Low-elevation Sites Research Articles

Will climate change constrain the altitudinal range of threatened species? Experimental evidence from a biodiversity hotspot.

A fundamental goal in ecology and evolution is to explain the factors that shape species' abundance and range limits. Evaluating the performance of early life-stages across an altitudinal gradient can be valuable for understanding what factors shape range limits and for predicting how plant species may respond to climate change. To experimentally evaluate the presence of local adaptation in a threatened palm (Euterpe edulis) at early life-stages, we reciprocally sowed seeds at two contrasting elevations. In addition, to evaluate the effect of seed predation on E. edulis seed germination and seedling establishment, seed addition experiments were conducted at three different elevations. Our results showed no evidence of local adaptation in the early life-stages for the two E. edulis populations. We observed lower germination and seedling performance of both E. edulis populations at the low-elevation site. The exclusion of seed predation increased seedling establishment across all elevations. Seed predation and dry soil conditions were the main factors that constrained seedling establishment at the upper altitudinal limit and at the lower elevation, respectively. Climate change in the study area will result in warmer and drier environmental conditions. The lack of local adaptation and the lower performance of both E. edulis populations in warm and dry conditions, combined with a higher seed predation at the upper altitudinal limit, might cause an altitudinal range contraction, increasing the vulnerability of this threatened species to climate change.

Distinct responses of climate-growth and iWUE in Fagus sylvatica L. at two low elevation sites in southern Italy

In this study, using a dendrological and isotopic approaches, we investigated the responses to climate of two pure Fagus sylvatica L. stands (Campobraca and Falode) in the southernmost part of the distribution range in southern Italy. The δ13C data were used for calculating the intrinsic water use efficiency (iWUE) as a proxy of the balance between the water and carbon cycles. The results showed that the iWUE of both stands was sensitive to the amount of precipitation during the summer months (negative, significant effect) and to atmospheric CO2 concentration. Growth was sensitive to climate only in the Campo Braca site; the most influential variables were the VPD (vapour pressure deficit) and precipitation of the summer months that had a negative and a positive effect, respectively. The iWUE showed a negative correlation with growth in Campo Braca and a non-significant one in Falode. Water availability was the most influential variable on F. sylvatica growth and physiology. The iWUE increase was mainly driven by atmospheric CO2 concentration, and by decreased precipitation, as a response of the trees to drought. Our results highlight the importance of understanding the hydrological changes due to climate change for forecasting/modelling forest responses. CO2 increase does not compensate for the effect of adverse climate on F. sylvatica in the forests of southern Italy, while local conditions play an important role in determining tree growth.

Habitat type controls microarthropod community changes across a Magellanic sub-Antarctic elevation gradient

IntroductionElevation gradients are often used as a proxy for climate change as they allow comparisons of ecological responses over much larger temporal and spatial scales than is possible through experimental manipulations.MethodsHere, we tested how microarthropod communities (Collembola and Acari) are affected by climatic differences between sea level and 600 m a.s.l. on Navarino Island, in the Magellanic sub-Antarctic ecoregion of southern Chile (mean annual temperatures of 5.6 vs 3.1°C, respectively). We quantified microarthropod abundance, richness and community trait characteristics in dominant moss (Racomitrium lanuginosum and Polytrichum strictum) and lichen (Usnea trachycarpa, Pseudocyphellaria freycinetii and Stereocaulon alpinum) vegetation growing at both elevations. These moss and lichen genera are characterized by large morphological differences and allow testing of how habitat characteristics affect microarthropod community response across elevation gradients.ResultsCollembola and Acari community composition differed between the low and high elevation sites. Total abundance levels of Acari were maintained in each habitat across elevation, whereas Collembola richness strongly declined (50%) at high elevation in the moss habitats. Acari community differences across elevation were driven by relative abundance changes whereas the Collembola community lost species at higher elevation. An anticipated decline of smaller eudaphic Collembola at high elevation was only observed in the moss Racomitrium, reflecting potentially lower temperature buffering capacity and shelter options compared to Polytrichum. Lichens mostly supported larger epigeic species irrespective of elevation. There were no consistent patterns linking microarthropod communities with habitat water holding capacity or water loss rates across the studied habitats and elevation.DiscussionHabitat type and the genus of moss or lichen were associated with microarthropod community changes across elevation, including examples of declines, increases and no change. These findings highlight that community responses across gradients may not always relate to the generally hypothesized environmental variables (e.g. temperature variability) and that habitat characteristics should be taken into account when using elevation as a proxy for climate change.

Rooting meta-ecosystems with reciprocal lateral carbon and nitrogen flows in a Yangtze coastal marsh

Abstract The dynamics of lateral nutrient fluxes through hydrological movements are crucial for understanding ecological functions related to the flow of energy, materials, and organisms across various spatiotemporal scales. To investigate the connectivity of multiple spatial flow processes, we conducted a one-year field study to measure lateral hydrologic carbon (C) and nitrogen (N) fluxes across the continental shelf in the Yangtze estuary. We observed a significant correlation between the differences in remote sensing-based estimates of gross primary production (GPP) (ΔGPPMODIS) and the differences in eddy covariance (EC) tower-based GPP (ΔGPPEC) at both high-elevation and low-elevation sites. Our findings indicate that the saltmarsh acts as a net source of dissolved total C while serving as a net sink for dissolved total N. Furthermore, there was a significant correlation in the total dissolved stoichiometry of the C/N ratio between imports from and exports to adjacent aquatic systems. These findings highlight the importance of integrating ecological stoichiometric principles to improve our understanding of the complex relationships among physical, chemical, and ecological processes, particularly within the context of the meta-ecosystem framework. Additionally, when reciprocal hydrological lateral C and N flows are considered, a single ecosystem can function as both a source and sink within the meta-ecosystem framework.

Competition between resprouting chaparral and the recruits of a serotinous conifer following stand-replacing fire

In western North America, fire regimes are shifting towards more frequent, larger, and more severe wildfire. There is concern that this will shift the vegetation type in many areas, especially on the lower, drier slopes. In northern California, mature serotinous conifers and resprouting shrub species easily regenerate in severe patches of any size. There is no consensus, however, regarding the effects of shrub competition on conifer recruitment; conifer response to shade varies with shade tolerance and abiotic factors. Many conifers and almost all chaparral shrubs are shade intolerant, and we expect shading to be the main driver of the inter-species competition between these taxa on dry low-elevation, slopes We chose to examine early post-fire regeneration of knobcone pine (Pinus attenuata), a shade intolerant serotinous conifer, because (a) as a serotinous species we could be assured of a high initial density of recruits, and (b) it is mainly found on lower-elevation slopes in a matrix of chaparral. We examined the competitive interactions of the pine and shrubs within the 2018 Carr and Delta fires at the third and fourth post-fire years, as well as at the 2008 Motion Fire at the 14th post-fire year, focusing on two measurements of shrub shading: inter-shrub porosity (% shrub cover) and intra-shrub porosity (species-specific ground-level light availability). Our response variables included recruitment success (recruits per ovulate cone) and growth (height). We only chose stands where knobcone pine was a minor pre-fire component to ensure a high density of vigorously resprouting shrubs. We found (1) there were significantly fewer pine recruits under shrubs, with the bulk of the shrub-induced mortality of knobcone pine occurring before the third growing season; (2) knobcone pine averaged about six established recruits per burned parent tree by the third year following fire; and (3), extrapolating from height reconstruction of post-fire knobcone pine regeneration from the 2008 Motion Fire, the remaining tree recruits are expected to persist and dominate the stand within a decade of the fire. We conclude that competition with shrubs on low elevation sites in northern California does have a negative effect on knobcone pine density but is insufficient to seriously impede a dramatic post-fire increase in conifer density when conifer regeneration arrives promptly following fire.

Mesoplastic and Microplastic Pollution in the Soil of Small-Scale Agricultural Areas in Iligan, Mindanao, Philippines

ABSTRACT The Philippines is primarily an agricultural country in which most Filipinos depend on the health of the soil for livelihood. Plastic pollution adversely affects agriculture by degrading soil quality, fertility, and crop growth. However, the prevalence of plastic particles such as mesoplastics (>5 mm to 25 mm) and microplastics (<5 mm) in agricultural soils in the Philippines remains poorly understood. This study investigated the prevalence of mesoplastics and microplastics in agricultural soils in Iligan City, Philippines. We collected soil samples from the six sampling stations in high-elevation and low-elevation sites. Mesoplastics and microplastics were examined through manual sorting, categorized based on color, shape, and size, and identified using Fourier-transform infrared spectroscopy (FTIR). Mesoplastics were found to be more prevalent, averaging 2.22 items/kg compared to microplastics 0.83 items/kg. Mesoplastics were mainly white-colored (42%), mostly fragmented (55%), 5–10 mm in size (55%), and were predominantly polypropylene (85%). Microplastics were mainly transparent (40%), composed of fragments and film shapes(46%), and 3–4 mm (93%) in size. Polyethylene was the abundant microplastic polymer type (47%). It was observed that the low-elevation sites had a higher abundance of plastic particles, stressing the need to address local factors in tackling plastic pollution.

Intraspecific variation in photosynthetic thermal acclimation in Fagus crenata seedlings from two populations growing at different elevations in northern Japan.

Plants can acclimate their photosynthesis to growth temperature, but the contribution of local adaptation to intraspecific variation in thermal acclimation of photosynthesis is not fully understood. Here, we experimentally investigated the photosynthetic thermal acclimation in Fagus crenata Blume seedlings from two populations growing at different elevations and temperature regimes (low- and high-elevation sites) in northern Japan. We acclimated seedlings for 14 to 23days at daytime temperatures of either 22°C (control) or 27°C (warm treatment) and obtained photosynthetic temperature-response curves in the range of 19 to 32°C. The optimum temperature of photosynthesis (Topt) was ~0.6°C higher in seedlings acclimated at 27°C than in those acclimated at 22°C, and it was significantly lower in seedlings with higher stomatal sensitivity to leaf-to-air vapor pressure deficit than in those with lower sensitivity. The effects of warm treatment, population and treatment-population interaction on Topt were not significant in the two-way analysis of variance, but the effect of treatment became significant when stomatal sensitivity to leaf-to-air vapor pressure deficit was included as a covariate in the model. Structural equation modeling indicated that seedlings with lower root biomass had lower Topt because of the high stomatal sensitivity to leaf-to-air vapor pressure deficit. Structural equation modelling also indicated that the way of shifting the Topt differed between the two populations: seedlings from a high-elevation site depended on decreasing photosynthetic rates at low temperatures for the increase in Topt but seedlings from a low-elevation site did not. We suggest that the difference in thermal acclimation of photosynthesis between the two populations may reflect adaptation to different climate regimes and that belowground traits should be considered when investigating thermal acclimation capacity, especially in seedlings.

Difference in the production and elemental composition of litter in Kandelia obovata mangrove forests due to site elevation

Site elevation is a crucial driver for mangrove restoration, and litter production restoration is a significantly important target of mangrove restoration, but little attention has been paid to impact of site elevation on the production and elemental composition of litter in the restored mangrove forests. This study compared the production and elemental composition of mangrove litter at the three intertidal elevations, to explore impacts of site elevation on the production and elemental composition of mangrove litter. Compared with the upper elevation site, significantly lower annual litter production was found at the lower elevation site. Leaf litter was the main component of litter, up to 60.49% of total litter production at the upper elevation site, while reproductive materials (flower and fruit) were the key part of litter and accounted for 50.80% (the lower elevation site) and 57.02% (the middle elevation site) of total litter production. As site elevation decreased, element stocks within total litter decreased by approximately 65.39% (organic carbon), 65.17% (total nitrogen) and 63.66% (total phosphorus), respectively, which was attributed more to element stocks within leaf litter instead of element stocks within the other litter. Results showed that site elevation decreases resulted in decreased litter production, altered composition percentages of litter production, and reduced element stocks within total litter. In the future mangrove restoration projects, it is advisable to prioritize upper elevation (above local mean level) for promoting litter production.

Spruce trees have stronger drought sensitivity at low- than high-elevation sites across China’s aridity zones

The ecological relationships between tree growth and climate factors are important for the adaptation, growth prediction, and forest management of tree species against a background of global warming. Yet how these relationships for drought-sensitive conifer trees are changed and affected by elevation remains unclear. To investigate the effect of elevation on spruce tree growth–climate interactions, we collected a total of 1886 tree-ring cores (two cores per tree) from four spruce species, including Picea crassifolia Kom., Picea meyeri Rehd. et Wils., Picea schrenkiana Fisch. et Mey., and Picea wilsonii Mast., in 10 pure forests at a pair of high- and low-elevation alpine sites with the same slope across two aridity zones in China. We then constructed 20 stand tree-ring chronologies for the low- and high-elevation sites. Overall, the growth of spruce trees was more sensitive to drought variability at sites in the semi-arid zone whereas it was weakly limited by drought in the semi-humid zone. Further, spruce trees growing at high-elevation sites were sensitive to temperature unlike the stronger positive drought responses of those at low-elevation sites. In the latter half of the 20th century, the positive drought–growth relationships of spruce were enhanced at both high and low elevation across both aridity zones due to warming and increased drought intensity. Our dendrochronology-based findings suggest that spruce trees’ radial growth in stands at high elevation may have faced drought stress during three recent decades. Nevertheless, the low-elevation trees incurred stronger drought stress compared to the first half of the 20th century.

Causes for Decadal Trends in Surface Solar Radiation in the Alpine Region in the 1981–2020 Period

AbstractExtending across seven countries, the Alps represent an important element for climate and atmospheric circulation in Central Europe. Its complex topography affects processes on different scales within the atmospheric system. This is of major relevance for the decadal trends in surface solar radiation (SSR), also known as periods of global dimming and brightening (GDB). In this study we analyzed data from 38 stations in and around the Swiss and Austrian Alps, over a period ranging from the 1980s up to the 2020s, with the aim of characterizing the spatio‐temporal variations of the GDB and understanding the causes for such trends in this region. Our results show a different behavior in the SSR decadal trends in the western part of the Alps in comparison to the eastern part. Our results also suggest a remarkable difference between the causes of such trends at the stations at low altitudes in comparison to the stations at higher altitudes. Significant contributions from changes in cloud optical depth and surface albedo to the SSR decadal trends at high elevation sites were also found, in contrast to a substantial clear‐sky forcing that strongly dominates at low elevations. Results from previous literature and available data suggest that cloud optical depth changes at high altitudes and clear‐sky forcing at low altitudes could be associated with the indirect and direct aerosol effects, respectively, due to differing pollution levels at low and high elevation sites.

Late Holocene high-resolution paleoenvironmental reconstruction from Beaver Lake in the northwest lowlands of the Olympic Peninsula, Washington (USA)

Fire is an essential component of the landscapes and forests of the Pacific Northwest, including the temperate rainforests of the Olympic Peninsula. Previous fire history reconstructions from the peninsula show that fire return intervals varied throughout the postglacial period, primarily in response to climatic changes and corresponding shifts in vegetation. However, much less is known about the fire history of the low-elevation forests of the Olympic Peninsula and the role of cultural fire regimes in these environments. The purpose of this study was to reconstruct the paleoenvironmental history of a low-elevation study site, Beaver Lake, located in the northwestern part of the peninsula. Using macroscopic charcoal, pollen, and sedimentological analyses of a ca. 3440-year-long record, we reconstructed a high-resolution record that shows fire activity was remarkably high during the late Holocene for an area considered part of a temperate rainforest. However, patterns of burning varied throughout the record, with the first third (ca. 3440 to 2350 cal yr BP) and last third (ca. 800 cal yr BP to the present day) recording much higher amounts of fire activity compared to the middle portion (ca. 2350 to 800 cal yr BP), which recorded very little fire activity. Larger and/or more severe fires that likely burned during multi-year droughts correlate with peaks in magnetic susceptibility and pollen trends that indicate substantial geomorphic responses and successional changes in forest structure following these events. Cooler temperatures and a wetter climate, indicated by nearby glacial advancements, may have staved off fire activity during the period of low fire activity. Cultural burning by the Indigenous tribes of the Olympic Peninsula likely contributed to the observed fire activity at Beaver Lake as nearby prairies were managed for resource procurement, indicated in particular by an increase in herbaceous morphotype charcoal during the past 800 years.

Landscape position mediates drought vulnerability in California valley oak (Quercus lobata)

Future climate change will exacerbate drought stress in water-limited ecosystems. However, topography can alter the fine-scale climatic and hydrologic conditions that mediate plant response to meteorological drought. Here, with six new valley oak (Quercus lobata) tree-ring width chronologies, we assess how topography acts as a mediating factor on tree growth and drought sensitivity. Because valley oaks are known to be highly dependent on subsurface water, we predicted that trees growing in riparian sites would be less sensitive to precipitation variability due to greater access to groundwater. Trees were sampled in the Tehachapi Mountains of California across a landscape gradient of sites ranging from 375–1650 m elevation and across upland (55–69 m mean height above nearest drainage) and riparian (2–6 m mean height above the nearest drainage) hillslope positions. Interannual tree growth patterns and drought sensitivity varied substantially in association with hillslope position and elevation. Valley oak radial growth showed a consistently weaker response to precipitation at riparian sites. The influence of hillslope position on drought sensitivity varied with elevation, such that the riparian buffering effect was weakest at sites higher in the watershed and strengthened, progressively, toward the lower elevation sites with greater climatic water deficit. Upland tree growth exhibited a strong response to high-frequency interannual precipitation variability at the high elevation site, whereas trees at lower elevation upland sites responded more to low-frequency decadal trends in precipitation, possibly reflecting hydrogeological processes by which precipitation feeds groundwater lower in the watershed. Our results are consistent with groundwater-dependence of valley oak and indicate that riparian habitats are the most likely refugia for the species during prolonged drought.

Abundance, diversity and distribution of soil nematodes in Kangaita and Weru tea catchments of Kirinyaga and Tharaka Nithi counties, Kenya

Nematodes are the most abundant animals on earth and play essential roles in ecosystem functioning hence their abundance and diversity affect soil health. Nematodes have been reported in tea fields in some parts of Kenya and previous studies indicate that they may be a cause for the decline of tea population in some tea fields in Kenya. Nematodes of Moloidogyne spp have also been reported to be responsible for death of tea plants in nursery conditions. A survey was carried out in Weru and Kangaita tea factories catchment areas in Tharaka Nithi and Kirinyaga counties respectively. The survey aimed to determine the abundance and diversity of nematodes in small holder tea farms. Kangaita represented the high elevation site while Weru represented the low elevation site. Soil samples were collected from smallholder tea farms from which nematodes were extracted, identified based on their morphological characteristics, and classified according to their feeding habits then quantified using standard protocols. Nematodes from 23 genera were recovered in the two study sites representing all the five feeding groups: plant feeders, fungal feeders, bacterial feeders, omnivores, and predatory nematodes. Of the 23 genera, 11 were plant feeders, 6 bacterial feeders, 3 fungal feeders 2 omnivores and 1 predatory nematode. Kangaita, being a high elevation site reported higher population density in most genera reported than Weru which is a low elevation site. This is a departure from most studies that have reported higher nematode population densities in low altitudes. This can be attributed to differences in climatic and soil conditions in the two study sites in the same season. Kangaita was cooler with deep, well-ventilated, and loose soils while Weru was hotter with mostly compacted, shallow, and poorer soils in the tea farms. There is need for further research on the effect of elevation and farming practices on the distribution, abundance, and diversity of nematodes in tea fields. Key words: Nematodes, abundance, soil health, tea fields, elevation, diversity, feeding group

Assessing intra-annual growth dynamics in climatically contrasting years, sites, and tree species using dendrometers and wood anatomical data

Detecting the intra-annual dynamics and courses of secondary tree growth enables the accurate identification of crucial steps in the forming of a new tree ring. Furthermore, comparing the high-resolution recordings of tree growth with environmental conditions allows assessment of the influence of weather on wood formation processes. This study investigates the intra-annual growth performance of conifer species and European beech at two high- and two low-elevation sites in Bavaria, southeast Germany. We measured stem circumference changes with electronic band dendrometers and cambial dynamics by collecting microcores at biweekly intervals. We analyzed growth variations between the consecutive years 2020 and 2021, which showed distinct climatic differences during the growing seasons. While warm and dry conditions prevailed in spring and summer in 2020, spring in 2021 was comparatively cold, and summer precipitation was high. Different tree growth patterns were observed in the contrasting years 2020 and 2021. Distinct growth reductions occurred in the drier year 2020 for most of the studied tree species, while trees showed wider tree rings in 2021 despite of low growth rates at the beginning of the growing season. Climate-growth correlations exposed the intraseasonal influence of climatic conditions, particularly available soil water, water vapor pressure deficit, and soil temperature, on short-term tree responses. Wood anatomical analysis and daily stem diameter variations proved to be valid monitoring methods to assess individual wood formation processes and to identify species-specific tree responses to the influence of climatic conditions. However, combining both methods represents the most reliable approach due to the mutual ability to compensate for each other’s deficiencies. While dendrometers provided a very accurate and high-resolution record of intra-annual tree growth, wood anatomical analyses were more reliable in determining the exact onset and cessation of wood formation. For this reason, combining both is recommended for assessing prospective tree growth performance in the context of climate change.

Vegetation Affects the Responses of Canopy Spider Communities to Elevation Gradients on Changbai Mountain, China.

Forest canopies, an essential part of forest ecosystems, are among the most highly threatened terrestrial habitats. Mountains provide ideal conditions for studying the variation in community structure with elevations. Spiders are one of the most abundant predators of arthropods in terrestrial ecosystems and can have extremely important collective effects on forest ecosystems. How the diversity and composition of canopy spider communities respond to elevation changes in temperate forests remains poorly understood. In this study, we collected canopy spiders from four elevation sites (800 m, 1100 m, 1400 m, and 1700 m) on Changbai Mountain using the fogging method in August 2016. With the methods of ANOVA analysis, transformation-based redundancy analysis, and random forest analysis, we explored the responses of canopy spider communities to elevation. In total, 8826 spiders comprising 81 species were identified and the most abundant families were Thomisidae, Clubionidae, Linyphiidae, and Theridiidae (77.29% of total individuals). Species richness decreased whereas evenness increased with increasing elevation, indicating that elevation has an important impact on community structure. The pattern of absolute abundance was hump shaped with increasing elevation. We found that the community compositions at the three taxonomic levels (species, family, and guild) along the elevation gradient were obviously altered and the variation in community composition was higher at low-elevation sites than at high-elevation sites. There were 19 common species (23.46%) among the four elevations. Regression and RDA results showed that vegetation variables contributed to the variation in the diversity and composition of canopy spiders. Furthermore, the influence of factors would be weakened with the taxonomic level increasing. Therefore, our findings greatly highlight the important role of vegetation in the diversity and composition of canopy spiders and the influence is closely related to the taxonomic level.

Northern pikas experience reduced occupancy due to surrounding human land use despite the occurrence of suitable microclimates

AbstractAimDespite warming temperatures, some species are found persisting at the trailing edge of their distribution. Microclimates provided by complex topography are considered a key factor in these cases of range stationarity, buffering stress from exposure to warming and enabling persistence. However, for species with trailing‐edges located in human‐modified landscapes, refugial conditions provided by microclimates could be disrupted by human activities. Here, we aimed to understand the determinants of trailing‐edge occupancy for a small lagomorph found in rocky patches harbouring cool microclimates.LocationHokkaido Island, Japan.TaxonNorthern pika (Ochotona hyperborea).MethodsWe surveyed the occupancy of northern pikas across a wide elevational gradient (350–2200 m) for two consecutive summers. Ambient air and microhabitat (i.e. rock interstices) thermal conditions were measured to assess their relationship. We then analysed their effects on occupancy at two nested spatial scales: (1) whole‐distribution, and (2) at identified trailing‐edge sites where we explored the effects of microclimates and surrounding human activities (i.e. distance to nearest road and area of human land use such as plantation forests or agricultural fields).ResultsOverall, rock interstices exhibited cooler conditions than ambient air with temperature differences of 1–2°C. The overall distribution of northern pikas was affected by both mean ambient temperature and microhabitat availability, with warmer (lower elevation) sites with less microhabitats corresponding to the trailing edge of its distribution. Interestingly, trailing edge occupancy patterns were best explained by the negative effect of surrounding human land despite the existence of suitable microclimates in the rocky patches.Main ConclusionsOur findings suggest that the local refugial conditions supported by cool microclimates are likely to be disrupted by the effects of human land alterations at the larger landscape scale. This result highlights the importance of considering the effects of human activities and landscape alteration for effective microrefugia conservation.

Old-growth mixed dipterocarp forests show variable losses and gains in aboveground biomass and standing carbon over forty years

BackgroundNo studies have documented long-term trends in aboveground biomass (AGB) for mixed-dipterocarp forests (MDF), the dominant rain forest type in tropical wet equatorial Asia. In our study, we sought to document such trends over forty years across three sites representing lowland to lower montane elevations. MethodsTo do this, we established fifty 100 ​m ​× ​25 ​m plots in 1978 across three sites sampled along an elevation gradient, identified as mature old-growth forest. We measured trees for diameter at breast height that we identified to species and tagged. We took wood samples to calculate species wood-specific gravity. We re-measured plots in 1998 and again in 2018. ResultsWe show standing AGB for all sites combined to be 517.52 ​Mg⋅ha−1 in 1978, but this declined by 17% over 40 years to 430.11 ​Mg⋅ha−1. No differences exist among sites in AGB primarily because of considerable within site variation; but interactions of time with site show declines across sites were not uniform, one remained about the same. Relatively few species represented a high proportion of the AGB with the top five species comprising between 34% and 65%, depending upon site and year sampled. One species, Mesua nagassarium, represented a disproportionately large amount of AGB and decline over time, particularly at the low elevation site. ConclusionsOur results are directly relevant to estimating AGB and standing carbon sequestered in MDF. Our study is the first to demonstrate varying but overall, declining trends in amounts of AGB among forests making predictions of biomass and standing carbon in MDF difficult over wide regions.

Into the danger zone: How the within-host distribution of parasites controls virulence.

Despite the importance of virulence in epidemiological theory, the relative contributions of host and parasite to virulence outcomes remain poorly understood. Here, we use reciprocal cross experiments to disentangle the influence of host and parasite on core virulence components-infection and pathology-and understand dramatic differences in parasite-induced malformations in California amphibians. Surveys across 319 populations revealed that amphibians' malformation risk was 2.7× greater in low-elevation ponds, even while controlling for trematode infection load. Factorial experiments revealed that parasites from low-elevation sites induced higher per-parasite pathology (reduced host survival and growth), whereas there were no effects of host source on resistance or tolerance. Parasite populations also exhibited marked differences in within-host distribution: ~90% of low-elevation cysts aggregated around the hind limbs, relative to <60% from high-elevation. This offers a novel, mechanistic basis for regional variation in parasite-induced malformations while promoting a framework for partitioning host and parasite contributions to virulence.

Previously introduced braconid parasitoids target recent olive fruit fly (Bactrocera oleae) invaders in Hawai’i

The olive fruit fly Bactrocera oleae (Diptera: Tephritidae) was detected on Maui and Hawai’i Islands in 2019, affecting yields and quality of the state’s emerging olive oil industry. Given previous parasitoid releases to control other invasive frugivorous tephritids in Hawai’i, we were interested in determining whether these parasitoids were naturally targeting recent olive fly invaders in field, if local olive cultivar differences affected parasitization rates, and if there was a seasonal pattern of parasitization that could inform future management decisions. To address these questions, we collected data from olive growing in Hawai’i during 2021 and 2022. During the fruiting season we collected monthly samples and reared out B. oleae in the lab. We detected two previously introduced braconid wasps: first Diachasmimorpha tryoni during 2021 and 2022 and later Fopius arisanus during the 2022 collection. Cultivar effects were limited to a single site in our study, where more D. tryoni were reared from ‘Arbequina’ olives. Seasonality of olive fruit fly and parasitoid activity was earlier in lower elevation sites, as expected based on tree phenology and temperature-dependent insect development. This represents the first report of D. tryoni parasitism activity against B. oleae and may reflect elevational effects combined with the ecological complexity in interactions between multiple invasive arthropod pests, their invasive and cultivated plant hosts, and introduced braconid parasitoids.

Assisted Migration of Sequoiadendron Genotypes for Conservation and Timber: Performance and Morphology in a Warmer Climate Outside of Their Range

Sequoiadendron giganteum (giant sequoia) has a fragmented distribution of 75 groves found along the western slope of the Sierra Nevada Mountains, California, USA. Outplanting and range expansion or assisted migration of this iconic species for the objectives of genetic conservation and timber production would be supported by information on growth and morphology to guide seed-collection decisions. We measured and assessed giant sequoia planted as seedlings and clonal stock originating from 22 groves in two common-garden experiments at Foresthill, California, north of the current species range, after 29 growing seasons. Traits examined were tree-size parameters, fluting and asymmetry of the lower stem, basal swelling, fullness of the live crown, epicormic sprouting, and heartwood decay resistance in cut stumps. Performance in terms of tree size after 29 years varied widely among genotypes with different grove origins. Morphology and decay resistance also exhibited some variation according to grove origins. The seedling stock outperformed the clonal stock of the same grove origins in terms of size and is therefore recommended when faster early growth is desired to outcompete other trees or for other management objectives. However, more fluting was exhibited by the larger fast-growing giant sequoia, while fewer seedlings had epicormic sprouts than the clonal stock of the same grove origins. At our warm low-elevation study site, giant sequoia from Mountain Home, Giant Forest, and Converse Basin consistently exhibited above-average growth among other giant sequoia in a pure planting and in an intimate mixture with five common conifer associates. Therefore, seed collected from these three groves should perform relatively well at other locations with a similar climate. When conservation of the species and its genetic diversity is the primary objective, we recommend collecting from a wide range of groves and undertaking assisted migration by planting at multiple locations inside and outside giant sequoia’s range as a hedge against the loss of native groves.