Abundance and Leaf Damage Caused by Gall‐Inducing Insects in a Mexican Tropical Dry Forest1

We evaluated the temporal and spatial patterns of abundance and the amount of damage caused by gall‐inducing insects (GII) in deciduous and riparian habitats in a seasonal tropical dry forest in Mexico. Plants occurring in these habitats differ in their phenology and moisture availability. Deciduous habitats are seasonal and xeric, while riparian habitats are aseasonal and mesic. We found 37 GII species and each one was associated with a specific plant species. In total, 19 species (51.3%) were present in deciduous habitats, 13 species (35.2%) in riparian habitats, and only 5 species (13.5%) occurred in both. Abundance and leaf damage by GII were greater in deciduous than in riparian habitats during the wet season. For each GII species that occurred in both habitats, host plant species supported greater abundance and leaf damage by GII in deciduous habitats during the wet season. These results indicate a greater association of GII species with host plants in deciduous than in riparian habitats during the wet season. In riparian habitats, 11 plant species (61.1%) had greater density of GII in the dry than in the wet season. Similarly, leaf damage by GII was significantly greater in the dry than in the wet season in riparian habitats for 12 plant species (66.7%). Dry forest plants of riparian habitats presented two peaks of leaf‐flushing: GII colonized leaves produced in the first peak at the beginning of the wet season, and accumulated or recolonized leaves in the second peak at the beginning of the dry season. The levels of leaf damage by GII detected in this study in the rainy season were considerably higher than those obtained for folivorous insects in other neotropical forests, suggesting that this GII guild might have an important impact on their host plant species in this tropical community.     

Differences in leaf phenology between juvenile and adult individuals of two tree species in a seasonally dry tropical woodland

In temperate forests, juvenile trees anticipate leaf phenology compared to adults, thus avoiding shading and herbivory. This is also expected to occur in seasonal tropical forests due to intense herbivory and shading during the rainy season; however, the anticipation of leaf phenology by juveniles in seasonal tropical forests has yet to be demonstrated. Stem‐succulent species are expected to be prone to juvenile phenological anticipation because these species are able to use water stored in their stems for leaf flushing in the dry season. We investigated this hypothesis by comparing leaf phenology (bud break, leaf expansion) of juveniles and adults of two species with contrasting wood densities in the transition between dry and rainy seasons in a tropical dry woodland. We also investigated the level of light limitation that juveniles experience in the rainy season. Both species exhibited bud break during the dry season, but only expanded their leaves with the occurrence of the first rains. In general, the stem‐succulent species had a more precocious bud break; however, anticipation by juveniles occurred only in the species with more dense wood. Canopy openness was lower than in temperate deciduous forests, but the fact that the full expansion of leaves occurred only with rainfall indicates that bud break in anticipation of canopy closure contributes only to keeping leaf photosynthetic balance from going negative, and not to higher carbon gain. The importance of anticipated budding for escaping herbivory remains an alternative explanation in need of investigation.     

Leaf flushing during the dry season: the paradox of Asian monsoon forests

Aim Most deciduous species of dry monsoon forests in Thailand and India form new leaves 1–2 months before the first monsoon rains, during the hottest and driest part of the year around the spring equinox. Here we identify the proximate causes of this characteristic and counterintuitive ‘spring‐flushing’ of monsoon forest trees. Location Trees of 20 species were observed in semi‐deciduous dry monsoon forests of northern Thailand with a 5–6‐month‐long severe dry season and annual rainfall of 800–1500 mm. They were growing on dry ridges (dipterocarp–oak forest) or in moist gullies (mixed deciduous–evergreen forest) at 680–750 m altitude near Chiang Mai and in a dry lowland stand of Shorea siamensis in Uthai Thani province. Methods Two novel methods were developed to analyse temporal and spatial variation in vegetative dry‐season phenology indicative of differences in root access to subsoil water reserves. Results Evergreen and leaf exchanging species at cool, moist sites leafed soon after partial leaf shedding in January–February. Drought‐resistant dipterocarp species were evergreen at moist sites, deciduous at dry sites, and trees leafed soon after leaf shedding whenever subsoil water was available. Synchronous spring flushing of deciduous species around the spring equinox, as induced by increasing daylength, was common in Thailand's dipterocarp–oak forest and appears to be prevalent in Indian dry monsoon forests of the Deccan peninsula with its deep, water‐storing soils. Main conclusions In all observed species leafing during the dry season relied on subsoil water reserves, which buffer trees against prolonged climatic drought. Implicitly, rainfall periodicity, i.e. climate, is not the principal determinant of vegetative tree phenology. The establishment of new foliage before the summer rains is likely to optimize photosynthetic gain in dry monsoon forests with a relatively short, wet growing season.     

Modification of Vegetative Phenology in a Tropical Semi‐deciduous Forest by Abnormal Drought and Rain1

The control of vegetative phenology in tropical trees is not well understood. In dry forest trees, leaf abscission may be enhanced by advanced leaf age, increasing water stress, or declining photoperiod. Normally, it is impossible to dissect the effects of each of these variables because most leaves are shed during the early dry season when day length is near its minimum and leaves are relatively old. The 1997 El‐Niño Southern Oscillation caused a ten‐week long, severe abnormal drought from June to August in the semi‐deciduous forests of Guanacaste, Costa Rica. We monitored the effect of this drought on phenology and water status of trees with young leaves and compared modifications of phenology in trees of different functional types with the pattern observed during the regular dry season. Although deciduous trees at dry sites were severely water stressed (Ψstem < ‐7MPa) and their mesic leaves remained wilted for more than two months, these and all other trees retained all leaves during the abnormal drought. Many trees exchanged leaves three to four months earlier than normal during the wet period after the abnormal drought and shed leaves again during the regular dry season. Irrigation and an exceptional 70 mm rainfall during the mid‐dry season 1998/1999 caused bud break and flushing in all leafless trees except dormant stem succulents. The complex interactions between leaf age and water stress, the principal determinants of leaf abscission, were found to vary widely among trees of different functional types.     

Do seasonal changes in light availability influence the inverse leafing phenology of the neotropical dry forest understory shrub Bonellia nervosa (Theophrastaceae)?

In tropical dry forests most plants are deciduous during the dry season and flush leaves with the onset of the rains. In Costa Rica, the only species displaying the opposite pattern is Bonellia nervosa. To determine if seasonal changes in light availability are associated with the leaf and reproductive phenology of this species, we monitored leaf production, survival, and life span, as well as flower and fruit production from April 2000 to October 2001 in Santa Rosa National Park. Leaf flushing and flower bud production took place shortly after the autumnal equinox when day length starts to decrease. Leaves began expansion at the end of the wet season, and plants reached 70 % of their maximum leaf area at the beginning of the dry season, maintaining their foliage throughout the entire dry period. Leaf shedding occurred gradually during the first three months of the wet season. Leaf flushing and shedding showed high synchrony, with leaf numbers being related to light availability. Maximum leaf production coincided with peaks in radiation during the middle of the dry season. Decreasing day length induces highly synchronous flower bud emergence in dry forest species, but this is the first study indicating induction of leaf flushing by declining day length.     

Factors Influencing Tree Phenology in Taï National Park,Côte d'Ivoire1

Entrained phenology patterns of tropical trees are expected to be sensitive to short‐term fluctuations in typical rainfall and temperature. We examined 47 mo of data on the flowering, fruiting, and new leaf phenology for 797 trees from 38 species in the Taï National Park, Côte d'Ivoire. We determined the timing of the phenology cycles in relation to seasonal rainfall, temperature, and solar radiation. Regression analysis was used to examine how variations in rainfall and temperature influenced deviations in the peaks and troughs of phenology cycles. We also investigated whether populations that fruit during periods of community‐wide fruit scarcity were those populations with relatively long‐ or short‐fruiting duration. Flower, fruit, and leaf‐flushing phenophases all exhibited 12‐mo cycles. The broad peak in flowering began with the northward zenithal passing in April and ended with the southward zenithal passing in September. Fruiting peaks occurred in the long dry season, and leaf flushing peaked in the long dry season but continued into the wet season. Deviations from phenology cycles were largely attributable to short‐term fluctuations in rainfall and/or temperature. Fruiting durations of species were related to the mean diameter at breast height. Species with long‐ and short‐fruiting durations contributed equally to fruit abundance during periods of community‐wide fruit scarcity.     

Water relations of “trailing-edge” evergreen oaks in the semi-arid upper Yangtze region,SE Himalaya

Unlike the well-understood cold limit of trees, the causes of the dry trailing edge of trees await explanation. Here we aimed at explaining the drought limit of an evergreen oak species (Quercus pannosa s.l.) in a typical dry valley of the upper Yangtze region, SE Himalaya, where rains (ca. 250 mm/a) are largely confined to the typical monsoon season (July–August) with drought during the remaining 9–10 months. We capitalized on an unintentional year-round irrigation treatment with trees growing along the overflow of a water reservoir serving as moist controls. We measured shoot water potential (Ψ), leaf conductance (g), flushing phenology, leaf mass per area (LMA), foliar and stem δ¹³C, leaf nutrients, and non-structural carbohydrates across the transition from non-monsoon to monsoon season, from April to August 2018. At the dry site, Ψ and g were high during the monsoon but declined to <−3 MPa as drought proceeded in the non-monsoon season. Irrigated oaks retained high values year-round. Oaks experiencing the natural drought flushed at the full strength onset of the monsoon only, that is, 80 days later than irrigated oaks. The annual shoot increment in oaks under natural drought was ca. 10% of that in irrigated oaks. However, mature foliage showed no difference in LMA and δ¹³C between dry and moist sites. We conclude that these oaks drastically reduce their activity in response to drought, with growth strictly confined to the monsoon season, the minimum duration of which, presumably is setting the range limit.     

Two phenological variants of Terminalia alata coexist in a dry dipterocarp forest

Two morphological variants of Terminalia alata (Combretaceae) differed in leaf flushing phenology and spatial distribution in a Cambodian deciduous forest. The hairy‐type trees displayed leaf exchange behavior in the middle of the dry season. The glabrous type flushed new leaves 3 months after the wet season started. The leafless period of the hairy type was estimated to be <1 month, whereas that of the glabrous type lasted more than 5 months. The landscape‐scale leaf exchange behavior was similar to that of the hairy type. The two types showed clear spatial separation. The hairy type was limited to flat areas with deep soils. The dominance of the glabrous type in hilly areas with shallow soils suggests that it is adapted to water‐limited environments. The abundance of the glabrous type in hilly areas and its unique leaf phenology probably influence the carbon, energy and water balance at the landscape level.     

Phenology of Acacia albida trees in Zambezi riverine woodlands

The phenology of Acacia albida trees was studied over eight years in Mana Pools National Park, Zimbabwe. Leaf flush occurred towards the end of the rains. It was followed by flowering, with ripe fruit-fall in the late dry season. Leaf-fall occurred early in the following wet season. After seasons of low rainfall, trees were severely defoliated by caterpillars soon after leaf flush and this prompted a second flush of leaves. In these years there were also two periods of flowering and fruit production. During dry years, the proportion of trees which failed to set fruits after flowering increased, fruit production by those trees which did bear fruit was reduced and fruit-fall started earlier in the year.     

Environmental control of flowering periodicity in Costa Rican and Mexican tropical dry forests

Aim We analyse the proximate causes of the large variation in flowering periodicity among four tropical dry forests (TDF) and ask whether climatic periodicity or biotic interactions are the ultimate causes of flowering periodicity. Location The four TDFs in Guanacaste (Costa Rica), Yucatan, Jalisco and Sonora (Mexico) are characterized by a 5–7 month long dry season and are located along a gradient of increasing latitude (10–30°N). Methods To dissect the differences in flowering periodicity observed at the community level, individual tree species were assigned to ‘flowering types’, i.e. groups of species with characteristic flowering periods determined by similar combinations of environmental flowering cues and vegetative phenology. Results Large variation in the fraction of species and flowering types blooming during the dry and wet season, respectively, indicates large differences in the severity of seasonal drought among the four forests. In the dry upland forests of Jalisco, flowering of leafless trees remains suppressed during severe seasonal drought and is triggered by the first rains of the wet season. In the other forests, leaf shedding, exceptional rainfall or increasing daylength cause flowering of many deciduous species at various times during the dry season, well before the summer rains. The fraction of deciduous species leafing out during the summer rains and flowering when leafless during the dry season is largest in the Sonoran TDF. Main conclusions In many wide‐ranging species the phenotypic plasticity of flowering periodicity is large. The distinct temporal separation of spring flowering on leafless shoots and subsequent summer flushing represents a unique adaptation of tree development to climates with a relatively short rainy season and a long dry season. Seasonal variation in rainfall and soil water availability apparently constitutes not only the proximate, but also the ultimate cause of flowering periodicity, which is unlikely to have evolved in response to biotic adaptive pressures.     

Phenology, Lignotubers, and Water Relations of Cochlospermum vitifolium, a Pioneer Tropical Dry Forest Tree in Costa Rica

We examined structural and physiological traits relevant to the phenology of the tropical dry forest (TDF) pioneer tree Cochlospermum vitifolium . Despite marked seasonality in rainfall, meristem activity occurred throughout the year. Leaves were produced almost continuously during the rainy season, while leaf shedding started early during drought, before changes in soil water content were observed. Phenological activity under drought included flowering and fruiting of leafless trees; bud break and shoot extension took place before the end of the dry season. Low wood density of C. vitifolium stems (0.17 g/cm³) and lignotubers (0.14 g/cm³) provided water and starch storage needed to support phenological events such as branch extension, leaf flushing, and reproduction during the dry season, and probably also contributed to survival following mechanical damage and fire, typical of early TDF successional stages. Lignotuber water and starch contents showed substantial seasonal variation, declining from the beginning of the dry season to their lowest levels at the time of reproduction and dry-season flushing. Stems progressively replaced lignotubers as main storage organs as tree size increased. Evidence for a role of water stores in buffering daily water deficits was weak. Leaf water potentials remained above −1.2 MPa and stomatal conductance below 350 mmol/m²/s, suggesting that gas exchange during the rainy season was limited to prevent xylem cavitation. Leaf shedding occurred when early-morning and mid-day Ψ_L converged at the rainy–dry season transition, without changes in lignotuber or soil water content, suggesting that leaves of C. vitifolium are closely tuned to atmospheric drought.
Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp .     

Leaf shedding and weather in tropical dry-seasonal forest shape the phenology of fungi – Lessons from two years of monthly surveys in southwestern Panama

In the present study, conducted in a secondary dry-seasonal forest in the pacific lowlands of southwestern Panama over 2 years, fungal diversity is linked to plant phenology, litter, and climatic data. Agaricales fungi showed maximum species richness at the beginning of rainy seasons, probably due to the important litter accumulation during the dry season and the increase in humidity favoring fungal growth. Species richness declined during the wet season possibly due to torrential rains, moulds, and decreasing availability of nutrients. Occurrence of foliar pathogenic microfungi correlated negatively with flushing of new leaves at the beginning of the rainy season. Their incidence increased during the wet season and remained high during the dry season. Synchronization of leaf shedding in most tree species significantly reduced the yearly incidence of foliar pathogenic fungi causing an annual turn-over of fungal pathogens that probably contributes to maintain a high diversity of plant pathogenic species.     

Seasonal variation in insect abundance among three Australian rain forests,with particular reference to phytophagous types

Monthly sweep net and light trap samples were used to examine seasonal changes in the abundance of insects in subtropical, warm and cool temperate rain forest in New South Wales. Maximum insect abundance, especially of phytophages, coincided with leaf flushing in the canopy trees. Cool temperate insect numbers were highest during the month just following the beech leaf flush, a rapid and synchronous growth event. Conversely, numbers of subtropical insects fluctuated over a longer period, in a pattern similar to the continuous growth of leaves that occurred throughout spring and summer there. The warm temperate was intermediate in its vegetation growth phenology and insect patterns. Rainforest insect abundance varied both temporally and spatially.     

Seasonality of insect herbivory on the leaves of Neoboutonia macrocalyx in the Kibale National Park, Uganda

The seasonality of herbivory on the leaves of Neoboutonia macrocalyx Pax. in Kibale Forest National Park, Uganda, was studied. A total of 2929 fallen leaves was collected during 15 months under randomly-selected trees in three different habitats; natural forest and two selectively cut forest sites. The percentage of leaf area eaten and leaf size were estimated. Leaf herbivory was highly seasonal and correlated with rainfall in the previous 2 months, but less than 100 mm monthly rainfall had no effect. There was no correlation between leaf size and rainfall. Although Kibale Forest has two wet seasons, insect feeding on leaves had only one peak during the major rainy season from September to December. Three to four months after peak herbivory, leaves had very low rates of insect damage. Habitat had only a small effect on the amount of insect feeding. The sampling time accounted for 71% of variation in leaf herbivory. New leaves were formed continuously year-round. The constant leaf production by Neoboutonia trees may be an adaptation to escape generalist herbivorous insects which might be synchronized with the major wet season when the leaf flush of the most other deciduous species occurs. Thus, the availability of fresh leaves is not acting as a regulating factor in seasonality of Neoboutonia herbivory.     

Litterfall seasonality and adaptive strategies of tropical and subtropical evergreen forests in China

中国热带和亚热带常绿林凋落物季节特征及适应策略 本研究收集了来自中国热带/亚热带常绿林共85个站点的凋落物量季节性变化数据,并采用线性回归、结构方程模型构建以及相位差分析等方法,综合探究中国热带/亚热带地区常绿阔叶林和针叶林叶片脱落对土壤水分、饱和水气压差和辐射强度等气候因子的响应机制。研究结果显示,在雨热同期和雨热异期两种热带/亚热带气候类型中,呈现出两种典型凋落物的物候类型(单峰季节型/双峰季节型)。在雨热同期气候条件下,光照强度和降水呈现季节性正相关,单峰的凋落物峰值和双峰的第一个峰值约出现在3–4月,不断增加的光照能促进新叶的萌发,老叶被代谢更强的新叶所替代,该类型属于一种最大程度利用光照来实现树木生长的自适应策略。双峰的第二个峰值出现在雨季末期,约在8–10月,是由不断增强的水分亏缺所导致的(常绿阔叶林：大气水分亏缺;常绿针叶林：土壤水分亏缺),这种类型是一种凋落老叶减少水分丢失来应对水分胁迫的自适应策略。在雨热异期气候条件下,光照强度和降水呈现季节性负相关,饱和水气压差与光照强度表现出一致的季节性动态变化,诱导了常绿阔叶林单峰和双峰物候的第一个凋落峰(约在3–4月),是一种权衡大气干旱胁迫和最大程度利用光照进行生长的综合自适应策略。在雨季初期,显著的土壤水分亏缺加速叶片凋落,诱导了常绿阔叶林双峰物候的第二个凋落峰(约在11月),属于凋落老叶应对土壤水分胁迫的自适应策略。这些研究结果可以为地球系统模式中热带物候的精确模拟提供重要参考。     

Vegetative Phenology and Growth of a Facultatively Deciduous Bamboo in a Monsoonal Climate1

Canopy closure, leaf flush, and ramet recruitment in Bambusa arnhemica, a semelparous, clumping bamboo from the Australian monsoonal tropics, were monitored monthly for 2.5 years at three sites along a flood gradient. Bambusa arnhemica was facultatively deciduous, remaining evergreen at a downslope riparian site but suffering total loss of canopy on a hillside for up to 4 mo during the dry season. Leaf flush was flexible, occurring after as little as 25 mm of rain at the onset of wet season, in response to unusual dry season storms, and apparently also in response to fire independent of rainfall. New culms emerged soon after leaf flush early in the wet season. Culm growth took place during the middle and late wet season, with peak elongation rates of 15–30 cm/day. Some growth continued into the dry season, mostly on branches and leaves of new culms at riparian sites. Not all culms completed elongation before the onset of the dry season, and those that did not were permanently stunted. The demands of culm elongation may limit the occurrence of bamboo in wet‐dry climates to areas with predictable and sustained wet season rainfall, but the flexibility of branching and leaf processes facilitates coping with, and permits exploitation of less predictable pre‐ and postmonsoonal rains. The bamboo growth form and phenological patterns differ markedly from those of dicotyledonous trees and shrubs.     

Phenology of the red mangrove, Rhizophora mangle L., in the Caeté Estuary,Pará, equatorial Brazil

The current study presents phenology data for Rhizophora mangle from two equatorial mangrove stands with different salinity regimes in Brazil. Observations based on litter fall and individual shoot development were compared and related to environmental factors. Patterns observed in litter fall were consistent with results of direct monitoring. While both reproductive organs and leaves were produced throughout the year, rates of formation followed seasonal trends. Distinct differences in propagule production between low and high salinity sites and between years of observation were detected; main propagule release was, however, restricted to the wet season which offers enhanced conditions for propagule establishment. Emergence of flowers was linked to leaf production. While there was no obvious single peak in leaf production, it was reduced towards the end of the dry season at both high and low salinity sites. Time series analysis revealed an independent pattern of leaf development superimposed on this annual seasonal trend, indicating slower development of leaf primordia during periods of low light availability in the wet season. No significant difference in age structure was detected between sun and shade leaves; maximum leaf life-time was approximately 1 year.     

Phenology of Ficus variegata in a seasonal wet tropical forest at Cape Tribulation, Australia

Abstract. We studied the phenology of 198 mature trees of the dioecious fig Ficus variegata Blume (Moraceae) in a seasonally wet tropical rain forest at Cape Tribulation, Australia, from March 1988 to February 1993. Leaf production was highly seasonal and correlated with rainfall. Trees were annually deciduous, with a pronounced leaf drop and a pulse of new growth during the August-September drought. At the population level, figs were produced continually throughout the study but there were pronounced annual cycles in fig abundance. Figs were least abundant during the early dry period (June-September) and most abundant from the late dry season (October-November) through the wet season (December-April). The annual peak in reproduction actually reflected two staggered peaks arising from gender differences in fig phenology. In this dioecious species, female and male trees initiated their maximal fig crops at different times and flowering was to some extent synchronized within sexes. Fig production in the female (seed-producing) trees was typically confined to the wet season. Male (wasp-producing) trees were less synchronized than female trees but reached a peak level of fig production in the months prior to the onset of female fig production. Male trees were also more likely to produce figs continually. Asynchrony among male fig crops during the dry season could maintain the pollinator population under adverse conditions through within- and among-tree wasp transfers.     

Rainfall and topo-edaphic influences on woody community phenology in South African savannas

Woody community phenology was studied in the central lowveld, South Africa, over a twelve month period at three sites along a rainfall gradient, with both toplands and bottomlands sampled at each site. Each month, individual plants, in replicated samples, were scored into a number of categories describing their phenological state. Position on the rainfall gradient influenced: (1) onset and magnitude of leaf emergence, (2) onset and duration of mature leaves, and (3) the proportion of leafless trees. Generally, the moist site demonstrated earlier leaf growth than the intermediate or arid sites. Emergent and mature leaves were recorded earlier, and in the case of mature leaves, retained longer. Overall, there was a lower proportion of leafless trees during the dry season at the moist site, followed by the semi-arid site, followed by the arid site. Differences with respect to catenal position were evident for the proportion of trees in winter with mature leaves, and the proportion of trees with senescent leaves. Bottomlands had a greater proportion of trees with leaves during winter, but a lower proportion of trees recorded with senescent leaves. Both of these findings were a result of the greater proportion of evergreen species in bottomlands, as well as increased leaf retention by the deciduous species. Phenological activity of leaves was related to plant stem size. In particular, there was greater leaf retention during the dry period by small stems, relative to large stems.     

Phenology and Stem Diameter Increment Seasonality in a Costa Rican Wet Tropical Forest

The relationship between phenology and tree stem diameter increment is largely unexplored in tropical species, especially in wet tropical forests. To explore links between these phenomena, we measured stem diameter increment and phenology of ten canopy tree species from a range of functional types in the Atlantic lowlands of Costa Rica to test for seasonal and interannual patterns. We measured stem diameter increment using band dendrometers and visually assessed leaf and reproductive phenology monthly from 1997 to 2000. We categorized the species into groups based on patterns of leaf exchange and reproduction. Species were either deciduous with synchronous or asynchronous leaf drop, or evergreen with continuous or seasonal leaf flushing. Flowering occurred supra-annually, annually, or continuously. Of the ten species studied, four species, Cecropia insignis, Dipteryx panamensis, Lecythis ampla, and Simarouba amara , had consistent seasonal stem diameter increment patterns in both years. Dipteryx panamensis and L. ampla were deciduous with synchronized leaf drop . Cecropia insignis was evergreen and produced new leaves continuously. Simarouba amara , also evergreen, exchanged leaves over a brief period once a year. We tested whether stem diameter increment was correlated to phenology using logistic regression. Leaflessness significantly explained patterns in stem diameter increment but reproductive phenology did not. Deciduous trees were 2.6–9.3 times more likely to grow less than average the month following leaffall than in months when trees had full crowns.