In the phloem samples, analyzed by GC–MS, αP and βP predominated over monoterpenes 3-carene, myrcene, limonene, 1.8-cineole, and bornyl acetate. GC × GC–TOF–MS analysis of phloem showed a higher relative abundance of resin acid methyl esters in the forest interior trees and higher relative abundances of dehydro-p-cymene in the trees at the forest edge. Our findings are discussed in the context of the enhanced predisposition of trees at the newly formed forest edge to bark beetles attack.

Toward the Integration of an Attract-and-Kill Approach with Entomopathogenic Nematodes to Control Multiple Life Stages of Plum Curculio (Coleoptera: Curculionidae).

Efforts to reduce insecticide inputs against plum curculio, Conotrachelus nenuphar, a key pest of apples in eastern North America, include perimeter-row insecticide sprays applied after the whole-orchard petal fall spray to manage dispersing adults and, more recently, insecticide sprays confined to odor-baited trap trees. Entomopathogenic nematodes (EPNs) are virulent to ground-dwelling stages of C. nenuphar, and may be applied to the ground underneath trap-tree canopies. Here, we (1) compared the efficacy of the odor-baited trap tree approach with grower-prescribed (=grower standard) sprays to manage C. nenuphar populations over a six-year period in seven commercial apple orchards in New England; and (2) assessed the performance of the EPN Steinernema riobrave at suppressing ground-dwelling stages of C. nenuphar. In addition, the performance of S. riobrave was compared against that of S. carpocapsae and S. feltiae in one year. Across the six years, percent fruit injury on trap tree plots averaged 11.3% on odor-baited trap trees and 1.4% on unbaited trees in grower standard plots, highlighting the ability of trap trees to aggregate C. nenuphar activity and subsequent injury. Mean percentage injury on fruit sampled from interior trees, the strongest measure of treatment performance, in trap tree plots did not differ significantly from that recorded on interior trees in grower standard spray plots (0.95 vs. 0.68%, respectively). Steinernema riobrave consistently reduced C. nenuphar populations as indicated by the significantly lower number of adult C. nenuphar that emerged from the soil, when compared to water control. Steinernema carpocapsae and S. riobrave performed similarly well, and both EPN species outperformed S. feltiae. Our combined findings indicate that an IPM approach that targets multiple life stages of C. nenuphar has the potential to manage this pest more sustainably in a reduced-spray environment.

Adjacency to a harvest trail increases drought resistance of interior Douglas-fir (Pseudotsuga menziesii var. glauca) in partially harvested stands in central British Columbia

Drought tolerance of trees may be affected by competition, but most studies quantifying the relationship do not consider the effect of stem clustering. Trees are often clustered in interior Douglas-fir (Pseudotsuga menziesii var. glauca (Mayr) Franco) forests near the grassland interface in central British Columbia due to past harvesting practices or habitat management for mule deer (Odocoileus hemionus hemionus (Rafinesque, 1817)). Climate change projections indicate continued increases in temperature, an outcome that would stress trees growing in dry environments. Trees placed in different states of competition by mechanical harvesting in the 1970s were sampled to provide a 40-year comparison of three levels of competition during 1–2 year droughts. Tree-ring analysis was used to assess the reduction in growth during drought years and resumption of growth in subsequent years. A clear separation of growth rates was evident between open-growing trees, trees on the edge of harvesting trails, and trees within the unharvested interior. Edge trees had intermediate growth rates but no differences were found in the long-term climate–growth relationship compared with open-growing trees. Both Edge and Open classes showed less relative growth reduction during droughts than Interior trees growing between harvest trails. Precipitation throughfall rates and competition for resources are likely driving short-term drought tolerance in combination with other factors.

The influence of anthropogenic edge effects on primate populations and their habitat in a fragmented rainforest in Costa Rica.

When a forest is fragmented, this increases the amount of forest edge relative to the interior. Edge effects can lead to loss of animal and plant species and decreased plant biomass near forest edges. We examined the influence of an anthropogenic forest edge comprising cattle pasture, coconut plantations, and human settlement on the mantled howler (Alouatta palliata), white-faced capuchin (Cebus capucinus), Central American spider monkey (Ateles geoffroyi), and plant populations at La Suerte Biological Research Station (LSBRS), Costa Rica. We predicted that there would be lower monkey encounter rate, mean tree species richness, and diameter at breast height (DBH) in forest edge versus interior, and that monkeys would show species-specific responses to edge based on diet, body size, and canopy height preferences. Specifically, we predicted that howler monkeys would show positive or neutral edge effects due to their flexible folivorous diet, large body size, and preference for high canopy, capuchins would show positive edge effects due to their diverse diet, small body size, and preference for low to middle canopy, and spider monkeys would show negative edge effects due their reliance on ripe fruit, large body size, and preference for high upper canopy. We conducted population and vegetation surveys along edge and interior transects at LSBRS. Contrary to predictions, total monkey encounter rate did not vary between the forest edge and forest interior. Furthermore, all three species showed neutral edge effects with no significant differences in encounter rate between forest edge and interior. Interior transects had significantly higher mean tree species richness than edge transects, and interior trees had greater DBH than edge trees, although this difference was not significant. These results suggest that forest edges negatively impact plant populations at La Suerte but that the monkeys are able to withstand these differences in vegetation.

Are Scots pine forest edges particularly prone to drought-induced mortality?

Climate change is expected to exacerbate the frequency of drought-induced tree mortality world-wide. To better predict the associated change of species composition and forest dynamics on various scales and develop adequate adaptation strategies, more information on the mechanisms driving the often observed patchiness of tree die-back is needed. Although forest-edge effects may play an important role within the given context, only few corresponding studies exist. Here, we investigate the regional die-back of Scots pine in Franconia, Germany, after a hot and dry summer in 2015, thereby emphasizing possible differences in mortality between forest edge and interior. By means of dendroecological investigations and close-range remote sensing, we assess long-term growth performance and current tree vitality along five different forest-edge distance gradients. Our results clearly indicate a differing growth performance between edge and interior trees, associated with a higher vulnerability to drought, increased mortality rates, and lower tree vitality at the forest edge. Prior long-lasting growth decline of dead trees compared to live trees suggests depletion of carbon reserves in course of a long-term drought persisting since the 1990s to be the cause of regional Scots pine die-back. These findings highlight the forest edge as a potential focal point of forest management adaptation strategies in the context of drought-induced mortality.

Radial Growth Response of Black Spruce Stands Ten Years after Experimental Shelterwoods and Seed-Tree Cuttings in Boreal Forest

Partial cutting is thought to be an alternative to achieve sustainable management in boreal forests. However, the effects of intermediate harvest intensity (45%–80%) on growth remain unknown in black spruce (Picea mariana (Mill.) B.S.P.) stands, one of the most widely distributed boreal species with great commercial interest. In this study, we analysed the effect of three experimental shelterwood and one seed-tree treatments on tree radial growth in even-aged black spruce stands, 10 years after intervention. Our results show that radial growth response 8–10 years after cutting was 41% to 62% higher than in untreated plots, with stand structure, treatment, tree position relative to skidding trails, growth before cutting and time having significant interactions. The stand structure conditioned tree growth after cutting, being doubled in younger and denser stands. Tree spatial position had a pronounced effect on radial growth; trees at the edge of the skidding trails showed twice the increase in growth compared to interior trees. Dominant trees before cutting located close to the skidding trails manifested the highest growth response after cutting. This research suggests that the studied treatments are effective to enhance radial wood production of black spruce especially in younger stands, and that the edge effect must be considered in silvicultural management planning.

Effects of traditional coppice practices and microsite conditions on tree health in a European beech forest at its southernmost range

Abstract: European beech (Fagus sylvatica) grows at the southern limit of its range in the mountain-Mediterranean vegetation belt up to the timberline. The southernmost beech forests of Sicily (southern Italy) show peculiar ecological, structural and silvicultural characteristics, growing in fragmented and isolated stands near the timberline and in topographically marginal unfavorable habitats. Past silvicultural practices increased the heterogeneity of stand structure at these sites. We compared stand structural characteristics and tree health in coppice-cut and control beech stands with respect to the local topographic gradient (bottom, slope and ridge) and canopy cover (clearing/border vs. interior trees). Our results clearly showed a correlation between declining tree health (crown and bark damage, higher percentage of dead trees and lower seedling density) and recent coppice-cuts, poor (marginal) site quality (on ridges and slopes) and reduced canopy cover (in clearing/border trees). The decrease of tree health indicate an increasing threat to the long-term viability of beech stands facing multiple environmental stress factors (such as those related to southern latitude and topographic position). Declining tree health in the control plots also supports this hypothesis. We concluded that traditional forest management practices, such as coppice-cuts applied regardless to the specific microenvironmental conditions, may pose a risk to beech forest health at the southernmost edge of the species’ range.

Early human settlement and natural formation of the Florida Everglades, USA: The Ichthyoarchaeological evidence

The Everglades, the largest subtropical wetland in North America, was initially formed by natural processes approximately 5000years ago and has since dominated the interior landscape of south Florida. Scattered throughout this vast freshwater marsh are tree islands, small clusters of trees situated on slightly elevated ground, which stand out conspicuously amid the surrounding lower vegetation. As the only dry land available, tree islands were ideal for human settlements in the distant past and contain numerous archeological sites. Recent excavations at several sites lend further support to existing evidence that human populations had initially camped on these interior tree islands quite early in time. One such site is Heartleaf Hammock, where rich well-preserved midden deposits demonstrate that people intensively occupied and used locally available aquatic resources, especially fish, as early as 4400years ago. Moreover, the kinds and relative quantities of fish and other freshwater fauna represented indicate that the Everglades wetland marsh ecosystem was already in existence at the time of this early human occupation.

Fog as a source of nitrogen for redwood trees: evidence from fluxes and stable isotopes

Summary A defining feature of the redwood forest in coastal California is the presence of fog in the summer months, a time when there is typically little rainfall. Our goal was to determine the role of summer fog in canopy transformation of nitrogen, nitrogen uptake by trees and photosynthesis within a coastal redwood forest ecosystem. We measured horizontal and vertical inputs of nitrogen, the isotopic composition of nitrogen in a variety of atmospheric sources (summer fog, winter rain and throughfall throughout the year), nitrogen pools (soil solution) and plant tissue (roots and foliage), as well as rates of photosynthesis and nitrogen uptake by trees. Throughfall nitrogen fluxes were greater at the forest edge compared to the interior both within the canopy (sampled 10 m above‐ground) and onto the forest floor (sampled 1 m above‐ground; P &lt; 0.05). Similarly, soil solution and total inorganic nitrogen were greater at the forest edge compared to the interior (P = 0.0014 and 0.009, respectively). Whereas natural abundance δ15NO3 values were not significantly different between winter rain (measured as bulk precipitation) and summer fog water (average δ15N = −1.2 ± 0.680/00), δ15NH4 values were significantly greater in fog water (11.4 ± 2.70/00) compared to rain (1.2 ± 0.90/00). We found no difference in δ15N in roots from forest edge trees compared to interior trees. In contrast, nitrogen concentrations and δ15N in foliage from forest edge trees were significantly greater compared to interior trees (P &lt; 0.0001), suggesting that the leaves of forest edge trees may be obtaining a greater proportion of their nitrogen from fog compared to those of the interior trees. Natural abundance 13C of leaf sugars and rates of photosynthesis were significantly higher at the forest edge compared to the interior during the fog season (P &lt; 0.05), but not different between locations in the rain season (P &gt; 0.05). Nitrification in the forest floor, rather than the canopy, is the primary source of in these soils throughout the year. Synthesis. Summer fog provides nitrogen directly and indirectly to redwood trees, especially those at the forest edge, and affects the physiologic function of redwood trees.

Higher tree transpiration due to road-associated edge effects in a tropical moist lowland forest

Newly created forest edges have significant ecophysiological effects on bordering trees. We studied edge effects on microclimate and tree transpiration rates during wet and dry seasons along a 250m transect spanning the edge of an unpaved road into an old growth tropical lowland forest in the Central Brazilian Amazon. Canopy openness decreased only minimal from the road (3.68%) towards the forest interior (1.69%). Vapor pressure deficit (measured at 2.2m height above ground) was lower in the forest interior. The edge effect on microclimate penetrated deeper into the forest (>100m) during the dry season compared to the wet season (<100m). Overall, sap flux, and therefore transpiration rate, was 54% higher in trees adjacent to the road compared to forest interior trees. Higher transpiration rates at the forest edge can be explained by higher turbulences and energy exchange of the canopy boundary layer and by a shift in species composition to high water using secondary forest species 25 years after the road construction. Similar changes might be expected for other disturbances affecting local relative humidity and in situations that favor plants with water use traits differing from those found in the forest interior.

Sap flow responses to seasonal thaw and permafrost degradation in a subarctic boreal peatland

Key message We demonstrate the negative impacts of ground thaw on sap flow in black spruce. Climate warming is accelerating permafrost thaw; our study may inform observed warming-related productivity declines in subarctic forests. Abstract Many of Canada's northern boreal peatlands are situated on discontinuous permafrost. Here, permafrost provides the physical foundation on which forests persist. However, climate warming is leading to increased rates of permafrost thaw resulting in both increased active layer thickness (ALT) as well as shrinkage of the area underlain by permafrost due to lateral thaw at plateau margins. Such changes to the substrate likely impact growth and physio- logical processes of the trees. Despite this, little is known about the role of active layer development, and changes to it, including thaw of the underlying permafrost on tree water relations. Here, we measured sap flow in black spruce from a peatland experiencing rapid permafrost thaw and quantified drivers of changes in sap flow. Time series analyses revealed that of the environmental drivers exam- ined, vapour pressure deficit was the strongest predictor of diurnal sap flow, while seasonal patterns were driven lar- gely by energy inputs; however, the environmental drivers of importance did not change as a function of ground thaw conditions. To understand the implications of changing permafrost and active layer conditions, we quantified dif- ferences in sap flow between trees in interior positions of permafrost plateaus and trees on degrading plateau edges. We found (65 % reductions in sap flow in edge trees, attributable to reduced root function at waterlogged edges. Seasonal thaw processes also influenced sap flow. Paired measures of ALT indicated a negative linear relationship with sap flow that was stronger for interior trees. Greater ALT, which corresponds with deeper frost and water tables reduced sap flow by up to 60 % and is likely attributable to drying in surface soil layers where rooting occurs. Climate warming will accelerate permafrost thaw, which our data suggests will drive decreases in the productivity of black spruce-dominated subarctic forests. These findings may thus enhance our understanding of widespread reductions in productivity in boreal forests in northwestern North America.

Leaf traits of Eucalyptus arenacea (Myrtaceae) as indicators of edge effects in temperate woodlands of south-eastern Australia

Despite recent trends in using plant functional traits to describe ecosystem responses to environmental change, few studies have examined the capacity of traits to represent environmental variation for individual species at small spatial scales, such as across forest edges. We examined the utility of 12 easy-to-measure leaf traits (fresh weight to dry weight ratio, specific leaf area (SLA), osmolality, δ13C, δ15N, and concentrations of key nutrients) to detect edge effects on the function of a dominant woodland tree, Eucalyptus arenacea Marginson &amp; Ladiges. The study included replicate E. arenacea trees at the woodland edge (0 m) and interior (75 m from edge) of three woodlands adjoined by pasture and three woodlands adjoined by plantation established on pasture. Leaf traits proved useful in identifying potentially degrading processes at woodland edges. Notably, greater leaf P concentrations and δ15N in edge than interior trees irrespective of edge type (pasture versus plantation) indicated persistent effects of nutrient enrichment from agricultural practices; and leaf osmolality and Na concentrations indicated greatest exposure of woodland trees to salinity at pasture edges. Nonetheless, leaf traits proved less useful in detecting edge effects on tree physiology, with most traits being non-responsive to a pronounced interactive effect of edge type and distance from edge on physiological measures. In addition, negative correlations between SLA and physiological measures of tree productivity were contrary to global relationships. Overall, we found that although particular leaf traits indicated potentially degrading processes of nutrient enrichment and salinisation, they were not reliable indicators of small-scale edge effects on the physiological function of E. arenacea.

EFFECTS OF THINNING ON TRANSPIRATION BY RIPARIAN BUFFER TREES IN RESPONSE TO ADVECTION AND SOLAR RADIATION

EFFECTS OF THINNING ON TRANSPIRATION BY RIPARIAN BUFFER TREES IN RESPONSE TO ADVECTION AND SOLAR RADIATION

Edge type affects leaf-level water relations and estimated transpiration of Eucalyptus arenacea

While edge effects on tree water relations are well described for closed forests, they remain under-examined in more open forest types. Similarly, there has been minimal evaluation of the effects of contrasting land uses on the water relations of open forest types in highly fragmented landscapes. We examined edge effects on the water relations and gas exchange of a dominant tree (Eucalyptus arenacea Marginson & Ladiges) in an open forest type (temperate woodland) of south-eastern Australia. Edge effects in replicate woodlands adjoined by cleared agricultural land (pasture edges) were compared with those adjoined by 7- to 9-year-old eucalypt plantation with a 25m fire break (plantation edges). Consistent with studies in closed forest types, edge effects were pronounced at pasture edges where photosynthesis, transpiration and stomatal conductance were greater for edge trees than interior trees (75m into woodlands), and were related to greater light availability and significantly higher branch water potentials at woodland edges than interiors. Nonetheless, gas exchange values were only ∼50% greater for edge than interior trees, compared with ∼200% previously found in closed forest types. In contrast to woodlands adjoined by pasture, gas exchange in winter was significantly lower for edge than interior trees in woodlands adjoined by plantations, consistent with shading and buffering effects of plantations on edge microclimate. Plantation edge effects were less pronounced in summer, although higher water use efficiency of edge than interior woodland trees indicated possible competition for water between plantation trees and woodland edge trees in the drier months (an effect that might have been more pronounced were there no firebreak between the two land uses). Scaling up of leaf-level water relations to stand transpiration using a Jarvis-type phenomenological model indicated similar differences between edge types. That is, transpiration was greater at pasture than plantation edges in summer months (most likely due to greater water availability at pasture edges), resulting in significantly greater estimates of annual transpiration at pasture than plantation edges (430 vs. 343lm(-2)year(-1), respectively). Our study highlights the need for landscape-level water flux models to account for edge effects on stand transpiration, particularly in highly fragmented landscapes.

Efeito de borda na diversidade, composição e estrutura da comunidade arbórea em uma floresta estacional decidual no Brasil Central

O efeito da distância da borda na estrutura, composição e diversidade da comunidade de árvores, considerando todos os tamanhos de indivíduos, foi estudado em um fragmento bem preservado de Floresta Estacional Decidual no Nordeste do Estado de Goiás, Brasil. Parcelas foram sistematicamente estabelecidas em seis distâncias (0, 40, 80, 160, 280 e 400 m) da borda, ao longo de 10 transecções ortogonais na borda floresta-pastagem. Foram amostrados 602 indivíduos adultos/ha, 8.927 indivíduos juvenis/ha e 54.167 plântulas/ha distribuídas em 58 espécies. Embora a composição de plântulas e adultos tenha variado significativamente ao longo do gradiente floresta-pastagem, a variação explicada pela distância da borda foi abaixo de 4%. Entre as variáveis de estrutura da comunidade e os índices de diversidade testados houve variação significativa apenas na diversidade de plântulas e na altura de adultos entre as distâncias da borda floresta-pastagem. O fragmento de floresta estacional apresentou apenas tênue efeito de borda, considerando-se os parâmetros de comunidade avaliados. Essa conclusão contrasta com resultados encontrados em florestas tropicais úmidas, os quais indicam diferenças abruptas entre a comunidade de árvores da borda e as do interior de fragmentos florestais.

Enhanced transpiration by riparian buffer trees in response to advection in a humid temperate agricultural landscape

Riparian buffers are designed as management practices to increase infiltration and reduce surface runoff and transport of sediment and nonpoint source pollutants from crop fields to adjacent streams. Achieving these ecosystem service goals depends, in part, on their ability to remove water from the soil via transpiration. In these systems, edges between crop fields and trees of the buffer systems can create advection processes, which could influence water use by trees. We conducted a field study in a riparian buffer system established in 1994 under a humid temperate climate, located in the Corn Belt region of the Midwestern U.S. (Iowa). The goals were to estimate stand level transpiration by the riparian buffer, quantify the controls on water use by the buffer system, and determine to what extent advective energy and tree position within the buffer system influence individual tree transpiration rates. We primarily focused on the water use response (determined with the Heat Ratio Method) of one of the dominant species ( Acer saccharinum) and a subdominant ( Juglans nigra). A few individuals of three additional species ( Quercus bicolor, Betula nigra, Platanus occidentalis) were monitored over a shorter time period to assess the generality of responses. Meteorological stations were installed along a transect across the riparian buffer to determine the microclimate conditions. The differences found among individuals were attributed to differences in species sap velocities and sapwood depths, location relative to the forest edge and prevailing winds and canopy exposure and dominance. Sapflow rates for A. saccharinum trees growing at the SE edge (prevailing winds) were 39% greater than SE interior trees and 30% and 69% greater than NW interior and edge trees, respectively. No transpiration enhancement due to edge effect was detected in the subdominant J. nigra. The results were interpreted as indicative of advection effects from the surrounding crops. Further, significant differences were document in sapflow rates between the five study species, suggesting that selection of species is important for enhancing specific riparian buffer functions. However, more information is needed on water use patterns among diverse species growing under different climatic and biophysical conditions to assist policy and management decisions regarding effective buffer design.

Habitat disturbance reduces seed dispersal of a forest interior tree in a fragmented African cloud forest

Habitat fragmentation and disturbance are known to impact animals and plants in different ways, depending on species’ characteristics and the type and scale of habitat modification involved. In contrast, direct or indirect ramifications on mutualistic relationships between plants and animals are less clear, possibly because general patterns are confounded by the diffuse nature of many of these interactions. Here, we examine how fragment size and/or severe disturbance of a Kenyan mountain cloud forest affects the frugivore community and seed removal of a large‐seeded, bird‐dispersed tree of the forest interior, for three consecutive years. Forest deterioration reduced avian visitation and seed removal rates independent of fragment size, consistently so despite strong temporal variation in fruit production over the three‐year study. In disturbed forest fragments, seed removal rates were on average 3.5 times lower than in more intact ones. Strong differences in both visitation and seed removal rates were largely attributable to shifts in frugivore assemblages, characterized by loss or reduced abundance of the most effective seed dispersers, most of which were forest specialists. Although some disturbed fragments benefited from visits of non‐forest dependent seed dispersers, such ‘resilience’ was not predictable or reliable in time or space. We conclude that disruption of seed disperser‐seed interactions in highly fragmented and disturbed tropical forests may be persistent in time when resiliency is inadequate, possibly posing long‐term effects on tree communities.