Shoot Recruitment Research Articles

A pilot restoration of Enhalus acoroides by transplanting dislodged rhizome fragments and its effect on the microbial diversity of submarine sediments

Enhalus acoroides, the largest seagrass species in terms of morphology, has been observed to be declining significantly. In an effort to restore seagrass meadows, we conducted a transplantion utilizing dislodged rhizome fragments of E. acoroides as the donor materials. The growth of transplanted seagrass was monitored over a period of three years, and the impact of seagrass recolonization on sedimentary environment was assessed through analysis of sediment microbial diversity. The transplanted plants displayed notable growth, resulting in the successful recolonization of experimental plots by seagrass. The 3-year data also revealed the following findings: 1) the new shoot recruitment rate (per year) (NSR) of transplanted seagrass was 2.33 in the first year, 1.36 in the second year, and 0.83 in the third year, indicating a rapid initial growth rate of E. acoroides that subsequently slowed down; 2) the numbers of shoots and aboveground biomass of transplanted seagrass had increased by 13.0 and 15.9-fold, respectively, whereas only 3.3 and 5.3-fold increases of the natural seagrass were observed, suggesting that the transplantation of seagrass leads to a significantly accelerated recovery compared to its natural regeneration process. Furthermore, the restoration of E. acoroides resulted in a higher microbial diversity in the submarine sediments within the restoration area, as compared to the adjacent unvegetated area. This suggests that the re-vegetation of E. acoroides has a positive influence on the overall health of the sedimentary environment. This study strongly advocates for the active transplantation of dislodged E. acoroides plants resulting from human activities as a potential approach for future coastal management, specifically for the restoration of E. acoroides meadows.

Seasonal shifts in morphology, physiology and population traits in the seagrass Halodule wrightii (Cymodoceaceae) in a subtropical arid area

A seasonal field monitoring study was carried out to evaluate for the first time in Bahía Balandra (Southern Gulf of California) the changes in morphology, phenology and physiological traits in the seagrass Halodule wrightii. Seasonally, traits associated with morphology (leaf, sheath and rhizome), shoot density, biomass and physiology (non-structural carbohydrates, carbon and nitrogen contents) were measured between winter 2016 and spring 2017. Overall, all the traits varied across the seasons, with most of morphological characteristics, density and biomass peaking during autumn and showing the lowest values in winter-spring. Sexual reproduction was not observed, thus vegetative (asexual) propagation was the main strategy in this population. Both branching and shoot recruitment explained the increase in above- and belowground biomass in summer-autumn. The high starch concentrations found during winter, suggested that autumn is a suitable season for the growth of H. wrightii, investing a large fraction of their energy in producing biomass, but also in carbon storage (i.e. starch) in both tissues (above and belowground). This kind of study is needed in the protected area of Bahía Balandra in the Gulf of California and in general in Mexico, since H. wrightii has been recently categorized as a threatened species in Mexico and management actions demand current and accurate biological data for appropriate conservation actions.

Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea nodosa: Evidence from volcanic seeps

Population reconstruction techniques was used to assess for the first time the population dynamics of a seagrass, Cymodocea nodosa, exposed to long-term elevated CO2 near three volcanic seeps and compared them with reference sites away from the seeps. Under high CO2, the density of shoots and of individuals (apical shoots), and the vertical and horizontal elongation and production rates, were higher than at the reference sites. Nitrogen limitation effects on rhizome elongation and production rates and on biomass were more evident than CO2 as these were highest at the location where the limitation of nitrogen was highest. At the seep where the availability of CO2 was highest and nitrogen lowest, density of shoots and individuals were highest, probably due to CO2 effects on shoot differentiation and induced reproductive output, respectively. At the three seeps, there was higher short- and long-term shoot recruitment than at the reference sites, and growth rates was around zero, indicating that elevated CO2 increases the turnover of C. nodosa shoots.

Tropical seagrass Halophila stipulacea shifts thermal tolerance during Mediterranean invasion.

Exotic species often face new environmental conditions that are different from those that they are adapted to. The tropical seagrass Halophila stipulacea is a Lessepsian migrant that colonized the Mediterranean Sea around 100 years ago, where at present the minimum seawater temperature is cooler than in its native range in the Red Sea. Here, we tested if the temperature range in which H. stipulacea can exist is conserved within the species or if the exotic populations have shifted their thermal breadth and optimum due to the cooler conditions in the Mediterranean. We did so by comparing the thermal niche (e.g. optimal temperatures, and upper and lower thermal limits) of native (Saudi Arabia in the Red Sea) and exotic (Greece and Cyprus in the Mediterranean Sea) populations of H. stipulacea. We exposed plants to 12 temperature treatments ranging from 8 to 40°C for 7 days. At the end of the incubation period, we measured survival, rhizome elongation, shoot recruitment, net population growth and metabolic rates. Upper and lower lethal thermal thresholds (indicated by 50% plant mortality) were conserved across populations, but minimum and optimal temperatures for growth and oxygen production were lower for Mediterranean populations than for the Red Sea one. The displacement of the thermal niche of exotic populations towards the colder Mediterranean Sea regime could have occurred within 175 clonal generations.

Carbon and nitrogen allocation strategy in Posidonia oceanica is altered by seawater acidification

Rising atmospheric CO2 causes ocean acidification that represents one of the major ecological threats for marine biota. We tested the hypothesis that long-term exposure to increased CO2 level and acidification in a natural CO2 vent system alters carbon (C) and nitrogen (N) metabolism in Posidonia oceanica L. (Delile), affecting its resilience, or capability to restore the physiological homeostasis, and the nutritional quality of organic matter available for grazers. Seawater acidification decreased the C to N ratio in P. oceanica tissues and increased grazing rate, shoot density, leaf proteins and asparagine accumulation in rhizomes, while the maximum photochemical efficiency of photosystem II was unaffected. The 13C-dilution in both structural and non-structural C metabolites in the acidified site indicated quali-quantitative changes of C source and/or increased isotopic fractionation during C uptake and carboxylation associated with the higher CO2 level. The decreased C:N ratio in the acidified site suggests an increased N availability, leading to a greater storage of 15N–enriched compounds in rhizomes. The amount of the more dynamic C storage form, sucrose, decreased in rhizomes of the acidified site in response to the enhanced energy demand due to higher shoot recruitment and N compound synthesis, without affecting starch reserves. The ability to modulate the balance between stable and dynamic C reserves could represent a key ecophysiological mechanism for P. oceanica resilience under environmental perturbation. Finally, alteration in C and N dynamics promoted a positive contribution of this seagrass to the local food web.

Effects of Copper Exposure on Photosynthesis and Growth of the Seagrass Cymodocea nodosa: An Experimental Assessment.

Seagrasses form some of the most important coastal habitats. They may be negatively affected by trace metal contamination in certain coastal areas. In this study we experimentally assessed selected morphological and physiological traits of the seagrass Cymodocea nodosa, with increasing concentrations of copper (Cu) under controlled laboratory conditions. Short term (21days) sub-lethal effects such as decreased maximum quantum yield, increased leaf necrosis and decreased shoot growth and shoot recruitment were clearly observed at the highest Cu exposure (5mgL(-1)), while the effects were weaker at the intermediate concentration (2.5mgL(-1)) and almost absent at the lowest concentration (1mgL(-1)), indicating that this species is highly tolerant to copper exposure, at least in the short term. This fact could help to explain its distribution in relatively polluted coastal waters.

Designing and Evaluating Bamboo Harvesting Methods for Local Needs: Integrating Local Ecological Knowledge and Science.

Dendrocalamus hamiltonii, a large, clump-forming bamboo, has great potential to contribute towards poverty alleviation efforts across its distributional range. Harvesting methods that maximize yield while they fulfill local objectives and ensure sustainability are a research priority. Documenting local ecological knowledge on the species and identifying local users’ goals for its production, we defined three harvesting treatments (selective cut, horseshoe cut, clear cut) and experimentally compared them with a no-intervention control treatment in an action research framework. We implemented harvesting over three seasons and monitored annually and two years post-treatment. Even though the total number of culms positively influenced the number of shoots regenerated, a much stronger relationship was detected between the number of culms harvested and the number of shoots regenerated, indicating compensatory growth mechanisms to guide shoot regeneration. Shoot recruitment declined over time in all treatments as well as the control; however, there was no difference among harvest treatments. Culm recruitment declined with an increase in harvesting intensity. When univariately assessing the number of harvested culms and shoots, there were no differences among treatments. However, multivariate analyses simultaneously considering both variables showed that harvested output of shoots and culms was higher with clear cut and horseshoe cut as compared to selective cut. Given the ease of implementation and issues of work safety, users preferred the horseshoe cut, but the lack of sustainability of shoot production calls for investigating longer cutting cycles.

Tending the meadows of the sea: A disturbance experiment based on traditional indigenous harvesting of Zostera marina L. (Zosteraceae) the southern region of Canada’s west coast

Indigenous Peoples of the Northwest Coast Cultural Area of North America managed plant populations of many of the 100–200 species used for food and other purposes, through cultivation and selective harvesting. Eelgrass (Zostera marina, L.; Zosteraceae) was one of these species. The Kwakwaka’wakw harvested its sweet rhizomes in the springtime. Directed by the traditional knowledge of Clan Chief Adam Dick, whose hereditary name is Kwaxsistalla, of the Tsawataineuk First Nation of Kingcome Inlet (one of the many communities of Kwakwaka’wakw, or Kwak’wala speaking Indigenous peoples of the West Coast of British Columbia), we investigated the protocols of traditional harvesting and tending on typical Z. marina populations in the Discovery Islands area. We interviewed 18 Kwakwaka’wakw knowledge holders and conducted six harvesting demonstrations to determine traditional harvesting protocols. Based on traditional protocols and traditional Z. marina management inferences, we developed an in situ, subtidal, Complete Randomized Block Design removal experiment in an eelgrass meadow on Quadra Island, BC. In a first exploratory study, we removed Z. marina shoots at three different intensities using SCUBA in defined quadrats in the springtime. Shoots were counted at the end of summer to examine shoot recruitment post treatment over the growing season. Our preliminary results showed no significant difference between treatments. However, with more replicates, we might have strengthened the tendency of more shoots in the harvested quadrats. Here our main intention is to describe our unique study of a marine plant resource harvested in traditional times by Kwakwaka’wakw peoples and to outline a new experimental methodology to examine ecological rationale behind traditional knowledge. We hope to stimulate new and important avenues of research on this topic.

Annual and perennial life history strategies of Zostera marina populations under different light regimes

The seagrass Zostera marina is geneti- cally considered to be perennial, but annual popula- tions of this species exist as well and are under severe environmental stress in many geographical locations. We investigated why Z. marina in Jindong Bay (Korea) exhibited a typical perennial life history at a shallow site but an annual life history at a deep site. We hy- pothesized that Z. marina shoots in the deep popula- tion die off after fall due to severe light reductions, and that the re-establishment of this population is completely dependent on sexual reproduction. Life histories of these populations were examined by con- structing life tables using monthly measurements of shoot recruitment and mortality. In the deep popu - lation, new shoot recruitment was only achieved by seedlings, and approximately 95% of the surviving seedlings flowered. No shoots overwintered in the deep population. In contrast, shoot recruitment in the shallow population was primarily achieved by asexual reproduction. High summer water temperatures and subsequent severe underwater light reduction during summer and fall probably led to the high mortality in Z. marina shoots in the deep population, resulting in no shoot survival after fall. The deep population likely exhibits an annual life history strategy to achieve pop- ulation persistence under repetitive and acute unfa- vorable environmental conditions. From an evolution- ary perspective, the life history traits of Z. marina would define this species as an intermediate between annual and perennial.

Seasonal uncoupling of demographic processes in a marine clonal plant

In temperate regions, climatic factors impose a general seasonal pattern on seagrass growth that can be observed in leaf growth rates and, in small species, also in shoot density. Large variations in shoot density suggest a strong temporal uncoupling between shoot recruitment and shoot mortality, and the dependence of each of these processes on different drivers. Here we examine seasonal patterns of recruitment and mortality in the seagrass Cymodocea nodosa, one of the species most sensitive to seasonal forcing in the Mediterranean. We sampled two local populations submitted to different nutrient availability in Alfacs Bay (NW Mediterranean) and determined recruitment and mortality rates, as well as other plant traits, on a monthly basis. Our results confirm the hypothesized uncoupling, with maximum mortality 2 months after maximum recruitment. Whereas timing of recruitment was associated with light availability, and was supported by carbohydrate remobilisation, mortality was related to high water temperatures and probably also to light limitation in late summer due to self-shading. In the high-nutrient population, algal overgrowth caused further light deprivation, with mortality rates higher than in the low-nutrient population. It is emphasised that the demographic balance of the studied populations was negative for most of the year, with the exception of August and September. Therefore, caution is necessary when overall population trends are inferred from single annual sampling events.

Estimation of dieback process caused by herbivory in an endangered root-sprouting shrub species, Paliurus ramosissimus (Lour.) Poir., using a shoot-dynamics matrix model

Mortality, a critical parameter for population dynamics, is difficult to measure in long-lived trees or clonal herbaceous species because of the extremely low frequency of deaths. A model based on shoot recruitment would be helpful to estimate the population fate of species without a sufficient number of observed deaths. Existing matrix models are applicable to the dynamics of physiologically independent shoots, but not to physiologically dependent ones. We developed a shoot-dynamics model for plants with physiologically-dependent shoots, and used the model to estimate the effects of herbivory and conservation measures on the dynamics of a long-lived, shoot-sprouting shrub species, Paliurus ramosissimus (Rhamnaceae). Two populations of the endangered shrub have been severely damaged by herbivory by sika deer. The damage was mainly to new sprouting shoots. No deaths of individual plants were observed during an 8-year survey, and we could not estimate mortality. Thus, prediction of population dynamics based on births and deaths of individuals was impossible. Because P. ramosissimus is a shoot-sprouting species, we instead estimated the decline of individuals using a shoot-dynamics model. Using this model, we estimated the time to an 80 % decrease in shoot number per individual in the two populations at 37.8 and 37.2 years. These lengths suggest an immediate need for conservation measures to prevent herbivory even though no death of any individual was observed in the field survey. The estimated recovery times from the herbivory damage were 28.7 and 29.2 years if herbivory of new shoots is completely prevented by conservation measure.

Stand structure, growth and biomass of Arundinaria alpina (highland bamboo) along topographic gradient in the Choke Mountain, northwestern Ethiopia

Three landforms were evaluated for their effect on stand structure, growth and yield of Arundinaria alpina K. Schum in the Choke Mountain, northwest Ethiopia. Parameters on stand characteristics and soil properties were assessed. The landforms were (1) 5-15% level to sloping land, (2) 40-60% straight slope (ridge) and (3) 40-60% concave slope (valley). Altitude ranged from 2,870 to 2,938 m a.s.l. All parameters on stand characteristics, except the number of plants per hectare and shoot recruitment rate, were higher in the lower slope position (40-60% concave slope). On the other hand, except clay content and soil moisture, chemical soil properties had similar or better status on 5-15% level to sloping land followed by 40-60% straight slope. Significantly bigger diameter (average 8.4 cm) and emerging height culms (average 15 m) with high growth rate (average maximum of 43 cm day -1 ) and high biomass (117 t ha -1 ) were obtained in 40-60% concave slope landform. Hence, it can be concluded that landform is more influential than nutrient availability for performance of A. alpina in the Choke Mountain. Consequently, future bamboo afforestation practices are advised to focus primarily on 40-60% concave slope landform. The 40-60% straight slope is the second most important site for expanding A. alpina . Moreover, valleys and ridges are not suitable for annual crop production due to their steep slope. Therefore, superior performance of bamboo on these sites can be excellent opportunity for the area and the community. Key words/phrases : Afroalpine bamboo, Landform, Slope.

Contrasting bud bank dynamics of two co-occurring grasses in tallgrass prairie: implications for grassland dynamics

Because most shoot recruitment in perennial grasses occurs from belowground axillary buds, bud dynamics determine plant population dynamics and meristem limitation to population growth. Therefore, grassland vegetation responses to environmental change or disturbance may be influenced by interspecific differences in bud banks and the patterns and environmental controls of bud development and demography. We examined bud bank dynamics in Andropogon gerardii and Dichanthelium oligosanthes in tallgrass prairie by enumerating and classifying buds throughout 15 months to determine whether grass buds live for multiple years and accumulate; whether bud natality, dormancy and outgrowth are synchronous or variable; and whether bud bank dynamics differ between these co-occurring species. Andropogon gerardii (a C4 species) maintained a larger dormant bud bank, showed synchrony in bud development and transition to tiller, and its buds lived for multiple years. Thus, multiple previous years’ bud cohorts contributed to recruitment. By contrast, D. oligosanthes (a C3 species) maintained a smaller dormant bud bank, had asynchronous bud development with active buds present year-round, and its buds lived for 1 year. Buds played different roles in the dynamics of each species, allowing A. gerardii to over-winter and recruit new spring tillers and D. oligosanthes to survive and recruit new tillers following summer dormancy. These differences in bud bank age structure, phenology, and dynamics between these species suggest greater demographic buffering and time-lag effects in A. gerardii populations. Interspecific differences in bud bank structure and dynamics may explain and help predict grassland responses to environmental change.

Mediterranean warming triggers seagrass (Posidonia oceanica) shoot mortality

AbstractRapid warming of the Mediterranean Sea threatens marine biodiversity, particularly key ecosystems already stressed by other impacts such as Posidonia oceanica meadows. A 6‐year monitoring of seawater temperature and annual P. oceanica shoot demography at Cabrera Archipelago National Park (Balearic Islands, Western Mediterranean) allowed us to determine if warming influenced shoot mortality and recruitment rates of seagrasses growing in relative pristine environments. The average annual maximum temperature for 2002–2006 was 1 °C above temperatures recorded in 1988–1999 (26.6 °C), two heat waves impacted the region (with seawater warming up to 28.83 °C in 2003 and to 28.54 °C in 2006) and the cumulative temperature anomaly, above the 1988–1999 mean annual maximum temperature, during the growing season (i.e. degree‐days) ranged between 0 °C in 2002 and 70 °C in 2003. Median annual P. oceanica shoot mortality rates varied from 0.067 year−1 in 2002 to 0.123 year−1 in 2003, and exceeded recruitment rates in all stations and years except in shallow stations for year 2004. Interannual fluctuations in shoot recruitment were independent of seawater warming (P>0.05). P. oceanica meadows experienced a decline throughout the study period at an average rate of −0.050±0.020 year−1. Interannual variability in P. oceanica shoot mortality was coupled (R2>0.40) to seawater warming variability and increasing water depth: shoot mortality rates increased by 0.022 year−1 (i.e. an additional 2% year−1) for each additional degree of annual maximum temperature and by 0.001 year−1 (i.e. 0.1% year−1) for each accumulated degree water temperature remained above 26.6 °C during the growing season. These results demonstrate that P. oceanica meadows are highly vulnerable to warming, which can induce steep declines in shoot abundance as well indicating that climate change poses a significant threat to this important habitat.

Morphological plasticity of submerged macrophyte Potamogeton wrightii Morong under different photoperiods and nutrient conditions

The morphological plasticity of the submerged macrophyte Potamogeton wrightii under different nutrient conditions and photoperiods was measured in a laboratory controlled experiment for 70 days in Japan. Six treatments were used in this experiment (3 × 2 factorial design with three replications) which consisted of three photoperiods and two nutrient conditions. Both photoperiod and nutrient condition had a pronounced effect on shoot and leaf morphology in P. wrightii. New shoot recruitment, and the length of main and new shoots gradually decreased with shortening photoperiod under both nutrient treatments. Plants under an 8 h photoperiod and high nutrient levels generated significantly more dead leaves (7.42 leaf·shoot−1) and decomposed shoots (1.3 shoots·pot−1) than plants under other treatments. Under short photoperiods (12 and 8 h) plants failed to produce flowering spikes in both nutrient conditions. In high nutrient conditions, P. wrightii produced shorter shoots, fewer leaves with shorter and narrower laminas, and smaller petioles compared with plants in the low nutrient condition. This may be adaptive under high nutrient conditions because it lowers foliar uptake and, thus, nutrient toxicity.

Population dynamics of the seagrass Cymodocea nodosa in Ria Formosa lagoon following inlet artificial relocation

The population dynamics of the seagrass Cymodocea nodosa was investigated in three meadows differently affected by the artificial relocation of an inlet in the western sector of the Ria Formosa lagoon, southern Portugal. One meadow was subjected to increasing currents that caused erosion, another one was subjected to an initial episode of burial and a third meadow was undisturbed by the inlet opening. The hydrodynamic/sedimentary condition of meadows was assessed through comparative sediment analysis between the meadow and the adjacent unvegetated area. The studied C. nodosa meadows clearly reflected the resultant hydrodynamic changes and consequent sedimentary disturbances caused by the inlet opening, eleven months prior to sampling. In all meadows except the eroded one, C. nodosa promoted the accumulation and stabilization of sediments with grain-size dominated by a mode of 2.75 ϕ, much finer than the surrounding sediments, which grain-size was dominated by modes of 0.75–1.25 ϕ. Under the strong currents of the eroded meadow, the sediment was much coarser (mode of 0.75 ϕ), had less organic matter content and was not significantly different from the adjacent unvegetated area. A lower horizontal rhizome elongation, higher shoot mortality and lower shoot recruitment was observed at the eroded meadow indicating a strong population regression. Based on the sediment grain-size of the eroded meadow, it was inferred that the current velocity thresholds for C. nodosa decline occur at water current >60 cm s −1. Sediment burial resulted in longer leaf sheaths, higher vertical and horizontal rhizome elongation, lower shoot age, lower total biomass and higher shoot recruitment, which suggests population recovery after disturbance. The net recruitment of all studied meadows, including the undisturbed one, was negative, even though the buried meadow was close to zero. If environmental conditions will remain the same, all studied meadows are predicted to decline to extinction. Results thus suggest that the inlet relocation may alter the landscape distribution of C. nodosa meadows in Ria Formosa, but it was not the main cause of C. nodosa decline.

Seasonal dynamics of Posidonia oceanica in Magalluf Bay (Mallorca, Spain): Temperature effects on seagrass mortality

We recorded seasonal and interannual population dynamics of the endemic Mediterranean seagrass Posidonia oceanica in a shallow meadow, Magalluf Bay, Spain (39°30.25′N, 2°32.59′E), performing direct monthly‐bimonthly censuses from June 2001 to November 2004, in 12 permanent plots. Initially, there were 568 ± 54 (mean 6 SE) shoots m22. An average decline of ‐63 ± 10 SE shoots m−2 yr−1 was detected. Shoot mortality (median: 1.2% month−1; range: 0% to 12.1% month−1) increased in summer, enhanced by seawater temperature. There was also substantial interannual variability characterized by very high mortality in summer‐autumn 2001 and in autumn‐winter 2003–2004, coinciding with hot summers and meadow flowering in autumn (2001: 2.0% ± 1.4% of shoots; 2003: 53.8% ± 10.4% of shoots), but fruiting and seedling recruitment were only observed in 2004. Annual vegetative recruitment (0.034 ± 0.007 yr−1) was 53 times higher than annual sexual recruitment (0.0006 ± 0.0007 yr−1), and total recruitment (vegetative + sexual) was on average 4.5 times lower than mortality. Specific net population growth was always negative during the study. No seasonality was detected in shoot recruitment (median: 0.002 month−1; range: 0 to 0.021 month−1), which did not correlate with solar radiation or temperature. Shoots recruited during the study had a steeper exponential depletion rate (rr = ‐0.34 ± 0.05 SE yr−1) than the global population (rN0 = ‐0.16 ± 0.01 SE yr−1). Shoot probability to survive to the next age class (px) increased with shoot age. Our results suggest that the general decline of P. oceanica meadows could be enhanced by the decadal Mediterranean warming trend.

Spatial-temporal patterns of Bashania fargesii bamboo shoot emergence and giant panda herbivory

Bashania fargesii is an important food resource for giant panda in the Qinling Mountains, China, especially in winter and spring when giant panda prefers new shoots. Therefore, regeneration of B. fargesii is a key factor for conservation of the giant panda. B. fargesii regenerates mainly via new shoot recruitment. To identify spatial-temporal patterns of B. fargesii new shoot emergence and giant panda herbivory as well as spatial and quantitative associations between them, we established one 40 m 40 m permanent plot in Foping National Nature Reserve, and investigated new shoots of B. fargesii and giant panda herbivory from 2002 to 2 Biodiversity Science 17 2008 (except 2007). Results of univariate and bivariate Ripley’s K function demonstrated that new shoots of B. fargesii were aggregated in the plot, maybe due to clonal growth, resource heterogeneity, and giant panda herbivory and trampling. Giant panda herbivory was also clumped at most scales from 0 m to 20 m. This pattern may be explained by spatial patterns of a restricted food resource (B. fargesii new shoots), giant pandas’ herbivory habits, and topography of the forging sites. Giant panda herbivory was significantly spatially correlated to B. fargesii new shoots, confirming the importance of B. fargesii as an important food resource for giant panda in the Qinling Mountains. Regression analysis revealed no relationship between giant panda herbivory intensity (percentage of eaten shoots in the plot) and B. fargesii new shoot density, possibly indicating the existence of other bamboos as a food source for giant panda, suggesting a partial dependence of giant panda on B. fargesii.

Patch dynamics of the Mediterranean seagrass Posidonia oceanica: Implications for recolonisation process

Patch dynamics of the Mediterranean slow-growing seagrass Posidonia oceanica was studied in two shallow sites (3–10 m) of the Balearic Archipelago (Spain) through repeated censuses (1–2 year −1). In the sheltered site of Es Port Bay (Cabrera Island), initial patch density (October 2001) was low: 0.05 patches m −2, and the patch size (number of shoots) distribution was bimodal: most of the patches had less than 6 shoots or between 20 and 50 shoots. Mean patch recruitment in Es Port Bay (0.006 ± 0.002 patches m −2 year −1) exceeded mean patch loss (0.001 ± 0.001 patches m −2 year −1), yielding positive net patch recruitment (0.004 ± 0.003 patches m −2 year −1) and a slightly increased patch density 3 years later (July 2004, 0.06 patches m −2). In the exposed site of S’Estanyol, the initial patch density was higher (1.38 patches m −2, August 2003), and patch size frequency decreased exponentially with size. Patch recruitment (0.26 patches m −2 year −1) and loss (0.24 patches m −2 year −1) were high, yielding a slightly increased patch density in the area 1 year later (October 2004, 1.40 patches m −2). Most recruited patches consisted of rooting vegetative fragments of 1–2 shoots. Seedling recruitment was observed in Summer 2004 at both sites. Episodic, seedling recruitment comprised 30% and 25% of total patch recruitment in Es Port Bay and S’Estanyol, respectively. Patch survival increased with patch size and no direct removal was observed among patches of 5 shoots or more. Most patches grew along the study, shifting patch distribution towards larger sizes. Within the size range studied (1–150 shoots), absolute shoot recruitment (shoots year −1) increased linearly with patch size ( R 2 = 0.64, p < 4 × 10 −5, N = 125), while specific shoot recruitment was constant (about 0.25 ± 0.05 year −1), although its variance was large for small patches. Given the slow growth rate and the high survival of patches with 5 or more shoots, even the low patch recruitment rates reported here could play a significant role in the colonisation process of P. oceanica.

Comparing shoot population dynamics methods on Posidonia oceanica meadows

Prediction capacity of three main shoot population dynamics methods (age structure, net shoot recruitment per plagiotropic rhizome and shoot census) have been tested for a period of four years (2002–2006) on a Posidonia oceanica meadow. Accuracy of each method was checked by comparing measured and predicted densities at the end of the study period. Predicted densities came from the evolution of initial densities (measured in 2002) by a basic exponential model of population growth. The exponential model used the different net shoot recruitment rate estimates by each population dynamics method on three depths (upper, medium and lower limit) and three localities at each depth. Predictions performed by shoot census and net shoot recruitment per plagiotropic rhizome methods matched with measured densities at the end of the study period. Conversely, age structure method underestimated shoot densities at each depth, indicating an unreal decrease of shoot population in the meadow.