Native Dry Forest Research Articles

Monitoring native, non-native, and restored tropical dry forest with Landsat: A case study from the Hawaiian Islands

Tropical dry forests are highly threatened at a global scale. Long-term monitoring of remaining stands is needed to assess forest health, efficacy of management practices, and potential impacts of climate change. Using a multi-seasonal Landsat time series, we examined Normalized Difference Vegetation Index (NDVI) patterns in native dry forest, non-native vegetation types, and dry forest restoration sites from 1999 to 2022 in the Hawaiian Islands. We calculated trends in median NDVI and robust coefficient of variation of NDVI for dry and wet seasons, and used Breaks for Additive Seasonal and Trend analysis to detect trend departures. To assess the impact of regional drying trends, NDVI trends were compared to the seasonal long-term precipitation anomaly and cumulative precipitation anomaly. We found that native dry forest was less green than non-native forest, particularly during the dry season, and that median NDVI increased in both native and non-native dry forests over the study period despite negative precipitation anomaly trends. This result differs from coarser-scale studies in Hawaii, but is supported by trends in other dry forest regions. Greening was also observed in restoration study sites, especially larger sites where native species establishment and recruitment has been reported. Non-native grassland NDVI exhibited a strong positive link to precipitation anomalies, suggesting that drier climate scenarios may exacerbate the invasive grass-wildfire cycle that threatens native dry forest. These results demonstrate that Landsat time series may be used to detect seasonal variation in dry forest plots and to support restoration site monitoring in a highly fragmented ecosystem.

Ligustrum lucidum invasion alters the soil water dynamic in a seasonally multi-specific dry forest

Plant invasion is one of the major global environmental threats with the potential to alter the ecosystem stability and functioning. In water-limited ecosystems, the impacts of non-native invasive trees on the water balance are particularly relevant since they can compromise the use of water by native taxa of the ecosystem and water provision for humans. In this paper, we assessed the hydrological impacts of the Ligustrum lucidum (Chinese glossy privet) invasion on a mountain seasonally dry forest of the Chaco region (Central Argentina). More specifically, we determined volumetric soil water content, runoff, and actual evapotranspiration, and their relations to the size of rainfall events in native forest stands and its adjacent invaded stands. We combined three-years field measurements and remote sensing data. L. lucidum stands showed less water content through the soil profiles than the native forest (0–70 cm depth; 19.6 and 23.1 %, respectively), particularly during the dry conditions. The drier condition in the deeper soil layers compared to the upper ones in the invaded stands indicated less rainwater percolation throughout the soil profile over the year, independently of the magnitude of the rainfall events. Daily variation of deep-water content (60–70 cm depth), only observed in L. lucidum stands, showed nightly increase and day-time decrease in dry conditions. Runoff was similar and almost nil in both native and invaded forests, even after large rainfall events (>30 mm). L. lucidum stands showed ∼ 18% higher annual actual evapotranspiration rates than native stands. Based on our results, relatively higher water consumption for mono-specific L. lucidum stands in periods when photosynthetic activity of multi-specific native dry forest is still low may represent a competitive advantage in terms of plant invasion, and at the same time it generates negative impacts on water resources, reducing soil water content and limiting deep-water recharge in a water-limited ecosystem.

Native palms and trees mediate drought impacts on dry neotropical pastures

Abstract Dry forests are the most threatened biome across the global tropics. Despite their massive conversion into agricultural landscapes, local farmers often retain disperse trees and palms within grazing pastures. Understanding how on‐farm tree cover in the dry neotropics impacts the environmental and productive functions of pastures is key for biodiversity conservation and the development of climate‐resilient production systems. We studied tree composition of 23 dry cattle pastures in Yucatan, Mexico. We assessed the effects of palms, N2−fixing trees and non‐N2‐fixing trees on microsite environmental conditions, bare soil cover and the performance of grasses and woody plants in their understory during the dry and wet seasons of 2018 and 2019. We found that 45% of the total pool of tree species of the native dry forest is conserved in the pastures of Yucatan. Palms were the most abundant overstory functional group with a relative abundance of 45%, followed by N2‐fixing trees and non‐N2‐fixing trees with 33% and 22%. Palms and trees ameliorated the impact of seasonal drought on grasses but slowed down their recovery during the wet season. Palms had overall higher positive effects on grass greenness and height than N2‐fixing trees and non‐N2‐fixing trees and these effects were higher during the driest season. Palms decreased bare soil less than trees. Shrubs and tree seedlings tended to increase in the understory of all functional groups as the canopies of palms and trees became denser. Synthesis and applications. Climate warming and the alteration of precipitation regimes are expected to compromise pasture and cattle productivity worldwide. Our results show that fostering the maintenance of a diversity of native palms and trees has positive effects on the functioning of cattle pastures, especially during dry periods. A larger appreciation and understanding of the facilitative effects of remnant palms and trees on pastures during seasonal droughts may help developing more climate‐resilient livestock systems that maintain productivity during dry conditions while contributing also to tree biodiversity conservation.

Past and present effects of habitat amount and fragmentation per se on plant species richness, composition and traits in a deforestation hotspot

Worldwide, human activities are rapidly changing land cover and its spatial configuration. While it is widely acknowledged that habitat loss is a major cause of biodiversity loss, there is less agreement on how biodiversity responds to changes in habitat configuration. We assessed the effects of forest amount and forest fragmentation per se (the number of patches for a given forest amount, an aspect of configuration) on woody species richness, composition, and traits in the Dry Chaco forest, a global deforestation hotspot. We sampled woody plants in 24 forest sites varying in forest amount and fragmentation per se in the surrounding landscapes. Using Generalized Linear Modeling we tested whether a model with just forest amount was at least as able to predict species richness as a model with either patch size or isolation or the combination of both. We also tested whether forest amount and fragmentation per se influenced species richness, composition, and the density of four species traits. Finally, we compared these responses to forest amount and fragmentation per se measured in the past (2009) vs. in the present (2017) to look for time-lagged responses. We found that: 1) in support of the habitat amount hypothesis, species richness was more strongly related to forest amount than to the size and/or isolation of the forest patch containing the sample plot; 2) the positive effect of forest amount on species richness was more important than the effect of fragmentation per se (also positive); 3) fragmentation per se changed species composition such that plots in landscapes with more fragmented forest had species with smaller leaves and seeds, and higher wood density; and 4) species richness showed a time-lagged response to forest amount but not to forest fragmentation per se. Our results suggest that preservation of native Dry Chaco forest should be prioritized regardless of its fragmentation level, for conserving woody plant species diversity.

Land‐use change alters the stocks of carbon, nitrogen, and phosphorus in a Haplic Cambisol in the Brazilian semi‐arid region

AbstractLand‐use change (LUC) can impact soil quality. In semi‐arid areas of Brazil, impacts of LUC need to be understood for better soil management. This study evaluated the impact of LUC on soil organic carbon (SOC), nitrogen (N), and phosphorus (P) distributions through the soil profile and stocks of a Haplic‐Cambisol in the Brazilian Semi‐arid region. Three land‐use systems (LUS) were investigated: agricultural management (30 years), regeneration under controlled grazing (25 years) after 5 years arable management, and native dry forest. Soil contents of P, total C, total N, and N fractions were used to calculate stocks and their stoichiometric ratios for layers 0–5, 5–10, 10–20, and 20–40 cm. Data from these LUS were compared using Kruskal–Wallis non‐parametric tests. Changes to soil microbial biomass reflected the substantially reduced SOC concentration and stock in managed soils compared with that of the natural dry forest area. Total N stock was not affected by LUC, although increases in nitrate and ammonium offset a significantly reduced organic N fraction in the agricultural area. The largest P stock was found in agricultural land, followed by the grazed fallow regeneration site. LUC significantly influenced the stoichiometric ratio of C, N, and P, with the change from Caatinga to agriculture affecting the equilibrium between organic residues’ input and mineralization. LUC resulted in significant changes to C, N, and P stocks, which did not recover to the original values, even after 25 years of regeneration under controlled grazing.

Assessment of pollen and honey diet of Tetragonisca angustula fiebrigi Schwarz in the Chaco dry forest by using pollen analysis

Pollen and honey resources composing the diet of Tetragonisca angustula fiebrigi Schwarz were assessed using pollen analysis of wild colonies sampled in two kinds of native dry forests of the Chaco region. Different measurements: direct pollen count, relative volume, diversity and evenness indices, value of importance of species (SI), and index of relative importance (IRI) were compared. The IRI identified the most important pollen resources as Prosopis (IRI = 1619), Schinopsis type (IRI = 1578), Trithrinax schizophylla (IRI = 972) and Capparicordis/Sarcotoxicum (IRI = 587), and according to SI the honey resources were Schinopsis type (SI = 117.41), Maytenus type (SI = 101.89), Prosopis (SI = 86.47) and Ziziphus mistol (SI = 50.93). The absolute pollen analysis of honey revealed that all samples were rich in pollen grains. Floral resources were most homogeneously foraged during spring and summer when a high number of flowerings were available and the highest temperatures were recorded. These optimal conditions for bee foraging activity also allowed for the highest diversity indices in these seasons. However, heterogeneous foraging and low diversity were detected during winter and autumn. Most pollen and honey resources belonged to generalised small flowers of diverse plant lineages. The IRI was more comprehensive to identify the most important pollen resources than the commonly used direct pollen count, as it also includes relative volume and frequency of occurrence, and SI was the most thorough for studying the honey resources. This study provides helpful information for sustainable meliponiculture and forest conservation.

Changes in rainfall partitioning caused by the replacement of native dry forests of Lithraea molleoides by exotic plantations of Pinus elliottii in the dry Chaco mountain forests, central Argentina

The replacement of native dry forests by commercial (exotic) tree plantations could generate changes in rainfall partitioning, which further affects the water cycle. In this study, we determined (i) the rainfall partitioning into interception, throughfall and stemflow, (ii) the role of rainfall event size on rainfall partitioning, (iii) the pH of water channelized as throughfall and stemflow, and (iv) the runoff in Lithraea molleoides (a native species) and Pinus elliottii (an exotic species) stands in the dry Chaco mountain forests, central Argentina. On average, interception, throughfall and stemflow accounted for 19.3%, 79.5% and 1.2% of the gross rainfall in L. molleoides stand, and 32.6%, 66.7% and 0.7% of the gross rainfall in P. elliottii stand, respectively. Amounts of interception, throughfall and stemflow presented positive linear relationships with the increment of rainfall event size for both tree species (P<0.01 in all cases). Percentages of interception, throughfall and stemflow were all related to the increment of rainfall event size, showing different patterns. With increasing rainfall event size, interception exponentially decreased, throughfall asymptotically increased and stemflow linearly increased. Both P. elliottii and L. molleoides stands presented significant differences in the pH values of water channelized as throughfall (6.3 vs. 6.7, respectively; P<0.01) and stemflow (4.5 vs. 5.8, respectively; P<0.01). Runoff occupied only 0.3% of the gross rainfall in P. elliottii stand and was zero in L. molleoides stand. Our results showed that the native species L. molleoides presented 13.6% more water reaching the topsoil (i.e., net rainfall; net rainfall=gross rainfall—interception—runoff) than the exotic species P. elliottii. This study improves our understanding of the effects of native vegetation replacement on the local water balance in the dry forest ecosystems.

Changes in water fluxes partition related to the replacement of native dry forests by crops in the Dry Chaco

Land-use change has been the strongest driver of vegetation cover change in the world. In the South American Dry Chaco (~1 M km2; PPT/ET0 < 0.65), native dry forests are experiencing high deforestation rates that tend to continue in the coming years. Here, we used a hydrological model (Hydrus 1-D) to analyze changes in the water balance triggered by the replacement of dry forests by annual rainfed summer crops. We found that transpiration represented the main water vapour flux in both vegetation covers (59 and 48% of annual rainfall in dry forest and cropland, respectively), followed by evaporation (31 and 30%, respectively) and interception (11 and 9%, respectively). Runoff was five times higher in the cropland compared to the dry forest (10 vs. 2%; p < 0.01). Deep drainage was a negligible water flux in dry forests but it represented 4% of annual rainfall in croplands (p < 0.01), reaching values of zero and 130 mm year−1 for dry and wet years, respectively. Our results highlight the key role of vegetation cover controlling ecosystem water fluxes in the Dry Chaco. More generally, we suggest that the expansion of dryland cultivation can modify the regional water balance and threaten the primary production of ecosystems in the long run.

Records of seven species of native and exotic bark beetles new to Pu’u Wa’awa’a Dry Forest Unit, Hawai‘i Island (Coleoptera: Curculionidae, Scolytinae)

As part of ongoing surveys for native bark beetles (Coleoptera: Curculionidae: Scolytinae) across the Hawaiian Islands, we undertook targeted sampling at Pu’u Wa’awa’a Experimental Forest Unit, North Kona, on the northwestern part of Hawai‘i Island during February to April of 2018 and 2019. This is one of the few areas containing remaining native dry forest on the leeward, dry side of the island. Our sampling revealed the presence of seven species of bark beetles not previously recorded from Pu’u Wa’awa’a. These included two native and endemic Hawaiian species belonging to the genus Xyleborus Eichhoff (tribe Xyleborini). The other five species are the exotic Hypothenemus hampei (Ferrari, 1867), or the coffee berry borer, belonging to the tribe Cryphalini, which is a serious pest of coffee in the Hawaiian Islands, and four widespread adventive species belonging to the tribe Xyleborini, including Xyleborus ferrugineus (Fabricius, 1801), whose frass has been demonstrated to be able to contain a fungus that is a causative agent of the plant disease Rapid ʻŌhiʻa Death which currently poses a threat to native ʻōhiʻa lehua trees. These records are presented and discussed in detail, and the newly recorded species are illustrated in colour photographs.

A short review of leucaena as an invasive species in Hawaii

Keynote paper presented at the International Leucaena Conference, 1‒3 November 2018, Brisbane, Queensland, Australia.Leucaena leucocephala subsp. leucocephala was introduced to Hawaii after European settlement and spread widely for cattle fodder and fuelwood. As in many other tropical locations where it has been introduced, it has naturalized and spread in disturbed and drier habitats. While it is common in disturbed areas, it is much less common in intact native dry forests. It is resilient to wildfire and mammalian grazing, which conversely threaten the integrity of remnant native dryland forest. The successional trajectory of areas dominated by leucaena has not been well studied in Hawaii, but it is probable that other non-native rather than native species will replace it. As a result of its widespread distribution, especially on steep slopes, priority for its eradication or control is low. Current biocontrol options are limited in effectiveness. Control of leucaena can and should be given greater priority to protect native dryland forests and inhibit spread of seeds. Restoration of dryland habitats requires intensive, sustained efforts, usually involving volunteers. Combining cultural and/or use values in restoration projects holds promise for stimulating and sustaining community involvement.

Long-term decline of native tropical dry forest remnants in an invaded Hawaiian landscape

Tropical dry forests are among the most threatened vegetation types as a result of human activities, yet relatively few datasets exist that give insight into the long-term impacts of human activity in these diverse biomes, especially in insular systems. In this study we revisited remnant dry forest patches previously surveyed in 1950 and 1970 in the Mokulēʻia Forest Reserve on Oʻahu, Hawaiʻi to assess long-term native woody species’ persistence. Between June 2016 and May 2017 we resurveyed the seven original remnants and found that natives declined in basal area in every plot except one, and maintained basal area dominance over non-natives in only three of seven plots. There was a dramatic decline in the richness of native woody species in 2017 (10 species), when compared with observations in 1950 (27 species) and 1970 (32 species). Natives experienced substantial declines in densities, and the greatest reductions in basal area and species richness occurred in plots which previously had the highest native diversity. Only the most common native species were able to maintain their populations, and they are aging. At the same time, non-native woody species richness increased from 1950 (3 species) to 1970 (7 species) to 2017 (13 species). Non-native relative basal area also increased substantially from 1950 (9%) and 1970 (5%), to where it nearly equals native basal area currently (49%). These results indicate that despite there being no obvious change in disturbance levels since these areas were last surveyed, native Hawaiian dry forest remnants are being invaded by nearby non-natives, and will likely continue to decline if not supported by active management.

Avian community characteristics and demographics reveal how conservation value of regenerating tropical dry forest changes with forest age.

Expansion of secondary forests following the abandonment of agriculture may have important implications for bird conservation, but few studies have examined the dynamics of this process. We studied bird use of a chronosequence of differently-aged abandoned pastures regenerating to dry forest to better understand how the value of these habitats to birds changes over time. In a five year study on Hispaniola, we recorded 7,315 net captures of 60 species of landbirds in sites that began the study at two, five, 10, and 20 years post-abandonment, and in mature native dry forest. Twenty-five species made up 97% of all net captures. Highest capture rates were in the two youngest sites. These early-successional habitats had many over-wintering Neotropical migrants; among residents, granivores and frugivores predominated. In contrast, both the twenty-year-old and mature forest sites had few migrants, more resident insectivores and omnivorous species, and a greater proportion of endemics. Age and sex ratios, body condition and site persistence suggest early successional sites were sub-optimal for most over-wintering migrants, but habitat improved with age for three migratory species; results for permanent residents varied among species. Remnant trees and understory shrubs in the agroecological matrix likely contributed to avian diversity in regenerating dry forest sites, and proximity to mature forest also likely affected the diversity and abundance of birds in regenerating habitat. Our study shows that regenerating forests do not fully compensate for loss of mature dry forest habitat, even after 24 years of regeneration; natural restoration of complex microhabitats in dry forest sites converted to agriculture may take decades or longer. The highest value of regenerating forests may be as habitat for some over-wintering Neotropical migrants, and in creating a buffer zone that enhances biodiversity conservation by re-integrating these lands into the protected tracts of mature forest needed by the islands more unique and endemic bird species.

Patterns and controls of carbon dioxide and water vapor fluxes in a dry forest of central Argentina

Covering 16% of global land surface, dry forests play a key role in the global carbon budget. The Southern Hemisphere still preserves a high proportion of its native dry forest cover, but deforestation rates have increased dramatically in the last decades. In this paper, we quantified for the first time the magnitude and temporal variability of carbon dioxide and water vapor fluxes and their environmental controls based on eddy covariance measurements in a dry forest site of central Argentina. Continuous measurements of CO2 and water vapor exchanges spanning a 15-month period (Dec. 2009 – March 2011) showed that the studied dry forest was a net sink of carbon, with an overall integrated net ecosystem exchange (NEE) of −172gCm−2 (−132.8gCm−2 for year 2010). The cool dry season (May–Sept.) accounted for a quarter of the total annual NEE of year 2010 with low but steady CO2 uptake rates (1gCm−2d−1 on average) that were more strongly associated with temperature than with soil moisture. By contrast, in the warm wet season (Oct.–April), almost three times greater CO2 uptake rates (2.7gCm−2 d−1 on average) resulted from a highly pulsed behavior in which CO2 uptake showed sharp increases followed by rapid declines after rainfall events. Cumulative evapotranspiration (ET) during the whole study (595mm) accounted for most of the rainfall inputs (674mm), with daily water vapor fluxes during the wet season being four times greater compared to those observed during the dry season (1.7mmd−1 vs. 0.45mmd−1). Modeling of the partition of all evaporative water losses suggested that transpiration was the dominant vapor flux (67% of ET), followed by interception (20%) and soil evaporation (13%). The influence of air temperature on half-hourly CO2 fluxes was notably different for the dry and wet seasons. In the 11–34°C air temperature range, CO2 uptake rates were higher in the warm wet rather than the cool dry season, yet this difference narrowed with temperatures >26°C. The dry forest became a net CO2 source at 40°C. Our study provides new insights about the functioning of dry forests and the likely response of their CO2 and water vapor exchange with the atmosphere under future climate and land use/cover changes.

Land Use Effect on the CN Model Parameters in a Tropical Dry Environment

Dry tropical forests account for over 1,000,000 km2, and there is still lack of knowledge on their hydrologic processes. The curve number (CN) hydrologic model developed by the Natural Resources Conservation Service (NRCS) is widely applied for runoff determination in various parts of the world, but not so in tropical semiarid regions. This study analyzes the impact of land use changes on the CN model in a tropical semiarid environment, in two catchments of native dry tropical forest and thinned dry tropical forest land use from 2009 to 2012. The CN model was calibrated and validated for the NRCS recommended initial abstraction ratio λ = 0.2, and for λ evaluated from rainfall and runoff data. A reliability analysis was performed using Monte Carlo simulation. Model goodness-of-fit was assessed with statistical criteria. A total of 42 and 40 rainfall-runoff events were analyzed for the native and thinned dry tropical forest, respectively. Characteristic λ values of 0.15 and 0.11 were determined for the two respective catchments. Although CN values were similar for both land uses, CNλ=0.20 = 80 and CNmedian λ = 77, the thinned catchment showed a higher CN model parameters variability. The CN model was more sensitive to variations of CN values than to those of λ. This study showed that no matter the vegetation management in a dry tropical forest environment, modeled runoff is not affected by λ, but rather affected by CN, which represents soil, landuse and management.

Novelty and Its Ecological Implications to Dry Forest Functioning and Conservation

Tropical and subtropical dry forest life zones support forests with lower stature and species richness than do tropical and subtropical life zones with greater water availability. The number of naturalized species that can thrive and mix with native species to form novel forests in dry forest conditions in Puerto Rico and the US Virgin Islands is lower than in other insular life zones. These novel dry forests are young (&lt;60 years) with low structural development, high species dominance, and variable species density. Species density is low during initial establishment and increases with age. At the 1-ha scale, novel forests can have greater species density than mature native forests. Species groups, such as nitrogen-fixing species, and other naturalized species that dominate novel dry forests, have a disproportional influence on forest element stoichiometry. Novel dry forests, compared to the mean of all forest species assemblages island-wide, tend to have fallen leaf litter with lower than average manganese and sodium concentrations and lower than average C/N and C/P ratios. After accounting for significant differences in stand age, geology, and or precipitation, novel dry forests compared to native dry forests have higher C anomalies, lower Ca and Na anomalies, and lower C/N ratio anomalies. Taken together, these characteristics may influence litter decomposition rates and the species composition, diversity, and food web dynamics in litter and soil. Novel dry forests also contribute to the conservation of native plant species on highly degraded lands.

Shifts in an invasive rodent community favoring Black rats (Rattus rattus) following restoration of native forest

AbstractOne potential, unintended ecological consequence accompanying forest restoration is a shift in invasive animal populations, potentially impacting conservation targets. Eighteen years after initial restoration (ungulate exclusion, invasive plant control, and out planting native species) at a 4 ha site on Maui, Hawai'i, we compared invasive rodent communities in a restored native dry forest and adjacent non‐native grassland. Quarterly for 1 year, we trapped rodents on three replicate transects (107 rodent traps) in each habitat type for three consecutive nights. While repeated trapping may have reduced the rat (Black rat, Rattus rattus) population in the forest, it did not appear to reduce the mouse (House mouse, Mus musculus) population in the grassland. In unrestored grassland, mouse captures outnumbered rat captures 220:1, with mice averaging 54.9 indiv./night versus rats averaging 0.25 indiv./night. In contrast, in restored native forest, rat captures outnumbered mouse captures by nearly 5:1, averaging 9.0 indiv./night versus 1.9 indiv./night for mice. Therefore, relatively recent native forest restoration increased Black rat abundance and also increased their total biomass in the restored ecosystem 36‐fold while reducing House mouse biomass 35‐fold. Such a community shift is worrisome because Black rats pose a much greater threat than do mice to native birds and plants, perhaps especially to large‐seeded tree species. Land managers should be aware that forest restoration (i.e. converting grassland to native forest) can invoke shifts in invasive rodent populations, potentially favoring Black rats. Without intervention, this shift may pose risks for intended conservation targets and modify future forest restoration trajectories.

Ecohydrological transformation in the Dry Chaco and the risk of dryland salinity: Following Australia's footsteps?

AbstractDuring the last century, the massive conversion of Australian dry forests to crops and pastures triggered the massive soil and groundwater degradation process known as dryland salinity. Currently, South American Chaco's dry forests are undergoing a similar transformation, leading global deforestation rates. The goal of this study was to review existing ecohydrological information about natural and cultivated systems in the Chaco to assess the dryland salinity risks. We review deep soil water, salt stocks, and groundwater recharge from agriculture or native dry forests stands located in a precipitation range of 450–1100 mm. We complement this with water table level records and geoelectric profiles together with personal observations. We use data from 15 Australian studies for comparison. Strong salt leaching, especially after 20 years of forest clearance, indicates the onset of deep drainage following forest conversion to agriculture in the Dry Chaco. Water stocks were more than double in the cleared stands compared to their dry forest pairs, and recharge rates were up to two order magnitude higher in agricultural areas. Although lower atmospheric salt deposition, younger sediments, and relatively high water‐consuming agricultural systems in the Dry Chaco attenuate salinization risks compared to Australia, the very flat topography and related shallow water table levels of the South American region could make groundwater recharge and salt mobilization processes more widespread and difficult to manage. The lack of awareness among the general public, farmers, and decision makers about this issue amplifies the problem, making land management plans for the Argentine dry forest territories essential.

Effect of Rainfall Characteristics on Runoff and Water Erosion for Different Land Uses in a Tropical Semiarid Region

Rainfall intensity, duration, frequency and magnitude influence both runoff generation and sediment yield. In this study, 176 rainfall events over a five-year period were classified into four regimes based on rainfall depth, duration and 30-minute maximum intensity, using hierarchical cluster analysis in the semiarid region of Brazil. Rainfall Regimes were grouped from higher to lower rainfall depth, longer to shorter duration, and higher to lower I30. Rainfall regime impact on surface runoff and sediment yield was studied in three watersheds under different land use - native tropical dry forest, thinned tropical dry forest, and slash and burn followed by grass cultivation. Thinning of native dry tropical forest reduced surface runoff and sediment yield due to the protective effect of the well-developed herbaceous layer. Runoff generation in the three watersheds showed strong dependence on antecedent soil moisture and the type of rain. Rainfall depth was the major factor for highest sediment yields.

Is crop yield related to weed species diversity and biomass in coconut and banana fields of northeastern Brazil?

The ability to accommodate crop production for an ever-growing human population and achieve conservation of rapidly declining biodiversity remains a challenging task worldwide. In agroecosystems, weed diversity and biomass are frequently assumed to be negatively related to crop yield and biomass. However, positive effects of weed species (pollinator and parasitoid attraction) and different resource acquisition strategies may reduce the competitive character of weeds—a potential that can be exploited within land-sharing approaches (i.e., biodiversity conservation and agriculture on the same site). This study aimed at analyzing the relationships of weed diversity and biomass to crop yield and biomass in coconut and banana fields within an irrigation farming scheme established in former Caatinga seasonal dry forest ecosystems around the Itaparica Reservoir, Pernambuco, Brazil. Within each of 21 selected crop fields, we collected weed diversity and biomass data in the fields’ center and edge along with general information on crop yield and the use of fertilizers and other agrochemical inputs. We found no evidence for a negative relationship of crop yield or biomass and weed diversity. On the contrary, crop yield and weed alpha diversity were significantly positively correlated (Shannon and Simpson indices, evenness). In contrast, weed biomass showed a significant negative correlation to crop yield. The use of organic fertilizer had a significant positive effect on crop yield, whereas no impact of herbicides or insecticides was detected. In addition, the field edge provided habitat for more weed species than the field center. Overall, our data show that in perennial tropical crop fields high yield is not opposed to high weed diversity. Moreover, the data suggest that organic farming in the area will likely not lead to yield losses. Nevertheless, the related weed assemblages inhabited only a few typical species of the native dry forest vegetation which makes their contribution to biodiversity conservation at the landscape scale debatable.

Variabilidade espacial de propriedades hidrodinâmicas de um Neossolo Regolítico sob pastagem e caatinga

As propriedades hidrodinâmicas dos solos de pastagem e de caatinga, são afetadas por diversos fatores, sobretudo associados a aspectos espaciais e temporais relacionados às diferentes características dos sistemas radiculares e das taxas de pisoteio do gado, mas poucos resultados que avaliem o efeito da magnitude dessas fontes de variabilidade sobre as propriedades hidrodinâmicas dos solos têm sido relatados na literatura. Objetivou-se analisar a variabilidade espacial dos parâmetros que descrevem as curvas de retenção (van Genuchten) e da condutividade hidráulica (Brooks &amp; Corey) da água do solo, obtidos com a metodologia denominada "Beerkan", que se baseia em ensaios de infiltração simplificados e nas informações texturais do solo. Para isto foram realizadas medidas de infiltração e coletadas amostras de solo em duas áreas: uma área de pastagem (Brachiaria decumbens) e outra de caatinga. Os resultados mostraram que o uso do solo com pastagem alterou significativamente as propriedades analisadas quando comparadas com as do solo com caatinga, com alterações mais expressivas na densidade do solo e na condutividade hidráulica. A análise geoestatística identificou a existência de dependência espacial de alguns atributos estudados, permitindo o mapeamento das áreas experimentais.