K.—BOTANY 205 
the soil surface vegetation consists mainly of shade-loving shrubs, herbs, 
ferns and mosses. The leaf fall from the trees and the general organic 
remains, along with that of the undergrowth, produce a soil covering of 
disintegrating organic matter, generally referred to as the humus layer. 
This layer acts like a mulch and ameliorates and conserves soil moisture 
and temperature. The tree roots penetrate more deeply into the sub- 
stratum than most forms of other vegetation, this increasing its aeration, 
permeability, and water-holding capacity. Although it has not been 
definitely decided whether forests increase the rainfall or not, it can be 
claimed with every justification that the forest is of great importance as 
a conservator of water and as an equaliser in the drainage of the land. 
Where no forests exist in the upland or collecting regions of watersheds, 
the rain falls unhindered, beating the surface hard or eroding it down to 
the bare rock. ‘There is nothing to check the downward rush of water, 
which collects into mountain torrents which gush unbridled into the 
main rivers and streams, causing them to become swollen and flooded. 
These in turn race through the fertile valleys to their outlets, tearing down 
and overflowing their banks. The damage done by severe and sudden 
floods to roads, bridges, agricultural crops and stock, including human 
habitations, is well-nigh incalculable. Nor does the matter end there : 
millions of tons of valuable soil is washed away in these turbulent floods, 
and deposited as barriers in the river beds or in the sea at the river bar. 
Harbours and docks at the outlet of our main rivers become silted up 
with mud and debris: this in turn—apart from the loss of soil—involves 
costly dredging operations to keep the navigation channels clear. 
Where forest exists in the upland districts or collecting ground of the 
water, rivers are more uniform in their flow, year in year out, and carry 
much less silt and debris. ‘The crowns of the trees break the force of the 
falling rain ; the humus layer on the forest floor has an enormous water- 
absorbing capacity, and when saturated it allows the water to percolate 
slowly into the deeper loosened layers of mineral soil, from which in turn 
it gradually finds its way into springs and watercourses. Further, the 
influence of the forest is such that the melting of snow is more gradual 
and water is slowly absorbed and held, thus again avoiding floods. The 
forest regulates the off-flow of water after heavy rains or melting snow. 
This water is fed into springs and watercourses more gradually throughout 
the year, thus preventing floods at one season and equally serious drought 
at another. As regards the influence of the forest in lessening the 
destructive effects of cloudbursts, we have it on the authority of Fernow 
that : ‘ The Forest litter, the moss-covered leaf-strewn ground, is capable 
of absorbing water at the rate of 40,000,000 to 50,000,000 cubic feet per 
square mile in 10 minutes, water whose progress is delayed by some 
12-15 hours after the first effects of a heavy freshet have passed.’ I do 
not claim that afforestation or forest conservation in the high ground and 
valley slopes will entirely prevent floods and drought, but what the 
forester is doing or leaves undone in the remote hinterland will go a long 
way to check or ameliorate the evil effects of both. I have referred to 
these facts because the biological influence of the forest is so important 
and widespread in regard to drainage and water supplies. 
