Bumblebees and butterflies have seen their numbers plum-met after another year of unsettled weather.
Mild winters and bad weather in summer created bad conditions for small plants.
But whilst insects suffered, grass growth rose, meaning a good year for livestock farmers.
Conservationists and farmers must work together, the trust said.
Warmer winter months and bad summers have become the norm.
Specific sites have now seen a big change in their wildlife, especially due to the surge in grass growth.
The number of bumblebees had fallen by 85% on the previous year as wildflowers that attract the bees in field margins were outgrown by grass.
A drop in numbers, with volunteers recording a fall in sightings of marbled white numbers by 73% and 23% fewer common blue butterflies.
But the grass growth meant good hay and silage harvests for tenant farmers on Trust sites and improvements on other sites.
The extended growing season also saw better conditions for damsons, acorns and hazelnuts.
However, there were falls in the number of field voles, which could lead to problems for barn owls and kestrels who feed on them.
And whilst slugs have benefited from the mild and wet weather, gardeners have had to suffer the effects on their plants.