How did the Mesozoic ecosystem find its balance before the expansion of the flowering plants? Other than ferns and horsetails, which can grow quickly, most gymnosperms are slow growing and intolerant of much damage. How did they cope with the enormous sauropods of the time? How the sauropods coped with their toxins and resins, and sustained themselves when all large plants were grazed off from an area, and how then plants regenerated without getting immediately eaten? Also, do we have any idea about the Mesozoic groundcover before flowering weeds? Where then more sun and drought tolerant ferns than now that would fill the same ecological niche as weeds or grass in modern seasonally dry habitats or grasslands?

sorry no-one seems to know the answer to your question.