| Calliandra calothyrsus - Production and use: A Field Manual |
Joanne R. Chamberlain, Alan J. Poffinger, and Rajesh Rajaselvam
Flowering and fruiting characteristics
In many areas, Calliandra calothyrsus can flower throughout the year, but the species usually has a peak flowering period three months before the onset of the dry season. Buds are held on a racemose inflorescence and open sequentially from the base to the apex of the inflorescence. Each flower opens at approximately 1600 furs, remains receptive for one night only, and wilts the following day. An individual inflorescence can flower for 90 to 120 days. Calliandra calothyrsus is andromonecious, which means that the plant produces both hermaphrodite (bisexual) and staminate (functionally male) flowers. The staminate flowers lack the female parts (ovary, style, and stigma) and can never produce fruits. After the flowers are fertilized, mature fruits and seeds develop in approximately 90 days. The plant always produces more flowers than fruits: fruit-to-flower ratios of 1:20 are common.
Calliandra calothyrsus is outcrossing and has a low tolerance of selfing The species is pollinated by bats (Chiroptera) and hawkmoths (Sphingidae). The most efficient pollinators are small, nectivorous bats in the subfamilies Glossophaginae (New World fruit bats) and Macroglossinae (Old World fruit bats), although larger, primarily fruit-eating bats are also efficient pollinators of the species. Bats pollinate C. calothyrsus by hovering over the flower for a second or two. They insert their long tongues into the base of the flower and drink the nectar. Sometimes, larger fruit-eating bats land on the inflorescence, which bends under the weight of the bat allowing access to the nectar. In Honduras, a small nectivorous bat, Glossophaga sp., has a very small foraging range (less than 600 m), but other, frugivorous bats can travel much greater distances (up to 50 km) for food.
In its native range, C. calothyrsus generally forms small scattered populations within river systems and areas of disturbance. There is a great deal of variation in seed production, both between populations and within populations, from year to year. This variation may have a genetic basis (i.e. some populations are genetically better seed producers than others), or it may result from environmental factors such as climatic conditions or pollinator type. Calliandra calothyrsus produces less seed that several other multipurpose-tree species, such as Leucaena spp. or Gliricidia sepium, and is known as a shy seed-producer both in its native range and when planted as an exotic species.
Seed collection, processing, and storage
When collecting C. calothyrsus seed in the native range or from naturalized stands, pods should be sampled from trees spaced evenly and widely across a population. To prevent selecting seed from closely related individuals, sampling more than one tree in a patch of dense C. calothyrsus should be avoided. Pods should be collected from all positions in the crown. The pods of C. calothyrsus are dark brown and dry when ready for collection, and contain an average of five to eight seeds per pod. An individual tree may possess branches with pods at all stages of maturity, hence ripe pods can be collected from the same tree over a period of four to six weeks.
The pods dehisce explosively and can scatter the mature seeds several meters from the tree. Seed can be collected by placing matting below and around trees that have mature pods and removing the dehisced seed from the matting on a daily basis. Alternatively, the mature pods can be hand-picked from the tree and left to dry in the sun under netting to extract the seed. Seed can also be extracted by hand but must be dry and hard to ensure good germination and viability. Once collected and extracted, the seed should be stored in sealed containers in a refrigerator at 4°C. Stored in this manner, C. calothyrsus seed can retain its viability for at least five years. If the seed is going to be planted soon after collection, it should be stored in sacks in a cool dry place and protected from pests such as rats or mice.
To date, large quantities of Calliandra calothyrsus seed have only been collected from natural populations or naturalized stands. Seed orchards are currently being established in the native range and elsewhere in order to produce large quantities of seed with known and desirable traits, such as good wood production or forage quality. These seed orchards have not yet reached a productive stage, however.
Seed orchards should be planted in an isolated site to reduce the risk of pollination from other, unselected sources and should be managed to produce frequent, abundant, and easily harvested seed crops. Although there has been little research on the best method of establishing C. calothyrsus seed orchards, it is possible to make some suggestions:
1. The seed orchard should be located on a uniform site that is accessible and secure.
2. It should be located away from other C. calothyrsus trees to make sure that the orchard trees are not contaminated by pollen from outside.
3. One of two types of seed orchard can be established: (a) Seed is collected from individual trees and kept separate in "families." Seed or seedlings from these families are planted, and their identities are maintained. The performance of each family can be measured and ranked, and less-desirable families can be removed; (b) Seed is collected from individual trees and bulked, and seed or seedlings are planted from the bulk seedlot. The second type of seed orchard is simpler to establish and maintain than the first, and the seed crop will have a broader genetic base.
4. The seed orchard can have a number of possible designs, but the pollinators require good access to the flowers to allow abundant seed production. Possible designs might include planting at a very wide spacing, such as 3 x 3 m, or planting in widely spaced rows, such as 2 x 4 m.
5. Coppicing or pollarding can be used as a management technique to improve seed production and ease of collection.
6. Early flowering in the seed orchard will not necessarily guarantee good seed yields in the first year, but seed production can be expected to improve with time.