Water and population are the two that stand out to me.
I've worked outdoors or the past 30 years or so in Horticulture, Viticulture and I've also dabbled in the mortar trades.
We'd often get rained off for the day but I haven't seen that for a while now.
I'm seeing alot of change in the trees, we have a problem with Chlorotic decline in large Eucalyptus due to the ground water becoming alkaline. Another is a fungal infection affecting Norfolk pines. Its always been there but due to a change in rainfall and water quality the trees are becoming weakened and allowing infection to take over. We're loosing alot of significant trees in Perth and with all of our wisdom we can only apply band aid measures to prop them up for the time being.
Viticulture and wine making is a canary in the coal mine at the moment. A degree or two of variance can wreak havoc on the vines and in turn fruit and product quality. Alot of research is being done in this field at the moment and will have a trickle down effect to the rest of agriculture.
I'd say the days of lush bentgrass greens on golf courses are numbered aswell.
Unfortunately we seem to be incapable of change though, the backlash on urban forest policies has been extreme, "Not in my backyard!" is the cry when it comes to planting trees that, shock horror, they may drop leaves on my irrigated front lawn which serves no other purpose than to keep the lawn mower regular.
...and then theres population... Too many monkeys in the jungle
