Neighboring Vegetation Research Articles

Drivers of tree colonization, species richness, and structural variation during the initial three decades of natural forest colonization in abandoned agricultural soils

Natural colonization of abandoned agricultural soils has been proposed as a cost-effective strategy for simultaneously mitigating the climate crisis, restoring ecological integrity, and promoting the re-establishment of native biodiversity. The success and speed at which forests develop in the presence of land-use legacies are highly variable, and empirical knowledge on the drivers of the initial phase of temperate forest colonization in a range of site conditions is lacking. We analyzed and compared drivers of the initial three decades of natural forest colonization in 33 afforestation sites laid out between 1990 and 2018, in Denmark. We analyzed how the age of colonization, size of the area, soil type, topography, and abundance of neighboring woody vegetation influenced woody vegetation cover, species richness, and variation in vegetation structure of the colonizing woody species. We found that woody vegetation cover, species richness, and structural variation increased significantly with time since abandonment. Woody vegetation cover was significantly higher in sites with abundant neighboring vegetation and on loamy soils compared to sand or clay. Woody vegetation cover tended to be higher in sites with sloping terrain. Species richness increased significantly in sites with loamy or clay soil and sites with sloping terrain. After accounting for the other drivers, none of the elements were influenced by the size of the area. The results suggest that time since abandonment, neighboring mature woody vegetation, soil and topography are key drivers of the different elements of colonization. This knowledge can be used to prioritize areas for natural colonization and to improve active afforestation methods, especially in new forests where the main focus is on nature quality and biodiversity.

Machine-Learning Applications in Geosciences: Comparison of Different Algorithms and Vegetation Classes’ Importance Ranking in Wildfire Susceptibility

Susceptibility mapping represents a modern tool to support forest protection plans and to address fuel management. With the present work, we continue with a research framework developed in a pioneristic study at the local scale for Liguria (Italy) and recently adapted to the national scale. In these previous works, a random-forest-based modeling workflow was developed to assess susceptibility to wildfires under the influence of a number of environmental predictors. The main novelties and contributions of the present study are: (i) we compared models based on random forest, multi-layer perceptron, and support vector machine, to estimate their prediction capabilities; (ii) we used a more accurate vegetation map as predictor, allowing us to evaluate the impacts of different types of local and neighboring vegetation on wildfires’ occurrence; (iii) we improved the selection of the testing dataset, in order to take into account the temporal variability of the burning seasons. Wildfire susceptibility maps were finally created based on the output probabilistic predicted values from the three machine-learning algorithms. As revealed with random forest, vegetation is so far the most important predictor variable; the marginal effect of each type of vegetation was then evaluated and discussed.

Climate and the biotic community structure plant resistance across biogeographic groups of yellow monkeyflower.

Characterizing correlates of phytochemical resistance trait variation across a landscape can provide insight into the ecological factors that have shaped the evolution of resistance arsenals. Using field-collected data and a greenhouse common garden experiment, we assessed the relative influences of abiotic and biotic drivers of genetic-based defense trait variation across 41 yellow monkeyflower populations from western and eastern North America and the United Kingdom. Populations experience different climates, herbivore communities, and neighboring vegetative communities, and have distinct phytochemical resistance arsenals. Similarities in climate as well as herbivore and vegetative communities decline with increasing physical distance separating populations, and phytochemical resistance arsenal composition shows a similarly decreasing trend. Of the abiotic and biotic factors examined, temperature and the neighboring vegetation community had the strongest relative effects on resistance arsenal differentiation, whereas herbivore community composition and precipitation have relatively small effects. Rather than simply controlling for geographic proximity, we jointly assessed the relative strengths of both geographic and ecological variables on phytochemical arsenal compositional dissimilarity. Overall, our results illustrate how abiotic conditions and biotic interactions shape plant defense traits in natural populations.

Leaf trait plasticity and site-specific environmental variability modulate the severity of visible foliar ozone symptoms in Viburnum lantana.

The assessment of Visible Foliar Symptoms (VFS) is commonly adopted by forest monitoring programs to evaluate ozone impact on vegetation. The occurrence of ozone VFS may differ among individuals of the same species at the same site, and within leaves of the same individual. The aim of this study was to identify site and plant characteristics as well as functional leaf traits associated with the occurrence and severity of VFS in Viburnum lantana (an ozone-sensitive species) and at the scale of an individual site. V. lantana plants growing at one site of the ViburNeT monitoring network (Trentino, North Italy) experiencing high ozone levels were surveyed in relation to 1) sun exposure, 2) shading effect from neighbor vegetation, 3) plant height and 4) presence and severity of VFS. Leaves from three different sections of each plant were subjected to a phenotypic characterization of leaf area, dry weight, specific leaf area (SLA), chlorophyll content (ChlSPAD), percentage of VFS, and adaxial and abaxial trichome density (Tr). We showed that plants at high irradiation levels had significantly lower SLA (p<0.05), higher Tr (p<0.01) and greater ChlSPAD (p<0.01) when compared to shaded and/or west- and north-exposed plants, thus indicating a strong influence of site-specific characteristics on leaf trait plasticity. Similar differences were observed for taller vs. shorter plants and apical vs. basal branches (p<0.05). Ozone-induced VFS at leaf level were associated with lower SLA (p<0.001) and higher Tr in the abaxial leaf surface (p<0.05). Both leaf traits showed significant differences also within the south and east exposed plant category, thus suggesting the increase in leaf thickness and Tr as a potential adaptive strategy under multiple stress conditions. Our results provide evidence of a strong relationship between VFS, leaf traits and site-specific variables, offering new insights for interpreting data on the impact of ozone on vegetation.

A copula incorporated cellular automata module for modeling the spatial distribution of oasis recovered by ecological water diversion: An application to the Qingtu Oasis in Shiyang River basin, China

Assessing the impact of ecological water diversion on oasis restoration is critical for water resources and environmental management in arid inland basins. This study proposed a copula incorporated cellular automata (CA) module for modeling the oasis’s spatial distribution driven by ecological water diversion. Given the effects of groundwater depth and community expansion on oasis evolution, a water availability index and a neighbor vegetation index were proposed. These two indices were joint using the Clayton copula function, producing a vegetation suitability index that quantified vegetation growth’s habitat quality and provided the CA module’s basis to identify cellular categories. The CA module was integrated into a previously developed conceptual lumped ecohydrological model (CLEM), resulting in an improved CA-CLEM that outputted groundwater depth, oasis area, oasis NDVI, and oasis distribution data. The CLEM provided the oasis area changes for the CA module, which specified the spatial distribution of these changes. The CA-CLEM had a simple structure, low computation cost, and good performance, indicated by the application in the Shiyang River basin in Northwest China. Results show that an ecological water diversion of 30 million m3, with an average groundwater depth of 2.95 m, an oasis area of 25 km2, and an oasis NDVI of 0.36, would successfully recover the terminal Qingtu Oasis in 2020. The oasis distribution and its dynamic evolution processes were irregular because of the spatial heterogeneity of vegetation habitat suitability. The present Qingtu Oasis was fragile, and its sustainability relied on ecological water diversion. The reduction in water diversion would cause water table decline, oasis area shrinkage, vegetation degradation, and oasis fragmentation. The CA-CLEM combined with scenario analysis provides practical and reliable implications for managers and policymakers to improve ecological water diversion strategies.

Diversidad de arañas (Arachnida, Araneae) sinantrópicas de la ciudad de Morelia, Michoacán, México, ¿qué tanto influye el tiempo de construcción de las viviendas en la comunidad de arañas?

Spiders have been used to evaluate changes in systems by anthropization effect, some species showing sensitivity to gradual and drastic changes such as urbanization, and other species have been documented as tolerant to this effect. The goal of this work was to describe the change in the spider community in relation to the age of buildings. at the west of Morelia, Michoacán, Mexico. Three categories of construction time and the neighboring vegetation as the pre-urbanization environment were used for comparison. Using direct capture, pit-fall traps and beating nets, 3,619 spiders were collected, and 3,219 (315 males, 630 females and 2,274 immatures) were used for the analysis after removal juveniles that was not possible to identify. A total of 28 families, 93 genera, 47 species and 55 morphospecies were identified. This represents the greatest richness and abundance recorded in urban environments of the country. It describes changes in alpha diversity from colonization in recent constructions to those built 17 years ago. I t was observed that abundance, richness, and diversity decrease with the age of a building, but with high equitability in every age of construction. The age of a building is an important factor for the process of succession in urban environments.

Effects of forest preservation, livestock exclusion, and use of shrubs as potential nurses on planting success of an endangered tree

Domestic livestock are widespread in seasonally dry forests, likely causing forest degradation and limiting tree seedling establishment. Shrubs can play an important role in facilitating tree regeneration, by protecting trees from livestock damage and ameliorating unfavorable abiotic conditions. We aimed at disentangling the relative contribution of grazing exclusion, long‐term forest conservation, and the potential facilitation effect of shrubs on the performance of saplings of the native tree Kageneckia lanceolata. We planted 400 saplings in grazed and ungrazed areas situated both in a preserved and a degraded forest. In each situation, we established planting plots in three accompanying vegetation treatments: herbs, a nonleguminous spiny shrub and a leguminous spiny shrub. Survival of 3‐year‐old saplings was 10‐fold higher in the preserved than in the degraded forest and 2‐fold higher in the ungrazed than in the grazed site. Differences in survival among accompanying vegetation treatments were much smaller than between grazing treatments. Survival significantly increased with increasing protection by shrubs only in the degraded site. Sapling growth patterns were fairly similar to survival patterns, with no growth in the degraded forest, except for limited growth under both shrubs in the ungrazed site. We conclude that, in selecting plantation sites for the study species, forest condition and grazing exclusion should be prioritized over microsite selection based on neighboring vegetation.

Phytochrome-interacting factor 4 (PIF4) inhibits expression of SHORT HYPOCOTYL 2 (SHY2) to promote hypocotyl growth during shade avoidance in Arabidopsis

Plants sense the presence of competing neighboring vegetation as a change in light quality. These changes initiate shade avoidance syndrome (SAS) responses. PHYTOCHROME INTERACTING FACTORS (PIFs) are crucial factors in the SAS response. In particular, they mediate the expression of multiple phytohormones and cell expansion genes. Many positive regulatory factors in the SAS response have been identified, but the negative regulation of SAS transcription factors remains poorly understood. The functions of the short hypocotyl 2 (SHY2) transcription factor during the SAS response have not been established, although its roles in the participating hormone and stress responses are well documented. Here, the SHY2 loss-of-function (shy2-31) mutant had a longer hypocotyl, but the gain-of-function (shy2-2) hypocotyl was shorter than that of the wild type under white and shade conditions. We showed that the SHY2 expression level and its associated protein significantly accumulated under shade conditions. Furthermore, SHY2 transcript levels significantly increased in mutant pifQ, but decreased in PIF4OX compared to the wild type, which indicated that PIF4 is a transcriptional repressor of SHY2. ChIP assays have consistently shown that PIF4 directly binds to the promoters of SHY2. We further show that PIF4OX partially rescued the short hypocotyl characteristic of shy2-2 under white and shade conditions. Our results provide new insights into the regulatory mechanisms controlling SAS mediated elongation of the hypocotyl by PIF4-SHY2 modules in Arabidopsis.

Dicamba translocation in soybean and accumulation in seed

AbstractThe dicamba-resistant cropping system was developed to be used as a tool to control multiple-resistant weed species, particularly Palmer amaranth (Amaranthus palmeri S. Watson). However, dicamba applications have resulted in off-target movement of the herbicide to susceptible neighboring vegetation, with frequent damage to non–dicamba resistant soybean [Glycine max (L.) Merr.]. Pod malformation and subsequent auxin-like injury to progeny is common when parent soybean plants are exposed to the herbicide post-flowering. Yet no publication to date has conveyed the presence of dicamba in seed. The objective of this study was to determine whether dicamba exists and at what quantities inside soybean seed following a low-dose exposure in the pod-filling stage using radiolabeled herbicide as a tracer. Non–dicamba resistant soybean plants were grown in the greenhouse until the pod-filling growth stage and then treated with 2.8 g ae ha−1 of dicamba (1/200 of the recommended rate of 560 g ae ha−1). Immediately afterward, [14C]dicamba (approximately 6.4 kBq per plant) was applied to the adaxial surface of one trifoliate leaf located in the midportion of each plant. The greatest amount of [14C]dicamba recovered was in seeds and in pods, and these plant parts accumulated 44% and 38% of the total absorbed, respectively. Chromatography results showed that the totality of the [14C]dicamba present in the soybean seeds was in the phytotoxic form, except for a single sample, in which one metabolite was detected (possibly 5-hydroxy dicamba). Precautions should be taken to avoid dicamba exposure to sensitive soybean fields, especially those dedicated to seed production, as this may result in low seed quality and symptomology on progeny plants.

Plant killing by Neotropical acacia ants: ecology, decision‐making, and head morphology

AbstractMutualistic species often associate with several partners that vary in the benefits provided. In some protective ant–plant mutualisms, ants vary in the extent at which they kill neighboring vegetation. Particularly, in acacia ants (Pseudomyrmex), the area around the host tree that ants keep free from vegetation (“clearings”) vary depending on the species. This study assessed whether interspecific variation in clearing size corresponds to workers biting on plant tissue of different thickness. As expected, workers from species making the largest clearings bit more often on thicker plant tissues than workers from species making smaller clearings. Because head shape affects mandible force, I also assessed whether pruning on thick tissue in mutualistic ant species or being a predator in non‐mutualistic species correlated with broader heads, which yield stronger mandible force. The species with the broader heads were non‐mutualistic predators or mutualistic pruners of thick tissues, which suggest that pruning neighboring vegetation in non‐predatory species demands force even when the ants do not kill prey with their mandibles. The findings reveal that clearing size variation in mutualistic ant partners of plants can also be observed at the level of individual decision‐making processes among workers, and suggest that head morphology could be a trait under selection in protective ant–plant mutualisms.Abstract in Spanish is available with online material.

Shade Avoidance and Neighbor Detection.

Plants detect neighboring vegetation as potential competitors for resources. Vegetation proximity is perceived by changes in the red (R) to far-red (FR) ratio (R:FR) through the phytochrome photoreceptors. To face this challenge, many plants have evolved the strategy to avoid shade, displaying a series of responses known as the shade avoidance syndrome (SAS). The SAS responses have been mostly studied at the seedling stage, and cover hypocotyl elongation as well as cotyledon and primary leaf expansion. In adult stages, SAS responses include an increase in petiole elongation and a decrease in leaf expansion, and an increase in plant height. Thus, the analysis of these responses provides a valuable and simple way to study how vegetation proximity affects plant development in both seedlings and adult plants. Here we describe a simple protocol to simulate shade in the laboratory and to evaluate these responses. Overall, our protocol can be easily used to expand the set of SAS responses of plants at different stages of development.

Pequeños pero importantes: las comunidades de vegetales leñosa de los afloramientos de arenisca de Teyú Cuaré (Misiones, Argentina).

Pequeños pero importantes: las comunidades de vegetales leñosa de los afloramientos de arenisca de Teyú Cuaré (Misiones, Argentina). Los afloramientos rocosos son ambientes comúnmente rigurosos que mantiene importantes componentes de la biodiversidad por estar habitados por especies endémicas o relictuales. El objetivo del presente estudio fue evaluar la diversidad y estructura de la planta leñosa de la vegetación rupestre ubicada en el departamento de San Ignacio (Misiones, Argentina) y evaluar la diversidad beta con respecto a otras formaciones vegetales vecinas (esto es bosque y sabana). Se encontraron 32 especies de plantas leñosas, la mayoría arbóreas de pequeño tamaño. Qualea cordata (Mart.) Spreng., Monvillea euchlora Backeb., Ocotea lancifolia (Schott) Mez y Myrciaria delicatula (DC.) O. Berg fueron las más importantes en la estructura de la comunidad. La vegetación rupestre del conjunto de afloramientos estudiados mostró una diversidad leñosa media en comparación con las formaciones de bosque y sabana, con una alta diversidad beta, principalmente estructurada por la diferencia de riqueza. Estos ambientes tienen una alta prioridad para la conservación, debido a que las comunidades vegetales son fisionómica y florísticamente singulares, además de estar en condiciones edáficas y geomorfológicas con una expresión geográfica restricta.

Nonhost neighborhood increases biocontrol weevil damage to the nontarget, federally threatened Pitcher's thistle (Cirsium pitcheri)

Studies that monitor the intensity of biocontrol insect damage on target and nontarget hosts in the field often consider the effects of neighboring vegetation that serve as acceptable alternative hosts. Whether nonhost neighboring plants can also influence damage to hosts has received less attention. The nonnative, seed-eating weevil Larinus planus has been distributed as a biocontrol agent for weedy thistles in the U.S., but also attacks native thistles including the federally threatened Cirsium pitcheri. To test the hypothesis that nonhost Ammophila breviligulata grass neighbors increase susceptibility of C. pitcheri to L. planus damage, we clipped the neighboring vegetation within a 1 m radius around focal C. pitcheri, and assessed weevil infestation in flower heads of plants with clipped or unclipped neighbors. We also examined elevational effects by surveying weevil presence along an environmental gradient and comparing infestation rates between primary and secondary dune habitats with intact neighboring vegetation. Larinus planus infestation was more prevalent at low than at high dune elevations. At low elevations, clipping neighboring vegetation surrounding C. pitcheri significantly decreased the proportion of flower heads infested by weevils. Grasses may aid L. planus dispersal to C. pitcheri hosts and/or provide a refuge from environmental stress or natural enemies. Our results highlight two factors that predict L. planus attack, as well as areas of the dune on which to focus Cirsium pitcheri management or weevil control efforts. More broadly, our results suggest that nonhost neighboring vegetation may be an important factor determining the intensity of damage by invasive and biocontrol insects.

TCP Transcription Factors Regulate Shade Avoidance via Directly Mediating the Expression of Both PHYTOCHROME INTERACTING FACTORs and Auxin Biosynthetic Genes.

Light quality surrounding a plant is largely determined by the density of its neighboring vegetation. Plants are able to sense shade light signals and initiate a series of adaptation responses, which is known as shade avoidance syndrome (SAS). PHYTOCHROME INTERACTING FACTORS (PIFs) are key factors in the SAS network by regulating the biosynthesis of multiple phytohormones and the expression of cell expansion genes. Although the protein levels of PIFs were found to be acumulated in shade, the transcriptional regulation of PIFs in response to such an environmental signal remains poorly understood. Here we show that TCP17 and its two closely related homologs, TCP5 and TCP13, play an important role in mediating shade-induced hypocotyl elongation by up-regulating auxin biosynthesis via a PIF-dependent and a PIF-independent pathway. In constitutive white light, a tcp5, 13, 17 triple mutant (3tcp) showed a subtle hypocotyl defective phenotype. In shade, however, 3tcp showed a significantly reduced hypocotyl elongation phenotype, indicating a positive role of TCPs in regulating SAS. Our in-depth biochemical and genetic analyses indicated that TCP17 can be significantly accumulated in shade. TCP17 binds to the promoters of PIFs and YUCCAs to indirectly or directly up-regulate auxin levels in shade. These data provide new insights into our better understanding of the regulatory mechanisms of SAS in plants.

Crop Discrimination Using Multispectral Sensor Onboard Unmanned Aerial Vehicle

This paper presents the results and observations made from pilot exercises on crop discrimination using Parraot Sequoia multispectral sensor onboard a Unmanned Arial Vehicle (UAV). The exercise was carried out in two selected sites in West Jaintia Hills district of Meghalaya state with mixed horticultural crops. Parraot Sequoia sensor having four bands has been found to be effective in crop discrimination based on variation in spectral response and crop height. Discrimination of three horticultural crops viz. banana, orange, and plum and the neighbouring bamboo grooves were evaluated using three commonly used indices viz., Normalized Difference Vegetation Index (NDVI), Normalized Difference Red Edge Index (NDRE) and Green Normalized Difference Vegetation Index (GNDVI). NDVI and GNDVI showed nearly similar spectral response, whereas separability among the crops marginally improved with the use of NDRE. The percent variations of spectral response for orange and bamboo were 14 and 19 in terms of NDVI and GNDVI respectively, whereas the same value is 49 in case of NDRE. Similarly percent variations of spectral response for banana and bamboo were 7 and 15 in terms of NDVI and GNDVI against 27 in case of NDRE. In the second study site, variation in Digital Surface Model (DSM) and Digital Terrain Model (DTM) was generated to discriminate different crops grown at different elevation. The difference in the surface model has helped in discriminating different crops and other neighboring vegetation with rice recording difference of − 0.05 to 0.05, followed by maize (0.05–0.5) and pineapple (0.5–10).

Flora en playas y dunas costeras de México

Antecedentes y Objetivos: Se presenta el primer listado florístico de las playas y dunas costeras de México, actualizado y respaldado por ejemplares de herbario.Métodos: Se revisaron 14 herbarios nacionales y extranjeros. Se sobrepuso una retícula de 2 × 2 km al mapa de la costa y de las dunas costeras de México para referir todos los registros que corresponden a 2180 sitios con 12,419 ejemplares de plantas. Se calcularon índices de diversidad, similitud, diversidad taxonómica y redundancia.Resultados clave: La flora registrada consta de 153 familias, 897 géneros y 2075 especies de plantas vasculares, las cuales representan 9.5% de la flora vascular de México. Las cinco colecciones con índices de redundancia altos IR≥0.7 son los herbarios de la Universidad Nacional Autónoma de México (MEXU, IR=0.9), del Centro de Investigación Científicas de Yucatán (CICY, IR=0.8), y los del Centro de Investigaciones Biológicas del Noroeste (HCIB), el Instituto de Ecología, A.C. (XAL) y el del Museo de Historia Natural de San Diego (SD), cada uno con un IR de 0.7. Se reconocen cinco regiones florísticas que corresponden a los mares de México. El Pacífico Norte tiene mayor diversidad taxonómica y el Pacífico Sur menor diversidad taxonómica. El Golfo de California, Golfo de México y Mar Caribe tienen diversidades taxonómicas similares. Las especies con más registros son Trianthema portulacastrum (165), Croton punctatus (107), Echites umbelllatus (106) e Ipomoea pes-caprae (90). Por el carácter de ecotono de las dunas costeras, la mayoría de las especies se comparten con los tipos de vegetación vecinos (selvas, matorrales, y humedales como las marismas y manglares).Conclusiones: Esta primera lista de la flora en playas y dunas de México es la base para múltiples estudios florísticos regionales y locales, biogeográficos, y ecológicos; además, que será importante para su uso en temas de impacto ambiental y manejo costero.

Effects of interspecific competition from surrounding vegetation on mortality, growth and stem development in young oaks (Quercus robur)

Facilitation by a neighboring woody understory has been suggested as a cost-effective and sustainable way to regenerate oaks. However, concerns about reduced plant growth and quality due to competing neighboring vegetation have hindered implementation. Here we studied competitive effects from herbaceous and woody vegetation on survival, growth, canopy development and stem quality in pedunculate oak (Quercus robur) in an open-field experiment in southern Sweden. Oaks were grown for eight years in four different competition treatments: no competing vegetation, with herbaceous vegetation (mainly grasses), with woody vegetation, and with both herbaceous and woody vegetation. During the first four years, competition had little effect on oak survival. However, after eight growing seasons, survival rates decreased to about 20% for oaks surrounded by woody vegetation, in contrast to oaks grown with only herbaceous vegetation that had a survival rate of near 100%. Competition from herbaceous and woody vegetation both reduced oak stem diameter and height growth, but they affected height growth differently. During the first growing seasons, oaks in the treatment with woody vegetation were able to keep up with the height growth of the surrounding vegetation. Thereafter, height growth stagnated, and after eight growing seasons heights of oaks in the treatment with woody competitors were only 30–39% that of oaks in the treatment without competing vegetation. In contrast, competition from herbaceous vegetation only restricted oak height development marginally. Interspecific competition not only restricted growth and survival but also shifted shoot architecture, resulting in a greater frequency of oaks with straight monopodial stems. Although competition from both herbaceous- and woody vegetation positively affected stem straightness, plots with woody vegetation had a greater proportion (0.42) of oaks with a single straight monopodial stem. Our results demonstrate that the facilitative competitive effects from herbaceous and woody vegetation could be used to control allocation patterns in young oaks, promoting development of tall straight monopodial stems. Considering the observed trade-off between high stem quality and survival, we recommend long-term assessment of this trade-off prior to application in practical forestry.

Uso y manejo de leña combustible en viviendas de seis localidades de Yucatán, México

Se analizó el patrón de preferencias en el uso de leña combustible en 1153 viviendas de seis localidades de Yucatán, mediante la aplicación de cuestionarios estructurados a informantes clave y muestreos en los sitios de extracción. Las localidades de estudio presentan heterogeneidad en la composición florística y distancia a la ciudad capital de estado, factores que modifican las preferencias y hábitos de consumo. El promedio de consumo en las localidades de estudio oscilo entre 1,26 y 2 ,89 kg/día/habitante, el promedio general de los sitios estudiados fue de 2,06 kg/día/habitante. La leña se extrae de la vegetación aledaña, la milpa y el solar. La colecta se hace a una distancia promedio de 3,8 km respecto a la vivienda. Los medios básicos para su transporte son el triciclo, la carga directa en la espalda del usuario y mediante uso de vehículo automotor. La leña se colecta fundamentalmente como material seco desprendido o seco en pie, debido a su menor peso, facilidad de acarreo y rápida ignición. Los usos fundamentales son la cocción de alimentos y calentamiento de agua de baño. 41 son las especies más usadas como combustible, pero las principales son: Acacia gaumeri, Havardia albicans, Lysiloma latisiliquum, Gymnopodium floribundum, Bursera simaruba, Caesalpinia gaumeri, Conocarpus erectus y Piscidia piscipula, debido a su mayor abundancia, fácil encendido, duración en el fuego y/o baja emisión de humo.

Light acclimation in submerged macrophytes: The roles of plant elongation, pigmentation and branch orientation differ among Chara species

Light acclimation plays a fundamental role for plant survival. Using an experimental setup where light could only penetrate from above, we studied light acclimation of Chara intermedia and C. contraria, i.e. submerged macroscopic algae which grow in an upright position. Both species produced taller plants at higher light intensities. These results are in contrast to earlier studies which found shorter plants at higher light intensities. This may be explained by light-induced inhibition of shoot-cell elongation. Since Chara shoot-cells point upward, the inhibition can only operate when light reaches plants laterally. We suggest that calcium-encrustation, periphyton-cover and dense neighboring vegetation may reduce lateral light such that plants exposed to such conditions will show increased elongation with increasing light intensity.In contrast to expectations, the uppermost Chara parts had higher chlorophyll a/carotenoid ratios, indicating less light protecting capacity, than the lower parts. This is explained by branches of the uppermost parts generally pointing upward such that they become less light exposed than branches of lower parts, which were less inclined. We found that the more nearly horizontal Chara branches had steeper slopes in their chlorophyll a/carotenoid ratio in relation to light intensity, indicating that the intensity of adjustments in pigmentation depends on branch orientation. C. intermedia adjusted orientation of growing branches to incident light, with branches pointing steeply upward at high light conditions, while C. contraria did not. The combination of branch-orientation and adaptations in pigmentation may give C. intermedia a competitive advantage over C. contraria in high light environments.

An invasive clonal plant benefits from clonal integration more than a co-occurring native plant in nutrient-patchy and competitive environments.

Many notorious invasive plants are clonal, however, little is known about the different roles of clonal integration effects between invasive and native plants. Here, we hypothesize that clonal integration affect growth, photosynthetic performance, biomass allocation and thus competitive ability of invasive and native clonal plants, and invasive clonal plants benefit from clonal integration more than co-occurring native plants in heterogeneous habitats. To test these hypotheses, two stoloniferous clonal plants, Alternanthera philoxeroides (invasive), Jussiaea repens (native) were studied in China. The apical parts of both species were grown either with or without neighboring vegetation and the basal parts without competitors were in nutrient- rich or -poor habitats, with stolon connections were either severed or kept intact. Competition significantly reduced growth and photosynthetic performance of the apical ramets in both species, but not the biomass of neighboring vegetation. Without competition, clonal integration greatly improved the growth and photosynthetic performance of both species, especially when the basal parts were in nutrient-rich habitats. When grown with neighboring vegetation, growth of J. repens and photosynthetic performance of both species were significantly enhanced by clonal integration with the basal parts in both nutrient-rich and -poor habitats, while growth and relative neighbor effect (RNE) of A. philoxeroides were greatly improved by clonal integration only when the basal parts were in nutrient-rich habitats. Moreover, clonal integration increased A. philoxeroides's biomass allocation to roots without competition, but decreased it with competition, especially when the basal ramets were in nutrient-rich sections. Effects of clonal integration on biomass allocation of J. repens was similar to that of A. philoxeroides but with less significance. These results supported our hypothesis that invasive clonal plants A. philoxeroides benefits from clonal integration more than co-occurring native J. repens, suggesting that the invasiveness of A. philoxeroides may be closely related to clonal integration in heterogeneous environments.