A pruning saw is a form of hand saw with a curved, serrated saw blade, which can be held one-handed and used, from ground level, to saw through branches up to 450mm (18in) higher than the user’s height.
Though a pruning saw’s handle offers less height than the longest two-handled lopper handle (2m [6½ft]), its cutting capacity is much larger.
A pruning saw can also be used in combination with a pole lopper, extending the maximum pole lopper reach of up to 5m (16ft) even further.
While the largest diameter branch that can be cut with a lopper is 100mm (4in), a pruning saw can cut branches as thick as you are able to keep sawing; from smaller branches of 100mm (4in) or less, to branches up to 245mm (10in), or even thicker, depending on your stamina!
Though a suitable alternative for cutting thick branches, using a pruning saw does require far more physical effort than using a lopper, so be mindful of your own ability before making your decision.
Secateurs, also called hand pruners and pruning shears, are based on a similar, scissor-like design to loppers, but are shorter and less powerful, and should not be used to prune branches or stems thicker than 20mm (0.7in).
Loppers can be used to cut through branches of up to 100mm (4in) diameter, and are therefore far more powerful than secateurs. Secateurs are only a suitable alternative to loppers if you will be cutting through much thinner branches and stems, such as when pruning hedges or shrubbery.
Gardening knives are much less powerful than loppers or secateurs, and are intended for use as weeding, light pruning and flower-collecting tools. This type of tool should never be used to cut through branches, and is not a suitable alternative to a lopper.