Mesic Vegetation Research Articles

An Interseasonal Comparison of Soil Respiration in Xeric and Mesic Pine Forest Ecosystems in Central Siberia

An understanding of how boreal forest composition responds to global environmental changes is an important challenge to predicting the future global carbon balance. Boreal forests are the most significant sink for atmospheric carbon dioxide; however, their sequestration capacity is highly sensitive to ongoing climate changes. The combination of the hydrothermal conditions of a territory strongly regulates its biogeochemical processes. The carbon fluxes in boreal forests are strongly mediated by the ground vegetation cover, composed of mosses (mesic) and lichens (xeric). Despite the concurrence of xeric and mesic vegetation types, their responses to climate variations varies significantly. Soil emission is an informative indicator of ecosystem functioning. In this study, we focused on the soil CO2 dynamics during frost-free seasons with different precipitation regimes in the xeric and mesic boreal ecosystems of Central Siberia. Seasonal measurements of soil CO2 emissions were conducted during frost-free seasons using the dynamic chamber method. Our findings reveal that the precipitation regimes of each year may control the seasonal soil emission dynamics. The soil moisture is the most important driver of emissions growth in the water-limited lichen pine forest (R2adj. = 18%). The soil temperature plays the largest role in the feather moss pine forest during the dry (R2adj. = 31%) seasons, and in the lichen pine forest during the wet (R2adj. = 41%) seasons. The cumulative efflux for the xeric and mesic sites is mostly related to the hydrothermal conditions, and not to the differences in ground vegetation cover. During the dry seasons, on average, the soil CO2 emissions are 45% lower than during the wet seasons for both sites. These findings emphasize the need for estimating and including the hydrothermal characteristics of the growing season for detailed emission assessments.

Plant species richness, not hygrothermal stress, is the main predictor of gall‐inducing insect richness in Peruvian Amazon forests

AbstractPatterns of gall‐inducing insect diversity tend to be influenced by both habitat‐related and plant‐related characteristics. We investigated the distribution patterns of galling insects in four vegetation types (terra firme forest, white‐sand dry forest, white‐sand wet forest and palm swamp forest) of the Peruvian Amazon to test if the insect gall diversity (1) differs among different types of vegetation and (2) depends on host plant richness. In total, we found 11,579 galls belonging to 249 insect gall morphotypes, distributed across 30 botanical families and 75 plant species. Among host plant families, Fabaceae showed the greatest richness of insect gall morphotypes. We found that galling species richness was lower in palm swamp forest than in white‐sand forests, which can be explained by the lower richness of plants in this type of vegetation. However, we found no evidence of greater richness in xeric habitats (e.g., white‐sand dry forest) than in more mesic vegetation (terra firme forest), contradicting the hypothesis of hygrothermal stress. We also found that plant species richness was positively influenced with the richness and abundance of galling species, regardless of vegetation type. Galling insect species composition differed significantly between vegetation types, similarly to the floristic composition. Our findings show that the diversity of galling insects in the tropical rainforests of Peruvian Amazon are mainly influenced by host plant composition and host plant richness.Abstract in Spanish is available with online material.

Leveraging high resolution classifications and random forests for hindcasting decades of mesic ecosystem dynamics in the Landsat time series

Mesic ecosystems are fundamental to conservation efforts in semi-arid systems, but are threatened by climate change and development. Newer earth observation datasets, including Sentinel-1 and −2, provide opportunities to monitor mesic ecosystems at meaningful spatial scales, but are insufficient for measuring decadal-scale changes. Conversely, the Landsat time series has decades of data, but images are spatially coarse relative to many of the mesic ecosystem areas that sustain dryland systems, resulting in classifications with mixed pixels inadequate for effective monitoring. We developed a workflow that uses 10-m classifications produced from fusion of the Sentinel-1 and −2 time series (2017–2020) to estimate sub-pixel proportions of Landsat time series observations (2004–2020). Using random forest regression models, we quantified water resource proportions (WRP) of surface water, mesic vegetation, and upland land covers within each 30-m Landsat pixel. We incorporated ancillary covariates to account for varying topographic conditions, land cover, and climate. Results indicate that our approach consistently estimates sub-pixel proportions of Landsat pixels more accurately compared to spectral mixture analysis (SMA). The WRP product for surface water had up to 8% less error than SMA as measured by Mean Absolute Error (MAE) and up to 17% less error as measured by Root Mean Squared Error (RMSE). For mesic vegetation, the WRP product outperformed SMA by up to 4% (MAE) and 7% (RMSE). Finally, we demonstrated the ability of our time series to characterize historical water resource availability at a case study site with a well documented restoration history by qualitatively examining the mesic vegetation dynamics time series to identify system responses to restoration efforts. Our approach allows us to hindcast observations of Sentinel products and measure water resource dynamics with greater precision over larger temporal scales. We envision these WRP data to be useful for measuring the impacts of conservation interventions, disturbance recovery, or land use changes that pre-date the Sentinel time series.

A satellite-based monitoring system for quantifying surface water and mesic vegetation dynamics in a semi-arid region

Semi-arid and arid systems cover one third of the earth’s land surface, and are becoming increasingly drier, but existing datasets do not capture all of the types of water resources that sustain these systems. In semi-arid environments, small surface water bodies and areas of mesic vegetation (wetlands, wet meadows, riparian zones) function as critical water resources. However, the most commonly-used maps of water resources are derived from the Landsat time series or single date aerial photographs, and are too coarse either spatially or temporally to effectively monitor water resource dynamics. In this study, we produced a Sentinel Fusion (SF) water resources product for a semi-arid mountainous region of the western United States, which includes monthly maps of both a) surface water and b) mesic vegetation at 10 m spatial resolution using freely available Earth observation data on an open access platform. We applied random forest classifiers to optical data from the Sentinel-2 time series, synthetic aperture radar (SAR) data from the Sentinel-1 time series, and topographic variables. We compared our SF product with three commonly used and publicly available datasets in the western U.S. We found that our surface water class contained fewer omission errors than a leading global surface water product (94 % producer’s accuracy (PA) vs 84 %) and comparable user’s accuracy (UA) (91 % vs 97 %) with commission errors occurring largely in mixed water pixels. Our mesic vegetation class had up to 43 % higher PAs compared to the National Wetlands Inventory (NWI) estimates and up to 78 % higher UAs over the Sage Grouse Initiative mesic resources maps during the most critical part of the water year. We found that while inclusion of SAR data from the C-band Sentinel-1 sensor consistently improved estimates of water resources in each of the last four months of the 2021 water year when compared to optical-only + topographic variables, only in September did those improvements lie outside of the 95 % confidence interval. With nine times finer spatial resolution and more frequent image collection, our SF maps characterize intra-annual dynamics of smaller water bodies (<30 m wide) and mesic vegetation integral to ecosystem functioning in semi-arid systems compared to leading Landsat-derived products. Further, our workflow is easily reproducible using freely available data on an open access platform, and can be adopted to help guide land use decisions related to water resources by farmers, ranchers, and conservationists in semi-arid environments.

Observed water and light limitation across global ecosystems

Abstract. With a changing climate, it is becoming increasingly critical to understand vegetation responses to limiting environmental factors. Here, we investigate the spatial and temporal patterns of light and water limitation on photosynthesis using an observational framework. Our study is unique in characterizing the nonlinear relationships between photosynthesis and water and light, acknowledging approximately two regime behaviours (no limitation and varying degrees of limitation). It is also unique in using an observational framework instead of using model-derived photosynthesis properties. We combine data from three different satellite sensors, i.e., sun-induced chlorophyll fluorescence (SIF) from the TROPOspheric Monitoring Instrument (TROPOMI), surface soil moisture from the Soil Moisture Active Passive (SMAP) microwave radiometer, and vegetation greenness from the Moderate Resolution Imaging Spectroradiometer (MODIS). We find both single-regime and two-regime models describe SIF sensitivity to soil moisture and photosynthetically active radiation (PAR) across the globe. The distribution and strength of soil moisture limitation on SIF are mapped in the water-limited environments, while the distribution and strength of PAR limitations are mapped in the energy-limited environments. A two-regime behaviour is detected in 73 % of the cases for water limitation on photosynthesis, while two-regime detection is much lower at 41 % for light limitation on photosynthesis. SIF sensitivity to PAR strongly increases along moisture gradients, reflecting mesic vegetation's adaptation to making rapid usage of incoming light availability on the weekly timescales. The transition point detected between the two regimes is connected to soil type and mean annual precipitation for the SIF–soil moisture relationship and for the SIF–PAR relationship. These thresholds therefore have an explicit relation to properties of the landscape, although they may also be related to finer details of the vegetation and soil interactions not resolved by the spatial scales here. The simple functions and thresholds are emergent behaviours capturing the interaction of many processes. The observational thresholds and strength of coupling can be used as benchmark information for Earth system models, especially those that characterize gross primary production mechanisms and vegetation dynamics.

FISH HABITAT USE AND FOOD WEB STRUCTURE FOLLOWING POND-AND-PLUG RESTORATION OF A MONTANE MEADOW IN THE SIERRA NEVADA, CALIFORNIA

Montane meadows are areas of high biodiversity and provide many important ecosystem services; however, degradation of 40–60% of these habitats in the Sierra Nevada region of California has left many of these areas impaired. The “pond-and-plug” meadow-restoration technique is 1 type of treatment implemented to restore montane meadows. The objectives of this technique are to re-water the meadow and promote downstream flow by increasing the water-table elevation and providing additional water storage that will promote the growth of mesic and hydric vegetation that maintains and stabilizes stream channels. However, aquatic habitat and the composition and functioning of aquatic communities in these systems post-treatment are poorly documented or understood. We evaluated: (1) fish habitat, community composition, and relative abundance among recently created ponds spanning the range of pond habitats; (2) seasonal movement and survival of fish within and among ponds; and (3) food web structure in ponds. We documented over-summer and winter survival in the fish community and short-distance movement by 1 species occupying the ponds. Mark-recapture data suggest that all fish species present are capable of surviving both summer and winter conditions when pond conditions could be most limiting. Food web structure among intensively sampled ponds was similar, with overlapping isotopic niche width for dominant taxa. However, basal resource diversity (BRD) varied among ponds, with those having higher macrophyte cover also showing greater BRD. Our findings suggest that pond-and-plug techniques can provide habitat for native fishes that are able to tolerate departures from the species thermal and dissolved oxygen optima. Future meadow treatments could benefit from short-term restoration techniques such as pond-and-plug to allow for longer-term processes to influence meadow condition over time.

Islands in the desert: environmental distribution modelling of endemic flora reveals the extent of Pleistocene tropical relict vegetation in southern Arabia.

Southern Arabia is a global biodiversity hotspot with a high proportion of endemic desert-adapted plants. Here we examine evidence for a Pleistocene climate refugium in the southern Central Desert of Oman, and its role in driving biogeographical patterns of endemism. Distribution data for seven narrow-range endemic plants were collected systematically across 195 quadrats, together with incidental and historic records. Important environmental variables relevant to arid coastal areas, including night-time fog and cloud cover, were developed for the study area. Environmental niche models using presence/absence data were built and tuned for each species, and spatial overlap was examined. A region of the Jiddat Al Arkad reported independent high model suitability for all species. Examination of environmental data across southern Oman indicates that the Jiddat Al Arkad displays a regionally unique climate with higher intra-annual stability, due in part to the influence of the southern monsoon. Despite this, the relative importance of environmental variables was highly differentiated among species, suggesting that characteristic variables such as coastal fog are not major cross-species predictors at this scale. The co-occurrence of a high number of endemic study species within a narrow monsoon-influenced region is indicative of a refugium with low climate change velocity. Combined with climate analysis, our findings provide strong evidence for a southern Arabian Pleistocene refugium in Oman's Central Desert. We suggest that this refugium has acted as an isolated temperate and mesic island in the desert, resulting in the evolution of these narrow-range endemic flora. Based on the composition of species, this system may represent the northernmost remnant of a continuous belt of mesic vegetation formerly ranging from Africa to Asia, with close links to the flora of East Africa. This has significant implications for future conservation of endemic plants in an arid biodiversity hotspot.

Structural Control of Mesic Vegetation Communities within the Owl and Bear Creek Watersheds, Fort Hood Military Installation, Texas

Structural Control of Mesic Vegetation Communities within the Owl and Bear Creek Watersheds, Fort Hood Military Installation, Texas

Remote sensing of Arctic percent vegetation cover and fAPAR on Baffin Island, Nunavut, Canada

Percent vegetation cover (PVC) and the fraction of absorbed photosynthetically active radiation (fAPAR) are important functional variables for assessing Arctic vegetation density and vigor. In this study, field measures of PVC, fAPAR and normalized difference vegetation index (NDVI) were collected from July 5 to August 8, 2015 (i.e., summer season) along a moisture gradient in the Apex River Watershed (ARW) (63°45′N, 68°30′W), Baffin Island, Nunavut, Canada. Two field methods for estimating PVC (i.e., the point-frame and image classification methods) were examined and it was determined that the image classification approach provided a suitable alternative to the point-frame method, especially for detecting changes in Arctic PVC. Meanwhile, fAPAR was measured based on the method presented by Tagesson et al. (2012): fAPAR=(1−PARReflectedPARIncoming)×PVC. The spatial and temporal patterns of PVC and fAPAR in the context of NDVI derived from remote sensing data were examined. For this site, vegetation types exhibited contrasting patterns of PVC as a result of differing moisture regimes: (1) vegetation types with saturated soils (e.g., sedge dominated) exhibited a continuous increase in PVC throughout the growing season; (2) mesic vegetation types with moderate soil moisture (e.g., mosses dominated with a mixture of sedges and shrubs) exhibited an increase in PVC from July to early August followed by a decline in mid-August; and (3) semi-desert vegetation types that tended to dry early in the growing season (e.g., dominated by prostrate dwarf shrubs, herb tundra and large areas of bare soil and rock) exhibited little variation in PVC. Field measures of PVC and fAPAR demonstrated strong relationships to field NDVI data and the vegetation indices (VIs) derived from 2 m-resolution WorldView-2 data, thereby providing further evidence that VIs are well-suited for modelling PVC and fAPAR of Arctic vegetation.

The onset of islandscapes in the Balearic Islands: A study-case of Addaia (northern Minorca, Spain)

Paleoenvironmental and archaeological data show that Mediterranean landscapes result from long-term socio-environmental interactions. Mediterranean islands constitute a place of passage where the creation of cultural landscapes can be traced through colonization and anthropization histories. Palynological studies carried out in the Balearic Islands highlight a deep vegetation change from the mid- to late-Holocene, but the climate-environmental-human interactions are not fully understood yet. In this study, we aim to disentangle the causalities of landscape changes during the last six millennia using a multi-proxy approach on an off-site core for the first time in Minorca island. We find that, during the mid-Holocene, the climate was wetter than today with less rainfall seasonality than in the current Mediterranean. This climate, favoured the expansion of box formations and the predominance of forested formations with minimal anthropized conditions. First agropastoral activities appeared in the sequence between ca. 3500–2650 cal BCE in north-eastern Minorca, coinciding with other sporadic archaeological evidence (Cova dels Morts rock-shelter) which support the possibility of a pre-Chalcolithic discovery and frequentation of the island. We record deep environmental change during the third millennium cal BCE, reflected in the substitution of the former mesophytic vegetation by Mediterranean maquis formations dominated by wild olive trees, heathers, mastic and Cistaceae. We propose that maquis, garrigues and open-land vegetation were favoured by human action in a context of increasing climatic dryness and seasonality, promoting vegetation flammability and substitution of former mesic communities to more adapted termophilous vegetation. The comparison of our new record from Addaia with other pollen studies from the Balearic Islands highlights the resilience of mesic vegetation to climate change. This is shown by the survival of box formations to the increased aridification initiated at ca. sixth–fifth millennium cal BCE (ca. 7–6 cal kyr BP) in the Western Mediterranean which culminated at ca. fourth–third millennium cal BCE (ca. 5–4 cal kyr BP). Additionally, whilst sporadic human presence versus stable occupation are difficult to detect in archaeological records, the coupling with paleoenvironmental studies may offer new scenarios and information for human arrival in the Balearic Islands.

Нитрофитные травяные сообщества класса Epilobietea angustifolii Tx. et Preising ex von Rochow 1951 в Сожско-Деснинском междуречье

Нитрофитные травяные сообщества класса Epilobietea angustifolii Tx. et Preising ex von Rochow 1951 в Сожско-Деснинском междуречье

Distribution of insect galls in xeric and mesic habitats of Floresta Nacional de Silvânia, Brazil

ABSTRACT We investigated the insect gall distribution along savanna (xeric) and forest (mesic) vegetation in the Floresta Nacional de Silvânia, Goiás, Brazil. We tested if the insect gall diversity is higher in the xeric vegetation than in the mesic vegetation, as predicted by the hygrothermal stress hypothesis. The insect gall fauna was surveyed between December 2009 and June 2010 in two transects established each vegetation type. In total we found 186 insect gall morphotypes, distributed on 35 botanical families and 61 plant species. Cecidomyiidae (Diptera) induced the most insect galls (34.1%), and the plant family Fabaceae had the greatest richness of insect gall morphotypes (18). We recorded 99 insect gall morphotypes in the forest and 87 morphotypes in the savanna vegetation, being that none insect gall morphotype occurred in both habitats. We found that the insect gall richness and abundance did not differ between forest and savanna transects. On the other hand, the estimated insect gall richness was higher in the forest than in the savanna. Our findings contrary the hygrothermal stress hypothesis possibly because forest habitats have higher plant architecture complexity and occurrence of super-host taxa than the savanna habitats.

Vegetation Greening Trends at Two Sites in the Canadian Arctic: 1984–2015

ABSTRACTThis study examined vegetation greening at two arctic sites: the Apex River Watershed (ARW), Baffin Island, Nunavut (a Low Arctic site) and the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut (a High Arctic site). The vegetation at both study sites was characterized using a supervised land-cover classification approach using high spatial resolution satellite remote sensing data (i.e., IKONOS [4 m] and WorldView-2 [2 m]). Meanwhile, Normalized Difference Vegetation Index (NDVI) data spanning the past 30 years were derived from intermediate spatial resolution data (i.e., Landsat TM/ETM/OLI [30 m]). The land-cover classifications were used to partition the Landsat NDVI time series by vegetation type. Climate variables (i.e., temperature, precipitation, and growing season length [GSL]) were examined to explore potential relationships of NDVI to climate warming trends. The results of the land-cover classifications demonstrated inherent trends of vegetation types along elevation and moisture gradients. The NDVI time series for the CBAWO (1985–2015) demonstrated an overall significant increase in greening, specifically in the dry and mesic vegetation types. Conversely, similar greening (overall or by vegetation type) was not observed for the ARW (1984–2015). Based on climate data from the nearest permanent weather station (Mould Bay, Nunavut), the overall increase in NDVI at the CBAWO was largely attributed to a significant increase in July temperatures and GSL.

Effect of Fire on Ant Assemblages in Brazilian Cerrado in Areas containing Vereda Wetlands

Cerrado is a biome whose evolution is intimately influenced by constant fire events. Although many species are capable of dealing with this predictable impact, many others may be negatively affected, resulting in community changes after fire. Using ants as bioindicators of changes in biodiversity and environmental conditions, this study evaluated the effects of fire in two Cerrado vegetation types: “cerrado” sensu stricto , a xeric savanna, and wetland “veredas”, a mesic vegetation on floodable soils, where water concentrates and ultimately flows towards rivers. We examined the effects of fire on both habitats in two independent sites, but with special consideration to the wetlands, which are not fully adapted to fire. Ant sampling was conducted twice before and twice after a fire event, using 288 baits and 416 pitfall traps (soil and arboreal), and 16 hand collections along three random replicate transects per area. Ant species richness and abundance were resilient to fire, and exhibited a remarkably consistent seasonal variation at unburned and burned sites. On the other hand, the fire markedly changed the ant species composition. In the wetlands, the fire spread underground due to the high concentration of peat. The impact on ant assemblages was substantial and visually perceptible for some species like Camponotus rufipes , which suffered a considerable reduction in the number of individuals after fire in this habitat. In the cerrado, a similar result was observed for Crematogaster nr. obscurata , which disappeared after fire. The wetland vegetation having little adaptation to fire, plus low resilience in the ant community resulted in a severely changed fauna, both in guild predominance and species composition, and return to an original state is uncertain.

Impacts of mesic and xeric urban vegetation on outdoor thermal comfort and microclimate in Phoenix, AZ

Urban vegetation is an effective way in mitigating excessive heat and improving the outdoor thermal environment for residents in cities via evaporative cooling. Different urban vegetation forms (mesic or xeric) alter surface energy and water budgets in different ways, which is further complicated by interactions with buildings and anthropogenic controls. Mesic vegetation such as lawns reduces urban temperatures by evaporative cooling but requires large amounts of water for continuous irrigation. On the other hand, xeric vegetation such as shade trees reduces urban temperatures mainly through shading and has low water demand. The objective of this study is to investigate the impacts of different vegetation forms on microclimate in a hot desert city – Phoenix, AZ. We applied an advanced urban canopy model coupled with a single-column atmospheric model to simulate urban boundary layer dynamics over different landscaping scenarios with different combinations of mesic and xeric vegetation forms. We subsequently compared the urban land surface temperatures, near-surface air temperatures, outdoor thermal comfort in the urban canopy layer, as well as atmospheric dynamics (temperature, humidity) in the overlying boundary layer for a set of different scenarios.

Post-fire ponderosa pine regeneration with and without planting in Arizona and New Mexico

Forest fires are increasing in size and severity globally, yet the roles of natural and artificial regeneration in promoting forest recovery are poorly understood. Post-fire regeneration of ponderosa pine (Pinus ponderosa, Lawson and C. Lawson) in the southwestern U.S. is slow, episodic, and difficult to predict. Planting of ponderosa pine after wildfire may accelerate reforestation, but little is known about survival of plantings and the amount of post-fire natural regeneration. We compared ponderosa pine regeneration between paired planted and unplanted plots at eight sites in Arizona and New Mexico that recently (2002–2005) burned severely. Two sites had no natural regeneration and no survival of planted seedlings. Seedling presence increased with number of years since burning across all plots, was positively associated with forb and litter cover on planted plots, and was positively associated with litter cover on unplanted plots. Survival of planted seedlings, measured five to eight years after planting, averaged 25% (SE=8) and varied from 0% to 70% across sites resulting in seedling densities of 0–521 trees ha−1. Based on a projected 44% survival of seedlings to mature trees and target density of mature trees determined by historical range of variability and ecological restoration principles, four of eight sites have a seedling density in planted plots (125–240ha−1) that will produce a density of mature trees (55–106ha−1) close to desired levels, whereas seedlings are currently deficient at three planted sites, and in surplus at one site, which had abundant natural regeneration. Natural regeneration in unplanted plots during the first decade after burning produced seedling densities inconsistent with desired numbers of mature trees. Natural regeneration in unplanted plots produced less than 33 seedlings ha−1 at seven of eight sites, but produced 1433 seedlings ha−1 at one high-elevation site that supported a more mesic vegetation community before burning than the other sites. Our results show that current practices for planting ponderosa pine after severe fires in Arizona and New Mexico produce desired numbers of seedlings in approximately half of all projects, whereas natural regeneration rarely does within the first decade after burning.

Las arañas de los oasis de la región meridional de la península de Baja California, México

A spider inventory from 4 oases at the xeric and mesic environments was undertaken. Ground and vegetation spiders were captured with pit fall traps and collected by sweeping and beating. Thirty four families, 130 genera and 243 species were captured which represent 63.2% of the species recorded for the Baja California Peninsula. One genus and 11 species are cited for the first time for Mexico, 13 genera and 18 species are new records for Baja California Sur. Salticidae (36), Araneidae (29), Theridiidae (27), and Gnaphosidae (24) families had the highest specific richness. Thirty two families, 125 genera, and 215 species are reported for the xeric environment and 26 families, 96 genera, and 157 species for the mesic environment. Both environments shared 128 species; 87 and 29 species were exclusive to xeric shrub and mesic vegetation, respectively. Complementarity between xeric and mesic environment was 47.5%. Twenty eight families, 89 genera, and 144 species, and 16 families, 45 genera and 119 species were captured in soil and vegetation strata, respectively with a complementarity of 92.2%.

Xeromesic and mesic meadow vegetation in southern boreal zone of Karelia. ecological and topological approach

A new typology of mesic and xeromesic meadow vegetation in the Southern Boreal zone of Karelia is introduced based on the contemporary meadow vegetation conditions and modern multivariate methodological approaches. The main differentiating environmental factors are identified. Currently they include soil nitrogen pool, soil moisture and particle size. Generally, the importance of soil nitrogen is two to three times higher than soil moisture region-wide due to intensive anthropogenic pressure in the second half of the 20 th century. Four consolidated associations of meadow vegetation are defined, each characterized by a set of diagnostic species. The shift towards a high soil nitrogen content has been recorded.

Vegetation response to southern California drought during the Medieval Climate Anomaly and early Little Ice Age (AD 800–1600)

High-resolution studies of pollen in laminated sediments deposited in Santa Barbara Basin (SBB) core SPR0901-02KC reflect decadal-scale fluctuations in precipitation spanning the interval from AD 800–1600. From AD 800–1090 during the Medieval Climate Anomaly (MCA) SBB sediments were dominated by xeric vegetation types (drought-resistant coastal sagebrush and chaparral) implying reduced precipitation in the southern California region. Drought-adapted vegetation abruptly decreased at AD 1090 and was rapidly replaced by mesic oak (Quercus) woodlands associated with an increased pollen flux into the basin. After a mesic interval lasting ∼100 years, pollen flux and the relative abundance of Quercus pollen dropped abruptly at AD 1200 when the rapid rise of chaparral suggests a significant drought similar to that of the MCA (∼AD 800–1090). This brief resurgence of drought-adapted vegetation between AD 1200–1270 marked the end of the MCA droughts. A gradual increase in mesic vegetation followed, characterizing cool hydroclimates of the Little Ice Age (LIA) in coastal southern California.The presence of xeric vegetation in SBB coincides with major drought events recorded in tree rings and low lake levels elsewhere in California except for the brief drought between AD 1130–1160. Correlative diatom and terrigenous sediment input proxy records from SBB are largely supportive of the pollen record predominantly linking the MCA with drought and La Niña-like conditions and the LIA with wetter (more El Niño-like) conditions. Differences between paleoclimate proxies (pollen, diatoms, and terrigenous sediment) in SBB exist, however, possibly reflecting the temporal and spatial differences in the generation of each proxy record, as well as their individual sensitivity to climate change.

The effect of spatially marginal localities in modelling species niches and distributions

AbstractAimWe introduce and evaluate the potential effect of spatially marginal localities (specifically those protruding into unsuitable regions), in overestimating species niches and distributions when using ecological niche models (ENMs).LocationNorth‐western South America.MethodsWe built anENMfor the Caribbean spiny pocket mouse (Heteromys anomalus) usingMaxEntand climatic variables. This species typically inhabits extensive tropical forests but can also range into drier habitats through patches of mesic vegetation. We ranked occurrence records according to the suitability value they received, and retrieved habitat information from collectors' field notes and the literature to determine whether those receiving lower values correspond to spatially marginal localities protruding into unsuitable regions. We then built a model excluding a subset of such localities and compared its geographic and environmental prediction with that of the original model.ResultsModels differed substantially in their estimates of suitability. The original model resulted in an overly extensive prediction, considering as suitable hot and dry regions dominated by xerophytic vegetation. Records receiving the lowest suitability values in this model corresponded mainly to captures in patches of mesic forest surrounded by thorn scrub or savannas. The model calibrated without such records restricted suitability mostly to regions characterized by the typical habitat of the species.Main conclusionsWhen it is not possible to use variables that are more proximal or have finer resolutions, we recommend building complementary models that, together, can provide a more realistic estimate of the species' niche and corresponding geographic distribution. Jointly interpreting these models, researchers may better differentiate between areas harbouring typical habitat and those where the species can be found only if locally favourable conditions exist. Such a distinction is of relevance for a wide range of applications relying on inferences obtained fromENMs.