there should be additional information about the condition or type of the areas (you would like to discuss) when we discuss about succession (seed recruitment) after fire. It is forest (woodland) or grassland? It is situated at tropical, subtropic, boreal, or other? Fire aspect is also important, it is surface, Crown or Ground fires because it give different impact of degree of severity. All these information will influence how much time pioneer species need to grow at the open or semi open canopy after disturbance because its related to their seed bank. For boreal forest for example fire will create conditions suitable for the establishment of shade-intolerant species such as trembling aspen or jack pine (within 5-6 yr they are already in 1-2 m height). high intensity of fire will not kill the jack pine, in fact it will initiate strobilus opening. In tropical forest, fire will favor herbs and lianas, how much time the recruitment depending on seed arrivals or available seeds in the seed bank (highly influenced by insect attack, its viability, and fire intensity). you could access interesting articles in google or RG focusing on your topic or chronosequence succession after fire, or other keywords correlated to seed reqruitment after fire (including: Puerta Piñero C, Muller-Landau HC, Calderón O, Wright SJ. 2013. Seed arrival in tropical forest tree fall gaps. Ecology 94(7): 1552–1562). I hope this will help you...Good luck

It really depends on your ecosystem and species involved, as S. Hari indicates.  In many places the pulse of recruitment can last decades, with gradual infilling; in others, if recruitment doesn't happen right away, grasses, sedges, and other species can out compete seedlings for water and succession much delayed.  There are many things that influence this rate- climate in the following years, distance from the intact edge, whether it's a good seed crop year for the survivors, herbivory/seed predation, etc.  Also the intensity of the fire may matter, if it alters the biogeochemistry or physical properties of the soil in some way (at least some abnormal way).

So overall, it really depends on the system and species.  In most places, though, you've got to give it a few years for seed from the outside.

I would recommend looking for post-fire studies in your ecosystem and then looking into the methods sections to see how long post-fire the study was done.  But again, other things will matter which vary, like climate, distance from edge, etc...

Some good papers on this topic in these ecosytems by Jon Keeley (https://www.researchgate.net/profile/Jon_Keeley) and Juli Pausas http://www.uv.es/jgpausas/

good luck

I have to agree with Brian Buma... highly variable across space and time, across species, and across fire severity gradients. Time to put in some seed traps, regeneration plots, and start some multi-year (preferably multi-decade) monitoring. Probably not the easy answer you are looking for.

However, I think we all need to keep in mind that recovery will happen. The notion that forests need our help to recovery is solely based on our impatience. If the goal of informing forest management is to save costs by relying on natural regeneration to create evenly stocked forests to maximize production, then the answer is pretty simple, "do you have adequate stocking of desired species after year 2 or so". If not, you had better plant, the economic clock is ticking. If the goal is ecosystem management for multiple services we may want to consider the fact that we should just leave it alone. Look at some of the work from DC Donato and JL Campbell for nice discussion on this: a good one can be found here:

https://www.researchgate.net/publication/259926443_Multiple_successional_pathways_and_precocity_in_forest_development_can_some_forests_be_born_complex  

I think a lot of our efforts globally have been focused on the rarity of old forests, it's possible that naturally recovering early seral ecosystems that began from fire are just as rare.   

Article Multiple successional pathways and precocity in forest devel...

Much depends on the quality of the understory before the burns occurred.  Here in the Western USA forests, if too much grazing removed the forest perennial grasses, then there were not grass seeds being produced during non-fire years, to sprout as colonizing plants once the fires went through.  If the perennial native grasses have been gone for decades, then you end up for a few years with a barren area with potential massive erosion problems, until the trees and shrubs. By missing the understory of grasses, you can also lose your topsoil.  

Based on experience working in tropical savanna in Indonesia, seed dispersal is significantly assisted by grazing animals. Usually water buffalo, deers, and bos javanicus ate pods of Acacia nilotica in dry season, when they excreted their scats in areas of their range including post fire sites in the savanna, the seeds remain viable in their droppings and usually not long after the first rain in the wet season, the seeds germinate.

Have a look at post-burn seedlings of a pine and various broad-leaf (sub-) Mediterranean shrubs and trees in the attached.

Article From monospecific to mixed forest after fire?: An early fore...