Partly decoupled tree-ring width and leaf phenology response to 20th century temperature change in Sweden

The recent warming trend, and associated shifts in growing season length, challenge the principle of uniformitarianism, i.e., that current relations are persistent over time, and complicates the uncritical inferences of past climate from tree-ring data. Here we conduct a comparison between tree-ring width chronologies of Pinus sylvestris L. (Scots pine), Picea abies (L.) Karst. (Norway spruce) and Betula pubescens Ehrh. (Downy birch) and phenological observations (budburst and leaf senescence) of Fagus sylvatica L. (European beech), Quercus robur L. (European oak), Betula sp. (Birch), Norway spruce and Scots pine) in Sweden to assess to what extent the tree-ring width–temperature relationship and the timing of phenological phases are affected by increased temperature. Daily meteorological observations confirm a prolongation of the thermal growing season, most consistently observed as an earlier onset of around 1–2 weeks since the beginning of the 20th century. Observations of budburst closely mimic this pattern, with budburst of the deciduous trees occurring 1–2.5 weeks earlier. In contrast to the changes seen in phenology and observational temperature data, the tree-ring width–temperature relationships remain surprisingly stable throughout the 20th century. Norway spruce, Scots pine and Downy birch all show consistently significant correlations with at least one 30 day-long window of temperature starting in late June–early July season. Norway spruce displays the largest degree of stability, with a consistent 60 day-long temperature window with significant correlation starting around Julian calendar day 150. Thus, our results suggest that the principle of uniformitarianism is not violated during the period covered by modern meteorological observations. Further research is needed to determine at what thresholds the temperature sensitivity of these species may alter or deteriorate as a consequence of the ongoing climate change.     

Performance of several models for predicting budburst date of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.)

The budburst stage is a key phenological stage for grapevine (Vitis vinifera L.), with large site and cultivar variability. The objective of the present work was to provide a reliable agro-meteorological model for simulating grapevine budburst occurrence all over France. The study was conducted using data from ten cultivars of grapevine (Cabernet Sauvignon, Chasselas, Chardonnay, Grenache, Merlot, Pinot Noir, Riesling, Sauvignon, Syrah, Ugni Blanc) and five locations (Bordeaux, Colmar, Angers, Montpellier, Epernay). First, we tested two commonly used models that do not take into account dormancy: growing degree days with a base temperature of 10°C (GDD₁₀), and Riou’s model (RIOU). The errors of predictions of these models ranged between 9 and 21 days. Second, a new model (BRIN) was studied relying on well-known formalisms for orchard trees and taking into account the dormancy period. The BRIN model showed better performance in predicting budburst date than previous grapevine models. Analysis of the components of BRIN formalisms (calculation of dormancy, use of hourly temperatures, base temperature) explained the better performances obtained with the BRIN model. Base temperature was the main driver, while dormancy period was not significant in simulating budburst date. For each cultivar, we provide the parameter estimates that showed the best performance for both the BRIN model and the GDD model with a base temperature of 5°C.     

Timing is everything? Phenological synchrony and population variability in leaf‐chewing herbivores of Quercus

Abstract.  1. Specialization on ephemeral resources (e.g. new leaves) should produce large annual variation in herbivore population size when the timing of availability of those resources is unpredictable. Despite considerable evidence for impacts of synchrony with budburst on survival of larval Lepidoptera, previous studies of adult Geometridae and Noctuidae found no correlations between insect phenology and population variability.
2. We surveyed larval Lepidoptera feeding on Quercus alba and Q. velutina in Missouri from 1993 to 2003 and examined population variability, measured as the coefficient of variation of population density (CV), in a subset of abundant species. We compared CV values among species whose larvae feed only in spring, early summer, mid-summer, late summer, or all season. We predicted that univoltine species whose larvae eclose and complete development in spring during leaf expansion would have higher variability than species feeding later in the season, having multiple generations, or having longer development times.
3. As predicted and consistent with hypotheses, spring-feeding species had CV values 32% higher than species feeding in summer months. Coefficients of variation were also 34% higher in leaf-rolling and mining guilds compared with free-feeders, suggesting that mobile species may compensate for asynchrony with budburst by dispersing to higher quality plants or plant parts. Multivoltine species, however, did not differ from univoltine species in population variability.
4. Our results suggest that asynchrony with plant phenology and factors that might exacerbate it, such as climate change, will have the largest impacts on the dynamics of spring-feeding Lepidoptera, particularly species with limited mobility.     

Effects of constant and fluctuating temperature on time to budburst in Betula pubescens and its relation to bud respiration

 Effects of fluctuating and constant temperatures on budburst time, and respiration in winter buds were studied in Betula pubescens Ehrh. Dormant seedlings were chilled at 0°C for 4 months and then allowed to sprout in long days (LD, 24 h) at constant temperatures of 6, 9, 12, 15, 18 and 21°C, and at diurnally fluctuating temperatures (12/12 h, LD 24 h) with means of 9, 12, 15 and 18°C. No difference in thermal time requirements for budburst was found between plants receiving constant and fluctuating temperatures. The base temperature for thermal time accumulation was estimated to 1°C. Respiration in post-dormant (dormancy fully released) excised winter buds from an adult tree increased exponentially with temperature and was 20 times as high at 30°C than at 0°C. However, respiration in buds without scales was 30% higher at 0°C, and it was 2.7 times higher at 24°C than in intact buds. Thus, the tight bud scales probably constrain respiration and growth and are likely to delay budburst in spring. Arrhenius plots of the respiration data were biphasic with breaks at 13–15°C. However, this phase transition is unlikely to be associated with chilling sensitivity since the present species is hardy and adapted to a boreal climate. Received: 10 January 1997 / Accepted: 23 June 1997     

Stem galls affect oak foliage with potential consequences for herbivory

Abstract.   1. On two dates, foliar characteristics of pin oak, Quercus palustris , infested with stem galls caused by the horned oak gall, Callirhytis cornigera , were investigated, and the consequences for subsequent herbivory assessed.
2. Second-instar caterpillars of the gypsy moth, Lymantria dispar , preferred foliage from ungalled trees.
3. Ungalled trees broke bud earlier than their galled counterparts.
4. Galled trees produced denser leaves with higher nitrogen and tannin concentrations, but foliar carbohydrates did not differ among galled and ungalled trees.
5. Concentrations of foliar carbohydrates in both galled and ungalled trees increased uniformly between the two assay dates. Nitrogen concentrations were greater in leaves from galled trees, and decreased uniformly in galled and ungalled trees over time. Foliar tannins were also greater in foliage from galled trees early in the season; however, foliar tannins declined seasonally in galled tissue so that by the second assay date there was no difference in tannin concentrations between galled and ungalled foliage.
6. In spite of differences in foliar characteristics, performance of older, fourth instar gypsy moth caterpillars did not differ between galled and ungalled trees.     

Phenological olive chilling requirements in Umbria (Italy) and Andalusia (Spain)

Phenological observations in olive tree (Olea europaea L.), on the first reproductive phase (budburst) and the winter chilling temperatures required for its onset, were analysed over a 4-year period (1998 - 2001). Research was carried out on two different cultivars growing in two Mediterranean olive-growing areas: 'Ascolana' in central Italy and 'Picudo' in southern Spain. The two main objectives of the study were: (1) to evaluate the different amounts of winter chilling, and their relationship with the budburst dates in outdoor olive plantations; and (2) to test the validity in the study areas of two chilling calculation methods, the Aron and the Utah method. Results show that for the Spanish cultivar the average chilling requirement of 997 h was approximately half of that recorded for the Italian cultivar (1848 h). Also, the year-to-year variability in chilling accumulation and the reproductive development date was observed to be higher in the Spanish area than in the Italian one, indicating a more consistent and predictable winter chilling response in the latter. As regards the validity of the methods, the Aron method seems to be more appropriate for use in warmer places, since it yielded better results in the Spanish site.     

浙江天童常绿阔叶林栲树爆芽物候格局研究

芽的活动和芽库动态反映了植物对环境的适应方式以及生活史对策。为了研究栲树（Castanopsis farge-sii）爆芽物候特征及其生活史对策,在2008年3～6月间对栲树自然种群的爆芽物候及芽变化进行了观察,定期记录了栲树的爆芽情况,包括被标记标准枝的芽数、芽所处阶段等参数,分析研究了栲树的爆芽物候特征。结果表明：栲树芽的发育集中在3～4月下旬,芽发育过程依其形态可分为：休眠期（第一阶段B0）、萌动期（第二阶段B1）、爆芽期（第三～第五阶段B2～B4）3个时期。爆芽各阶段种群、个体、小枝的物候参数基本相同。爆芽物候进程在第三阶段为双峰曲线,在第四阶段和第五阶段呈单峰曲线。在林下和林窗两种生境下第三阶段爆芽物候在时间上基本相同,而第四、第五阶段在时间上林下比林窗滞后。栲树在爆芽阶段并不存在早开始早结束的关系,虽然芽进入各阶段的时间不同,但最终出叶时间相对集中。作为亚热带常绿阔叶树种栲树,爆芽物候受气候等多方面因素的影响,其中春季温度为最重要的影响因素,长期适应的结果使得栲树爆芽物候与环境条件的变化相协调。