Cone Crop Research Articles

Seed dispersal of Japanese stone pine by the Eurasian Nutcracker

Seed dispersal of Japanese stone pine Pinus pumila by the Eurasian Nutcracker Nucifraga caryocatactes was studied at Mt. Apoi in Hokkaido, northern Japan. The seed foraging and caching behavior of diurnal birds and mammals was observed, and the relative importance of each species for pine seed dispersal was examined. All mature cones disappeared from the pine shrubs by mid-October each year regardless of the cone crop size. Eurasian Nutcrackers, Varied Tit Parus varius, Eurasian Nuthatch Sitta europaea, Red Squirrel Sciurus vulgaris, and Siberian Chipmunk Tamias sibiricus were all potential seed dispersal agents, however, observations revealed that nutcrackers carried 96% of all seeds transported from the pine trees. The nutcracker carried 142 seeds on average (max. 209) in one trip. Nutcrackers mainly carried pine seeds into their mixed coniferous forest, breeding habitat, where stone pines cannot normally become established and cached them in the soil there. Nutcracker caches averaged 12 seeds with a maximum of 51 seeds. Pine seedlings were found growing in clusters (in groups of two or more trees). The number of seedlings per cluster closely resembled the number of seeds in nutcracker caches. Results suggest that most stone pine seedlings originated from nutcracker caches. Eurasian Nutcrackers thus play an important role in the regeneration of Japanese stone pine despite their small number of caches.

Pre-dispersal seed predation of white spruce cones in logged boreal mixedwood forest

Predation of white spruce (Picea glauca (Moench) Voss) cones by red squirrels (Tamiasciurus hudsonicus Erxleben) was quantified in the mixedwood boreal forest of Alberta in cutblocks with seed tree retention and in adjacent uncut forest, during 3 years with varying levels of cone crop (1998, 1999, 2000). Percent cone loss was quantified by comparison of paired pre- and post-caching photographs of tree crowns. Cone loss from seed trees in cutblocks was significantly lower than from control trees in adjacent uncut forest (48.5 vs. 54.9%). Although the number of cones produced per tree declined by 42% and the percentage of trees producing cones declined by approximately 48% between 1998 and 2000, there was no corresponding increase in the percentage of cones harvested by squirrels. Percent cone loss was significantly lower from single seed trees in cutblocks, as compared with seed trees left in patches of more than 20 trees (33.4 vs. 50.5%). Cone predation significantly reduced the amount of seed available for natural regeneration using a seed tree system. Although blowdown may be reduced if seed trees are left in patches, leaving white spruce seed trees as singles in cutblocks may reduce the level of cone predation.

Cone enhancement in Abies amabilis using GA 4/7, fertilizer, girdling and tenting

The demand for Abies amabilis (Dougl. Ex Loud) Dougl. Ex Forbes, Pacific silver fir seed has increased in British Columbia in recent years but the supply of wild seed is limited due to periodic cone crops and difficulty and high cost of cone harvest. Several clonal seed orchards have been established but cone production is very low. A study was undertaken to enhance cone production in a clonal seed orchard grafted in 1984. Five treatments were applied with 20 trees per treatment. Treatments began on 20 May 1998. Each tree was given two applications of GA 4/7 at 1 week interval, 20 and 27 May (early application) or 27 May and 3 June (late application). Ramets in treatment 2 received early GA 4/7 application+ fertilizer+ girdling . Ramets in treatment 3 received a similar treatment but given late. Ramets in treatment 4 received early GA 4/7 application+ fertilizer+ girdling+ tenting . Ramets in treatment 5 received a similar treatment but given late. Ramets in treatment 1 received one injection of 80% ethanol but no GA 4/7 on 30 May. Each treatment had 10 trees in which vegetative bud burst was early and 10 trees in which bud burst was late. Pollen and seed cone abundance was measured in April 1999. Only 10% of control ramets produced seed cones (0.75 cones/ramet). In treatment 2, 45% of ramets produced seed cones (8.4 cones/ramet). In treatment 3, 35% of ramets produced seed cones (2.3 cones/ramet). In treatment 4, 70% of ramets produced seed cones (23.1 cones/ramet). In treatment 5, 75% of ramets produced seed cones (21.2 cones/ramet). Pollen cone enhancement was statistically significant for treatments 2–5 over controls but production was not as dramatic as for seed cones because most control ramets produced some pollen cones.

Frugivory at Juniperus communis depends more on population characteristics than on individual attributes

Summary We investigated the spatio‐temporal variation in the interactions between the juniper Juniperus communis and its vertebrate frugivores (avian dispersers of Turdus spp. and predatory rodents Apodemus sylvaticus) in the Mediterranean mountains of south‐east Spain. Frugivore activity was evaluated at six sites and for 3 years, in relation to both plant reproductive traits (plant size, cone crop and cone size) and characteristics of the immediate environment (distance to the nearest female, abundance of perches, fruiting environment and habitat). Plant characteristics and levels of frugivory varied strongly among the six populations. Cone production, cone size and frugivory also differed significantly among years for the same population. Avian frugivory was only occasionally affected by density of cones per plant, abundance of perches or abundance of other fruiting species, or by habitat. Rodent predation was positively related only to the density of cones per plant and then only in two sites. Levels of both avian frugivory and rodent predation significantly increased in populations with higher cone production. Both groups of vertebrate frugivores responded to the spatio‐temporal variation in cone abundance at a regional scale, discriminating more between juniper populations than between individual plants within a population. The outcome of interactions with frugivores at the individual plant level thus proved more dependent on the whole‐population characteristics than on individual attributes.

Impact and control of the cone tortricid Pseudococcyx tessulatana (Staudinger), damaging the cone crop of a selected clone of cypress (Cupressus sempervirens L.) in Italy

The green cypress (Cupressus sempervirens) is of great interest for ornamental, reforestation and windbreak use in the whole Mediterranean basin. In Italy, seed material selected for resistance to the fungus Seiridium cardinale is produced in seed orchards by controlled crosses of parent trees. The insect pest showing the highest impact on seed cone production is Pseudococcyx tessulatana (Lep.; Tortricidae), which attacks cones during the initial growth period as well as full-grown cones. The impact on the seed cone crop of the tortricid was estimated on a clone patented for its resistance to cypress canker (Agrimed 1). The attack was inversely related to the cone crop, as it concerned 36.7 % of cones in 1999 (high crop year) and the 66 % in 2000 (low crop year). In both years, about 90 % of the surveyed branches revealed cones attacked by P. tessulatana by the 1st life-cycle larvae, whereas only 40 % of branches were also attacked by the larvae of the 2nd life cycle. The highest attack rate per branch was always observed on branches bearing a low number of cones. The potential of two control methods against P. tessulatana to protect cones which result from crossing a mother tree “Agrimed 1” with selected father trees was also evaluated in 2000. The protection given by a sleeve surrounding the branch was almost complete (0.4 % cone mortality), whereas a cone mortality of 24.3 % was observed on branches treated by the insecticide diflubenzuron. Sleeves appear to be useful to protect branches on which special crosses were done, but are expensive and time-consuming and may favour the attack of the mealybug Planococcus vovae inside the sleeve. The insecticide application may represent a valid alternative, especially when protection should be directed toward a high number of branches.

Dispersal ecology of lodgepole pine ( Pinus contorta Dougl.) in its native environment as related to Swedish forestry

Lodgepole pine ( Pinus contorta Dougl.) covers extensive areas of the mountains of western North America. It has evolved into four subspecies, each adapted to slightly different environmental conditions. All are adapted to reproduce following fire. Subspecies latifolia is the most extensive and economically important in North America. Serotiny is common in this subspecies, but trees bearing nonserotinous cones can be found in most stands, sometimes constituting more that 70% of the trees. Cone crops are produced yearly and seed loss to seed predators, insects and diseases are minimal. Germination and establishment occurs across a broad range of conditions allowing lodgepole pine to grow on poor sites as well as highly productive sites. These characteristics give lodgepole pine the ability to be highly invasive in new areas of suitable habitat.

Body weights in grey and red squirrels: do seasonal weight increases occur in conifer woodland?

AbstractSeasonal body weight changes were investigated in red and grey squirrels in spruce‐dominated conifer plantations in the north of England. Annual seed food availability, particularly in the spruce plantations, varies markedly and is characterized by years with large cone crops (‘mast crops’) followed by several years of intermediate or low crops. The last mast crop in Kielder Forest District occurred in 1991 and we studied the two squirrel species when food availability was intermediate and low between 1992 and 1999. Neither red nor grey squirrels in the conifer plantations significantly increased their body weight for the autumn or winter. The responses of red and grey squirrels to the different foraging conditions in deciduous and conifer woodlands and the accumulation of seasonal fat stores may have to be seen in the context of habitat type and the pattern and predictability of seed availability. Our findings suggest that fat accumulation is likely to be less pronounced in conifer habitats where autumn and winter food supplies are more predictable, and manoeuvrability to feed on cones in the canopy is important.

Cono‐ and seminiphagous insects of Norway spruce Picea abies (L.) Karst. and their parasitoids in lower and upper montane zone of the Tatra National Park in Poland

Abstract: A study of the insects inhabiting of cones of Norway spruce Picea abies (L.) Karst. in the Tatra National Park was conducted during 1987–92. As a result of breeding and analyses of the cones collected from trees at various altitudes above sea level, 53 746 specimens of cono‐ and seminiphagous insects were collected. Interior damage to cones and the losses of spruce seeds caused by pests were measured, with regard both to the variable cone crop abundance of spruce and to different altitudes above sea level. The role of parasitoids in limiting the numbers of some cono‐ and seminiphagous insects was also estimated.

The breeding biology of the Common Crossbill Loxia curvirostra in the Central Pyrenees

The breeding biology of the Common Crossbill Loxia curvirostra was studied over ten consecutive years in forests of Mountain Pine Pinus uncinata in the Pyrenees, France. The breeding season lasts from summer to the next spring following the maturation and the opening of the pine cones. Pairs with dependent young were most common in November and March–May. The greatest number of clutches was observed in December and January (53%, n = 30). Average clutch size was 3.43 eggs (sd = ±0.57; n = 30), the number of fledged young was 1.32 per completed clutch (sd = ±1.7; n = 25) and the proportion of breeding attempts that were successful was 27.8% in the winter/spring period (n = 36). The number of successful pairs was found to be positively correlated to the number of cones, and in the winter/spring period negatively correlated to the mean depth of snow. Breeding only failed completely during the year in which the density of birds was highest. In years with a good cone crop, breeding that starts early and continues over a long period appears to be an adaptation which increases productivity in this sedentary population dependent on fluctuating food resources. An irruption by birds from northern Europe in 1990 did not affect the numbers or breeding success of the Pyrenean crossbills.

Spatiotemporal variation in black spruce cone and seed crops along a boreal forest - tree line transect

To assess the relationship between the regenerative potential of black spruce (Picea mariana (Mill.) BSP) and the latitudinal and thermal gradients, the cone crop was monitored in the same selection of trees during the 1989-1995 period in the northern boreal forest (sites A, n = 49, and B, n = 48), in the southern forest-tundra transition zone (site C, n = 35), and at the tree line (site D, n = 21). The size of the cone crop, the amount of seeds extracted per cone, along with the percentages of filled seed and germination were measured on each tree. There was no south to north trend associated with the cone crop. The cone crop at tree line was not significantly lower than in either of the southerly sites in six of the seven observed years. The number of seeds extracted per cone, the percentage of filled seeds, and the germination of filled seeds showed significant decrease northward according to year. Although there was no significant relationship between temperature and the cone production over the study area, the percentages of filled seeds and germination were significantly (0.51 [Formula: see text] r2 [Formula: see text] 0.44; p < 0.001) associated with the regional variation in heat sum.

Spatiotemporal variation in black spruce cone and seed crops along a boreal forest - tree line transect

To assess the relationship between the regenerative potential of black spruce (Picea mariana (Mill.) BSP) and the latitudinal and thermal gradients, the cone crop was monitored in the same selection of trees during the 1989-1995 period in the northern boreal forest (sites A, n = 49, and B, n = 48), in the southern forest-tundra transition zone (site C, n = 35), and at the tree line (site D, n = 21). The size of the cone crop, the amount of seeds extracted per cone, along with the percentages of filled seed and germination were measured on each tree. There was no south to north trend associated with the cone crop. The cone crop at tree line was not significantly lower than in either of the southerly sites in six of the seven observed years. The number of seeds extracted per cone, the percentage of filled seeds, and the germination of filled seeds showed significant decrease northward according to year. Although there was no significant relationship between temperature and the cone production over the study...

Factors affecting natural regeneration of Abies lasiocarpa and Picea engelmannii in a subalpine silvicultural systems trial

An experiment was established in 1991-1992 in northern British Columbia to investigate factors influencing natural regeneration rates of Engelmann spruce (Picea engelmannii Parry) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) in three stand structures created by harvesting. Harvest treatments were a 32-ha clearcut, 0.2-ha patch cuts, and single-tree selection. Cone crop periodicity was independent of harvesting system. Natural seedfall was higher in the selection treatment and small patch cut than the clearcut treatment every year. Five years after harvest, the selection and patch cut treatments had 7 times as many spruce germinants and 10 times as many subalpine fir germinants as the clearcut treatment. Seed availability appears to be the primary limiting factor for establishment of both subalpine fir and spruce in the clearcut treatment. For spruce establishment in the selection and small patch cut treatments, availability of both seed and mineral soil seedbeds were limiting factors, while for subalpine fir, germinant establishment appears primarily limited by availability of disturbed forest floor seedbeds. Foresters could increase opportunities for natural regeneration in these subalpine forests by (i) modifying harvest patterns to enhance conifer seed distribution over harvested areas and (ii) applying seedbed preparation treatments prior to anticipated heavy seedfalls.

Tree and cone selection by crossbills Loxia sp. and red squirrels Sciurus vulgaris at Abernethy forest, Strathspey

Tree and cone selection by crossbills and red squirrels foraging on Scots pine in winter at Abernethy Forest were described from the distribution of predated cones dropped under trees. Crossbills and red squirrels fed in different parts of the forest. These distributions were related to differences in tree size, shape and density. Crossbills preferred taller, larger trees with broader crowns; these were growing at a low density. In contrast, red squirrels preferred tall trees with short crown depth and growing at a high density. Two hypotheses are put forward to account for tree selection by these species. Selection may be related to predator avoidance. Widely-spaced old trees may provide crossbills with better all-round visibility. In contrast, red squirrels may prefer denser stands where there is less need to come to the ground to cross between trees. Alternatively, crossbills may prefer old, large trees because they have smaller cones. Although smaller cones have fewer and slightly smaller seeds than the larger ones, they still may be more profitable for crossbills because their scales are easier to prise open. Red squirrels are about six times heavier than crossbills and tear or cut into cones with sharp incisors, so probably have less difficulty in opening large cones. The differing preferences for trees and cones by red squirrels and crossbills in native Scots pine forests probably reduces competition, whilst annual fluctuations in the cone crop from area to area may allow the competitively inferior, but more mobile crossbills, to avoid competitive exclusion.

A survey of insects attacking seed cones of Pinus cembra in the Alps, the Pyrenees and Massif Central

The composition and impact of the entomofauna exploiting seed cones of Swiss stone pine (Pinus cembra L.) was surveyed in native stands and plantations of France, Italy, Switzerland and Austria during 1992-1996. A total of 2785 cones were collected from 25 sites. The cone entomofauna consisted of five species, of which three (Dioryctria abietella, Eupithecia abietaria, Cecidomyia pini) were regularly observed. The two other insects, Polydrusus atomarius and Zeiraphera diniana were observed on first-year cones, and only in two stands. No spermatophagous insect was detected. None of these insect species could be considered specific to cones of P. cembra. The overall damage never exceeded 40% of the cone crop. The importance of cone damage varied with year, cone abundance, and the position of the tree in the stand. The cone entomofauna of Swiss stone pine largely deviated from that recorded in cones of other high altitude conifers but resembled that of other stone pines growing in Eurasia. The question: why cones of P. cembra were less damaged by insects than those of other alpine conifers is discussed.

Stem demography and post‐fire recruitment of a resprouting serotinous conifer

Abstract. The contribution of resprouts and seedling recruitment to post‐fire regeneration of the South African fynbos conifer Widdringtonia nodiflora was compared eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all plants were multi‐stemmed (4–9 stems/plant) and multi‐aged, indicating continuous sprout production between fires. All stems were killed by these 1990 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground level and those left standing. Individual genets usually had all ramets incinerated to ground level or all ramets charred, but intact, suggesting certain micro‐sites burned hotter, whereas other sites were somewhat protected. Although not true of the 1990 fires, there was evidence that occasionally Widdring‐tonia stems may survive fire. At one site, four of the 16 plants sampled had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (ca. 1970) and this conclusion was supported by fire‐scars on these four stems that dated to ca. 1970. Based on the highly significant correlation between stem diameter and cone density left standing after the 1990 fires, we calculated that for most sites > 80 % of the initial cone crop was incinerated by fire. This is important because we observed a strong relationship between size of the canopy cone crop surviving fire and post‐fire seedling recruitment. Under these conditions we hypothesize that sprouting confers a selective advantage to genets when fires cause heavy losses of seed. The infrequent occurrence of sprouting in the Cupressaceae suggests the hypothesis that resprouting is an apomorphic or derived trait in Widdringtonia. Data from this study suggests resprouting provides a selective advantage under severe fynbos fires, which are not only 'stand‐replacing fires,’but also are intense enough to incinerate cone‐bearing stems.

Patch to landscape patterns in post fire recruitment of a serotinous conifer

Obligate seeding species are highly specialized to fire disturbance and many conifers such as cypress, which are adapted to high intensity stand-replacing fires, have canopy seed banks stored in serotinous cones. Resilience of these trees to fire disturbance is a function of disturbance frequency and one focus of this study was to determine the effect of patch age on postfire recruitment. A second focus was to determine the extent to which fire induced a landscape level change in the location of the forest boundary. Prior to a fire in 1994, a large Cupressus sargentii forest was a mosaic landscape of different aged patches of nearly pure cypress bordered by chaparral. Patches less than 60 years of age were relatively dense with roughly one tree every 1‐2 m 2 but older patches had thinned to one tree every 3‐15 m 2 . Older trees had substantially greater canopy cone crops but the stand level seed bank size was not significantly correlated with stand age. Fire-dependent obligate seeding species are sensitive to fire return interval because of potential changes in the size of seed banks ‐ facing both a potential ‘immaturity risk’ and a ‘senescence risk’. At our site, C. sargentii regeneration was substantial in stands as young as 20 years, suggesting that fire return interval would need to be shorter than this to pose any significant risk. Reduced seedling recruitment in stands nearly 100 years of age may indicate risk from senescence is greater, however, even the lowest density seedling recruitment was many times greater than the density of mature forests ‐ thus this cypress would appear to be resilient to a wide range of fire return intervals. Changes in landscape patterning of forest and chaparral are unlikely except after fire. Factors that inhibit tree establishment within the shrubland, as well as factors that affect shrub establishment within the forest border likely affect the ‘permeability’ of this ecotone. After the 1994 fire this boundary appeared to be stable in that cypress recruited best within the shadow of burned canopies and cypress were weak invaders of adjacent shrublands.

Les arthropodes liés aux galbules et aux graines du genévrier thurifère, Juniperus thurifera L., dans les Atlas marocains

The arthropods inhabiting cones (berries) and seeds of incense-juniper, Juniperus thurifera L., were surveyed in six sites of the High Atlas mountains and in seven sites of the Middle Atlas mountains. A total of 17 species, including six major phytophagous pests, were identified. The attack periods of the pest species were synchronised with the different phases of cone development. The annual fluctuations in cone crop resulted in a large variation in the percentage of cone damage. However, more than 50 % of the berries were usually damaged. Cone damage increased from the base to the top of the tree crown but the position of the cone within the crown did not influence pest attack. Overall and specific pest damage differed between sites in the High and Middle Atlas mountains. At Tizrag (High Atlas), an average number of 1.1 seeds per cone was observed before insect attack, but the number of full, sound seeds was only evaluated to 0.13 per cone after insect attack. In this stand, we estimated that a tree disseminated 3382 full seeds on the average whilst 24454 were likely to be released before pest attack ; i.e. a decrease of 86.2 %.

The effects of NPK fertilization for nine years on boreal forest vegetation in northwestern Canada

Abstract. Plant productivity is limited by mineral nutrient availability in many boreal forest ecosystems. This study is an analysis of the growth responses of components of a boreal plant community (cryptogams, herbaceous and woody perennials, the dominant shrubs Salix glauca (grey willow) and Betula glandulosa (bog birch) and the dominant tree Picea glauca (white spruce), to the addition of an NPK fertilizer over a nine‐year period. The study was carried out in a low‐nutrient boreal forest ecosystem in the Yukon territory in northwestern Canada. The following predictions were tested: (1) that there would be an overall increase in abundance (measured either as cover, density, or dry mass) of all components of the vegetation, (2) that vegetation composition would change as more competitive species increased in abundance and (3) that initial community changes in response to fertilization would be transient. In general, all predictions were found to be true. Species composition changed rapidly in response to fertilizer. Graminoids (e.g. Festuca altaica) and some dicots (e.g. Mertensia paniculata and Achillea millefolium) increased in cover, while other dicots (e.g. Anemone parviflora), dwarf shrubs (e.g. Arctostaphylos uvaursi), bryophytes and lichens declined. There was a significant increase in the growth rate of the two dominant shrubs and of Picea, but not in the cone crop or seed production by Picea. Surveys after 1 or 2 years showed responses by the vegetation but more stable patterns of response did not emerge until after 5 or 6 years. There were consistent and directional changes in the percent cover of some of the herbaceous species on control plots. Growth rates of Salix and Betula varied considerably from year to year, independently of treatment. Long‐term studies are essential if we are to understand the role of nutrient limitation in this ecosystem.

Proximate and ultimate factors influencing oviposition site selection by endoparasites on conifer seed cones: two sympatric dipteran species on larch

AbstractA three‐year field study was carried out to investigate proximate and ultimate influences on oviposition site selection by Strobilomyia laricis Michelsen and S. viaria (Huckett) (Diptera: Anthomyiidae), two sympatric flies whose maggots develop in young seed cones of eastern larch, Larix laricina (Du Roi) K. Koch. In 1990 and 1991, when the cone crop was light, the egg distribution at peak egg lay was uniform for both species, suggesting that females of both species recognized and avoided oviposition sites previously occupied by conspecifics. Strobilomyia viaria, which emerged two weeks after S. laricis, also avoided ovipositing on seed cones occupied by S. laricis. Thus, the egg distribution of S. laricis determined, to a large extent, the distribution of S. viaria. In 1992, a year when the cone crop was very light, and egg densities per cone were high, ovipositing females of both species apparently preferred cones with few versus many conspecifics. Host size also influenced oviposition site selection in S. laricis and S. viaria. In two of three years, both species selected longer cones for oviposition. A significant proportion of the variation in egg densities of both species was attributable to trees but not to cone density per tree. Egg distribution was influenced occasionally by cone phenology and cone location within tree crowns.During the only year when egg densities per cone were high, preference for unoccupied oviposition sites resulted in increased larval survival, and in one of the other two years, preference for longer cones resulted in greater weight by the end of larval development, suggesting that oviposition preferences were adaptative. Cone phenology (at the time of oviposition) and position (crown aspect or level) had no significant influence on larval weight. Our results are consistent with the hypothesis that oviposition preference and offspring performance should be closely linked when females oviposit on the host in which their offspring must complete development.

The importance of mature conifers to red crossbills in southeast Alaska

Red crossbills ( Loxia curvirostra) in southeast Alaska feed mostly on seeds in the cones of western hemlock ( Tsuga heterophylla) and Sitka spruce ( Picea sitchensis). During a year of poor cone production, red crossbills did not forage in young stands. Within mature stands, crossbills tended to forage preferentially on trees with large cone crops. These favored trees were also the larger and older trees because cone production increases with tree size. The avoidance of young stands is especially pronounced during poor seed years and may be related to the absence of mature trees containing numerous cones with many seeds. We suggest that mature stands are critical for maintaining crossbill populations and possibly other conifer seed-eating species.