Prosopis Flexuosa Research Articles

Tree genetic resources at risk in South America: A spatial threat assessment to prioritize populations for conservation

AbstractBackgroundHumans threat the populations of tree species by overexploitation, deforestation, land use change, and climate change. We present a novel threat assessment at intraspecific level to support the conservation of genetic resources of 80 socioeconomically viable tree species in South America. In this assessment, we evaluate the threat status of Ecogeographic Range Segments (ERSs). ERSs are groups of populations of a specific species in a certain ecological zone of a particular grid cell of a species’ geographic occupancy.MethodsWe used species location records to determine the species distributions and species‐specific ERSs. We distinguished eight threat situations to assess the risk of extirpation of the ERSs of all 80 species. These threat situations were determined by large or little tree cover, low or high human pressure, and low or high climate change impact. Available layers of tree cover and threats were used to determine the levels of fragmentation and direct human pressure. Maxent niche modelling with two Global Circulation Models helped determining climate change impact by the 2050s.ResultsWhen all 80 species are considered, in total, 59% of the ERSs are threatened by little tree cover or high human pressure. When climate change is also considered, then 71‐73% of the ERSs are threatened. When an increased risk of extirpation of populations outside protected areas is considered, then 84–86% of the ERSs are threatened. Seven species warrant special attention because all their ERSs are threatened across their whole distribution in South America: Balfourondendron riedelianum, Cariniana legalis, Dalbergia nigra, Handroanthus pulcherrimus, Pachira quintana, Prosopis flexuosa, and Prosopis pallida.ConclusionsOur results confirm the urgency to set up a regional action plan for the conservation of tree genetic resources in South America. With this threat assessment, we aim to support governments and organizations who are taking up this task.

Diferencias en el hábito de crecimiento como variable explicativa de la influencia climática en Prosopis flexuosa en el Desierto del Monte Central (Argentina).

Los métodos dendroclimatológicos representan una de las herramientas más valiosas para analizar la influencia del clima sobre la dinámica del incremento radial y la morfología de las plantas leñosas. En el Desierto del Monte Central, Prosopis flexuosa DC (algarrobo dulce), crece como árbol uni-fustal pero también como multi-fustal. Investigaciones anteriores han evidenciado la utilidad del ancho de anillo de esta especie como registro de eventos climáticos. Sin embargo, estas investigaciones han diferido metodológicamente, considerando o descartando los individuos multi-fustales. Este trabajo analizó si la variabilidad en el hábito de crecimiento expresa diferencias en la señal dendroclimática del algarrobo dulce. Dos cronologías de ancho de anillos, una derivada de individuos uni-fustales (UF) y otra de multi-fustales (MF) presentes en un mismo ambiente ecológico fueron desarrolladas. Se observó que hay una mayor sensibilidad de la cronología MF respecto de la UF en relación a la incidencia en el crecimiento de eventos climáticos extremos y del clima en general en el largo plazo. Esto sugiere que los individuos multi-fustales constituyen una buena representación de la variabilidad del clima local. Debido a la gran extensión territorial de especie, otros estudios que abarquen la extensión geográfica de P. flexuosa son deseables para profundizar los resultados logrados.

Nesting ecology of sympatric species of wool carder bees (Hymenoptera: Megachilidae: Anthidium) in South America

Using a total of 14,043 trap-nests (potential nest for bees), we documented the nest architecture, host plants, seasonality, and associated organisms of the following six native species of Anthidium (Megachilidae: Anthidiini) from the Central Monte Desert in Mendoza, Argentina: A. andinum Jörgensen; A. chubuti Cockerell; A. decaspilum Moure; A. friesei Cockerell; A. rubripes Friese; and A. vigintipunctatum Friese. Each species exhibited unique features in the arrangement of the fibers used to make their cells, and in the type of material used in the nest plug. Bees used a total of 41 plant species, but relied heavily on Prosopis flexuosa (Fabaceae) and Larrea spp. (Zygophyllaceae). Most bee species are univoltine and exhibited delayed emergence. The oil beetle Nemognatha sp. (Coleoptera: Meloidae) and the cuckoo wasp Chrysis striatula Bohart (Hymenoptera: Chrysididae) are recorded for the first time for Anthidium. Nemognatha sp. was the most common brood parasite but C. striatula caused the highest brood mortality.

Small mammal abundance and seed predation across boundaries in a restored‐grazed woodland interface

Passive restoration is an effective tool for the maintenance and conservation of biodiversity. Often areas in recovery are immersed in a matrix of land uses, in which the expansion and intensification of human activities exert new visible pressures at their boundaries. The degree of connectivity between these areas and their peripheral lands can be analyzed by mobile link species, organisms that actively move in the landscape by connecting areas to one another through their functional roles. We focus our design on the interface generated by the long‐term restoration area and surrounding grazing lands. We analyze the changes on boundary structure, small mammal abundance, and on the function of native seed dispersal by these vertebrate species. We captured small mammals and determined seed removal of Prosopis flexuosa at three distances inside and outside a fence that delineates passively restored and currently grazed areas. Our results indicate that small rodents find more suitable habitats at the site under restoration than in grazing lands. The restored‐grazing interface shows a decrease in small mammal abundance from the protected area to the grazed lands. From a functional perspective, an increase in small mammal abundance results in an increase in their seed removal activity with implications for seed fate, because the long‐term recovery of vegetation could enhance seed predation on a native tree species.

Implications of mating system and pollen dispersal indices for management and conservation of the semi-arid species Prosopis flexuosa (Leguminosae)

Recruitment by fencing of semi-arid trees is a common woodland conservation strategy that may have both positive and negative implications. Domestic herbivores can act as efficient dispersal seed agents but they can also affect the survival and growth of the trees first stages. Prosopis flexuosa (algarrobo) woodlands represent the most important plant community in the Monte region in Argentina and as this resource is affected by deforestation, grazing, natural fires and replacement of natural ecosystems by croplands, in order to protect the “algarrobo” a reserve had been established. As efficient management and conservation program depends on the information on population structure and mating system, the objectives of this work were to estimate mating and pollen dispersal patterns in a wild P. flexuosa population from the Ñacuñan fenced to exclude domestic cattle for 40years. This population is mainly outcrosser (tm=0.996), sensitive to inbreeding depression at seed stage, having relative reduced pollen mediated gene dispersal distance (4.56–20.35m), which favors inbreeding as a consequence of mating between related individuals. Our results suggest that for ex situ conservation the distance that would be enough to avoid full sib sampling among harvested seed-trees is about 20m. Collecting seeds from different pods reduce the proportion of full sibs within progeny arrays. For in situ conservation it is important to take into account that forest patches separated by more than 250m are expected to be isolated, increasing the risk of genetic variability loss, inbreeding increase and population extinction. The results are discussed in reference to the “algarrobo” management program; while in some case excluding big mammals from the stands should be advisable, the interaction with long dispersal big herbivores might be considered as a strategy to promote increased outbreeding reducing the rate of mating between related individuals.

Seed removal by different functional mammal groups in a protected and grazed landscape of the Monte, Argentina

AbstractMammal species contribute in different ways to seed dispersal effectiveness, acting as endozoochorous dispersers, scatter-hoarders and seed predators. Seed removal by these functional mammal groups could be affected by anthropogenic drivers, such as grazing management, a common practice in drylands. We evaluated removal of seeds from a native tree species (Prosopis flexuosa) by terrestrial wildlife mammals with different functional roles, on grazed and ungrazed sites and at different times during the fruiting periodof Prosopis. We offeredProsopisfruits, each containing 15 seeds, to animals and used camera traps to identify the species removing them. We obtained the number of seeds removed (1 fruit removed = 15 seeds removed) by each animal species and each functional group. Native and domestic mammals removed 65.4% of the total seeds offered; 69.5% of offered seeds were removed from the grazed area and 61% from the ungrazed site. Considering removal times, 64.25% of offered seeds were removed during the beginning of the fruiting period ofProsopisand 67% towards the end of this period. Small mammals acting either as seed predators (Graomys griseoflavusandAkodon dolores) or scatter-hoarders (Microcavia australis) were the functional mammal groups removing the highest amount of seeds. Seed predators removed more seeds from the ungrazed site, whereas the scatter-hoarder did so at the grazed site. In the ungrazed area, it would be important to ensure habitat heterogeneity in order to improve seed removal by functional groups that disperse seeds, such as endozoochorous dispersers and scatter-hoarders.

Anthropogenic disturbance impact on the stem growth of Prosopis flexuosa DC forests in the Monte desert of Argentina: A dendroecological approach

Anthropogenic disturbance acts globally as an ecological process with long-term implication on the ecosystem equilibrium. In the central-western Argentina (Desierto del Monte Central: DMC), the desert Prosopis flexuosa woodlands has been intervened by man with differential incidence, e.g. through logging, fire and grazing. Despite recognizing a history of disturbances in these forests, the local removal of trees and its incidence in the stem growth of the surviving trees is still poorly known. Dendroecological methods were applied to 10 plots distributed along a landform gradient, aiming to analyze how disturbance, together with possible modulation effects of the spatial variability on growth, can influence forest dynamics. Tree removal was an intensive practice during the second half of the 20th century in the DCM, in synchrony with the expansion of wine-growing activity. Our results suggest that removal of P. flexuosa individuals in any considered plot was the main driver of changes in the forest dynamics. This argument is based on the weak climatic incidence in years considered critical with respect to the beginning of abrupt tree-growth releases. This disturbance impact seemed to be landform-dependent, as suggested by the higher relative basal area values at mesic sites in relation to sites linked to drier landforms. The presented findings represent the first attempt in reconstructing the disturbance regime experienced by the DMC P. flexuosa woodlands. Our research contributes to interpret how logging practices coupled with landform-related heterogeneities may influence the forest dynamics at desert environments, providing elements for implementing policies for conservation and management of these natural resources.

Management of Protected Areas and Its Effect on an Ecosystem Function: Removal of Prosopis flexuosa Seeds by Mammals in Argentinian Drylands.

The ecological function of animal seed dispersal depends on species interactions and can be affected by drivers such as the management interventions applied to protected areas. This study was conducted in two protected areas in the Monte Desert: a fenced reserve with grazing exclusion and absence of large native mammals (the Man and Biosphere Ñacuñán Reserve; FR) and an unfenced reserve with low densities of large native and domestic animals (Ischigualasto Park; UFR). The study focuses on Prosopis flexuosa seed removal by different functional mammal groups: “seed predators”, “scatter-hoarders”, and “opportunistic frugivores”. Under both interventions, the relative contribution to seed removal by different functional mammal groups was assessed, as well as how these groups respond to habitat heterogeneity (i.e. vegetation structure) at different spatial scales. Camera traps were used to identify mammal species removing P. flexuosa seeds and to quantify seed removal; remote sensing data helped analyze habitat heterogeneity. In the FR, the major fruit removers were a seed predator (Graomys griseoflavus) and a scatter-hoarder (Microcavia asutralis). In the UFR, the main seed removers were the opportunistic frugivores (Lycalopex griseus and Dolichotis patagonum), who removed more seeds than the seed predator in the FR. The FR shows higher habitat homogeneity than the UFR, and functional groups respond differently to habitat heterogeneity at different spatial scales. In the FR, because large herbivores are locally extinct (e.g. Lama guanicoe) and domestic herbivores are excluded, important functions of large herbivores are missing, such as the maintenance of habitat heterogeneity, which provides habitats for medium-sized opportunistic frugivores with consequent improvement of quality and quantity of seed dispersal services. In the UFR, with low densities of large herbivores, probably one important ecosystem function this group performs is to increase habitat heterogeneity, allowing for the activity of medium-sized mammals who, behaving as opportunistic frugivores, did the most significant seed removal.

Role of small rodents in the seed dispersal process: Microcavia australis consuming Prosopis flexuosa fruits

AbstractUnderstanding the functional role of animal species in seed dispersal is central to determining how biotic interactions could be affected by anthropogenic drivers. In the Monte Desert, mammals play different functional roles in Prosopis flexuosa seed dispersal, acting as opportunistic frugivores (endozoochorous medium‐sized and large mammals) or seed hoarders (some small sigmodontine rodents). Our objective was assessing the functional role of Microcavia australis, a small hystricognathi rodent, in the fruit removal and seed deposition stages of P. flexuosa seed dispersal, compared to sympatric sigmodontine rodents. In situ, we quantified fruit removal by small rodents during non‐fruiting and fruiting periods, and determined the distance seeds were transported, particularly by M. australis. In laboratory experiments, we analysed how M. australis stores seeds (through scatter‐ or larder‐hoarding) and how many seeds are left in caches as living seeds, relative to previous data on sigmodontine rodents. To conduct field studies, we established sampling stations under randomly chosen P. flexuosa trees at the Ñacuñán Man and Biosphere Reserve. We analysed fruit removal by small rodents and seed dispersal distance by M. australis using camera traps focused on P. flexuosa fruits covered with wire screen, which only allowed entry of small animals. In laboratory trials, we provided animals with a known number of fruits and assessed seed conditions after removal. Small rodents removed 75.7% of fruit supplied during the non‐fruiting period and 53.2% during the fruiting period. Microcavia australis and Graomys griseoflavus were the main fruit removers. Microcavia australis transported seeds to a mean distance of 462 cm and cached seeds mainly in scatter‐hoards, similarly as Eligmodontia typus. All transported seeds were left in fruit segments or covered only by the endocarp, never as predated seeds. Microcavia australis disperses P. flexuosa seeds by carrying fruits away from a source to consume them and then by scatter‐hoarding fruits and seeds.

Demography and population growth rate of the tree Prosopis flexuosa with contrasting grazing regimes in the Central Monte Desert

One of the most important current challenges for ecologists is to evaluate how human-induced changes in ecosystems would impact viability of populations. Demographic response to anthropogenic impact could help us to understand how to manage those impacts. Using demographic techniques and population projection models, here we assess if demography and population dynamics of the tree Prosopis flexuosa change in cattle grazed areas compared to ungrazed areas in the Central Monte desert, Mendoza, Argentina. To this end, we quantified vital rates and constructed a population projection matrix model to compare the deterministic population growth rate (λ) between grazed and ungrazed areas. We also estimated elasticities of vital rates to evaluate their potential importance for future changes in λ and performed a life table response experiment (LTRE) to identify the life cycle transitions that contribute the most to the observed differences in λ between the two treatments. Although we found differences in demographic processes, such as lower seed production and higher probability of reversion to smaller size classes in young individuals when cattle were present, our results indicate that cattle grazing had no significant effect on λ for this species. According to the elasticity analysis, survival of large trees is the main driver of the population growth rate (λ) of P. flexuosa, and the vital rates related to tree reproduction, such as seed production and germination, have a poor contribution to λ. Therefore, limitations of activities that can affect survival of large trees should be considered as part of the conservation strategy for this species. Our study provides a compilation of demographic information that can be useful to set policies connecting the conservation objectives for this woodlands with that of ranch managers of the area.

Diet mixing and condensed tannins help explain foraging preferences by Creole goats facing the physical and chemical diversity of native woody plants in the central Monte desert (Argentina)

The aim of this study was to understand the benefit of diet mixing for Creole goats grazing native forage species in the central Monte desert of Argentina and the drivers of preference in the mixed diet. To achieve this goal, cafeteria-style experiments were conducted with thirty female Creole goats (2 years old; 44±1.4kg) and forage species that are typically ingested by goats in this region: Two tanniniferous (Tricomaria usillo, Mimosa ephedroides) and three non-tanniniferous shrubs (Prosopis flexuosa, Capparis atamisquea, Atriplex lampa). In Experiment 1, goats were assigned to three groups (n=10); two groups were offered single tannin-containing shrubs as their basal diet (T. usillo; SDTU or M. ephedroides, SDME), whereas the third group received a combination of all five forages (Mixed diet of forages, MD). After a fifteen-day adaptation period, half the animals in each group (n=5) were dosed with polyethylene glycol (PEG), a polymer that neutralizes the negative effects of tannins, whereas the other half (Control) were not dosed (CG). Daily dry matter intake (DMI), in vivo apparent digestibility of the diet (ADD) and nitrogen (ADN) were determined. For goats fed MD, preference was estimated based on the DMI of each of the forages offered. Jugular blood samples were collected on the first and last days of the experiment to determine concentrations of blood urea nitrogen (BUN) and serum metabolites indicative of liver damage. In experiment 2, intake rates (IR) of the five forage species were estimated. No significant differences in DMI were detected among treatments. However, goats offered a choice of forages (MD) in the CG treatment had greater diet digestibility and lower BUN than animals fed the single shrubs, showing evidence of a nutritional benefit with dietary diversity. Goats changed their foraging preferences in response to PEG supplementation. Animals in the CG treatment preferred M. ephedroides whereas animals in the PEGG treatment preferred A. lampa. There was a positive correlation between forage preference and IR of crude protein (r=0.65; P<0.001) in PEGG goats, and between forage preference and IR of total tannins (r=0.77, P<0.001) in CG goats. When PEG attenuated biological effects of condensed tannins, goats switched their preference from forages that offered the greatest IR of total tannins (i.e., M. ephedroides) to those that led to the greatest IR of crude protein (i.e., A. lampa). In summary, a mixed diet led to greater nutritional benefits than single diets, which contribute to explain the diverse array of food items goats typically show when browsing in the central Monte desert of Argentina. Our results also show that CP, tannins and plant structure (which offer variable intake rates) play significant roles in goats’ foraging preferences in this environment.

Assessing the Sensitivity of Riparian Algarrobo Dulce (&lt;i&gt;Prosopis flexuosa&lt;/i&gt; DC) Radial Growth to Hydrological Changes

Ecotones, as for example riparian zones, have long interested ecologists, due to their potential role in generating species biodiversity and evolutionary novelty, as well as their sensitivity to environmental changes. Along riparian areas, vegetation is recognized for its ecological importance in several ecosystemic processes. In the Central Monte Desert (central-west Argentina), &lt;i&gt;Prosopis flexuosa&lt;/i&gt; grows in territories characterized by a permanent access to water reservoirs, e.g. along riverbanks, where the species forms the classic gallery forests. Despite the ecosystemic role of the different &lt;i&gt;Prosopis&lt;/i&gt; species distributed in arid lands, thus far no analysis has been conducted regarding the relation between their radial growth and hydrological changes, namely streamflow variability, in riparian settings. To fill this gap of knowledge, we performed a dendrochronological analysis considering several riparian &lt;i&gt;P. flexuosa&lt;/i&gt; trees differing in their spatial position in relation to the riverbank. Pointer years, correlation function, and regression analyses show differences in the dendrohydrological signal of the studied species, probably function of tree distance from the river. In this sense, radial growth of trees distributed near the riverbank is tightly coupled to spring-summer (September to March) stream-flow variability, whereas for farthest trees the ring development is driven by a combination of winter and spring river discharge and late-summer precipitation amount. The presented results demonstrate the potentiality of &lt;i&gt;P. flexuosa,&lt;/i&gt; and in a broader sense of the &lt;i&gt;Prosopis&lt;/i&gt; genus, in dendrohydrological studies.

Almacenadores y frugívoros oportunistas: el papel de los mamíferos en la dispersión del algarrobo (Prosopis flexuosa DC) en el desierto del Monte, Argentina

Campos, C.M., Velez, S. 2015. Opportunistic scatter hoarders and frugivores: the role of mammals in dispersing Prosopis flexuosa in the Monte desert, Argentina . Ecosistemas 24(3): 28-34. Doi.: 10.7818/ECOS.2015.24-3.05 Prosopis flexuosa woodlands provide multiple goods and services. Currently, they are undergoing a strong retraction as a result of a historical extractive use; hence it becomes urgent to promote the conservation and sustainable management of these woodlands as a system. The objective of this study is synthesizing the knowledge of mutualistic and antagonistic interactions between mammals and Prosopis fruits and seeds, particularly considering opportunistic animals that consume fruits: scatter hoarders and frugivores. Small rodents (such as Eligmodontia typus and Microcavia australis ) are potential seed dispersers because they predate on a few seeds and store the rest in caches on the ground surface. Opportunistic frugivores, like wild mammals ( Dolichotis patagonum, Lepus europaeus, Lycalopex griseus, Lama guanicoe, etc.), and domestic mammals (donkey, horse, cow) disperse seeds by endozoochory, affording benefits such as transport of huge numbers of seed, removal of the barriers maintaining dormancy and disinfection of insect-attacked seeds. However, endozoochory brings costs to the viability and germination capacity of seeds, depending on the disperser involved. In a scenario of continuous land use changes and global climate change, knowledge of the diverse array of animals that benefit dispersal provides scientific grounds for considering that the biodiversity associated with woodlands must be included in their management and conservation.

Seed predation and removal from faeces in a dry ecosystem

The fate of dispersed seeds from mammal faeces depends both on the animal that finds the seeds and environmental conditions. We explored the simultaneous influence of microhabitat and food availability on seed predation and removal from faeces by different animals in a protected Prosopis flexuosa open woodland site of the central Monte desert (Argentina). Using exclusion trials on simulated cattle faeces, we quantified seed predation in situ (within cages) and seed removal from faeces by rodents and ants in two different microhabitats (under shrub cover and on bare soil). This was done for two levels of availability of P. flexuosa fruits (during the fruiting season of P. flexuosa and when there are no fruits on the ground). We found that 67.9% of seeds remained in faeces, 28.9% were removed, and 3.2% were depredated in situ. Rodents removed more seeds under shrub cover than on bare soil, and during the non-fruiting period than during the fruiting period, whereas ants removed similar proportions of seeds in different microhabitats but almost exclusively during the fruiting season. This work acknowledges the complexity of dispersal processes and identifies the relative importance of some environmental factors for seed fate.

Does land use change alter water and nutrient dynamics of phreatophytic trees in the Central Monte desert?

AbstractIn the woodlands of the Central Monte desert (Argentina), phreatophyte vegetation is exposed to different levels of disturbance. Livestock and settlement activity produce mainly nutrient inputs and partial vegetation removal, with a consequent reduction on water use by vegetation. We hypothesize that because of the increased soil water and nutrient resources associated with livestock stations, water stress will be relieved for the remaining Prosopis flexuosa trees, favouring water and nutrient status, and plant growth at the plant scale. The goal of this research was to analyse the physiological responses of P. flexuosa trees that grow in interdune valleys under different land uses, and the changes in relative importance of environmental factors controlling these responses. We compared the ecophysiological responses of adult P. flexuosa trees in two contrasting types of disturbance: disturbed (livestock stations) and relatively undisturbed (control woodlands) stands, in the 2011–2013 growing seasons. Pre‐dawn and midday leaf water potential and stomatal conductance were higher in livestock stations than in control woodlands, suggesting a better water status of P. flexuosa in livestock stations. Isotopic composition (lower δ13C, and higher δ15N) and foliar nitrogen concentration (lower C:N ratios) indicated lower water use efficiency and higher nitrogen absorption from the soil in livestock stations. Both growth of new leaves (foliar area) and the length of young branches were higher in the first season for both land uses, but branch length was higher in livestock stations. This is consistent with the idea that vegetation removal and nutrient contribution of settlement activities improved water and nutrient status of remaining vegetation, and modified the relative importance of factors controlling ecophysiological processes. We concluded that physiological responses and vegetative growth of P. flexuosa were not only affected by meteorological conditions (rainfalls, vapour pressure deficit), but also by the ecohydrological changes caused by changes in land use. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Pruning effects on ring width and wood hydrosystem of Prosopis flexuosa DC from arid woodlands

Pruning is a silvicultural practice that could potentially improve the productivity in arid woodlands. However, there is not enough information about the influence of this practice on the tree-ring wood anatomy of desert Prosopis woodlands. We analyzed the effect of pruning trees of different diameter class (small and large, PDDC) and pruning intensity in small trees (heavy and intermediate, PDI). We evaluated tree-ring width, number of vessels, total vessel area, mean vessel size (total vessel area/number of vessels), vessel density (number of vessels/tree-ring area) and ratio of vessel area to tree-ring area in Prosopis flexuosa, a species widely used for firewood and poles in arid and semiarid areas of South America. For PDDC, trees were pruned during the winter of 2003, for which we focused on the period between 1995 and 2010 (8 years before and after pruning, respectively) and for PDI, trees were pruned during the winter of 2004, and we focused on the period between 1997 and 2010 (7 years before and after pruning, respectively). The data was analysed using Mixed Models. We observed that, small trees had a greater response to pruning than large individuals. In this sense, pruning increased radial growth (F2,247=6.08, p≤ 0.01) and number of vessels (F2,247=6.36, p≤0.01), and decreased the mean vessel size (F2,247=6.91, p≤ 0.001) and ratio of vessel area to tree-ring area (F2,247=4.84, p≤ 0.01) in small trees. Moreover, the response depended on pruning intensity, which was more evident in intermediate pruning. The increase in the vessel number and the decrease in mean vessel size observed in small trees denoted that pruning induces the generation of new, small-diameter vessels. This is considered a strategy to protect the water-conducting system in response to pruning. Studies at the anatomical level conducted in the present research revealed in detail how pruning influences wood production and anatomical modifications, indicating the importance of conducting wood anatomical analyses on tree rings in order to refine interpretations of the effect of pruning on stem growth.

Geomorphological-related heterogeneity as reflected in tree growth and its relationships with climate of Monte Desert Prosopis flexuosa DC woodlands

Across the Central Monte Desert district in Argentina, landform and soil variability drive radial growth of Prosopis flexuosa and its relation with precipitation. Desert forests grow under diverse ecological conditions, mainly resulting from the spatial heterogeneity of drylands with consequences on tree growth and its interactions with climate. In the Monte Desert, geomorphological processes generate landform and soil variability, determining the distribution and growth of plant species. Prosopis flexuosa DC., a dominant tree species in the Central Monte Desert, grows in territories characterized by a high variability of landform and soil. We applied classical dendrochronological and statistical analysis to disentangle the effect of spatial heterogeneity upon the species radial growth and its further relation with precipitation fluctuations. Trees from 11 plots distributed in seven P. flexuosa forests encompassing the most important geomorphological/landform units in the Central Monte Desert were analyzed. Tree-ring development at both high and low frequencies reflects spatial landform variability. Soil heterogeneity drives ring growth within landform. Regionally, precipitation influences radial growth at the beginning and the end of the growing season, while locally dependent mechanisms related to landform/soil variability emerged. In this sense, the negative influence of late-summer precipitation found for a riparian chronology is a function of soil permeability. Ring growth at the paleo-river environment depends on late spring and early mid-summer precipitation, with within-landform differences probably related to soil heterogeneity. In the case of inter-dune and lowland units, radial growth depends on early spring rainfall. Our findings highlight the influence of the heterogeneity of desert environments on tree growth. The information is relevant to management and conservation policies, particularly for the forests of P. flexuosa in Argentine Monte.

Hydrotropism in lateral but not in pivotal roots of desert plant species under simulated natural conditions

Root hydrotropism has been widely studied in seedling radicles through artificial experiments that reduce the influence of gravity and soil. In this work we aimed to study hydrotropism of primary lateral and pivotal roots in developed root systems of desert plants under simulated natural conditions. We grew Bulnesia retama Griseb. (non phreatophyte), Prosopis flexuosa DC. (facultative phreatophyte) and Prosopis alpataco Phil.(obligate phreatophyte) seedlings in observation boxes with sand. Lateral and pivotal roots were stimulated by lateral water gradients and hydrotropic responses, root proliferation and root : shoot ratios were measured. We found that 65 ± 15 % of lateral roots that grew in response to water gradients in B. retama, 84 ± 8 % in P. flexuosa and 88 ± 8 % in P. alpataco displayed hydrotropism. Conversely, pivotal roots did not show hydrotropic growth. This was accompanied by root proliferation inside water patches, and biomass partitioning to shoot growth. Our results provide evidence that root hydrotropism is a relevant response that could occur in nature. Lateral and pivotal roots manifest different hydrotropic responses under the conditions assayed. The combination of hydrotropism and precise root proliferation can shape root architecture, leading to optimum water patch exploration.

Identification of single nucleotide polymorphisms (SNPs) at candidate genes involved in abiotic stress in two Prosopis species of hybrids

Aim of the study: Identify and compare SNPs on candidate genes related to abiotic stress in Prosopis chilensis, Prosopis flexuosa and interspecific hybridsArea of the study: Chaco árido, Argentina. Material and Methods: Fragments from 6 candidate genes were sequenced in 60 genotypes. DNA polymorphisms were analyzed.Main Results: The analysis revealed that the hybrids had the highest rate of polymorphism, followed by P. flexuosa and P. chilensis, the values found are comparable to other forest tree species.Research highlights: This approach will help to study genetic diversity variation on natural populations for assessing the effects of environmental changes.Keywords: SNPs; abiotic stress; interspecific variation; molecular markers.

From forest to shrubland: Structural responses to different fire histories in Prosopis flexuosa woodland from the Central Monte (Argentina)

We estimated post-fire population trajectories, and analyzed the effect of fire recurrence on the post-fire recovery of seven different fire histories in the Central Monte. The structure of stems showed that unburned woodlands and woodlands with the longest post-fire recovery time, presented higher proportion of stems with basal diameter (BD) > 5 cm. On sites with higher recurrence of fires, the stems with BD > 5 cm almost disappeared. Tree height and crown diameter showed a significant decrease at sites recently burned, and this pattern was reinforced in areas with recurrent fires. Results suggest that the structure of woodland in the southeast of the Province of Mendoza in Argentina has been strongly controlled by fire history. Fire generates a population dominated by individuals with numerous smaller-sized stems, which becomes more evident in environments where fire recurrence is higher. Structural changes induced by fire indicate that logging may not be possible in the area. The development of forestry practices for post-fire management is needed for the burned areas. An increase in fire frequency is expected in the area, therefore this would cause the modification in the structure of the Prosopis flexuosa population. Furthermore, this will lead to the conversion from woodland to shrubland, and the loss of its capacity for natural recovery.