Treeline Research Articles

Predicting arctic-alpine lake dissolved oxygen responses to future tree line advance at the Swedish forest-tundra transition zone.

High latitude regions of the globe are experiencing higher warming rates than many other areas and are expected to undergo dramatic change with future warming (Carpenter et al., 2011; Kuhn et al., 2021). One such change is the poleward advance of tree line into prior tundra environments. While nominally a terrestrial ecosystem change, this advance may dramatically alter aquatic ecosystems, with lakes in particular being highly responsive to events that occur in the surrounding landscape. Klaus et al. (2021) address this important issue by using a space-for-time substitution across 40 Swedish arctic-alpine lakes to understand how a transition from tundra to forested watersheds will influence lake dissolved oxygen (DO).

A new endemic species of Mollinedia (Mollinedieae, Monimiaceae) from the southern limit of the Atlantic coastal moist forest

A revision of Monimiaceae from the Southern limit of the Atlantic forest domain resulted in the discovery of a species heretofore undescribed. Mollinedia leucantha, a treelet endemic to the Atlantic coastal moist forest in southern Brazil, is described and illustrated. Morphologically the new species is most similar to Mollinedia schottiana, from which it is set apart by characteristics in the rhytidome, leaves, trichomes, flowers and fruitlets, as well as by distinct flowering times. Additionally, scanning electron microscopy (SEM) images of the flowers and a key to distinguish morphologically similar or related species in the subtropical Atlantic forest are presented. A preliminary extinction risk assessment is also provided for the new species.

Effect of Long-Term Nitrogen and Phosphorus Additions on Understory Plant Nutrients in a Primary Tropical Forest

Humid tropical forests are commonly characterized as N-rich but P-deficient. Increased N deposition may drive N saturation and aggravate P limitation in tropical forests. Thus, P addition is proposed to mitigate the negative effects of N deposition by stimulating N cycling. However, little is known regarding the effect of altered N and P supply on the nutrient status of understory plants in tropical forests, which is critical for predicting the consequences of disturbed nutrient cycles. We assessed the responses of N concentration, P concentration, and N:P ratios of seven understory species to N and P addition in an 8-year fertilization experiment in a primary forest in south China. The results showed that N addition had no effect on plant N concentration, P concentration, and N:P ratios for most species. In contrast, P addition significantly increased P concentration, and decreased N:P ratios but had no effect on plant N concentration. The magnitude of P concentration responses to P addition largely depended on the types of organs and species. The increased P was more concentrated in the fine roots and branches than in the leaves. The gymnospermous liana Gnetum montanum Markgr. had particularly lower foliar N: P (~9.8) and was much more responsive to P addition than the other species studied. These results indicate that most plants are saturated in N but have great potential to restore P in primary tropical forests. N deposition does not necessarily aggravate plant P deficiency, and P addition does not increase the retention of deposited N by increasing the N concentration. In the long term, P inputs may alter the community composition in tropical forests owing to species-specific responses.

Forests buffer the climate‐induced decline of body mass in a mountain herbivore

Climate change is known to affect key life‐history traits, such as body mass, reproduction, and survival in many species. Animal populations inhabiting mountain habitats are adapted to extreme seasonal environmental conditions but are also expected to be especially vulnerable to climate change. Studies on mountain ungulates typically focus on populations or sections of populations living above the tree line, whereas populations inhabiting forested habitats are largely understudied. Here, we investigate whether forested areas can mitigate the impact of climatic change on life‐history traits by evaluating the interactive effects of temperature and habitat characteristics on body mass variation in the Alpine chamois Rupicapra rupicapra rupicapra. We examined data of 20,573 yearling chamois collected from 1993 to 2019 in 28 mountain ranges in the Austrian Eastern Alps, characterized by different proportion of forest cover. Our results show that the temporal decline of chamois body mass is less pronounced in areas with greater proportion of forest cover. For chamois living in forest habitats only, no significant temporal change in body mass was detected. Variation in body mass was affected by the interaction between density and snow cover, as well as by the interaction between spring temperatures and forest cover, supporting the role of forests as thermal buffer against the effects of increasing temperatures on life‐history traits in a mountain ungulate. In turn, this study suggests a buffering effect of forests against climate change impacts. Assessments of the consequences of climate change on the life‐history traits and population dynamics of mountain‐dwelling species should thus consider the plasticity of the species with respect to the use and availability of different habitat types.

Climate-induced reversal of tree growth patterns at a tropical treeline.

Globally, cold-limited trees and forests are expected to experience growth acceleration as a direct response to warming temperatures. However, thresholds of temperature limitation may vary substantially with local environmental conditions, leading to heterogeneous responses in tree ecophysiology. We used dendroecological and isotopic methods to quantify shifting tree growth and resource use over the past 143 years across topographic aspects in a high-elevation forest of central Mexico. Trees on south-facing slopes (SFS) grew faster than those on north-facing slopes (NFS) until the mid-20th century, when this pattern reversed notably with marked growth rate declines on SFS and increases on NFS. Stable isotopes of carbon, oxygen, and carbon-to-nitrogen ratios suggest that this reversal is linked to interactions between CO2 stimulation of photosynthesis and water or nitrogen limitation. Our findings highlight the importance of incorporating landscape processes and habitat heterogeneity in predictions of tree growth responses to global environmental change.

Consistent shift in nutritional ecology of ants reveals trophic flexibility across alpine tree‐line ecotones

1. Studying the feeding ecology of ants can reveal their trophic position and allow inferences on interactions with other organisms. We investigated the nutritional ecology of ants at the Alpine tree line (from subalpine forests to alpine grasslands), testing the hypothesis that changing food availability reflects upon ant feeding preference and trophic position. Five slopes with five sites each were sampled using a combined experimental (baiting) and chemical (stable isotope) approach.2. Sugar resources were most preferred by the whole ant community in the alpine environment and on the tree line and were therefore likely limiting in these habitats. This shift was not detected in the two dominant ant taxa occurring over the investigated gradient, viz. the slave ant Formica lemani and mound‐building wood ants (Formica s. str.).3. Yet, stable carbon (C) and nitrogen (N) isotope signatures of both these ant species likewise revealed a shift in resource use over the ecotone, from a lower trophic position in subalpine forests to a more carnivore‐dominated lifestyle in alpine grassland. Moreover, wood ants were found to occupy a higher trophic position compared to F. lemani.4. In conclusion, energy resources turned out to be more limiting for ants in the alpine environment, but less so in subalpine forests. The low trophic position of these ant species in the forest is considered to be a result of abundant trophobiotic associations with honeydew‐producing homopterans that occur in far larger numbers on conifer trees in the forest.

Small Landscape Elements Double Connectivity in Highly Fragmented Areas of the Brazilian Atlantic Forest

The Atlantic Forest in Brazil is a biodiversity hotspot, yet its diverse ecosystems and species are becoming increasingly threatened by habitat loss and extreme habitat fragmentation. Most habitat patches of Atlantic Forest are dispersed across agricultural landscapes (e.g., grazing and cropping) in relatively small and isolated fragments (80% < 50 ha). Forest fragments < 1 ha, scattered trees in pastures, tree lines on trenches and fences, and remnant riparian forest, collectively called here Small Landscape Elements (SLEs), are very common in this context. While these SLEs make up much of the Atlantic Forests footprint, very little is known about their role or impact on the persistence and conservation of species. In this study, we investigate the role of SLEs on landscape configuration, particularly their contribution toward landscape connectivity of individual species and the genetic flow of species between larger forest fragments. We randomly selected 20 buffers of 707 hectares within a 411,670 hectare area of the Atlantic Forest that was completely covered by forest in the past located in the south of Minas Gerais State, Brazil. The forest cover randomly varied between these buffers. We used graph theory to measure landscape connectivity as the probability of connectivity for different disperser movement types between landscape knots (habitat patches). We used three estimated dispersal distances in the models: pollen disperser insect (50 m), low-mobility seed disperser bird (100 m) and high-mobility seed disperser bird (760 m). The SLEs together increased the probability of connection by roughly 50%, for all model dispersers, if compared to a theoretical baseline landscape containing no SLEs. Of all SLEs, riparian forests contribute the most toward enhancing landscape connectivity. In these highly fragmented landscapes, such as the Atlantic Forest (>70%), the position of SLEs within the landscapes was more important than their respective areas for connectivity. Although the landscapes were deeply fragmented, we showed that the presence of SLEs can increase connectivity and reduce further biodiversity loss in the Atlantic Forest.

Climate Change, Ecosystem Processes and Biological Diversity Responses in High Elevation Communities

The populations, species, and communities in high elevation mountainous regions at or above tree line are being impacted by the changing climate. Mountain systems have been recognized as both resilient and extremely threatened by climate change, requiring a more nuanced understanding of potential trajectories of the biotic communities. For high elevation systems in particular, we need to consider how the interactions among climate drivers and topography currently structure the diversity, species composition, and life-history strategies of these communities. Further, predicting biotic responses to changing climate requires knowledge of intra- and inter-specific climate associations within the context of topographically heterogenous landscapes. Changes in temperature, snow, and rain characteristics at regional scales are amplified or attenuated by slope, aspect, and wind patterns occurring at local scales that are often under a hectare or even a meter in extent. Community assemblages are structured by the soil moisture and growing season duration at these local sites, and directional climate change has the potential to alter these two drivers together, independently, or in opposition to one another due to local, intervening variables. Changes threaten species whose water and growing season duration requirements are locally extirpated or species who may be outcompeted by nearby faster-growing, warmer/drier adapted species. However, barring non-analogue climate conditions, species may also be able to more easily track required resource regimes in topographically heterogenous landscapes. New species arrivals composed of competitors, predators and pathogens can further mediate the direct impacts of the changing climate. Plants are moving uphill, demonstrating primary succession with the emergence of new habitats from snow and rock, but these shifts are constrained over the short term by soil limitations and microbes and ultimately by the lack of colonizable terrestrial surfaces. Meanwhile, both subalpine herbaceous and woody species pose threats to more cold-adapted species. Overall, the multiple interacting direct and indirect effects of the changing climate on high elevation systems may lead to multiple potential trajectories for these systems.

Tree line advance reduces mixing and oxygen concentrations in arctic-alpine lakes through wind sheltering and organic carbon supply.

Oxygen depletion in lake bottom waters has adverse impacts on ecosystem health including decreased water quality from release of nutrients and reduced substances from sediments, and the reduction of fish growth and reproduction. Depletion occurs when oxygen is consumed during decomposition of organic matter, and oxygen replenishment is limited by water column stratification. Arctic-alpine lakes are often well mixed and oxygenated, but rapid climate change in these regions is an important driver of shifts in catchment vegetation that could affect the mixing and oxygen dynamics of lakes. Here, we analyze high-resolution time series of dissolved oxygen concentration and temperature profiles in 40 Swedish arctic-alpine lakes across the tree line ecotone. The lakes stratified for 1-125days, and during stratification, near-bottom dissolved oxygen concentrations changed by -0.20 to +0.15mgL-1 day-1 , resulting in final concentrations of 1.1-15.5mgL-1 at the end of the longest stratification period. Structural equation modeling revealed that lakes with taller shoreline vegetation relative to lake area had higher dissolved organic carbon concentrations and oxygen consumption rates, but also lower wind speeds and longer stratification periods, and ultimately, lower near-bottom dissolved oxygen concentrations. We use an index of shoreline canopy height and lake area to predict variations among our study lakes in near-bottom dissolved oxygen concentrations at the end of the longest stratification period (R2 =0.41). Upscaling this relationship to 8392 Swedish arctic-alpine lakes revealed that near-bottom dissolved oxygen concentrations drop below 3, 5, and 7mgL-1 in 15%, 32%, and 53% of the lakes and that this proportion is sensitive (5%-22%, 13%-45%, and 29%-69%) to hypothetical tree line shifts observed in the past century or reconstructed for the Holocene (±200m elevation; ±0.5° latitude). Assuming space-for-time substitution, we predict that tree line advance will decrease near-bottom dissolved oxygen concentrations in many arctic-alpine lakes.

Seminatural habitats and their proximity to the crop enhances canola (Brassica napus) pollination and reproductive parameters in Argentina

AbstractThe diversity and abundance of pollinators increase in cultivated areas in proximity to natural and seminatural habitats (pastures, forests, tree lines, etc.). Managing ecosystem services, such as insect pollination, is essential to increase crop yields. Although insect pollination is linked to better yields in many crops, pollinators are usually not considered as an input to be managed in crop production. In this study, we evaluate, for the first time, the influence of pollinators on the reproductive parameters of three canola (Brassica napus L.) stands placed at different distances from seminatural habitats in central Argentina. Insect visits to inflorescences with exposed and nonexposed flowers (covered with voile bags) were compared in plants growing in proximity (<50 m) and distant from (>50 m) seminatural habitats. Observations of flower visitations by the insects were recorded during the flowering period. The most frequent pollinator was Apis mellifera, although 12 additional pollinator morpho‐species were registered. Seven of them were observed in canola flowers for the first time. Pollinators increased the amount of pollen deposited on stigmas and all measured reproductive parameters (fruit set, seeds per pod, seed mass). Seed production per infructescence increased with proximity to seminatural habitats and with pollinators by 34 and 35%, respectively. Therefore, the pollination ecosystem service is a relevant input for canola production in central Argentina. It will be important to develop policies that encourage diversified farming systems securing the protection of natural flora and pollinators.

Balsam Fir and American Beech Influence Soil Respiration Rates in Opposite Directions in a Sugar Maple Forest Near Its Northern Range Limit

Conifers and deciduous trees greatly differ in regard to their phylogenetics and physiology as well as their influence on soil microclimate and chemical properties. Soil respiration (Rs) in forests can therefore differ depending on tree species composition, and assessments of the variation in Rs in various forest types will lead to a more thorough understanding of the carbon cycle and more robust long-term simulations of soil carbon. We measured Rs in 2019 and 2020 in stands of various species composition in a sugar maple forest near the northern range limit of temperate deciduous forests in Quebec, Canada. Seasonal variations in soil temperature had the largest influence on Rs, but conditions created by the stands also exerted a significant effect. Relative to the typical sugar maple-yellow birch forest (hardwoods), Rs in stands with >20% of basal area from balsam fir (mixedwoods) was increased by 21%. Whilst, when American beech contributed >20% of litterfall mass (hardwood-beech stands), Rs was decreased by 11 and 36% relative to hardwoods and mixedwoods, respectively. As a whole, Rs was significantly higher in mixedwoods than in other forest types, and Rs was significantly higher in hardwoods than in hardwood-beech stands. Sugar maple and American beech at the study site are near their northern range limit, whereas balsam fir is near its southern limit. Rs in mixedwoods was therefore higher than in hardwoods and hardwood-beech stands due to high root activity in the presence of fir, despite colder and drier soils. We estimated that root respiration in mixedwoods was more than threefold that in hardwoods and hardwood-beech stands. The lower Rs in hardwood-beech stands compared to hardwoods points to the lower soil temperature as well as the poor quality of beech litter (low decomposability) as indicated by a generally lower heterotrophic respiration. Other than soil temperature, regression models identified mixedwoods, soil water potential and Mg2+ activity in the soil solution as important predictor variables of Rs with about 90% of its variation explained. Our study shows the benefits of combining forest-specific properties to climatic data for more robust predictions of Rs.

Changes in different land cover areas and NDVI values in northern latitudes from 1982 to 2015

Climate warming leads to vast changes in the land cover types and plant biomass in the northern high-latitude regions. The overall trend is of shrubland and tree lines moving northwards, while changes in different land cover types and vegetation growth in response to climate change are largely unknown. Here, we selected land areas with latitudes higher than 50°N as the study area. We compared the land cover type changes and explored relationships between the normalized difference vegetation index (NDVI) values of different land cover types, air temperature, and precipitation during 1982–2015 based on dynamic grid. The results indicated that forest and shrubland areas increased as a large area of grassland shifted to forest and shrubland. The snow/ice, tundra and grassland largely have decreased from 1982 to 2015. Although approximately 277.3 × 103 km2 of barren land (6.2% of the total barren land area in 1982) changed to tundra, the tundra area still decreased because some tundra shifted to forest and grassland. The NDVI values of tundra significantly increased, but the shrubland showed a decreasing trend. Temperature in the growing season (June to September) showed the largest positive correlation coefficients with the NDVI values of forest, tundra, grassland, and cropland. However, due to shrubification processes and plant mortality in shrubland areas, the shrubland NDVI showed negative relationship with annual temperature but positively correlated with monthly t. Taken together, although there is large room for improvement of the land cover type data accuracy, our results suggested that the land cover types in high-latitude regions changed significantly, while the NDVI values of the different land cover types showed different responses to climate change.

Freeze tolerance in neotropical frogs: an intrageneric comparison using Pristimantis species of high elevation and medium elevation

AbstractParamos are high-elevation tropical Andean ecosystems above the tree line that display variable temperature and frequent freezing spells. Because a significant anuran community lives in this environment, physiological protection against freezing must characterise individuals in this community. Antifreeze protection has been studied in amphibians from other communities, and it is likely that Paramo anurans rely on the same underlying molecules that convey such protection to Nearctic species. However, given the pervasive presence of freezing spells in the Paramos year-round, the processes of activating protection mechanisms may differ from that of seasonal counterparts. Accordingly, this study investigated cryoprotection strategies in high-elevation tropical frogs, using as a model the terrestrial and nocturnal genus Pristimantis, specifically P. bogotensis, P. elegans and P. nervicus from Paramos, and the warm ecosystem counterparts P. insignitus, P. megalops and P. sanctaemartae. We focused on freeze tolerance and its relationship with glucose accumulation and ice formation. Under field conditions, the highest elevation P. nervicus exhibited higher glucose concentration at dawn compared to noon (1.7 ± 0.6 mmol/L versus 3.5 ± 1.32 mmol/L). Under experimental thermal freeze exposure for 2 hours between −2 and −4 ºC, the glucose concentration of the three Paramo species increased but physiological diversity was evident (P. nervicus 126%; P. bogotensis 100%; and P. elegans 55%). During this test, body ice formation was assessed calorimetrically. The species with the highest body ice formation was P. bogotensis (17% ± 5.37; maximum value: 63%; n = 8), followed by P. nervicus (5% ± 3.27; maximum value: 11%; n = 5) and P. elegans (0.34% ± 0.09; maximum value: 1%; n = 4). The study shows physiological diversity both within a genus and across the amphibian community around the freezing contour. Overall, Paramo species differ in freezing physiology from their low-elevation counterparts. Thus, climate shifts increasing freezing spells may affect the structure of communities in this zone.

Defoliation heights for palisade grass cv. Marandu in silvopastoral system

ABSTRACT The objective was to test the response of Urochloa brizantha cv. Marandu in monoculture and in silvopastoral system (SPS), at two distances from the trees, and define the best defoliation height for SPS. Four intermittent defoliation heights (25, 35, 45 and 55cm) and two distances from tree lines (2.5 and 5.0m) were evaluated in the SPS with a control defoliated with 25cm in full sun. The experiment was performed in a randomized block design with 3 replicates in a 4 × 2 + 1 split plot scheme. The control had higher forage accumulation (46.9kg/ha. day) than the SPS (31.1kg/ha. day). The bulk density was also higher in the control (0.89mg/cm³) than in SPS (0.48mg/cm³). The percentage of leaves (78.06%) and leaf/stem ratio (6.04) did not differ among the treatments. In the SPS, there was an increase of 31.07% in forage accumulation from 25 to 55cm. The forage accumulation and bulk density of Urochloa brizantha cv. Marandu in monoculture is greater than in the SPS regardless of the management goal and the distance from trees. The goal of 55cm in the SPS presented greater forage accumulation.

Seismic line width and orientation influence microclimatic forest edge gradients and tree regeneration

Ecological impacts of linear anthropogenic disturbances may be underestimated due to edge effects extending into adjacent forests. Seismic lines are the most pervasive linear disturbance associated with oil and gas development in the boreal forests of western North America. The width and orientation of seismic lines may influence microclimatic edge effects that could alter biotic responses, including tree recruitment. We examined light intensity, air temperature, relative humidity, and tree regeneration within seismic lines and adjacent forests to: (1) compare abiotic conditions between wide (6–8 m) and narrow (3–4 m) seismic lines; (2) quantify microclimatic edge effects of seismic lines of different widths and orientations; and (3) relate patterns in tree regeneration density to local patterns in the abiotic environment. We sampled interior forests and 24 seismic lines that were wide or narrow and orientated east-west or north-south in poor mesic ecosites of northeast Alberta, Canada. Microclimatic conditions in seismic line centres were generally intermediate between interior forest and well pads, with narrow seismic lines more similar to interior forest and wide seismic lines more similar to well pads. Light intensity on wide seismic line centres was at least 1.5 times higher than on narrow seismic line centres and up to 3.8 times higher than interior forest. Edge effects on light intensity extended up to 10 m into the forest adjacent to wide lines, but were restricted to the forest edge (at the interface) of narrow lines. Compared to interior forest, day temperature was up to 2.8 °C and 0.8 °C higher at edges of wide and narrow seismic lines, respectively. Relative humidity during the day was up to 7.3% and 3% lower at the edges of wide and narrow seismic lines, respectively, as compared to interior forest. At night, wide seismic line centres were up to 1.7 °C cooler and up to 8.2% more humid than narrow seismic line centres. Tree regeneration was highest where light intensity was highest (the centre of wide north-south seismic lines) and a 10-fold increase in light intensity resulted in 5.8 times more regenerating trees. This study reveals that seismic line width and orientation affect abiotic factors within the linear disturbance and up to 10 m into the adjacent forest. Edge effects on the microclimate of seismic lines were most pronounced in wider seismic lines and along north (south-facing) forest edges. These findings provide a better understanding of the abiotic factors influencing biotic responses to linear anthropogenic disturbances.

Bryophyte Diversity along an Elevational Gradient on Pico Island (Azores, Portugal)

The study of elevational patterns is a valuable method for inferring the influence of the climate and other variables in the regional distributions of species. Bryophytes are ideal for revealing different environmental patterns in elevational studies, since they occur from sea level to above the tree line. Taking advantage of the long elevational transect of Pico Island and the use of standardized survey methods, our main aims were: (1) to identify and characterize the alpha and beta diversities of bryophytes across the full elevational gradient (12 sites of native vegetation, ranging from 10 to 2200 m above sea level [a.s.l.]); (2) to detect the ecological factors driving bryophyte composition; (3) to identify bryophytes’ substrate specificity; and (4) to check the presence of rare and endemic species. The identification of 878 microplots yielded 141 species (71 liverworts and 70 mosses), almost half of those known to occur on Pico Island. The bryophyte species richness followed a parabolic unimodal pattern with a mid-elevation peak, where the richest native forests occur. A canonical correspondence analysis (CCA) of the bryophyte composition and explanatory variables revealed the effect of the elevation, precipitation, disturbance, richness of vascular plants and bark pH in explaining bryophyte compositions at regional levels. Very few species of bryophytes showed substrate specificity. Pico Island’s elevational gradient could be an asset for studying long-term changes in bryophyte species composition and alpha diversity under global change.

Water productivity of tree wind break agroforestry systems in irrigated agriculture – An example from Ferghana Valley, Kyrgyzstan

Central Asia is largely dominated by drylands; so agriculture depends on irrigation in most parts of the region, which results in large scale water withdrawal, mainly from rivers, and, consequently, water scarcity. Climate change is expected to aggravate such water shortages as river flows are predicted to be substantially reduced during the second half of this century, which will put additional strain on irrigated agriculture. Tree wind breaks are one option to reduce water consumption in irrigated agriculture, add to farm income, and are therefore prioritized by government policies. Still, many farmers fear that tree wind breaks may compromise crop yields and income. Therefore, based on preceding studies this paper investigates the water productivity – net present value by unit of water consumed – of tree wind break systems of single row tree rows combined with cotton (Gossypium hirsutum L.), corn (Zea mays L.), and rice (Oryza sativa L.) compared with those crops under open field conditions. The tree wind break systems attained higher water productivities across all crops, different discount rates, tree ages of tree wind breaks, and varying crop yields. Tree wind break systems at 200 m spacing attained higher water productivities than those at 1000 m spacing. In conclusion, tree wind breaks can be inserted into the irrigated agriculture as an additional source of farm income, source for wood resources, and help reducing overall water consumption in irrigated agriculture. Simple tree lines are put forward, as multiple tree rows have been shown not to attain financial gains and save less water than the single tree lines.

Betula utilis D. Don: an Ecologically and Economically Important Timberline Species of Himalayan Region in Jeopardy

Betula utilis D. Don (Betulaceae), commonly known as Himalayan Birch or Bhojpatra especially in Indian Himalayan Region is socio-culturally and ecologically valued and considered a keystone species which plays a significant role in the functioning of the timberline ecosystem. It forms an integral part of day-to-day life of the Himalayan people, as it is deeply associated with the culture of the locals. The historical uses of Betula utilis and its subsequent over exploitation to meet-out day-to-day requirements, market forces coupled with global warming put pressure on its natural population and have caused loss of habitat in many of its native grooves in the entire Himalayan Region. The decline in the size of population of Betula utilis is due to its area of occupancy, extent of occurrence, potential level of exploitation, effects of introduced taxa and attack of pathogens. Further, it grows in high altitude tree line zone which is almost inaccessible and most vulnerable region due to global warming or climatic shift. In this backdrop, keeping in view the multiple uses of the species, the present study aims to review and document the ecological parameters, traditional uses, commercial aspects and conservation and management concerns of this valuable species.

Interactions between drought and shade on the productivity of winter pea grown in a 25‐year‐old walnut‐based alley cropping system

AbstractIn the face of climate change, more frequent drought events are expected in the Mediterranean regions. Alley cropping is an agroforestry practice that represents a promising adaptation strategy to sustain yield productivity under drier conditions. However, the presence of trees limits the productivity of the intercrop by reducing light availability and by competing for soil water resources, which could potentially exacerbate the yield losses due to drought conditions. Furthermore, the effects of co‐occurring drought and shade stresses on annual crops are still poorly understood. To tackle this issue, we performed a rainfall manipulation experiment on winter pea (Pisum sativum L.) grown in full‐sun conditions (agricultural control) and under different levels of shade in a 25‐year walnut‐based alley cropping system located in southern France. We evaluated first the effect of trees on light and water availability, and we then studied the effects of early drought (135 mm excluded from April to the end of May) and light conditions on crop performances and yield components. At 3.5 m from the tree line, light availability was reduced on average by 19% at south and 35% at north of trees over the entire crop cycle and mostly after tree budburst. The impact of trees on soil water content in the crop root zone was weak thanks to the good complementarity of the respective root systems. Under normal rainfall conditions, tree shade decreased pea yield from −25% to −77% compared to full‐sun conditions. In case of spring drought, pea yield was decreased by −22% in full‐sun conditions. The negative effect of tree shade was reduced and decreased pea yield only by −1% to −47%. Under the most intense shade conditions, pea yield was even higher under drought than in normal rainfall conditions. The analysis of crop dynamics and yield components revealed that the vegetative development of pea ceased under drought to the benefit of biomass allocation towards the reproductive organs. Pea yield was less impacted by tree shade under spring drought because yield elaboration relied less on the success of pod set, sensitive to shade and, more on grain filling, improved in case of early drought event. This study supports the hypothesis that agroforestry systems may be more resilient in the case of early drought.

Seasonal Dynamics of Soil Moisture in an Integrated-Crop-Livestock-Forestry System in Central-West Brazil

Integrated-crop-livestock-forestry (ICLF) systems are currently promoted as a measure for sustainable intensification of agricultural production. However, due to complex interactions among ICLF components, we are still lacking evidence about the system’s resilience regarding water availability, especially for regions characterized by pronounced wet and dry seasons and frequent droughts. For a mature ICLF system in the Cerrado biome of central-west Brazil comprising rows of eucalyptus trees (Eucalyptus grandis x Eucalyptus urophylla, H13 clone) at a spacing of 22 m in combination with Brachiaria brizantha cv. BRS Piatã pasture we continuously measured soil moisture (SM) until 1 m depth and supported this data with measurements of photosynthetically active radiation (PAR) and aboveground green grass biomass (AGBM) across transects between the tree rows for almost two years. Across the seasons a distinct gradient was observed with SM being lower close to the tree rows than in the space between them. During winter SM decreased to critical values near the tree lines in the topsoil. During spring and summer, incident PAR was 72% and 86% lower close to the trees than at the center point. For autumn and winter PAR was more evenly distributed between the tree rows due to inclination with notably up to four times more radiation input near the tree lines compared to spring and summer. AGBM showed a clear distribution with maximum values in the center and about half of the biomass close to the tree rows. Our data suggest that, restrictions in AGBM accumulation shifted among seasons between water limitations in winter and light limitations during summer. Interestingly, SM changes during wetting and drying events were most pronounced in subsoils near the tree rows, while the topsoil showed much less fluctuations. The subsoil in central position showed the lowest SM dynamics in response to drought maintaining a relative high and constant SM content, therefore functioning as important water reservoirs likely improving the resilience of the system to drought stress. Results of this study could help to improve management and the design of ICLF systems in view of sustainability and resistance to (water) crises but should be further supported by in depth analysis of soil water dynamics as affected by climate gradients, soil types and different management practices.