The New Zealand government commissioned him in 1884 to compile a report on the indigenous forests of the country and appointed him as chief conservator of forests the following year.
Although not trained as a forester, he was in favour of sound forest conservation.
He founded the forest and agriculture branch of the Crown Lands Department, implemented regulations to curb the misuse of forests, and was instrumental in setting aside some 800 000 acres as forest reserves by 1888.
Kirk was recalled in 1889 from retrenchment to work on the Forest flora of New Zealand, but died in the midst of this great work.
At the time it was hoped that the work could be published under the supervision of his son, H. B. Kirk.

Retrenchment did not dampen Kirk's botanical enthusiasm.
He explored The Snares, Auckland Island, Campbell Island and Antipodes Islands and Stewart Island in 1890, and in later years the headwaters of the Turakina and Rangitikei Rivers.

Kirk died in straitened circumstances and was buried in an unmarked grave in Karori Cemetery in Wellington.
He was survived by his wife, Sarah, and five of his nine children.
His daughter Cybele Ethel Kirk worked with unmarried and abandoned women whist another daughter Lily May Atkinson, was a well-known suffragette and temperance campaigner.
Despite appeals, his widow was denied any compassionate grant from the Government.
Sir Joseph Dalton Hooker wrote of Kirk's death: “This is a great loss to Botany, for indeed except the late Baron von Mueller there was no other cultivator of Botany in the Southern Hemisphere who could compare with him and I have been looking for years for the Forest Flora of New Zealand by him as to a work of very great scientific importance".

Kirk wrote some 130 papers on botany and plants, published in New Zealand and British journals.
In 1875 his report on The Durability of New Zealand Timbers appeared, then The Forest Flora of New Zealand in 1889, followed by Students' Flora of New Zealand, published after his death in 1898.
The Forest Flora of New Zealand was described by printer and journalist Robert Coupland Harding as:
From the Government Printer we have received a copy of one of the most interesting as well as the most valuable works yet issued by the Government of this colony—the Forest Flora of New Zealand.
The book is foolscap folio, and like all Mr Didsbury's productions, is well and correctly printed.
All our varied forest trees and shrubs are minutely described and illustrated; the native and vulgar names are given, the properties and uses are set forth in popular language as well as in the ordinary scientific style.
The plates number one hundred and forty-two, and are chiefly executed by the draftsmen of the Survey Department.
Most of them are signed by Mr Hugh Boscawen, and reflect great credit on his skill as a botanical artist.
We notice other names of the survey staff, as well as those of Mr A. Hamilton of Napier, and Mr D. Blair.
The work is written and compiled by Mr T. Kirk, f.l.s.,
and is highly creditable to the author.
The contents might have been more systematically arranged, as we find closely allied species widely separated, altogether alien forms coming in between.
The illustrations as a rule are excellent, but being by different hands exhibit a want of uniformity.
Some are fully shaded; others in almost pure outline.
In an appendix the plants are systematically classified, and to have followed this arrangement in the body of the work would have been an improvement.
A comparative table at the end showing at one view the particulars scattered through the work as to strength, specific gravity, &c, of the various woods, would have been an acceptable addition.
We would be sorry to criticise so excellent and valuable a work in any spirit of faultfinding.
A limited number, we believe, were printed on large paper.
It would have been well to have issued a number for sale, as the narrow margin to some of the plates will not be pleasing to book-lovers.

— Robert Coupland Harding, Typo: A Monthly Newspaper and Literary Review, Volume 3
Thomas Kir
The New Zealand government commissioned him in 1884 to compile a report on the indigenous forests of the country and appointed him as chief conservator of forests the following year. Although not trained as a forester, he was in favour of sound forest conservation. He founded the forest and agriculture branch of the Crown Lands Department, implemented regulations to curb the misuse of forests, and was instrumental in setting aside some 800 000 acres as forest reserves by 1888. Kirk was recalled in 1889 from retrenchment to work on the Forest flora of New Zealand, but died in the midst of this great work. At the time it was hoped that the work could be published under the supervision of his son, H. B. Kirk.
Retrenchment did not dampen Kirk's botanical enthusiasm. He explored The Snares, Auckland Island, Campbell Island and Antipodes Islands and Stewart Island in 1890, and in later years the headwaters of the Turakina and Rangitikei Rivers.
Kirk died in straitened circumstances and was buried in an unmarked grave in Karori Cemetery in Wellington. He was survived by his wife, Sarah, and five of his nine children. His daughter Cybele Ethel Kirk worked with unmarried and abandoned women whist another daughter Lily May Atkinson, was a well-known suffragette and temperance campaigner. Despite appeals, his widow was denied any compassionate grant from the Government. Sir Joseph Dalton Hooker wrote of Kirk's death: “This is a great loss to Botany, for indeed except the late Baron von Mueller there was no other cultivator of Botany in the Southern Hemisphere who could compare with him and I have been looking for years for the Forest Flora of New Zealand by him as to a work of very great scientific importance".
Kirk wrote some 130 papers on botany and plants, published in New Zealand and British journals. In 1875 his report on The Durability of New Zealand Timbers appeared, then The Forest Flora of New Zealand in 1889, followed by Students' Flora of New Zealand, published after his death in 1898. The Forest Flora of New Zealand was described by printer and journalist Robert Coupland Harding as:
From the Government Printer we have received a copy of one of the most interesting as well as the most valuable works yet issued by the Government of this colony—the Forest Flora of New Zealand. The book is foolscap folio, and like all Mr Didsbury's productions, is well and correctly printed. All our varied forest trees and shrubs are minutely described and illustrated; the native and vulgar names are given, the properties and uses are set forth in popular language as well as in the ordinary scientific style. The plates number one hundred and forty-two, and are chiefly executed by the draftsmen of the Survey Department. Most of them are signed by Mr Hugh Boscawen, and reflect great credit on his skill as a botanical artist. We notice other names of the survey staff, as well as those of Mr A. Hamilton of Napier, and Mr D. Blair. The work is written and compiled by Mr T. Kirk, f.l.s., and is highly creditable to the author. The contents might have been more systematically arranged, as we find closely allied species widely separated, altogether alien forms coming in between. The illustrations as a rule are excellent, but being by different hands exhibit a want of uniformity. Some are fully shaded; others in almost pure outline. In an appendix the plants are systematically classified, and to have followed this arrangement in the body of the work would have been an improvement. A comparative table at the end showing at one view the particulars scattered through the work as to strength, specific gravity, &c, of the various woods, would have been an acceptable addition. We would be sorry to criticise so excellent and valuable a work in any spirit of faultfinding. A limited number, we believe, were printed on large paper. It would have been well to have issued a number for sale, as the narrow margin to some of the plates will not be pleasing to book-lovers.
— Robert Coupland Harding, Typo: A Monthly Newspaper and Literary Review, Volume 3
Thomas Kir
Thomas Kirk (botanist)