Al:
Thanks for your pictures. Cr@ppy computer competence at home disallows viewing of images in any quality fashion at the moment, so I'm just now appreciating these fruit fully today at work. Is that first one a Celastrus? Not so bad, if it's C. scandens. Those crabapples look just scrumptious. Gotta clone?
Resin:
No fair flaunting Sorbus and Cotoneaster, though I imagine they are all stellar in the kind of climes in which you cavort. Beautiful, just beautiful.
Runk:
I'll unabashedly borrow that combo idea -- I've got some tea viburnum to move around and they might as well have a fun new dance partner. Hydrangea quercifolia it is. Shorter forms like 'Pee Wee' and 'Sikes Dwarf' should generate a flouncy skirt around the knobby knees of V. setigerum.
And someday, I'll get to see these places from whence the names derive.
I agree with Resin to a point on the flowering/fruiting flagrancy. Additional info for on/off seasons could include pollinator levels. If the anecdotal evidence of less bees and other busy bodies is true, then less movement of pollen from flower to flower could well result in less fruit. If one is referring to native populations of plants, then the mixing of males/females (Ilex) is already present. Same for cross-pollination of viburnums and Rosaceae members, for example. In the garden, however, if you are the sole provider of the appropriate pairings, it may be performance of the partner which proves paltry. Thus pronounceth Porky Pig.
In the garden, all the microclimatic manipulations are manifest. Light, aspect, soils, moisture, nutrition -- in addition to the heat of that year's growing season. Ilex species respond tremendously well to additional nitrogen at the beginning of the growing season. Winterberries will reward you with wondrous windfalls if given this kind of boost. Many sage members (not Salvia!) of the Great Rivers Chapter of the Holly Society of America would bring award-winning sprigs to annual meetings, and then modestly remark on the subtle simplicity.
Depending on the clone, many Malus bear better in alternating years. This is a reason for clonal selections for the ornamental landscape, if you want annual accolades.
Drier years many times result in fewer finished fruit; more are shed to accommodate less resources. Light availability often changes with time in a garden, as trees grower taller and wider and cast more shade.
In other words -- it all depends.
