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Some Questions on Protea mortality and Growth Rates


Some ramblings by Tony in response to questions by John Silander

 Question.  CANDIDATE SPECIES FOR MEASURING GROWTH RATES AND MORTALITY

What are some candidate proteas that are re-seeders after a fire, and for which it would be relatively easy to measure year-to-year growth (as estimated from internode sizes), <* all bigger plants: only Serruria & Spatalla might be a problem> might be able to estimate individual age and thus time since last fire,  <* all terminal flower species: Protea, Leucadendron, Aulax, - in fact only Leucospermum a problem> might be able to estimate in each year whether or not flowering occurred (i.e. evidence of fruit retained, and even some qualitative, categorical estimate of fruit size or seed number), <* all serotinous species: Protea, Leucadendron, Aulax> and for which one might be able to find a number of populations that vary in age from 1 or a few years to as old as one can get (15-20 years?), plus some populations that have had fires since they we last censused by PAP up to 10 years ago, and populations across a range of climate regimes with populations doing well or not well across <* widespread species, species biased in area to the west coast and swartberg> the CFR (i.e. allowing us to capture something like the Aloe story)?  Is there any seed bank? 

We will have to deal with resprouters separately which will be more difficult.
!! we dont even know if they are hundreds versus thousands of years old - less than 5% die per 15-20year fire cycle - do the sums!  Perhaps some carbon dating of central cores of lignotubers?>

Answer: The best to do will be the serotinous species, with widespread ranges.  Most will do, but those with West Coast and Swartberg ranges will show any drought effects best.  Those marked # are too rare.  Those marked ***will do best.

Any erect Protea
Pr repens*** lanceolata;
Spoonbract: Pr eximia*** susannae, obtusifolia, longifolia, pudens#, Pr burchellii**;
Bearded: Pr laurifolia*** lorifolia**, neriifolia, stokoei#, coronata, magnifica**, grandiceps, holosericea#;
White: Pr punctata*** mundii, lacticolor#, venusta#, aurea;
Penduline: Pr namaquana#, effusa#, sulphurea, recondita, pendula;
Rose: Pr scolymocephala **, acuminata**, canaliculata**, nana, witzenbergiana??, pityphylla??.
Aulax (pallasia**, cancellata).

The above are all serotinous and thus the entire seed bank is visible on the plant.  With Ld the ones marked !! drop their seeds and have soil-stored seed banks

Leucadendron:
Sandveld: Ld thymifolium!!, levisanus#, concavum#!!, dubium!!, cinereum**, linifolium, gapinii#;

Arid - all !!: but Ld pubescens***;
Ld corymbosum!!**;
Silver: all !! - all but Ld rubrum***;
Sun: all !! But Ld loranthifolium**, Ld glaberrimum**;
Delta seed: Ld uliginosum, loeriense, rourkei, conicum, salicifolium** - all like water??;
Sunshine: Ld procerum***, coniferum, meridianum, eucalyptifolium***, xanthoconus*, laureolum*, gandogeri, strobilinum#;
Needleleaf: Ld teretifolium.
 


Question.  CO2 RESPONSES AND GLOBAL WARMING

What information is there on protea response to changes in CO2.  We are still getting questioned on this by the reviewers, i.e that CO2 response will be confounded with temperature unless we specifically measure it too.  Is there any thing published?  Could we actually address this experimentally with some supplementary trials that look at temp and CO2 responses?  Or at least say we can do this and look at the costs later? 

Answer: My theoretical response to this will be:

Because carbon is not limiting to proteas, plants will grow faster, produce more biomass and burn more often.  Regeneration times will thus favour more strongly serotinous species with shorter regeneration times.  Plants will become less palatable.

Physiologically more will be invested in flowers and fruit, but because nitrogen and other elements are limiting only flowering will really benefit, not seed set.  So more flowerheads, but less seed set per flowerhead with total seed production per plant staying constant.  However, if higher temperatures result in chemical changes in soil biochemistry, then this becomes irrelevant.  However, I am aware that Guy does not buy this, but he will after we have some results.


Question.  MORTALITY IN PROTEAS

Are there any reference to the effect that not much mortality occurs in proteas once they become established?

Answer: This is based on observation.  There are exceptions - the Silver Tree has a mortality of about 1-5% per year.  Most other proteas have such a low death rate that even 1 or 2 dead plants on a mountain side are very conspicuous and generate comment.  Under normal conditions, death rate must be well less than 0.5% per annum.  During serious droughts it may reach 10%, although I have seen a population of Ld "touwsrivierensis" at Baviaanskloof where a seep was obviously drying up and almost 60% of the population died - all on the periphery.  I have also seen one case of inexplicable mortality, where most species were affected, and survivors contained only live branches on the SE side of the plants - no fire, plenty water, must have been a severe hot wind or (unlikely given the area, but not impossible) a defoliant/herbicide brought in on a wind.  Restios and fine-leaf dicots were unaffected, but all broad leafed plants were hammered.

OK:  SO YOU WOULD SAY THAT MOST MORTALITY OCCUURED ONLY DURING THE FIRST FEW YEARS AFTER ESTABLISHMENT IN THE VAST MAJORITY OF POPULATIONS, UNTIL SENESCENCE MAY KICK IN.  HOW OFTEN DO YOU ENCOUNTER HERBIVORY?  IS IT QUITE RARE?

Answer:  No data, I can only offer my casual field observations.  I will check up on some of Henri and Penny Mustarts work though tonight.

Mortality.  If it occurs - apart from exceptional drought years, which may (how do you model this?) get more common with global enhanced warming -  occurs in year 1.  After year 2 until year 30 it is exceptional in most larger proteas.  Note that there are exceptions.  Serruria florida disappears between years 5 and 8, Orothamnus largely disappears between years 10 and 15.  These though are cases of early senescence - make your seeds, put them in ants nests and vanish.  Interestingly Orothamnus is gone by ca12 years but "co-exists" with Mi arboreus which is reputed to flower for the first time at 8 years.

Herbivory:  what level?

Witches Broom: this Phytoplasma kills branches and young plants, but most species cope with it.  It seems to become more prevalent in older veld, and where older veld abuts younger veld and where fires are patchy, but this is an impression and I have no data to support it.

Leaf miners: present all the time, difficult to assess damage.

Leaf feeders: leaves are only available for herbivory as they grow big, before hardening.  At this time protea leaves are bright red.  Any herbivory results in huge chunks missing from the leaves as the missing chunks enlarge with the leaf - this means that you can calculate the proportion of leaf eaten, but not the actual amount.  It is easy to measure this herbivory! - but how do you relate the proportion of leaf to its size when eaten?  Only Protea nitida has a major problem in this regard and I have seen thousands of small black beetles heavily eating the bright red leaves: but only locally 2 or 3 times over the past 20 years (sample = Sept-Oct months only when new leaves are produced).  Otherwise, leaf predation is almost non-existent.

No indigenous herbivores are recorded eating proteas at Cape of Good Hope Nature Reserve.  But cows heavily eat  Pr odorata, Pr mucronifolia and occasionally other very young proteas.  In heavily overgrazed areas predation by livestock may result in the tops of proteas being chewed off.  Protea Atlas Data: We have 551 records of "New Growth": about half of these document aseasonal growth or observations about new growth.  Half of the remainder are baboon damage (more below). That leaves about 100-150 (no time to go through them now) records of herbivory out of 250 000 records.  Horse pastures feature but mainly for Leucadendrons.

Plant damage: Baboons: baboons damage plants a lot.  Accidentally by using proteas as sentry posts they break branches (off!) and damage leading stems so that they die.  They also remove flowerheads for eating nectar and insects, and appear - someone must have told me this, where I get the idea from I don't know - to prefer those with grubs in the receptacle.  They also very occassionally remove cones from Conebushes.

Otomys Vlei Rat damage:  (I assume Otomys, based on habitat, I am probably wrong).  Otomys (mus?) chops off stems of plants at about head height (i.e. 15cm) to get at seeds, flowers and growth tips way above it.  This can seriously affect plants (obligate reseeders do not invest in stem buds and once the leaves die those stems cannot regenerate so that if chopped off by Otomys or gardeners, that stem, or in single-stemmed plants - the entire plant, dies).  Although I have seen this mainly in Spatalla and Serruria - almost always near vleis, rivers or seeps - it is also recorded for Orothamnus, and it has been proposed (who?  my memory fades-old age: Jan Vlok? Charlie Boucher?) that the rapid erect, unbranched growth of Orothamnus is primarily to remove it from predation by Otomys.

 I believe that this is Tony's claim. i.e. that most of the mortality occurs during the establishment after a fire and early growth phases? 

Answer:  This is assumed.  Tony would claim that if there is any mortality, then it will occur during the early growth phases.  However, in many situtations there may well be no mortality worth speaking of, or else because plants are small, it is not noticeable.  There is some mortality of plants after first reproduction, but it is also small, but enough to generate notable differences in sex ratios in Leucadendron.  However, the best bias ratios are in resprouting species.

BUT AGAIN NO ONE HAS DOCUMENTED THIS OR PUBLISHED ON THIS?  SEEMS SURPRISING.

Answer:  How on earth do you publish the mundane and obvious?   Having been brought up in Fynbos the idea of density dependent mortality, self thinning and  between fire mortality are concepts confined to the vegetable garden.  Even the Pine and Acacia invaders in Fynbos seem not to care about mortality - they just - like proteas at high seedling densities- grow old as thin and weedy runts: and William has shown that seed production per unit area remains constant (until very high densities), even though seed production per plant can be negligible.  This is all basic to Fynbos and it is a wonder to go to systems that operate in bizzarre and unreal ways.  It takes outsiders to come in and discover the obvious: but then the principles are so obvious they are just mentioned as strategies.  We don't have enough scientists here to measure the obvious.  Witness all of Guy's wild physiological extrapolations based on 1 (or 2) protea, 1 restio, 1 erica and 1 grass, all of one ecotype over 1 season!

It goes without saying that many of our preconceptions might be wrong!

 The idea here is to help us in laying out demographic models for a set of protea species -- that what is important is reproduction in the population (cumulative or right before the fire) then fire then establishment (with growth and mortality  responding to local climate conditions in those years), then just growth and reproduction (little mortality) until the next fire.

Answer: No - after 20-30 years senescence kicks in and mortality increases.  By 50-year old veld most adult plants are dead and serotinous seed banks are lost.

There is lots of references to seed germination and that seedling recruitment is confined to a year or two after the fire.  On senescence it is much less.

I will look at home for references - Kruger is the most likely.

Plant community Diversity and dynamics in relation to fire.  FJ Kruger 1983. 445-472. in Mediterranean-type Ecosystems: the role of nutrients.  Eds FJ Kruger, DT Mitchell & JUM Jarvis Springer-Verlag, Berlin.

In summary: no data on early post fire survival.  Extremely little on senescence, but Pr neriifolia declines from 860/1000 at 25 years to 300/1000 at 30 years to 50/1000 at 38 years (unpubl records SA Directorate of Forestry).  Minimal mortality until > 25 years  is the norm.

Resprouters have 92-100% survival. Specht 1981 (in above) suggests that surface soil moisture content above 80% is important in the first year and then soil moisture is irrelevant and mortality patterns change.  But no data for Fynbos on  rates of mortality.

 GREAT!  BUT SURPRISING TO SEE NO PUBLISHED INFORMATION ON EARLY POST FIRE SEEDLING SURVIVAL. 


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