Plant Community Phenology Research Articles

Gender dimorphic species flower earlier than cosexuals

Abstract The timing of flowering is central to plant life‐history as it initiates sexual reproduction, thus controlling plant interaction with pollinators and climate factors. A fundamental question is: what are the drivers of flowering time strategy in a species? We assembled mean flowering times for the indigenous dicotyledonous flora of New Zealand (n = 1303 species, including 177 tree species) and used phylogenetic models to determine how climate, plant traits, and evolutionary history (phylogeny) controlled interspecific variation in flowering times across an island flora. Across all species, on average, flowering was 19 days earlier in abiotically pollinated species relative to biotically pollinated species, 23 days earlier in woody species, relative to herbaceous species, 45 days earlier in species with fleshy‐fruits, relative to species with dry fruits and 31 days earlier in gender dimorphic species, relative to cosexual species. Species in warmer and drier climates flowered earlier than those growing under cool, moist climates. When all factors were considered together, the strongest influence on flowering time was sexual system: gender dimorphic species flowered earlier than cosexuals, even after accounting for other factors. Synthesis. We propose that these differences in flowering time arise because of sexual selection for early male flowering and sexual conflict between male and female individuals. As sexual selection and conflict may be stronger in gender dimorphic species than in cosexual species, our study suggests that plant sexual system is an important force structuring the phenology of plant communities, with potential consequences for ecological interactions and ecosystem processes.

Differences in individual flowering time change pollen limitation and seed set in three montane wildflowers.

Changes to flowering time caused by climate change could affects plant fecundity, but studies that compare the individual-level responses of phenologically distinct, co-occurring species are lacking. We assessed how variation in floral phenology affects the fecundity of individuals from three montane species with different seasonal flowering times, including in snowmelt acceleration treatments to increase variability in phenology. We collected floral phenology and seed set data for individuals of three montane plant species (Mertensia fusiformis, Delphinium nuttallianum, Potentilla pulcherrima). To examine the drivers of seed set, we measured conspecific floral density and conducted pollen limitation experiments to isolate pollination function. We advanced the phenology of plant communities in a controlled large-scale snowmelt acceleration experiment. Differences in individual phenology relative to the rest of the population affected fecundity in our focal species, but effects were species-specific. For our early-season species, individuals that bloomed later than the population peak bloom had increased fecundity, while for our midseason species, simply blooming before or after the population peak increased individual fecundity. For our late-season species, blooming earlier than the population peak increased fecundity. The early and midseason species were pollen-limited, and conspecific density affected seed set only for our early-season species. Our study shows that variation in individual phenology affects fecundity in three phenologically distinct montane species, and that pollen limitation may be more influential than conspecific density. Our results suggest that individual-level changes in phenology are important to consider for understanding plant reproductive success.

Phenological patterns of herbaceous Mediterranean plant communities in spring: is there a difference between native and formerly-cultivated grasslands?

Background and aims – Plant phenology, defined as the timing of recurring life events like leaf flushing, flowering, or fruiting, is highly sensitive to environmental factors such as photoperiod, temperature, and moisture. Phenological synchrony between interacting species – such as plants and their pollinators – is of major importance to the structure and functioning of ecosystems. Plant phenology might also be affected by changes in edaphic conditions. However, whether former agricultural activities may shift phenological patterns of plant communities remains poorly understood. In this study, we evaluated the impact of past agricultural practices on herbaceous plant community phenology in the protected Mediterranean xeric grassland of La Crau (France). Material and methods – We compared (1) species composition, and (2) phenological patterns of annuals, perennials, Bromus rubens (annual), and Lobularia maritima (perennial), in formerly-cultivated plots – abandoned for 30 years – and intact native grassland plots (steppe), both subjected to itinerant sheep grazing. Key results and conclusion – Our results suggest that former agricultural activities can affect species composition of Mediterranean xeric grassland communities with differences visible after 30 years of abandonment, but only altered phenological patterns slightly. We suggest that climatic factors and sheep grazing acted as strong habitat filters constraining community assembly at the phenological level.

Phylogenetic restriction of plant invasion in drought-stressed environments: Implications for insect-pollinated plant communities in water-limited ecosystems.

BackgroundPlant–pollinator community diversity has been found to decrease under conditions of drought stress; however, research into the temporal dimensions of this phenomenon remains limited. In this study, we investigated the effect of seasonal drought on the temporal niche dynamics of entomophilous flowering plants in a water‐limited ecosystem. We hypothesized that closely related native and exotic plants would tend to share similar life history and that peak flowering events would therefore coincide with phylogenetic clustering in plant communities based on expected phenological responses of plant functional types to limitations in soil moisture availability.LocationGaliano Island, British Columbia, Canada.MethodsCombining methods from pollinator research and phylogenetic community ecology, we tested the influence of environmental filtering over plant community phenology across gradients of landscape disturbance and soil moisture. Floral resource availability and community structure were quantified by counts of flowering shoots. We constructed a robust phylogeny to analyze spatial and temporal variation in phylogenetic patterns across the landscape, testing the significance of the observed patterns against a randomly generated community phylogeny. Phylogenetic metrics were then regressed against factors of disturbance and soil moisture availability.ResultsCritical seasonal fluctuations in floral resources coincided with significant phylogenetic clustering in plant communities, with decreasing plant diversity observed under conditions of increasing drought stress. Exotic plant species in the Asteraceae became increasingly pervasive across the landscape, occupying a late season temporal niche in drought‐stressed environments.Main conclusionResults suggest that environmental filtering is the dominant assembly process structuring the temporal niche of plant communities in this water‐limited ecosystem. Based on these results, and trends seen elsewhere, the overall diversity of plant–pollinator communities may be expected to decline with the increasing drought stress predicted under future climate scenarios.

Targeted Grazing of an Invasive Grass Improves Outcomes for Native Plant Communities and Wildlife Habitat

Rangelands provide ecosystem services that are economically and ecologically critical for humans. Globally, invasion of exotic grasses drives loss of biodiversity and resilience of rangelands. In South Texas, buffelgrass (Cenchrus ciliaris syn. Pennisetum ciliare [L.] Link), a C4 perennial grass, was brought from Africa for range improvement as early as the 1930s. Buffelgrass generally increases forage biomass for livestock yet reduces habitat suitability for wildlife. Interest in controlling buffelgrass has increased due to its negative impacts on iconic wildlife, such as whitetailed deer (Odocoileus virginianus, Zimmermann 1780) and northern bobwhite (Colinus virginianus, Linnaeus 1758). The objective of this study was to evaluate the effect of a targeted grazing strategy that used buffelgrass and plant community phenology as indicators to determine the timing of cattle movement. On two private ranches in different ecoregions, we tracked targeted grazing versus light grazing in native-dominated and buffelgrass-dominated plant communities across variable precipitation through five growing seasons. We measured the effects of grazing type, plant community type, and precipitation on buffelgrass cover, native plant species richness, foliar cover, and Shannon diversity. Targeted grazing had a strong impact on diversity, increasing 0.37 ± 0.07 from a mean of H = 1.29 under the targeted grazing management. Conversely, buffelgrass cover was negatively correlated with Shannon diversity, decreasing it by 0.075 ± 0.03 for every 10% increase in buffelgrass cover from a mean of H = 1.29. Despite a variability in precipitation across seasons and years (93−455 mm), targeted grazing improved species richness and cover of native plants throughout the study. Our findings suggest that targeted grazing shows promise as an adaptive grazing strategy that reduces the impact of buffelgrass across highly variable precipitation. In unpredictable environments, management techniques that improve the resilience of plant communities through preserving biodiversity are critical.

Divergent Responses of Community Reproductive and Vegetative Phenology to Warming and Cooling: Asymmetry Versus Symmetry.

Few studies have focused on the response of plant community phenology to temperature change using manipulative experiments. A lack of understanding of whether responses of community reproductive and vegetative phenological sequences to warming and cooling are asymmetrical or symmetrical limits our capacity to predict responses under warming and cooling. A reciprocal transplant experiment was conducted for 3 years to evaluate response patterns of the temperature sensitivities of community phenological sequences to warming (transferred downward) and cooling (transferred upward) along four elevations on the Tibetan Plateau. We found that the temperature sensitivities of flowering stages had asymmetric responses to warming and cooling, whereas symmetric responses to warming and cooling were observed for the vegetative phenological sequences. Our findings showed that coverage changes of flowering functional groups (FFGs; i.e., early-spring FFG, mid-summer FFG, and late-autumn FFG) and their compensation effects combined with required accumulated soil temperatureto codetermined the asymmetric and symmetric responses of community phenological sequences to warming and cooling. These results suggest that coverage change in FFGs on warming and cooling processes can be a primary driver of community phenological variation and may lead to inaccurate phenlogical estimation at large scale, such as based on remote sensing.

Spatial and temporal variation in plant community phenology in the Jebel Marra region of Darfur

This study was designed to examine the subtle effects of habitat, aspect and altitude on plant diversity and the timing of phenological stages. In this increasingly arid region, within-species differences would cause more reproductive isolation of local populations, making species more vulnerable to regional extinction. Fifty-two sites in the Jebel Marra region of the Central Darfur state of Sudan were compared in terms of species diversity and local variation in the phenology of plant communities. Five habitat types were compared: sandy plains, clay plains, wadis, north-facing slopes and south-facing slopes. Sites were classified into five altitudinal zones ranging from 750 m to > 1,150 m above sea level, and the phenology of three categories of plant life form (phanerophytes, chamaephytes and therophytes) was tracked in terms of the duration of each phenophase (vegetative, reproductive and dormant). Overall, most plants were dormant from December to April. Peak vegetative growth was in July, coinciding with peak rainfall in all study sites in the region (July-August). This was followed by peak reproduction in October. Life form and habitat type significantly affected the length of all phenological phases; altitude significantly affected all stages except the duration of dormancy. Some of the interactions between these factors were also statistically significant, indicating subtle regulation of the duration of phenophases. The possible impacts of overgrazing and ongoing climate change are discussed, with the concern that initiation of vegetative growth in most habitats (except the clay plains) appears to be triggered by day length, ‘anticipating’ the beginning of the rainy season. Further climate change may uncouple this signal and the beginning of the rainy season, impacting plant survival.

Response of primary and secondary rainforest flowers and fruits to a cyclone, and implications for plant-servicing bats.

The response of primary (PF) and secondary (SF) rainforests to cyclones has broad implications for servicing fauna and the resilience of forest functions. We collected fine-scale data on the reproductive phenology of plant communities in Fijian PF and SF in 12 monthly surveys before and after Cyclone Tomas (2010). We generated a resource index from the reproductive loads of 2218 trees and 1150 non-trees (>190 species) and trunk and stem diameter to assess patterns in resource abundance for nectarivores and frugivores (hereafter NF resources). We aimed to determine (i) whether species richness of NF resources differed between forests; (ii) the patterns of resilience of NF resources at community level in both forests after a cyclone; and (iii) the effect of response on NF resources for plant-servicing bats (Pteropodidae). In 12months preceding the cyclone, NF resources were greater in PF trees; non-tree resources fluctuated and were greater in SF. Lower species richness of NF resources in SF indicated that fewer opportunities exist there for exploitation by a diverse fauna. More resources were available for bats in PF. In 12months following the cyclone, PF flowers and fruits, and SF fruits specifically used by pteropodid bats decreased for trees. Non-tree resources were especially susceptible to the cyclone. No universal pattern of decline was associated with the cyclone; instead, some NF resources declined and others were resilient or responded rapidly to a post-cyclone environment. Both PF and SF demonstrated resilience at the community level via increased flower survival (PF) and rapid flower production (SF). Reduced species richness of NF resources in SF will compromise future resilience and response to disturbance, including for threatened pteropodid bat species. These findings are critical for long-term management of forests, given predicted increases in cyclone frequency and intensity associated with anthropogenic climate change.

Intrinsic and extrinsic factors acting on the reproductive process in alpine‐snowbed plants: roles of phenology, biological interaction, and breeding system

AbstractPollinator activity and competition for pollinators lead to quantitative and qualitative pollen limitations on seed production and affect the reproductive success of plant species, depending on their breeding system (e.g., self‐compatibility and heterospecific compatibility) and genetic load (e.g., inbreeding depression and hybrid inviability). In alpine ecosystems, snowmelt regimes determine the distribution and phenology of plant communities. Plant species growing widely along a snowmelt gradient often grow with different species among local populations. Their pollinators also vary in their abundance, activity, and behavior during the season. These variations may modify plant–pollinator and plant–plant interactions. We integrated a series of our studies on the alpine dwarf shrub, Phyllodoce aleutica (Ericaceae), to elucidate the full set of intrinsic (species‐specific breeding system) and extrinsic factors (snow condition, pollinator activity, and interspecific competition) acting on their reproductive process. Seasonality of pollinator activity led to quantitative pollen limitation in the early‐blooming populations, whereas in the late‐blooming populations, high pollinator activity ensured pollination service, but interspecific competition for pollinators led to qualitative and quantitative pollen limitation in less competitive species. However, negative effects of illegitimate pollen receipt on seed‐set success might be reduced when cryptic incompatibility systems (i.e., outcross pollen grains took priority over self‐ and heterospecific pollen grains) could effectively prevent ovule and seed discounting. Our studies highlight the importance of species‐specific responses of plant reproduction to changing pollinator availability along environmental gradients to understand the general features of pollination networks in alpine ecosystems.

Plant phenology and life span influence soil pool dynamics: Bromus tectorum invasion of perennial C3–C4 grass communities

In water-limited ecosystems, small rainfall events can have dramatic impacts on microbial activity and soil nutrient pools. Plant community phenology and life span also affect soil resources by determining the timing and quantity of plant nutrient uptake, storage, and release. Using the replacement of C3–C4 perennial grasses by the invasive annual grass Bromus tectorum as a case study, we investigated the influence of phenology and life span on pulse responses and sizes of soil carbon (C) and nitrogen (N) pools. We hypothesized that available and microbial C and N would respond to small rainfall events and that B. tectorum invasion would increase soil C and N pools by reducing inter-annual plant C and N storage and alter seasonal pool dynamics by changing the timing of plant uptake and litter inputs. We tested our hypotheses by simulating small rainfall events in B. tectorum and perennial grass communities three times during the growing season. Microbial pools responded strongly to soil moisture and simulated rainfall events, but labile C and N pools were affected weakly or not at all. All pools were larger beneath B. tectorum than perennial grasses. Soil C and N pools increased after senescence in both communities. Our results suggest that transforming a perennial into a B. tectorum dominated community increases the overall size of soil C and N pools by decreasing plant C and N storage and changes seasonal pool dynamics by altering dominant plant phenology. Our results indicate strong roles for water, life span and phenology in controlling soil C and N pools and begin to elucidate the biogeochemical effects of altering plant community phenology and life span.

Net ecosystem CO2 exchange in Mojave Desert shrublands during the eighth year of exposure to elevated CO2

AbstractArid ecosystems, which occupy about 35% of the Earth's terrestrial surface area, are believed to be among the most responsive to elevated [CO2]. Net ecosystem CO2 exchange (NEE) was measured in the eighth year of CO2 enrichment at the Nevada Desert Free‐Air CO2 Enrichment (FACE) Facility between the months of December 2003–December 2004. On most dates mean daily NEE (24 h) (μmol CO2 m−2 s−1) of ecosystems exposed to elevated atmospheric CO2 were similar to those maintained at current ambient CO2 levels. However, on sampling dates following rains, mean daily NEEs of ecosystems exposed to elevated [CO2] averaged 23 to 56% lower than mean daily NEEs of ecosystems maintained at ambient [CO2]. Mean daily NEE varied seasonally across both CO2 treatments, increasing from about 0.1 μmol CO2 m−2 s−1 in December to a maximum of 0.5–0.6 μmol CO2 m−2 s−1 in early spring. Maximum NEE in ecosystems exposed to elevated CO2 occurred 1 month earlier than it did in ecosystems exposed to ambient CO2, with declines in both treatments to lowest seasonal levels by early October (0.09±0.03 μmol CO2 m−2 s−1), but then increasing to near peak levels in late October (0.36±0.08 μmol CO2 m−2 s−1), November (0.28±0.03 μmol CO2 m−2 s−1), and December (0.54±0.06 μmol CO2 m−2 s−1). Seasonal patterns of mean daily NEE primarily resulted from larger seasonal fluctuations in rates of daytime net ecosystem CO2 uptake which were closely tied to plant community phenology and precipitation. Photosynthesis in the autotrophic crust community (lichens, mosses, and free‐living cyanobacteria) following rains were probably responsible for the high NEEs observed in January, February, and late October 2004 when vascular plant photosynthesis was low. Both CO2 treatments were net CO2 sinks in 2004, but exposure to elevated CO2 reduced CO2 sink strength by 30% (positive net ecosystem productivity=127±17 g C m−2 yr−1 ambient CO2 and 90±11 g C m−2 yr−1 elevated CO2, P=0.011). This level of net C uptake rivals or exceeds levels observed in some forested and grassland ecosystems. Thus, the decrease in C sequestration seen in our study under elevated CO2– along with the extensive coverage of arid and semi‐arid ecosystems globally – points to a significant drop in global C sequestration potential in the next several decades because of responses of heretofore overlooked dryland ecosystems.

An analysis of relationships among plant community phenology and seasonal metrics of Normalized Difference Vegetation Index in the northern part of the monsoon region of China.

This study focuses on relationships between the phenological growing season of plant communities and the seasonal metrics of Normalized Difference Vegetation Index (NDVI) at sample stations and pixels overlying them, and explores the procedure for determining the growing season of terrestrial vegetation at the regional scale, using threshold NDVI values obtained by surface-satellite analysis at individual stations/pixels. The cumulative frequency of phenophases has been calculated for each plant community and each year in order to determine the growing season at the three sample stations from 1982 to 1993. The precise thresholds were arbitrarily set as the dates on which the phenological cumulative frequency reached 5% and 10% (for the beginning) and 90% and 95% (for the end). The beginning and end dates of the growing season were then applied each year as time thresholds, to determine the corresponding 10-day peak greenness values from NDVI curves for 8-km2 pixels overlying the phenological stations. According to a trend analysis, a lengthening of the growing seasons and an increase of the integrated growing season NDVI have been detected in the central part of the research region. The correlation between the beginning dates of the growing season and the corresponding threshold NDVI values is very low, which indicates that the satellite-sensor-derived greenness is independent of the beginning time of the growing season of local plant communities. Other than in spring, the correlation between the end dates of the growing season and the corresponding threshold NDVI values is highly significant. The negative correlation shows that the earlier the growing season terminates, the larger the corresponding threshold NDVI value, and vice versa. In order to estimate the beginning and end dates of the growing season using the threshold NDVI values at sites without phenological data from 1982 to 1993, we calculated the spatial correlation coefficients between NDVI time-series at each sample station and other contiguous sites year by year. The results provide the spatial extrapolation area of the growing season for each sample station. Thus, we can use the threshold NDVI value obtained at one sample station/pixel for a year to determine the growing season at the extrapolation sites with a similar vegetation type for the same year.