Quote:
Originally Posted by Paul mabbott  The recent 'British Wildlife' summary by Alexander et al has been quoted elsewhere.
Species diversity, of course, is usually interpreted as a product of biomass (individual numbers) and species number. There have been plenty of examples in the entomological literature of interesting, even rare, species living on sycamore. I'm not sure what you mean by 'UK specialists'. Nor am I sure how there can be a 'negative influence' on biodiversity except in the case of unproductive trees such as plane. 
I think your definition of invasion is different from mine. You describe sycamore filling gaps in woods - not growing into woods at the expense of trees already there. I think that a lot of the "problem" is purely in the mind of the beholder - if you become obsessed with removing it then you will only see that problem recurring. You, for instance, are talking about seedlings &c - what happens if you leave them? My bet is that most would die, the occasional one will grow to maturity and have no effect on the overall balance of the woodland. In effect, we shall never know what the effects of this putative invasion are because no one lets it proceed! I restate my observation that I have never seen evidence of sycamore invasion in any reasonably sized, undisturbed, semi-natural wood. |
I'm going to make this my last post on this thread for fear of the risk of being labelled an obsessive, which I'm not (I hope). First off, I just want to say how enjoyable it is to have a debate about sycamore where my views are challenged by statements a hell of a lot more substantive than 'they look nice'. Good stuff. Also, thanks to you Paul, and to Rob Sutton, for pointing me in the direction of very interesting articles on the subject. I have learnt a lot from those.
That said, I remain to be fully convinced. I accept that I didn't appreciate the range of species that sycamore hosts, and I am grudgingly yielding on the idea of the biodiversity that they support.
As far as the native/non-native debate, I have read various articles now suggesting that it might be native, particulalry in the NW, but I don't find them compelling, and there is at least as much (more?) research with very good evidence about it's recent arrival, albeit disagreement about exactly when.
A few comments in reply to the quoted posting.
Diversity - the way I was using this is related not just to the tree specifically, but also the contribution that a tree makes in the community of other trees it lives alongside. My understanding (being re-appraised in light of the articles I have since read) is that while there is a large biomass, even with a decent species count, the contribution sycamore makes to biodiversity is relatively low compared to what a native species would have added to the area, as sycamore did not host species not otherwise supported by 'native' trees. By the term 'UK specific' I clumsily tried to express 'endemic specialists dependant on sycamore'.
Regarding sycamore invasion of woodlands - I stand by what I said, although you may be right to say that it is only a problem if I choose to see it that way, which I do. I disagree with the idea that there is such a thing as an 'undisturbed semi-natural woodland' anywhere in the UK, as the dynamics of woodland constantly open up new spaces, disturbance to the canopy, disturbance to light falling on the woodland floor, etc. Distubance is a vital process, and sycamores do exploit this at the expense of other trees. Near where I live, Bursted Woods was a beech woodland before the '87 storms, at least as far back as 1780. OK, '87 was extreme disturbance, but Bursted is now pre-dominantly sycamore secondary woodland. A bit further up the road at Stanmer Woods, much less impact from the storm, but with a few mature sycamores in the Beech canopy, the understorey is now dominated by sycamore saplings of all sizes, and no, if left in place they don't die. They grow tall, (very skinny) and reach into the canopy, waiting for disturbance (
a la '87?)to allow them to take over the space from other species.
It would be interesting to see what would happen if a sycamore wood was left to mature, to see if other species find a place after a while as suggested with the ash/sycamore cycle hypothesis, but I won't be around to argue about the results, so where's the fun in that? Meanwhile, whatever the merits of the sycamore for whatever invertebrate species it supports, I will follow my instinct (prejudice?) and looking at the evidence from woods I know, and others I visit and survey.
On balance, I'm still for removal wherever an option. I am now looking at things with more of an open mind though, and my position may change with time.
Thanks again to all for an interesting debate.