Flowering phenology of myrtaceous trees and their relation to climatic, environmental and disturbance variables in northern New South Wales

Abstract

Patterns of flowering phenology, which represent a partial description of food availability for nectarivores, are described for 20 species of myrtaceous trees on the mid-north coast of New South Wales (NSW), Australia.

Data were recorded monthly between 1982 and 1992 across 23 sites that sample a variety of local environmental conditions and disturbance histories. Flowering periodicity and intensity were highly variable between species and sites, ranging from annual flowering to no flowering over the 10 year period.

Cool temperatures experienced prior to floral budding was a strong predictor of flowering for nine species. Extraordinary climatic events also influenced flowering.

The period of greatest flowering for all species combined occurred nine months after the highest monthly rainfall recorded in the survey (March 1985). An 18 month extreme drought led to poor flowering in Corymbia variegata, Eucalyptus acmenoides, E. grandis and E. resinifera, but recovery after drought broke was rapid.

In contrast to climate, few site-based environmental variables explained the inter-site variation in flowering performance of the tree species.

Site disturbance from logging at two sites during the survey did not influence flowering in the remaining canopy over following years. No species showed a negative correlation with a history of recent logging and direct comparisons of the percentage of foliage in flower, between large and medium sized trees, did not differ for any species.

At a timber production forest scale, the negligible effect of tree size (if > 10 cm dbhob) and high stem density resulting from selective logging leave about half of the net harvestable area producing flowers at a similar density to unlogged forest. However, larger trees flowered more frequently than medium-sized trees in C. variegata (medium: every 5.9 years; large: every 2.3 years) and there was also a trend in this direction for 13 of 17 species. Low intensity and wildfires caused differing amounts of crown scorch, sometimes resulting in bud loss, but most species flowered at pre-fire levels 1-3 years after the disturbance. Eucalyptus microcorys and Angophora costata flowered poorly at sites that experienced frequent low-intensity burns.

Regionally, blossom shortages occur through a combination of spatial and temporal patchiness in flowering and due to the clearing of those species that occurred on soils preferred for agriculture. On the north coast of NSW, these shortages commonly occur from late winter to spring. Species that flower reliably in this period include E. robusta, E. tereticornis and E. siderophloia in late winter and E. siderophloia and E. acmenoides in spring. 

Tree Species

Summer

Autumn

Winter

Spring

Summer

Click on species names to view flowering patterns as they occurred at each site

Dec

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Jan

E. resinifera

A. floribunda

L. confertus

E. propinqua

C. gummifera

C. variegata

E. signata

E. saligna

E. grandis

M. quinquenervia

E. pilularis

E. robusta

E. bancroftii

E. tetrapleura

E. tereticornis

S. glomulifera

E. microcorys

E. siderophloia

A. costata

E. acmenoides

Flowering seasons of 20 species of myrtaceous trees collated over 10 years from 23 study sites on the north coast of NSW. Frequency of flowering was characterised by calculating the percentage of all flowering events occurring in each month.

	Represents periods of frequent flowering (>50% events occurred in that month)
	Represents regular flowering (25-49%)
	Represents occasional flowering (5-24%)
	Months where <5% of flowering events occured have been omitted