Shoot growth phenology of co-existing evergreen and deciduous species in an oak forest

Shoot growth phenology was compared for the saplings of evergreen and deciduous woody species sharing the same microsite. Growth initiation occurred earlier in evergreens (among co-stratal species) while deciduous species completed their growth earlier. Shoot growth rate was significantly greater (P<0.01) for deciduous trees than evergreen trees. The amount of shoot elongations and shoot diameter was also significantly greater (P<0.01) for deciduous trees than evergreens. On the other hand, among shrubs the amount of shoot elongation and shoot diameter was greater for evergreens but the rate of elongation and diameter was more or less similar for both. The duration of shoot elongation and shoot diameter was significantly longer in evergreens than the deciduous species. Leaf packing (number of leaves per shoot) was significantly more dense in evergreen trees (P<0.01) than in deciduous tree species. Leaf packing was more dense in evergreen than deciduous shrubs but the difference was not significant. Leaf area (per individual leaf) at full expansion was significantly greater (P<0.01) in deciduous species. Leaf dry mass and specific leaf mass in the initial stage was significantly greater for evergreen species than for deciduous species. The number of buds/10 cm of shoot was higher in evergreens. However, the per cent mortality was also higher in them.     

The structure and phenology of a moist deciduous forest in the Central Indian Highlands

The vegetation structure and phenology of a 74.5 ha block of moist deeiduous forest in Kanha Tiger Reserve, Madhya Pradesh, India were investigated during primatological fieldwork. Within a grid of 0.25 ha quadrats all 9935 trees (woody plants > 2 m tall), of 63 species, were enumerated and their girth measured. The forest was dominated by the dipterocarp sal (Shorea robusta). Most species were rare and showed clumped distributions within the sea of sal whilst the dispersion of five large canopy trees could not be distinguished from random.The phenology of 215 trees, of 61 species, was monitored over 14 months using an index of phytophase abundance. Leaf renewal was highly synchronous between and within species, mostly occurring between February and June. One species was evergreen, 5 were semi-evergreen and 55 were deciduous. Flowering generally occurred between leaf fall and flush whilst fruiting peaked late in the hot weather and early monsoon.     

Leaf flushing phenology and herbivory in a tropical dry deciduous forest,southern India

Patterns of leaf-flushing phenology of trees in relation to insect herbivore damage were studied at two sites in a seasonal tropical dry forest in Mudumalai, southern India, from April 1988 to August 1990. At both sites the trees began to flush leaves during the dry season, reaching a peak leaf-flushing phase before the onset of rains. Herbivorous insects emerged with the rains and attained a peak biomass during the wet months. Trees that flushed leaves later in the season suffered significantly higher damage by insects compared to those that flushed early or in synchrony during the peak flushing phase. Species whose leaves were endowed with physical defenses such as waxes suffered less damage than those not possessing such defenses. There was a positive association between the abundance of a species and leaf damage levels. These observations indicate that herbivory may have played a major role in moulding leaf flushing phenology in trees of the seasonal tropics.     

Extended leaf phenology in deciduous forest invaders: mechanisms of impact on native communities

Many high‐impact invaders of temperate deciduous forests of Eastern North America exhibit extended leaf phenology compared to native species, with leaf emergence occurring earlier in the spring and abscission occurring later in the autumn. This observation indicates that extended phenology may be an important invasion mechanism for this system. However, most evidence that extended leaf phenology drives species invasion is anecdotal, and most studies that directly address the role of leaf phenology in invasion focus solely on increased invader growth. Beyond increasing invader growth, extended leaf phenology may drive invader impact on natives by (1) facilitating resource competition through nutrient pre‐emption and shading, (2) altering production of secondary chemicals by invasive plants, (3) altering apparent competition dynamics mediated by native herbivores, (4) allowing temporal enemy escape, and (5) altering behaviour of native pollinators. I review current evidence from the literature regarding each of these possible consequences of extended invader phenology and emphasize the need for experimental manipulations to measure the extent to which extended leaf phenology mediates impact on the native community. Understanding the importance of leaf phenology in species invasion will facilitate prevention of future invasions while elucidating the role of seasonality in shaping species interactions.     

Applicability of remote sensing-based surface temperature regimes in determining deciduous phenology over boreal forest

Aims The study of deciduous phenology over boreal forest is important for understanding forest ecology and better management. In this paper, our objective was to determine the phenological stages of deciduous leaf out (DLO) over the deciduous-dominant [i.e. trembling aspen (Populus tremuloides)] stands in the Canadian Province of Alberta.Methods During the period 2006–2008, we used Moderate Resolution Imaging Spectroradiometer (MODIS)-based 8-day surface temperature (T S) images to calculate accumulated growing degree days (AGDD: a favourable temperature regime for plant growth). The temporal dynamics of AGDD in conjunction with in situ DLO observations were then analysed in determining the optimal threshold for DLO in 2006 (i.e. 80 degree days).Important findings The implementation of the above-mentioned optimal threshold revealed reasonable agreements (i.e. on an average 91.9% of the DLO cases within ±2 periods or ±16 days of deviations during 2007–2008) in comparison to the in situ observed data. The developments could be useful in various forestry-related applications, e.g. plant growth and its ability of exchanging atmospheric carbon dioxide, forest ecohydrology, risk of insect infestation, forest fire and impact of climate change, among others.     

Diversity of flowering and fruiting phenology of trees in a tropical deciduous forest in India

BACKGROUND AND AIMS: In the dry tropics, vegetative phenology varies widely with tree characteristics and soil conditions. The present work aims to document the phenological diversity of flowering and fruiting with reference to leafing events in Indian dry-tropical tree species. METHODS: Nine tree species, including one leaf-exchanging and eight deciduous showing varying leafless periods, were studied. Monthly counts of leaves, flowers and fruits were made on 160 tagged twigs on ten individuals of each species for initiation, completion and duration of different phenological events through two annual cycles. KEY RESULTS: Variation in flowering relative to leaf flushing (which occurred just prior to or during a hot, dry summer) revealed five flowering types: summer flowering (on foliated shoots), rainy-season flowering (on foliated shoots following significant rains), autumn flowering (on shoots with mature leaves), winter flowering (on shoots undergoing leaf fall) and dry-season flowering (on leafless shoots). Duration of the fruiting phenophase was shortest (3-4 months) in dry-season and winter-flowering species, 6-9 months in rainy-and autumn-flowering species, and maximum (11 months) in summer-flowering species. A wide range of time lag (<1 to >8 months) between the start of vegetative (first-leaf flush) and reproductive (first-visible flower) phases was recorded in deciduous species; this time lag was correlated with the extent of the leafless period. A synthesis of available phenological information on 119 Indian tropical trees showed that summer-flowering species were most abundant (56 % of total species) amongst the five types recognized. CONCLUSIONS: The wide diversity of seasonal flowering and fruiting with linkages to leaf flush time and leafless period reflect the fact that variable reproductive and survival strategies evolved in tree species under a monsoonic bioclimate. Flowering periodicity has evolved as an adaptation to an annual leafless period and the time required for the fruit to develop. The direct relationship between leafless period (inverse of growing period) and time lag between onset of vegetative and reproductive phases reflects the partitioning of resource use for supporting these phases. Predominance of summer flowering coupled with summer leaf flushing seems to be a unique adaptation in trees to survive under a strongly seasonal tropical climate.     

Forest-to-pasture conversion influences on soil organic carbon dynamics in a tropical deciduous forest

On a global basis, nearly 42% of tropical land area is classified as tropical deciduous forest (TDF) (Murphy and Lugo 1986). Currently, this ecosystem has very high deforestation rates; and its conversion to cattle pasture may result in losses of soil organic matter, decreases in soil fertility, and increases in CO₂ flux to the atmosphere. The soil organic matter turnover rate in a TDF after pasture conversion was estimated in Mexico by determining natural abundances of¹³C. Changes in these values would be induced by vegetation changes from the C₃ (forest) to the C₄ (pasture) photosynthetic pathway. The rate of loss of remnant forest-soil organic matter (fSOM) was 2.9 t ha^–1 year^–1 in 7-year-old pasture and decreased to 0.66 t ha^–1 year^–1 by year 11. For up to 3 years, net fSOM level increased in pastures; this increment can be attributed to decomposition of remnant forest roots. The sand-associated SOM fraction was the most and the silt-associated fraction the least depleted. TDF conversion to pasture results in extremely high rates of loss of remnant fSOM that are higher than any reported for any tropical forest.     

辽宁白石砬子保护区早春类短命植物研究

调查和分析了白石砬子保护区早春类短命植物物种组成的数量特征,应用物种丰富度指数、Shannon-Wiener多样性指数、Pielou均匀度指数、Simpson优势度指数,定量描述了不同林型下早春类短命植物的物种多样性.结果表明:研究区有早春类短命植物12种2变型,隶属7科11属.黑水银莲花是早春类短命植物层片的优势种.花曲柳林下早春类短命植物物种数最多,枫桦林、红松阔叶林、落叶松林次之,蒙古栎林、杂木林、鱼鳞云杉臭冷杉林最少.多样性指数的变化趋势总体上表现为针阔混交林>落叶阔叶林>针叶林.均匀度指数的变化与多样性指数的变化趋势基本一致,与优势度指数的变化趋势相反.红松阔叶林下早春类短命植物物种多样性最高且各物种均匀分布,层片结构稳定.     

Use of digital webcam images to track spring green-up in a deciduous broadleaf forest

Understanding relationships between canopy structure and the seasonal dynamics of photosynthetic uptake of CO₂ by forest canopies requires improved knowledge of canopy phenology at eddy covariance flux tower sites. We investigated whether digital webcam images could be used to monitor the trajectory of spring green-up in a deciduous northern hardwood forest. A standard, commercially available webcam was mounted at the top of the eddy covariance tower at the Bartlett AmeriFlux site. Images were collected each day around midday. Red, green, and blue color channel brightness data for a 640 × 100-pixel region-of-interest were extracted from each image. We evaluated the green-up signal extracted from webcam images against changes in the fraction of incident photosynthetically active radiation that is absorbed by the canopy (f _APAR), a broadband normalized difference vegetation index (NDVI), and the light-saturated rate of canopy photosynthesis (A _max), inferred from eddy flux measurements. The relative brightness of the green channel (green %) was relatively stable through the winter months. A steady rising trend in green % began around day 120 and continued through day 160, at which point a stable plateau was reached. The relative brightness of the blue channel (blue %) also responded to spring green-up, although there was more day-to-day variation in the signal because blue % was more sensitive to changes in the quality (spectral distribution) of incident radiation. Seasonal changes in blue % were most similar to those in f _APAR and broadband NDVI, whereas changes in green % proceeded more slowly, and were drawn out over a longer period of time. Changes in A _max lagged green-up by at least a week. We conclude that webcams offer an inexpensive means by which phenological changes in the canopy state can be quantified. A network of cameras could offer a novel opportunity to implement a regional or national phenology monitoring program.     

Eastern deciduous tree seedlings advance spring phenology in response to experimental warming,but not wetting,treatments

Changing global climate, particularly rising temperatures, has been linked through observations with advanced spring phenology in temperate regions. We experimentally tested if regional climate change predictions of increased temperature and precipitation alter the spring phenology of eastern US tree seedlings. This study reports the results of a 3-year-field experiment designed to study the responses of eastern deciduous tree species planted in a post-harvest environment to a 2 °C increase in temperature and a 20 % increase in precipitation. Species were monitored for timing of germination and leaf out in four treatment combinations (ambient, warmed, irrigated, and warmed + irrigated) on 16 plots located in a recently harvested central Pennsylvania forest. The 2 °C warming advanced day of seed germination by an average of 2 weeks and seedling leaf out by 10 days among all species (both p < 0.001). However, increased precipitation did not result in a significant change in spring phenology. Species responded uniquely to treatments, with germination advancing in three of five species in response to warming and leaf out advancing in six of six species. Southern species projected to expand northward into the study region with rising temperatures did not show responses to warming treatments that would provide them an advantage over current resident species. Timing of germination and leaf out varied among years of the experiment, most likely driven by year-to-year variability in spring temperatures. The climate change experiment highlighted the potential of a moderate 2 °C temperature increase to advance spring phenology of deciduous tree seedlings by up to 2 weeks, with a lack of a phenological response to a 20 % increase in precipitation.     

How plant allometry influences bud phenology and fruit yield in two Vaccinium species

Background and AimsUnderstanding how plant allometry, plant architecture and phenology contribute to fruit production can identify those plant traits that maximize fruit yield. In this study, we compared these variables and fruit yield for two shrub species, Vaccinium angustifolium and Vaccinium myrtilloides, to test the hypothesis that phenology is linked to the plants’ allometric traits, which are predictors of fruit production.MethodsWe measured leaf and flower phenology and the above-ground biomass of both Vaccinium species in a commercial wild lowbush blueberry field (Quebec, Canada) over a 2-year crop cycle; 1 year of pruning followed by 1 year of harvest. Leaf and flower phenology were measured, and the allometric traits of shoots and buds were monitored over the crop cycle. We hand-collected the fruits of each plant to determine fruit attributes and biomass.Key ResultsDuring the harvesting year, the leafing and flowering of V. angustifolium occurred earlier than that of V. myrtilloides. This difference was related to the allometric characteristics of the buds due to differences in carbon partitioning by the plants during the pruning year. Through structural equation modelling, we identified that the earlier leafing in V. angustifolium was related to a lower leaf bud number, while earlier flowering was linked to a lower number of flowers per bud. Despite differences in reproductive allometric traits, vegetative biomass still determined reproductive biomass in a log–log scale model.ConclusionsGrowing buds are competing sinks for non-structural carbohydrates. Their differences in both number and characteristics (e.g. number of flowers per bud) influence levels of fruit production and explain some of the phenological differences observed between the two Vaccinium species. For similar above-ground biomass, both Vaccinium species had similar reproductive outputs in terms of fruit biomass, despite differences in reproductive traits such as fruit size and number.     

Early spring leaf out enhances growth and survival of saplings in a temperate deciduous forest

Saplings of many canopy tree species in winter deciduous forests receive the major portion of their light budget for their growing season prior to canopy closure in the spring. This period of high light may be critical for achieving a positive carbon (C) gain, thus contributing strongly to their growth and survival. This study of saplings of Aesculus glabra and Acer saccharum in Trelease Woods, Illinois, USA, tested this hypothesis experimentally by placing tents of shade cloth over saplings during their spring period of high light prior to canopy closure in three consecutive years. Leaf senescence began 16 days (year 0) and 60 days (year 1) earlier for shaded A. glabra saplings than control saplings. No change in senescence occurred for A. saccharum. The annual absolute growth in stem diameter of both species was negligible or negative for shaded saplings, but positive for control saplings. Only 7% of the shaded A. glabra saplings were alive after 2 years, while all control saplings survived for 3 years; only 20% of the shaded A. saccharum saplings survived for 3 years, while 73% of control saplings were alive after the same period. Early spring leaf out is a critical mechanism that allows the long-term persistence of saplings of these species in this winter deciduous forest. Studies and models of C gain, growth, and survival of saplings in deciduous forests may need to take into account their spring phenology because saplings of many species are actually “sun” individuals in the spring prior to their longer period in the summer shade.     

Experimental warming alters spring phenology of certain plant functional groups in an early successional forest community

Experimental study of the effects of projected climate change on plant phenology allows us to isolate effects of warming on life‐history events such as leaf out. We simulated a 2 °C temperature increase and 20% precipitation increase in a recently harvested temperate deciduous forest community in central Pennsylvania, USA, and observed the leaf out phenology of all species in 2009 and 2010. Over 130 plant species were monitored weekly in study plots, but due to high variability in species composition among plots, species were grouped into five functional groups: short forbs, tall forbs, shrubs, small trees, and large trees. Tall forbs and large trees, which usually emerge in the late spring, advanced leaf out 14–18 days in response to warming. Short forbs, shrubs, and small trees emerge early in spring and did not alter their phenology in response to warming or increased precipitation treatments. Earlier leaf out of tall forbs and large trees coincided with almost 3 weeks of increased community‐level leaf area index, indicating greater competition and a condensed spring green‐up period. While phenology of large trees and tall forbs appears to be strongly influenced by temperature‐based growth cues, our results suggest that photoperiod and chilling cues more strongly influence the leaf out of other functional groups. Reduced freeze events and warmer temperatures from predicted climate change will interact with nontemperature growth cues to have cascading consequences throughout the ecosystem.     

近40年沈阳城市森林春季物候与全球气候变暖的关系

1960-2005年期间,沈阳气候受全球气候变暖的影响,年平均气温总体呈上升趋势,气温升幅为0.96℃,但以1982年为界,1960-1982年为偏冷阶段,气温降幅最大值为1.95 ℃:1983-2005年为偏暖阶段,气温升幅最大值为1.60 ℃.一年四季气温处于上升阶段,以冬、春季气温升幅最大,分别为2.3 ℃和1.35℃.城市森林主要树种的春季物候期,在气候偏冷阶段,春季物候期出现较晚,而在偏暖阶段,春季物候期提前发生.同时,物候春季开始日期与结束日期有密切的同步相关性,并与物候季节节奏的长短呈负相关.树木萌动期早晚与冬季和早春气温高低呈显著的负相关,冬春季气温越高,芽萌动越提前.展叶早晚主要受展叶前的春季气温高低的影响,与冬季气温相关性不显著.始花前2-8旬,特别是2-14旬气温对始花期影响最显著.寒冷指数(CI)与树木芽萌动期、展叶始期呈显著正相关,而与开花始期相关性不显著.预测了CO2倍增和气温升高条件下,沈阳城市森林主要树种的萌动期、展叶始期和开花始期分别提前40.41、43.08和24.13 d.     

Danish deciduous forest types

In this study, the first comprehensive multivariate statistical analysis of Danish native forest vegetation, based on 1768 sample plots, is presented. Data were composed of data from literature sources and newly collected data. A series of cluster analyses resulted in 24 forest community types, grouped in beech (Fagus sylvatica), oak (Quercus robur-Q. petraea), hornbeam (Carpinus betulus), alder-ash (Alnus-Fraxinus) and lime (Tilia cordata, T. platyphyllos) types, in addition to mixed forest communities with several co-dominant tree species. The described communities are provisionally arranged syntaxonomically, when possible, according to the international phytosociological system. The distribution of ecological indicator values of pH, soil moisture and nitrogen is gradual in relation to the perceived plant communities. Many forest types, such as beech and oak dominated types, obtain indicated values for pH that span most of the indicated gradient. It is suggested that natural Danish forests probably would be composed of a multitude of canopy forming tree species. The present stands with one or a few tree species forming the canopy is the result of long anthropogenic influence and selective logging.