There are a lot of species out there being sold as hedges. That is all well and good, but the truth is, a good deal of woody plants, including trees, can work nicely in this respect even if they haven’t occurred to you. At the end of the post is a list of just a few candidates that maybe you haven’t thought of to border the yard, keep the animals in or out, or simply because it just might look cool. Any bush, shrub or tree that responds well to pruning can work. Respond well means generally that it stays in good health, but the use or look will determine how vigorously you want it to resprout. A plant of low vigor in general can be expected to regrow slowly. Younger, healthy plants rebound more readily than sad old-timers. In most situations, you will want a good regrowth because it often means a nice, compact and dense system. Think about christmas tree shearing or trimming privet hedge and you will know what I mean. Do not forget that this method produces superb windbreaks, and can be used as privacy hedge.
This can be particularly useful when the desire is an inpenetrable hedge to keep animals out of an orchard or garden, or to keep chickens from wandering too far. Prickly choices like hawthorn or locust are obvious candidates, but even many native plums and wild pears can prove quite formidable. I have often used the prunings to stuff holes in the lower areas of the hedge, or in openings, the new growth tangling around it. This is similar to the old European practice of dead hedging, where farmers would create an impressive barrier by layering nasty dead brush 6 foot wide and at least that tall.
You get bonus from some for dual use, for example locust as a nitrogen fixer, plums and other fruits for edibles, kindling, and smoking wood. Small wood can also be used in projects and general building.
Plashing is an age-old method developed in the old world. It consisted of slashing the stem of a hedge plant partly through its diameter and bending it down to a particular angle (often 45 or more degrees). Some practitioners would take the time to also weave the branches around each other to both hold the bent stem in place, and to add to the strength and impenetrability of the living fence. Note that any horizontal orientation of the limbs will result in vertical growth, which can in turn be bent in the future. The very act of any pruning will also yield resprouting, both in the plant aerial portions, but also in some species with root suckering.
Some species for hedges aka living fences :
plum– especially native species like prunus americana and p. nigra, which are often sharp spurred. Will often resprout readily, especially when young.
locust– honey and black locust are common, and very thorny. They also have an irritant in the thorn. Black locust is rot resistant. Rank growth sometimes breaks, so trim stocky.
hawthorn– another very spikey species, and also has an irritation associated with a prick from a thorn. A tough plant with strong wood.
siberian pea shrub – an absolutely beautiful species. Can be trimmed quite bushy for a tree (this “shrub” can get 20 feet tall). Easy to manage. This is a zone 2 plant, with edible (kind of) pods and seeds, and is an awesome nectary for beneficials like bumblebee. Good windbreak or privacy hedge.
apple, plum and cherry – not as dense as other woody plants, they are often espaliered, trimmed, and woven to produce novel fences more akin to fancy split rails in purpose. They can however be nearly sheared (use secateurs please, not hedgeclippers), to make a denser specimen. More wild members, like crabapples and seedling pears can be brushier or pokier. Some species, like malus sargentii (like roselow), are more accurately a shrub than a tree.
shade trees – many species will allow themselves to be hedged, particularly if started young (before 6 inch diameter for instance). Look at the list on this post for more details – https://waldenheightsnursery.com/coppice-or-pollard
Another helpful technique when looking to create a barrier is to commingle species. A successful plan can be to gang woodier examples like plum or crabapple with lower growing simpler species like rugosa rose or blackberry. This will grow well especially if grouped to avoid excess shading in the lower plants. A wide as well as long tangle will result, keeping out unwanted guests.