Because of a lack of field data, ontogenetic patterns of herbaceous climbers like germination site and changes in root/shoot connection with the soil remain unclear. We provide rare quantitative data regarding this aspect and species richness and abundance in a tropical lowland forest. Few species fall neatly in the so far applied categories of vines, nomadic vines and hemiepiphytes.

Abstract

Background

In contrast to woody climbers, information on community composition or vertical extension within the forest is scarce for herbaceous climbers, even in well-studied field sites like Barro Colorado Island. Moreover, questions regarding ontogenetic patterns (site of germination, changes in root/shoot connection with the soil) are unresolved because of a lack of field data.

Location

Barro Colorado Island, Panama.

Methods

In 17 plots of 400 m² each, which were distributed all over the island, we recorded all potential hosts (trees, palms, lianas) with a diameter at breast height larger than 1 cm, and all climbing aroids attached to them. For aroids, we recorded species identity, number of shoots, root connections to the ground, and vertical shoot extension. By distinguishing three size classes for each species in our analyses we deduced the site of germination and ontogenetic changes in the root/shoot connection with the soil.

Results

Only 16% of all potential hosts were occupied by climbing aroids. We recorded 1196 individuals of 17 species. Aroids preferred larger trees and old-growth forest. Species differed strongly in vertical distribution. Hemiepiphytic species germinate epiphytically, often high up in tree crowns and later establish root contact with the soil, while the majority of species establish on or close to the ground and reach moderate heights of 5–15 m (forest height ca. 35 m). In all of these species, we observed dieback of the proximal portion of the shoot to a varying extent but contact with the soil was invariably retained via adventitious roots.

Conclusions

We provide rare quantitative data on species richness and abundance of herbaceous climbers in a tropical lowland forest. Few species fall neatly into the categories of vines, nomadic vines and hemiepiphytes. This highlights the need for longitudinal observational and experimental studies to resolve the current debate on the appropriate grouping of these climbers.

We investigated the variation of soil microclimate in time and space in a relict alpine system of northern Spain. Spatial microclimatic variation in one year was higher than in 10 years of microclimate monitoring in permanent plots, supporting the buffer effect of topography in alpine landscapes. Protected sites with relatively longer snow cover are key microclimatic refugia for preventing local extinctions.

Abstract

Questions

In alpine landscapes, topography creates a mosaic of microclimatic niches that might prevent local extinctions, but the influence of this spatial heterogeneity on plant communities is largely unknown. Here we ask (1) how soil microclimatic variation is comparable at temporal and spatial scales, and (2) how such variation influences species composition and local extinctions in relict alpine communities.

Location

Picos de Europa National Park, northern Spain.

Methods

We resurveyed permanent plots in four alpine sites following the recording of soil temperatures (temporal survey) for 10 years. We then sampled the spatial variation in species composition and microclimatic temperatures in 80 plots around the permanent plots (spatial survey). We evaluated the variation of six microclimatic indices between the temporal and the spatial surveys, and calculated the temporal trends observed in species cover. We finally predicted local extinction rates under microclimatic scenarios based on the observed microclimate–community relations.

Results

Despite high interannual variation, we found a 10-year trend of temperature warming on (microridge) fellfields and (microvalley) snowbeds. Microclimatic variation was larger in space than in time, with little temperature variation in snowbeds and extreme low temperatures recorded in fellfields. Species composition was mainly influenced by growing degree days (GDD) and freezing degree days (FDD), which were both related to snow cover duration. Plant cover of 16 species (out of 36 frequent species) showed significant responses to microclimatic variation. Local extinctions were mainly predicted under relatively hotter and more freezing conditions.

Conclusions

Our results support the idea that microclimatic spatial heterogeneity can reduce the negative influence of climate change on alpine plant communities. However, a continuous reduction of snow cover will result in a tipping point beyond which the buffer effect of this spatial heterogeneity will not be effective in protected microsites, leading to community homogenization. This process may have started in relict alpine communities where species from snowy microclimates are being outcompeted by species adapted to below-zero winter temperatures.

For the first time, we test whether ecological indicator values (EIVs) of forest plant communities are solely able to capture macroclimate or also microclimate temperature. Vascular plant and bryophyte communities successfully inferred macroclimatic differences across forests but largely failed to do so for microclimate variation within forests. Refined temperature EIVs are needed to capture microclimates experienced by understorey species.

Abstract

Question

Ecological indicator values (EIVs) reflect species‘ optimal conditions on an environmental gradient, such as temperature. Averaged over a community, they are used to quantify thermophilization stemming from climate change, i.e. the reshuffling of communities toward more warm-adapted species. In forests, understorey plant communities do not keep up with global warming and accumulate a climatic debt. Although the causes are still debated, this thermal lag may be partly explained by forest microclimate buffering. For the first time, we test whether community means of EIVs are able to capture microclimate (here, under forest canopies) temperature across, or also within forests.

Location

157 forest plots across three French deciduous forests covering a large macroclimatic gradient.

Methods

To assess whether EIVs can be used to infer the mean and range of microclimate temperature in forests, we measured understorey air temperature for ca. 1 year (10 months) with sensors located 1 m above the ground. We surveyed bryophytes and vascular plants within 400-m² plots, and computed floristic temperature from ordinal-scale EIVs (Ellenberg, Julve) and degree-scale EIVs (ClimPlant, Bryophytes of Europe Traits) for both temperature and continentality, i.e. temperature annual range. Finally, we fitted linear models to assess whether EIVs could explain the mean and range of microclimate temperature in forests.

Results

Vascular plant and bryophyte communities successfully reflected differences in mean annual temperatures across forests but largely failed to do so for microclimate variation within forests. Bryophytes did not perform better than vascular plants to infer microclimate conditions. The annual range of microclimate temperatures was poorly associated with ordinal-scale EIVs for continentality but was positively correlated with degree-scale EIVs for annual range within lowland forests, especially for vascular plant communities.

Conclusion

Overall, the capabilities of EIVs to infer microclimate was inconsistent. Refined EIVs for temperature are needed to capture forest microclimates experienced by understorey species.

The data along Tibetan Alpine Vegetation Transects indicate that, to maximize nitrogen use efficiency of canopy production, forest trees tend to have a higher mean residence time of nitrogen in the plants through increased leaf life span, whereas alpine shrubs and grasslands tend to have higher nitrogen productivity through increased below-ground fraction of biomass. Similar patterns are found in phosphorus use efficiency.

Abstract

Question

Knowledge of how nutrient use strategies differ between forest trees and alpine shrubs/grasses is important to understand the mechanisms of vegetation changes from montane forests to alpine shrubs/grasslands along altitudinal gradients. We tested the hypothesis that, to maximize the nitrogen use efficiency (NUE) of canopy production, forest trees tend to have a higher mean residence time (MRT) of nitrogen in the plants through increased leaf life span, whereas alpine shrublands and grasslands tend to have higher nitrogen productivity through increased below-ground biomass fraction. We further tested whether similar patterns are found in phosphorus use efficiency (PUE).

Location

Twenty-one sampling sites along Tibetan Alpine Vegetation Transects (TAVT) at altitudes from 1900 m to 4900 m.

Methods

We measured the maximum biomass of new canopy leaves and twigs and the concentrations of their nutrients N and P and associated ecosystem variables along the TAVT. NUE (PUE) was calculated as the product of nutrient productivity (dry matter production per unit N or P in new canopy leaves and twigs) and MRT (the ratio of foliage nutrient pool to annual nutrient uptake).

Results

With increasing altitude, leaf life span increased in forest trees but decreased in shrublands and grasslands, while below-ground fraction increased when vegetation changed from montane forests to alpine shrubs/grasslands. In forest trees, higher N-MRT and P-MRT and lower P productivity were associated with longer leaf life span and lower below-ground fraction, while N productivity varied little. In alpine shrublands and grasslands, N-MRT, P-MRT and P productivity varied little with leaf life span and below-ground fraction, while N productivity was positively correlated with below-ground fraction.

Conclusions

Our data supported the hypothesis, suggesting that NUE of canopy production would be a measure of changes in ecosystem functioning from montane forests to alpine shrublands and grasslands along altitudinal gradients. The findings provide an insight into the linkage between biogeochemistry and phytogeographic processes across ecosystems.

We found that three important conifer species of the Eastern Canadian boreal mixed woods (white spruce, balsam fir and white cedar) have reduced seedling recruitment during warmer growing seasons, which is not the case for the main deciduous trees (trembling aspen, paper birch) in this ecosystem. This effect could aid the northward migration of temperate deciduous species in a warming climate.

Abstract

Aim

Seedling recruitment is a vital process for forest regeneration and is influenced by various factors such as stand composition, climate, and soil disturbance. We conducted a long-term field experiment (18 years) to study the effects of these factors and their interactions on seedling recruitment.

Location

Our study focused on five main species in boreal mixed woods of eastern Canada: trembling aspen (Populus tremuloides), paper birch (Betula papyrifera), white spruce (Picea glauca), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis).

Methods

Sixteen 1-m² seedling monitoring subplots were set up in each of seven stands originating from different wildfires (fire years ranging from 1760 to 1944), with a soil scarification treatment applied to every other subplot. Annual new seedling counts were related to growing-season climate (mean temperature, growing degree days and drought code), scarification, and stand effects via a Bayesian generalized linear mixed model.

Results

Soil scarification had a large positive effect on seedling recruitment for three species (aspen, birch and spruce). As expected, high mean temperatures during the seed production period (two years prior to seedling emergence) increased seedling recruitment for all species but aspen. Contrary to other studies, we did not find a positive effect of dry conditions during the seed production period. Furthermore, high values of growing degree days suppressed conifer seedling recruitment. Except for white cedar, basal area was weakly correlated with seedling abundance, suggesting a small number of reproductive individuals is sufficient to saturate seedling recruitment.

Conclusion

Our findings underscore the importance of considering multiple factors, such as soil disturbance, climate, and stand composition, as well as their effects on different life stages when developing effective forest management strategies to promote regeneration in boreal mixed-wood ecosystems.

We compared surveys from 1881 with modern vegetation to test for changes in a big sagebrush landscape in a National Monument in New Mexico, USA. We found an increase in sagebrush over 140 years, which contrasts with the sagebrush decline occurring in the Great Basin. These results provide insights into different trends and processes affecting similar vegetation in different regions.

Abstract

Questions

Big sagebrush (Artemisia tridentata) ecosystems across the western United States have experienced many changes in ecosystem dynamics and vegetation composition over the last century due to livestock grazing, non-native species, and changing climate and fire regimes. We conducted the first systematic investigation of historical vegetation composition and vegetation change in a sagebrush landscape in the southwestern United States, asking whether sagebrush or grass dominated the landscape historically?

Location

The Rio Grande del Norte National Monument (RGDN), northern New Mexico, USA.

Methods

We combined General Land Office (GLO) surveys from 1881 with modern vegetation maps, field vegetation surveys, and sagebrush ages from growth ring analysis to test for changes in vegetation in the RGDN over the last 140 years.

Results

We found that big sagebrush presence across the study area increased significantly, from being present on 16% of section lines in 1881 to 79% in 2019, and only three section lines lost sagebrush presence during that period. Concurrently, the number of section lines with low grass index more than doubled since 1881, while moderate and high grass index declined. Grass declined equally in areas where sagebrush increased and areas with no change in sagebrush, suggesting that changes in both vegetation types were catalyzed by external factors, likely including overgrazing. The growth ring analysis of 93 sagebrush revealed a maximum age of 87 years and establishment in every decade since the 1930s, consistent with the GLO results.

Conclusions

The significant vegetation changes in the RGDN over the last century, including an increase of sagebrush, provide important context about the shifting mosaic of grasslands and shrublands relevant to current and future management and ecosystem dynamics.

Habitat mosaics due to shrub establishment in mixed conifer forest after fire creates high spatial heterogeneity at broader scales. However, reburned patches from high to high and low and moderate to low and moderate severities have less spatial heterogeneity. Under climate change-induced increase in wildfire within short return interval, conifer regeneration within large stand-replaced patches is uncertain.

Abstract

Aims

Prolonged fire suppression in conifer forests of the Sierra Nevada Mountain range, California, USA, has led to ingrowth of conifer seedlings, converting the open heterogeneous structure into uniformly dense and layered forest. The threat of a stand-replacing fire has increased because of fuel buildup in combination with rising drought and extreme heat frequency caused by climate change. With such high severity fire, there is also rising concern regarding conifer forest converting to shrublands as severe fire favors the establishment of large shrub patches altering landscape vegetation pattern and heterogeneity. However, a clear understanding of the effects of increased fire severity, size, and frequency on landscape-scale heterogeneity and postfire patch dynamics is lacking, which is critical in implementing restoration and forest management activities. Our aim was to understand multiscale dynamics and spatial heterogeneity patterns of conifer forests and chaparral shrublands due to repeated mixed-severity fire.

Location

A mosaic of burned and unburned patches spanning the boundary of Lassen and Plumas National Forests, CA, USA.

Methods

We used secondary geospatial landcover data classified by cover type before modern fires (1999) and after eight modern fires (2014). We calculated various landscape diversity and fragmentation metrics at patch and landscape scales using FRAGSTATS for comparison before and after fires.

Results

At the fire severity patch scale, high-severity fire reduced vegetation cover type heterogeneity by half, but reburning at low to moderate severity nearly doubled cover type heterogeneity. At the full landscape scale mixed-severity fire, including all burn severities, increased vegetation cover type heterogeneity. Fragmentation indexes confirmed that fire created larger patches of shrub and fragmented patches of conifer forest.

Conclusions

The effects of frequent large fire events on vegetation pattern and heterogeneity vary with the scale of analysis. Hence, heterogeneity and vegetation pattern change need to be evaluated at more than one scale to understand past and future ecological processes before prioritizing management actions for the conifer forests of the Sierra Nevada Mountain range.

We explored variation in plant community processes in sites spanning the latitudinal extent of the boreal biome of western North America. We found that the majority of variation in plant community composition and functional traits occurred within sites, suggesting that local-scale environmental gradients were more strongly driving plant community dynamics than the regional-scale climatic gradient across our sites.

Abstract

Questions

Rapid climate change in northern latitudes is expected to influence plant functional traits of the whole community (community-level traits) through species compositional changes and/or trait plasticity, limiting our ability to anticipate climate warming impacts on northern plant communities. We explored differences in plant community composition and community-level traits within and among four boreal peatland sites and determined whether intra- or interspecific variation drives community-level traits.

Location

Boreal biome of western North America.

Methods

We collected plant community composition and functional trait data along dominant topoedaphic and/or hydrologic gradients at four peatland sites spanning the latitudinal extent of the boreal biome of western North America. We characterized variability in community composition and community-level traits of understorey vascular and moss species both within (local-scale) and among sites (regional-scale).

Results

Against expectations, community-level traits of vascular plant and moss species were generally consistent among sites. Furthermore, interspecific variation was more important in explaining community-level trait variation than intraspecific variation. Within-site variation in both community-level traits and community composition was greater than among-site variation, suggesting that local environmental gradients (canopy density, organic layer thickness, etc.) may be more influential in determining plant community processes than regional-scale gradients.

Conclusions

Given the importance of interspecific variation to within-site shifts in community-level traits and greater variation of community composition within than among sites, we conclude that climate-induced shifts in understorey community composition may not have a strong influence on community-level traits in boreal peatlands unless local-scale environmental gradients are substantially altered.

Natural reforestation through secondary succession in marginal agricultural land is an important component of climate mitigation and adaptation, but the fundamental ecological processes promoting or constraining it are poorly understood. This study provides national-scale evidence that species accumulation in post-agricultural forest successions may be slowed by intense mammalian herbivory and low rates of biotic seed dispersal. Naturally reforesting post-agricultural land, South Island, New Zealand.

Abstract

Question

Natural reforestation is an important component of climate mitigation and adaptation, but the ecological processes promoting or constraining it are poorly understood. In this study we employ a stand reconstruction approach (which uses ages of extant trees to estimate year of establishment for each individual tree) to test for general trait-based effects on tree species arrival order in post-agricultural forest successions.

Location

Naturally reforesting post-agricultural landscapes throughout New Zealand.

Methods

Ages were obtained for 2434 individuals spanning 30 tree species across a nationwide network of 128 plots in 14 naturally reforesting post-agricultural sites. These ages were used to calculate individual-level arrival times (relative to the oldest individual in each plot). We estimated species-level arrival times by fitting linear mixed-effects (LME) regressions (with species identity as the fixed effect, and plots nested within sites as the random effects) to individual arrival time data. We used back-casting (where arrival time data are used to document individual-level presence in plots through time) to track annual changes in species abundance and community-weighted mean (CWM) trait values.

We used standardised major axis (SMA) regressions to examine the effect of traits related to resource use strategy, herbivory avoidance, seed dispersal and disturbance response on species-level arrival times. We used LME regressions to test for changes in CWM trait values with stand age.

Results

The earliest-arriving species had traits associated with herbivory avoidance, were abiotically dispersed and had short predicted dispersal distances. There was no evidence that traits linked to resource use strategy or disturbance response affected species arrival times. Every significant species-level relationship was recovered in community-level LME analyses.

Conclusions

Our findings suggest that mammalian herbivore control and enhancement of biotic (bird) seed dispersal may be key management interventions in realising the full climate mitigation and adaptation potential of natural reforestation in post-agricultural landscapes.