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The term phenology is derived from the Greek word phaino meaning to show or to appear. Hence, phenology is defined as the study of the seasonal timing of life cycle events. For plants the seasonal timing of such events can be critical to survival and reproduction. In agriculture the most common failure of introduced crops is the inability to adjust to the seasons imposed by the new, environment (68). In the past few years, interest in the ecology and evolution of timing of life cycle events has grown. Here we review the literature on phenological patterns of germination, flowering, and fruiting (including dispersal).The phenological pattern of any life cycle event can be quantitatively defined as a statistical distribution characterized by such parameters as time of occurrence (onset, mean, mode), duration (range), synchrony (variance), and skewness. For each life cycle event we discuss each parameter for which data are available. Because parameters at one level can contribute to parameters at higher levels, parameters are sometimes related. For example, the degree of synchrony within and among individuals can determine duration at the population level. Therefore, we discuss phenological patterns at the levels of individuals, populations, species, and communities. Also, we use the word phenology in its strict sense of seasonal timing within years; and we address variation among years only when it pertains to the discussion of within-year patterns.The purpose of this review is to present hypotheses about possible evolutionary causes and consequences of different phenological patterns and to discuss the evidence for each hypothesis. We also briefly summarize information about the environmental and genetic controls of timing because these are the proximate factors that can influence the evolution of phenological patterns. We divide our review into four sections. The first three address germination, flowering, and fruiting separately. Each section covers possible selective factors, proximate environmental cues, and genetic determinants of different phenological parameters. The last section focuses on the relationships of germination, flowering, and fruiting, to the whole life cycle of the plant. Here we address possible ecological and evolutionary constraints that may direct the evolution of all life cycle events.Space prevents an exhaustive literature review, particularly of descriptive studies, so we mention representative studies and reviews that provide the reader access to additional literature. We do not address phenological patterns of leaf production (43,146) or the specific methodologies for collecting and analyzing phenological data (151, 194, 20 1). GERMINATIONThe seedling stage is the most vulnerable time in the life cycle of a plant (10 1). Mortality is often severe because small seedlings have minimal capacity for homeostatic responses or physiological retrenchment in the face of unfavorable abiotic or biotic conditions (10). Therefore, the timing of germination should be under strong selection to occu...

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Studies of plants in fragmented habitats have focused on single ecological processes, such as seed production or seed dispersal, that may be altered by increased fragmentation and that operate as the mechanism(s) that increase extinction probability. We examined a suite of potential mechanisms to explain demographic shifts toward extinction in populations of Trillium ovatum, a long‐lived herbaceous perennial found in the understory of western North American conifer forests. Past work has shown that populations of T. ovatum found within ∼65 m of forest‐clearcut edges in southwestern Oregon have had almost no new recruitment since the edges were formed. We hypothesized that changes in abiotic conditions and biotic interactions present along edges are responsible for reduced recruitment. In eight populations in eight separate fragments, we evaluated the relationship of distance of the populations to the forest edge with respect to six processes: flowering phenology (timing), seed production, pollination‐ and resource‐limitation of seed set, seed dispersal, seed predation, and germination. Those factors that showed a significant relationship with edge distance were then compared with recruitment of younger age classes. Two processes were significantly different near edges and were highly correlated with decreased recruitment: decreased seed production due to changes in pollination and increased seed predation by rodents. Our study (in conjunction with previous studies) suggests that several ecological processes show no significant relationship with edge distance and can be eliminated as possible mechanisms of reduced recruitment: flowering phenology, resource‐limitation of seed set, seed dispersal, germination, herbivory, and survivorship of established plants. Edges influence some but not all components of a plant's life history. Thus, determining shifts in only one part of a life history will be inadequate for testing the prediction of increasing extinction probabilities in fragmented landscapes. Future studies should include enough information to conduct comprehensive analyses, such as matrix projections and sensitivity analyses.

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